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INITIAL RELEASE DDJC Tracy DDJC Tracy sampled operating wells and analyzed the samples for metals and selected pesticides every three years, but only water samples collected between 1987 and 1991 from WSW 7 were analyzed for VOCs. Although WSWs 8 and 9 were not sampled for VOCs, these wells are located approximately 2,000 feet upgradient from known areas of groundwater and, therefore, are not likely to be affected by site-related contaminants. Table 3 summarizes the water quality monitoring results of the DDJC Tracy water supply wells. As the table indicates, no pesticides were detected in any well, nor were TCE, PCE, or carbon tetrachloride were detected in WSW 7. Additionally, the metals arsenic, lead, and mercury were detected, but only sporadically at levels above comparison values (Woodward-Clyde Consultants, 1992b; DDJC Tracy 1998). Manganese levels (up to 180 ppb) frequently exceeded EPA's secondary MCL (50 ppb) for aesthetic quality and ATSDR's RMEG for a child (50 ppb) in WSW 8; however, the levels were below the RMEG for an adult of 200 ppb. (The secondary MCL is intended to provide an guideline for aesthetic aspects such as taste, odor, and color that do not present a health hazard.) While this naturally occurring metal may impart undesirable taste, odor or color, it is unlikely to pose undue health hazards at the detected levels. Because WSW 4 was located in the path of the plume, ATSDR evaluated the likelihood of exposure to contaminants in this well. In absence of monitoring data for WSW 4, ATSDR reviewed data gathered from a nearby monitoring well (LM43) (see Figure 8). No TCE or PCE were detected in the monitoring well up to 1991 when WSW 4 was closed (Woodward-Clyde Consultants, 1992b). Assuming similar conditions exist for both wells, WSW 4 was unlikely to have been affected by TCE and PCE at levels exceeding the MCLS. Current and Future Exposures In January 1998, DDJC Tracy placed WSW 7 on standby status (meaning that it will be used for emergency or maintenance purposes only) because of low level TCE contamination detected in a Middle Horizon of the Upper Tulare Aquifer groundwater monitoring well located near WSW 7. Although WSW 7 is not screened in the Upper Tulare Aquifer, it may draw water from the contaminated aquifer through its potentially damaged casing (ASCW-BE, 1997). Currently, WSWs 8 and 9 supply water for DDJC Tracy. As stated above, these wells are not likely to be affected by site-related contaminants because they are located approximately 2,000 feet upgradient from known areas of groundwater contamination. As a precautionary measure, DDJC Tracy will monitor VOCs in the WSW 7 and the other water supply wells for one year, and will take immediate action to correct any threat to the water supply (ASCW-BE, 1997). ATSDR will review these data and determine whether any additional measures protective of public health are necessary. 9