21 st Annual Conference. Soil and Groundwater Screening Levels Developing Soil and Groundwater Screening Levels for International Service Station Sites

21st Annual Conference

Soil and Groundwater Screening Levels

Developing Soil and Groundwater Screening Levels for International Service Station Sites

Lynn SpenceSpence Environmental Engineering

Eric Daniels and Renae MagawChevron, ETC

Soil and Groundwater Screening Levels 3

Soil & Groundwater Screening Levels:Outline

Introduction

Business Case – Why do we need them?

What are they?

What are their intent?


Derivation Basis

Example Tables?

Comparison with screening levels from around the world


Project Objective

• Establish human health risk based screening levels at service station sites in countries that have no environmental regulations.

• Provide sets of generic tables for determining appropriate screening levels.

• Enable site-specific application based on a few key parameters.

Annual precipitation

Depth to groundwater

Future use of the site


Motivation for Project

The inconsistency of local regulations and standards creates legal and business uncertainty that can negatively impact project schedule and cost

Delays in UST upgrades

Prolonged remediation activities

Directing large quantities of waste to waste facilities

Improve consistency in internal risk-based decision-making

Proactive advocacy can result in cost-effective regulations


Soil & Groundwater Screening Levels:What Are They?

Screening levels of hydrocarbon impacts in soil and groundwater

Used for long-term site liability management decision making

Apply to soil and groundwater remaining at retail sites

Assumes reliable/accurate lab analysis results are available for BTEX, TPH, and metals

Specific to refined petroleum products such as gasoline and diesel and not for crude oil and other heavier materials

Developed based on a human health risk assessment software tool

Screening levels are to be used at locations where there are no existing regulations

Screening levels provide:

Consistent, conservative human health risk-based approach

Defensible scientific basis for environmental management


Soil & Groundwater Screening Levels:Limitations

Screening Levels don’t take the place of existing regulations

Screening Levels may not be the solution for all sites; site-specific risk assessment will always be an option

Screening Levels don’t address vapor intrusion

Screening Levels don’t address Light Non Aqueous Phase Liquids (LNAPL) and how to recover/manage them


Screening Level Assumptions

Water Use:

Default assumption is that any and all groundwater on site may potentially be used for drinking water.

Site Remediation Specialists may determine that the groundwater is not suitable for drinking water.

Site Remediation Specialists may determine where water standards must be met (e.g. at the property boundary or at some point further downgradient).

Land use:

Default assumption is that the site will be used for residential purposes if it is to be transferred.

Site Remediation Specialists can override residential assumption, for example:

If region has zoning laws and the site is not zoned for residential

If directed by Property Transfer Team

If other land uses can be assumed based on site specific conditions.

Reason(s) for exception (decision) must be documented and site-specific screening level must be developed.


Site Conceptual Model Summary

Two types of sites: (1) ongoing service station (2) site to be transferred

Two types of receptors:(1) resident(2) on-site worker

Screening levels were developed for:(1) soil (two tables)(2) groundwater (one table)

There are two soil screening level tables, for two different exposure scenarios:(1) surface soil (2) leaching to groundwater

Chemicals of concern:Benzene TPH GROEthylbenzene TPH DROToluene LeadXylenes MTBE


Soil Screening Levels: Direct Contact

Chemical For Sites that are Being

Transferred*

For Sites that are to Remain Service

Stations

Impacted Soil Will be Covered With Concrete

or Asphalt

(mg/kg) (mg/kg)

Benzene XX NL

Ethlybenzene XXXX NL

Toluene XXXX NL

Xylenes XXXX NL

TPH GRO XXXX NL

TPH DRO XXXX NL

Lead XXX NL

NL: No Level. It is assumed that people will not have direct contact with impacted soils when the soil is covered with concrete or asphalt.

*Surface soil for these sites is defined as the top 3 meters of soil.

Risk Assessment Assumptions:

Exposure pathways include ingestion of soil, dermal contact with soil, inhalation of volatiles and particulates.

Depleting source

Default human exposure parameters from WHO.

Cancer risk target = 1 x 10-5


Site Conceptual Model (Soil Leaching to Groundwater): Site to be Transferred

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Depth to Groundwater from Bottom of

Impacted Soil(4 Categories)

Thickness of impacted soil

(2 m)

Precipitation (3 Categories)

Well location(Assumed to

be directly underneath impacted soil)

Impacted Soil


Depth to Groundwater

from Bottom of Impacted Soil

(4 Categories)

Thickness of impacted soil

(2 m)

PrecipitationInfiltration assumed to be less than 5 cm/year

Asphalt or Concrete (for on-going service stations)

Impacted Soil

10 m

Only potential exposure pathway: leaching to groundwater- 2 potential “well” locations

Site Conceptual Model (Soil Leaching to Groundwater): Site to Remain Ongoing Service Station

Soil Screening Levels: Leaching to GroundwaterDecision Matrix


Soil Screening Levels: Leaching to GWSite Will Be Transferred

Table Number

Average Annual

Precipitation

Depth to Groundwater*

Benzene (mg/kg)

