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r- <br /> grounO.water data support the maw that the source for a signii,..,ant portion of the TPHd <br /> plume is related to the above-ground storage tanks (ASTs) . The information presented <br /> below is from Site Assessment Report dated September 5, 2008, submitted by Conestoga- <br /> Rovers and Associates (CRA) . <br /> Between May 27 - 29, 2008, thirteen soil borings were advanced to approximately thirty <br /> feet below surface grade (bsg) . Sixty soil and thirteen grab groundwater samples were <br /> collected from soil borings B-29 through B-41. <br /> The highest soil concentrations of TPHd and TPH-motor oil (TPHmo) were 8,600 mg/kg and <br /> 2,500 mg/kg, respectively, detected in boring B-31 at sixteen feet bsg. This boring was <br /> advanced directly east of the ASTs. <br /> The highest soil concentration of gasoline-range hydrocarbons (TPHg) was detected at 350 <br /> mg/kg in boring B-32 at twenty-four feet bsg. B-32 was advanced approximately seventy <br /> feet northeast of the ASTs. <br /> TPHd and TPHmo were detected in grab groundwater samples collected from all 13 borings. <br /> The highest groundwater concentrations of TPHd and TPHmo were 1,400, 000 ug/L and 510,000 <br /> ug/L, respectively, detected in boring B-32 advanced approximately seventy feet northeast <br /> of the ASTs. <br /> There appears to be two TPHd plumes which may be comingled. One is near the former diesel <br /> UST and the other plume is near the diesel pump station located near the ASTs. CRA stated <br /> that the low concentrations of TPHd in soil and groundwater detected in borings B-39 and <br /> B-40 are an indication that there exists "a non-impacted area between the former diesel <br /> UST and the diesel pump station", although low concentrations are an impact. <br /> The vertical extent of TPHd in soil is defined. Soil is impacted near the ASTs from <br /> approximately 2 .5 feet bsg to approximately 25 feet bsg. <br /> The lateral extent of impacted soil appears to be defined both in the area near the former <br /> diesel UST and near the ASTs. <br /> The vertical extent of TPHd in groundwater may or may not be defined. <br /> CPT-2 was advanced near the former diesel UST. At 90 to 93 feet bsg, TPHd was reported <br /> less than 50 ug/L with silica gel cleanup and 75 ug/L without silica gel cleanup. CPT-3 <br /> was advanced approximately 75 feet northeast of the ASTs. At 72 -75 feet bsg, TPHd was <br /> reported less than 50 ug/L with silica gel cleanup and 81 ug/L without silica gel cleanup. <br /> The lateral extent of TPHd impacted groundwater is defined in all directions except toward <br /> the south (Ripon Farm Services property) . <br /> Groundwater was collected from MW-2 and MW-3 located at the Ripon Farm Services site <br /> during the fourth quarter 2008 sampling event. I do not have the groundwater results yet. <br /> I believe this gives you a very brief oversight of the TPHd contamination at the JIMCO <br /> Truck Plaza. Please let me know if you have any questions. <br /> Vicki McCartney, Senior REHS <br /> San Joaquin County <br /> Environmental Health Department <br /> 600 East Main Street <br /> Stockton, California 95202 <br /> Phone: (209) 468-9852 <br /> Fax: (209) 468-3433 <br /> Email: vmccartney@sjcehd.com <mailto:vmccartney@sjcehd.com> <br /> 2 <br />