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SOP #: GW 0001 <br />Region I Low Stress <br />(Low Flow) SOP <br />Revision Number: 2 <br />Date: July 30, 1996 <br />Page 1 of 13 <br />U.S. ENVIRONMENTAL PROTECTION AGENCY <br />REGION I <br />LOW STRESS (low flow) PURGING AND SAMPLING PROCEDURE <br />FOR THE COLLECTION OF GROUND WATER SAMPLES <br />FROM MONITORING WELLS <br />SCOPE & APPLICATION <br />This standard operating procedure (SOP) provides a general framework <br />for collecting ground water samples that are indicative of mobile <br />organic and inorganic loads at ambient flow conditions (both the <br />dissolved fraction and the fraction associated with mobile <br />particulates). The SOP emphasizes the need to minimize stress by low <br />water-level drawdowns, and low pumping rates (usually less than 1 <br />liter/min) in order to collect samples with minimal alterations to <br />water chemistry. This SOP is aimed primarily at sampling monitoring <br />wells that can accept a submersible pump and have a screen, or open <br />interval length of 10 feet or less (this is the most common <br />situation). However, this procedure is flexible and can be used in a <br />variety of well construction and ground-water yield situations. <br />Samples thus obtained are suitable for analyses of ground water <br />contaminants (volatile and semi-volatile organic analytes, <br />pesticides, PCBs, metals and other inorganics), or other naturally <br />occurring analytes. <br />This procedure does not address the collection of samples from wells <br />containing light or dense non-aqueous phase liquids (LNAPLS and <br />DNAPLs). For this the reader max wish to check: Cohen, R.M. and J.W. <br />Mercer, 1993, DNAPL Site Evaluation; C.K. Smoley (CRC Press), Boca <br />Raton, Florida and U.S. Environmental Protection Agency, 1992, RCRA <br />Ground-Water Monitoring: Draft Technical Guidance; Washington, DC <br />(EPA/530-R-93-001). <br />The screen, or open interval of the monitoring well should be <br />optimally located (both laterally and vertically) to intercept <br />existing contaminant plume(s) or along flowpaths of potential <br />contaminant releases. It is presumed that the analytes of interest <br />move (or potentially move) primarily through the more permeable zones <br />within the screen, or open interval. <br />Use of trademark names does not imply endorsement by U.S.EPA <br />but is intended only to assist in identification of a specific <br />type of device. <br />