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QUARTERLY REPORT Arco Mini Mart 4511 Pacific Avenue Stockton, California September 1994 1.0 INTRODUCTION In accordance with a request from Mr. Arthur Wyatt, Geological Audit Services, Inc. (GeoAudit) has prepared this Quarterly Report of activities conducted at 4511 Pacific Avenue in Stockton, California (the site). The location of the site is illustrated in Figure 1. A plan of the site is illustrated in Figure 2. 2.0 BACKGROUND 2.1 Site Location The site is located on the northwest comer of Pacific Avenue and Rose Marie Lane in a flat commercial area of central Stockton (Figure 1). The facility consists of a building and three pump islands covered by a canopy (see Figure 2).The site currently operates as a Mini Mart and gasoline station. 2.2 Initial Investigation In February 1991, a broken coupling in a product line was discovered at the site and repaired. Impacted soil was discovered beneath the product line. Subsequently, the San Joaquin County Public Health Services - Environmental Health Division (PHS/EHD) required investigation into the extent of impacted soil. In October 1992, four soil borings were installed at the site by GeoAudit. Strong hydrocarbon odors were observed in borings B-1, B-2 and B-4 from approximately 20 feet to 40 feet. No hydrocarbon odors were detected in boring B-3.-Boring B-1 was completed as a vadose-zone remediation well. 2.3 Monitoring Well Installation and Sampling Due to the proximity of impacted soil to groundwater, the PHS/EHD required the installation and sampling of groundwater monitoring wells. In January 1993, three borings were installed at the site by GeoAudit and completed as groundwater monitoring wells MW- 1, MW-2 and MW-3. Groundwater conditions at the site have been monitored on seven occasions since the wells were installed. The groundwater flow direction has remained consistently east to northeast. Gwbpsl Audit S—i...I.c, 1 Anm aRanav�s.i e