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Groundwater- Monitoring Wefts LGC proposes eight monitoring wells across the site. To help reduce costs, (continued) we propose to place seven of the eight wells at the locations of previously planned geotechnical investigation borings by extending those borings to the depths considered necessary for groundwater review. We recommend six _groundwater monitoring wells and two open standpipe piezometers be placed at select locations across the site. The following wells are planned for the site: ► Three (3) 50 -foot groundwater monitoring wells, ► Three (3) 120 -foot groundwater monitoring wells, ► One (1)120 -foot open standpipe piezometer, and ► One (1) 200 -foot open standpipe piezometer. Again, to help reduce costs, we are planning for three different types of drill rigs to be used to achieve these goals - a CM&55 for the 50 -foot borings, a CMF,95 for the 120 -foot borings anda. mud rotary rig for the 200 -foot boring. Please note that it may be necessary to revise drill rigs according to conditions encountered in the field and availability of drill rigs at the time of planned installation and additional costs may occur due to unforeseen or unanticipated conditions such as caving, excessive water, voids and other phenomena. Please also note that we are planning to use a mud rotary drill rig for the 200 -foot open standpipe piezometer for the same reasons as indicated within Task -6. Thus the advantages and risks associated with this drilling method are the same as described above. Methodology The monitoring wells will be drilled to the selected depth. Slotted pipe to allow water infiltration will be placed -within the t oriaig except for the upper approximate 10 feet, where a solid wall pipe will be placed. The annular space around the pipe will be backfilled with gravel and the upper few feet of the boring will be slurry filled in order to reduce surface water infiltration and in order to set a surface monument. The standpipe piezometers will be drilled to the selected depth, and slotted pipe will only be placed in the bottom approximate 10 to 20 feet of the borings. Gravel will be placed within the annular space, subsequently capped by bentonite chips. Slurry will then be used to fill the remaining annular space above the bentonite. It is the goal of the standpipe piezometers to record only the water that occurs at those depths (approximately 120 and 200 feet, respectively). The 120 and 200 -foot standpipe piezometers are located at or just above the i interpreted basal rupture surfaces identified within previous investigations P S O M A S Scope of Services I LGC Geotechnical — 38