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Dopaco, Inc. - 3 - 18 September 2012 800 W. Church St., Stockton San Joaquin County The Report states the wells will be installed, developed, surveyed, and sampled within 45 days of Regional Board staff approval. Comments: The approved Workplan stated that the screened intervals would be set based on actual field conditions. DMW-1 and DMW-4 appear to be adequately sited as proposed to begin monitoring the toluene plume, based on current and historical concentrations reported in groundwater, and a groundwater plume map drawn over Figure 5 by this Report reviewer. However, the locations for DMW-2 and DMW-3 need to be closer to the source area, to better monitor the groundwater plume. Moving DMW-3 will also provide additional delineation towards the southeast of the groundwater plume. Also, an additional shallow well screened above the sand unit needs to be installed between B-1 and CPT-MIP-2012-13 (source area). Therefore, the Report recommendations are approved with the following modifications. 1. Figure 7, the cross section of proposed wells, shows a 10' screen, not the 5' screen proposed in the text. The well screens length and depths shall be based on field conditions and professional judgment exercised in the field. 2. DMW-2 and DMW-3 shall be moved to a distance approximately half of their proposed locations on Figure 5 (DMW-2 approximately 20' to the east of the proposed location, DMW-3 approximately 20' to the east of the proposed location). 3. Add a source area monitoring well (DMW-5) screened from approximately 10' bgs to no deeper than 30' bgs (CPT-MIP-2012-13 depth to water was 22' bgs, B-1 depth to water was 16' bgs in 2005) entirely in the fine grained unit. Since there are GPS coordinates for CPT-MIP-2012-13, I strongly suggest DMW-5 be located at the corresponding CPT grab groundwater position. 4. Groundwater sample analyses for USEPA Method 8260B will continue to report all peaks, including toluene, in the data provided in the reports. 5. In addition to the previously proposed and approved Workplan submittals not included in the Report, include all of the field notes (the Report's and the future wells installation) in the final report, which is due 90 days from the date of this approval letter.