An Empirical Analysis of Gas Well Design and Pumping Tests for Retrofitting Landfill Gas Collection

Abstract

Retrofitting a landfill with a gas collection system is an expensive and time consuming endeavor. Such an undertaking usually consists of longer-term extraction testing programs and the installation of deep, large diameter extraction wells. Installation and longer-term testing of these wells can be expensive, and yet, few, if any, documented field studies have been reported in the literature to evaluate the necessity of longer-term extraction tests and expensive well designs. Therefore, the aims of this thesis are as follows: 1) The primary goal of this work was to evaluate the performance of landfill gas extraction wells to the various aspects of their design and construction. 2) A secondary goal was to evaluate the performance of the gas wells using various short-term and longer-term testing methodologies. Accordingly, several different short-term and longer-term pumping tests were carried out on the landfill gas extraction wells which were constructed to varying design specifications. As well, the efficacy of two different longer-term pumping methodologies was compared to determine if one method of longer-term extraction proved superior to another. In order to interpret these results, it was necessary to select a measure for the efficiency of a particular landfill gas extraction well that was appropriate yet simple. The parameter principally used for this purpose in this study is the specific capacity which was determined for each well. Following the completion of the short- and longer-term pumping tests, three important conclusions were reached. Firstly, it appeared that construction well specifications had no impact on the efficiency of the extraction wells. Further, there was no significant difference in pneumatic response of the extraction wells between short-term and longer-term testing programs. Lastly, the constant pressure type longer-term extraction test (opposed to constant flow type test) showed lower levels of oxygen ingress into the waste mass and landfill gas, and resulted in an overall higher gas extraction rate.