ARCHIVED REPORTS XR0000209 - Laserfiche WebLink

Home Browse Search

is because waters in the screened interval and the sand pack are free to interact with the formation water, while the bore volume water is cut-off from communication with the formation water, subject to different physical and geochemical regimes Recommended purge volumes found in the literature range from one (1) to twenty (20) bore volumes, depending on which contaminant or suite of contaminants is present, Humenick, et al. found that representative samples could be obtained after purging only one bore volume It should be noted that nearly all of these early researchers used some sort of pumping mechanism to purge the wells, and then collected samples using a check-valve bailer, or simply collected the sample from the pump effluent. A summary graph of suggested purged bore volumes is presented in flus paper Well Purging- Low Flow Low-flow purging removes considerably less water from the well, disturbs the surrounding geology only minimally, and has been well documented over the past four or five years. Puls, et al,have conducted a considerable amount of work in this area noting that samples obtained from wells where the low-flow or passive purging technique was employed indicated a higher degree of reproducibility. The method provides for the slow insertion of a pump so that its inlet is placed in the screened interval of the well at the point where sampling is desired Purging is begun at a rate of 01 to 0.5 L/min, although rates up to 1 L/min may be possible in lughly permeable formations The usual parameters (DO, Eh, T) are monitored to determine when stable flow has been reached, at which time a sample is obtained. The No-Purge Scenario The importance of closely-spaced discrete point-interval groundwater sampling has been demonstrated in the literature for field experiments and monitoring aqueous-phase contaminants Data obtained from discrete point-interval sampling (DPIS) devices provide a more complete understanding of the three-dimensional nature of a contaminant plume relative to surface sampling using a common check-valve bailer Pre-purge DPIS samples more adequately describe the in situ environment than do "mixed" water column samples retrieved by a bailer or high-flow pump The elimination of the practice of well purging combined with DPIS sampling can effectively reduce the overall costs of sampling while increasing the quality and reliability of the data acquired Reliable and cost-effective sampling devices are now available to enable discrete point-interval groundwater sampling Discrete point-interval samplers must be flexible in design to be consistent with future trends in contaminant monitoring. KABIS Sampler Efficacy Testing -- SIBAK Industries Limited, Inc., conducted efficacy testing of its lead product, The KABIS Discrete Point-interval Sampler (KABIS SamplerTm), through the summer and fall of 1994 in a cooperative venture with TEXACO Refining and Marketing, Inc. The test was conducted on a randomly chosen service station site in Southern California which had been under environmental investigation for several years and for which there was a considerable library of data previously collected. TEXACO's contract environmental consultant conducted the test under the observation of SIBAK personnel Testing methods included sampling each selected well on the site prior to purging using the KABIS SamplerT', purging