Removal of MTBE from Drinking Water Using Air … Air stripping performance at Culver City, California. ... Results indicate that a variety of different treatment train configurations

Removal of MTBE from Drinking WaterUsing Air Stripping: Case Studies

A Publication of:

The California MTBE Research Partnership

Association of California Water AgenciesOxygenated Fuels Association

Western States Petroleum AssociationNational Water Research Institute

October 2006

Published by theNational Water Research Institute

NWRI-2006-03

10500 Ellis Avenue ✦ P.O. Box 20865Fountain Valley, California 92728-0865

(741) 378-3278 ✦ Fax: (714) 378-3375www.NWRI-USA.org

Limitations

This document was prepared by Malcolm Pirnie, Inc. and is intended for use by members ofthe California MTBE Research Partnership (Partnership) pursuant to the Partnershipagreement. Malcolm Pirnie and the Partnership do not warrant, guarantee, or attest to theaccuracy or completeness of the data, interpretations, practices, conclusions, suggestions, orrecommendations contained herein. Use of this document, or reliance on any informationcontained herein, by any party or entity other than members of the Partnership, is at the solerisk of such parties or entities.

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Acknowledgements

This report was prepared by Rula Deeb, Elisabeth Hawley, Andrew Stocking, MichaelKavanaugh, Amparo Flores, Stephanie Sue, Douglas Spiers, Michael Wooden, GeraldCrawford, and Guillermo Garcia of Malcolm Pirnie, Inc. The authors would like toacknowledge Rey Rodriguez (H2O·R2 Consulting Engineers, Inc.) and Jim Davidson(currently with Exponent, formerly of Alpine Environmental) for their assistance incollecting the data discussed in this report.

The authors would like to thank the California MTBE Research Partnership and the NationalWater Research Institute (NWRI) for sponsoring this work. The authors especially wish toacknowledge Ronald Linsky (1934-2005), former Executive Director of NWRI, for hisexcellent leadership of the Partnership and for his direction and support of this work. Theauthors are also grateful to the many members of the Partnership's Research AdvisoryCommittee who provided valuable support and review, especially David Pierce(ChevronTexaco Energy Research and Technology Co.) and Bill Reetz (Kansas Departmentof Health and Environment).

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Table of Contents

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Research Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 Research Approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.4 Report Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2. Air Stripper Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1 Packed Tower Air Stripper – Lacrosse, Kansas . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Low Profile Air Stripper – Somersworth, New Hampshire . . . . . . . . . . . . . 11

2.3 Packed Tower Air Stripper – Culver City, California . . . . . . . . . . . . . . . . . . 15

2.4 Low Profile Air Stripper – Bridgeport, Connecticut. . . . . . . . . . . . . . . . . . . 22

2.5 Low Profile Air Stripper – Chester, New Jersey . . . . . . . . . . . . . . . . . . . . . . 27

2.6 Packed Tower Air Strippers – Ridgewood, New Jersey . . . . . . . . . . . . . . . . 29

2.7 Packed Tower Air Stripper – Rockaway Township, New Jersey . . . . . . . . . 32

2.8 Low Profile Air Stripper – Mammoth Lakes, California . . . . . . . . . . . . . . . 38

2.9 Low Profile Air Stripper – Elmira, California . . . . . . . . . . . . . . . . . . . . . . . . 40

3. Analysis Of System Cost And Performance . . . . . . . . . . . . . . . . . . . . . . . 46

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

3.2 Treatment Train Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

3.3 Treatment System Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

3.4 Treatment System Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

4. Model Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

4.1 Overview of Modeling Software Programs . . . . . . . . . . . . . . . . . . . . . . . . . . 54

4.2 Low Profile Air Stripper – Somersworth, New Hampshire . . . . . . . . . . . . . 55

4.3 Low Profile Air Stripper – Chester, New Jersey . . . . . . . . . . . . . . . . . . . . . . 56

4.4 Packed Tower Air Stripper – Lacrosse, Kansas . . . . . . . . . . . . . . . . . . . . . . . 56

4.5 Packed Tower Air Stripper – Culver City, California . . . . . . . . . . . . . . . . . . 57

4.6 Packed Tower Air Stripper – Rockaway Township, New Jersey . . . . . . . . . 58

4.7 Summary of Modeling Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

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5. Summary Of Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

5.1 Case Study Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

5.2 Case Study Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

5.3 Model Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

5.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Appendices

Appendix A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Appendix B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

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Tables

1 Timeline for Remediation and Treatment at LaCrosse, Kansas . . . . . . . . . 7

2 Average Influent Water Quality Parameters at LaCrosse, Kansas . . . . . . . 8

3 Design/Operating Parameters for Packed Tower at LaCrosse, Kansas . . . 9

4 Capital and Annual O&M Costs (1997) at LaCrosse, Kansas . . . . . . . . . . 12

5 Timeline for Remediation and Treatment atSomersworth, New Hampshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6 Average Influent Water Quality Parameters atSomersworth, New Hampshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

7 Design/Operating Parameters for Low Profile Air Stripper atSomersworth, New Hampshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8 Capital and Annual O&M Costs (1996) at Somersworth, New Hampshire . . . 16

9 Average Influent Water Quality Parameters at Culver City, California. . . 17

10 NPDES Permit Limitations at Culver City, California . . . . . . . . . . . . . . . . 18

11 Design/Operating Parameters for Packed Tower Air Stripper atCulver City, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

12 Influent Contaminant Design Criteria at Culver City, California . . . . . . . 18

13 Influent Hydrocarbon Concentrations at Culver City, California . . . . . . . 19

14 Air Stripper Performance Data for MTBE at Culver City, California. . . . 20

15 Capital and Annual O&M Costs (1999) at Culver City, California. . . . . . 22

16 Average Influent Water Quality Parameters at Bridgeport, Connecticut . . . 23

17 Design/Operating Parameters for Low Profile Air Stripper atBridgeport, Connecticut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

18 Air Stripper Performance Data for MTBE at Bridgeport, Connecticut . . 24

19 Air Stripper Performance Data for BTEX Compounds atBridgeport, Connecticut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

20 Capital and Annual O&M Costs (1995) at Bridgeport, Connecticut. . . . . 27

21 Average Influent Water Quality Parameters at Chester, New Jersey . . . . . 28

22 Design/Operating Parameters for Low Profile Air Stripper atChester, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

23 Capital and Annual O&M Costs (1998) at Chester, New Jersey . . . . . . . . 29

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24 Average Influent Water Quality Parameters at Ridgewood, New Jersey . . . 29

25 Design/Operating Parameters for Packed Tower Air Stripper atRidgewood, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

26 Capital and Annual O&M Costs (1991, 1997) atRidgewood, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

27 Design/Operating Parameters for Packed Air Stripping Tower atRockaway Township, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

28 VOC Criteria for 1995 Air Stripping Tower atRockaway Township, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

29 Average Influent Water Quality Parameters atRockaway Township, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

30 Capital and Annual O&M Costs (1995) atRockaway Township, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

31 Timeline of Events at Mammoth Lakes, California. . . . . . . . . . . . . . . . . . . 39

32 Influent Constituent Concentrations at Mammoth Lakes, California . . . . 39

33 MTBE Air Stripping Performance Data at Mammoth Lakes, California . . . 40

34 MTBE Off-Gas Treatment Performance Data atMammoth Lakes, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

35 Timeline of Remediation at Elmira, California . . . . . . . . . . . . . . . . . . . . . . 41

36 Average Influent Water Quality Parameters at Elmira, California. . . . . . . 41

37a Design/Operating Parameters for the Low Profile Air Stripper atElmira, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

37b Design/Operating Parameters for the Off-Gas Treatment System(ADDOXTM) at Elmira, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

38 Capital and Annual O&M Costs (1997) at Elmira, California . . . . . . . . . . 45

39 Comparison of the Design Parameters, Performance, and CostsAssociated with each of the Packed Tower Air Stripper Systems . . . . . . . 46

40 Comparison of the Design Parameters, Performance, and CostsAssociated with each of the Low Profile Air Stripper Systems . . . . . . . . . 48

41 Modeling Scenarios for Low Profile Air Stripper atSomersworth, New Hampshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

42 Modeling Scenarios for Packed Tower Air Stripper at LaCrosse, Kansas. . . 57

43 Modeling Scenarios for Packed Tower Air Stripper atRockaway Township, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

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A-1 Air Stripper Performance Data for MTBE at LaCrosse, Kansas . . . . . . . . 65

A-2 Air Stripper Performance Data for MTBE atSomersworth, New Hampshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

A-3 Air Stripper Performance Data for MTBE at Culver City, California. . . . 69

A-4a Air Stripper Performance Data for MTBE at Bridgeport, Connecticut . . 70

A-4b Air Stripper Performance Data for BTEX atBridgeport, Connecticut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

A-5 Air Stripper Performance Data for MTBE atRockaway Township, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

A-6 Off-Gas System Performance Data for MTBE at Elmira, California . . . . 73

B-1 Modeling Data Comparison for Low Profile Air Stripper atSomersworth, New Hampshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

B-2 Modeling Data Comparison for Packed Tower Air Stripper atLaCrosse, Kansas(Water Flow Rate = 480 gpm, Air to Water Ratio = 156) . . . . . . . . . . . . . . 76

B-3 Modeling Data Comparison for Packed Tower Air Stripper atLaCrosse, Kansas(Water Flow Rate = 350 gpm, Air to Water Ratio = 214) . . . . . . . . . . . . . . 77

B-4 Modeling Data Comparison for Packed Tower Air Stripper atCulver City, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

B-5 Modeling Data Comparison for Packed Tower Air Stripper atRockaway Township, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

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Figures

1 MTBE concentrations at LaCrosse, Kansas.. . . . . . . . . . . . . . . . . . . . . . . . . 10

2 Removal efficiency reliability at LaCrosse, Kansas. . . . . . . . . . . . . . . . . . . 11

3 MTBE concentrations at Somersworth, New Hampshire. . . . . . . . . . . . . . 14

4 MTBE removal efficiency at Somersworth, New Hampshire. . . . . . . . . . . 14

5 Removal efficiency reliability at Somersworth, New Hampshire. . . . . . . . 15

6 MTBE concentrations at Culver City, California. . . . . . . . . . . . . . . . . . . . . 19

7 MTBE removal efficiency at Culver City, California.. . . . . . . . . . . . . . . . . 20

8 Air stripping performance at Culver City, California. . . . . . . . . . . . . . . . . . 21

9 MTBE concentrations at Bridgeport, Connecticut. . . . . . . . . . . . . . . . . . . . 25

10a MTBE removal efficiency at Bridgeport, Connecticut.. . . . . . . . . . . . . . . . 25

10b BTEX removal efficiency at Bridgeport, Connecticut. . . . . . . . . . . . . . . . . 26

11 Removal efficiency reliability at Bridgeport, Connecticut.. . . . . . . . . . . . . 26

12 MTBE concentrations versus time at Rockaway, New Jersey. . . . . . . . . . . 35

13 MTBE removal efficiency versus time at Rockaway, New Jersey. . . . . . . 36

14 Removal efficiency reliability at Rockaway, New Jersey. . . . . . . . . . . . . . . 36

15 MTBE influent concentrations at Elmira, California. . . . . . . . . . . . . . . . . . 43

16 Off-gas treatment influent concentrations of BTEX and TPH-G(1998 to 2000) at Elmira, California.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

17 ADDOXTM performance summary test data at Elmira, California. . . . . . . 44

18 Cost summary of MTBE removal by air stripping. . . . . . . . . . . . . . . . . . . . 53

19 Comparison of modeling results to actual performance.. . . . . . . . . . . . . . . 59

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List of Acronyms, Symbols, and Abbreviations

ASAPTM Aeration System Analysis Program

BTEX Benzene, toluene, ethylbenzene, and xylenes (o-, m-, p-xylene)

CaCO3 Calcium carbonate

cfm Cubic feet per minute

DCE Dichloroethylene

DIPE Di-isopropyl ether

ETBE Ethyl tertiary butyl ether

GAC Granular activated carbon

gpm Gallons per minute

Hp Horsepower

H2O2 Hydrogen peroxide

kwh Kilowatt hour

LUST Leaking underground storage tank

MTBE Methyl tertiary butyl ether

µg/L Microgram per liter

mg/L Milligram per liter

NEEP North East Environmental Products

NHDES New Hampshire Department of Environmental Services

NPDES National Pollutant Discharge Elimination System

O&M Operation and maintenance

PCE Perchloroethylene

ppbv Parts per billion by volume

ppmv Parts per million by volume

scfm Standard cubic feet per minute

StEPP Software to Estimate Physical Properties

SVE Soil vapor extraction

TAME Tertiary amyl methyl ether

TBA Tertiary butyl alcohol

TCE Trichloroethylene

TPH-D Total petroleum hydrocarbons quantified as diesel

TPH-G Total petroleum hydrocarbons quantified as gasoline

USEPA U.S. Environmental Protection Agency

UST Underground storage tank

UV Ultraviolet

VOC Volatile organic compound

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1

Executive Summary

In response to an identified research need to assess the performance of air stripping toremove methyl tertiary butyl ether (MTBE) from contaminated groundwater, the CaliforniaMTBE Research Partnership undertook this project to:

• Collect design, performance, and cost summary data from several packed tower and lowprofile air stripper treatment systems addressing MTBE contamination in groundwatersupplies.

• Use the data from these case studies to develop a series of cost and reliability curves.

• Assess the accuracy of several available models used to predict the cost and performanceof packed tower and low profile air strippers.

Data from nine case study sites operating during the late 1990s were obtained and analyzed.Two models were chosen for evaluation: the Aeration System Analysis Program (ASAPTM)Packed Tower Model and the North East Environmental Products (NEEP) ShallowTray®

Modeler software.

Results indicate that a variety of different treatment train configurations can use air strippersto successfully remove a wide range of MTBE concentrations (i.e., from 10 to 2,400,000micrograms per liter [µg/L]). Removal efficiencies ranged from 65 percent to greater than99.9 percent.

Capital costs (expressed in year 2000 dollars) ranged from $0.47/1,000 to $104/1,000 gallonssystem capacity. Operation and maintenance (O&M) costs were a function of flowrate andpercent MTBE removal. Annual O&M costs ranged from $1/1,000 to $10/1,000 gallons toachieve greater than 90-percent removal and from $0.15/1,000 to $1/1,000 gallons to achievegreater than 65-percent removal.

Commercially available models were found to predict actual removal efficiencies within15 percent, demonstrating that modeling can be a valuable tool for assessing air stripper costand performance during conceptual design or remedy selection

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1. Introduction

1.1 Background

In 1995, the Lawrence Livermore National Laboratory reported that greater than 90 percentof the groundwater plumes (defined as the 10 micrograms per liter [µg/L] benzene isoconcen-tration level) emanating from underground storage tank (UST) gasoline releases in Californiawere likely to stabilize (i.e., stop increasing in size) at distances less than 250 feet down-gradient of leaking underground storage tank (LUST) releases (Rice et al., 1995). Theseplumes — identified primarily by one or more benzene, toluene, ethylbenzene, and xylene(BTEX) components — moved slowly and eventually stabilized due to natural biodegradationand retardation. Lawrence Livermore National Laboratory concluded that many BTEXplumes might not require active remediation due to these natural attenuating processes andthat monitored natural attenuation could be a remedial strategy at many UST sites inCalifornia and other states.

Shortly thereafter, methyl tertiary butyl ether (MTBE), an oxygenate added to gasoline toincrease octane levels and to meet federal and state fuel specifications for oxygen content,was detected in drinking water wells in the City of Santa Monica, California (US WaterNews, 1996). This discovery caused regulatory agencies in California to immediatelyreassess cleanup strategies at gasoline UST sites. Groundwater samples collected at USTsites in California and elsewhere confirmed MTBE occurrence and, with it, new remediationchallenges for UST owners.

Some of the remediation challenges are apparent from MTBE’s physical and chemicalproperties. MTBE is highly soluble in water, is only weakly sorbed to most soils, and exhibitsa low tendency to volatilize from water. Consequently, MTBE partitions relatively easily intowater from a gasoline/MTBE mixture, moves approximately at the rate of groundwater flow,and — if no active remediation is undertaken — can threaten downgradient water supplywells. Moreover, depending on the release scenario, MTBE may move farther than BTEXcompounds, ultimately impacting a larger volume of groundwater compared to BTEX-onlyplumes. The ether structure of MTBE is not very susceptible to biodegradation. MTBE andother ether oxygenates were initially found to be resistant to biodegradation, thereby limitingthe use of natural attenuation for contaminated groundwater cleanup at UST sites (Suflita andMormile, 1993; Yeh and Novak, 1995). These characteristics of MTBE have increased theneed for active remediation technologies at UST sites and the level of interest in the cost andperformance of available ex situ groundwater treatment technologies. For example, the needfor information on drinking water treatment technologies for MTBE was highlighted in aU.S. Environmental Protection Agency (USEPA) report titled “Oxygenates in Water: CriticalInformation and Research Needs” (U.S. Environmental Protection Agency, 1998).

In February 2000, the California MTBE Research Partnership (Partnership) published areport summarizing the feasibility of using several technologies to remove MTBE from

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drinking water (California MTBE Research Partnership, 2000). This report contained atheoretical analysis of treatment technologies with some reference to field applications. Tofurther elucidate the ability of these technologies to remove MTBE from drinking water, thePartnership also funded efforts to gather information from field applications to verify theestimated cost and efficiency of these technologies to remove MTBE from contaminatedwater. For example, the Partnership published two reports focusing on MTBE removal usingsynthetic resins (California MTBE Research Partnership, 1999) and granular activatedcarbon (California MTBE Research Partnership, 2001). Recently, the Partnership publisheda comprehensive evaluation of MTBE remediation options (California MTBE ResearchPartnership, 2004). Additional data on MTBE treatment systems and costs is availablethrough the USEPA’s Technology Innovation Office (U.S. Environmental Protection Agency,2005) and the Partnership.

Air stripping is a well-established technology for removing volatile organic compounds(VOCs) from groundwater. Two configurations of air strippers include the low profile andpacked tower systems. In a low profile aeration system, contaminated water is pumped to thetop of the stripper, where it flows over an inlet weir onto a baffled aeration tray. Air is forcedupward through perforations in the tray bottom, creating highly turbulent conditions tomaximize the contact of water and air. In a packed tower air stripping system, contaminatedwater passes downward by gravity through a circular or rectangular column that is filled witheither randomly packed or structured packing material. Air is introduced into the tower belowthe packed bed and flows upward through the column countercurrent to the flow of water.

The successful and cost-effective application of air stripping to remove MTBE has not yetbeen demonstrated or widely accepted. The Partnership identified a research need to evaluatethe effectiveness of air stripping for MTBE removal from groundwater, including actual costand performance data from operating groundwater treatment systems. Air stripping systemperformance and cost data were collected between 1995 and 2001, at the same time as thecollection of data for two other published Partnership reports (California MTBE ResearchPartnership, 1999, 2001). The analysis of these data is presented in this report. Between 2001and 2005, numerous air strippers — both packed tower and shallow tray configurations —have been successfully used for both municipal drinking water treatment and remedialapplications. The installation of these treatment systems has contributed to the recognition ofair stripping as a cost-effective option for MTBE treatment. However, a summary of cost andperformance data for MTBE removal via air stripping has still not been published, to ourknowledge. Therefore, the summary presented in this report is unique.

