Laserfiche WebLink
2 <br /> Report on Additional Site Assessment March 5,2001 <br /> 7-Eleven Inc,Store#19976, 1399 N Main St Manteca,California <br /> A workplan for initial site assessment was requested in February 1998 by the SJCPHS Geoprobe soli <br /> borings GP-1 through GP-3 were subsequently installed on April 29, 1998 near the hydrocarbon source <br /> area (the underground storage tank(UST) pad and pump island) (Figure 2) Nineteen sod samples <br /> were collected from depths ranging between 5 and 45 feet below grade for analysts for BTEX,MTBE, <br /> and TPH-G (EPA Methods 8020/modified 8015) One sample from each soil boring was also analyzed <br /> for MTBE,TBA, DIPS, ETRE, and TAME using EPA method 8260 Hydrocarbons were reported to <br /> detectable levels in seven of the nineteen tested samples, most of the samples containing detectable <br /> concentrations were obtained from depths of 15-25 feet below grade (the upper part of the shallow <br /> water-bearing zone) Sod MTBE identified using EPA Method 8020 in some of the samples was not <br /> detected when the same samples were analyzed by EPA Method 8260 (Table 2) <br /> Anomalously high levels found at 35 feet below grade in boring GP-3 were bracketed by non-detectable <br /> concentrations at 30 and 40 feet below grade (Table 2),these anomalous data have since been <br /> unverifiable by later sampling, and are now thought to be indicative of borehole wall caving from <br /> shallower sod depths during drilling of GP-3 <br /> Grab groundwater samples collected from the base of each boring were also analyzed for the same <br /> constituents and contained up to 5,800 pg/L benzene and 290,000 pg/L TPH-G Dissolved MTBE levels <br /> ' ranged up to 3,700 pg/L (EPA Method 8260) (Table 3) <br /> Additional assessment was requested by the SJCPHS in June 1998 Groundwater monitoring wells MW- <br /> 1,MW-2, and MW-3 were installed in September 1998 (Figure 2) Well MWAA is a dual-nested well <br /> completed to depths of 30 and 66 feet below grade Twelve sod samples were analyzed for BTEX, <br /> MTBE, and TPH-G by EPA methods 8020/8015 modified, and two of the samples were also analyzed for <br /> oxygenates MTBE,TBA, DIPE, ETRE, and TAME using EPA method 8260 (Table 2) The highest <br /> benzene concentration was detected in capillary fringe soils (0 0708 mg/kg in MW-2@25'),the highest <br /> confirmed MTBE concentrations were detected at 50 feet below grade in soil from well MWA (0 0187 <br /> mg/kg) The highest TPH-G concentration was detected in sample MW-1 @45' at 17,000 mg/kg <br /> 19978 45A <br />