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R 4WD Depth to groundwater beneath the facility during this monitoring event ranged from 14 57 (MW-8) to 16 11 (MW-3) feet below land surface (bls) Depth to groundwater measurements across the study area during this quarter indicate that the groundwater table rose approximately 2 25 feet from the last monitoring event Table 1 presents the groundwater elevation data Water table elevations and a groundwater contour map for December 10, 1996, are depicted on Figure 1 The data indicate that groundwater flows generally to the northwest The average hydraulic gradient is approximately 0 0013 foot per foot The flow direction and gradient are similar to the third 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 all of the monitoring wells TPHg concentrations ranged from below detection limit (MW-3, MW-4 and MW-6) to 46,000 µg/L (MW-5) TVOA concentrations ranged from 13 µg/L (MW4) to 3,136 1 pg/L (MW-5) MTBE concentrations ranged from below detection limit (MW-3 and MW;7) to I 1 µg/L (MW-2) Table 1 presents the analytical testing data The analytical data is depicted on a site plan as Figure 2 The complete analytical laboratory report with the chain of custody is included as Appendix G I ' 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-2) and one equipment blank Hydrocarbon constituents were not detected in the equipment blank The duplicate and original sample results are within an acceptable range Figure 2 lists the original sample result t CONCLUSIONS AND RECOMMENDATIONS BRE recommended installing an additional well to the east to complete the delineation of the' hydrocarbon plume This well was proposed in a Workplan for Conttnued Assessment, submitted ` on August 28, 1996 The'Workplan also recommended installing six shallow soil bonngs and two deep soil borings to define the extent of soil contamination The Workplan was approved on September 23, 1996 The results'of the fourth quarter monitoring indicate the activities outlined, �r I in the approved Workplan are valid I I