1.2 Research Objectives

The overall objective of the work summarized in this report is to evaluate the cost andperformance of air strippers and associated off-gas treatment systems for removing MTBEfrom groundwater supplies. The primary objectives of the project include:

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• Collect performance data, water quality information, and cost summaries for severalpacked tower and low profile air strippers and their respective off-gas treatment processesfor treating MTBE.

• Use the data from these case studies to develop a series of cost curves and reliability curvesfor packed tower and low profile air strippers as a function of removal efficiency, flow rate,and water quality. Identify the most sensitive parameters (e.g., water quality) that influencethe cost and reliability of air stripping systems.

• Identify several available models used to estimate the cost and performance of packedtower air strippers and low profile air strippers. Use the performance data to assess theaccuracy of the predictions generated by these models.

Due to data limitations, the objectives were not fully met. For example, off-gas treatmentsystem performance data were not available at every site. Data were not sufficient to conducta quantitative sensitivity analysis of the most important parameters impacting air stripperperformance. Thus, a qualitative review of air stripper operational and maintenancechallenges was conducted.

1.3 Research Approach

To evaluate the cost and performance of air stripping for MTBE, data from nine case studieswere examined. At each site, air stripping was used to remove MTBE from contaminatedgroundwater. Five of the sites used low profile air strippers, and the other four sites usedpacked tower air strippers. The case studies included:

1. Packed tower air stripper — LaCrosse, Kansas

2. Low profile air stripper — Somersworth, New Hampshire

3. Packed tower air stripper — Culver City, California

4. Low profile air stripper — Bridgeport, Connecticut

5. Low profile air stripper — Chester, New Jersey

6. Packed tower air stripper — Ridgewood, New Jersey

7. Packed tower air stripper — Rockaway Township, New Jersey

8. Low profile air stripper — Mammoth Lakes, California

9. Low profile air stripper — Elmira, California

Data for this study were provided by environmental consultants, air stripper manufacturers,and regulators. At some of the sites, cost and performance data could not be shared with thePartnership due to ongoing litigation.

The site background, description of the air stripping system, system performance, andtechnology cost were summarized for each site. System design parameters were tabulated

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and performance data were plotted. Similarities and differences between the case studieswere examined. For example, the treatment train design, performance, maintenancerequirements, and costs were compared to identify common elements and potentialadditional considerations impacting system performance and cost. Cost data were expressedin year 2000 dollars and were normalized by flow rate to facilitate comparisons betweendifferent case study sites.

Two commercially available and widely used models for air stripping performance wereevaluated to assess the accuracy of their predictions. Case study parameters (e.g., flow rate,water temperature, reactor size, and influent contaminant concentrations) were entered intoeach model. Model predictions were compared with actual measurements of effluent waterquality at case study sites.

1.4 Report Overview

The research approach provided the framework for the organization of this report.

Section 2 presents the data collected for each of the air stripping systems and associated off-gas treatment, and includes a summary of site history, air stripper design, and operating data.

Section 3 presents a summary of cost and performance trends for air stripping that wereidentified during the case study data analysis, including system operating parameters,percent MTBE removal, and unit costs (normalized by system flow rate). The most criticaloperating parameters for reducing costs and increasing system reliability were identified.

Section 4 describes two models that are commonly used for predicting air stripper systemcost and performance: the Aeration System Analysis Program (ASAPTM) Packed TowerModel and the North East Environmental Products (NEEP) ShallowTray® Modeler software.Key model input parameters and model-predicted system performance are summarized inthis section. Modeling predictions are compared with actual system operating parameters toevaluate the accuracy of these models.

Section 5 summarizes the main findings of this report and presents strategies for predictingwhether or not air stripping will be a cost-effective and reliable treatment strategy forremoving MTBE and other VOCs from groundwater at a given site.

Section 6 contains a list of publications and other data referenced in this report.

7

2. Air Stripper Case Studies

2.1 PACKED TOWER AIR STRIPPER — LACROSSE, KANSAS

2.1.1 Site Background

In 1992, three gasoline service stations in LaCrosse, Kansas, were identified as sources ofsoil and co-mingled groundwater contamination. The LUSTs at each of these three sitesresulted in free-phase gasoline product and a petroleum hydrocarbon plume with MTBEconcentrations exceeding 55,000 µg/L. The extent of groundwater contamination wascharacterized using numerous shallow monitoring wells. Sampling results indicated that theBTEX plume extended approximately 800 feet downgradient of the gasoline station tanks. Aremediation system consisting of soil vapor extraction (SVE), groundwater pump-and-treat,and product recovery using skimmer pumps was installed in late 1995/early 1996. Due to theproximity of nearby receptors, the pump-and-treat and product recovery systems were keptin operation to provide hydraulic containment. The timeline of events related to remediationand treatment is presented in Table 1.

In January 1997, a nearby resident complained of a chemical odor coming from an irrigationwell located less than a mile downgradient of the gasoline service stations. Analytical studiesconfirmed that MTBE was present in the well at a concentration of 2,100 µg/L. Two adjacentmunicipal wells were subsequently sampled and were also found to be contaminated withMTBE concentrations of up to 1,050 µg/L. Because the two municipal wells were the onlysource of water for the community, an emergency response was formulated to notify localofficials and evaluate treatment options.

Additional monitoring wells were installed between the source area and municipal wells toconfirm that contamination was coming from the three service stations. Nested wells weredrilled to the base of the aquifer and screened at the same depth as the two public supply

Milestone/Event Date

Irrigation well sample February 17, 1997

Public water supply sample April 7, 1997

City notification April 23, 1997

Installation of temporary low profile stripper April 24, 1997

Additional (deeper) wells drilled April 24, 1997

ORC® installation May 10, 1997

Permanent air stripper towers turned on September 16, 1997

Soil excavations August 17, 1998

SVE/sparge on November 13, 1998

Additional deep aquifer sparge on September 1, 1999

ORC®: Oxygen release compound.

Table 1. Timeline for Remediation and Treatment at LaCrosse, Kansas

8

wells (50 to 70 feet below ground surface [bgs]). Groundwater analytical data from thenested wells revealed high concentrations of MTBE (up to 1,290 µg/L) in the deeper wells,with lower to non-detectable concentrations in the shallow wells.

2.1.2 Description of Air Stripping System

Since the two municipal wells were the only sources of potable water for a nearbycommunity, a treatment system had to be quickly designed to ensure that the wells couldcontinue to operate. Initially, a five-tray air stripper from the gasoline station pump-and-treatsystem installation was relocated to the water treatment facility as an emergency responsemeasure to remove MTBE from the groundwater prior to water distribution. The tray stripperwas designed to extract water from the clear well at one end and return the treated water atthe opposite end. This pumping arrangement allowed a circulation of treated and raw water,which diluted MTBE concentrations in the water prior to its delivery into the distributionsystem. Flow rates into the tray stripper were limited to 250 gallons per minute (gpm). Thetray stripper was used for 5 months until the packed tower air stripper system was installed.

The permanent air stripping system was designed to treat up to 500 gpm. Influent waterquality parameters are presented in Table 2. The influent to the permanent air strippingsystem is pre-chlorinated (0.5 to 1.0 milligrams per liter [mg/L] as residual) at each municipalwell. Prior to entering the air stripping unit, the water is softened with lime, decreasinghardness from approximately 700 to 110 mg/L as calcium carbonate (CaCO3), and routedinto a settling basin for flocculation. It is then pumped into air stripper towers. Water exitingthe packed towers is recycled back into the settling basin. Overflow water from the settlingbasin is directed through a sand and anthracite filter bed, then into a 200,000-gallonunderground clear well and the distribution system.

Water Quality Parameter Concentration

Alkalinity as CaCO3 (mg/L) 131

Aluminum (mg/L) 432

Chloride (mg/L) 127

Corrosivity (mg/L) 0.17

Iron (mg/L) 0.021

Magnesium (mg/L) 17

Nitrate (mg/L) 0.07

Sulfate (mg/L) 347

Total dissolved solids (mg/L) 858

Hardness (mg/L) 115

Turbidity (NTU) <0.5

pH 8.7

Temperature Not available

NTU: Nepheleometric turbidity unit.

Table 2. Average Influent Water Quality Parameters at LaCrosse, Kansas

9

The permanent stripping system consists of two 33-foot tall, 6-foot diameter packed towers.The towers are partially enclosed within a steel pre-engineered building and contain 21 feetof 2-inch Jaeger TripackTM packing material. The two units are operated in series to provideredundancy. The first packed tower air stripper is designed to decrease MTBE concentrationsfrom up to 1,000 µg/L to less than 20 µg/L, while the second tower is used for water qualitypolishing to meet a treatment goal of less than 10 µg/L. The system flow rate ranges from350 to 480 gpm (in summer months). The blowers can circulate 11,500 cubic feet per minute(cfm) of air through each tower. The air-to-water design ratio is 150 to 1. Other importantdesign and operating parameters for the air stripping system are presented in Table 3. The airstrippers are operated by city employees during normal pumping hours (8 am to 4 pm, 6 daysper week). Sampling and routine maintenance duties are performed by facility employeeswith as-needed contractor support.

All off-gases released from the packed tower air strippers are directly discharged into theatmosphere without treatment.

2.1.3 Air Stripping System Performance

Temporary Tray Strippers

The five-tray air stripper reduced influent MTBE concentrations (200 to 600 µg/L) by anaverage of 40 percent. Effluent MTBE concentrations from the tray strippers ranged from 17to 375 µg/L. The system operated as an emergency response measure until the packed towerair stripper was installed.

Parameter Design Operating

Tower specifications 6-feet diameter x 33-feet tall Fiberglass

Packing material 2-inch Jaeger Tri-Pack filled to 21 feet

Configuration Two towers in parallel Two towers in series

Blower size (Hp) 2 x 15

Pump size (Hp) 3 x 15

Water flow rate (gpm) 500480 in summer350 in winter

Air flow rate (cfm) 10,000

Air-water ratio 150:1 156:1 to 214:1

Maximum MTBE concentration (µg/L) 1,000 973

Average MTBE concentration (µg/L) — 141

Maximum BTEX concentration (µg/L) Non-detect Non-detect

MTBE treatment goal (µg/L) <10 <10

Removal efficiency (%) 90 84

Table 3. Design/Operating Parameters for Packed Tower at LaCrosse, Kansas

10

Permanent Packed Tower Air Strippers

MTBE influent concentrations ranged from non-detect (less than 10 µg/L) to 973 µg/L. Inmost cases (greater than 90 percent of the time), effluent MTBE concentrations were lessthan 10 µg/L. The removal efficiency of the air strippers averaged 84 percent over the periodof operation between 1997 and 2000. No significant operation and maintenance (O&M)problems have been reported to date, and there have been no problems with fouling orscaling. Manholes on the side of each tower provide visible evidence that the tower packingmaterial has remained clean. System pressures in each tower have been stable since startup.

The results of sampling events from the temporary tray air strippers (April 25, 1997, toSeptember 10, 1997) and packed tower air strippers (September 16, 1997, to early 2000) arepresented in Figure 1. The removal efficiency reliability for the two towers is presented in

Figure 2. Samples of the influent, first stripper effluent, second stripper effluent, and tapwater are collected on a monthly basis. Detailed performance data is contained in Table A-1of Appendix A. Total removal rates for MTBE average 95 percent after the second air strippertower. As can be seen from available data (Figure 1), occasional spikes in MTBEconcentrations are apparent in the influent water quality, which may be related to the use ofa second public water supply well on Saturdays as the source of pumped groundwater. Thesecond well has higher concentrations of MTBE (380 to 973 µg/L) compared to the first well(39.5 to 180 µg/L). Based on these findings, the city has decreased its usage of the secondwell by up to a factor of 4. The well is now only used for 5 to 10 hours per month.

Figure 1.MTBE concentrations at LaCrosse, Kansas.

MT

BE

Con

cent

ratio

n (µ

g/L)

11

2.1.4 Technology Cost

A breakdown of expenses for the permanent packed tower air strippers is presented inTable 4. Capital costs in 1997 were approximately $190,000. Annual O&M costs in the late1990s were approximately $25,300. However, combined with the cost for remedial actions atthe three gasoline station sites, the total cost of site remediation work exceeded 1 milliondollars as of 2000. This includes the installation and 2-year operation of the pump-and-treatsystem, installation of two Oxygen Release Compound (ORC) barriers, source excavations,and in situ sparging systems in both the source and downgradient areas.

2.2 LOW PROFILE AIR STRIPPER — SOMERSWORTH, NEW HAMPSHIRE


During a routine tank inventory monitoring event in September 1996, a gasoline leak from aUST was detected at a retail gasoline dispensing facility in Somersworth, New Hampshire.It was estimated that 2,200 gallons of gasoline had leaked from the tanks, resulting in thepresence of separate-phase hydrocarbons (SPH) in the subsurface and a dissolved-phasehydrocarbon plume. The site was added to the New Hampshire Department of Environ-mental Services (NHDES) list of spill response sites on October 4, 1996.

In November 1996, three USTs were replaced. An SVE system, temporary groundwaterextraction, and treatment system were installed. The SVE system was installed to address thearea with free-phase hydrocarbon contamination. The temporary groundwater extraction

Figure 2.Removal efficiency reliability at LaCrosse, Kansas.

Rem

oval

of T

ikm

e E

xcee

ding

Rem

oval

Effi

cien

cy (

%)

Removal Efficiency (%)

12

system pumped groundwater from six recovery wells into a 21,000-gallon fractionation tankthrough a trailer-mounted oil-water separator. The groundwater was then routed through acarbon treatment system consisting of four granular activated carbon (GAC) vesselsoperating in series. In December 1996, a low profile air stripper and an equalization tankwere installed. The system was set up so that the oil-water separator drained into the 200-gallon equalization tank. Water was pumped out of the equalization tank and passed throughthe low profile air stripper. The chronology of groundwater treatment and soil remediation atthe site is summarized in Table 5.

Capital Costs

Towers (x 2) $119,916

Building $26,765

Concrete pad $11,142

Intake screens $3,300

Blowers and pumps $5,724

Freight $4,384

Control panel $2,031

Electrical, heating, and lighting $11,000

Stripper spare parts (including freight) $5,706

Total Capital Costs $189,968

Amortized annual costs at 7 percent for 30 years $15,309

Annual O&M Costs

Labor (1 hour/week at $70/hour) $3,640

Electricity $13,200

Sampling (four/month at $39.25 each) $1,884

Monthly reports (12 at $50 each) $600

Quarterly reports (four at $1,500 each) $6,000

Total Annual O&M Costs $25,324

Total annual costs $40,633

Amortized Costs/1,000 Gallons $0.57 to 0.76*

*Based on 350- to 480-gpm flow rate and 8-hours/day, 6-days/week operation.

Table 4. Capital and Annual O&M Costs (1997) for LaCrosse, Kansas


Gasoline leak detected September 26, 1996

Temporary treatment system start-up November 22, 1996

Permanent treatment system start-up December 10, 1996

Treated effluent ceases discharge to wastewater treatment plantand begins discharge to stormwater system

August 4, 1999

Treatment system shut-down, due to low concentrations in the influent to theair stripper and low concentrations in the groundwater monitoring wells

May 2000

Table 5. Timeline for Remediation and Treatment at Somersworth, New Hampshire

13


The air stripper in use at this site is a shallow tray low profile air stripper manufactured byNEEP. The operating water flow rate ranges from 3 to 10 gpm and the air-to-water ratio is900 to 1. Influent water quality parameters are presented in Table 6, and design and operatingparameters for the air stripper are presented in Table 7.

The system is operated automatically on a continuous basis. Since treatment started, samplinghas been performed once a month on the combined influent of six recovery wells. Theeffluent samples are collected from a sampling port at the base of the air stripper. Samplesare analyzed for purgeable organics (USEPA Methods 8021B and 8260B) and total petroleumhydrocarbons (USEPA Method 418.1).

Treatment system discharge was initially permitted under an NHDES Temporary SurfaceWater Discharge Permit and Temporary National Pollutant Discharge Elimination System(NPDES) Permit Exclusion. The treated groundwater was initially discharged to the municipalwastewater treatment facility. Since August 1999, all discharges have been made to the stormdrainage system, which leads to Salmon Falls River.

Air stripper off-gas is directly released into the atmosphere without treatment.

Water Quality Parameter Value

Iron (mg/L) 5.6

Effluent temperature (°F) 68

Table 6. Average Influent Water Quality Parameters at Somersworth, New Hampshire


Unit specificationsFour trays~5-feet wide, 6-feet long, and 6.5-feet high

Configuration Single low profile air stripper

Blower size (Hp) 7.5

Pump size (Hp) 1.5

Water flow rate (gpm) 160 3 to 10, typically 10

Air flow rate (cfm) 900 900

Air-water ratio 42:1 1,070:1

Maximum MTBE influent concentration (µg/L) 1,670,000

Average MTBE influent concentration (µg/L) 76,700

Removal efficiency (%) 98.3

Table 7. Design/Operating Parameters for Low Profile Air Stripper at Somersworth, New Hampshire

14


Influent concentrations of MTBE have ranged from approximately 200 to 1,000,000 µg/L, asshown in Figure 3. Removal efficiency typically ranged between 95 to 99 percent, with anaverage of 98 percent. The only exception occurred in March 1998, when the removalefficiency dropped to approximately 70 percent due primarily to silt build-up in the airstripper. Once the air stripper was cleaned, removal efficiencies improved to previous levels.Currently, the air stripper requires 16 hours of cleaning every quarter. Measured removalefficiency of the air stripper is graphically represented in Figures 4 and 5, based on datashown in Table A-2 of Appendix A.

Figure 3. MTBE concentrations at Somersworth, New Hampshire.

MT

BE

Con

cent

ratio

n (µ

g/L)

Figure 4. MTBE removal efficiency at Somersworth, New Hampshire.

MT

BE

Rem

oval

Effi

cien

cy (

%)

12/1

2/19

96

2/12

/199

7

4/12

/199

7

6/12

/199

7

8/12

/199

7

10/1

2/19

97

12/1

2/19

97

2/12

/199

8

4/12

/199

8

6/12

/199

8

8/12

/199

8

10/1

2/19

98

12/1

2/19

98

2/12

/199

9

4/12

/199

9

6/12

/199

9

8/12

/199

9

10/1

2/19

99

12/1

2/19

99

2/12

/200

0

15

The air stripping system has been operating reliably since December 1996. No major repairsor replacement parts have been needed since system operation began. During operation ofthe temporary treatment system (November 22, 1996, to December 9, 1996), a total of92,400 gallons of groundwater were recovered, treated, and discharged. A status report showsthat 2,566,300 gallons of water had been recovered, treated, and discharged from the start-update of December 10, 1996, to February 28, 2000.


