ARCHIVED REPORTS XR0001330 - Laserfiche WebLink

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iz September 14, 1993 Working To Restore Nature ARCO Service Station 2168, Stockton, California Dissolved gasoline hydrocarbons were detected in water samples collected from the three wells Purgeable halocarbons were not detected, except for 1,2-dichloroethane which was detected in monitoring well MW-2 Fecal and total coliform bacteria were not detected in the sample collected from well MW-3 In January 1993, RESNA observed drilling of seven soil borings and the installation of two groundwater monitoring wells and four vapor-extraction wells GROUNDWATER MONITORING: SECOND QUARTER 1993 1 On June 10, 1993, a technician from EMCON measured depths to water and collected groundwater samples from the wells for subjective and laboratory analyses The technician noted no floating product or sheen in the five wells (Table 1) 1 The wellhead elevations of the monitoring wells at the site were previously surveyed by Tom O Morrow, Inc of West Sacramento California, a licensed land surveyor (Califorrua Land Surveyors No 3275) The surveyed elevations and the depth-to-groundwater measurements, summarized in Table 1, were used to evaluate the potentiometric surface beneath the site On June 10, 1993, a linear depression trending northwest-southeast near well MW-4 was 1�} present in the potentiometric surface The hydraulic gradient was 0 01 (Plate 3) The groundwater elevation increased by approximately 186 feet since the previous morutoring event Groundwater samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) 1 and benzene, toluene, ethyibenzene, and total xylene isomers (BTEX) using Environmental Protection Agency (EPA) Methods 5030 and 8020 and standard methods prescribed by the State of California Samples were also analyzed for halogenated volatile organic compounds using EPA Methods 5030/601 These samples were analyzed at Columbia Analytical Services, Inc in San Jose, California (Hazardous Waste Testing Laboratory Certificate No 1426) The results of analyses are summarized in Tables 1 and 2 Copies of the laboratory analysis reports are in the appendix Results of analyses indicated TPHg and BTEX were detected in samples from the five wells The highest co ntrations of TPHg and benzene were detected in wells MW-4 and MW-3 � 46at 10,000 and�;000 parts per billion, respectively 1,2-Dichi oro ethane was detected in 1 � ' `' groundwater samples from wells MW-1, MW-2, MW-4, and MW-5, 1,2,-dichloropropane was detected in wells MW-1 and MW-2, and methylene chloride was detected in well MW-2 Concentrations of TPHg and benzene are shown on Plate 2 ,.1 0712ccar 2 31009 9