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Additional Soil Borings Two additional soil borings are planned for the site, and these borings will be installed ' prior to installation of MWS. Boring B5 will be located near existing MW2 (see attached map) and be completed to a maximum depth of 80' BGL. Boring B6 will be located at roughly a mid-point between MWl and MW4 (see attached map) and be completed to a ' maximum depth of 130' or until saturated conditions associated with the uppermost aquifer are encountered(estimated at 108 feet BGL), whichever occurs first. ' Soil borings will be advanced using 8-inch nominal diameter hollow stem augers and an attempt will be made to collect a soil sample after every 5-feet of drilling using the California modified Standard Penetration Test. A detailed drilling log shall be maintained by the field geologist and will include any signs of water and a description of retrieved soil samples consistent with the Unified Soil Classification System. Should a soil sampling attempt fail to retrieve a sample, then the reason and cause will be noted on ' the geologist's field log. Retrieved soil samples in 6-inch steel cylinders will be sealed with plastic end-caps and duct tape and labeled for subsequent description and/or archiving. Soil samples will either be logged in the field during drilling or in the laboratory after drilling is completed. Once the boring has reached total depth, a tremie pipe will be inserted to the base of the ' augers, and a grout mixture will be pumped through the tremie pipe assesmbly. The grout mixture will consist of 5 to 10 gallons of potable water for each 94 lbs bag of Portland cement with up to 5%by weight of bentonite added to control shrinkage. As ' grout progressively fills the augers, the augers will be progressively removed from the boring. Prior to the last few augers being removed, a small excavation will be made surrounding the bore hole at the surface (approximate dimensions will be three feet deep ' and 20" diameter) and the final application of grout will fill the bottom 1 foot the excavation. No sooner than 24 hours after grouting is complete, the surface will be graded level using a clean backfill material. All waste material generated during over- drilling will be either disposed of off site at a landfill or used as fill material on site. Installation of MW5 The purpose of MW5 is to serve as a replacement for the abandoned MW3. Procedures for installing MW5 will be those identified in the Groundwater Investigation Workplan, ' October 1, 2004 (amended October 15, 2004) except as modified herein. The proposed location for MW5 is shown on Figure 1. Well bore drilling will be conducted using 8-inch nominal diameter hollow stem augers and an attempt will be made to collect a soil sample after every 5-feet of drilling using the California modified ' Standard Penetration Test. A detailed drilling log shall be maintained by the field geologist and will include any signs of water and a description of retrieved soil samples consistent with the Unified Soil Classification System. Should a soil sampling attempt fail to retrieve a sample, then the reason and cause will be noted on the geologist's field ' June 21,2005 Page 3