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

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examples include the soil direct-exposure CHHSL for dioxin (e.g., 0.0000046mg/kg for residential exposure).2.7 Substitution of Naturally Occurring Concentrationsfor CHHSLsNaturally occurring background concentrations of arsenic, beryllium, cadmium,chromium and other metals in soils may exceed their respective soil CHHSLs.Cal/EPA generally does not require cleanup of soil to below background levels.This issue is frequently encountered with arsenic. Natural backgroundconcentrations of arsenic in California are often well above the health-based,direct-exposure goals in soil of 0.07 mg/kg for residential land use and 0.24mg/kg for commercial/industrial land use (e.g., Bradford et. al, 1996; LBNL2002). Background concentration of arsenic or other metals of potential concernat a site should be determined from analysis of site-specific samples inuncontaminated areas using guidance published by Cal/EPA and/or reference topublished data for nearby sites (Cal/EPA 1997). However, background data fornearby sites may only be used as a surrogate for uncontaminated site data if thosedata are obtained from soil of the same lithology as that found on-site.2.8 Cumulative Risks at Sites with MultipleContaminantsRisks posed by exposure to multiple chemicals with similar health affects areconsidered to be additive or "cumulative." For example, the total excess lifetimerisk of cancer posed by the presence of several carcinogenic chemicals in allexposure media is the sum of the risk posed by each individual chemical. Thesame is true for chemicals that cause noncarcingenic health effects.A stepwise approach for screening of sites with multiple contaminants issuggested (after USEPA 2004):Step 1: Identify potential chemicals of concern.Step 2: Record CHHSLs for each chemical separated by media type (soil, soilgas and/or indoor air). Include CHHSLs for both cancer and noncancereffects, if available (refer to Appendix 1). If CHHSLs are not availablefor specific chemicals, evaluate those chemicals using the approachesdiscussed in Appendix 1 and in the PEA manual.January 20052-10CHHSLS
Step 3: Calculate cumulative cancer risk estimates by taking the assumedexposure point concentration for each chemical (maximum or approved95% UCL) and divide by the respective CHHSL concentrationdesignated for cancer evaluation. Multiply the ratio by 10 -6 (the targetrisk used to develop the CHHSLs) to calculate the estimated cancer riskfor that specific chemical for a reasonable maximum exposure (RME).⎛ concx⎞ ⎛ concy⎞ ⎛ concz⎞Risk = [ ⎜ ⎟ + ⎜ ⎟ + ⎜ ⎟]× 10E− 06⎝ CHHSLx⎠ ⎝ CHHSLy⎠ ⎝ CHHSLz⎠For multiple chemicals, simply add the risks for individual chemicals orsum individual ratios and multiply the total by a factor of 10 -6 :Step 4: Calculate cumulative noncancer hazard estimates by taking the assumedexposure point concentration for each chemical (maximum or approved95% UCL) and divide by the respective CHHSL concentrationdesignated for noncancer effects. This generates an individual HazardQuotient for that chemical. Calculate a cumulative Hazard Index byadding the individual Hazard Quotients. A Hazard Index of one or lessis generally considered “safe”. A ratio that is greater than one suggeststhat further evaluation is necessary. (Note that carcinogens may haveCHHSLs for both cancer effects as well as noncancer effects. Refer toAppendix 1).For more information, refer to the USEPA Preliminary Remediation Goals⎛ concx⎞ ⎛ concy⎞ ⎛ concz⎞HazardIndex = [ ⎜ ⎟ + ⎜ ⎟ + ⎜ ⎟ ]⎝ CHHSLx⎠ ⎝ CHHSLy⎠ ⎝ CHHSLz⎠document (USEPA 2002). OEHHA has also developed a spread sheet tool forcalculating cumulative risk. This spread sheet is available on Cal/EPA’s,DTSC’s, the State Board’s and OEHHA’s web pages.2.9 Evaluation of School SitesDTSC’s Schools Property Evaluation and Cleanup Division is the lead agency forthe environmental assessment of potential contamination at new, expanding, orexisting schools. Since January 2000, school districts have been required toconduct an environmental assessment under the oversight and approval of DTSCprior to the construction of new schools. By law, DTSC uses specific guidanceand protocols for school projects. Because of this, the CHHSLs may not beapplicable for these sites. Contact DTSC for further information and direction forJanuary 20052-11CHHSLS
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