Contamination of Ground Water Contamination of Ground Water by Perchloroethene (PCE) – by Perchloroethene (PCE) –

A National PerspectiveA National Perspective

By Michael MoranBy Michael MoranU.S. Geological SurveyU.S. Geological Survey

U.S. Department of the InteriorU.S. Geological Survey

Ground Water Resources Association of California, 13th Symposium Series on Groundwater Contaminants Conference, Newport Beach, California, November 10, 2004

• PCE use in dry cleaning began in 1940sPCE use in dry cleaning began in 1940s

Production and Use of PCEProduction and Use of PCE

• Production declined after peak in 1970sProduction declined after peak in 1970s

• As of 2002, PCE was primary solvent for As of 2002, PCE was primary solvent for 85% of drycleaners85% of drycleaners

- this constitutes 25% of PCE production- this constitutes 25% of PCE production- remainder is used as industrial solvent- remainder is used as industrial solvent

Production of PCEProduction of PCE

0

50

100

150

200

250

300

350

400

1960 1970 1980 1990 2000

Year

PC

E P

rod

uct

ion

(m

illio

n o

f ki

log

ram

s)

Physicochemical Properties Physicochemical Properties of PCEof PCE

• Denser than waterDenser than water

• High solubility relative to MCL High solubility relative to MCL

• Moderate organic carbon partitioningModerate organic carbon partitioning

• Relatively high Henry’s coefficient Relatively high Henry’s coefficient

• Relatively long half-life in water Relatively long half-life in water

Behavior of PCE in SubsurfaceBehavior of PCE in Subsurface

Data on PCE in Ground WaterData on PCE in Ground Water

Data on PCE in Ground WaterData on PCE in Ground Water

0

500

1000

1500

2000

2500

3000

3500

4000

Major aquifers Urban landuse

Ag land use Domesticwells

Public wells

Nu

mb

er o

f w

ells

sam

ple

d

These data represent aselect subset of all wells

PCE in Ground WaterPCE in Ground Water

0

1

2

3

4

5

6

7

8

9

10

Majoraquifers

Urban landuse

Ag land use Domesticwells

Public wells

Det

ecti

on

fre

qu

ency

(in

per

cen

t)

2

16

3

3

3

3 – ranking of PCE among all detected VOCs

(assessment level of 0.2 g/L)

Occurrence Using UncensoredOccurrence Using UncensoredConcentrationsConcentrations

0

5

10

15

20

25

30

Majoraquifers

Urban landuse

Ag land use Domesticwells

Public wells

Det

ecti

on

fre

qu

ency

(in

per

cen

t)

detection frequency using no assessment level

PCE ConcentrationsPCE Concentrations

0.0001

0.0010

0.0100

0.1000

1.0000

10.0000

100.0000

1000.0000

Concentration (ug/L)

0.750

0.775

0.800

0.825

0.850

0.875

0.900

0.925

0.950

0.975

1.000

Fra

ctio

n of

Dat

a

PWSDOMESTICURBANMASAG

Quantified ConcentrationsQuantified Concentrations

0.01

0.1

1

10

100

1000

Co

nce

ntr

atio

n (

ug

/L)

Major aquifers

Urban land use

Ag land use

Domesticwells

Publicwells

median

25th percentile

75th percentile

outlier (> 1.5 IQR)

1.5 IQR

Concentrations Relative to MCLConcentrations Relative to MCL

Major aquifersUrban land use

0 0.5 1 1.5 2

PCE

Benzene

TCE

VC

1,2-DCE

cis-1,2-DCE

Exceedance frequency (in percent)

0 0.2 0.4 0.6 0.8

DBCP

PCE

TCE

1,1-DCE

1,2-DCP

EDB

DCM

Benzene

VC

Exceedance frequency (in percent)

0 0.2 0.4 0.6 0.8

DBCP

TCE

PCE

EDB

1,2-DCP

1,1-DCE

Exceedance frequency (in percent)

Domestic wells

0 0.5 1

PCE

TCE

EDB

DCM

1,1-DCE

VC

Exceedance frequency (in percent)

Public wells

Occurrence of TCE With PCEOccurrence of TCE With PCE

• Among 4 solvents in ground water, Among 4 solvents in ground water, PCE-TCE was most common mixturePCE-TCE was most common mixture

• TCE may be daughter product ofTCE may be daughter product of reductive dechlorination of PCEreductive dechlorination of PCE

Occurrence of TCE With PCEOccurrence of TCE With PCE

• PCE occurred more frequently in PCE occurred more frequently in oxic ground water compared to anoxicoxic ground water compared to anoxic

• Molar concentration ratios of PCE/TCEMolar concentration ratios of PCE/TCE were 3 times higher in oxic ground water were 3 times higher in oxic ground water compared to anoxiccompared to anoxic

Associations With Associations With PCE OccurrencePCE Occurrence

Major aquifers:Major aquifers:

1. Redox conditions1. Redox conditions

2. RCRA facilities within 1 km2. RCRA facilities within 1 km

3. Depth to top of aquifer3. Depth to top of aquifer

Associations With Associations With PCE OccurrencePCE Occurrence

Domestic wells:Domestic wells:

1. Population density1. Population density

2. RCRA facilities within 1 km2. RCRA facilities within 1 km

Public wells:Public wells:

1. Population density1. Population density

3. Proximity to dry-cleaner LUST3. Proximity to dry-cleaner LUST

2. Well depth2. Well depth

Dry Cleaners as RCRA FacilitiesDry Cleaners as RCRA Facilities

Most dry cleaners thatMost dry cleaners that use PCE are probably use PCE are probably regulated under RCRAregulated under RCRA

We estimate that aboutWe estimate that about 30% of RCRA sites are30% of RCRA sites are dry cleaning facilitiesdry cleaning facilities

6,000 RCRA-regulated6,000 RCRA-regulated dry cleanersdry cleaners

Summary and ConclusionsSummary and Conclusions

• At a national scale, PCE is one of the most At a national scale, PCE is one of the most frequently detected VOCs in ground waterfrequently detected VOCs in ground water

• PCE concentrations exceed the MCL more PCE concentrations exceed the MCL more frequently than most other VOCsfrequently than most other VOCs

• RCRA facilities and dry cleaners areRCRA facilities and dry cleaners are associated with PCE occurrenceassociated with PCE occurrence