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JUL 13 '97 04 55PM CLEARWATER GROUP P 4/5 <br /> A� <br /> M <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 relatively flat and wells are slow to recover (i e, <br /> groundwater monitoring wells routinely become dry pnor to evacuating minimum <br /> purge volumes) These wells can be sampled after groundwater to the monitonng <br /> well recovers to a mtnimum 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 spargmg and/or vapor <br /> extraction <br /> If a leaking UST case is evaluated by Regional Board std`as a low-n!k sim. 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 monitoring wells <br /> In areas where municipal supply wells have been impacted by gasoline and/or gasoline additives, j <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 /> produc. thickness measured and reported <br /> lieAll 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 effectiveness of the non- <br /> purge method of groundwater sampling, changes and/or updates to this document will be made <br /> If you have any generalquestions please contact Mr Jay Huang at(213)266-7608,or contact the <br /> Regional Board staff assigned Io your UST case at (213)266-7500 <br /> =LAE�CEKOLB <br /> Acting Executive Officer <br /> cc Regional Board Members <br /> Allan Patton,Underground Storage Tank Program, SWRCB <br /> Regional Board UST Program Managers <br /> Ventura County Local Oversight Program <br /> Local Implementing Agencies <br /> ' I I c r <br /> I " it <br /> Roe""Paw I Ow 41018W q m pr nM■ee raMnoo ft Q4Md Y of WIDM r Z W"F ffi=VA &8" <br /> 1Atwr Y r proprr�iarJo�•rid sAb4wl w+ArO�a OPMIk d p►fyaf•so MtrA 9@PMAew4 <br /> r <br />