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Summary of Northern California Youth Center Sampling Results Week of May 14,2007 Forward Landfill-Austin Road Unit,California Page 3 Water Supply Well Sample Results Samples of each of the three operating water supply wells were collected during the Week of May 14. The concentration of tetrachloroethene in Well No. 2 was 6.6 ug/1, in Well No. 3 was 13 ug/l, and in Well No. 4 was 0.21 ug/1 in both a primary and a duplicate sample. Well No. 4 is reported to be the primary well supplying water to the facility,with Well No.2 operating about 20%of the time to supply supplemental water during periods of peak demand such as lawn irrigation. We were informed by NCYC personnel that Well No.4 was operating immediately prior to,during,and after the storage tank cleaning operations. These water supply sample results are reasonably comparable to previous sample results. Sampling conducted in February 2007 at Well No. 2 yielded a tetrachloroethene concentration of 3.4 ug/1 compared to the May concentration of 6.6 ug/l. The tetrachloroethene concentration in Well No. 3 in February 2007 was 17 ug/1 in both a primary and a duplicate sample, compared to a May 2007 concentration of 13 ug/l. The tetrachloroethene concentration in Well No. 4 in February 2007 was 1.3 ug/1,compared to a May 2007 concentration of 0.21 ug/1 in both the primary and duplicate sample. Tentative Conclusions The storage tank sediment removal operations do not appear to have measurably affected the water quality in the storage tanks or the indoor faucet. The tetrachloroethene concentration at the well supplying water to the system(reported to be Well No. 4) is below the MCL and significantly lower than the water quality in the storage tanks and at the indoor faucet, both prior to tank sediment removal activities and after completion of tank sediment removal activities. The concentrations of tetrachloroethene in the storage tanks and at the indoor faucet suggest a source other than the water from Well No.4. The concentration of tetrachloroethene in Well No. 2 is lower than the concentration of tetrachloroethene at the indoor faucet,based on data collected by Herst&Associates,Inc. These data ' suggest a source other than the water from Well No. 2, which reportedly only operates about 20% of the time. ' The concentration of tetrachloroethene in Well No. 3 is higher than the concentration of tetrachloroethene in the storage tanks and the indoor faucet, but previous discussions with NCYC personnel indicate that Well No. 3 has not been used to supply water to the facility at any time during the last 10 years. Accordingly, it does not appear that water from Well No. 3 is the source of the observed tetrachloroethene in the storage tanks or the indoor faucet. ' Well No. 2 yields tetrachloroethene concentrations that range from slightly below the MCL to slightly above the MCL. The results are ambiguous in terms of the need to treat the water pumped from Well No.2 in order to meet the tetrachloroethene MCL. ' The indoor faucet sample continued to exhibit tetrachloroethene concentrations above the MCL. The source of the tetrachloroethene to the faucet is not clearly identifiable based on sample results collected to date. Evaluations continue regarding appropriate corrective measures to address the current situation.