An Interactive Excel Spreadsheet To Calculate Time-Varying Efficiencies for Pump-and-Treat Wells

Monday, December 4, 2017
Prashanth Khambhammettu, PE , SS Papadopulos & Associates Inc, Bethesda, MD
Matthew J. Tonkin , S.S. Papadopulos and Associates Inc., Bethesda, MD
Steven Larson , S.S. Papadopulos & Associates, Bethesda, MD

An interactive excel spreadsheet has been developed to estimate time-varying efficiencies for pump-and-treat wells (extraction and injection) at a contaminated site. The spreadsheet uses convolution and superposition techniques to calculate water levels in each well based on the pumping at the well, interference from neighboring pumping wells, effect of a neighboring river, and time-varying linear and non-linear well losses. Aquifer and well loss parameters can be interactively adjusted until the calculated water levels match measured data. Well efficiency is automatically calculated by the spreadsheet as a function of the time-varying well loss parameters and the expected theoretical drawdown.

This spreadsheet is currently being used at two operating units of a contaminated site.

In the first operating unit, water levels in an unconfined aquifer respond to pumping, and fluctuating stage in a neighboring river. Here, the spreadsheet is used to calculate efficiencies for 160 pump-and-treat wells. The second operating unit is inland and not impacted by the fluctuations in the river stage. However, the pumping wells in this operating unit are periodically cleaned resulting in sudden increases in well efficiencies. The spreadsheet tool was successfully able to model the water levels and efficiencies at these pumping wells after factoring in the maintenance history.

This spreadsheet tool can be used at other contaminated sites, provided, the local geology and hydrological processes are consistent with the underlying theoretical assumptions. The interactive and visual nature of the tool enables better communication with stakeholders and regulators.

Prashanth Khambhammettu, PE, SS Papadopulos & Associates Inc, Bethesda, MD
Mr. Khambhammettu is experienced in handling various facets of water resources project work including data organization / analysis, conceptual model development, numerical modeling, and documentation, for groundwater and surface water flow evaluations and contaminant investigations. He has significant experience with groundwater modeling codes (MODFLOW, MODFLOW-SURFACT), surface-water modeling codes (HSPF, HEC-RAS, HEC-HMS, and TR-55) and integrated groundwater-surfacewater modeling codes (MODHMS, MIKE-SHE). He has experience working for various state agencies in Florida and federal agencies. His background also includes risk assessment work for the US EPA. He is a licensed Professional Engineer in Maryland.

Matthew J. Tonkin, S.S. Papadopulos and Associates Inc., Bethesda, MD
Matt Tonkin has been with SSP&A for 15 years. His focus is on the design of data gathering efforts; the synthesis and interpretation of data; and, the application of models to support decision-making. He has completed contracts to the USGS, USEPA and California Department of Water Resources in the areas of contaminant transport and model uncertainty analysis. Matt is a former member of the Interstate Technology Research Council (ITRC) MTBE team.

Steven Larson, S.S. Papadopulos & Associates, Bethesda, MD
Mr. Larson is a recognized authority on numerical simulation models and their application in the analysis of a variety of groundwater problems. In addition, he has been in the forefront of combining these methods with linear programming techniques to optimize the development of groundwater supplies or remediation of contaminated groundwater. Mr. Larson has authored and co-authored publications on the application of aquifer simulation models that are widely used by practicing hydrologists.

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