SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Mr. Mike Lescisin - 2 - 18 December 2003 oxygen, oxidation-reduction potential, sulfate and zinc. In planning the list of analytes, DWG should predict what compounds present in the subsurface will react with the introduced reducing agents to form new compounds that could degrade groundwater quality and beneficial uses. 2. The Work Plan specifies a discrete volume of soil and groundwater to be collected. The laboratory should specify how much soil and groundwater is necessary to accomplish all of the specified testing considering the additional analyses. 3. The Work Plan provides for two controls using contaminated soil and groundwater from the site but no reducing agent. This provides a method to measure how much pollutant would react in the laboratory environment and is a necessary control. However, another control should measure the amount of reducing agent used by site-specific clean soil and groundwater. The additional control should yield the amount of reducing agent consumed by reactions with constituents other than the pollutant. The additional control should be considered during in-situ or scale up design and will help estimate the appropriate amount of reducing agent to introduce into the subsurface. 4. The Work Plan proposes to conduct the test using soil-groundwater slurries rather than soil columns. This strategy will yield an estimate for the dose necessary to treat the pollutant mass in soil and groundwater. However,it does not provide the information necessary to determine if the reducing agent will leach through the soil column and reach the target pollutant depths or will react in the shallow soil column, restricting treatment depth to the injection depth. DWG needs to provide the rationale for eliminating soil column testing or incorporate them into the treatability study. 5. The Work Plan says, "Analyses for Cr VI will be performed by PRIMA Environmental using the diphenyl carbazide method, which has a detection limit of 0.01 mg/l." The two proposed reducing agents have been used at other sites to remediate hexavalent chromium, so we expect near complete conversion of hexavalent chromium to trivalent chromium. Thus, if each test using the two proposed stoichiometric doses and each of the two reducing agents produces a non-detect result, there seems to be no way to compare the results. DWG needs to provide the rationale for selecting the proposed analytical method and detail how the test results will be evaluated to determine the optimal reducing agent and stoichiometric dose. 6. The Work Plan includes post treatability study analyses that include total and hexavalent chromium,pH, sulfate and iron. The list is not complete. Post treatability analyses should include the same constituents analyzed to develop the baseline concentrations (see Comment 1) and any other constituents likely to form during the reduction reactions. Post treatability testing should also confirm the fate of all the reducing agent introduced. California Environmental Protection Agency CO Recycled Paper