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hammers, etc.) to prevent the casing from rising. The Contractor shall notify the Engineer of the amount of rise. 3. The Contractor shall place the sand pack into the annular space around the screened interval. Clean water and a tremie pipe may be used to assist with the sand pack tremie operation. If the well assembly is installed through the hollow stem augers, the augers shall be pulled slowly during sand pack installation. 4. The Contractor shall monitor the sand pack settlement by measuring the sand level with a weighted tape. The Contractor shall also monitor the top of the well casing to detect any movement due to settlement or from drive casing removal. If the top of the well casing moves upwards at any time during the well installation 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 Engineer of the amount of rise. D. Sand pack shall be added in the presence of the Engineer until it is above the top of the screened interval as shown on the Plans. 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 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. E. Once the placement of the sand packed interval is completed, the depth to the top of the pack shall be measured and recorded by the Contractor. F. The Contractor shall install a bentonite seal in the annular space above the sand pack. Add bentonite 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 grouting. G. Install the neat cement in a single pour. H. The Contractor shall pump 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 layer within the well. Construction Specifications San Joaquin County Groundwater Monitoring Wells Page 7 of 9 Public Works Dept Revised 11-23-09 Solid Waste Division