Mining and Construction Dewatering Projects
Southerly Wastewater Plant Dewatering – Columbus, Ohio: Eagon & Associates provided support to the Construction Management Team and the City during dewatering for numerous construction projects at the facility. Initially, work involved evaluation of system failures, upgrades, and continuing operation of the dewatering system for the new Headworks Raw Sewage Pump Building. Model simulations were run to evaluate system performance at various stages of operation and to analyze the requirements for successful completion. Because timing of the Effluent Pump Building and Pipeline construction completion was critical to subsequent phases of the project, Eagon & Associates was tasked with the design and oversight of that dewatering system. A total of 45 wells were installed and operated for 14 months. The system effectively dewatered the excavation and the project was completed on schedule. Eagon & Associates conducted pumping tests, developed groundwater models, prepared technical reports and specifications for bidding, and monitored dewatering contractor's efforts for four additional phases of the project. Upon completion of the work, a report was prepared documenting the operations and dewatering results for use during design of future construction projects at the facility.
Dearborn CSO No. 2 Dewatering Plan, Dearborn, Michigan: Eagon & Associates prepared a dewatering plan to facilitate completion of the construction of a 125-foot diameter by 130-foot deep caisson. The structure was planned to be part of a comprehensive Combined Sewer Overflow (CSO) Control Project near Detroit, Michigan. Eagon & Associates was contracted to troubleshoot hydrogeologic conditions that lead to a blow-in of sediments at the base of the caisson as the caisson was being lowered to bedrock at a depth of approximately 100 feet. The blow-in caused major subsidence to occur outside the caisson and halted further construction of the structure. Eagon & Associates performed a field investigation in which personnel directed the installation of piezometers and test wells, and supervised pumping tests. The information gathered in the field was then analyzed to develop a conceptual model of the site hydrogeology and construct a groundwater flow model to assess the feasibility of installing a dewatering system to stabilize the sediments and allow construction of the caisson to proceed. Upon determining that a dewatering system was feasible, Eagon & Associates developed a design for the system along with a plan for its implementation. The plan consisted of installing 32 sand wells and 12 bedrock wells to produce a combined pumping rate of 1,200 gpm.
City of Columbus, Upground Reservoir No. 2: During the later stages of construction, the Construction Management Team (CMT) retained Eagon & Associates to perform a groundwater model analysis to be used to resolve a dispute with the Contractor over dewatering system shortfalls. Specifically, the questions to be answered were: 1) how much construction dewatering at off-site pipeline excavations reduced the amount of water that could be pumped by reservoir wells; 2) how much a recent drought reduced the amount of water that could be pumped; and 3) how much more water could be pumped by reservoir wells without violating the contract specifications. A four layer model was constructed and transient simulations were run separately for each dewatering system and then in combination. The Palmer Drought Index for the current and prior years was incorporated into the background data. Conclusions were provided relative to the amount of reduction in dewatering system capacity due to pipeline dewatering and drought conditions. It also was determined that pumping capacity of the system could be increased by redistribution of pumping rates among the reservoir dewatering wells.
Wyandot Dolomite Quarry: Eagon & Associates performed a groundwater flow model analysis in order to estimate the impacts on groundwater levels that may occur from dewatering for a proposed quarry expansion, as required by the Ohio Department of Natural Resources (ODNR) permitting process. The quarry is situated adjacent to another operating rock quarry and in close proximity to a municipal well field. As required by ODNR, drawdowns must be computed relative to conditions that existed before either quarry began operation; and it was essential to separate the drawdowns produced by Wyandot Dolomite from impacts being caused by the other existing quarry. A five layer model was constructed and calibrated to levels measured in existing wells, as well as to an analysis of water levels reported on well logs on file at ODNR for wells within a four mile radius of the site. The expansion was divided into four phases and the area where drawdown of 10 feet or more would occur was determined from the model simulation for each phase.
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