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MMM I= 7 r 2.0 PROPOSED ACTIVITIES IT recognizes the following concerns in defining this work scope: • Need to replace the groundwater monitoring system, r Need for additional data to aid in determining the vertical and lateral extent of hydrocarbons in soil vadose zone. • The possible utility of a soil vapor collection and tre.'iuient system. Although the full distribution of hydrocarbons in not yet known, constructing elements of a soil remediation system would be mo_t '._ easily done while the station is undergoing renovation. 6 2.1 GROUNDWATER INVESTIGATION IT proposes installing three groundwater monitoring wells at the site. Four groundwater monitoring wells were installed in April 1990 and groundwater was found to contain TPH-G in the two wells along Pershing Avenue. At that time, -- groundwater was present at 23 to 25 feet below grade. By December, water levels had dropped at least five-feet and the 30-foot deep wells were dry. Also, the upgradient monitoring well was intentionally destroyed (properly, per State and County requirements) in February of 1991, as part of station renovation (Appendix B). IT proposes initially replacing the groundwater monitoring network with three monitoring wells: or,e upgradient well and two downgradient, placed as shown ' on Figure 3. Each of the downgradient wells would be within 10-feet of the downgradient edges of the former oil and gasoline UST excavations. Additional wells are unnecessary until it is determined that the fallen water levels have not left all hydrocarbons locked in the vadose zone. If this is the case, the three proposed wells will serve to confirm this. If this is not the case, additional wells will be proposed. Well construction (Section 3.2) will be followed by development and sampling (Section 3.4). Groundwater samples will be tested for TPH-G and BTEX (Table 2). A:ENG:9205/031291