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- <br /> ------------------------------- <br /> L AR idE <br /> c. R o u r, <br /> Environmental Services <br /> Ferrous iron concentrations in the injection wells have generally decreased to 0 mg/L. The increased <br /> DO concentrations fall within the expected ranges, and the ferrous iron concentrations were expected <br /> to diminish as the DO increased. <br /> ,,;. <br /> DO concentrations in monitoring well MW-513 increased to 3.5 mg/L from an initial level of 1.3 <br /> mg/L, then decreased back to 1.4 mg/L. Ferrous iron concentrations in MW-513 have diminished to 0 <br /> mg/L, which suggests that an oxidizing condition may have developed in MW-513. Conversion of <br /> ferrous iron to ferric iron and other chemical and/or biological factors may have consumed the <br /> increased DO. Groundwater chemistry may also be affected by variations in flow direction and <br /> velocity, precipitation rates, and other factors. The results of these field measurements and tests are <br /> presented in Tables 4 and 5. Clearwater's field data collection forms are provided in Appendix C. <br /> The DO and ferrous iron concentration changes in MW-5B suggest that iSOC may have delivered <br /> DO from IW-1 through the clay/silt formation to MW-5B, which is located near IW-1. No other <br /> << =` significant effects have been observed in the other monitoring wells. Clearwater will be continuing <br /> with periodic monitoring of the iSOC system and groundwater chemistry for the foreseeable future. <br /> 4.6 Quarterly Groundwater Monitoring <br /> Clearwater will continue with the existing Quarterly Monitoring schedule and analytical protocol as <br /> directed by the SJC/EHD: quarterly sampling of the eight monitoring wells for TPHg, BTEX, and <br /> MTBE by EPA Method 8260B. Groundwater monitoring will occur at regular intervals through the <br /> course of the proposed remedial activities to document and verify clean-up efficacy. In addition, <br /> r--s <br /> Clearwater will continue with quarterly field measurements of DO, ORP, and pH, to be performed <br /> concurrently with the groundwater monitoring events. Additional laboratory analyses for bio- <br /> �'' attenuation parameters will be periodically conducted along with the regular quarterly monitoring <br /> analyses to monitor biodegradation activity, and to evaluate for possible relocation of system <br /> ' components, nutrient requirements, and other system adjustments. <br /> ZB178E WC System Installation/Start-up 14 Nov.24,2004 <br />