Ethylbenzene (mg/kg)

Toluene (mg/kg)

Xylenes (mg/kg)

TPH GRO(mg/kg)

TPH DRO (mg/kg)

Lead (mg/kg)

Table 2A

<50 cm/yr

0 to 1 m X.XX XX XX XX XXX 8000 NA

1 to 3 m XX 60 XX XXX 3000 8000 NA

3 to 5 m XXX 60 360 240 3000 8000 NA

> 5 m XXX 60 360 240 3000 8000 NA

Table 2B

50 to 200 cm/yr

0 to 1 m X.XX XX X.X X.X XXX 8000 NA

1 to 3 mX.XX XX XX XX XXX 8000 NA

3 to 5 m X.X XX XXX 240 3000 8000 NA

> 5 m XX 60 360 240 3000 8000 NA

Table 2C

200 to 400 cm/yr

0 to 1 mX.XX X.X X.X X.X XX 8000 NA

1 to 3 m X.XX XX X.X X.X XXX 8000 NA

3 to 5 mX.XX 60 XX XX XXX 8000 NA

> 5 m X.X 60 XX XXX XXX 8000 NA

Numbers in italics represent mobility limits, not risk-based numbers.


TPH Mobility Calculations

Cres for Various Total Porosities

0

50,000

100,000

150,000

200,000

250,000

300,000

1 1.2 1.4 1.6 1.8 2

Soil bulk density (g/cm 3)

Cre

s (m

g/k

g) 0.5

0.4

0.3

0.25

Porosity

Cres = what's left in the soil after gravity drainage (of product)Mobility calculations using Equation 5 of Brost and DeVaull (2000)Density of oil assumed to be 0.75 (for gasoline)


Summary of Annual Precipitation for Countries where Chevron Operates*

*And most likely do not have soil and groundwater regulations

Annual Precipitation (cm)

0

50

100

150

200

250

300

350

400

1 5 9 13 17 21 25 29 33 37 41 45 49num ber of countries

An

nu

al P

reci

pit

atio

n (

cm)

Low end of range

High end of range


Groundwater Screening Levels Default assumption is that

groundwater may be used for drinking water.

All values are from the World Health Organization “Guidelines for Drinking Water Quality” (2004), which are human-health risk-based guidelines for safe drinking water.

If groundwater cannot be used for a drinking water supply, this table does not apply and site-specific risk assessment should be considered.

Chemical concentrations above these screening levels do not automatically mean that remediation is required. However, exceeding these levels suggests that further evaluation of the potential risks is appropriate.

ChemicalGroundwater

Concentrations (ug/L)

TPH N.L.

Benzene 10

Toluene 300

Ethylbenzene 700

Xylenes 500

MTBE* 15

Lead 10

*Screening level for MTBE is based on taste and/or odor considerations. N.L. -- “No Level” indicates WHO does not have a safe drinking water standard for TPH.


How do the Screening Levels Compare to Other Countries’ Screening Levels?

• The project included compilation of international screening levels from 81 countries and/or regions into a database.

• The intent was to use this database to compare results obtained from modeling with regulatory numbers from around the world.

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How do the Screening Levels Compare?

Constituent

Belgium (Flanders) Switzerland Denmark

Soil(mg/kg)

Groundwater(ug/L)

Soil(mg/kg)

Groundwater(ug/L)

Soil(mg/kg)

Groundwater(ug/L)

TPH 1000 500 --Specific fractions

100 9

Benzene .5 10 -- 10 1.5 1

Ethylbenzene 1.5 300 -- 3000

10

--

Toluene 5 700 -- 7000 5

Xylenes 3.5 500 -- 10000 5

Lead 200 20 200 50 40 --

Screening levels vary dramatically by agency Not all values are health-risk based, may consider different exposure

pathways. Individual agencies incorporate policy decisions that may not be

appropriate for all sites Chevron screening levels provide consistent, scientifically defensible

values, applicable to a broad portfolio of sites

-- no standard given


Screening Levels Vary Sometimes by Orders of Magnitude Even in the US

Chemical

Direct Soil Contact

Residential Land Use

USEPA RSLs

(mg/kg)

Texas TRRP PCLs

(mg/kg)

California

RWQCB ESLs

(mg/kg)

Benzene 1.1 66 0.12

Toluene 5000 5900 63

Ethylbenzene 5.7 5300 2.3

Xylenes 600 6000 31

Naphthalene 3.9 220 1.3

MTBE 39 800 30

TPHgasolineNA 1600 110

TPHmid-distillateNA 2300 110


Site-Specific Risk Assessment

(As always,) Site-specific risk assessment and development of site-specific cleanup objectives are available options for every site.

However, it turns out that the scenarios selected cover most sites.

21st Annual Conference

Documents

21 st Annual Conference. Soil and Groundwater Screening Levels Developing Soil and Groundwater Screening Levels for International Service Station Sites