Presentation on theme: "21 st Annual Conference. Soil and Groundwater Screening Levels Developing Soil and Groundwater Screening Levels for International Service Station Sites."— Presentation transcript:
21 st Annual Conference
Soil and Groundwater Screening Levels Developing Soil and Groundwater Screening Levels for International Service Station Sites Lynn Spence Spence Environmental Engineering Eric Daniels and Renae Magaw Chevron, ETC
Soil and Groundwater Screening Levels3 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
Soil and Groundwater Screening Levels 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
Soil and Groundwater Screening Levels5 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 and Groundwater Screening Levels6 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 and Groundwater Screening Levels7 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
Soil and Groundwater Screening Levels8 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.
Soil and Groundwater Screening Levels 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: BenzeneTPH GRO EthylbenzeneTPH DRO TolueneLead XylenesMTBE
Soil and Groundwater Screening Levels10 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) BenzeneXXNL EthlybenzeneXXXXNL TolueneXXXXNL XylenesXXXXNL TPH GROXXXXNL TPH DROXXXXNL LeadXXXNL 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
Soil and Groundwater Screening Levels Site Conceptual Model (Soil Leaching to Groundwater): Site to be Transferred 11 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
Soil and Groundwater Screening Levels Depth to Groundwater from Bottom of Impacted Soil (4 Categories) Thickness of impacted soil (2 m) Precipitation Infiltration 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 Groundwater Decision Matrix
Soil and Groundwater Screening Levels14 Soil Screening Levels: Leaching to GW Site Will Be Transferred Table Number Average Annual Precipitation Depth to Groundwater* Benzene (mg/kg) Ethyl benzene (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.XXXX XXX8000NA 1 to 3 m XX60XXXXX NA 3 to 5 m XXX NA > 5 m XXX NA Table 2B 50 to 200 cm/yr 0 to 1 m X.XXXXX.X XXX8000NA 1 to 3 m X.XXXX XXX8000NA 3 to 5 m X.XXXXXX NA > 5 m XX NA Table 2C 200 to 400 cm/yr 0 to 1 m X.XXX.X XX8000NA 1 to 3 m X.XXXXX.X XXX8000NA 3 to 5 m X.XX60XX XXX8000NA > 5 m X.X60XXXXX 8000NA Numbers in italics represent mobility limits, not risk-based numbers.
Soil and Groundwater Screening Levels TPH Mobility Calculations C res = 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)
Soil and Groundwater Screening Levels Summary of Annual Precipitation for Countries where Chevron Operates* *And most likely do not have soil and groundwater regulations
Soil and Groundwater Screening Levels17 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. Chemical Groundwater Concentrations (ug/L) TPHN.L. Benzene10 Toluene300 Ethylbenzene700 Xylenes500 MTBE*15 Lead10 *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.
Soil and Groundwater Screening Levels 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. 18
Soil and Groundwater Screening Levels19 How do the Screening Levels Compare? Constituent Belgium (Flanders)SwitzerlandDenmark Soil (mg/kg) Groundwater (ug/L) Soil (mg/kg) Groundwater (ug/L) Soil (mg/kg) Groundwater (ug/L) TPH Specific fractions 1009 Benzene Ethylbenzene Toluene Xylenes Lead 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
Soil and Groundwater Screening Levels 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 Toluene Ethylbenzene Xylenes Naphthalene MTBE TPH gasoline NA TPH mid-distillate NA
Soil and Groundwater Screening Levels21 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.