Application of DP_LAQ to Leaky Aquifer Pumping Test Data
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(This is a technical page on leaky aquifer testing. Click the link to see a nontechnical page on leaky aquifer testing.)
Introduction to DP_LAQ Leaky Aquifer Web Page
The purpose of this web page is to describe the results of an application of DP_LAQ pumping test analysis software (Moench, 1985) to actual data. The pumping test selected for this study is described by Green and others (1991). The test includes data from the pumped well and one observation well.
Description of the Leaky Aquifer Tested
The aquifer that was tested is composed of sand lenses interbedded with lenses of silt and clay. Its thickness is 320 feet. The aquifer is overlain by 320 feet of clay, siltstone, and very fine to fine grained sandstone, which is in turn overlain by a water table aquifer. This 320 foot thick unit is treated as a leaky aquitard in this pumping test analysis. The aquifer is underlain by 450 feet of sandy clay and siltstone which is in turn underlain by alternating layers of bentonitic clay and siltstone. This subjacent 450 foot thick unit is treated as a leaky aquitard.
Pumped Well Description
The pumped well was a 20-inch diameter bore-hole. The screened interval extended through the entire thickness of the aquifer, and consisted of alternating sections of 8-inch diameter casing and 8-inch diameter wire wrapped screen with 0.025-inch openings. The total length of screen was 180 feet. The annulus between the alternating screen and casing and the wall of the hole was packed with gravel.
Observation Well Description
One observation well was used. It was cased with 2-inch PVC pipe. The same intervals were screened as in the pumped well. The distance from the pumped well to the observation well was 100 feet.
Description of the Pumping Test and the Original Analysis
The original pumping test is described by Green and others (Green and others, 1991). The well was pumped at a constant rate of 405 gpm for 98 hours with less than 3 percent discharge variation. The original analysis used a type curve method developed by Papadopulos and Cooper and presented in Reed (1980). (The Papadopulos and Cooper method is a special case covered by DP_LAQ.) The analysis was applied to time-drawdown data from the the monitoring well. This method of analysis assumes a fully penetrating well of finite diameter in a non-leaky aquifer. It improves on the type curve method based on the Theis equation by considering the effect of depletion of water stored in the well resulting from drawdown during the test.
The result was as follows:
Transmissivity: 2,244 gpd/ft
Storativity: 3E-4 (dimensionless)
DP_LAQ Constant Rate Pumping Test Analysis
The present analysis of the data used DP_LAQ, which is described by Moench (1985). DP_LAQ computes type curves for constant rate leaky aquifer tests for three cases:
