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�y h� E11C�t® Ms Pamela Lopez September 1997 Page 2 greatest concentrations were detected at the location of SBA On the basis of these results, RAH Environmental, Inc concluded that the source of the petroleum hydrocarbons identified at the location of drill hole SBA most probably resulted from the former UST on the Lopez property Ground water analytical results are included in Attachment 1 In February 1996, Fugro West, Inc , witnessed the advancement of five drill holes (MW-1, MVV 2, MW-3, SB-A1, and SB-A2) at the locations illustrated on Figure 2 The dnll holes were advanced to approximate depths ranging from 20 5 to 35 5 feet Drill holes MW-1, MW-2, and MW-3 were completed as 2-inch diameter ground water monitoring wells Soil samples collected from the dnll holes were analyzed for the presence of TPHg and BTEX by U S EPA Method 8015M/8020 The analytical results are summarized in Table 3 of Attachment 1 GROUND WATER MONITORING Ground Water Levels On July 22, 1997, ENSR collected depth to ground water measurements at the locations of monitoring wells MW-1 through MW-3 prior to purging and sampling All depth to ground water measurements were recorded according to the ENSR standard operating procedures (SOPs) included in Attachment 2 All field documentation is included in Attachment 3 Ground water level data are summarized in Table 1 Since the last sampling event conducted in March 1997, the ground water elevation in all monitoring wells has decreased an average of 7 78 feet A ground water elevation hydrograph is included on Figure 3 - Ground Water Elevation Hydrograph On the basis of the July 22, 1997, data, ground water is estimated to flow to the southeast at an average hydrogeologic gradient of approximately 0 006 feet per foot (ft/ft) (Figure 4 - Potentiometric Surface Map, July 22, 1997) Ground Water Sampling and Analysis On July 22, 1997, ENSR collected ground water samples at the locations of monitoring wells MW-1, MW-2, and MW-3 The ground water samples were collected according to the ENSR SOPs included in Attachment 1, and were delivered under chain-of-custody documentation to Sequoia Analytical Laboratory, a state-certified analytical laboratory The samples were analyzed for concentrations of TPH identified as gasoline by modified U S EPA Method 8015, and benzene, toluene, ethylbenzene, total xylenes and methyl tert-butyl ether by U S EPA Method 8020 The analytical results are summarized in Table 2 The analytical report and chain-of-custody documentation are included in Attachment 4 Concentrations of TPHg and benzene are illustrated on Figure 5 - Distribution Map of TPHg and Benzene in Ground Water, July 22, 1997 •1 f, 8796002 130MA[e'Sc 015IC nk5