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SATE CONDITIONS This section presents a summary of Site conditions compilation of data collected prior to beginning of 1 based on HLA's review of all previous work groundwater extraction and treatment operations is performed at the Site The summary is modified Included(WaterWork, 199 1, Table 1) Depths to from the previous summary presented in HLA's groundwater beneath the Site have varied from August 5, 1997 report(HLA, 1997a)to approximately 3 5 to 13 feet bgs Incorporate new data collected by HLA Most of the data discussed In the following sections is GROUNDWATER ANALYTICAL DATA presented on Plates 4, 5, and 6 Analytical data presented in SECOR's draft report(SECOR, Analytical data from the monitoring wells are 1997)are not utilized in this summary In compiled in Table 1 In compliance with the addition, borings HP-1 and HP-2 (SSI)were request from PHS/EHD, all historical depth-to- drilled in the same Iocations as SB-10 and SB-9 groundwater and groundwater elevation data have (SECOR, 1997), lithological data from these two been included in Table 1 Monitoring well MW-4 SECOR borings were therefore not used is the only well that has consistently(until August However, lithological data from boring SB-8 1999)contained detectable concentrations of (SECOR, 1997)were included hydrocarbons SOIL PROFILE During the period of February 1988 through June 1994, TPHg concentrations In well MW-4 ranged The soil profile at the Site is summarized based on from 9 1 miIIigrams per liter(mg/1) (February HLA's review of boring logs from previous 1988)to 0 24 mg/l (June 1993) Regular quarterly Investigations and HLA's boring logs for HP-1, sampling was discontinued when the pump and HP-2, HP-3, and MW-7 Copies of boring logs treat system was turned off in June 1994 I from this Investigation are included in Appendix Approximately three years later, HLA sampled the A In compliance with the request from wells in August 1997 TPHg and benzene PHS/EHD, all previous boring logs are included in concentrations in well MW-4 had decreased from Appendix B Based on these boring logs, soils 0 264 mg/L and 0 011 mg/L,respectively in June beneath the Site consist of a heterogeneous 1994,to 0 054 mg/L and 0 00068 mg/L, assemblage of mainly fine-grained sediments with respectively in August 1997 The August 1997 minor amounts coarse-grained sediments Plate 6 sampling event marks the first time the benzene is an east-west cross-section(A-A')constructed concentration in well MW-4 had dropped below from HLA's borings and previously completed the California Max num Contaminant Limit borings, the location of A-A' is shown on the Site (MCL)of 10 ug/L In Plate 5,the concentrations Plan(Plate 3) of TPHg and benzene versus time are plotted The graph shows decline of the concentrations with GROUNDWATER GRADIENT AND FLOW time and supports the classification of the Site in 1 DIRECTIONS the low-risk category The available analytical data on fuel oxygenates and I,2-DCA are Based on monitoring data collected from summarized In a later section with the results of September 1987 to March 1991 (22 sets of the SSI measurements), groundwater flow directions have varied from northeast through northwest and As previously discussed, an irrigation well Is towards the southwest and south The dominant located on the adjacent Lopez property 1 flow directions appear to be southwest through approximately 150 feet northeast of the former . northwest Groundwater gradients varied from TVG USTs location Analytical results from three 0 0023 to 0 018 feet per foot(ft/ft), averaging samplings of this well (March, 1989, September approximately 0 004 ft/ft In Appendix C,a 1993, and July 1999)that were performed in L 13000M387371WP138737N19 Harding Lawson Associates 7