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Report: Applying the Extended Drawdown Method to Interpret Pumping Tests in British Columbia

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An assessment of the applicability and limitations of the extended drawdown method for enhancing the interpretation of aquifer pumping tests.

Author:  Garth van der Kamp, Anna Grunsky, and Mike Wei

Date Published:  Mar 2021

Report ID:  59432

Audience:  Government and Public

Groundwater pumping tests lasting from one to three days are commonly performed in support of groundwater license applications. These pumping tests are used to assess the adequacy of long-term supply of water from the well, characterize well performance, determine aquifer hydraulic properties, assess drawdown in the aquifer and in neighbouring wells, and determine if there is any connections to surface water bodies. To estimate the long-term water supply and drawdown impacts, pumping test data may be extrapolated over months to years., which leads to large uncertainty in the estimates of long-term supply and impacts on nearby surface waters. This report describes the application of an extended drawdown method to improve interpretation of aquifer pumping tests. The extended drawdown method, developed by Garth van der Kamp in 1989, uses the principle of superposition to calculate and extend drawdown into the recovery phase of a pumping test, provided groundwater level data in the recovery phase are available. This method has not been widely applied in B.C. but holds promise because it can provide greater insight and certainty of expected drawdown for days or even weeks beyond the pumping phase of the test. The extended drawdown method was applied to data for 20 available pumping tests to evaluate and demonstrate the utility of this method in the complex hydrogeological environments across B.C. Results show the method is generally applicable in B.C., so long as the fundamental principle of superposition and the conditions of the constant rate pumping test are satisfied. As part of this study, a list of criteria for ideal pumping test datasets was developed. To facilitate application of the extended drawdown method, an Excel spreadsheet was also developed to input, plot and summarize the pumping test data. The Excel spreadsheets are embedded into the MS Word version of the report document. They are also included as a separate data attachment.

Report Type
  Region - Province Wide
  Water Information - Groundwater
  Water Information - Water Management
  Water Information - Water Supply

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