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Iff ZWA&.�Alft Working to Restore Nature approximately 0.01 (Plate 9). The direction of groundwater flow has generally been southeast since our investigation began. The groundwater surface has risen an average of 2.16 feet since the last monitoring event. Groundwater samples from each well were analyzed for TPHg and BTEX using EPA Methods 5030 and 8020 using DHS/LUFT Method. The sample from well MW-1 was also analyzed for total oil and grease (TOG) using Standard Methods 5520C and 5520F. The samples were analyzed at Columbia Analytical Services, Inc. in San Jose, California (Hazardous Waste Testing Laboratory Certificate 1426). The results of these analyses are summarized in Table 1. Copies of the laboratory analysis reports are Appendix D. Results of analyses indicated TPHg and BTEX concentrations were below laboratory detection limits in groundwater samples collected from onsite well MW-4 and offsite well MW-6. TPHg was detected in wells MW-1, MW-3, and MW-5 at concentrations of 110 parts per billion (ppb), 140 ppb, and 820 ppb, respectively. Benzene was detected in wells MW-I, MW-2, and MW-5 at concentrations of 1.3 ppb, 2.9 ppb, and 34 ppb, respectively. TOG was not detected in the sample from well MW-1. Concentrations of benzene and TPHg are shown on Plate 2. WORK IN PROGRESS ARCO will continue quarterly monitoring. SUMMARY OF SITE CONDITIONS Site Geolo Sediments underlying the site consist primarily of silt with some clay and silt with fine- to medium-grained sand (see attached Logs of Borings and those presented in RESNA Report 30004-4, dated June 26, 1992 and RESNA Report 30004-8, dated June 21, 1993). • Residual H drocarbons in Soil The results of laboratory analyses from soil borings (B-1 through B-21), product line sample and soil collected beneath the clarifier were used to evaluate the vertical and lateral extent of residual hydrocarbons in soil (RESNA, June 26, 1992, 30004-4, RESNA, June 21, 1993, Report 30004-8 and EA Engineering, Science and Technology, August 1992, Report 80633.01). Residual gasoline hydrocarbons (quantified as TPHg) were detected in soil samples collected from soil borings at concentrations ranging from 1.1 ppm to 260 ppm. Residual gasoline hydrocarbons are present in soil near the underground storage tanks from 10 feet bsg to the top of the groundwater surface and near the southwestern dispenser island y 1213ccar/3M_g 4