CORRESPONDENCE_2007 (1/07 - 6/07)

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process, the Contractor shall not set drilling equipment (drill pipe, hammers, etc.) on the top of the casing to prevent further movement. The Contractor shall notify the on-site geologist of the amount of rise. G. Sand pack shall be added in the presence of the on-site geologist until its height is 5 feet above the top of the screened interval. The driller shall gently surge the water inside the well casing and screen to compress the sand pack. The top of the sand pack shall be re -measured and additional sand shall be added to acquire the desired height of sand pack. This is to ensure that the sand pack does not compress after installation of the bentonite seal and cause bridging within the annulus of the well bore. H. Once the placement of the sand packed interval is completed, the depth to the top of the pack is measured and recorded on the Driller's Log. 1. The Contractor shall install a 5 -foot thick bentonite seal in the annular space on top of the sand pack. The pellets or chips shall be added gradually to avoid bridging. The Contractor shall take depth soundings using a weighted tape to ascertain the top of the bentonite seal. The bentonite seal shall be allowed to hydrate for at least one hour before proceeding with the grouting operation. J. The Contractor shall pump the neat cement through a tremie pipe filling the annular space from the top of the bentonite seal upward. The bottom of the tremie pipe shall be maintained below the top of the cement to prevent free fall and bridging. When drilling with hollow stem augers, the hollow stem augers may be substituted for the tremie pipe, provided the bottom of the augers are no more than 10 feet above the top of the neat cement. K. The Contractor shall cease grouting when the cement level has risen to two feet from the ground surface. Cement levels shall be monitored by the Contractor to assure that cement taken into the formation is replaced by additional cement, this will allow placement of the steel protective casing. If settling of the cement occurs, additional topping -off of the cement seal will be necessary. L. The Contractor shall install a protective steel surface casing around the well casing and insert it into the grouted annulus approximately 2 feet. Prior to installation, a 2 -inch thick temporary spacer will be placed between the PVC well cap and the bottom of the protective casing cover to keep the protective casing from settling onto the well cap. Typical well design is shown on Figure 4. M. The Contractor shall record the following additional information on the Driller's Log: 1. Depth of all encountered water -bearing zones 2. Total depth of bore hole 3. Depth from ground surface to top and bottom of the bentonite interval Corral Hollow EMP WPlan Rev2Mar 22-07.DOC Pegs 6 of a February 28, 2007