ARCHIVED REPORTS XR0001318 - Laserfiche WebLink

Home Browse Search

URS Ms Lori Duncan Page 2 San Joaquin County Environmental Health Department March 25, 2004 In July 1997, the SJCEHD sent ARCO a letter stating that the former Shell service station approximately 300 feet east of the ARCO site had reported increasing concentrations of methyl tertiary- butyl ether (MtBE) in the Shell upgradient wells These wells were to the northeast of the ARCO station, northeast is a dominant historical groundwater flow direction near the ARCO site The gasoline stored at the Shell Station reportedly never contained MtBE The Shell site was granted closure by the California Regional Water Quality Control Board (RWQCB) and the groundwater monitoring wells at the Shell site were subsequently abandoned On February 10, 11, and 12, 1999, four groundwater monitoring wells (MW-1 through MW-4) were installed at the ARCO site under the direction of SECOR International, Inc (SECOR) Analysis of groundwater samples collected from the newly installed wells indicated that total petroleum hydrocarbons as gasoline (TPHg) were present in two wells (MW-1 and MW-4) Benzene was reported in two wells (MW-1 and MW-4) MtBE was reported in monitoring wells MW-3 and MW-4 Concentrations of MtBE have decreased in these wells since monitoring was initiated, suggesting that the source of contamination has been removed In June of 2000, shallow monitoring wells MW-5 through MW-7 were installed at the site, downgradtent of the former source area The wells are located on a north-to-south line on the east side of Center Street, across from the former source area The wells were installed to help define the downgradient extent of gasoline-related compounds in site groundwater In May of 2002, one dual-completion groundwater monitoring well set (MW-8MID) was installed by SECOR on the west side of Center Street, downgradtent of the former ARCO pump islands, two dual- completion groundwater monitoring well sets (MW-9M/D and MW-10M/D) were installed on the east side of Center Street (Figure 2) Ongoing groundwater monitoring indicates that groundwater near MW- SM and 8D is impacted with petroleum hydrocarbons Hydrocarbon concentrations have decreased in MW-8M and 8D since groundwater monitoring was initiated Initial rounds of groundwater sampling indicated that groundwater in the vicinity of MW-9M/D and MW-10M/D was also impacted with petroleum hydrocarbons With the exception of low concentrations of MtBE, all analytes have been reported as below laboratory detection limits since the fourth quarter of 2002 in well MW-9M In MW-9D, all gasoline-related compounds and MtBE have been reported below laboratory detection limits since the first quarter of 2003 In MW-IOM, all gasoline-related compounds and MtBE have been reported below laboratory detection limits since the fourth quarter of 2002 In MW-IOD, all gasoline-related compounds and MtBE have been reported below laboratory detection limits since the second quarter of 2003 f� K MprocessVS BP ARC01044931Well InstaIl\4493 well installation repon04 doc