ARCHIVED REPORTS_XR0004990 - Laserfiche WebLink

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C\V/ � • A S S O C I A T E S I N C SAMPLING ACTIVITIES On September 24, 2002, ATC personnel collected groundwater samples from monitoring wells MW1, MW3 through MW10, and the on-site groundwater supply well DW A groundwater sample was not collected from well MW2 because of the presence of floating free product in the well The locations of the wells are shown on Figure 2 Prior to collection of groundwater samples, the depth to water, pH, electrical conductivity, and temperature were measured in the monitoring wells and recorded A minimum of three well casing volumes were purged from each monitoring well prior to sampling The wells were allowed to recover and samples were collected from each well using dedicated disposable bailers After the groundwater samples were collected, dissolved oxygen was measured in each well The groundwater samples collected from each well were submitted to State-certified Argon Laboratories Inc (ELAP Cert No 2359) in Ceres, California for chemical analysis of total petroleum hydrocarbons as gasoline (TPHg) utilizing EPA method 8015 modified, benzene, toluene, ethylbenzene, and xylenes (BTEX) utilizing EPA method 8020, and methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE) di-isopropyl ether (DIPE), tertiary amyl ether (TAME), tertiary butyl ether (TBA), 1,2-dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB) utilizing EPA method 8260 Groundwater well purge and sample logs are contained in • Attachment 1 GROUNDWATER FLOW DIRECTION Water level measurements were collected from wells MW1 through MW10 on September 24, 2002 Water levels ranged from 67 22 to 68 61 feet below the tops of the well casing elevations, representing an average decrease in the water table elevation of approximately 4 11 feet since June 202 The water level data were used to develop the groundwater elevation contour map ',�,,(FigureA Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost �10 aquifer beneath the site flowed towards the southeast The average hydraulic gradient on a� September 24, 2002 was calculated to be 0 003 ft/ft or approximately 16 ft/mile A summary of groundwater monitoring data is presented in Table 1 �5 GV '� � ANALYTICAL RESULTS 4� Groundwater samples collected from wells MW1, MW3,,\and MW6 contained the highest concentrations of TPHg and BTEX Well MW2 contained free product and was not sampled Groundwater samples collected from wells MW4, MW7, and MWS also contained detectable concentrations of TPHg and BTEX constituents Concentrations of TPHg ranged from 280,000 parts per billion (ppb) in well MW3 'Eo 2,900 ppb in well MW7 Concentrations of benzene ranged from 29,000 ppb in well MW3 to 14 ppb in well MW4 The groundwater samples collected from wells MW5, MW9, and MW10 contained no detectable concentrations of TPHg or BTEX Groundwater samples collected from wells MW1 and MW3 through MWI0 contained no detectable concentrations of oxygenate fuel additives although many of the reporting limits w A63931quartlyl3gr-2002 doe 3