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r CLEARWATER G R O ti r I N C • Environmental Services range hydrocarbons were detected in soil samples collected from all soil borings except SB-3 and SB-4 Three of the soil borings were converted to groundwater morutonng wells(MW-1,MW-2,and MW-3) Water samples from wells MW-1 and MW-3 contained elevated concentrations of gasoline range hydrocarbons,however, gasoline compounds in the water sample form MW-2 only slightly exceeded laboratory reporting limits Results of this phase of investigation were presented in Clearwater's Subsurface Investigation Report dated November 20, 1997 In January 1999,Clearwater supervised the installation of three additional monitoring wells (MW-4, MW-5, and MW-6) to further evaluate the extent of contaminants in the subsurface Results of sampling indicated that the extent of sorbed- phase contamination surrounding the former UST complex had been adequately delineated The results of groundwater sampling, however, indicated that the downgradient extent of dissolved-phase gasoline contaminants remained undelineated The presence of high concentrations of dissolved hydrocarbons cross-gradient (MW-6) from the former USTs also suggested the presence of possible additional off-site sources Preliminary inquiries regarding the nature of possible additional sources indicated that fuel transport pipelines may be present in the immediate %icinity of the site Based on these results, Clearwater recommended additional downgradient investigation to detemune the extent of the contaminant plume and also to evaluate the possible contribution from potential off-site sources The results of this phase of investigation were presented in Clearwater's Well Installation and Groundwater Monitoring Report- First Quarter 1999 dated May 7, 1999 The site is predominantly underlain by silts and clays to a depth of approximately 25 feet,bgs with localized, non- continuous sand lenses An apparently laterally continuous sand unit is present from approximately 25 to 35 feet bgs, which is underlain by a clay Depth to groundwater fluctuates between approximately 6 and 1 1 teet bgs annually, and observed flow directions have historically been toward the south-southeast Proposed Scope of Additional Investigation hk The purpose of the proposed work is further evaluation of the distribution of gasoline contaminants downgradtent from the former UST system, and to destroy and reinstall monitoring well MW-5 To accomplish this goal, the following scope of work will be performed • Install three soil borings to approximately 36 feet bgs for collection of soil and groundwater samples to complete the northeast lateral and vertical delineation of dissolved-phase petroleum hydrocarbons associated with the subject release, and to investigate the possible impact of off-site sources Locations are shown on Figure 2 • Install two additional monitoring wells to delineate the southeast lateral and vertical direction of the plume These wells will be bored to a depth of 36 feet bgs for soil sample collection, however well construction will end at a depth of only 25 feet bgs, which is consistent with previously installed wells on site Locations are shown on Figure 2 • Destroy and re-install monitoring well MW-5 as shown in Figure 2, the casing of which was damaged during recent resurfacing activities • • Perform a utility survey for Fresno Avenue and a file review on the UST site on the corner of Fresno Ave and Charter Way, Ms Lon Duncan 2 November9 1999