WORK PLANS_PRE 2019 - Laserfiche WebLink

Home Browse Search

Mr Sergio IViorescalchi - 2 - 8 April 2009 Atlantic Richfield Company In April 2008, the Regional Water Board adopted Waste Discharge Requirements (WDRs) Order No. R5-2008-0064 to regulate the proposed pilot study. The WDRs include a contingency plan that requires groundwater extraction if there are sustained exceedences of baseline concentrations observed outside the treatment zone in MW-1A, which is the downgradient point of compliance. to the Response, ARCO requests that Order No. R5-2008-0064 be rescinded and that the pilot study be regulated by Order No. R5-2008-0149, Genera! Order for In-Situ Groundwater Remediation (General Order). Since our meeting in January, Regional Water Board staff has received further information regarding the applicability of the General Order. Based in part on that information, our comments on the Response and Work Plan are presented below. 1. Due to concerns over existing elevated concentrations of salts in groundwater in the Central Valley, Regional Water Board staff needs additional information before concurring with the injection of calcium sulfate into groundwater because it is a salt bearing material. The General Order states in Finding No. 16 that the "use of non salt-containing injectants is preferred, and the Discharger is required to demonstrate that there are no non salt-containing injectant alternatives that will cost-effectively promote the degradation of the target constituent before being allowed to use a salt-containing injectant." Therefore, ARCO must evaluate the use of non salt-containing injectants in order to make this demonstration. 2. Groundwater monitoring data has established the background TDS concentration in the site vicinity at 680 mg/L, which exceeds the Water Quality Objective (WQO) of 450 mg/L listed for TDS in Finding No. 15 of the General Order. The Work Plan proposes to inject calcium sulfate at 250 mg/L, which includes 176 mg/L of sulfate and 74 mg/L of calcium. Since this injectant concentration is below the WQO, the existing salt concentration in the groundwater would not prevent ARCO from enrolling in the General Order as long as it makes the demonstration in Item 1 above. In no case would the concentration of injectant be allowed to exceed 450 mg/L. 3. Regional Water Board staff does not concur with the fructose injection contingency plan because in-situ treatability studies conducted at the Site by EMCON in 1996 and by URS in 2005 both independently concluded that the lateral influence of substances injected into the aquifer is significant only within a small radius of the injection points. Given this information, there is no assurance that fructose injected into the aquifer to mitigate sulfate and/or TDS will disperse sufficiently throughout the subsurface to effectively reduce excess concentrations. 4. Regional Water Board staff does not concur with ARCO's proposal to oxidize excess sulfide to sulfate. Neither the Response nor the Work Plan provides a description of the methodology, equipment, or oxygen concentrations necessary to complete this process. In addition, if implemented, this process may generate excess sulfate which could trigger implementation of the sulfate contingency plan which, in turn, could produce more sulfide. These processes could become circular. Therefore, implementation of this contingency plan is impractical. 5. Regional Water Board staff does not concur with ARCO's proposed method of choosing the highest historical concentrations of sulfate, sulfide, and TDS in monitoring well AR/MW-1A as the baseline concentrations for these constituents. The California Code of Regulations Title