ABSTRACT
CONTENTS Objectives of Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Purging Strategies for High-Yield Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Traditional Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Fixed Well-Volume Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Purging to Stabilization of Indicator Parameters . . . . . . . . . . . . . . . . . . . . . . . . 104 Use of a Packer during Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Low-Flow Purging and Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Purging and Sampling Strategies for Low-Yield Wells . . . . . . . . . . . . . . . . . . . . . . . 112
Traditional Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Purging to Dryness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Purging Water from the Casing Only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Other Methods for Purging and Sampling Low-Yield Wells . . . . . . . . . . . . . . . . . 116 Minimum-Purge Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 ‘‘Coring’’ the Water Column in the Well Screen . . . . . . . . . . . . . . . . . . . . . . . . . 118
Field Measurement of Water-Quality Indicator Parameters and Turbidity . . . . . . . . 121 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Most traditional approaches to ground-water sampling are based upon the assumption that all water that resides in sampling points between sampling events is stagnant (i.e., does not interact with formation water) and does not represent the chemistry of water in the formation. Thus, the historical means of meeting the objectives of sampling programs has been to remove all of the water from the well and to induce fresh formation water to enter the well so it can be collected as a sample. This process is referred to as well purging. Several purging strategies, described in detail in the following sections, are in common use.
