SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Mr. Doc Heath -2- 30 December 2010 the strong reducing conditions that facilitate the microbial reduction of the chlorinated compounds. The second phase of the remediation will focus on inducing reducing conditions south of the first phase injections, where the pollutants are found in lower concentrations. A supplemental work plan will be submitted for the second phase remediation after the results of the first phase remediation are available. Monitoring Wells In the In Situ Work Plan, OxyChem proposes to install three injection wells and three additional monitoring wells. The Source Group submitted the 8 December 2010 Monitoring Well Installation Work Plan, which Central Valley Water Board staff concurred with in its 9 December 2010 email. Aquifer Test The In Situ Work Plan proposes an aquifer test to be conducted by pumping groundwater from existing monitoring well MW-5B and observing drawdown in the new injection wells. The aquifer characteristics derived from the test will be used to refine estimates of treatment zone, reaction rates, and could be used to refine the contingency plan. Contingency Plan The groundwater monitoring data shows that the existing phytoremediation plantation is exerting hydraulic control on the shallow groundwater, and this hydraulic control is relied on as the contingency plan for the in situ remediation. However, this contingency plan does not provide for a strategy if the injection itself displaces pollutants beyond the treatment zone. OxyChem needs to provide a revised Contingency Plan that provides a strategy to manage off-site pollutants if sustained concentration increases occur in downgradient monitoring wells. Baseline Sampling Baseline or background sampling is intended to present groundwater quality conditions that existed prior to remediation, including water quality beyond the anticipated treatment zone. The In Situ Work Plan proposes obtaining baseline groundwater samples from the new injection and monitoring wells. In addition to the proposed analytes for baseline sampling within the treatment zone, Oxychem should add ammonium and alkalinity, and should substitute dissolved organic carbon for total organic carbon. OxyChem should extend baseline sampling to include monitoring wells outside of the treatment zone in order to track ambient water quality changes that may be occurring independently of the treatment. The General Order will require that the groundwater quality disturbances resulting from remediation not extend beyond the treatment zone. Baseline sampling outside the treatment zone provides a means of determining if observed geochemical disturbances are independent of the remediation. OxyChem should add regular baseline sampling of an upgradient and sidegradient monitoring well for the geochemical parameters of nitrate, ammonium, dissolved manganese, dissolved iron, alkalinity, and dissolved organic carbon. This sampling should continue throughout the remediation period. This sampling will also provide necessary baseline information for the second phase of treatment. A baseline sampling schedule should be incorporated into a proposed monitoring and reporting program.