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' QUARTERLY GROUNDWATER RAONf FORING REPOFIT 1399 East Yosemite Avenue Manteca California 1.0 INTRODUCTION This report documents the results of groundwater monitoring conducted by Aegis ' Environmental, Inc (Aegis), from January through April 1992, at the Moore Petroleum, Inc (Moore Petroleum), service station located at 1399 East Yosemite Avenue in Manteca, California (Figure 1) The monitoring included the collection of monthly depth-to-groundwater measurements and quarterly groundwater samples from five monitoring wells, MW-1 B, MW-2, MW-3, MW-4, and MW-5, located on site (Figure 2) This report is based, in part, on information obtained by Aegis from Moore Petroleum and is subject to modification as newly acquired information may warrant ' 2 0 SITE DESCRIPTION ' The Yosemite Avenue Moore Petroleum service station is located on the northwest corner of the intersection of Northwoods and East Yosemite Avenues in Manteca, California (Figure 2) The site is located in a commercial area of eastern Manteca The site is bounded on the north by a small shopping complex, on the west by a fast food restaurant, on the south by East Yosemite Avenue, and on the east by Northwoods Avenue Details of the sae's current and former facilities, including previous and existing underground storage tanks, were reported by Aegis in a "Problem Assessment Report, Including Quarterly Monitoring Report," dated November 12, 1991 30 BACKGROUND In August 1988, Earth Treatment Systems drilled four soil borings (SB-1 through SB-4) on site One boring was completed (SB-4) as 2-inch-diameter monitoring well MW-1 to an approximate depth of 36 5 feet below surface In April 1989, Delta Environmental Consultants, Inc , of Rancho Cordova, California, drilled and installed wells MW-2 and MW-3 with 2-inch-diameter casing to an approximate depth of 36 5 feet each On September 26, 1989, three underground storage tanks and associated product lines were removed In June 1990, Nations Groundwater Associates supervised the abandonment of MW-1 The well had been damaged during the removal of the underground storage tanks in I September 1989 Monitoring well MW-1A was then drilled and installed approximately 10 feet east of the former location of MW-1, and was completed as a 2-inch-diameter well to a total depth of approximately 36 5 feet Aegis began a program of quarterly groundwater monitoring in February 1991 Monthly monitoring of groundwater levels and quarterly sampling of groundwater has continued ' since then On June 20, 1991, Aegis installed monitoring wells MW-113, MW-4, and MW-5 on the site Wells MW-4 and MW-5 were completed with 4-inch-diameter casing to an approximate depth of 35 feet below grade Well MW-1B was completed with 6-inch-diameter casing by "over-coring" the former MW-1A 90-098A QMR 1