ARCHIVED REPORTS_20100427 ATC 1Q2010 GWMR COMPLETE

Home Browse Search

Ms.Amy Terrell April 27,2010 Page 8 of 10 submitted a Work Plan to the RWQCB on August 20, 2007, which included details of the Expanded Pilot Test. Two test plots were included in the Expanded Pilot Test, one located at the northern portion of the Site (near well MW-2) and one east of the Site and west of Welty Road (near well MW-5; Figure 2). Each pilot test plot consisted of two rows, spaced approximately eight to ten feet apart, with 21 injections of HRC-X® per row emplaced between approximately 24 to 48 feet below ground surface. Prior to the injections, two new monitoring wells were installed in August 2007 to monitor the performance of the Expanded Pilot Test: (1) MW-6R, which is located within the center of the on- site test plot and (2) MW-7, which is located approximately 10 feet downgradient of the on-site test plot. The injections were conducted in October and November 2007. The seepage velocity was previously calculated to range from four to 377 feet per year (Geosyntec, 1998). Details regarding implementation of the Expanded Pilot Test were submitted in an Implementation Report to the RWQCB on January 30, 2008. Geochemical Parameters for Expanded Pilot Test Analytical Results The Expanded Pilot Test monitoring program is summarized in Table 1. Results of geochemical parameters measured during the baseline monitoring event and the five monitoring events performed since the injections are presented in Table 6 and are summarized below. Baseline samples were collected in August and September 2007 prior to implementation of the HRC-X®injections. A suite of reactive zone indicator analyses were sampled during the baseline and subsequent monitoring events. • Groundwater quality indicators of a reactive zone are subsiding: o Oxidation-reduction potential (ORP) continued to increase in the intergrid and downgradient monitoring wells during the March 2010 groundwater monitoring event. Even though ORP levels are increasing, the average ORP (113 millivolts) overall value is still generally low and may not warrant sufficient oxidative dechlorination. o Dissolved organic carbon concentrations have generally decreased since 2008, suggesting that HRC-X®may no longer be degrading into bioavailable carbon. • Terminal electron acceptors detected in groundwater during the March 2010 sampling event suggest that conditions in groundwater may no longer be suitable for effective reductive dechlorination. o Dissolved manganese concentrations continue to decrease or are currently not detected above the laboratory reporting level in the intergrid and downgradient monitoring wells. o Dissolved iron concentrations continue to decrease or are currently not detected above the laboratory reporting level in the intergrid and downgradient wells.