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ADDITIONAL ASSESSMENT WORKPLAN dAMAR SERVICE,STOCKTON APRIL 2402 Vapor/Groundwater Extraction Well Installation To provide for remediation pilot testing at the site, a groundwater/vapor extraction well (EW-1) will be installed at the location shown on Figure 4 Data from the CPT boring near this location may be used to refine the extraction well design and screen intervals Drilling and well installation activities will be reviewed by a California Registered Geologist or Licensed Civil Engineer The well will be drilled to approximately 80-feet bgs with hollow-stem auger drilling techniques using a truck-mounted drill rig using 10-inch auger flights The groundwater well will be screened from approximately 10 to 80-feet bgs to allow for seasonal fluctuations in water levels and for vapor extraction vadose zone remediation The well will be completed with 4-mch diameter,flush threaded, Schedule 40 PVC with 0 020-mch perforated and blank casing A threaded end cap will be placed at the bottom of the PVC casing, which will then be set through the augers These wells will be plumbed for groundwater and vapor extraction as well as having a future line for possible air sparging In the future air sparging as well as vapor extraction may be used to create a convection cell recirculating groundwater and mfluencmg a greater area for MTBE removal A#3 sand or equivalent sand pack will be placed in the annular space between the slotted casing and the boring wall, and will extend approximately 1-foot above the top of the screened interval The well annulus will be sealed with 2-feet of hydrated bentonite above the top of the sand The well will be sealed from the top of the bentonite to within 1-foot of ground surface with a neat cement/bentonite(<5%) grout To protect the integrity of the well,the top of the wellhead assembly will be enclosed at the surface in a traffic-rated, flush-mounted well box All work will be performed in accordance with the County Soil sampling will not be conducted due to the proximity to the existing groundwater monitoring well MW-1 and CPT boring CPT-1 Well Development The groundwater monitoring wells will be developed using a surge block and/or submersible pump to remove fines and develop the sand pack and nearby aquifer materials Turbidity will be monitored to check the effectiveness of development Development and purge water will be put into DOT approved 55-gallon drums and labeled accordingly The drums will be left on-site pending laboratory analyses and selection of an appropriate disposal,which will be completed by GHH 9