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clarifier can overflow with resultant release of contaminants to <br /> the surrounding soil . in addition to known releases at the <br /> clarifier, cracks and expansion joints in the washpad itself could <br /> possibly be a pathway for contamination into underlying soil . <br /> The washpad drain has now been closed and waste water is pumped to <br /> a collection vehicle pending proper disposal. A capital <br /> improvement project to install a new washpad and treatment system <br /> is in progress . <br /> The Central Valley Region Water Quality Control Board has requested <br /> the Office of the Adjutant General conduct a site investigation to <br /> determine the extent of existing contamination in and around the <br /> washpad system. A final site assessment workplan was prepared and <br /> submitted to the Board in February 1991 . Workplan approval was <br /> received July 3, 1991 . A proposal to conduct the workplan was <br /> submitted to the Office of the State Architect on July 17, 1991 . <br /> Authorization to proceed was received from OSA on August 20, 1991 . <br /> Approved boring permits were received from San Joaquin County, <br /> Environmental Health Division on September 6, 1991 . Field work <br /> commenced the following Monday, September 9, and concluded on <br /> September 13 , 1991 . <br /> 2. 0 SITE C'_AARACTERISTICS <br /> 2. 1 Site History <br /> The area surrounding the Stockton AASF has been a mix of airport <br /> and agricultural usage for over 40 years. The AASF facility was <br /> expanded to its present size in 1974 . it was during the 1974 <br /> expansion that the hanger, washpad and wastewater management system <br /> was constructed. <br /> The Stockton AASF is located on State property . The facility is <br /> under jurisdiction of the California Military Department . There is <br /> no planned change in site usage. The Stockton AASF will be used <br /> for aircraft support and maintenance indefinitely. <br /> The aircraft washpad and associated wastewater management system <br /> had been in continuous operation from 1974 to late 1989 . Various <br /> degreasing and cleaning agents have been used for aircraft <br /> maintenance over the years . Hydraulic fluids, solvents, oil, fuel <br /> and other aircraft residues also have been present at the washpad . <br /> There were two known and one suspected contaminant release points <br /> in the washpad system. The suspected release point is the concrete <br /> washpad itself which has large cracks and expansion joints . Since <br /> the washpad {but not the drainage/treatment system} is still in <br /> use, releases may still be occurring. <br /> 3 <br />