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Mr Daniel K Barber, P E ' September 9, 2003 . Page G of 17 ■ Groundwater is or is not a known or potential drinking water source ' Land use is also taken into account The DLM and RBSLs are useful in that they reference hydrocarbons as both diesel (TPHd) and gasoline (TPHg) The subject site residual contamination is mainly in the form of TPHd, as shown in Table 1 ' Groundwater Contamination The RWQCB evaluates site contamination and its impacts on the environment on a case-by- case basis using various criteria, including existing land use designation, groundwater use, location of sensitive receptors, etc We understand that SJCEHD, as LOP to the RWQCB, generally follows RWQCB entena for assessing potential impacts to groundwater According to SJCEHD policy, groundwater is always considered potentially useable While the Region 5 RWQCB does not publish such guidance, it often screens sites for concentrations above 10 times the drinking water Maximum Contaminant Levels (MCLS) In the case of this site, the ' 10-times MCL screening for BTEX is not exceeded For the site contaminants of concern with published MCLS, only benzene and total xylenes have been detected (and only in "grab" groundwater samples collected from exploratory boreholes), they have never been detected in excess of their respective MCLs There are no drinking water MCLs for TPHg or TPHd When dealing with gasoline or diesel hydrocarbon contamination in groundwater, some RWQCBs will use RBSLs (or ESLs that are replacing them) to evaluate whether contamination warrants remediation and/or further ' investigation However, we understand from discussions with Mr Wong that the SJCEHD does not use nsk-based considerations as part of its closure criteria The primary criterion for selecting the appropriate groundwater RBSL is whether a current or potential drinking water ' source is threatened by the contamination While the State of California considers all groundwaters to be a potential drinking water source, as does SJCEHD, until a site-specific variance has been obtained, it is our understanding that groundwater is not used as drinking water in this area due to high total dissolved solids/turbidity associated with the upgradient ' Victor Sausage site (Gallardo & Associates, 1999) While we understand that the groundwater RBSLs are not considered by SJCEHD, it can be instructive to examine the RBSLs for site contaminants such as TPHd and TPHg that have no MCLs ' RBSLs/ESLs are not clean-up goals, which should be determined based on potential risks to groundwater and human and ecological receptors (commonly via a risk-based assessment ' model) Reducing residual contamination to levels at or below RBSLs also does not necessarily allow for regulatory closure, that determination being up to SJCEHD Some site Stellar Environmental Solutions yyROlEC15003 M1 SYopNlOp)J0.pAp-ba We cb.iadAepuud FyunWEPORT-Sapmbsr A3001 doc