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spilling of a 5-gallon can of solvents, or the overturning of one <br /> of the portable solvent cleaning units observed at the Depot and <br /> reportedly formerly used throughout the site. <br /> 1.2.2.3.2 Given the scenario described above, it is evident that the <br /> specific details of what was spilled where, and when, will probably never <br /> be known, as numerous undocumented individual spills dating back to the <br /> early 1940s were probably involved. Therefore, measurements of the <br /> contaminants in groundwater, soils, and soil gas present the best available <br /> picture of contamination in the Depot. The primary conclusion derived from <br /> site visits, from the review of the data obtained from the_RI , from <br /> conversations with Mr. Wes Harris, Environmental Specialist at DDRW Tracy, <br /> from our understanding of the operation of the Depot, and from historical <br /> aerial photographs provided by Mr. Harris, is that the sources of the o <br /> solvents TCE and PCE presently detected in the soil and groundwater are not <br /> associated with continuing sources such as buried tanks or similar major <br /> "sources," but arise more from past solvent storage, handling, and use <br /> practices on the Depot. <br /> 1.2.2.4 The Depot also contains a stormdrain holding pond and two sanitary <br /> settling ponds. The stormdrain holding pond receives all stormwater runoff <br /> from the Depot. The sanitary settling ponds receive the discharge from the <br /> sewage treatment plant. In addition, two areas in one sanitary settling <br /> pond have been diked off and lined, and receive industrial wastewaters. <br /> Only these two .industrial waste ponds (and the appurtenant industrial waste <br /> collection system) are known or suspected to contain hazardous wastes. <br /> 1.2.2.5 Potential contaminants other than TCE and PCE were occasionally <br /> found in isolated samples, at concentrations generally below regulatory <br /> values. For reasons detailed in Sections 4.0.3, 4.3.5, and 6.0, these <br /> compounds are not otherwise addressed in this RI report. <br /> 1-9 <br />