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• 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 This workplan was approved by Mr Knoll on March 9, 2001 SAMPLING ACTIVITIES On September 24, 2001, ATC Associates personnel collected groundwater samples from monitoring wells MW 1, MW2, MW3, MW4, MW5, and MW6 The locations of the monitoring 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 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 sample was also collected from the Thornton Municipal Supply Well The groundwater samples collected from each well were submitted to State-certified Argon Laboratories (FLAP Cert No 2359) for chemical analysis of total petroleum hydrocarbons as gasoline (TPHg) utilizing EPA method 8015 modified, benzene, toluene, ethylbenzene, xylenes • (BTEX), and methyl tert butyl ether (MTBE) utilizing EPA method 8020 Groundwater monitoring well purge and sample logs are contained in Attachment 1 ANALYTICAL RESULTS Laboratory analyses results detected TPHg. at monitoring well MW4 at a concentration of 5,400 pg/L At monitoring well MW4, benzene was detected at a concentration of 6 9 pg/L, toluene was detected at a concentration of I4 pg/L, ethylbenzene was detected at a concentration of 140 µg/L, and xylenes were detected at a concentration of 140 gg/L MTBE was analyzed and not detected above the laboratory reporting limit of 10 pg/L at monitoring well MW4 Benzene, ethylbenzene, toluene, xylenes, MTBE, and TPHg were not detected above the laboratory reporting limit at monitoring wells MW1, 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 September 24, 2001 Depth to water measurements ranged from 11 14 feet to 16 09 feet below top of casing representing a decrease in the water table elevation of approximately 1 12 feet since June 2001 The water level elevations were used to develop the groundwater contour map (Figure 2) Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost aquifer beneath the site generally flows in a southwesterly direction There is a slight mounding present in the vicinity of monitoring well MW3 The w 1Wordpro1625821Quardy13QR-2001 doc 4