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Supplemental Investigation Report,Problem Assessment Report and Work Plan Cleanund .Abatement Order No 5-00-707 :,,,,,_,- EAI Prosect No 1232 4.0 EXTENT OF IMPACT Investigations at the Unocal and Wards sites have been completed over a period of several years, with vadose zone soil remediation work completed at the Unocal site in 1988 (see Section 2 3 2) and a remedial system installed and currently operating at the Wards site since November 1999 (see Section 2 2 3) 4,1 Soil Figure 5 is a map depicting the concentrations of TPH-G and benzene detected ins it samples collected from borings and wells associated with the Wards and Unocal sites, as well as the locations of cross sections A-A', B-B', C-C' and D-D' On cross sections A-A' through D-D', there are two points of release indicated for both the Wards and the Unocal sites Both sites had releases in the area of the former USTs and the in the area of the former dispenser islands It also should be noted that these cross-sections do not take into account the effects of the remediation work completed at the Unocal site in 1988 nor the ongoing remediation at the Wards site On cross section A-A' (see Figure 6), a release is indicated in the area of the former Unocal dispensers (B-2) and the former Unocal USTs (B-8) Note borings B-2 and B-8 were projected perpendicular onto cross-section A-A' Further, boring logs for these two borings were not available to EAI at the time the cross-sections were constructed A release in the area of the former Wards dispensers is indicated on cross-section B-B' (see Figure 7) near monitoring well MW-2 Cross—section C-C' (see Figure 8) indicates a release occurred on the Wards site near well MW-1 Analytical test data obtained from borings on the cross sections indicate soil is generally impacted in the saturated zone between 45 and 65 feet bgs Note, hydrocarbon impacted soil was excavated at the Unocal site to a depth of approximately 53 feet bgs in 1988 in the area of the former dispenser islands and USTs Cross-sections A-A' through D-D' also present TPH-G and benzene analytical test data obtained during the June 2000 ground water sampling event These data indicate the highest concentrations in ground water beneath the Wards site are in wells MW-2 (3,420 gg/L TPH-G) and MW-4 (216 µg/L benzene) The highest concentrations in ground water beneath the Unocal site are observed in wells MW-11 (15,400 gg/L TPH-G and 4,950 pg/L benzene) 4.2 Ground Water 4 2 1 Flow Direction and Magnitude Figure 9 presents the historic ground water flow direction and magnitude for the two sites During the summer months, when the RIW is in operation, the ground water flow direction for the Wards site is southwest, and for the Unocal site it is generally south to southwest, i e , BS 1232P IRW WP -10- ENVIRONMENTAL AUDIT, TNC.®