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' April 11, 1995 92-1177103 80 ' NORCAL Waste Systems, Inc Attention Mr Larry Sweetser, Director of Regulatory Affairs Subject REPORT - Quarterly Groundwater Monitoring - February 1995 ' Stockton Scavenger Association Facility 1240 Navy Drive Stockton, California ' Page 3 ■ Total petroleum hydrocarbon as gasoline (TPH-G) by EPA Method 8015, and ■ Benzene, toluene, cthylbenzene, and total xylenes (BTEX) by EPA Method 8020 ' Analytical ,Results TPH-G and BTEX were detected in samples collected from Monitoring Well MW-2 Monitoring Well MW-3 was sampled twice The samples collected on February 1, identified trace levels of BTEX This well was retested on March 28, 1995 and showed BTEX concentrations below the detection limit This retest sample was consistent with previous ' sampling events The anomalous detections of BTEX could be a result of laboratory or field sampling procedures TPH-D was detected in monitoring wells MW-2 and MW-4 TPH-G, BTEX and TPH-d were not detected 1n monitoring well MW-1 Analytical results are �{ summarized in Table 2 and copies of the laboratory report and Chain-of-Custody record are attached Evaluation The groundwater elevation data indicate the direction of groundwater flow for this monitoring period is toward pumping well MW-2 (see Drawing 3) This is a change from the previous monitoring period which showed the direction of groundwater flow was toward the ' southwest However, since the previous monitoring period, the volume of extracted groundwater has increased significantly, thereby creating a cone-of-depression (see Drawing 3) ' The analytical data suggests that groundwater quality underlying the site is relatively unchanged as compared with the previous monitoring period Concentrations of BTEX, TPH-D and TPH-G continue to be predominantly found in the vicinity of MW-2 Note that Drawings ' 4 through 6 indicate spatial concentration distributions similar to the November 1994 isoconcentration plots Trace concentrations of BTEX, however, were detected in groundwater samples collected from monitoring well MW-3 Diesel was also reported at a trace ' concentration of 0 28 mg/1- in monitoring well MW-4 during this quarter Professional Certification ' This report has been prepared by The MARK Group, Inc under the professional supervision of the Principal and or senior staff whose seal(s) and signature(s) appear hereon I