The capital cost of air stripper installation totaled $43,000 (1996 dollars). As noted in Table 7,the system was originally designed to treat 160 gpm. If the operating maximum flowrate of10 gpm had been anticipated, capital costs would have been even lower. Annual O&M costshave totaled $15,480 (actual costs during the late 1990s), as shown in Table 8. The total costfor site remediation and groundwater treatment at this site has exceeded 1 million dollars.Other approved capital costs in 1996 dollars for various aspects of the remediation projectinclude recovery well installation and start-up ($81,281), temporary groundwater treatmentsystem installation ($19,997), permanent treatment system installation ($76,091), and SVEsystem installation ($36,017).

2.3 PACKED TOWER AIR STRIPPER — CULVER CITY, CALIFORNIA


Groundwater treatment began in Culver City, California, in November 1999 to addresspetroleum hydrocarbons, BTEX, MTBE, and tertiary butyl alcohol (TBA) contamination.Groundwater is extracted from a total of eight wells screened in two drinking water aquifers.MTBE was first detected in the wells in late 1995, leading to the closure of the well field in

Figure 5.Removal efficiency reliability at Somersworth, New Hampshire.

Per

cent

age

of T

ime

Exc

eedi

ng R

emov

al E

ffici

ency

(%

)


16

1997. At the time of data collection, legal investigations and site characterization activitieswere being undertaken by the City of Santa Monica, USEPA, and the Los Angeles Region ofthe California Regional Water Quality Control Board.

An interim treatment system consisting of packed tower air stripper units was installed toremove contamination from a LUST at an operating gasoline service station. The extractionsystem was designed to provide hydraulic control over movement of the MTBE and BTEXplumes. The water is currently treated and discharged under an NPDES permit issued by theLos Angeles Region of the California Regional Water Quality Board. The treatment goal forMTBE under the NPDES permit is consistent with California’s primary drinking waterstandard of 13 µg/L.


The groundwater treatment system consists of multiple unit processes to ensure that theeffluent meets NPDES permit discharge requirements. Groundwater from the wells ispretreated with approximately 20 mg/L hydrogen peroxide (H2O2) to oxidize ferrous iron toinsoluble ferric iron. A series of three surge tanks is then used to precipitate the iron, followedby bag filters on the third surge tank to remove any remaining iron oxide particles. Theeffluent from the bag filters is treated with a sequestrant solution (20 mg/L of Betz DearbornScaletrol PDC9329) to reduce scaling in the stripper packing. After iron precipitation, thewater is routed through three air strippers in series, each of which can be bypassed, ifnecessary, due to cleaning or repairs.

Capital Costs

Low profile air stripper $20,683

Electrical, heating, and lighting $16,779

Air stripper installation $5,460

Total capital costs $42,923

Amortized annual cost at 7 percent for 30 years $3,459

Annual O&M Costs

Air stripper cleaning and maintenance(includes labor for 16 hours quarterly at $70/hour)

$6,480

Electricity (based on $0.12/kWh) $7,000

Sampling (two/month) $2,000



Amortized Costs/1,000 Gallons $22.001

Table 8. Capital and Annual O&M Costs (1996) at Somersworth, New Hampshire

1Based on treatment of 2,566,338 gallons between December 1997 and February 2000.

The packed tower air strippers, manufactured by Air Chem Systems, Inc., are operated inseries. Each air stripper is 6 feet in diameter, 40 feet in height, and contains 25 feet of No. 2NUPAC™ polypropylene packing material manufactured by Lantec Products, Inc. Typically,only two of the three stages are used in series during any given time. Treated water from theair stripper can undergo ultraviolet (UV) treatment in a 180 kilowatt (kW) medium pressure,horizontal PeroxPure reactor. H2O2 can be added, if desired, to improve the removalefficiency of MTBE, TBA, or other organic compounds. Water is also passed through GACprior to discharge into a stormwater drain.

Off-gas from the air stripping system is treated using a regenerative thermal oxidizer (RTO)manufactured by Telkamp Systems, Inc., which has a capacity of 10,000 cfm.

The inorganic parameters measured from samples collected at the air stripper inlet and outletin February 2000 are presented in Table 9. The major flow and discharge limitations of theNPDES permit are summarized in Table 10. The system design and operating parameters forthe air strippers are presented in Table 11, and the influent design parameters are presentedin Table 12.


MTBE Removal

Water samples are collected at the influent and effluent ports of the treatment system, as wellas at the outlet of each air stripper. MTBE concentrations in the groundwater were reducedby the air stripping system from up to 17,000 µg/L to less than 2 µg/L (detection limit). Thesystem has an overall removal efficiency of greater than 99.9 percent. The highestconcentration of MTBE measured in samples collected for the outlet of the first air strippingcolumn (S-01) was 8.4 µg/L (November 15, 1999). MTBE removal efficiency across the firstair stripper tower ranges between 99.8 and 99.9 percent (most removal occurs in the first airstripper unit).

17

Parameter Air Stripper Inlet Air Stripper Outlet

Alkalinity (bicarbonate) (mg/L as CaCO3) 402 376

Alkalinity (carbonate) (mg/L as CaCO3) Non-detect (<5) 24

Hardness (mg/L as CaCO3) 547 549

Iron (TTLC) (mg/L) 1.4 1.4

Iron (filtered) (mg/L) 2.4 2.5

Manganese (TTLC) (mg/L) 2.4 2.5

pH 6.8 8.5

Langlier Saturation Index –0.3 +1.48

Table 9. Average Influent Water Quality Parameters at Culver City, California

TTLC: Total threshold limit concentration.

18

Parameter Maximum Value

Discharge rate (gpm) 400

TPH-G (µg/L) 100

Benzene (µg/L) 1

Toluene (µg/L) 150

Ethylbenzene (µg/L) 700

Ethylene dibromide (µg/L) 0.05

Total xylenes (µg/L) 1,750

MTBE (µg/L) 13

TBA (µg/L) 1,750

Sulfides (mg/L) 1.0

Biochemical oxygen demand at 20°C (mg/L) 30

Total suspended solids (mg/L) 50

Settleable solids (mg/L) 0.3

Turbidity (NTU) 150

Temperature (°F) 100

pH Range from 6.0 to 9.0

Table 10. NPDES Permit Limitations at Culver City, California


Tower specifications (x 3) 6-feet diameter x 40-feet tall

Packing No. 2 NUPACTM packing filled to 25 feet

Configuration Three towers in series

Water flow rate (gpm) 400 200

Inlet water temperature (°F) 100 70

Air flow rate (cfm) 10,000 7,000

Inlet air temperature (°F) 55 to 85

Air-water ratio 200:1 700:1

Maximum MTBE concentration (µg/L)Influent normal: 8,000Influent maximum: 16,000

1st stage: 3,450 to17,0002nd stage: 8.43rd stage: 1.4

MTBE treatment goal (µg/L) Maximum: 35 All stages: Non-detect (<2)

Removal efficiency (%) >9 99.9

Table 11. Design/Operating Parameters for Packed Tower Air Stripperat Culver City, California

Constituent Normal (µg/L) Maximum (µg/L)

MTBE 8,000 16,000

Benzene 1,000 5,000

Toluene 5,000 10,000

Ethylbenzene 1,000 4,000

Total xylenes 10,000 20,000

Other petroleum hydrocarbons 2,000 4,000

Table 12. Influent Contaminant Design Criteria at Culver City, California

NTU: Nepheleometric turbidity unit.

19

Influent MTBE concentrations have decreased steadily since the start-up of the system. InNovember 1999, the concentration was 17,000 µg/L. In December 1999 and in March 2000,MTBE influent concentrations dropped to 7,750 and 3,650 µg/L, respectively. Influentconcentrations measured in April and May 2000 showed MTBE concentrations of 3,300 and2,900 µg/L, respectively. Influent concentrations over time of MTBE and other gasolineconstituents are presented in Table 13 and Figure 6. Performance data for the three airstrippers are summarized in Table 14 and Figures 7 and 8. Detailed performance data iscontained in Table A-3 of Appendix A.

ConstituentNov. 1999

(µg/L)Dec. 1999

(µg/L)March 20001

(µg/L)April 20001

(µg/L)May 20001

(µg/L)

TPH-G 14,000 14,000 10,000 10,000 10,000

Benzene 570 885 510 540 400

Toluene 860 3,500 1,800 1,800 1,500

Ethylbenzene 340 615 330 340 380

Xylenes 1,660 3,600 2,200 2,400 2,100

MTBE 17,000 7,750 2,800 3,300 2,900

TBA 3,500 1,200 570 330 260

1Influent concentration based on two to three sets of analytical results provided by two different analytical laboratories.

Table 13. Influent Hydrocarbon Concentrations at Culver City, California

Figure 6.MTBE concentrations at Culver City, California.

MT

BE

Con

cent

ratio

n (m

g/L)

Data Point ID

20

Date Influent (µg/L) S-01 (µg/L) S-02 (µg/L) S-03 (µg/L) Effluent (µg/L)

11/10/99 17,000 NA NA NA ND (<1)

11/15/99 3,818 8.4 1.4 1.4 NA

12/20/99 6,300 NA NA NA ND (<1)

12/21/99 2,400 NA NA ND (<1) NA

01/13/00 4,500 NA NA NA ND (<1)

01/21/00 5,100 1.3 ND (<1) 1.1 NA

02/01/00 4,200 1.1 Offline 1.0 ND (<1)

02/12/00 3,000 ND (<1) Offline ND (<1) ND (<1)

02/16/00 3,200 1.3 Offline 1.5 ND (<1)

02/25/00 3,000 ND (<1) Offline ND (<1) ND (<1)

03/01/001 2,500 ND (<1) Offline ND (<1) ND (<1)

03/09/00 2,900 ND (<1) Offline ND (<1) ND (<1)

03/15/00 4,100 ND (<1) Offline ND (<1) ND (<1)

04/04/001 3,300 NA Offline ND (<1) ND (<5)

05/09/001 2,900 NA Offline ND (<1) ND (<5)

1Influent concentrations based on two to three sets of analytical results provided by two different analytical laboratories.

NA: Not available.

ND: Non-detect.

Table 14. Air Stripper Performance Data for MTBE at Culver City, California

Figure 7.MTBE removal efficiency at Culver City, California.

Rem

oval

Effi

cien

cy (

%)

Trial #

21

Total Petroleum Hydrocarbon Quantified as Gasoline (TPH-G)/BTEX Removal

The air stripping system removed total petroleum hydrocarbon quantified as gasoline (TPH-G)/BTEX from groundwater to below laboratory detection limits (approximately 1 µg/L), withan overall removal efficiency equal to or greater than 99.9 percent. Moreover, all effluentsamples from the first stripping column had non-detectable levels of TPH-G/BTEX,suggesting that TPH-G/BTEX removal essentially occurred in the first stripping column.

TBA Removal

Average monthly influent concentrations of TBA ranged from 260 to 3,500 µg/L betweenNovember 1999 to May 2000. During this period, TBA removal efficiency in the air strippingsystem increased from approximately 74 percent to greater than 90 percent. Most of the TBAremoval occurred in the first air stripping column. The improvement in TBA removalefficiency over time is potentially due to the development of a microbial community on thesurfaces of the air stripper packing that is capable of TBA degradation.

The only apparent problem with air stripper operation was the build-up of scale in the pre-treatment system. The system operates continuously. Between its start-up date of November 12,1999, and March 15, 2000, this system treated 11,537,000 gallons of water. Based on thisdata, the flow rate of treated water is approximately 67 gpm. From March to May 2000,groundwater extraction rates were approximately 64 to 66 gpm.

Figure 8.Air stripping performance at Culver City, California.

MT

BE

Con

cent

ratio

n (µ

g/L)

22


The capital cost of the entire system (including pretreatment, the three air strippers, off-gastreatment, and GAC polishing) was approximately $1,714,000. Annual operating costs(including electricity, GAC, chemicals, labor, and supplies) are estimated to be $360,000. Abreakdown of these costs is presented in Table 15. These costs are based on June 1998estimates; actual costs may be higher or lower.

2.4 LOW PROFILE AIR STRIPPER — BRIDGEPORT, CONNECTICUT


In April 1995, groundwater treatment was installed to remediate a site impacted by a gasolinespill from a product terminal in Bridgeport, Connecticut. The system produced such consistentlylow MTBE concentrations that it ceased operation sometime in 1998.


A heat exchanger was used to increase the temperature of the water from 55°F toapproximately 65°F as a pretreatment step. After heating, the water enters the shallow traylow profile air stripping units, which are arranged in two parallel trains of two units. The airstrippers are manufactured by Ejector Systems, Inc. (Model LP-5005). Water exiting the airstrippers is further treated using GAC and sand dual media filtration. The water flow rate isapproximately 11 gpm and the gas flow rate is approximately 500 standard cubic feet perminute (scfm), resulting in an air-to-water ratio of 340 to 1. The influent water qualityparameters at the site are presented in Table 16. Design and operating parameters for the airstripping treatment system are summarized in Table 17.

Capital Costs

Pretreatment system, air strippers, off-gas treatment, and GAC polishing $1,714,000

Total capital costs $1,714,000

Amortized annual cost at 7 percent for 30 years $138,125

Annual O&M Costs

Utility costs (electrical power and natural gas) $145,000

Granular activated carbon $20,000

Chemical costs (catalyst and scale control) $67,000

General O&M (labor and miscellaneous supplies) $127,000



Amortized Costs/1000 Gallons1 $14.50

Table 15. Capital and Annual O&M Costs (1999) at Culver City, California

1Based on a calculated treated groundwater flow rate of 94,000 gallons per day at continuous operation.

23

The off-gas released from the primary air stripper is treated with a catalytic oxidizer.Off-gases released from the secondary air stripper are directly exhausted to the atmosphere.


Initially, concentrations of MTBE entering the primary air stripper unit ranged from 280,000to 2,400,000 µg/L. Concentrations entering the secondary air stripper unit ranged from 100to 14,000 µg/L. Treated effluent MTBE concentrations ranged from 50 to 200 µg/L. Sampleswere collected on a monthly basis for a period of 1 year following the start-up of thetreatment system, but regular sampling was discontinued soon after due to very low MTBElevels. By 1998, MTBE concentrations were low enough (i.e., 50 to 200 µg/L) for treatmentsystem operation to cease. Influent and effluent data for MTBE and BTEX are presented inTables 18 and 19, respectively. Influent and effluent MTBE data are represented in Figure 9.Removal efficiencies and performance data for the air stripper are illustrated in Figures 10a,10b, and 11. All figures were generated using the detailed performance data shown inTables A-4a and 4b of Appendix A.


Calcium (mg/L) 61

Iron (mg/L) 21

Manganese (mg/L) 5.2

Phosphate (mg/L) 0.2

Inlet pH 6.6

Temperature (°F) 55 to 65

Table 16. Average Influent Water Quality Parameters at Bridgeport, Connecticut


Unit specifications (x 4) Low profile air stripper

Configuration Two parallel systems of two in series

Water flow rate (gpm) 20 11

Gas flow rate (cfm) 1,000 500


Maximum influent MTBE concentration (µg/L)Primary AS: 2,400,000Secondary AS: 14,000

Maximum influent BTEX concentration (µg/L)Primary AS: 34,000Secondary AS: 70

MTBE treatment goal (µg/L) 50

Removal efficiency (%) 99.9

Table 17. Design/Operating Parameters for Low Profile Air Stripperat Bridgeport, Connecticut

AS: Air stripper.

24

DateInfluent(µg/L)

Primary Stripper Effluent(µg/L)

Secondary StripperEffluent (µg/L)

April 1995 2,400,000 3,100 <50

May 1995 1,100,000 14,000 <50

June 1995 1,100,000 2,700 <50

July 1995 960,000 1,100 <50

August 1995 630,000 90 <50

September 1995 360,000 150 <50

October 1995 490,000 160 <50

November 1995 480,000 250 <50

December 1995 480,000 3,500 100

February 1996 580,000 1,400 <50

March 1996 200,000 6,600 200

Table 18. Air Stripper Performance Data for MTBE at Bridgeport, Connecticut

Date Influent (µg/L)Primary Stripper Effluent

(µg/L)Secondary Stripper

Effluent (µg/L)

April 1995 34,000 50 <10

Mary 1995 14,600 <10 <10

June 1995 26,900 60 20

July 1995 22.600 70 20

August 1995 18,500 30 20

September 1995 11,000 <10 <10

October 1995 21,000 <10 <10

November 1995 15,900 <10 <10

December 1995 19,300 30 <10

February 1996 16,500 <10 <10

March 1996 15,100 30 <10

Table 19. Air Stripper Performance Data for BTEX Compounds at Bridgeport, Connecticut

25

Figure 10a.MTBE removal efficiency at Bridgeport, Connecticut.

Rem

oval

Effi

cien

cy (

%)

Through S1

Through S2

Through S1 & S2

Figure 9.MTBE concentrations at Bridgeport, Connecticut.

MT

BE

Con

cent

ratio

n (m

g/L)

26

Figure 11.Removal efficiency reliability at Bridgeport, Connecticut.

Per

cent

age

of T

ime

Exc

eedi

ng R

emov

al E

ffici

ency

(%

)


Figure 10b.BTEX removal efficiency at Bridgeport, Connecticut.

Rem

oval

Effi

cien

cy (

%)

Through S1

Through S2

Through S1 & S2

27


The capital cost of the system was approximately $530,000 (1995 dollars). Annual O&Mcosts were approximately $48,000 during the mid-1990s. A breakdown of these costs forremoving MTBE from groundwater is presented in Table 20.

2.5 LOW PROFILE AIR STRIPPER — CHESTER, NEW JERSEY


In 1998, a low profile air stripper was installed at a site in Chester, New Jersey, to removeMTBE from a domestic well. The well water is pumped on an as-needed basis at 50 gpm.The treated water is stored prior to its use and then pumped at 15 gpm through thedistribution system. The treatment system had been operating for over 18 months at the timeof data collection for this report.


Prior to air stripping, extracted groundwater is passed through a two-step pretreatmentsystem consisting of acid neutralization and water softening. Following pretreatment, thewell water is routed to a four-tray shallow tray low profile air stripper manufactured by NEEP(Model #2341-P). The well water is then polished using GAC and chlorinated prior to use.

Capital Costs

Towers (x 4) $132,500



Annual O&M Costs

Operating costs not related to MTBE treatment $84,000

Power requirement $6,000

Labor $5,760

Parts replacement $8,100

Air stripper cleaning $5,220

System oversight $6,000




Table 20. Capital and Annual O&M Costs (1995) at Bridgeport, Connecticut

1Based on an 11-gpm flow rate with continuous operation.

28

Influent water quality parameters of the extracted groundwater are shown in Table 21. Designand operating data for the air stripping system are presented in Table 22. Since the start-upof the system, no problems have been encountered and no parts have been replaced. Systemmaintenance (i.e., cleaning and inspection) is performed on a semi-annual basis.

The off-gas from the air stripper is directly exhausted to the atmosphere without priortreatment.


Trichloroethylene (TCE) was detected in the well water at the beginning of system start-up.However, the treatment system has successfully reduced TCE to non-detectable levels.

MTBE concentrations were reduced from up to 220 µg/L in the influent groundwater toconcentrations as low as 14 µg/L after the GAC polish, giving an average MTBE removalefficiency of 94 percent for the entire system. Unfortunately, the effluent MTBEconcentration out of the air stripper was not measured. Removal efficiency is less than orequal to 94 percent for the air stripper units.


