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rw Page 26 August 10, 1989 Job No.211-71-6 non-detected levels cf total petroleum hydrocarbons as gasoline(the detection limit was generally <0.6 mg/kg). Trace amounts of BETX constituents were present in the soil samples collected in monitoring well MW-15 at 61 feet and monitoring wells MW-17 and MW-22 at 66 feet. Boring B-3,located adjacent to the tanks,was drilled to a total depth of 82 1/2 feet and each soil sample was tested on-site using an OVA meter. Hydrocarbons were nc.t detected in this boring by the OVA meter below a depth of 74 feet. Anal ical Results- Ground Water The results of the grc!md-water chemical analyses are presented in Appendix B and summarized in Table F. Plates 4 through 14 are graphs showing the changes in TPHg and BETX concentrations with time. The chemical analytical results from previous investigations are also summarized in Table F. Monitoring wells MW-1,MW-15,MW-16,and MW-18 through MW-25 were last sampled on June 13, 1989. Monitoring wells MW-8, MW-10, and MW-17 ware not sampled due to the presence of free-floating product on March 15, 1989. Figures 10 and 11 are interpretive maps showing the approximate lateral extent of total petroleum hydrocarbons(as gasoline)and beazene concentrations based on the most recent sampling results. Low to non-detected levels of TPHg and benzene were present in monitoring wells MW-15,MW-I6, MW-18 through MW-21, MW-24 and MW-25 and as such, help define the "effective zero4ine"at s the site. As shown in Table F and in Figures 10 and 11, monitoring wells MW-8, MW-10, and MW-17 (located near the tank cluster in the north central portion of the site)continue to show measurable quantities of free product. Free product at tha site is presently being removed by a free-product skimmer pump. The product is being hauled for recycling (with the appropriate manifest documentation) by Alviso Independent Oil Company (a State registered waste hauler). To date, -- approximately 130 gallons of product have been removed from these three monitoring wells. ` A comparison of the analytical results from the most recent sampling with the previous quarterly i sampling (March 19891 indicates the following: I. TPHg concentrations have increased in monitoring wells MW-1 (510 ppb to 980 ppb), MW--18 (non-detected to 24 ppb), and MW-21 (40 ppb to 61 ppb). . The TPHg concentrations decreased in monitoring wells MW-15 (290 ppb to 92 ppb),MW-16 (120 ppb to 98 ppb), MW-23 (190 ppb to 170 ppb), MW-24(18 ppb to 5.7 ppb),and MW-25 (210 ppb to 52 ppb). TPHg in monitoring well MW-20 has remained non-detected for the majority of the samplings.