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t - Mr. James Barton,PG 30 January 2014 Page 2 13 and screened in the shallow B-zone aquifer, located 50 to 75 feet below mean sea level (bmsl)2, corresponding to 60 to 85 ft bgs in the CPT-13 area. The recommendation to install well DMW-5B was approved by the Regional Water Quality Control Board, Central Valley Region (RWQCB), by letter dated 21 October 20133. Prior to installation of well DMW-5B, approximately 300 cubic yards of soil will be excavated from the CPT-13 area, as proposed in the Soil Excavation Plan (SEP)4 and SEP Addendum 5. Soil excavation and backfill are currently scheduled to be completed in the first half of February 2014 and will reduce the risk of cross- contamination of the B-zone aquifer by toluene from shallower units. RECOMMENDATIONS FOR MONITORING WELL LOCATION, DRILLING METHOD,AND SCREEN-DEPTH-INTERVAL --- - The-..propo-sed-generals:location-.of.:well_DMW=5B- is-shown--in .Figure- 2. Weil-:installation- M --� ----- procedures-are detailed°in Attachment-A7-A-1 0-inch-diameter-steeI-conductor casing will first-be - -- - _ -a-depth-of -S0-f `b s`half-wa between-the- sand zones at-40 ft,b sand- -installed'to apProximatel -' 60 ft bgs shown oiithe log for CPT-13 which is provlded as Attachment B. Followirig installation-of-the-conductor-casing-, the-boring-will be-advanced-through the conductor casing,to ------- -- - approximately 75 ft bgs with 8-inch diameter hollow stem augers. Well DMW-5B will be installed through the conductor casing and screened in the shallow B-zone aquifer, as determined by conditions encountered in the field. A diagram of a typical monitoring well completion is provided in Figure 3. The boring for the well will be logged during drilling by a qualified Geosyntec engineer or geologist and reviewed by a California Professional Engineer or Geologist. Between ground surface and approximately 50 ft bgs, soil samples will be collected approximately every five feet and logged to confirm previously collected logs of nearby borings. Between approximately 50 ft bgs and the maximum depth of the boring; soil will be logged continuously. 2 U.S.Army Corps of Engineers,2007.2006 Groundwater Sampling Report,McCormick and Baxter Superfund Site,Stockton,California.Prepared for the U.S.Environmental Protection Agency Region IX.February. s RWQCB,2013.Letter Response to July-August 2013 Additional Investigation Report and Soil Excavation Work Plan.21 October. 4 Geosyntec,2013b. Soil Excavation Plan,Dopaco Inc.Area,800 West Church Street,Stockton,California 95203. 30 September. 5 Geosyntec,2013c.Addendum to Soil Excavation Plan,Dopaco Area,800 West Church Street,Stockton, California 95203. 15 November.. i DMW-513 Monitoring Well Installation Work Plan i engineers I scientists I innovators F I