SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

ChevronTexaco - Trimark - 2 - 19 May 2004 Mountain House Sites # 1 and# 2 According to the results provided on the attached table, TPH-d was reported at 10,000 pg/L in the groundwater sample from boring MH1-1, which is located closest to the former OVP. TPH-d at l00 gg/L was reported in the second boring, which is south (upgradient) of the first boring. Electrical conductivity was 1,700 and 1,800 µmhos/cm, total dissolved solids (TDS) was 1,100 and 1,200 mg/L, nitrate was 49 and 25 mg/L, respectively for the samples. BTEX and MTBE constituents were N/D. The results are consistent with shallow groundwater samples previously collected for analysis in the Tracy area. Other groundwater quality parameters were completed and are presented on the attached table. As seen in the attached photographs, it appears that the Mountain House Creek channel width was previously reduced north of Byron Road and possibly modified when the road and UPRR track crossings were installed. North of Byron Road, the stream channel is much narrower(Photos 1, 2 and 3) than on the south side (Photos 5 and 6). A temporary earthen dam (Photos 4 and 5) appears to stop runoff flow to the north and as seen in the photos; water is accumulating behind the dam and not allowed to flow north beneath the road and north to Old River. STREAMBED ALTERATION PROJECT At this time, it is not certain when excavation will commence for the streambed alteration project to be undertaken by Trimark. Additionally, ChevronTexaco is in the process of preparing a disposal plan for treatment and discharge of impacted groundwater pumped from dewatering wells that will be needed during construction of the new bridges. Subsequent to my site visit, SAIC submitted a proposed plan to install 24 dewatering wells for the excavation and streambed alteration project. Placement of the dewatering well locations was based on historical drilling results and the recent field investigation. According to the analytical results, soil and groundwater within the proposed excavation area, has been impacted only on the east side of Mountain House Creek.