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Report-Groundwater Inves,.sation First Student Bus Facility(Former A.W. Hayes Facility) 2005 Navy Drive—Stockton, CA 4.0 FINDINGS AND CONCLUSIONS Laboratory test results presented in this Report demonstrate that volatile organic compounds (VOCs) are present in groundwater beneath the Site. VOCs detected above the California Water Goals, Maximum Contaminant Levels (MCL) for drinking water during this investigation include cis-1,2—Dichloroethene, which was detected in MW-1 at a concentration of 1100 ug/L (MCL is 6 ug/L); and trans-1,2,-Dichloroethene, which was detected in MW-1 at a concentration of 94 ug/L (MCL is 10 ug/L). VOCs detected above the MCL during the investigation conducted by Ramcon in December 2003 include cis-1,2,-Dichloroethene, which was detected in MW-1 at a concentration of 220 ug/L; trans-1,2,-Dichloroethene, which was detected in MW-1 at a concentration of 31 ug/L; cis-1,2-Dichlorethene, which was detected in MW-2 at a concentration of 730 ug/L; trans 1,2,-Dichloroethene, which was detected in MW-2 at a concentration of 36 ug/L; and cis-1,2,-Dichloroethene, which was detected in MW-4 at a concentration of 20 ug/L. VOCs detected above the MCLS for both sampling events are summarized below in Table 5. Table 5 — Cumulative Laboratory Test Results Summary Date Cis-1,2 Trans- Dichloroethene 1,2,Dichloroethene MCL 6 ug/L) (MCL 10 ug/]L) 12/03 MW-1 220 ug/L 31 u MW-2 730 ug/L 36 u MW-3 ND ND MW-4 20 ug/1, 3 ug/L 11/08 MW-1 1100 ug/L 94 u MW-2 NA NA MW-3 ND ND MW-4 5.6 ug/L 1.2 ug/L ug/L—microgram/Liter(parts per billion) ND—Not detected at concentrations greater than the method detection limit(MDL) NA-Not Available—MW-2 Could Not Be Located Field measurements presented in this report demonstrate that groundwater flow direction is approximately north 45° west and the gradient is 0.0015 ft/ft. Because of the limited amount of data available during this reporting event (only 2 sampling events), it is difficult to determine whether the source of the VOC contaminants are from an on-site source (the former USTs or a failure in the existing wash rack and oil/water separator system), or from an off-site source (the surrounding properties are predominately industrial). As such, KR Environmental recommends to conduct a Quarterly Ground Water Monitoring in March 2009 (First Quarter 2009) to determine how the concentrations of VOCs may change in groundwater beneath the Site, and to determine if groundwater flow direction and gradient remain relatively constant. 8