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�'ftffi daft ROMMO Iht Pont Bios-N-,I - Page 3 August I0, 1989 Job No.211-71-6 BACKGROUND The location of the four 20,000-gallon underground fuel(gasoline and diesel)tanks is shown on the Site Plan (Figure 2). We understand that the tanks are of single-wall, steel construction (approxim"ely 9 feet in diameter and 40 feet in length)and are approximately 18 yearsald. The bottoms of the tanks have been measured at approximately 14 feet below the existing grade. Tank tests were conducted on the gasoline tanks during July and August 1985 by Heath Consultants.'The ;..; super-unleaded and the regular-leaded tanks reportedly tested"tight"; however, the unleaded tank (westernmost tank)did not pass the precision test. We understand that the problem was traced to a poor seal in the stage 2, vapor-return-line flange whicai was located on the tank. Repairs were made on the vapor-return-line circa 1985. A bulk rack was installed (circa 1970) at the Douglas Gas site approximately 100 feet east of the underground fuel tanks. We understand that the bulk rack was used primarily during the 1970's for the refueling of Fuel-tanker trucks. The fuel lines leading from the tanks to the bulk rack have been taken out of service and were plugged off prior to 1987. Prior to 1985,a regular-leaded gasoline pump was operated on the diesel island (located north of the fuel tanks - see Site Plan, Figure 2). The fuel line.; which supplied the pump were decommissioned and plugged off in 1985. The Douglas Gas Station has been the site of several previous investigations from 1985 to I987. All monitoring wells present at the Douglas Gas Station site were constructed using 2-inch diameter PVC screen and solid casing. The locations of the monitoring wells are shown on the Site Plan, Figure 2. A summary of construction details for the monitoring wells is presented in Table A Boring logs for all monitoring wells and exploratory borings,drilled in the immediate site vicinity - as part of the contamination assessment,are included in Appendix A, Well Logs and Boring Logs. The following is a brief summary of past subsurface exploratory activities at the site: I. Four monitoring wells (MW-1 through MW-4)were installed at the site in the vicinity ° of the underground fuel tanks by IT Corporation on February 24, 1985. Monitoring well _ MW-1 was advanced to a depth of 55 feet (ground water was reportedly encountered at a depth of 49 feet during drilling). Monitoring wells MW-2, MW-3,and MW-4 were each completed to a depth of 20 feet (within the unsaturated zone). 2. Three additional monitoring wells(MW-5, MW-6,and MW-7)were install_d adjacent to the underground tanks at the site by IT Corporation on March 26, 1985. All three wells were completed within the unsaturated zone.