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C*:AT C <br /> AS SOCIATES ! N C . <br /> February 1996. MTBE was detected at low concentrations (<3 ppb) for the first time in <br /> December 1998. The detection and rising concentration of petroleum hydrocarbons is most likely <br /> attributed to the rise of the water table. <br /> A review of the analytical data indicates that MTBE concentrations in groundwater in the <br /> immediate vicinity of the Bank of America property exceed the current California water quality <br /> goals for drinking water. The California Department of Health Services (DHS) adopted a <br /> secondary drinking water standard (maximum contaminant level, MCL) of 5 ppb for MTBE, <br /> effective January 7, 1999. The primary MCL established by DHS for MTBE is currently under <br /> development, however Cal/EPA's Office of Environmental Health Hazard Assessment (OHHA) <br /> has adopted a 13 ppb Public Health Goal for MTBE which is being utilized by DHS as an action <br /> level. None of the UNOCAL wells sampled in February contained MTBE at or above 13 ppb. <br /> The SWRCB is currently reviewing UNOCAL's petition for closure. The RWQCB had advised <br /> SWRCB that "In light of current concerns over the impacts of MTBE on groundwater, it seems <br /> prudent to us to continue monitoring at this site for one year to determine if the perceived <br /> "trends" noted by your staff are borne out by future data". <br /> The responsible party for the soil and groundwater petroleum release has been identified as <br /> UNOCAL and the former UNOCAL site is currently under regulatory enforcement of State and <br /> local agencies to perform corrective action measures if deemed appropriate based on the site's <br /> threat to human health and safety. At minimum, ATC recommends that those with an interest in <br /> the Property (previous and current landowners) protect their interest and follow the investigation <br /> and remediation activities of the UNOCAL site. <br /> If you should have any questions or comments regarding this report, please feel free to contact us at <br /> your convenience at(209)579-2221. <br /> Respectfully Submitted, . <br /> ATC Associates Inc. <br /> Tom J. Lutterman, R.E.A. <br /> Project Geologist <br /> Gt: lid.C.c4 10 � <br /> * Exp, 1 Z199 <br /> Jeanne Homsey, P.E. ,rJ, CIVIC. �4.. <br /> California Registered Civil Engineer C47410 '9TF(IF <br /> CAL\i��� <br /> Attachment <br /> WA17292.05\summarMLdoc 9 <br />