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Groundwater monitoring was performed by Ninyo and Moore (N&M) in May 1994 and consisted of the purging and sampling of wells MW-10 through MW-24 Wells MW-I through MW-6 were dry in May 1994 due to declining groundwater elevation levels and could not be sampled Other work completed by N&M concurrent with the groundwater monitoring event included the abandonment of wells MW-1 through MW-8 and MW-10 These wells were abandoned due to the declining ' groundwater elevations In addition, wells MW-9, MW-11, MW-13, MW-14, MW-16, MW-19, MW-20, and MW-24 were temporarily decommissioned by N&M by lowering the top of the well ' casings due to future planned onsite construction activities ' In September 1995, Geocon retained the services of a Class A General Engineering Contractor to perform the construction activities necessary to restore the sampling capability of groundwater monitoring wells MW-9, MW-11, MW-13, MW-14, MW 16, MW-19, MW-20, and MW-24 A ' representative of Geocon observed the restoration activities The restoration activities included excavation to expose the previously lowered well casings, retrofitting each well with a 4-Inch ' diameter coupling and blank casing riser, installing new traffic-rated well boxes and locking well caps, and resurfacing around each well with concrete or soil as appropriate Geocon has performed quarterly groundwater monitoring at the site since April 1996, with the most recent fourth quarter 1996 event completed on October 23, 1996 The fourth quarter 1996 groundwater monitoring report has been prepared and released separately from this report The locations of the former USTs, former and existing groundwater monitoring wells, soil borings ' and the current site improvements are depicted on Figure 2, Site Plan Historical soil boring analytical data for the previous investigations completed at the site are summarized on Table 2 The ' groundwater analytical data for the October 1996 sampling event, and previous sampling events are summarized on Table 3 ' 1.3 Summary of Current Environmental Study In accordance with the request of Caltrans, Geocon recently performed environmental engineering ' services at the site The investigative work was performed by Geocon in accordance with the Site Assessment Workplan, dated June 21, 1995 Phase 1 work included restoring groundwater sampling capability for the eight existing groundwater monitoring wells that were previously temporarily decommissioned and installing a new combination groundwater monitoring/vapor extraction test well VW-1 Phase 2 work included the installation of two vapor extraction test monitoring wells VM-1 and VM-2, the removal and replacement of well MW-11 due to well casing blockage, the installation of new wells MW-25 and MW-26, the performance of a vapor extraction pilot test and 1 the preparation of this Problem Assessment Report/Corrective Action Plan (PARICAP) ' Project No S8100-06-18A -4- December 9, 1996