Hardness (mg/L as CaCO3) 257

pH 6.1

Temperature range (°F) 40 to 45

Table 21. Average Influent Water Quality Parameters at Chester, New Jersey


Unit specificationsFour trays~5-feet wide, 3.5-feet long, and 6.5-feet high

Configuration Single low profile air stripper

Water flow rate (gpm) 1 to 50 15

Air flow rate (cfm) 300 150


Maximum MTBE influent concentration (µg/L) Not available 220

MTBE effluent concentration (µg/L) 14

Other contaminants TCE

Removal efficiency (%) 941

1Includes post-treatment GAC polishing step performance.

TCE: Trichloroethylene.

Table 22. Design/Operating Parameters for Low Profile Air Stripper at Chester, New Jersey

29


The capital cost for installing the air stripper was $15,000 (1998 dollars), and an annualamount of $4,460 is needed for O&M. A detailed description of the costs related to thetreatment system is presented in Table 23.

2.6 PACKED TOWER AIR STRIPPERS — RIDGEWOOD, NEW JERSEY


The treatment facility in Ridgewood, New Jersey, is an air stripping facility designed toremove VOCs from two municipal wells. The facility was originally designed to treat up to635 gpm, although only 525 gpm is currently being pumped from the wells, which operate75 percent of the time.

The treatment facility was originally constructed in 1991 and consisted of a single airstripping tower designed to remove 99 percent of perchloroethylene (PCE) in the blendedinfluent. Several influent water quality parameters for the blended groundwater supply aresummarized in Table 24. Raw water from the two wells was pumped through the air stripperand into a clear well where chlorine was added for disinfection. From the clear well, thetreated water was pumped into the municipal distribution system. In 1997, a second air

Capital Costs



Annual O&M Costs

Power requirements $3,267

Chemical addition (chlorine) $75

Labor (16 hours/year at $70/hour) $1,120




Table 23. Capital and Annual O&M Costs (1998) at Chester, New Jersey

1Calculation based on 15-gpm flow rate and operation for periods of 12 hours/day, 7 days/week.


pH 7.7

Alkalinity (mg/L as CaCO3) 160 to 170

Hardness (mg/L as CaCO3) 200 to 250

Table 24. Average Influent Water Quality Parameters at Ridgewood, New Jersey

30

stripping tower was added to the facility in response to the detection of MTBE in one of thewells. The facility was reconfigured such that the new air stripping tower (AST-2) wasdedicated to treating water from the well containing MTBE, while the original air strippingtower (AST-1) was dedicated to the well without MTBE. The treated water from both airstripping towers was discharged into the clear well, after which the water was disinfected anddistributed. The facility has continued to operate in this configuration.


As mentioned, AST-1 was originally designed to remove 99 percent of the PCE in the blendedinfluent from the two wells. The design information for AST-1 is presented in Table 25.AST-2 was added in 1997 and designed to reduce MTBE concentrations in the influent from689 to 15 µg/L (97.8 percent removal). This concentration was selected as a target concentra-tion since it is close to MTBE’s taste and odor threshold. The new air stripping tower has the

ParameterAST-1 AST-2

Design Operating Design Operating

Manufacturer Hydro Group, Inc.1 Hydro Group, Inc.1

Model number PCS-69.23 PCS-69.23

Year installed 1991 1997

Shell material Aluminum2 Aluminum with interior coating

Tower diameter (feet) 5.75 5.75

Packed bed depth (feet) 23 23

Packing media 2-inch Tri-Packs3 2-inch Tri-Packs

Other contaminants PCE PCE

Maximum influent MTBEconcentration (µg/L)

689

Average influent MTBEconcentration (µg/L)

90

Effluent MTBE concentration (µg/L)

15 (goal);70 (standard)

15

Percent removal (%) 97.8 83.3

Water flow rate (gpm) 635 300 225 225

Liquid loading rate (gpm/sf) 24.6 11.6 8.7 8.7

Air flow rate (cfm) 4,280 4,280 7,500 7,500

Air-water ratio 50:1 110:1 250:1 250:1

Number of air blowers 1 1

Blower motor size (Hp) 5 10

Table 25. Design/Operating Parameters for Packed Tower Air Stripperat Ridgewood, New Jersey

1Now Layne Christensen Company, Bridgewater, New Jersey.2Tower shell interior coated with epoxy in 1997.3Jaeger Products, Inc., Houston, Texas.

31

same physical dimensions as AST-1, but was designed to handle a lower liquid loading rateat a higher air-to-water ratio than AST-1 (see Table 25).

With the addition of AST-2, the operating parameters of AST-1 were modified because thisair stripper was now treating only one well. Neither AST-1 nor AST-2 required off-gastreatment systems. A summary of the current operating configurations for both towers isprovided in Table 25.


Following the installation of AST-2, MTBE was no longer detected in the raw well water. Thetreatment system continued operating to remove PCE. The only information availableregarding MTBE removal rates at this facility is from system performance reportsimmediately prior to the installation of AST-2. For the first few months following thedetection of MTBE, the original system was successful in reducing MTBE concentrations inthe water to levels below New Jersey’s maximum contaminant level (MCL) of 70 µg/LMTBE. At that time, the concentration of MTBE in the blended raw water from the two wellsaveraged approximately 90 µg/L. With AST-1 operating at a liquid loading rate of20 gpm/square feet (sf) and an air-to-water ratio of 60 to 1, approximately 30 percent MTBEremoval was achieved.

Although no operating data is available to confirm satisfactory operation of the air strippingtower that was specifically designed to remove MTBE (AST-2), this case study illustrates thatthe original air stripper, which was not designed for MTBE removal, was able to achievesome reduction in MTBE.


The construction cost of the original air stripping system (AST-1) in 1991 was approximately$450,000 (which includes the air stripper, blower, piping, and controls, in addition to aconcrete clear well, booster pumps, and a building to house the pumps, blowers, and controls).The cost associated with the addition of AST-2 in 1997 was approximately $200,000 (whichincludes the purchase of a new tower, blower, piping, and controls). This accounts for theconstruction costs associated with the extension of the existing building to house the newblower, in addition to the cost associated with an internal epoxy coating for the original airstripper (AST-1). Thus, the total capital cost of the facility is approximately $770,000. TheO&M costs associated with the facility are approximately $72,000 per year. A breakdown ofall the costs is presented in Table 26.

32

2.7 PACKED TOWER AIR STRIPPER — ROCKAWAY TOWNSHIP, NEW JERSEY


A packed tower air stripper was installed in 1982 to treat volatile organic contaminants,including TCE, PCE, trans-1,2-dichloroethylene (DCE), di-isopropyl ether (DIPE), andMTBE, in the groundwater supply for Rockaway, New Jersey. The air stripper was originallya pretreatment step for GAC, but replaced GAC in 1983 as raw water DIPE and MTBEconcentrations declined. The GAC system was maintained in operable condition to serve asa backup for the air stripper.

This mode of operation continued until 1995, when the original air stripper was replaced witha new one. The new air stripping tower was not designed to remove DIPE and MTBE becausetheir concentrations were declining over time. Within approximately 2 years of tower replace-ment, though, a second accidental UST release occurred, causing MTBE to appear onceagain in the supply wells. Since the MTBE levels resulting from the second release wererelatively low (approximately 5 to 10 µg/L), the Township was able to modify the existing airstripping tower to provide adequate treatment. The modified system configuration is stillmaintained and has been effective in producing treated water with MTBE levels below1 µg/L.

Capital Costs

Installation of AST-1(Includes tower, blower, piping, controls, concrete clear well, booster pumps andbuilding to house tower, blower, and controls)

$450,000

Installation of AST-2(Includes tower, blower, piping, controls, and building expansion)

$200,000

Total Capital Costs1 $770,000


Annual O&M Costs

Power requirements (unit cost of $0.12 kWh) $53,000

Sampling $5,000

Labor (5 hours/week at $40/hour) $11,000

Miscellaneous expenses $3,000


Total annual costs1 $134,000


Table 26. Capital and Annual O&M Costs (1991, 1997) at Ridgewood, New Jersey

1Cost is based on year 2000 values.2Based on a 525-gpm flow rate and 75 percent of the time operation.

33


1982 Treatment System

The air stripping tower installed in 1982 was manufactured by Layne (currently known asLayne Christensen Company of Bridgewater, New Jersey). It was one of the first air strippingsystems in the United States designed for VOC removal from municipal water supplies. Todetermine the design criteria for the air stripper, a series of pilot-scale tests was conducted atthe Township’s well site. Based on these tests, the air stripping tower was designed to achieve99.9-percent removal of DIPE, which was determined to be primarily responsible for tasteand odor problems. The design parameters of the 1982 air stripping tower are summarized inTable 27. The treated water was stored in a clear well followed by either polishing with GACand chlorine disinfection or chlorine disinfection and direct routing into the distributionsystem. No off-gas treatment was required for this system.

1982 Tower 1995 Tower

Parameter Design Operating Design Operating

Manufacturer Layne Remedial Systems, Inc.

Shell material Aluminum Fiberglass Reinforced Plastic

Tower diameter (feet) 9 9

Packed bed depth (feet) 25 25

Packing media 3-inch Tellerettes1 3.5-inch LanPacs2

Other contaminants TCE, PCE, trans-1,2-DCE, DIPE TCE, PCE, trans-1,2-DCE

Maximum MTBE influentconcentration (µg/L)

60 <1 5 to 10

Effluent MTBEconcentration (µg/L)

<1 <1

Removal efficiency (%) 95 65

Water flow rate (gpm) 1,400 1,500

Liquid loading rate (gpm/sf) 22 23.6

Air flow rate (cfm) 37,500 20,000


Number of air blowers 2 1

Blower motor size (Hp) 100 30 35

Table 27. Design/Operating Parameters for Packed Air Stripping Towerat Rockaway Township, New Jersey

1Ceilcote Co., Beria, Ohio.2Lantec Products, Inc., Agoura Hills, California.

DCE: Dichloroethylene.

DIPE: Di-isopropyl ether.

34


The replacement air stripping tower that was brought online in 1995 was manufactured byRemedial Systems, Inc., and was designed to meet VOC removal criteria (Table 28). Theexpected influent concentration for MTBE was relatively low. As a result, MTBE did notgovern the air stripping tower design. By 1995, detections of MTBE and DIPE had ceased inthe Township’s water supply. From the criteria listed in Table 28, it is clear that the moststringent requirement was the 99.9-percent removal of TCE that was still present in theTownship’s groundwater supply. The design parameters for the second air stripping tower tomeet these criteria are summarized in Table 27. The significant difference between the air-to-water ratios for the original and replacement air stripping towers is primarily due to thefact that TCE has a much higher Henry’s Law constant than MTBE and, therefore, is easierto remove from water. The design specifications for the replacement system were developedwithout the benefit of a pilot study. This was possible since the design of air stripping towersfor removal of common VOCs, such as TCE, had become fairly routine by 1995 andsufficient operating data was available to use for this design.

In 1997, MTBE was again detected in the Township’s water supply. The Township responded byreplacing the existing 30 horsepower (Hp) blower motor with a new 35 Hp motor to increaseair flow through the air stripping tower. This modification resulted in an air flow increase ofapproximately 200 cfm, which did not significantly affect the design air-to-water ratio.



Although sampling data are not available for analysis in this report, the air stripping towerconsistently achieved 95-percent removal of MTBE during the first 12 months of operation(February 1982 to February 1983). Influent MTBE concentrations during this period rangedfrom 50 to 60 µg/L and, thereafter, decreased to below 10 µg/L. Since the detection limit for

CompoundDesign Influent

Concentration (µg/L)Design Effluent

Concentration (µg/L)Design Removal

Efficiency (%)

Chloroform 10 1 90

cis-1,2-dichlorethylene 15 5 67

1,1-dicholorethane 10 1 90

1,1-dichlorethylene 10 1 90

MTBE 5 1 80

PCE 5 0.5 90

1,1,1-trichlorethane 30 10 67

TCE 500 0.5 99.9

Carbon tetrachloride 5 0.5 90

Table 28. VOC Criteria for 1995 Air Stripping Tower at Rockaway Township, New Jersey

35

MTBE is 0.5 µg/L, analyzing the air stripping tower performance after February 1983became difficult. The only measure of performance from 1983 to 1995 is that the airstripping tower operating alone was able to eliminate taste and odor problems in theTownship’s drinking water supply.


A summary of representative influent water quality parameters is provided in Table 29. Asshown in Figure 12 and Table A-5 of Appendix A, the concentration of MTBE in thecombined raw influent ranged from non-detect (less than 0.5 µg/L) to 11.4 µg/L. During thissame 30-month time period, the maximum MTBE concentration in the air stripping towereffluent was 2.0 µg/L. Furthermore, MTBE was non-detect in 47 of the 69 samples collected.



Total dissolved solids (mg/L) 374

Manganese (mg/L) 0.01

Iron (mg/L) 0.05

Hardness as CaCO3 (mg/L) 217

pH 7.37

Corrosivity –0.28–

Table 29. Average Influent Water Quality Parameters at Rockaway Township, New Jersey

Figure 12.MTBE concentrations versus time at Rockaway, New Jersey.

MT

BE

Con

cent

ratio

n (p

pb)

Sample Date

36

Although the low influent MTBE levels make it difficult to analyze the performance of thisair stripping tower, it was possible to draw some conclusions from the data where MTBE wasdetected in the effluent. Figure 13 shows that while the air stripping tower performancevaried widely over the period of operation, the average MTBE removal efficiency wasapproximately 65 percent. Figure 14, which depicts the performance reliability curve for thissystem, indicates that this tower removed 80 percent of MTBE approximately 45 percent ofthe time. However, the system was operating at low MTBE influent concentrations, which

Figure 13.MTBE removal efficiency versus time at Rockaway, New Jersey

MT

BE

Rem

oval

Effi

cien

cy

Sampling Date

Figure 14.Removal efficiency reliability at Rockaway, New Jersey.

Per

cent

age

of T

ime

Exc

eedi

ng R

emov

al E

ffici

ency

Removal Efficiency

37

may have resulted in reduced removal efficiency. Although percent MTBE removal was low,the data available for the 1995 air stripping tower indicate that this system is capable ofachieving a moderate degree of MTBE removal, even though it was not specifically designedfor this VOC.



The total construction cost of the air stripping system in 1982 was approximately $375,000.Using historical Consumer Price Index values published by the U.S. Department of Labor,this equates to $645,750 in year 2000 dollars. While this cost may seem excessive incomparison to modern air stripping systems, the cost should be considered in the context ofthe time: a limited number of manufacturers were available in 1982 and experience withfull-scale construction was limited.

The estimated annual O&M costs associated with the air stripping tower were approximately$160,000 (in year 2000 dollars). These costs include power ($135,000),1 sampling ($11,000),labor ($11,000),2 and an allowance for other miscellaneous repairs and replacement parts($3,000).


A breakdown of costs for the 1995 treatment system is shown in Table 30. The constructioncost associated with the replacement air stripping tower in 1995 was approximately$300,000, which included the costs for a new tower, clear well, air blower, piping, and a smallbuilding to house the blowers and booster pumps. This cost also included the demolition ofthe existing tower and blower, as well as the relocation of existing booster pumps. To developa representative cost estimate for the air stripping system that is currently in operation atRockaway Township, the following assumptions were made:

• First, an allowance for the demolition of the existing equipment was deducted from theconstruction cost given above since this would not be typically required for the constructionof a new air stripping tower.

• Second, the cost associated with the two booster pumps was added to the construction costsince these units would typically be installed as part of the air stripping system.

• Finally, the cost of upgrading the blower motor in 1997 was added to the total cost.

The net result, scaled to reflect year 2000 dollars, led to an estimated construction cost of$370,000.

1 Based on a unit cost of $0.12/kilowatt hour (kwh).2 Based on 5 hours per week at $40/hour (including fringe benefits).

38

The estimated annual O&M costs associated with the replacement air stripping tower areapproximately $120,000 in year 2000 dollars. These costs include power ($95,000),3

sampling ($11,000), labor ($11,000),4 and an allowance for other miscellaneous repairs andreplacement parts ($3,000). Note that the power costs for the replacement system aresignificantly lower due to the fact that the two original 100 Hp blower motors have beenreplaced with a single 35 Hp unit.

2.8 LOW PROFILE AIR STRIPPER — MAMMOTH LAKES, CALIFORNIA


In 1999, a fuel leak in a UST was detected in Mammoth Lakes, California. Concentrationsof MTBE measured in six groundwater monitoring wells in the vicinity of the leak rangedfrom non-detect (less than 5 µg/L) to as high as 463,000 µg/L. An interim groundwatertreatment system was installed and used from January 2000 until March 2000. During thisinterim period, treated water was stored onsite in a 21,000-gallon storage tank. The full-scaletreatment system was officially started in March 2000. Treated groundwater is nowdischarged to Dry Creek in accordance with an NPDES permit. An SVE system has alsobeen installed at the site. Organic vapors that are extracted from the subsurface are destroyedusing a catalytic/thermal oxidation unit. A timeline of events at the site is presented in Table 31.

3 Based on a unit cost of $0.12/kwh.4 Based on 5 hours per week at $40/hour (including fringe benefits).

Capital Costs

Installation of current air stripping operation in 1995 (Includes tower, blower,piping, controls, clear well, booster pumps, and building to house tower, blower,booster pumps, and controls)

$300,000



Annual O&M Costs

Power requirements (unit cost of $0.12/kWh) $95,000

Sampling $11,000

Labor (5 hours/week at $40/hour) $11,000

Miscellaneous expenses $3,000

Total Annual O&M Costs1 $120,000


Amortized Costs/1,000 Gallons2 $0.22

Table 30. Capital and Annual O&M Costs (1995, 2000) at Rockaway Township, New Jersey

1Cost is based on year 2000 values.2Based on a 1,300-gpm flow rate and continuous operation.

39


Four extraction wells are used to contain the groundwater plume. The system flow rate variesfrom approximately 2 to 15.5 gpm and averages 6.5 gpm. The water is heated and passedthrough two biologically activated GAC vessels to reduce concentrations of total nitrogen,total phosphorus, and bacteria prior to treatment with a shallow tray low profile air stripper.A liquid-phase GAC treats air stripper effluent prior to collection in a 21,000 gallon tank anddischarge to Dry Creek. Influent concentrations for a number of constituents in thegroundwater are shown in Table 32. Since the system start-up through June 2000, a total of1,016,000 gallons of water have been treated.

Air stripper off-gas is treated using two vapor-phase GAC vessels prior to discharge to theatmosphere. The flow rate of air through this treatment system is approximately 2,400 cfm.


MTBE effluent concentrations through the air stripper and the entire system can be found inTable 33. Removal efficiencies are greater than 99.9 percent through the air stripper. Off-gastreatment concentrations can be found in Table 34. Off-gas treatment removal efficienciesrange from 93 to 99.7 percent.


No cost data was readily available for this site.

