ARCHIVED REPORTS_XR0004414 - Laserfiche WebLink

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.A EXECUTIVE SUMMARY ti In March 1997, San Joaquin County Public Health Services, Environmental,Health Division (PHS/EHD), issued a request to Messrs Thomas O'Neill and Andrew Hyduke of Valley Motors for additional investigation of the extent of hydrocarbon contamination at the Valley Motors property in Stockton, California Specifically, PHS/EHD instructed Valley Motors to conduct a soil vapor survey of the property, install an additional monitoring well, and conduct a receptor survey In October 1997, Upgradient Environmental submitted a work plan to meet these requests We proposed to install 34 soil vapor probes, drill two soil borings to groundwater(estimated to be 50 feet)to confirm the results of the soil vapor survey, drill one monitoring well to 65 feet to complete the delineation of groundwater contamination, and perform one year of quarterly groundwater monitoring Subsequently, this work plan was amended to meet a request by PHS/EHD for deeper dnlling and additional sampling In particular, PHS/EHD requested that at least one boring be drilled to a depth of 75 feet (the historically lowest groundwater depth of record)to collect discreet samples of soil and groundwater and determine whether contamination extended to this depth If groundwater contamination was detected, Valley Motors was instructed to complete a dual or nested well, with screened intervals at both the present soil/water interface and at the 75-foot depth A cost estimate for this work was submitted in November 1997 and pre-approved by the State Underground Tank Cleanup Fund in January, 1998 The soil vapor survey and the drilling program were performed in March 1998, and the results are 0 presented in this report The report documents the extent of gasoline-contaminated soil beneath the site, discusses the results of groundwater samples collected during drilling, and makes recommendations based on these results Due to 1) limitations imposed by the City of Stockton Public Works department regarding drilling in public roadways, 2) buried underground utilities in these roadways, and 3) data collected during the vapor survey, the number of soil vapor probes was reduced from 34 to 16 Approximately half of the probes were drilled to a depth of 12 5 feet, with the remainder to 14 5 or 20 feet The probes were connected to a portable vacuum pump and vapors were extracted for several minutes before a photo-ionization detector(PID)was connected to the pump to measure organic vapor concentrations in the extracted vapor Hydrocarbon vapors were detected only in three probes, all in the vicinity of the former dispenser island Very low concentrations (5 ppm and 15 ppm) were detected in two of these, but concentrations of 360, 660, and 970 ppm were detected in the probe through the dispenser island at depths of 11, 12 5, and 14 5 feet, respectively These results suggested that contamination was more limited than previously suspected, and the drilling program was therefore modified accordingly Because the vapor data suggested that any "deep"contamination (i e at 75 feet)would likely be restricted to the dispen$er area,the first soil boring was moved closer to the dispenser and drilled to 75 feet The boring was continuously sampled to groundwater(approximately 40 feet)and was sampled at 5-foot intervals thereafter A hydropunch was used to collect a discrete groundwater sample at 40 feet, and a Simulprobe was used to collect discrete soil and water samples at 75 feet The two water samples and seven soil samples were selected for hydrocarbon analysis (TPH-g, BTEX, and gasoline oxygenates) Three 1