SITE INFORMATION AND CORRESPONDENCE

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HEALTH RISK ASSESSPIENTS • - 2 - following: 2 -following: water quality criteria, human health criteria, additivity considerations, and that which is technologically and economically achievable. The risk assessment document is fairly clear; however, additional information regarding specific aspects of the risk assessment follows. Section 4: Exposure Point Concentrations If necessary, a site can be broken down into several areas, and a risk assessment conducted on each area. For example, a pesticide applicator facility may have a wash pad at which the soils have very high levels of pesticides, and a chemical loading area at which the soils have much lower pesticide concentrations. If the Discharger wishes to consider a different type of remediation at each area, then separate risk assessments would be conducted for each area. A risk assessment must be conducted for each chemical found at the site, with the following qualifications: (a) if a chemical was known to have been used at the site, but turns up as non- detected during laboratory analysis, a risk assessment must still be completed (the non-detect level is used as the maximum value); and (b) for chemicals which are non-detected and are not suspected to have been used at the site, a risk assessment is not required. Section 5: Toxicity Values Cal/EPA's inhalation cancer potency slope factor and the oral cancer potency slope factor are found in Table 1, which is attached to the DTSC memo. Other slope factors and reference dose values are found through either the US EPA's Integrated Risk Information System (IRIS), an on-line database, or through the latest edition of the US EPA's Health Effects Assessment Summary Table (HEARST). If a chemical has no slope factor or reference dose, then the Discharger should call the Regional Board for guidance in deriving these numbers. Section 6: Risk/Hazard Characterization Equations Regional Board staff will make the decision as to whether the site falls into a Level I category (i), (ii), or (iii). Categories (iv) and (v) are not applicable, as the threat to surface or ground water will be known before the health risk assessment is required. Board staff will notify the Discharger which category the particular site falls into, because this will impact whether a risk assessment must be conducted for water exposure. If the site is a Level I category (i), then a health based risk assessment for water need not be conducted. This section gives equations to be used to determine both the risk and hazard of each chemical in each of three media (soil, water, air). The excess lifetime cancer risk for carcinogenic compounds is termed "risk", and is calculated only for those chemicals considered to pose a carcinogenic risk to humans. (Carcinogenic compounds are listed in a variety of sources, including Table 1, US EPA's IRIS database, US EPA's HEARST list, and the Proposition 65 list). The "hazard" value is calculated for all chemicals, and is a value which is believed to not produce adverse health effects.