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JUL 13 '97 04 55PM CLEARWATER GROUP P 4/5 <br />. Interested Parties-Use Of Non-Purge Sampling Method <br /> April 23, 1997 <br /> Page 3 <br /> 3 In fine grained sediments (predominately clayey/silty matenals) where the <br /> groundwater gradient is relanvely flat and wells are slow to recover (i e, <br /> groundwatermonitonng wells routmely become dry prior to evacuating minimum <br /> purge volumes) These wells can be sampled after groundwater in the monttonng <br /> well recovers to a minimum of 90% of the original groundwater elevation or 24 <br /> hours, whichever is less <br /> 4 The groundwater monitoring well is in use for air sparging and/or vapor <br /> extraction <br /> If a leaking UST case is evaluated by Regional Bcard staff'as a law-msk sire or if a responsible <br /> party requests site closure, Regional Board staff may require that a final purged groundwater <br /> sample(s) be taken from monitonng wells <br /> In areas where municipal Supply wells have been impacted by gasoline andlor gasoline additives, <br /> purging of groundwater monitoring wells may be required <br /> Groundwater wells with measurable free product should be on a regular program of free product <br /> removal If a monitoring wells is determined to contain free product at the time monitoring is <br /> atticipated, it should be bailed to remove any standing free product, purged to remove minimum <br /> well volumes (4-10 casing volumes), allowed to equilibrate back to pre purged levels, then free <br /> proauc, thickness measured and reported <br /> All reports containing the results of groundwater sampling and testing must adhere to QA/QC <br /> protocols and be submitted on this Regional Board's Laboratory Report Forms <br /> As new or updated information becomes available regarding the use and cffcctiveness of the non- <br /> purge method of groundwater sampling, changes and/or updates to this document will be made <br /> If you have any general,qutstions please contact Mr Jay Huang at (213)266-7608, or contact the <br /> Regional Board staff assigned to your UST case at (213) 266-7500 <br /> -7 � <br /> �Caq— I <br /> LAWRENCE P 7KOLB <br /> Acting Executive Officer <br /> cc Regional Board Members <br /> Allan Patton, Underground Storage Tank Program, SWRCH <br /> Regional Board UST Program Managers <br /> Ventura County Local Oversight Program <br /> Local Implementing Agencies <br /> R«.Xwd vtFw Ovr MMJJW A to Oa are wwd wnMnae Or vwmr of Gmrnn s wipt•r Pmuays and <br /> *wives YMir PAVOf&Ac o m■rid e1RxiPAe mw qr ON 0~4 4W 9LVA&M Ind f ftft p&"mLow. <br />