Constituent Influent Concentrations (µg/L)

TPH-G 2,000 to 940,000

MTBE 660 to 97,000

Benzene 62 to 1,500

Table 32. Influent Constituent Concentrations for at Mammoth Lakes, California


Vapor extraction system change-over from 250 to 350 cfm thermaloxidizer unit

January 13, 2000

Treatment system start-up and testing February 29, 2000

Treatment system begins discharge to Dry Creek March 10, 2000

Vapor extraction system unit shut down and maintenance May 24, 2000

Vapor extraction system restarted June 16, 2000

Table 31. Timeline of Events at Mammoth Lakes, California

40

2.9 LOW PROFILE AIR STRIPPER — ELMIRA, CALIFORNIA


In 1997, the remediation of a petroleum pipeline leak in Elmira, California, began with theinstallation of two extraction and treatment systems. A timeline of the site remediation eventsis included in Table 35. One of the systems included a low profile air stripping unit andadsorption off-gas treatment system. The air stripping system performance data and back-ground information at the site were limited. However, performance information was availablefor the off-gas treatment system.

Date Influent (µg/L) Air Stripper Effluent (µg/L) Discharge Effluent (µg/L)

02/29/00 4,100 1.7 <0.5

03/01/00 4,000 0.6 <0.5

03/10/00 5,300 2.1 <0.5

03/11/00 6,200 NA NA

03/13/00 660 <0.5 <0.5

03/16/00 900 0.6 <0.5

03/22/00 5,800 <0.5 NA

03/29/00 5,400 NA NA

04/05/00 12,000 NA NA

04/12/00 8,500 NA NA

04/19/00 12,492 <0.5 <0.5

04/26/00 38,000 NA NA

05/04/00 35,000 NA <0.5

05/10/00 35,000 NA NA

05/16/00 18,000 NA NA

05/24/00 8,600 1 <0.5

06/01/00 15,000 1 <0.5

06/14/00 9,900 2 <0.5

Table 33. MTBE Air Stripping Performance Data at Mammoth Lakes, California

NA: Not analyzed.

Date

MTBEInfluent Off-Gas

(ppmv)

MTBEEffluent Off-Gas

after First GAC Vessel(ppmv)

MTBEEffluent Off-Gas

after Second GAC Vessel(ppmv)

03/13/00 0.015 0.002 <0.001

06/01/00 0.59 0.001 0.002

06/14/00 0.34 0.002 <0.001

Table 34. MTBE Off-Gas Treatment Performance Data at Mammoth Lakes, California

41


Groundwater is extracted at an average rate of 25 gpm and passed through a treatment trainconsisting of the following: an oil/water separator, bag filter, solar heating array, low profileair stripper, and two liquid-phase GAC vessels operating in series. Anti-scalant, biogrowthcontrol, and anti-foaming chemicals are added prior to the air stripper. The solar heating stepimproves air stripper efficiency. Influent water quality parameters at this site are listed inTable 36. Design parameters for the air stripping system are included in Table 37a.


Residents in Elmira, California, begin complaining about petroleum odors. Petroleumleak is discovered. Saturation of soil in the area of municipal sewer is detected.

Prior to 1997

Installation of extraction and treatment system (air stripper, liquid-phase GAC vessels inseries, and vapor-phase GAC).

1997

Installation of new off-gas treatment system (ADDOXTM). February 2000

Table 35. Timeline of Remediation at Elmira, California


Low Profile stripper specifications4-foot, 2-inch wide x 6-foot, 2-inch long x 6-foot, 8-inch tallFour trays

Configuration One air stripper One air stripper

Blower size15 Hp, originally10 Hp blower added at inlet for off-gas treatment

Water flow rate (gpm)30 to 60 gpm115 gpm

25 (average)30 (maximum)

Air flow rate (cfm) 600300 (average)525 (maximum)

Air-water ratio 39 90

Maximum MTBE concentration (µg/L) 210,000 NA

Maximum BTEX concentration (µg/L) 9,800 NA

MTBE treatment goal (µg/L)13 (required)1 (design)

NA

Removal efficiency (%) >99.9 NA

Table 37a. Design/Operating Parameters for the Low Profile Air Stripper at Elmira, California


Alkalinity as CaCO3 (mg/L) 250 to 350

pH (estimated average) 7.5

Total organic carbon (estimated average) (ppm) 3.6

Temperature (average) (°F) 62

Table 36. Average Influent Water Quality Parameters at Elmira, California

NA: Not available.

42

The low profile air stripper is manufactured by NEEP. The system has operated continuouslywith the exception of brief shutdown periods for scheduled and unscheduled maintenanceand carbon changeouts. The system had been operating for approximately 3 years at the timeof data collection for this report. Approximately 23,300,000 gallons had been treated as ofJuly 2000. Samples are collected monthly at the air stripper influent and GAC effluent andare analyzed for total petroleum hydrocarbon (gas and diesel range), BTEX, MTBE, DIPE,TBA, ethyl tertiary butyl ether (ETBE), and tertiary-amyl methyl ether (TAME).

Vapor-phase GAC vessels were originally installed to treat the air stripper off-gas. Thesewere in use for approximately 3 years. In February 2000, a new off-gas treatment systemcalled ADDOXTM (Model ADDOX6), manufactured by NEEP, was installed to provide morecost-effective off-gas treatment. GAC vessels remained at the site on standby. The ADDOXTM

system had been in operation for several months at the time of data collection for this report.This unit remains under a “testing phase” by NEEP to assess the degree of O&M requiredby the system. An ADDOXTM system consists of two or more reaction chambers filled withan inorganic, non-combustible media. At least one chamber adsorbs, while the other desorbs,destroys, and regenerates. VOC-laden air enters the adsorbing chamber and the contaminantsare captured on the adsorbent beds; clean air is then allowed to exit the chamber. Thecontaminants are released from the bed when a stream of clean, preheated air is blown intothe chamber during the regeneration phase. The VOCs are oxidized into carbon dioxide andwater through an exothermic catalytic oxidation reaction. The heat from the reactionincreases VOC desorption from the media. According to a NEEP ADDOXTM system vendor,the adsorption/desorption cycle is every 4 hours for the system operating at this site.

The system is designed to treat a maximum air flow rate of 600 scfm and a maximum VOCadsorption and destruction rate of 4.4 pounds per hour. The system is 11.5 feet long, 7.5 feetwide, and 9 feet tall, and designed to treat an off-gas stream containing total VOCconcentrations of 255 parts per million by volume (ppmv), of which 151 ppmv is MTBE.Design parameters for the off-gas treatment system are included in Table 37b.


Specifications 7-feet, 6-inches wide x 11-feet, 6-inches long x 9-feet tall

Configuration Two inorganic media beds alternating between adsorption anddesorption/regeneration phases

Blower size (Hp) 2

Air flow rate (cfm)600 for adsorption,60 for desorption

600 for adsorption,60 for desorption

Maximum MTBE concentration (ppmv) 500 393

Maximum BTEX concentration (ppmv) 6.6 NA

MTBE treatment goal (ppmv) <3 NA

Removal efficiency (%) >98 >99

Table 37b. Design/Operating Parameters for the Off-Gas Treatment System (ADDOXTM)at Elmira, California

NA: Not available.

43


Influent MTBE concentrations range from 1,700 to 100,000 µg/L. The final effluent from thesystem has consistently met NPDES discharge requirements. From start-up in September1997 through December 1999, MTBE concentrations have decreased from a range of 70,000to 100,000 µg/L to a range of 20,000 to 26,000 µg/L. This influent data is presented inFigure 15, based on detailed performance data shown in Table A-6 of Appendix A.Unfortunately, the performance of the air stripper cannot be independently evaluated fromthe rest of the treatment train because air stripper effluent has not been regularly monitored.

VOC concentrations entering the off-gas treatment system (vapor-phase GAC) from December1998 through March 2000 are provided in Figure 16. In almost every sampling event, effluentconcentrations were reduced to non-detect (less than 0.1 ppmv). Unfortunately, a limitednumber of samples from the original off-gas treatment system contained detectable levels ofMTBE. As shown in Figure 17, the ADDOXTM off-gas treatment system is more reliable thanthe vapor-phase GAC. During the first 3 months of operation, the ADDOX6 system treated600 cfm off-gas containing 65 to 393 ppmv MTBE. Destruction efficiency ranged from 88.3percent to greater than 99.9 percent.


Annual operating costs for the air stripper include the costs of power, labor, sampling, parts, andchemicals associated with cleaning, maintenance, and repairs. Annual O&M costs range from$18,350 to $31,050 (late 1990s). Approximately 4 to 6 hours per week are required to

Figure 15.MTBE influent concentrations at Elmira, California. Note: Effluent MTBE data are not available.

MT

BE

Con

cent

ratio

n (µ

g/L)

44

Figure 16.Off-gas treatment influent concentrations of BTEX and TPH-G (1998 to 2000) at Elmira, California.

Note: MTBE influent concentrations are shown in Figure 17.

Con

cent

ratio

n (p

pmv)

Total Hydrocarbons

TPHg

Benzene

Toluene

Ethylbenzene

Xylenes

Note: Effluent samples were taken on12/01/98 and 1/12/99 show that constituentconcentrations were <0.1 ppmv (ND), withthe exception of the total hydrocarbonson 12/01/98, which had concentrationof 2.16 ppmv.

Figure 17.ADDOXTM performance summary test data at Elmira, California.

VO

C C

once

ntra

tion

(ppm

v)

Sample Date

45

maintain the entire treatment system. At the time of data collection, the air stripper had onlyrequired cleaning three times (approximately once per year). Minimal replacement parts havebeen needed. The capital cost for the air stripper unit and control system ranged from $25,000to $30,000 (1997 dollars); the capital cost for air stripper appurtenances, including the filters,oil/water separator, and vapor-phase GAC vessels, was between $75,000 and $100,000.

The capital cost of the ADDOX6 off-gas treatment system is approximately $70,000. Theannual operating cost is projected based solely on the initial operating costs, since the unithas only been in operation since February 2000. NEEP’s initial O&M cost estimate is basedon assumptions about contaminant levels, the time for adsorption and desorption cycles,quarterly sampling, and an electrical usage rate of $4,205 per year ($11.52/day). Actualmaintenance and cleaning costs for the system were unknown at the time of data collectionfor this report. No major repairs or problems have occurred since system start-up. Routinemaintenance and troubleshooting can be monitored by the NEEP headquarters in NewHampshire through a modem interface that is installed in the control panel. Capital andannual operating costs for the ADDOXTM system are included in Table 38.

Capital Costs

Air stripper $25,000 to $30,000

ADDOXTM $70,000

Controls and appurtenances $75,000 to $100,000



Annual O&M Costs

Labor (4 to 6 hours/week at $110/hour) $23,400 to $33,800

Electricity $7,500 to $10,000

Electricity for ADDOX6 $4,205

Parts for cleaning, maintenance, and repairs $10,000 to $20,000

Sampling (once per month at $400) $4,800

Total Annual O&M Costs1 $61,355


Amortized Costs/1,000 Gallons2 $3.53

Table 38. Capital and Annual O&M Costs (1997) at Elmira, California

1Total amounts are based on an average of the given amounts.2Based on continuous operation at 25 gpm.

46

3. Analysis of System Cost and Performance

3.1 INTRODUCTION

As illustrated by these case studies, a variety of air stripper designs and treatment systemconfigurations can successfully meet the challenges posed by a range of MTBEconcentrations, influent water quality profiles, and effluent requirements. The nine casestudies presented in Section 2 illustrate the variability in system flow rates, operatingparameters, and air stripper configurations used for full-scale groundwater treatment. Acomparison of the design parameters, performance data, and costs associated with each ofthe treatment system is presented in Tables 39 and 40. Although many differences in thetreatment systems are apparent in these tables, several common elements are noticeable aswell. These are detailed in the following sections discussing treatment train design, airstripper performance, and cost considerations.

LocationLaCrosse,Kansas

Culver City,California

Ridgewood,New Jersey

Rockaway Township,New Jersey

Drinking water Yes No Yes Yes

Off-gas treatment No Thermal oxidation No No

Iron (mg/L) 0.021 2.4 Not available 0.05

Alkalinity as CaCO3(mg/L)

131 400 160 to 170 Not available

Stripper configuration

6-feet diameterx 33-feet tall

Fiberglass(x 2 series)

6-feet diameterx 39.5-feet tall(x 3 in series)

5.75-feetdiameter

x 23-feet tallTwo aluminum

towers(AST-1 and

AST-2)

9-feet diameter x 25-feet tallTwo strippers

(AS-2 replacedAS-1 in 1995)

Stripperoperation start-up date

September 1997 October 19991991 (AST-1)1997 (AST-2)

February 1982 (AS-1)1995 (AS-2)

Stripper operationtermination date

Current Current Current1995 (AS-1)

Current (AS-2)

Flow rate (gpm)350 (winter)

480 (summer)200

300 (AST-1)225 (AST-2)

1400 (AS-1)1500 (AS-2)

Operation mode8hours/day;6 day/week

Continuous 75 percent Continuous

Air-water ratio 156:1 to 214:1 670:1110:1 (AST-1)250:1 (AST-2)

100:1

Maximum MTBEconcentration (µg/L)

973 17,000 689 (AST-1)60 (AS-1)10 (AS-2)

Table 39. Comparison of the Design Parameters, Performance, and Costs Associated with Each of the Packed Tower Air Stripping Systems

(Continued on Next Page)

47

LocationLaCrosse,Kansas

Culver City,California

Ridgewood,New Jersey

Rockaway Township,New Jersey

Average MTBE (µg/L) 153 4,000 90 (AST-1) 5 to 10 (AS-2)

Effluent MTBE (µg/L) <10 <2 <70 (Goal) <1 (Goal)

Other contaminants None BTEX, TPH-G,TBA PCE

PCE; TCE; 1,1,1-TCA;chloroform; cis-1,2-DCE;

1,1-DCE; 1,1-DCA;carbon tetrachloride

Total capital costs $189,968 $1,714,000 $770,000 $300,000

Annual O&M costs $25,324 $359,000 $72,000 $120,000

Annual cost $40,633 $497,125 $134,052 $150,000

$/1,000 gallons $0.57 to $0.76 $14.00 $0.64 $0.22

Capital costs(year 2000 dollars)

$203,816 $1,771,613 $826,131 $338,976

Amortized capital costsat 7 percent for 30years(year 2000 dollars)

$16,425 $142,768 $66,575 $27,317

Annual O&M costs(year 2000 dollars)

$27,170 $371,067 $77,249 $120,000

Annual cost(year 2000 dollars)

$43,595 $513,835 $143,824 $147,317

$/1,000 gallons(year 2000 dollars)

$0.65 $4.89 $1.62 $0.19

Table 39. Comparison of the Design Parameters, Performance, and Costs Associated with Each of the Packed Tower Air Stripping Systems

DCA: Dichloroethane.

DCE: Dichloroethylene.

TCA: Trichloroethane.

(Continued from Previous Page)

48

LocationSomersworth,

NewHampshire

Bridgeport,Connecticut

Chester,New Jersey

MammothLakes,

California

Elmira,California

Drinking water No No Yes No No

Off-gas treatment NoCatalyticoxidation

No GACADDOXTM

treatment

Iron (mg/L) 5.6 21 NA NA NA

Alkalinity asCaCO3 (mg/L)

NA NA NA NA 250 to 350

Stripperconfiguration

One 4 traylow profileair stripper

Two sets ofparallel lowprofile air

strippers (primaryand secondary)

One 4 traylow profileair stripper

Onelow profileair stripper

Onelow profileair stripper

Stripper operation start-up date

December 1996 April 1995 Fall 1998 February 2000 1997

Stripper operationtermination date

May 2000 1998 Current Current Current

Flow rate (gpm)2 to 10

Typically 1011 15

2 to 15.5Average 6.5

25

Operation mode Continuous Continuous12 hours/day,7 days/week

Continuous Continuous

Air-water ratio 1,070:1 340:1 75:1 1,870:1 90:1

Maximum MTBEconcentration(µg/L)

1,670,000 2,400,000 220 97,000NA

(210,000 design)

Average MTBE(µg/L)

77,000 780,000 NA NANA

(9,800 design)

Effluent MTBE(µg/L)

<5,000 50 14 <0.5 <1.0 (design)

Othercontaminants

BTEX BTEX TCE BTEX, TPH-GBTEX, TBA, DIPE,

ETBE, TAME,TPH-G, TPH-D

Total capital costs $42,923 $530,000 $15,000 NA $185,000

Annual O&M costs $15,480 $48,000 $4,462 NA $61,355

Annual cost $18,939 $90,710 $5,670 NA $76,263

Table 40. Comparison of the Design Parameters, Performance, and Costs Associated with Each of the Low Profile Air Stripping Systems


49

3.2 TREATMENT TRAIN DESIGN

3.2.1 Pretreatment

In seven of the nine case studies summarized in this report, the extracted groundwaterunderwent some type of pretreatment prior to air stripping. The types of pretreatment usedincluded pH adjustment, water softening, water heating, iron precipitation, oil/water separation,and biological GAC to reduce nutrient loading prior to the air stripper. The addition ofchemicals to reduce scaling, biological growth, and foaming was also common.

The two case studies examined in this report that did not employ pretreatment were bothpacked tower air stripper systems (located in Ridgewood, New Jersey, and Rockaway Town-ship, New Jersey). Both of the systems were primarily designed to treat other VOCs (PCEand DIPE). MTBE concentrations in the first system were variable, but never requiredsignificant reduction (i.e., the required percent removal was less than 22 percent). In thesecond system, influent MTBE concentrations were low, ranging from non-detect (less than0.5 µg/L) to 12 µg/L and, therefore, did not require significant reduction. Systems withoutpretreatment understandably may encounter more operational difficulties associated withscaling and biofouling, which will reduce the removal efficiency of the air stripper system.

LocationSomersworth,

NewHampshire

Bridgeport,Connecticut

Chester,New Jersey

MammothLakes,

California

Elmira,California

$/1,000 gallons $22.00 $15.69 $1.44 NA $3.53

Capital costs(year 2000 dollars)

$47,109 $598,858 $15,504 NA $198,486

Amortized capitalcosts at 7 percent for30 years(year 2000 dollars)

$3,796 $48,260 $1,249 NA $15,995

Annual O&M costs(year 2000 dollars)

$16,990 $52,681 $4,897 NA $67,338

Annual cost (year2000 dollars)

$20,786 $100,941 $6,147 NA $83,333

$/1,000 gallons (year2000 dollars)

$13.88 $17.46 $1.04 NA $6.34

Table 40. Comparison of the Design Parameters, Performance, and Costs Associated with Each of the Low Profile Air Stripping Systems

NA: Not available.


50

3.2.2 Air Stripper System

The configuration of the air stripper unit is one of the most obvious design choices. The casestudies included in this review demonstrate that the appropriate configuration is determinedprimarily by the system flow rate. Systems with flow rates greater than 100 gpm were packedtower configuration; those less than 100 gpm were low profile air strippers. Other siteconstraints may influence the choice of air stripper design, particularly for systems with flowrates between 50 and 200 gpm. Packed tower units are more compact and require a reducedfootprint area. However, the packed tower configuration is also more conspicuous than a lowprofile air stripper. The heights of packed tower systems analyzed in this report ranged from25 to 35 feet.

