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y. 4WD during this quarter indicate that the groundwater table decreased approximately 3 feet from the last monitoring event Table 1 presents the groundwater elevation data Water table elevations and a groundwater contour map for September 17, 1996, are depicted on Figure 1 The data indicate that groundwater flows generally to the northwest The average hydraulic gradient is approximately 0 003 feet per foot The flow direction and gradient are similar to the second quarter's monitoring event BRE personnel collected groundwater samples from 8 monitoring wells during this field event Groundwater samples were transported to a California certified laboratory, Centrum Analytical Laboratories, Inc , in Redlands California, and analyzed for Total Petroleum Hydrocarbons - Gasoline range organics (TPHg) by EPA Method 8015 (modified) and total volatile organic aromatics (TVOA), including methyl tertiary butyl ether (MTBE), by EPA Method 8020 Laboratory analysis of the groundwater samples indicated the presence of dissolved phase petroleum hydrocarbons above laboratory method detection limits (MDLs) in 5 of the monitoring wells Concentrations of TPHg ranged from below detection limit (MW-4, MW-6, MW-7, and MW-8) to 5,000 pg/L (MW-5), and concentrations of TVOA ranged from below detection limit (MW-3, MW-6, MW-7, and MW-8) to 1,263 pg/L. (MW-5) Concentrations of MTBE ranged from below detection limit (MW-3, MW-4, and MW-7) to 8 µg/L (MW-5) The contaminate concentrations in MW-1, MW-2 and MW-5 have decreased since the last monitoring event MW- 4 shows an increase in concentration for benzene The concentration of MTBE was higher for MW-8, while MW-3 and MW-7 concentrations remained. the same Table 1 presents the' analytical testing data The analytical data is depicted on a site plan as Figure 2 The complete analytical laboratory report, including the chain of custody, is included as Appendix C Quality assurance and quality control (QA/QC) samples were collected during this quarterly sampling event The QA/QC samples consisted of one duplicate sample (obtained from well MW- 1), one trip blank, and one equipment blank No hydrocarbon constituents were detected in either the trip blank or the equipment blank 1 , CONCLUSIONS AND RECOMMENDATIONS Perimeter monitoring wells MW-6, MW-7, and MW-8 did not contain hydrocarbon constituents during this quarterly sampling event as in the past several,quarterly'sampling events, indicating ' that the plume is defined to the north, west and south of the Site BRE recommends reducing'the frequency of monitoring for these wells to semi-annual events To complete the delineation of the hydrocarbon plume, BRE recommended installing an additional well to the east This well was proposed in a Workplan for Continued Assessment, submitted on August 28, 1996 The location of this proposed well is shown on Figure 1 of the Workplan The Workplan also .1 1 I I I {I I li II V1', �� IE I f t 1411 I i I I