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MAR-24-89 16 36 From WOODWARD CLYDE + T-T39 P 04/34 Jab-402 TABLE Number of borehole volumes requtmd for proper purging of groundwater mondonng w Wls Volumes Purrgzd Autri4r(s} Year FReferenced Work to GROUNDWATER Mothodoiogy far monitoring liumonick at al 1880 groundtaatar at uranium V 7 No 4, 1solution fomes s382-89 US EPA f Proc aures Manual for Groundwater Monitoring at - j Fenn,at d im Solid Waale Disposal EPA/530/SW611, Faculties t23ep Manual of Groundwrttar Nahanni Water Well �1 6aelf,es al 1ea1 Sampling Procedures Assadatlon,Dublin,OH U 5 Geological Survey paveiopment of a primer on Wilson and Dworkin 1984 uvater vmll sampling for Reston,VA volatile orpnic substances + Graundwct0r Sampling Groundm or for 4 PetFyjohn,et ei 1961 OMante Contaminants v 9 No 12 Proceedings of the Third A laboratory investigation of Annual Symposium on the Purging Behavior at Groundwater Monitoring and 20 Unwin and Hula 103 Smarr ofamoter monitoring Aquifer Restoration National Well Water Well Association. Dublin,ON,p.267.262 Clay and silt (some silts are organic)particles are electrically charged and may adsorb organic ring or chain molecules, making them unavailable for denaction using EPA standard analysis methods Clay and silt particles from the surrounding stratagrapnic tormations migrate,over time,through trio sand pace and into the Well casing Where they slowly settle-out The act of purging most wells disturbs these settled particles.creating highly turbid samples Even if the well is allowed to"settle"out,most of the clay platelets have already contacted the dissolved contaminants and created their bond/adsorption.Those platelets which settled out without adsorbing an organic molecule chain or nng will almost certainly be stirred again (id sampled at depth)with the introduction of a check-valve bailor or bladder--pump sampler A gain of dissolved volatiles by sampling through Free Product-is not uncommon in leaking underground storage tank(LUST) Investigations This problem is so evident and prevalent,that many sites are not sampled until all of the free product has been removed from the groundwater table Laboratory analyses from wells containing free product are generally useless as representative ground-Water samples due to the influence of free product This is because the bailer must be continuously lowered down through the free product during the purging process,creating a thick layer of emulsion and an enure well of contaminant-rich groundwater If another"ci®an"bailor is used to obtain a sample of this broth, it,too, must be lowered through whatever emulsion may be left, to obtain a sample,thereby 3 of 14 324!99 4 21 PM