SITE INFORMATION AND CORRESPONDENCE_2008-2015

Home Browse Search

8 LFR LFR proposes to implement the laboratory testing wells ERD-3 and ERD-18 because of their relatively elevated hazardous substance concentrations (1,300 and 1,720 micrograms per liter, respectively), their different placements vertically (ERD-18 is in the upper A-zone while ERD-3 is in the lower A-zone), their low resistance to flow during injections (indicating good communication with the surrounding aquifer), and their positions north (ERD-18) and south (ERD- 3) of the center of the array of injection wells. The two wells will be sampled semiannually and analyzed for: • VOCs and end products (e.g., ethene and ethane) • biogeochemical indicators of redox conditions (e.g., DO, ORP, nitrate, manganese, sulfate, iron (II), and methane) • organic substrate (as TOC) RWQCB Comment 2: The assumption has been made that based on the increased daughter products detected in MW- 108A, dehalococcoides populations must also have increased in MW-1084 and in the ERD Barrier Area in general. Dehalococcoides are the microbes responsible for driving ERD to innocuous end products. Staff concurs that it was a good idea to have performed this analysis on samples from the five wells listed on page 9. Please propose a sampling frequency for adding this analysis in those well to the monitoring program. Confirmation of dehlococcoides should be established, not assumed. Response 2: Laboratory analysis for the genus dehalococcoides was conducted voluntarily outside the current monitoring program as an additional line of evidence that the bacteria capable of mediating the complete dechlorination of tetrachloroethene (PCE) were present at the Site. As discussed in the Injection Completion Report, laboratory results confirmed that dehalococcoides is present in sufficient numbers to be detected by the microbial test in B-zone well MW-20513; however, dehalococcoides is not detected above the reporting limit in the other four wells tested, namely wells MW-108A, MW-122A-U, MW124A-L, and MW-21413. As discussed during the June 16, 2008 conference call, the four aforementioned wells will be sampled semiannually for one year to confirm that dehalococcoides is present in each well. It is important to note that the objective of this testing is to confirm that the microorganism is present, but not to monitor microbial population size or changes in microbial population over time. Therefore, testing for dehalococcoides will stop after two sampling events or after only one sampling event if its presence is confirmed by a laboratory result above the laboratory reporting limit. Itr-Response to RWQCR-Lincoln-JU108.06750.doc:LMT 3