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OVARTERLY GROUNDWATER MONRORING REPORT 1605 South EI Dorado Street.Stockton California 1.0 INTRODUCTION This report documents the results of the second quarterly groundwater monitoring conducted by Aegis Environmental, Inc. (Aegis), from November 1991, through January 1992, at the Exxon Company, U.S A (Exxon), inactive service station located at 1605 South EI Dorado Street in Stockton, California (Figure 1) The monitoring included Icollection of monthly depth-to-groundwater measurements and quarterly groundwater samples from the three wells, MW-1, MW-2, and MW-3, located on site (Figure 2) This report is based, in part, on information obtained by Aegis from Exxon 2.0 SITE DESCRIPTION The subject site is located between South EI Dorado and Center Streets in the City of Stockton, San Joaquin County, California (Figure 1) The site is situated ,n a commercial/residential/light industrial area of southern Stockton The site is bound on the north by East 2nd Street, on the east by South El Dorado Street, on the south by a car wash facility, and on the west by Center Street The Ekon service station is an inactive station that previously retailed leaded and unleaded gasolines The station's current facilities include a building and three inactive underground storage tanks (UST) with associated product piping The three UST are located immediately south of the dispenser islands on the southern half of the site The type of construction and the installation dates of the UST are unknown Figure 2 shows the location of the site's aboveground and underground features 3.0 BACKGROUND On February 5, 1991, a ground penetrating radar (GPR) survey was performed by NORCAL Geophysical Consultants, Inc , of Petaluma, California The survey was performed in the area of the existing UST basin to locate existing underground facilities for avoidance during drilling Upon completion of the GPR survey, two soil borings were drilled on February 22, 1990, at an angle of 30 degrees from vertical, adjacent to the existing UST basin (Figure 2) The actual vertical depth penetrated by the borings was approximately 53 feet below existing grade Soil samples collected from the two sod borings were analyzed for total petroleum hydrocarbons (TPH), as gasoline, benzene, I toluene, ethylbenzene, total xylenes (BTEX), ethylene dibromide, 1,2-dichloroethane, and total lead Results of the soil boring and sampling were reported by Aegis to Exxon, in a "Pre-Tank Replacement Site Assessment Results Report," dated March 5, 1991 I91-0440 FlFr 1