Air stripping units were used at two of the case study sites as interim treatment systems. Dueto site-specific time constraints for implementing the interim remedy, pilot-testing was notconducted prior to system installation and full-scale use. At another site (Ridgewood, NewJersey), the air stripping unit was originally designed to address VOC contamination.Therefore, the design process was quite different at these sites. The use of air stripping as atemporary or interim remedy at these sites illustrates the convenience of this technology forquickly addressing MTBE contamination.

Long-term or permanent air stripping system designs vary from site to site due to the desiredamount of redundancy (i.e., factor of safety) and desired effluent quality. Since MTBE is notregulated under the Safe Drinking Water Act, air stripper systems in different states arerequired to meet different effluent concentrations for MTBE. Two of the case studies appearto have been over-designed; treatment train components were installed to ensure systemreliability, but were not needed. At one of these two sites, the unused treatment traincomponent was taken offline, but was later needed in response to a second UST release thatincreased influent MTBE concentrations. The balance between over-designing and under-designing is site-specific. Long-term site plans, available funding, and state, local, and ownerperceptions of acceptable system reliability and redundancy must be taken into account.

The potential decline in MTBE influent concentrations over time should be consideredduring treatment system design. At five of the nine case studies discussed in this report,MTBE concentrations declined over time. Two of the systems no longer needed to operateafter the first 3 to 6 years because MTBE concentrations were consistently low or non-detect.The ability to scale down the treatment system in response to declining influentconcentrations would improve system cost-effectiveness.

3.2.3 Post-Treatment

Post-treatment processes were common at sites examined in this report, regardless of whethertreated water was used for drinking water or merely discharged into the environment. Post-treatment was not needed at only two systems prior to discharge or disinfection and use.

51

Liquid-phase GAC was employed at six treatment systems; sand and anthracite filtration wasused at the seventh site. These filtration systems were designed to polish water quality andprovide an extra degree of safety to ensure that treatment system effluent met dischargerequirements. Post-treatment filtration was not designed to achieve VOC removal at any ofthe case study sites.

One of the sites needed to employ additional post-treatment for VOC removal. At the packedtower air stripping system in Culver City, California, a UV/H2O2 system was installed afterthe air stripping unit to disinfect and provide additional removal of oxygenates, includingTBA. Although air stripping was found to remove up to 90 percent of TBA at one of the casestudy sites (Culver City, California), TBA is more difficult to remove from water than MTBEand may govern air stripping design or require the use of post-air stripper advanced oxidationto meet effluent TBA requirements. In summary, while post-treatment is commonly used toaddress other VOCs or provide a safety factor, it is not common to use several treatmenttechnologies in series to remove MTBE.

3.2.4 Off-Gas Treatment

Four of the nine sites included in the case study analysis treated off-gases from the air stripperunits before emitting them to the atmosphere. Technologies used include thermal oxidation,catalytic oxidation, vapor-phase GAC, and an adsorption/thermal desorption and destructionsystem commercially available as the ADDOXTM system. While regulations vary nationwide,the need for an off-gas treatment system is typically governed by the expected mass releasedto the atmosphere per day. Emission requirements depend on state and local air qualityregulations and on the proximity of potential receptors. Data from the four case studies wasnot sufficient to compare the design considerations of different types of off-gas treatmentsystems.

3.3 TREATMENT SYSTEM PERFORMANCE

3.3.1 MTBE Removal

The case studies demonstrate that air strippers can successfully treat groundwater withinfluent MTBE concentrations as high as 2,400,000 µg/L (Bridgeport, Connecticut) and aslow as 10 µg/L (Rockaway Township, New Jersey). Depending on the design and operationof the air stripping system, average MTBE removal efficiencies ranged from 65 percent togreater than 99.99 percent at the nine case studies included in this report.

For the packed tower air stripping systems, average MTBE removal efficiencies were greaterthan 90 percent, with the exception of the site in Rockaway Township, New Jersey (where,on average, only 65 percent of MTBE was removed), and the site in Ridgewood, New Jersey(where approximately 30 percent was removed). However, the system at RockawayTownship, New Jersey, had low influent MTBE concentrations. Effluent MTBE

52

concentrations at this system were typically non-detect (less than 0.5 µg/L) and neverexceeded 2 µg/L. The system at Ridgewood, New Jersey, was not designed for MTBEremoval, but rather for PCE treatment. At the other packed tower treatment systems, effluentMTBE concentrations ranged from less than 2 µg/L to approximately 70 µg/L and wereconsistently below the state-specific standard for MTBE.

For the low profile air stripping systems, average MTBE removal efficiencies were allgreater than 90 percent. Average MTBE concentrations in treatment system effluent rangedfrom non-detect (less than 1 µg/L) to approximately 460 µg/L (site at Somersworth, NewHampshire). As with the packed tower air strippers, low profile air stripper performance wassufficient to meet the state MTBE standard.

Although four of the case study air stripping systems implemented off-gas treatment,performance data were only available for two of the systems (Mammoth Lakes, California,and Elmira, California). At Mammoth Lakes, influent concentrations to the vapor-phaseGAC system ranged from 15 to 590 parts per billion by volume (ppbv) MTBE. Capture anddestruction values for MTBE ranged from 93.3 to 99.7 percent. At Elmira, California,influent concentrations to the ADDOXTM off-gas treatment system were higher, ranging from65,000 to 393,000 ppbv MTBE. Capture and destruction efficiency for the ADDOXTM

system ranged from 88.3 to 99.9 percent.

3.3.2 System Reliability

Fouling and scaling were not an issue for most of the case study treatment systems,presumably because of the pretreatment systems described in Section 3.2.1. Ironconcentrations were fairly low in treatment system influent, ranging from 0.02 to 21 mg/L.Iron precipitation is lessened by a neutral or slightly acidic pH. Typically, the pH of influentwater was neutral or slightly basic; pH ranged from 6.6 to 8.7. At one system (Somersworth,New Hampshire), a buildup of silt resulted in a temporary system shutdown. This wasaddressed by increasing the frequency of air stripper cleaning.

A common theme among the case studies was fluctuations in influent MTBE concentrationsthat resulted in fluctuations in effluent concentrations. One response to increase systemreliability is to address influent fluctuations. As discussed in Section 2.1.3, spikes in influentMTBE concentrations at the site in LaCrosse, Kansas, were dampened by limiting pumpingfrom the most contaminated well. Another possibility is to install a blending tank prior to theair stripper influent. At other sites (e.g., Somersworth, New Hampshire), the efficiency of theair stripper system declined gradually over time as silt and other particles built up. Aftercleaning, air stripper efficiency improved greatly. Swings in operating efficiency can beaddressed by better pretreatment systems or increasing the frequency of cleaning.

Air stripper efficiency also decreases with temperature. Several air stripper systems reportedthis as a consideration (LaCrosse, Kansas, and Bridgeport, Connecticut). However,

53

temperature effects do not seem to be as important as the buildup of silt or changes in influentconcentrations. For example, at the Connecticut site, the lowest removal efficiency wasmeasured in August 1995. The impact of reduced temperatures during the winter months isnot apparent in the case study performance data presented in this report. However, airstripping systems located in colder climates will have noticeably higher O&M costs duringthe winter months since these systems are typically equipped with heating elements.

3.4 TREATMENT SYSTEM COSTS

Capital costs for the air stripping systems were reported to range from $15,000 ($ 1998) to$1.7 million (late 1990s). When expressed in year 2000 dollars to enable a direct comparisonbetween system costs, capital costs ranged from $15,500 to $1.77 million. Normalized by thedesign capacity of the system, capital costs ranged from $0.47/1,000 to $104/1,000 gallonscapacity. Taking the design log removal of MTBE into account, capital costs still rangedwidely, from $0.47/1,000 to $85/1,000 gallons/log removal.

Based on our review of the nine case studies presented in this report, O&M costs for airstrippers were a function of both system flow rate and performance, as shown in Figure 18.The data illustrate efficiency of scale (i.e., lower unit O&M costs [$/1,000 gallons treated] asthe size of the air stripping unit increased). The data also demonstrate that costs increase withpercent removal of MTBE, as expected. Costs ranged from approximately $1 to $10/1,000gallons for systems achieving greater than 90 percent removal. Costs were approximately$0.15 to $1/1,000 gallons for treatment systems achieving between 65- and 90-percentremoval.

Figure 18.Cost summary of MTBE removal by air stripping.

Note: No cost data available for the site at Mammoth Lakes, California.

Cos

ts p

er k

iloga

llon

($20

00)

Flowrate (gpm)

54

4. Model Evaluation

4.1 OVERVIEW OF MODELING SOFTWARE PROGRAMS

The performance data from five of the nine air stripper case studies were used to evaluate theaccuracy of two models that are commonly used to estimate the performance of low profile andpacked tower air strippers. The models chosen for this exercise include NEEP ShallowTray®

Modeler software and the ASAPTM Packed Tower Model (Michigan Technological University,2005).

4.1.1 North East Environmental Products (NEEP) Shallow Tray®

Low Profile Air Stripper Model

NEEP is a manufacturer of packed tower air strippers and low profile shallow tray airstrippers (North East Environmental Products, 2005). As part of the quality testing, NEEPanalyzed the performance of its commercially available ShallowTray® low profile air stripperby analyzing over 10,000 samples to test the air stripper’s performance at full-scale forremoving VOCs (USEPA Method 624). Results were used to create performance curvesillustrating removal efficiency at different VOC concentrations, temperatures, and flow rates.These performance curves are used in the proprietary ShallowTray® Modeler software tosimplify the process of predicting the performance of ShallowTray® air stripping systemsunder different operating conditions. The ShallowTray® model calculates removal versusflow rate for several contaminants, including BTEX, MTBE, and chlorinated VOCs. Themodel accounts for contaminant solubility, vapor pressure, water temperature, air tempera-ture, and influent concentrations.

4.1.2 Aeration System Analysis Program (ASAPTM) Packed Tower Model

The ASAPTM model was developed at Michigan Technological University and is commer-cially available separately or in a package with other modeling software as a comprehensivemodeling tool known as the Environmental Technologies Design Option Tool (ETDOT)(Michigan Technological University, 2005). ASAPTM uses mass transfer calculations topredict the performance of various air stripping designs, including packed towers, systemswith bubble or diffused aeration, and systems with surface aeration. Since these calculationsrequire chemical-specific properties (e.g., molecular weight, boiling point, Henry’s lawconstant, liquid and gas diffusion coefficients, aqueous solubility), ASAPTM is linked to aprogram called Software to Estimate Physical Properties (StEPP), which contains thephysical and chemical properties for over 600 compounds, many of which are designatedUSEPA priority pollutants. StEPP calculates the value of these properties at the specifiedtemperature and pressure.

The ASAPTM Packed Tower Aeration Model is designed to predict the performance ofcounter-current packed tower air strippers. This model calculates removal efficiency using

55

several simplifying assumptions, including steady-state, plug-flow reactor conditions forboth air and water streams, clean influent air stream, and equilibrium of contaminantconcentrations in air and water phases, as described by Henry’s Law (ASAP, 2005). Themodel can be used to assess the preliminary design and feasibility of air stripping processes,plan pilot-scale studies, or interpret pilot-scale results.

Model calculations can be performed in either the design or rating mode. In the design mode,the user specifies the required removal efficiency and the packed tower is then sized to meetthe treatment objectives for all contaminants. Model output includes the packed tower designand effluent concentration for each contaminant of concern. In the rating mode, theperformance of an operating packed tower can be compared with the expected performanceto see if the air stripper is operating effectively. Actual operating parameters (e.g.,temperature, contaminants, concentrations, packing material characteristics) are entered intothe model by the user or chosen from the model’s built-in database. The model-predictedremoval efficiency is compared with observed removal efficiencies to see if the air stripperis meeting expectations. Additional information about the ASAPTM model can be foundonline (Michigan Technological University, 2005) or in Hokanson et al., 1995.

4.2 LOW PROFILE AIR STRIPPER — SOMERSWORTH, NEW HAMPSHIRE

4.2.1 Modeled Scenarios

The removal efficiency predicted by the NEEP ShallowTray® Model was compared with theactual performance of the low profile air stripper operating in Somersworth, NewHampshire. Six different sets of parameters, or “cases,” were modeled, as shown in Table 41.Each case was tested at temperatures ranging between 66 to 70°F, centered around theaverage temperature of the effluent of 68°F. Cases One and Two had water flow rates of 3 and10 gpm, respectively, to reflect the minimum and maximum water flow rates of the system.Case Three used an air-to-water ratio of approximately 800, which was typically maintainedduring system operation. For these three cases, the maximum air flow rate of 900 scfm washeld constant to reflect the measured air-to-water ratio of 1,070. For Cases Four, Five, andSix, the water flow rate of 10 gpm was kept constant and the air flow rate was varied at 600,675, and 750 scfm, respectively. Data for each case can be found in Table B-1 of Appendix B.

Parameter Actual Case 1 Case 2 Case 3 Case 4 Case 5 Case 6

Water flow rate(gpm)

3 to 10,typically 10

3 10 8.4 10 10 10

Air flow rate(scfm)

900 900 900 900 600 675 750

Air-water ratio 1,070:1 2,244:1 673:1 801:1 450:1 505:1 560:1

Temperature (°F) 68 66 to 70 66 to 70 66 to 70 66 to 70 66 to 70 66 to 70

Table 41. Modeling Scenarios for Low Profile Air Stripper at Somersworth, New Hampshire

56

4.2.2 Discussion

A comparison of the theoretical and actual effluent MTBE concentrations shows that themodel predicted greater MTBE removal than what was actually observed. From August 1997through April 1998, actual effluent concentrations were significantly higher than theestimated effluent concentrations, most likely due to the build-up of silt that occurred in thestripper. In Cases Four, Five, and Six, the effluent concentrations were greater than the firstthree cases, but the model still predicted lower effluent concentrations than produced by theactual system.

4.3 LOW PROFILE AIR STRIPPER — CHESTER, NEW JERSEY


Data from the site at Chester, New Jersey, was verified using the NEEP ShallowTray®Modeler software. Only one scenario was modeled for this site, which can be described asfollows:

• NEEP Shallow Tray Low Profile Air Stripper: Model # 2641.

• Water flow rate 15 gpm.

• Air flow rate 150 scfm.

• Typical air-to-water ratio 75 to 1.

• Operational water temperature 40 to 45°F.

Based on performance data, the influent MTBE concentration was fixed at 220 µg/L.

4.3.2 Discussion

The model estimated an effluent MTBE concentration ranging from 74 to 86 µg/L for thevarying temperatures, resulting in removal efficiencies ranging from 61 to 67 percent. Theonly effluent MTBE concentration provided for this site (less than 14 µg/L) was measuredafter the GAC polishing step, so no direct comparison to actual performance can be made.Therefore, the overall removal efficiency through the GAC polishing step is estimated to begreater than 81 percent, based on model data.

4.4 PACKED TOWER AIR STRIPPER — LACROSSE, KANSAS


The removal efficiency predicted by the ASAPTM Packed Tower Model was compared withdata from the packed tower air stripper operating in LaCrosse, Kansas. Two different caseswere modeled to reflect differences between summer and winter flow rates. Typical operating

57

parameters and modeled cases are shown in Table 42. As indicated, flow rates of 480 and 350gpm were used to represent summer and winter flow rates. Temperatures of 60 and 70°F wereused for all of the tested parameters since the influent water temperature was unknown. Anair flow rate of 10,000 cfm was used in the model, resulting in air-to-water ratios of 156 and214. MTBE influent concentrations ranged from 46 to 954 µg/L for both modeled and actualscenarios. Effluent data was modeled for each of the two stages of the packed towers.

4.4.2 Discussion

A comparison of the actual and theoretical concentrations modeled at each stage of the airstripper is presented in Tables B-2 and B-3 of Appendix B. The predicted effluentconcentrations demonstrate better removal efficiencies than the actual effluent data. For 480gpm, the model predicted a removal efficiency of 99 percent; for 350 gpm, the modelpredicted a removal efficiency of 99.5 percent. Actual data showed that the removalefficiency ranged from 41 to 100 percent.

4.5 PACKED TOWER AIR STRIPPER — CULVER CITY, CALIFORNIA


ASAPTM model predictions were compared with actual removal efficiencies at a packed towerair stripper operating in Culver City, California. Packing properties (i.e., nominal size 2.5inches, geometric surface area 55 square feet per cubic feet [ft2/ft3], polypropylene materialdensity 5.1 pounds per cubic feet [lbs/ft3]) were inputted to the user-defined databasebecause the actual packing material (No. 2 NUPACTM) was not available in the model. Atemperature of 70°F was tested in the model to reflect the temperature range observed in theoperational data for the system. Design parameters used in the model included the following:

• Water flow rate 200 gpm.

• Air flow rate 7,000 scfm.

• Typical air-to-water ratio 700 to 1.

• Operational temperature 70°F.

Parameter Actual Case 1 Case 2

Water flow rate (gpm)480 (summer)350 (winter)

480 350

Air flow rate (scfm) 10,000 10,000 10,000

Air-water ratio 156:1 to 214:1 156:1 214:1

Temperature (°F) Not available 60 to 70 60 to 70

Table 42. Modeling Scenarios for Packed Tower Air Stripper at LaCrosse, Kansas

58

Actual MTBE concentrations entering the air stripper at Culver City, California, fromNovember 1999 through March 2000 were used in the model.

4.5.2 Discussion

Based on a comparison of the data, the model predicted lower effluent concentrations (0.04to 0.06 µg/L) than the actual effluent data (1.1 to 8.4 µg/L). A comparison of the actual andtheoretical concentrations modeled at each stage of the air stripper is presented in Table B-4of Appendix B.

4.6 PACKED TOWER AIR STRIPPER — ROCKAWAY TOWNSHIP, NEW JERSEY

4.6.1 Modeled Scenario

The predicted air stripper removal using the ASAPTM model was compared with actualremoval from a packed tower air stripper operating in Rockaway Township, New Jersey.Temperatures of 50 and 55°F were used in the two modeling cases to reflect operational datafor the system. A water flow rate of 1,500 gpm and an air-to-water ratio of 100 were used inthe model. Actual influent MTBE concentrations observed in the performance data for the1995 treatment system were also used in the model. Actual operating parameters andmodeled input parameters for each case are shown in Table 43.

4.6.2 Discussion

A comparison of the actual and theoretical concentrations modeled at each stage of the airstripper is presented in Table B-5 of Appendix B. The comparison shows that the modelpredicted lower effluent concentrations than the actual effluent data. The model predictedremoval efficiencies ranging between 93 and 96 percent through the air stripper; actualremoval efficiencies ranged between 14 and 91 percent.

4.7 SUMMARY OF MODELING RESULTS

The ASAPTM model predicted slightly better removal efficiency and slightly lower effluentMTBE concentrations than actual packed tower air stripping units at the four sites included

Parameter Actual Case 1 Case 2

Water flow rate (gpm) 1,500 1,500 1,500

Air flow rate (cfm) 20,000 20,000 20,000

Air-water ratio 100:1 100:1 100:1

Temperature (°F) 50 to 55 50 55

Table 43. Modeling Scenarios for Packed Tower Air Stripperat Rockaway Township, New Jersey

59

in the modeling analysis. There may be several reasons for this discrepancy. The ASAPTM

model assumes that the hydraulic configuration of the packed tower reactor is plug flow forboth air and water streams. This is the most efficient configuration. During actual systemoperation, some mixing, short-circuiting, or other non-ideal flow patterns may occur,reducing the effectiveness of contaminant-phase transfer from liquid to vapor. The percentremoval predicted using the NEEP model was in general agreement with the observedconcentration at the field site. A comparison of modeling results and actual systemperformance is shown in Figure 19.

