Deep-well dewatering system
(1) Scope. The work provided for herein consists of furnishing all labor, material, equipment, and tools to construct, develop, test pump, and disinfect the filter sand, well, and pump for the dewatering wells to be installed around the perimeter of the excavation at the locations shown on the drawings and as specified herein. The work also includes installation of the pumps, diesel engines, gear drives, couplings, discharge pipes, valves, fitings, flow measurement devices, and discharge pipe.
(2) Design. The deep-well system specified has been designed to lower the groundwater table in the deep sand stratum beneath the excavation to elevation – 26.0 feet beneath the dam, elevation – 29.0 feet beneath the lock chamber, and elevation -35.0 feet beneath the gate bays for a design Red River stage of elevation of 60.0 feet (estimated maximum river stage for a frequency of 1 in 20 years). The purpose of the deep – well system is to lower the hydrostatic head in this sand stratum so as to prevent seepage into the bottom of the excavation and to prevent any heave of impervious soil strata that overlie the deep sand formation in certain areas of the excavation. It is imperative that there be no heave of the bottom of the excavation during either Phase II or Phase III construction of the lock and dam, If evaluation of the pumping test made at the completion of unwatering the Phase I excavation indicates the need for additional dewatering wells, pumps, engines, discharge piping, and appurtenances, the Government will design the supplemental system and furnish the design to the Contractor for installation. The Contractor will be reimbursed for the cost of installing any supplemental wells, pumps, engines, discharge piping, and appurtenances, when completely installed and ready for operation. The Contractor shall be responsible for designing any features of the well system not specifically covered by these specifications or drawings.