ARCHIVED REPORTS XR0011081 - Laserfiche WebLink

Home Browse Search

Geolog1w-r "icsInc. Page 7 Groundwater Monitoring Report Project No 724 2 Apn1 25,2006 premise that the data we considered, although incomplete, are representative of actual site conditions We acknowledge that there may be undiscovered conditions, which would upon their consideration, change our interpretation and thus our conclusions Our recommendations are based on our knowledge of site conditions, and on the state and ' limitations of subsurface investigative technology Conclusions • The groundwater plume does not display a typical "core" but exhibits wide variations in contaminant concentration in both vertical and lateral planes as shown in Figures 6 - 12 Generally the plume has migrated down gradient of the source and is displaced east of the former UST o The highest MTBE concentrations detected in the intermediate and deep aquifers were in wells MW-1.06 (17 3 µg/1) and MW-209 (4 4g/1), respectively ' o Water table well MW-7 contains trace (0 7 ug/L) MTBE o The contaminated shallow, intermediate and deep wells are down gradient from the former UST and dispenser locations areas in the predominant groundwater direction to the east o The highest TPH-G concentrations were detected to the east of the site in wells MW-108 and MW--208 o None of the wells contained benzene above the laboratory reporting limit o In their correspondence dated September 3, 2002, the San Joaquin County Environmental Health Department (SJC/EHD) identified two LUFF sites (701 E Charter Way and 749 E Charter Way) as being up gradient of the subject site The contamination detected in the MW-1081208 location may be partly or entirely ' originated from an offsite source • The SJC/EHD also stated in their above letter that a sandy interval at 70 — 80 bgs could be acting as lateral conduit for contaminant migration The presence of contamination in deep wells MW-208 and MW-209 support this theory However, GTI still suggests that the low concentrations of TPH-G & MTBE in these wells do not warrant an engineered clean up ' • The data shows that a relatively stable, wide spread, low concentration plume of petroleum hydrocarbon compounds is present in the groundwater at this site • The groundwater plume was further defined by the advancement of four Cone Penetrometer Testing (CPT) boreholes in January 2006 The CPT borings revealed that a local high of TPH-G is located in the vicinity of MW-208 The samples from the two locations down gradient (east) of wells MW-109/209 and MW-110/210 did ' not contain TPH-G above the laboratory reporting limits The presence of elevated levels of TPH-G along the edge of Charter Way (1580 ug/l MW-208) but not in the off site area due east of the former UST system supports the conclusion that the ' groundwater plume near MW-811081208 is being sourced by the contaminated sites to the northwest of the Morita parcel A review of the 4t` quarter 2005 data (Geotracker — State database) indicated that monitoring well MW-1 at the 749 E Charter Way 1