SITE INFORMATION AND CORRESPONDENCE

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URS ' Ms. Kathy Amaru Page 4 of 6 Regional Water Quality Control Board—Central Valley Region May 8,2011 ' GROUNDWATER MONITORING RESULTS The direction of groundwater flow beneath the site for this sampling event was to the northwest with a 1 gradient of 0.0016 feet per foot(ft/ft). Groundwater flow direction and gradient data are summarized in Table 1 and on Figure 4. ' The results of baseline sampling(April 2011)and post-injection quarterly sampling(May 2011) in all Site monitoring wells are presented in Table 2. As a result of the emulsified oil injection,there was a large increase in total organic carbon(TOC) concentrations,from 2.6 mg/L to 1,200 mg/L and a shift to reducing conditions,as manifested by a decrease in dissolved oxygen(DO), from 9 mg/L to 5.7 mg/L, and a decrease in oxidation-reduction potential(ORP), from 166 millivolts(mV)to -56 mV, in treatment zone well MW-6-BP. The reducing conditions likely led to a correspondingly large increase in anaerobic bacteria populations, which in turn destroyed chlorinated ethenes in the well. Starting at concentrations of 42 µg/L and 140 µg/L, respectively,PCE and TCE concentrations decreased to less than MCLS in MW-6-BP. The ' concentration of the less chlorinated daughter product, cis-1,2-DCE, also decreased from 260 µg/L to 57 µg/L but vinyl chloride remained undetected in the well. As a result of the bacterial metabolic activity, there was a decrease in pH levels in MW-6-BP, from7.25 to 5.74. pH levels will continue to be monitored closely in the well because pH levels below 6 are not conducive to bacterial growth. Also as a result of the reducing conditions, sulfate and nitrate concentration decreased but dissolved arsenic,barium,and manganese concentrations increased in MW-6-BP. These elevated dissolved metal levels may continue to be observed in the treatment area while the reducing conditions persist but should return to baseline levels once the emulsified oil is completely degraded and TOC levels return to background levels. For the most part,monitoring wells in the transition and compliance zones did not experience similarly large changes in the magnitude of any analytes. Additionally,the changes were not consistent from ' well to well,with some wells experiencing slight increases and some wells experiencing slight decreases in some parameters. The exception was in the case of arsenic,which increased slightly in all Site wells with the exception of the background well(MW-7-BP). However, arsenic levels remained quite low and well below MCLS. In conclusion,the results of the pilot test to date have been very promising, indicating chlorinated ' ethenes are being destroyed by the anaerobic bacteria in the treatment area, while concentrations of secondary water quality parameters have remained close to baseline levels in transition and compliance wells. For dissolved iron samples collected on May 2,2011,the results were not detected at the reporting limit of 89 ug/L. These reporting limits should be considered estimated values because the relative percent difference between the LCS and LCSD did not meet the laboratory criteria of less than or equal to 23%. HAWp=msU DIDW-Bum P9120111DW-BP-IQb l Repon.doc