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QUARTERLY GROUNDWATER MONITORING RESORT
<br /> 7910 Lower Sacramento Road Stockton California
<br /> ' 1.0 INTRODUCTION
<br /> ' This report documents the results of quarterly groundwater monitoring conducted by
<br /> Emcon Associates (Emcon) of Sacramento, California, on February 20, 1992, at the Shell
<br /> Oil Company (Shell) service station located at 7910 Lower Sacramento Road in Stockton,
<br /> ' California (Figure 1) The monitoring included collection of depth-to-groundwater
<br /> measurements and water samples from the three monitoring wells located on site, MW-1,
<br /> MW-2, and MW-3 (Figure 2) This report is based, in part, on information obtained by
<br /> ' Aegis Environmental, Inc (Aegis), from Shell, Emcon, and Delta Environmental
<br /> Consultants, Inc, (Delta), of Sacramento, California, and is subject to modification as
<br /> ' newly acquired information may warrant
<br /> ' 2 0 SITE DESCRIPTION
<br /> The Lower Sacramento Road Shell station is an active site that retails regular-unleaded,
<br /> ' super regular-unleaded, and super-unleaded gasolines The site's current facilities include
<br /> a building, two canopy-covered fuel dispenser islands, three 12,000-gallon underground
<br /> fuel storage tanks (UST), and one 550-gallon underground waste-oil tank (Figure 2) The
<br /> ' UST and waste-oil tank are constructed of double-walled fiberglass The site is located
<br /> within a commercial area of Stockton
<br /> 30 BACKGROUND
<br /> ' In June 1988, Delta personnel drilled eight soil borings on site as part of a pre-tank
<br /> replacement site assessment (letter to Shell dated June 7, 1988)
<br /> ' In December 1988, Delta personnel witnessed the excavation and removal of two 8,000-
<br /> gallon, and two 5,000-gallon steel UST and associated piping from the site Laboratory
<br /> analysis of soil samples collected from the product line trenches and tank basin indicated
<br /> ' concentrations of total petroleum hydrocarbons (TPH), as gasoline, and benzene,toluene,
<br /> ethylbenzene, and total xylenes (BTEX) Three new, double-walled fiberglass,
<br /> 12,000-gallon UST were installed in the original tank basin on December 29, 1988
<br /> 1
<br /> In August 1989, Delta personnel drilled six additional soil borings on site ("Phase l
<br /> Hydrogeological Assessment Report," dated October 20, 1989) Three of the borings
<br /> were completed as 4-inch-diameter groundwater monitoring wells MW-1, MW-2, and
<br /> MW-3 Analysis of soil samples collected from these borings also indicated
<br /> concentrations of TPH, as gasoline, and BTEX Delta began a program of quarterly
<br /> ' measurements of depths to and sampling of groundwater following the initial well
<br /> installations
<br /> ' 91 231A OMR 1
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