Use of California Human Health Screening Levels (CHHSLs) in ...

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Steps 4 - Determine the Desired Land UseScreening levels for residential land use are generally appropriate for othersensitive uses of the property (e.g., day-care centers, hospitals, etc.). If preparinga DTSC PEA, residential land use CHHSLs should be used. For evaluation ofcommercial/industrial properties, it is highly recommended that site data becompared to CHHSLs for both unrestricted/residential andcommercial/industrial land use. Commercial/industrial CHHSLs should beused only under the oversight of a regulatory agency, as that agency will likelyrequire a land use covenant that restricts use of the property to these purposes.Steps 5 - Select CHHSLsBased on the actual or proposed land use, select the appropriate soil and/or soilgas CHHSLs. Replace CHHSLs with naturally occurring, backgroundconcentrations of chemicals of concern (e.g., arsenic) or laboratory methodreporting levels if appropriate (see Sections 2.6 and 2.7).Step 6 - Compare Site Data To CHHSLs; calculate cumulative risks asnecessaryCompare site data to CHHSLs to identify areas where concentrations ofcontaminants pose potential human health concerns. For sites where sample dataare limited and/or if preparing a DTSC PEA, compare the maximum-detectedconcentrations of chemicals of concern to the CHHSLs.For sites where an adequate number of data points are available, statisticalmethods can be used to estimate site-specific exposure point concentrations. Theexposure point concentration is the lesser of the maximum-detected concentrationand the 95% upper confidence limit (UCL) of the arithmetic mean of sample data(Cal/EPA 1996a). The USEPA guidance document Calculating UpperConfidence Limits for Exposure Point Concentrations at Hazardous Waste Sitesrecommends evaluating the distribution of the data and choosing the best UCLestimate for the data set (USEPA 2002). Guidance for the estimation of exposurepoint concentrations, use of “non-detect” data, and other issues is also provided inthe Cal/EPA documents Preliminary Endangerment Assessment GuidanceManual (Cal/EPA 1994b), Supplemental Guidance For Human HealthMultimedia Risk Assessments of Hazardous Waste Sites and Permitted Facilities(Cal/EPA 1996a), among other sources. As discussed in these documents, sampledata collected outside of impacted areas should generally not be included inestimation of exposure point concentrations.January 20052-4CHHSLS
For residential land use scenarios, soil sample data should be averaged over nomore than a 1,000 ft 2 area (assumed area of a typical, urban area back yard andfootprint area of typical residence). For commercial/industrial properties, soilsample data can be averaged within affected areas of open spaces.Use the maximum soil gas concentration over an area of the footprint of existingor assumed future buildings to compensate for potentially isolated rooms within abuilding and the uncertainties in soil gas collection.If multiple chemicals with similar heath effects are present at a site, thecumulative excess cancer risk and/or noncancer hazard index should be calculatedbefore final consideration of the site for closure. This will be of particularconcern at sites where residual concentrations of chemicals with similarnoncancer health effects may approach CHHSLs following the proposed, finalcleanup of contaminated soil. Calculation of cumulative risks and hazard indicesis discussed in Section 2.8. The need to include calculation of cumulative healthrisks in final closure reports should be discussed with the overseeing regulatoryagency.Steps 7 - Evaluate the Need for Additional Investigation or Actions toAddress Human Health ConcernsBased on a comparison of available site data to the CHHSLs, the objectivesidentified in Step 3 should be evaluated. For example, comparison to CHHSLsmay show that a site does not pose an unacceptable health risk to residential users,or it may show that additional investigation is warranted. Summarize the resultsof this evaluation in the Tier 1 Human Health Risk Assessment report (orpreliminary endangerment assessment), and include recommendations foradditional investigations or remediation as needed. Decisions for or againstadditional actions should always be made in coordination with the overseeingregulatory agency.Step 8 - Evaluate Other Potential Environmental ConcernsThe soil CHHSLs presented in Table 1 are limited to human health concernsassociated with direct exposure to contaminated soil. In many instances, thepresence of a potential hazardous chemical in soil may pose other environmentalconcerns that outweigh the risk to human health through direct exposure (seeSections 1.4 and 2.2, Chapter 4 and Table 1). The purpose of the Conceptual SiteModel (Step 2) is to assist the user in identifying these concerns early in theprocess. For example, many metals and pesticides are significantly more toxic toflora and fauna than they are to humans (e.g., copper and nickel). Chemicals thateasily leach from soils (e.g., MTBE) may pose a threat to shallow groundwaterJanuary 20052-5CHHSLS
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