Laserfiche WebLink
OUR <br /> RWQCB Comment 2: <br /> 2. Per conference call discussions held on June 13, 2007, the Trust and the Regional Water Board <br /> have agreed to increased frequency of monitoring (to be discussed below)to better evaluate the <br /> need for implementing ERD in the B Zone in a timely manner. A progress report (letter format) <br /> needs to be submitted to the Regional Water Board evaluating the semiannual progress and rate of <br /> natural attenuation in the B zone. We recommend this report be submitted after the baseline data <br /> and first two quarters of monitoring data have been collected, which would be approximately seven <br /> to eight months after the implementation of ERD begins, <br /> Response 2: <br /> A report will be submitted to the RWQCB after the baseline data and first two quarters of <br /> groundwater monitoring data have been collected, which would be approximately seven to eight <br /> months after implementation of ERD within the A-zone begins. This will be in the form of a <br /> progress report(letter fonnat), and will evaluate the progress of the ERD remedy in the A-zone <br /> and rate of natural attenuation in the B-zone. <br /> RWQCB Comment 3: <br /> 3. We concur that natural degradation is occurring in the B Zone. However, our concern revolves <br /> around the current concentrations of PCE and the daughter products in the aquifer, the rate at <br /> which natural degradation is occurring, and how long that process will take to reduce all PCE to <br /> harmless end products. In December 2006, PCE was detected in MW-205B (beneath Bank of <br /> Stockton) and MW-2078 (about 1000 feet down gradient of MW-205B) at 4,020 uglL and 1,137 <br /> ug/L, respectively. These levels of PCE are two orders of magnitude too high to consider a plan <br /> that potentially allows natural degradation as the remedy for the B Zone in this area. <br /> Response 3: <br /> Both A-and B-zones are being remediated and contained by the existing groundwater extraction <br /> and treatment systems located on Pacific and Inglewood avenues. Implementing ERD in the A- <br /> zone in the vicinity of the Bank of Stockton is proposed due to persistent and relatively elevated <br /> concentrations observed in this zone. Natural attenuation is not proposed as a remedy for the B- <br /> zone at this time. The Phase V Plan contemplates collecting additional contaminant concentration <br /> and biogeochemical data (see comment N5) that will allow for a more thorough assessment of the <br /> rate at which natural attenuation is occurring in the B-zone. B-zone groundwater throughout the <br /> majority of site has naturally degraded to concentrations near or below the MCL for PCB and its <br /> daughter products, and the site data indicate that the B-zone in the Bank of Stockton may act <br /> similarly. However, due to the RWQCB's concern over the magnitude of the concentrations in the <br /> B-zone in this area of the site, the report under comment N2 above will include a regular update of <br /> progress within the B-zone and if necessary will assess whether additional B-zone remediation will <br /> be required based upon the data. <br /> 2 <br />