On average, observed removal efficiencies were approximately 15 percent lower (ranging2 percent higher to 50 percent lower) than modeling predictions. The highest discrepancybetween predicted and observed percent removal occurred for the site at RockawayTownship, New Jersey, where concentrations of MTBE were already fairly low in the influent(ranging from less than 0.5 to 6.9 µg/L MTBE over the period of operation used for themodeling exercise). Model predictions showed better agreement with actual systemperformance at systems with higher influent MTBE concentrations (e.g., Culver City,California, and Somersworth, New Hampshire). The ability of these models to accuratelypredict air stripper performance contributes to the growing acceptance of air stripping as aproven technology to remove MTBE from groundwater supplies.

Figure 19.Comparison of modeling results to actual performance.

Pre

dict

ed R

emov

al

Actual Removal

60

5. Summary of Findings

The California MTBE Research Partnership identified a research need to assess the efficacyof air stripping for removing MTBE from contaminated groundwater. MTBE contaminationhas been reported at UST sites across the country. Although air stripping is a well-establishedtechnology for VOCs, like PCE, the technology has not yet been demonstrated to be cost-effective or reliable for MTBE treatment. As summarized in this report, the Partnershipidentified nine sites where air strippers are being used to address MTBE contamination ingroundwater. The Partnership obtained cost and performance data for each of the sites andanalyzed the data to assess the benefits, limitations, and costs of air stripping for MTBE. Twocommercially available models for predicting air stripping performance were assessed bycomparing model predictions with operating performance at several of the case study sites.Study findings, conclusions, and recommendations are summarized in this section.

5.1 CASE STUDY DATA COLLECTION

Through research efforts, nine air stripper systems operating at full-scale to address MTBEcontamination were identified. Information about site history, air stripper system design,configuration, influent MTBE concentrations, other influent water quality parameters,effluent MTBE goals, capital costs, and annual O&M costs were collected for each site.These data were provided to the Partnership by environmental consultants, air stripper manu-facturers, and state regulators. Some of the data could not be shared with the Partnership dueto ongoing litigation. Nevertheless, enough data was available to proceed with data analysisand model validation.

5.2 CASE STUDY DATA ANALYSIS

The case study analysis indicated that a variety of different treatment train configurations canuse air strippers to successfully remove a wide range of MTBE concentrations. InfluentMTBE concentrations were as high as 2,400,000 µg/L and as low as 10 µg/L in the casestudies included in this report. Average MTBE removal efficiencies ranged from 65 percentto greater than 99.9 percent, with the lower range occurring in systems that did not requiresignificant MTBE reduction.

Most of the air stripper system designs included some form of pretreatment to reduce thepossibility of scaling, biological growth, and foaming. Heating elements were included priorto air stripping in colder climates. Fouling and scaling were not an issue for most of the casestudy treatment systems because of this pretreatment. A buildup of silt occurred in onesystem, resulting in a temporary system shutdown. This problem was addressed by cleaningthe air stripper more frequently. Sites that did not employ pretreatment were designed toprimarily remove other VOCs and did not require significant MTBE reduction.

61

Air stripper configuration was primarily determined by the economics of different flow rates.Systems with flow rates below approximately 100 gpm were low profile systems; those withflow rates greater than 100 gpm were packed tower configurations. Air strippers were usedas interim treatment systems at some of the sites. Since air stripping is quick to implement,it is advantageous compared to other treatment methods (e.g., biological systems). Anotheradvantage of air strippers is the applicability to other VOC contaminants. However, at siteswith MTBE and TBA, the desired TBA removal may drive air stripping design considerationsor necessitate post-treatment specific to TBA.

Post-treatment was not needed for MTBE removal; however, GAC or other filtration systemswere frequently used as a polishing step. Off-gases treatment technologies were needed atfour of the nine case study sites. Technologies included thermal oxidation, catalyticoxidation, vapor-phase GAC, and an adsorption/thermal desorption system known asADDOXTM. Data were not sufficient to compare the cost and performance of different typesof off-gas treatment systems.

Influent MTBE concentrations declined over time at five of the nine case study sites. Two ofthe air stripping systems were no longer needed after 3 and 6 years of operations sinceinfluent concentrations were below discharge standards or were non-detect. Fluctuations ininfluent MTBE concentrations and swings in operating efficiency were common at the airstripper case studies, but were successfully addressed by changing well usage patterns andincreasing the frequency of cleaning. Air stripper efficiency also decreases with temperature.However, temperature effects were secondary to the effects of silt buildup or changes ininfluent concentrations. Systems in colder climates will understandably have higher O&Mcosts in winter due to heating costs.

Capital costs for the air stripper systems ranged from $43,000 ($1997) to $1.7 million (late1990s). Normalized by flow rate and expressed in year 2000 dollars, capital costs rangedfrom $0.47/1,000 to $103/1,000 gallons ($0.47/1,000 or $85/1,000 gallons/log removal).O&M costs were also a function of system flow rate and percent MTBE removal. Costsranged from $1 to $10/1,000 gallons for systems achieving greater than 90-percent removal.Costs were approximately $0.15 to $1/1,000 gallons for systems achieving between 65- and90-percent removal.

5.3 MODEL VALIDATION

Two different air stripping models were validated using performance data from several lowprofile and packed tower air stripper case studies. The ASAPTM model created at MichiganTechnological University was used to simulate the performance of three packed tower airstrippers operating at LaCrosse, Kansas; Culver City, California; and Rockaway Township,New Jersey. In this modeling program, operating parameters, such as influent MTBEconcentrations, air-to-water ratio, water flow rate, temperature, tower dimensions, andpacking media, were specified. The model was used to predict effluent MTBE

62

concentrations. Predicted effluent concentrations were slightly lower than the observedconcentrations at all four sites. Thus, the model-predicted removal efficiencies were slightlygreater than observed efficiencies.

For the low profile air strippers, a model created by NEEP was used to estimate effluentMTBE concentrations. A number of parameters were specified in the model, including air-to-water ratio, temperature, and flow rates. As with the ASAPTM model, the NEEP modelpredicted slightly lower effluent MTBE concentrations than those observed at the low profileair stripper operating in Somersville, New Hampshire. Despite the optimistic bias of thesetwo models in predicting more MTBE removal than was actually observed, the modelsagreed with observed removal efficiency within 15 percent. Model predictions showed evenbetter agreement with actual system performance at systems with higher influent MTBEconcentrations. The data illustrate that commercially available models are fairly accurate inpredicting actual air stripper performance.

5.4 CONCLUSIONS

Based on this review of air stripper systems that are operating to address MTBEcontamination, air strippers can be used to successfully and reliably remove MTBE fromdrinking water supply systems or groundwater remediation systems. This study provides abrief overview of water quality parameters, air stripper design and performance data, andcost summaries for each case study. MTBE was successfully removed, with efficienciesgreater than 90 percent, over a wide range of influent concentrations. Commercially availablemodels have been demonstrated to predict actual MTBE removal efficiency to within 15percent. Although model predictions of removal efficiency were biased slightly high, themodels provide a valuable tool for assessing air stripper performance during remedyselection and conceptual treatment system design. Expressed in year 2000 dollars, capitalcosts ranged widely, from $0.47/1,000 to $103/1,000 gallons capacity. O&M costs associatedwith the case studies ranged from $0.15 to $11/1,000 gallons of water treated.

63

6. References

California MTBE Research Partnership (1999). Evaluation of the Applicability of Synthetic Resin

Sorbents for MTBE Removal from Water. National Water Research Institute, Fountain Valley,

California.

California MTBE Research Partnership (2000). Treatment Technologies for Removal of MTBE from

Drinking Water: Air Stripping, Advanced Oxidation Processes, Granular Activated Carbon, Synthetic

Resin Sorbents, Second Edition. National Water Research Institute, Fountain Valley, California.

California MTBE Research Partnership (2001). Treating MTBE-Impacted Drinking Water Using

Granular Activated Carbon. National Water Research Institute, Fountain Valley, California.

California MTBE Research Partnership (2004). Evaluation of MTBE Remediation Options. National

Water Research Institute, Fountain Valley, California.

Hokanson, D.R., T.N. Rogers, D.W. Hand, F. Gobin, M.D. Miller, J.C. Crittenden, and J.E. Finn

(1995). “A Physical Property Resource Tool for Water Treatment Unit Operations.” Proceedings of

AWWA Annual Conference, Anaheim, California, pp. 411-422.

Michigan Technological University (2005). Environmental Technologies Design Option Tool,

ETDOT TM. Available online at www.cpas.mtu.edu/etdot.

North East Environmental Products (2005). North East Environmental Products, Inc Integrated

Environmental Technologies. Available online at www.neepsystems.com

Suflita, J.M., and M.R. Mormile (1993). “Anaerobic Biodegradation of Known and Potential

Gasoline Oxygenates in the Terrestrial Subsurface.” Environmental Science and Technology, 27(6):

976-978.

US Water News (1996). “Santa Monica Water Supply Threatened by MTBE.” US Water News Online.

July. Available online at www.uswaternews.com/archives/arcquality/6smonica.html

U.S. Environmental Protection Agency (1998). Oxygenates in Water: Critical Information and

Research Needs. Office of Research and Development, Washington, D.C. EPA/600/R-98/048.

U.S. Environmental Protection Agency (2005). Contaminant Focus: Methyl Tertiary Butyl Ether.

Technology Innovation Program. Available online at www.clu-in.org.

Yeh, C.K., and J.T. Novak (1995). “The Effect of Hydrogen Peroxide on the Degradation of Methyl

and Ethyl Tert-Butyl Ether in Soils.” Water Environment Research, 67(5): 828-834.

64

65

Table A-1.Air Stripper Performance Data for MTBE at La Cross, Kansas

DateInfluent(µg/L)

BetweenStripper(µg/L)

1st TowerRemovalEfficiency

(%)

ToTower (µg/L)

2nd TowerRemovalEfficiency

(%)

Tap(µg/L)

4/25/1997 389 – 287 26 353

4/26/1997 398 – 242 39 255

4/27/1997 393 – 210 47 240

4/28/1997 400 – 224 44 250

4/29/1997 589 – 359 39 310

5/6/1997 80.6 – 56.1 30 57.6

5/13/1997 140 – 74.3 47 61.5

5/21/1997 129 – 146 -13 94.4

5/27/1997 153 – 153 0 131

6/4/1997 143 – 16.3 89 176

6/16/1997 66 – 83.3 -26 83.6

6/23/1997 130 – 275 -112 318

7/1/1997 129 – 77.3 40 82.6

7/8/1997 143 – 154 -8 –

7/10/1997 – – 154 154

7/16/1997 143 – 97.4 32 103

7/22/1997 84.3 – 84 0 86.4

7/30/1997 143 – 79.2 45 78

8/5/1997 139 – 162 -17 276

8/12/1997 156 – 76.5 51 56.1

8/26/1997 164 – 368 -124 310

9/2/1997 167 – 163 2 158

9/9/1997 162 – 149 8 149

9/10/1997 161 16.1 90 <0.2 99 152

9/16/1997 138 13.8 90 <0.2 99 6.88

9/17/1997 142 12.6 91 <0.2 98 5.75

9/18/1997 139 14 90 <0.2 99 <0.2

9/23/1997 151 13.3 91 <0.2 98 <0.2

9/24/1997 147 14.1 90 <0.2 99 <0.2

9/30/1997 136 14.3 89 <0.2 99 3.87

10/8/1997 107 11.4 89 <0.2 98 <0.2

10/14/1997 115 <0.2 100 <0.2 – <0.2

10/21/1997 46.1 14.9 68 <0.2 99 66.1

Appendix A


66


DateInfluent(µg/L)



(%)

ToTower (µg/L)


(%)

Tap(µg/L)

10/29/1997 129 11 91 <0.2 98 3.96

11/18/1997 140 14 90 <0.2 99 58

12/9/1997 52.6 13.1 75 3.33 75 3.64

12/29/1997 954 168 82 29.4 83 48.9

1/13/1998 159 35.1 78 19.3 45 231

1/26/1998 197 51.4 74 – – 71.2

2/11/1998 93.9 17.9 81 4.02 78 <0.2

2/24/1998 125 23.9 81 5.01 79 38.1

3/3/1998 290 171 41 51.1 70 12.9

3/3/1998 973 220 77 51.4 77 14.2

3/10/1998 71.8 15.8 78 3.92 75 6.07

3/10/1998 98.5 20 80 4.75 76 6.75

3/18/1998 93.2 19 80 2.99 84 7.41

3/18/1998 85.1 18 79 4.05 78 9.11

3/24/1998 90 17.1 81 – –

3/24/1998 99.3 18.6 81 – –

3/25/1998 – – 4 3.78

3/25/1998 – – 3.92 3.64

4/1/1998 88.4 17.2 81 3.68 79 9.83

4/1/1998 110 19.9 82 4.08 79 10.5

4/9/1998 115 18 84 3.1 83 17.3

4/15/1998 99.7 <0.2 100 <0.2 – <0.2

4/21/1998 84 13.9 83 <0.2 99 <0.2

4/28/1998 97.6 13.3 86 <0.2 98 5.32

5/6/1998 83 8.4 90 <0.2 98 11.4

5/13/1998 110 10 91 <0.2 98 5.5

5/20/1998 98 15 85 2.6 83 16

5/27/1998 39.5 6.92 82 1.26 82 4.36

6/2/1998 91 16 82 2.5 84 5.6

6/9/1998 100 16 84 2.9 82 12

6/16/1998 92 16 83 2.6 84 3.7

6/24/1998 73 12 84 7.4 38 3.5

7/1/1998 87 13 85 2 85 2.8

7/7/1998 82.9 11.4 86 1.2 89 1.17

7/14/1998 227 29.5 87 2.46 92 7.14

7/21/1998 62.6 10.5 83 <0.2 98 2.85

7/28/1998 94.9 10.4 89 1.04 90 4.39



67


DateInfluent(µg/L)



(%)

ToTower (µg/L)


(%)

Tap(µg/L)

8/4/1998 108 12.7 88 2.08 84 20.8

8/11/1998 110 12.2 89 <0.2 98 27.5

8/19/1998 87.7 11.2 87 1.34 88 10.7

8/26/1998 70.4 12.6 82 <0.2 98 2.84

9/1/1998 108 15.2 86 3.03 80 23.6

9/9/1998 86.1 16.7 81 2.42 86 4.94

9/16/1998 85.3 15 82 2.55 83 5.01

9/30/1998 731 124 83 19.6 84 6.52

10/6/1998 88.9 16.5 81 4.32 74 3.78

10/14/1998 101 19.7 80 4.55 77 <0.2

10/20/1998 86.4 12.4 86 2.37 81 7.02

10/28/1998 77.7 12.7 84 2.53 80 6.09

11/3/1998 107 11.7 89 3.19 73 2.83

11/12/1998 73.3 17.6 76 5.22 70 7.96

11/18/1998 116 15.1 87 7.41 51 14.8

11/24/1998 121 12.6 90 1.03 92 1.38

12/2/1998 94 9.86 90 0.58 94 1.63

12/8/1998 143 16.5 88 3.29 80 3.58

12/16/1998 102 16 84 3.05 81 4.85

12/21/1998 339 52.6 84 9.82 81 2.9

12/28/1998 93.3 11.6 88 1.31 89 7.38

1/6/1999 72.8 8.9 88 1.45 84 2.93

1/12/1999 76.7 11.4 85 1.78 84 11

2/3/1999 87.6 11.8 87 1.29 89 2.52

3/3/1999 108 14.3 87 2.65 81 2.82

4/6/1999 <0.2 <0.2 <0.2 <0.2

5/5/1999 108 4.9 95 0.28 94 35.8

6/1/1999 134 29.4 78 7.98 73 15.2

7/7/1999 87.4 12.2 86 2.53 79 13

7/7/1999 132 19.6 85 – –

8/3/1999 – – 4.11 8.68

9/1/1999 78 11.5 85 1.62 86 1.28

9/29/1999 127 24 81 4.81 80 7.05

11/3/1999 109 17.5 84 3.04 83 5.93

12/1/1999 136 32.1 76 8.13 75 12.2

1/5/2000 161 26.4 84 8.04 70 24.2

2/1/2000 137 39.7 71 9.34 76 12.2


68

Table A-2.Air Stripper Performance Data for MTBE at Somersworth, New Hampshire

DateFlow

(gallons) Influent(µg/L)

Midfluent(µg/L)

Effluent(µg/L)

11/22/96 4,463 988,000 8 <5.0

11/23/96 7,290 1,290,000 <2.0 <5.0

11/24/96 72,359 886,000 <2.0 <5.0

11/27/96 45,998 1,670,000 <2.0 <5.0

12/4/96 76,511 694,000 73,300 <5.0

12/10/96 1,376 NA NA <5.0

12/11/96 4,450 NA NA <5.0

12/12/96 12,590 129,000 33,900 149

12/16/96 61,908 412,000 31,100 388

12/23/96 85,713 322,000 709 15

12/30/96 129,389 305,000 1,200 15

1/8/97 173,845 380,000 5,520 13

2/4/97 1,240,000 <2.0

2/28/97 65,300 32

4/10/97 32,100 147

4/30/97 26,500 61

6/3/97 16,100 20

6/25/97 19,700 41

7/31/97 39,800 126

8/28/97 12,400 607

10/15/97 25,500 157

11/20/97 13,400 613

12/18/97 7,920 4

1/12/98 72,300 249

2/19/98 80,000 990

3/24/98 61,700 18,800

4/13/98 20,200 1,010

4/28/98 22,100 33

5/26/98 26,800 10

6/29/98 9,810 284

7/29/98 16,700 8

8/27/98 107,000 12

9/30/98 12,300 95

11/23/98 12,700 60

12/21/98 10,400 29

1/20/99 4,200 32


69

Table A-2.Air Stripper Performance Data for MTBE at Somersworth, New Hampshire

Table A-3.Air Stripper Performance Data for MTBE at Culver City, California

DateFlow

(gallons) Influent(µg/L)

Midfluent(µg/L)

Effluent(µg/L)

3/1/99 945 18

4/5/99 1,660 36

5/4/99 1,040 <2.0

6/2/99 1,400 22

7/7/99 1,100 <10.0

8/4/99 700 <5.0

8/11/99 2,400 <5.0

8/18/99 2,900 <5.0

8/25/99 3,000 41

8/31/99 8,800 <5.0

9/29/99 1,800 <5.0

10/27/99 540 <5.0

11/30/99 520 <5.0

12/28/99 470 <5.0

1/27/00 210 <5.0

2/28/00 230 <5.0

3/30/00 130 <5.0

Trial #Influent (µg/L)

Effluent S1

(µg/L)%

RemovalEffluent S2

(µg/L)%

Removal

1 3,818 8.4 99.78 1.4 99.96

2 2,400 <1.2 99.95 <1.2 99.95

3 5,100 1.3 99.97 1.1 99.98

4 3,100 <1.2 99.96 <1.2 99.96

5 3,200 1.3 99.96 1.5 99.95

6 2,500 <1.2 99.95 <1.2 99.95


NA = Not available.

