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i Ems • INTRODUCTION This report documents a request for No Further Action (NFA), to the San Joaquin County Public Health Services Environmental Health Division (PHSIEHD), for the subject property (Site Code 1930), located at 26500 Nowell Road, Thornton, California (refer to Figure 1 - Site Location Map, and Figure 2 - Site Map ' This NFA request has been prepared in general accordance with Appendix B, Th-Regional Board Staff Recommendations For Preliminary Investigation And Evaluation of Underground Tank Sites, No Further Action Requests, dated 1 March 1994 (draft revision October 1996), prepared by the staff of the Central Valley Regional Water Quality Control Board The checklist ' of required data is presented in Appendix A Based on the supporting data presented in this report, the subject property should be given a ' Low Risk Groundwater Designation Supporting data includes source removal, adequate site characterization, plume stabilization, mass balance calculations, and water supply well search ' 20 BACKGROUND The subject site is a private residence located on the east side of Nowell Road in a rural portion of Thornton, California Ms Lopez purchased the subject site in 1979 with an existing 500-gallon- capacity gasoline underground storage tank (UST) on the property According to the previous property owners, the UST had not been used for ten to 15 years ' On October 9, 1989, the 500-gallon UST was removed from the Lopez property One sod sample was collected from the base of the excavation and analyzed for the presence of total petroleum hydrocarbons identified as gasoline (TPH-g) and benzene, toluene, ethylbenzene, and total ' xylenes (BTEX) TPH-g was detected at 3 9 milligrams per kilogram (mg/Kg), and BTEX was not detected at or above the detection limits ' A Tri-Valley Growers canning facility is located adjacent and south of the Lopez property The canning facility includes former USTs and a forklift shop within 50 feet of the subject property It is ENSR's understanding that assessment activities began at this adjacent facility in 1987 and ' remediation activities (groundwater pumping) were started in 1991, and continued until about 1994 ' 30 SITE CONDITIONS The site is a residential property consisting of one building, a paved driveway and surrounding ' grass area The site is located at an approximate elevation of 10 feet above mean sea level Near surface sods beneath the site are classified as Sailboat silt loam This very deep, somewhat poorly drained nearly level sod is on flood plains It formed in alluvium derived from mixed rock sources Typically, the surface layer is brown silt loam about 0 7 feet thick The underlying ' material consists of intermittent layers of brown silty clay and silty sand to depths of 20 feet below grade surface (bgs) ' Water for agriculture, domestic, and industrial use in San Joaquin County is obtained from wells, • rivers, creeks, canals, and sloughs The water flows to the county mainly through the Mokelumne, Calaveras, Stanislaus, and San Joaquin Rivers The water in the northern and eastern parts of ' the county is of relatively good quality The natural source of this water is runoff from the L.IENSR18716100218716002 ds2 appb doc 1 11/13/98