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

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Soil and soil gas data collected at a site can be directly compared to CHHSLs foreach chemical of concern. Under most circumstances, and within the limitationsdescribed, the presence of a chemical in soil or soil gas at concentrations belowthe corresponding CHHSLs can be assumed to not pose a significant health risk topeople who may live or work at the site. The presence of a chemical atconcentrations in excess of a CHHSL does not necessarily indicate that adverseimpacts to human health are occurring but indicates that a potential for adverserisk may exist and that additional evaluation is warranted.Residential CHHSLs are appropriate for other types of sensitive property use,including hospitals, day care centers and schools. In order to assess themaximum, future beneficial use of a property, data collected at commercial orindustrial sites should be compared to both residential and commercial sets ofscreening levels. A formal restriction to the deed may be required for sites thatmeet requirements for commercial/industrial use but not residential use.Regulatory agency oversight would be needed in this circumstance.The scope of the CHHSLs is limited to human health concerns. For this reason,the CHHSLs cannot be used as a stand-alone tool to determine the extent ofremedial actions needed at sites with contaminated soils. Depending on siteconditions and the chemicals present, additional cleanup of contaminated soilsmay be required to protect groundwater resources, prevent toxicity to flora andfauna, address uptake in edible plants, and address nuisance and aestheticconcerns posed by odors and staining. A brief summary of these concerns and alist of references for evaluating these issues are provided at the end of the text.1.2 Tiered Approach to Environmental RiskAssessmentsHuman health risk assessments for regulatory purposes are usually carried outusing a step-wise or “tiered” approach. Comparison of site data to residential soilor soil gas CHHSLs (e.g., in a screening health risk evaluation performed usingthe DTSC PEA guidance) usually represents “Tier 1”. If multiple chemicals withsimilar health effects are present at a site then “forward mode,” cumulative healthrisks may also need to be calculated and compared to target Tier 1 goals before anevaluation of potential human health concerns can be completed (refer to Section2.8).If the results of the Tier 1 assessment indicate that further evaluation of humanhealth risks is warranted, site-specific exposure assumptions, target risks, etc., canJanuary 20051-2CHHSLS
e substituted for default parameter values used to develop the Tier 1 CHHSLsand alternative screening levels developed under a Tier 2 assessment. Thisassessment can be incorporated into the guidelines presented in the DTSC PEAdocument. Prior to modifying the Tier 1 default assumptions, concurrence fromthe appropriate regulatory agency should be obtained. Site data can then becompared to the revised screening levels. This provides an intermediate but stillrelatively rapid and cost-effective option for preparing more site-specificscreening or cleanup levels. Cumulative health risks or hazards should also bepresented under a Tier 2 assessment, as described in Section 2.8.If exposure pathways of concern and conditions at the site do not match thosetaken into account by the CHHSL framework or PEA methodology, a Tier 3,baseline human health and ecological risk assessment should be performed. In abaseline human health and ecological risk assessment, alternative models and sitespecificassumptions are used to quantify the risk/hazard posed to human and/orecological receptors by the impacted media in the “forward” mode. After abaseline health risk assessment is accepted by the regulatory agency, theassessment may be used in the “backward’ model to develop site-specificscreening or cleanup levels. An understanding of the methodologies used todevelop the CHHSLs is important to ensure consistency between all tiers ofassessments and to expedite their preparation and review.1.3 Chemicals Not Listed In CHHSL Lookup TablesThe lookup tables list 54 chemicals, including many that are commonly found atsites where releases of hazardous chemicals have occurred. Cal/EPA willincorporate CHHSLs for additional chemicals in future updates of this documentas needed and practical. Prior to that time, the PEA methodology should be usedto evaluate those chemicals for which CHHSLs do not exist. Toxicity factorspublished by Cal/EPA should be utilized in the PEA when available, unlessotherwise instructed by the overseeing regulatory agency.1.4 LimitationsThe CHHSLs presented in this document are NOT regulatory "cleanupstandards." Use of the CHHSLs as final cleanup levels to address human healthconcerns should be discussed with the overseeing regulatory agency andevaluated in terms of the cost/benefit of developing more site-specific cleanuplevels through a risk assessment.January 20051-3CHHSLS
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as a stand-alone tool for the evalu
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Similar ESLs are also provided for
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USEPA Region IX staff can be contac
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