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v 1 A S S O C I A T E S I N C extraction/air sparge system at the site is not warranted However, Mr Knoll also indicated that either long term monitoring or another alternative would be required prior to the site being considered for closure The workplan for performing a groundwater extraction pump test at the site was submitted on March 1, 2001 Mr Knoll approved this workplan on March 9, 2001 SAMPLING ACTIVITIES On April 3, 2002, ATC Associates personnel collected groundwater samples from monitoring wells MW2, MW3, MW4, MW5, and MW6 The locations of the monitoring wells are shown on Figure 2 Prior to collection of groundwater samples in the monitoring wells the depth to water, pH, electrical conductivity, and temperature were measured and recorded A minimum of three well casing volumes was purged from each well prior to sampling The wells were allowed to recover and samples were collected from each well using disposable bailers A similar sample was also collected from the Thornton Municipal Supply Well No 2 The groundwater samples collected from each well were submitted to State-certified Argon Laboratories (ELAP Cert No 2359) for chemical analysis of total petroleum hydrocarbons as gasoline (TPHg) utilizing EPA method 8015 modified, benzene, toluene, ethyl benzene, xylenes (BTEX), and methyl tertiary butyl ether (MTBE) utilizing EPA method 8020 MTBE was initially detected in well MW4 so this sample was also analyzed for fuel oxygenates utilizing EPA method 8260 Groundwater monitoring well purge and sample logs are contained in Attachment 1 ANALYTICAL RESULTS Laboratory analyses detected TPHg at monitoring well MW4 at a concentration of 5,700 µg/L, benzene at a concentration of 6 5 pg/L, toluene at a concentration of 6 7 gg/L, ethyl benzene at a concentration of 93 pg/L, and xylenes at a concentration of 49 pg/L MTBE was analyzed and initially detected by EPA method 8020 at a concentration of 25 µg/L in monitoring well MW4, but confirmation of the sample by EPA method 8260 determined MTBE to be below the laboratory reporting limit of 2 0 pg/L Benzene, ethyl benzene, toluene, xylenes, MTBE, and TPHg were not detected above the laboratory reporting limit at monitoring wells MW2, MW3, MW5, MW6, and the Municipal Supply Well The California Primary Maximum Contaminant Level (MCL) for benzene of 1 pg/L was exceeded at monitoring well MW4 Laboratory data sheets and chain-of-custody documentation are contained in Attachment 2 GROUNDWATER FLOW DIRECTION Water level measurements were collected from monitoring wells MW1, MW2, MW3, MW4, MW5, and MW6 on April 3, 2002 Depth to water measurements ranged from 9 11 feet to 14 05 feet below top of casing representing an increase in the water table elevation of approximately 0 68 feet since January 2002 The water level elevations were used to develop the groundwater contour map (Figure 2) Assuming that horizontal isotropic conditions prevail, the groundwater in the uppermost aquifer beneath the site generally flows in a southwesterly direction at an W 1Wordpro1625821Quarl1y12QR-2602 doc 4