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MAR-24-99 16 44 From WOODWARD CLYDE ¢ Y-I35 P 18/34 Job-402 waters. while at the same time, creatuig as little disturbance to the groundwater flow regime In all cases found in the literature,the most common reason for purging is to"refresh"the"stagnant"bore water volume In general,one well bore volume as deecnbed no the volume of water standing ist the well caamr,above the screened interval. This 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 $eOchemical 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. Humeruck, 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 this paper Nell Purging-Low Plots 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 Pula,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 unlet is placed in the screened interval of the well at the point where sampling is desired Pursing is begun at a rate of o 1 to 0 5 L/min,although rates up to 1 L/min may be possible in highly 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 Rho-purge Sceinano 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 tete 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 elimutation 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 samplmg Discrete point-interval samplers must be flexible in design to be consistent with future trends in contaminant monitoring ISIS Sampler [Efficacy Testing-- SIBAK Industries Limited, Inc, conducted efficacy testing of its lead product, The KABIS Discrete Famt-interval Sampler (KABIS Samplerrm), 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 whish there was a considerable library of data previously collected TEXACUs 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 SamplerTm. purging the well followed by check-valve bailer sampling, waiting 2 hours and resampling each well using the KAKIS Sampleem The results of the test mchcated the following 3ofi0 3/24194 422 PM