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Environmental Activities and Quarterly Monitoring Report October 1997 r WEST CLAY PROPERTIES J r _ 639 West Clay Street, Stockton, California 1.0 INTRODUCTION In accordance with the request of Ms Tina Mayhew of West Clay Properties, Advanced GeoEnvironmental, Inc (AGE) has prepared this report of various environmental activities ' conducted at 639 West Clay Street, Stockton, California The reported activities include backfilling of a`former underground storage tank (UST) excavation, an exploratory drilling and soil sampling program, installation of ground water monitoring wells, and one ground water monitoring event In Iaddition, the laboratory results of analyses of ground water samples during previous ground water monitoring events are presented fThe site and its surroundings are illustrated on Figure I-Location Map Structures, well and boring locations are illustrated on Figure 2 - Site Plan 20. BACKGROUND The site is located in a commercial area of low topographic relief in western Stockton, California At is the understanding of AGE that one 1,000-gallon UST was removed from the site in May 1990 The product line from the former UST to the dispenser was removed in October 1993 Subsequently, approximately 550 cubic yards of hydrocarbon-impacted soil were removed from the former UST area Soil was excavated to a depth of 38 feet below surface grade (bsg) Total petroleum hydrocarbons quantified as gasoline (TPH-g) was encountered in one excavation bottom sample at ' a concentration of 5,200 parts per million (ppm, reported as milligrams per kilogram) and in one I sidewall sample at 2,100 ppm, however the lateral and vertical extent of contamination was not = assessed Three monitoring wells and one additional soil boring were drilled and installed at the site Ground water was determined to be impacted and additional assessment was required by the San Joaquin County Public Health Services - Environmental Health Division (PHS-EHD) to define the lateral and vertical extent of impacted soil and ground water v ti r I3.0. SCOPE OF WORK The scope of work covered by this report includes providing a description of the excavation backfilling procedure, recalculating ground water gradients and flow directions for previous ground water monitoring events, sampling stockpiled soil for characterization, advancing and sampling of exploratory soil borings, installation of two additional ground water monitoring wells, and Advanced GeoEmironmental,Inc