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r CLEAmRW- ATER G R O U P, I N C E,nnonnrenial service, 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 Burro, u� nding the former UST complex had been adequately delineated The results of group for ___�---— 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 vicinity of the site Based on these results, Clearwater recommended additional downgradient investigation to determine 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- No continuous sand lenses An apparently laterally continuous sand unit is present from approximately 25 to 35 feet bgs, Sg- r which is underlain by.2 clay, Depth to groundwater fluctuates between approximately 6 and 11 feet bgs annually, and 5,141 Sobsterved flaw directions have historically been toward the south-southeast Z'1�f t <ad.�y j�O,y �``4 3'I.0 Proposed Scope of Additional Investigation 5 5- ' 5 35' S .e( [:��` h� f,-,The pit ose of the proposed work is further evaluation of the distribution of gasoline contaminants downgradient from -� ^6 5 uu Sow C1 25 zo' Sithe fol UST system, and to repair well MW-5 To accomplish this goal, the following scope of work will be 3S l pefformed q ZO1 1t i • Install up to eight Geoprobe soil borings to approximately 20 feet bgs for collection of soil and groundwater samples 5 � to attempt to complete lateral delineation of dissolved-phase petroleum hydrocarbons associated with the subject release,and to investigate the possible impact of off-site sources Three borings will be located on each side of South Fresno Avenue located so as to intersect groundwater flowing through and to the north and south of the current well 5s- configuration One boring will be located on each of the north and west site boundaries in order to Investigate possible off-site contamination extending from upgradient locations onto the subject property Proposed boring locations are shown on Figure 2 �`1 • Drill-out and re-install momtonng well MW-5,the casing of which was damaged during recent resurfacing activities i • Continue quarterly groundwater monitoring to determine trends in contaminant concentrations and hydrogeologic conditions All work will be conducted in accordance with the LUFT Field Manual, the Tri-Regional Board Staff Recommendations, • and Article 11 Corrective Action Regulations of Chapter 16 Under Storage Tanks Regulations Ms Lon Duncan 2 September 30 1999