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Californi^ Regional Water Quality Control Board Central Valley Region Katherine Hart, Chair >. 11020 Sun Center Drive,#200,Rancho Cordova,California 95670-6114 Matthew Rodriquez (916)464-3291 •FAX(916)464-4645 Edmund G.Brown Jr. Secreran for http:/hv".waterboards.ca.gov/centralvalley Environmental Protection Governer TO: Duncan A Austin, P. E. FROM: Amy Terrell Site and Groundwater Cleanup Pro ram Manager SIGNAT ,i ./ Steven W. Meeks, P DATE: 25 January 2012 SIGNATURE: SUBJECT: RATIONALE FOR CONSIDERING NO FURTHER ACTION AT TRINKLE AND BOYS FLYING SERVICE, 13114214-4 S. Hir'li►33, SAN .IO14 W"--Ul<rV COUIN T r Rationale: Residual soil contamination concentrations are below human health protective screening levels, based on California Human Health Screening Levels (CHHSLs) for residential land uses and Environmental Protection Agency Preliminary Remediation Goals (PRGs) for residential land uses. Pollutants identified in grab groundwater samples that exceeded water quality objectives (dichlorobenzene and diuron) were not detected in four quarters of groundwater monitoring. Issues: The site has been an airstrip and operations area for aerial pesticide applicators from 1949 to 2001 , when the current owners purchased the property. In 1986, pesticides were detected in a wastewater discharge area, and in 1987 and 1989, Cleanup and Abatement Orders requiring investigation were issued to different operators. In 1989, three underground fuel tanks were removed without permits. In 1990, Trinkle and Boys conducted an investigation and the Cleanup and Abatement Orders were rescinded. In 1992 one more underground fuel tank was removed without a permit, although San Joaquin County concurred that confirmation samples showed that no pollution occurred relating to this tank. Setting: A small aircraft landing strip in a formerly agricultural area currently undergoing large lot residential development Photographs of the property are found in Figure 1. Source: Discharge from airplane washwater and pesticide handling operations. Actions: Soil and groundwater investigations occurred in 1989, 2008, and 2009. Locations of the soil and groundwater samples are shown in Figure 2 • In 1989, soil samples from the operations area contained DDT, and soil samples from the drain and rinse basin contained endosulfan, parathion, and carbamates. One monitoring well, in the operations area, contained 2,4,5-T and carbamates, all substantially below water quality objectives. California Environmental Protection Agency 0d Recycled Paper