70

Table A-4a.Air Stripper Performance Data for MTBE at Bridgeport, Connecticut

Table A-4b.Air Stripper Performance Data for BTEX at Bridgeport, Connecticut

Date Influent(µg/L)

EffluentS1

(µg/L)

PercentRemoval

S1

EffluentS2

(µg/L)

PercentRemoval

S2

OverallPercent

Removal

4/1/95 2,400,000 3,100 99.87 50 98.39 99.998

5/1/95 1,100,000 14,000 98.73 50 99.64 99.995

6/1/95 1,100,000 2,700 99.75 50 98.15 99.995

7/1/95 960,000 1,100 99.89 50 95.45 99.995

8/1/95 630,000 90 99.99 50 44.44 99.992

9/1/95 360,000 150 99.96 50 66.67 99.986

10/1/95 490,000 160 99.97 50 68.75 99.990

11/1/95 480,000 250 99.95 50 80.00 99.990

12/1/95 480,000 3,500 99.27 100 97.14 99.979

2/1/96 580,000 1,400 99.76 50 96.43 99.991

3/1/96 200,000 6,600 96.70 200 96.97 99.900

Date Influent(µg/L)

EffluentS1

(µg/L)

PercentRemoval

S1

EffluentS2

(µg/L)

PercentRemoval

S2

OverallPercent

Removal

4/1/95 34,000 50 99.853 10 80.000 99.971

5/1/95 14,550 10 99.931 10 0.000 99.931

6/1/95 26,900 60 99.777 20 66.667 99.926

7/1/95 22,620 70 99.691 20 71.429 99.912

8/1/95 18,500 30 99.838 20 33.333 99.892

9/1/95 10,970 10 99.909 10 0.000 99.909

10/1/95 20,990 10 99.952 10 0.000 99.952

11/1/95 15,930 10 99.937 10 0.000 99.937

12/1/95 19,260 30 99.844 10 66.667 99.948

2/1/96 16,470 10 99.939 10 0.000 99.939

3/1/96 15,140 30 99.802 10 66.667 99.934

71

Table A-5.Air Stripper Performance Data for MTBE at Rockaway Township, New Jersey

DateInfluent(µg/L)

Effluent(µg/L)

Efficiency(%)

9/3/97 10.68 1.70 84

9/10/97 6.11 1.20 80

9/17/97 7.20 1.00 86

9/24/97 11.38 1.50 87

10/1/97 9.28 1.20 87

10/8/97 6.54 1.10 83

10/15/97 6.40 0.60 91

10/24/97 3.90 0.80 79

10/29/97 4.20 1.60 62

11/5/97 1.40 <0.5 64

11/12/97 1.60 <0.5 69

11/26/97 1.06 0.60 43

12/3/97 1.20 <0.5 58

12/24/97 0.80 <0.5 38

12/31/97 0.80 <0.5 38

1/14/98 0.70 <0.5 29

1/21/98 1.40 <0.5 64

1/28/98 3.50 0.90 74

2/4/98 1.60 0.60 63

2/18/98 1.10 0.80 27

2/25/98 2.00 <0.5 75

3/4/98 1.18 <0.5 58

3/11/98 0.90 <0.5 44

3/18/98 1.20 <0.5 58

3/25/98 1.12 0.80 28

4/1/98 2.10 0.70 67

4/8/98 1.32 0.90 32

4/15/98 1.38 1.20 13

4/22/98 0.90 <0.5 44

4/29/98 0.80 <0.5 38

5/6/98 0.77 <0.5 35

5/13/98 0.80 <0.5 38

5/20/98 0.60 <0.5 17

6/3/98 0.80 <0.5 38

7/1/98 0.60 <0.5 17

8/19/98 1.70 <0.5 71


72

Table A-5.Air Stripper Performance Data for MTBE at Rockaway Township, New Jersey

DateInfluent(µg/L)

Effluent(µg/L)

Efficiency(%)

9/2/98 5.00 2.00 60

10/14/98 6.90 1.20 83

10/21/98 4.70 0.90 81

10/28/98 2.70 0.60 78

11/4/98 1.60 0.80 50

11/18/98 1.19 <0.5 58

11/25/98 0.93 <0.5 46

12/30/98 <0.5 <0.5 0

2/24/99 <0.5 <0.5 0

5/6/99 <0.5 <0.5 0

5/20/99 <0.5 <0.5 0

6/3/99 <0.5 <0.5 0

6/17/99 <0.5 <0.5 0

7/1/99 1.14 <0.5 56

7/15/99 0.90 <0.5 44

7/29/99 1.09 <0.5 54

8/12/99 0.98 <0.5 49

8/26/99 <0.5 <0.5 0

9/23/99 0.95 <0.5 47

10/6/99 0.88 <0.5 43

10/21/99 0.85 <0.5 41

11/4/99 1.13 <0.5 56

11/18/99 0.89 <0.5 44

12/1/99 <0.5 <0.5 0

12/16/99 1.32 <0.5 62

12/30/99 0.65 <0.5 23

1/6/00 1.05 <0.5 52

1/13/00 1.01 <0.5 50

1/27/00 0.85 <0.5 41

2/3/00 1.02 <0.5 51

2/10/00 0.96 <0.5 48

3/7/00 <0.5 <0.5 0

3/21/00 <0.5 <0.5 0


73

Table A-6.Off-Gas System Performance Data for MTBE at Elmira, California

Date Influent (ppmv) Effluent (ppmv)

2/17/00 393 0

2/17/00 294 0

2/17/00 243 0

3/15/00 102 0

3/15/00 83 0

3/14/00 95 0.5

3/14/00 94 0.5

3/14/00 102 0

3/14/00 65 0

3/14/00 96 0

3/14/00 105 0

3/20/00 160 1

3/22/00 120 14

3/24/00 140 0

3/29/00 140 0

4/3/00 110 0

4/5/00 140 0

4/7/00 150 0

4/12/00 160 0

4/26/00 173 0

74

Table B-1.Modeling Data Comparison for Low Profile Air Stripper at Somersworth, New Hampshire

Appendix B

DateInfluent(µg/L)

Effluent(µg/L)

Case 11

(µg/L)Case 21

(µg/L)Case 31

(µg/L)Case 41

(µg/L)Case 51

(µg/L)Case 61

(µg/L)

11/22/96 988000 <5.0 0.02-0.08 0.44-1.18 0.23-0.66 2.64-6.32 1.48-3.69 0.92-2.36

11/23/96 1290000 <5.0 0.03-0.1 0.57-1.54 0.31-0.86 3.45-8.26 1.94-4.82 1.20-3.08

11/24/96 886000 <5.0 0.02-0.07 0.39-1.06 0.21-0.59 2.37-5.67 1.33-3.31 0.82-2.12

11/27/96 1670000 <5.0 0.04-0.14 0.74-1.99 0.40-1.12 4.47-10.7 2.51-6.24 1.55-3.99

12/04/96 694000 <5.0 0.02-0.06 0.31-0.83 0.16-0.46 1.86-4.44 1.04-2.59 0.65-1.66

12/12/96 129000 149 0-0.01 0.06-0.15 0.03-0.09 0.35-0.83 0.19-0.48 0.12-0.31

12/16/96 412000 388 0.01-0.03 0.18-0.49 0.10-0.28 1.10-2.64 0.62-1.54 0.38-0.98

12/23/96 322000 14.8 0.01-0.03 0.14-0.38 0.08-0.22 0.86-2.06 0.48-1.20 0.30-0.77

12/30/96 305000 14.8 0.01-0.02 0.13-0.36 0.07-0.20 0.82-1.95 0.46-1.14 0.28-0.73

01/08/97 380000 13.4 0.01-0.03 0.17-0.45 0.09-0.25 1.02-2.43 0.57-1.42 0.35-0.91

02/04/97 1240000 <2.0 0.03-0.10 0.55-1.48 0.29-0.83 3.32-7.94 1.86-4.64 1.15-2.96

02/28/97 65300 31.9 0-0.01 0.03-0.08 0.02-0.04 0.17-0.42 0.10-0.24 0.06-0.16

04/10/97 32100 147 0 0.01-0.04 0.01-0.02 0.09-0.21 0.05-0.12 0.03-0.08

04/30/97 26500 61.2 0 0.01-0.03 0.01-0.02 0.07-0.17 0.04-0.10 0.02-0.06

06/03/97 16100 20 0 0.01-0.02 0-0.01 0.04-0.10 0.02-0.06 0.01-0.04

06/25/97 19700 41.3 0 0.01-0.02 0-0.01 0.05-0.13 0.03-0.07 0.02-0.05

07/31/97 39800 126 0 0.02-0.05 0.01-0.03 0.11-0.25 0.06-0.15 0.04-0.10

08/28/97 12400 607 0 0.01 0-0.01 0.03-0.08 0.02-0.05 0.01-0.03

10/15/97 25500 157 0 0.01-0.03 0.01-0.02 0.07-0.16 0.04-0.10 0.02-0.06

11/20/97 13400 613 0 0.01-0.02 0-0.01 0.04-0.09 0.02-0.05 0.01-0.03

12/18/97 7920 4.3 0 0 0-0.01 0.02-0.05 0.01-0.03 0.01-0.02

01/12/98 72300 249 0-0.01 0.03-0.09 0.02-0.05 0.19-0.46 0.11-0.27 0.07-0.17

02/19/98 80000 990 0-0.01 0.04-0.10 0.02-0.05 0.21-0.51 0.12-0.30 0.07-0.19

03/24/98 61700 18800 0-0.01 0.03-0.07 0.01-0.04 0.17-0.39 0.09-0.23 0.06-0.15

04/13/98 20200 1010 0 0.01-0.02 0-0.01 0.05-0.13 0.03-0.08 0.02-0.05

04/28/98 22100 33.4 0 0.01-0.03 0.01 0.06-0.14 0.03-0.08 0.02-0.05

05/26/98 26800 9.8 0 0.01-0.03 0.01-0.02 0.07-0.17 0.04-0.10 0.02-0.05

06/29/98 9810 284 0 0-0.01 0-0.01 0.03-0.06 0.01-0.04 0.01-0.02

07/29/98 16700 8 0 0.01-0.02 0-0.01 0.04-0.11 0.03-0.06 0.02-0.04

08/27/98 107000 11.5 0 0.05-0.13 0.03-0.07 0.29-0.68 0.16-0.40 0.10-0.26

09/30/98 12300 94.9 0 0.01 0-0.01 0.03-0.08 0.02-0.05 0.01-0.031Data for all six cases ranges for 66 to 70°F. (Continued on Next Page)

75

Table B-1.Modeling Data Comparison for Low Profile Air Stripper at Somersworth, New Hampshire

DateInfluent(µg/L)

Effluent(µg/L)

Case 11

(µg/L)Case 21

(µg/L)Case 31

(µg/L)Case 41

(µg/L)Case 51

(µg/L)Case 61

(µg/L)

11/23/98 12700 59.7 0 0.01-0.02 0-0.01 0.03-0.08 0.02-0.05 0.01-0.03

12/21/98 10400 28.9 0 0-0.01 0-0.01 0.03-0.07 0.02-0.04 0.01-0.02

01/20/99 4200 32.2 0 0-0.01 0 0.01-0.03 0.01-0.02 0-0.01

03/01/99 945 17.8 0 0 0 0-0.01 0 0

04/05/99 1660 36.2 0 0 0 0-0.01 0-0.01 0

05/04/99 1040 <2.0 0 0 0 0-0.01 0 0

06/02/99 1400 22 0 0 0 0-0.01 0-0.01 0

07/07/99 1100 <10.0 0 0 0 0-0.01 0 0

08/04/99 700 <5.0 0 0 0 0 0 0

08/11/99 2400 <5.0 0 0 0 0.01-0.02 0-0.01 0-0.01

08/18/99 2900 <5.0 0 0 0 0.01-0.02 0-0.01 0-0.01

08/25/99 3000 41 0 0 0 0.01-0.02 0-0.01 0-0.01

08/31/99 8800 <5.0 0 0 0-0.01 0.02-0.06 0.01-0.03 0.01-0.02

09/29/99 1800 <5.0 0 0 0 0-0.01 0-0.01 0

10/27/99 540 <5.0 0 0 0 0 0 0

11/30/99 520 <5.0 0 0 0 0 0 0

12/28/99 470 <5.0 0 0 0 0 0 0

01/27/00 210 <5.0 0 0 0 0 0 0

02/28/00 230 <5.0 0 0 0 0 0 0

03/30/00 130 <5.0 0 0 0 0 0 01Data for all six cases ranges for 66 to 70°F.


76

Table B-2.Modeling Data Comparison for Packed Water Air Stripper at LaCrosse, Kansas

(Water Flow Rate = 480 gpm, Air-to-Water Ratio = 156)

ActualInfluent(µg/L)

ActualEffluent

1st Tower(µg/L)

ASAPTM

Influentat 60°F(µg/L)

ASAPTM

Effluentat 70°F(µg/L)

ActualEffluent

2nd Tower(µg/L)

ASAPTM


ASAPTM


136 14.3 1.303 0.407 ND 0.137 0.0428

107 11.4 1.03 0.32 ND 0.109 0.0341

115 ND 1.10 0.344 ND — —

46.1 14.9 0.442 0.138 ND 0.143 0.0445

129 11 1.24 0.386 ND 0.105 0.386

140 14 1.34 0.418 ND 0.134 0.0419

52.6 13.1 0.504 0.157 3.33 0.125 0.0392

954 168 9.14 2.85 29.4 1.61 0.502

159 35.1 1.52 0.475 19.3 0.336 0.105

197 51.4 1.89 0.589 NA 0.492 0.154

93.9 17.9 0.899 0.281 4.02 0.171 0.0535

125 23.9 1.197 0.374 5.01 0.229 0.0714

290 171 2.78 0.867 51.1 1.638 0.511

973 220 9.32 2.91 51.4 2.107 0.658

71.8 15.8 0.688 0.215 3.92 0.151 0.0472

98.5 20 0.944 0.294 4.75 0.192 0.0598

93.2 19 0.893 0.279 2.99 0.182 0.0568

85.1 18 0.815 0.254 4.05 0.172 0.0538

ND = Non-detect.NA = Not available.

77

Table B-3.Modeling Data Comparison for Packed Water Air Stripper at LaCrosse, Kansas

(Water Flow Rate = 350 gpm, Air-to-Water Ratio = 214)

ActualInfluent(µg/L)

ActualEffluent

1st Tower(µg/L)

ASAPTM

Influentat 60°F(µg/L)

ASAPTM


ActualEffluent

2nd Tower(µg/L)

ASAPTM


ASAPTM


136 14.3 0.627 0.170 ND 0.0659 0.0179

107 11.4 0.493 0.134 ND 0.0525 0.0142

115 ND 0.530 0.144 ND — —

46.1 14.9 0.212 0.0575 ND 0.0687 0.0186

129 11 0.594 0.161 ND 0.0507 0.0137

140 14 0.645 0.175 ND 0.0645 0.0175

52.6 13.1 0.242 0.0657 3.33 0.0604 0.0164

954 168 4.40 1.19 29.4 0.774 0.210

159 35.1 0.733 0.198 19.3 0.162 0.0438

197 51.4 0.908 0.246 NA 0.237 0.0642

93.9 17.9 0.433 0.117 4.02 0.0825 0.0223

125 23.9 0.576 0.156 5.01 0.110 0.0298

290 171 1.34 0.362 51.1 0.788 0.213

973 220 4.48 1.22 51.4 1.014 0.275

71.8 15.8 0.331 0.896 3.92 0.0728 0.0197

98.5 20 0.454 0.123 4.75 0.0922 0.0250

93.2 19 0.429 0.116 2.99 0.0875 0.0237

85.1 18 0.392 0.106 4.05 0.0829 0.0225

ND: Non-detect (<0.5 µg/L).NA = Not available.

78

Table B-4.Modeling Data Comparison for Low Profile Air Stripper at Culver City, California

DateInfluent(µg/L)

Effluent fromS-01 (µg/L)

ASAPTM

Effluent at 70°F(µg/L)

11/10/99 17,000 NA 0.205

11/15/99 3,818 8.4 0.0460

12/20/99 6,300 NA 0.0758

12/21/99 2,400 NA 0.0289

01/13/00 4,500 NA 0.0542

01/21/00 5,100 1.3 0.0614

02/01/00 4,200 1.1 0.0506

02/12/00 3,000 ND 0.0361

02/16/00 3,200 1.3 0.0385

02/25/00 3,000 ND 0.0361

03/01/00 2,500 ND 0.0301

03/09/00 2,900 ND 0.0349

03/15/00 4,100 ND 0.0494

ND = Non-detect.NA = Not available.

79

Table B-5.Modeling Data Comparison for Low Profile Air Stripper at Rockaway Township, New Jersey

DateInfluent(µg/L)

Effluent(µg/L)

ASAPTM


ASAPTM


10/15/97 6.4 0.6 0.40 0.27

10/24/97 3.9 0.8 0.24 0.17

10/29/97 4.2 1.6 0.26 0.18

11/05/97 1.4 0.5 0.087 0.059

11/12/97 1.6 0.5 0.10 0.068

11/26/97 0.7 0.6 0.044 0.030

12/10/97 0.8 1 0.050 0.034

01/07/98 0.7 1.3 0.044 0.030

01/14/98 0.7 0.5 0.044 0.030

01/28/98 3.5 0.9 0.22 0.015

02/04/98 1.6 0.6 0.10 0.068

02/11/98 1.7 1.8 0.11 0.072

02/18/98 1.1 0.8 0.069 0.047

03/25/98 0.7 0.8 0.044 0.030

04/01/98 2.1 0.7 0.13 0.089

04/08/98 0.8 0.9 0.050 0.034

04/15/98 0.8 1.2 0.050 0.034

10/14/98 6.9 1.2 0.43 0.29

10/21/98 4.7 0.9 0.29 0.20

10/28/98 2.7 0.6 0.17 0.16

11/04/98 1.6 0.8 0.10 0.068

10/06/99 0.88 <0.5 0.055 0.055

10/21/99 1.1 <0.5 0.069 0.069

11/04/99 1.13 <0.5 0.070 0.070

11/18/99 0.89 <0.5 0.055 0.055

12/16/99 1.32 <0.5 0.082 0.082

12/30/99 1.4 <0.5 0.088 0.087

01/06/00 1.21 <0.5 0.075 0.075

01/13/00 1.32 <0.5 0.082 0.082

01/27/00 1.32 <0.5 0.082 0.082

02/03/00 1.88 <0.5 0.12 0.12

02/10/00 1.43 <0.5 0.089 0.089

03/07/00 0.5 <0.5 0.031 0.031

03/21/00 0.6 <0.5 0.097 0.037

80

Documents

Removal of MTBE from Drinking Water Using Air … Air stripping performance at Culver City, California. ... Results indicate that a variety of different treatment train configurations