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EPA REGION 9 COMMENTS <br /> ON EPA EMSL's <br /> AERIAL PHOTOGRAPHY ANALYSES <br /> DDRW-TRACY <br /> General Comments <br /> EPA EMSL evaluated 10 historic aerial photographs taken from <br /> 1937 to 1987 . The DDRW-Tracy SWMU Engineering Report, in <br /> comparison, examined nine overhead aerial photographs and 22 <br /> photographs taken at some angle. Three of the same aerial <br /> photographs were evaluated for both reports. With a few <br /> exceptions, both the EMSL and the SWMU Engineering Reports <br /> identified the same significant issues that are visible on aerial <br /> photographs. <br /> Due to the scale of the available aerial photographs, <br /> information regarding SWMU Nos. 6, 14, 20, 21, 23 , 24 , 25, and <br /> 27, potential SWMUs at Buildings 7, 10, 28, 206, 236, 237 , and <br /> 238, and Warehouse 10 could not be evaluated by aerial survey <br /> review. Thus, the EMSL analysis can neither refute nor confirm <br /> speculation on past waste-producing activities at those areas. <br /> Other aspects of the SWMU Engineering Report, such as the <br /> overall adequacy of geophysical testing performed or number of <br /> soil borings proposed, have not been addressed in this comparison <br /> of the EMSL analysis and SWMU Engineering Report except where <br /> historic aerial evidence indicates an oversite. <br /> Specific Comments, Additional Areas of Potential Contamination <br /> Areas of potential contamination that were visible in the <br /> EMSL historic aerial photographs but not addressed in the SWMU <br /> Engineering Report include: <br /> 1. Aerial photographs (1952 to 1983) show a dark triangular <br /> shape located between Buildings 206 and 7 alongside the west <br /> side of a railroad spur in the northern portion of the <br /> facility. The dark triangular shape does not show up on the <br /> 1982 infrared photograph, however. Throughout the 1952 to <br /> 1983 time period it remains the same size and shape. A <br /> faint outline of the triangular shape can be detected in the <br /> 1985 photograph. Due to its shape, it does not appear to be <br /> a building; it appears to possibly be a surface <br /> impoundment. This "SWMU" could have been a significant <br /> contributor to the historical Contaminant Area 1, as defined <br /> by Radian' s 1985 soil gas survey. <br /> 2 . From aerial photographs, liquid appeared to be present from <br /> 1 <br />