{"id":6880,"date":"2018-01-26T22:16:36","date_gmt":"2018-01-26T14:16:36","guid":{"rendered":"https:\/\/www.envguide.com\/?p=6880"},"modified":"2018-04-05T22:23:00","modified_gmt":"2018-04-05T14:23:00","slug":"low-flow-purging","status":"publish","type":"post","link":"https:\/\/us.envguide.com\/low-flow-purging\/","title":{"rendered":"Low Flow Purging"},"content":{"rendered":"
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Abs: Purging strategies, as described in ASTM Standard D 6452 (ASTM, 2004g), are divided into two general categories: those appropriate for high-yield sampling points (points that do not go dry during purging and sampling) and those appropriate for low-yield sampling points (points that may go dry during purging and sampling).<\/em><\/p>\n Although it is important to purge some water from most wells before collecting a sample, purging too much water or purging at too high rate can cause mixing of water from zones of different quality and, potentially, contamination of noncontaminated zones by previously localized or stratified pollutants. Purging strategies, as described in ASTM Standard D 6452 (ASTM, 2004g), are divided into two general categories: those appropriate for high-yield sampling points (points that do not go dry during purging and sampling) and those appropriate for low-yield sampling points (points that may go dry during purging and sampling).<\/p>\n Purging Strategies for High-Yield Wells<\/p>\n\t\t\t\t\t<\/div>\n An improved method of purging wells evolved out of research conducted to improve sample accuracy and precision and to encourage the collection of more representative samples. This method of purging is known as low-flow purging and sampling. Low-flow purging involves removing water directly from the screened interval without physically or hydraulically disturbing the stagnant water column above the screen. This is done using a dedicated pump product 1\uff1bproduct 2\uff1bproduct 3\uff09(or by very carefully installing a portable pump) with the pump intake set at or near the middle of the screen and pumping the well at a low enough flow rate to maintain a stabilized water level in the well as determined through water-level measurement during pumping. Typically, flow rates on the order of 0.1 to 0.5L\/min are used; however, this is dependent on site-specific and well-specific factors. Some very coarse-textured formations have been successfully purged and sampled in this manner at flow rates up to 1 L \/min. Pumping water levels in the well and water-quality indicator parameters (such as pH, temperature, specific conductance, DO, and redox potential) are monitored during pumping, with stabilization indicating that purging is completed and sampling can begin.<\/p>\n