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._. dG..d.ra _ � _i"v '• .. Q' F512,- X III MON r 4.0 REl': MMENDED REMEDIAL,ACI'IVI7IE5 RS recommends remediation of the TPHg contain nated vadose soil in the former tank emplacement by in-situ vapor extraction technology. In-situ treatment of the soil offers the advantage of removal of VOC where contaminated soil is located close to or under a building at depths not readily excavated,as has occurred in this case. Specifications for the Soil Vapor Extraction System are presented in Appendix B of this Work Plan. The Health &Safety Plan to be implemented during the remedial activities is included in Section 10.0 of the Specifications. 5.0 GRQUNDWATER MQN]TORING ALM VITIE RS recommends monitoring of the groundwater to determine the extent of contamination beneath the site. However, due to the drought, the water table has dropped below the screened sections of the existing monitoring wells (70 feet deep) and groundwater samples cannot be obtained at this time. As an alternative, sampling of DWR Registered Wells 2, 5, & 7 (Table 4, WGR's November, 1989 report), located within an approximately one- quarter mile radius of the site,was considered. After reviewing pertinent information, this alternative is not recommended due to the technical difficulty of sampling for VOC in deep wells and information indicating the existence of underground fuel tanks located on other properties in the immediate vicinity of the welis and the site. If,during the 1991-1992 winter season,the groundwater elevation rises sufficiently to permit sampling of the onsite monitor wells,quarterly groundwater monitoring would be initiated by RS. If groundwater has not risen sufficiently by the end of the 1991-1992 rainy season, then three additional monitoring wells would be installed so that site roundwater monitoring can be re-established. -' During vapor extraction operation, it is anticipated that s nme reduction of VOC in the groundwater beneath the treatment cell may be achieved. By reducing TPHg concentrations - in the contaminated soil to low or non-detectable levels, further contamination of groundwater beneath this site would be minimized. 6.0 PROJECT SCHEDULE Figure 4 presents the project schedule for this Soil Vapor Extraction project. 3 1 w - REMEDIATION '� - _ SERVICES, INC.