21 st Annual Conference

1. 21st Annual Conference

2. Developing Soil and Groundwater Screening Levels for International Service Station Sites Lynn Spence Spence Environmental Engineering Eric Daniels and Renae Magaw Chevron, ETC

3. Soil & Groundwater Screening Levels:Outline • Introduction • Business Case – Why do we need them? • What are they? • What are their intent? • Soil and Groundwater Screening Levels • Derivation Basis • Example Tables? • Comparison with screening levels from around the world

4. 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

5. 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

6. 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

7. 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

8. 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.

9. 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 GRO • Ethylbenzene TPH DRO • Toluene Lead • Xylenes MTBE

10. Soil Screening Levels: Direct Contact 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 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.

11. Site Conceptual Model (Soil Leaching to Groundwater): Site to be Transferred Precipitation (3 Categories) Thickness of impacted soil (2 m) Impacted Soil Well location (Assumed to be directly underneath impacted soil) Depth to Groundwater from Bottom of Impacted Soil (4 Categories)

12. Precipitation Infiltration assumed to be less than 5 cm/year Asphalt or Concrete (for on-going service stations) Thickness of impacted soil (2 m) Impacted Soil Depth to Groundwater from Bottom of Impacted Soil (4 Categories) 10 m Site Conceptual Model (Soil Leaching to Groundwater): Site to Remain Ongoing Service Station Only potential exposure pathway: leaching to groundwater - 2 potential “well” locations

13. Soil Screening Levels: Leaching to GroundwaterDecision Matrix

14. Soil Screening Levels: Leaching to GWSite Will Be Transferred Numbers in italics represent mobility limits, not risk-based numbers.

15. TPH Mobility Calculations 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)

16. Summary of Annual Precipitation for Countries where Chevron Operates* *And most likely do not have soil and groundwater regulations

17. 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. *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.

18. 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.

19. How do the Screening Levels Compare? • 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

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

21. 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.

22. 21st Annual Conference