ARCHIVED REPORTS XR0000198 - Laserfiche WebLink

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Contract No. 53U495 Task Order No. 10-365101-01 Wage 2 Subsequently, five (5) additional monitoring wells in 1990 and three (3) monitoring wells in 1992 were placed on the site The groundwater levels from 1987 to 1992 dropped more than 20 feet In 1992 groundwater, from only five out of twelve monitoring wells could be sampled A Problem Assessment Report was prepared during July 1990 on Regional Water Quality Control Board's request Supplemental Site Investigations (July 1992) and Soil Vapor Testing (September 1992) were undertaken to determine the type, quantity and extent of contaminants detected in the soil and the groundwater The site is underlain by predominantly silty sand and poorly-graded sand with some silty clay units The groundwater average depth beneath the site was 66 feet below grade (fbg) on April 7, 1992 The soil contaminant concentration ranges were 270 to 4 ppm of total petroleum hydrocarbons as gasoline (TPH-G) 4 4 to 0 3 ppm of benzene at 46 to 56 flag beneath the former tank cavity The groundwater is also contaminated with dissolved phase hydrocarbons The contaminant concentration ranges in the groundwater samples are from 231 to 1 9 ppm for TPH-G, from 25 7 to 0 001, from 38 8 to 0 001, from 4 to 0 0004 and from 15 9 to 0 0004 ppm of BTEX respectively For detail information on previous investigations on this site please refer to the reports cited C Purpose The purpose of this TO is to determine the horizontal and vertical extent of hydrocarbon soil and groundwater contamination due to leaking underground fuel tanks or past practices from vehicle maintenance operations conducted on the site, and to produce a remedial action plan to clean-up the site in accordance with the county and the state regulatory requirements D. Scope The scope of work to be performed under this TO shall consist of 1 Review existing technical reports and background data to determine geologic and hydrologic conditions of the site and previous work done, develop an in- vestigation strategy and prepare a soils and groundwater workplan and site specific health and safety plan 2 Perform the field site investigation based on the workplan and health and safety plan approved by Caltrans The field investigation shall include mechanical drilling, hand and power augering, groundwater and soil sampling, and sample management 3 Collect and analyze groundwater samples from the existing monitoring wells 4 Arrange for laboratory analysis by state certified laboratory for constituents identified in the workplan according to EPA test methods for evaluating solid waste, SW 846, 1986 . 5 Preparation of a site investigation report with a review of all potential remedial actions and associated costs All elements of work identified by this TO shall meet applicable provisions of statewide Contract 53U495 and these TO provisions