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Interim Remediation Work Plan 419 S.Main Street,Manteca,CA June 25,2003 Page 5 MW-4 and MW-5 will be destroyed by over drilling the wells with 8-inch outside diameter, continuous- "' flight, hollow-stem auger and removing all well construction materials. Both monitor wells were completed to a depth of approximately 20 feet b s. The traffic boxes will be removed prior to over drilling the wells. 'v''� he resulting o—nngs will be ac filled with neat cement to the ground surface. The neat cement will be W q tremied into the borehole from the bottom of the borehole to the surface. The traffic boxes and well materials will be removed from the site. -to 2,_ KW.6 4.3 DRILLING PROCEDURES One groundwater monitor well will be installed at the site in the vicinity of MW-4 as a replacement for MW-4. The proposed location of the replacement monitor well is shown on Figure 2 in Appendix A. The monitor well boring will be drilled using 8-inch outside diameter, continuous-flight,hollow-stem auger. The hollow-stem auger and other down-hole equipment will be decontaminated by steam cleaning prior to drilling. The monitor well boring will be drilled to approximately 8 feet below the water table. It is anticipated the total depth of the well boring will be approximately 25 feet bgs. All drilling activities will be .� observed by a Condor geologist. OK b"j.- 1-t W S k, --h ' '_. Drill cuttings from the monitor well boring will be logged according to the USCS. Descriptions of soil types encountered and any other pertinent field observations will be recorded on boring logs. Cuttings will be placed in a polyethylene bag and checked with a PID for the presence of volatile hydrocarbons. All visual observations and PID measurements will also be noted on the boring logs. The drill cuttings and steam cleaning effluent will be placed in DOT-approved 55-gallon drums, sealed, labeled, and left on-site pending laboratory analyses. Disposal of hazardous materials, if any, will be the responsibility of the property owner. i 4.4 MONITOR WELL MW-4 REPLACEMENT WELL INSTALLATION `, The monitor well will be constructed with 10 feet of 2-inch outside diameter, Schedule 40, flush-threaded, machine-slotted PVC screen (slot size 0.010). A flush-threaded PVC bottom cap will be placed at the bottom of the screen section. Blank PVC casing will be installed above the screen to the ground surface. L A filter pack of#3 Monterey sand will be placed in the annular space to approximately three feet above the screen while the auger is in place. The depth of the sand in the well annulus will be monitored with a v weighted tape measure while the sand is being placed and the auger is being gradually retracted to avoid bridging. To form a protective seal, approximately three feet of bentonite pellets will be installed above the sand as the augers are retracted. The bentonite will be hydrated using potable water. A surface seal of neat cement will be poured into the annulus and will extend from the bentonite to the ground surface. Depending on the stability of the borehole, the augers may be removed before or during emplacement of the grout. The monitor well will be completed at the surface with flush mount locking traffic box. A proposed well i construction diagram is shown on Figure 4 in Appendix A. At least 48 hours following construction, the monitor well will be developed by surging and bailing the groundwater in each well until the discharge water is relatively free of sediment (clear to the unaided eye). `W The monitor well will be purged until the temperature, electrical conductivity, and pH of the water has stabilized. All well-development equipment will be cleaned prior to use in the well by washing in a solution i of laboratory-grade, non-phosphate detergent and deicnized water, and double rinsing with deionized water. v 1 a i� CONDOR