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1 <br />' Ground Water 5amphng <br /> (3) aquifers stressed by intermittent pumping of production, irrigation <br />' or supply wells, <br /> (4) aquifers being actively recharged because of recent precipitation, <br />' and <br /> (5) confined or semi-confined aquifers that demonstrate significant <br />' water level fluctuations in response to barometric pressure <br /> changes <br />' o Water level and well depth measurement equipment should be constructed <br /> of matenals that are chemically inert and not prone to sorption <br /> o Water level and well depth measurement equipment should be <br />' decontaminatedprior to use at each well to ensure sample integrity and to <br /> prevent cross-contamination of ground water <br />' o Measuring tapes and marked cables that are used to measure water levels <br /> and well depths should be periodically calibrated <br />' O Well depth measurements should be made each time ground water is <br /> sampled using a weighted tape measure or marked cable The weight <br /> should be heavy enough to keep the tape measure straight and it should be <br />' blunt so that it will not penetrate soft materials on the bottom of the well <br /> 0 The deeper the well, the heavier the weight has to be to "feel"the bottom <br /> of the well Standing water Ievel measuring devices are not appropriate <br /> for making well depth measurements <br />' 2.2.2 Detection of Immiscible Layers <br />' The SAP should include provisions for detecting and measuring the thicknesses of <br /> immiscible liquid contaminants (i e , light non-aqueous phase liquids [LNAPLs] <br /> and dense non-aqueous phase liquids [DNAPLs]) each time water level is <br /> measured if immiscible contaminants are known to occur, or could plausibly <br /> occur, in the subsurface at the facility LNAPLs (also known as "floaters") are <br /> relatively insoluble organic liquids, less dense than water, that tend to spread <br />' across the water table (in unconfined aquifers) DNAPLs, also known as <br /> "sinkers", are relatively insoluble organic liquids that are more dense than water, <br /> DNAPLs tend to migrate downward and accumulate on underlying confining <br />' layers The detection of immiscible layers requires specialized equipment that <br /> should be used before a well is evacuated for conventional sampling The SAP <br /> should specify the devices to be used to detect LNAPLs and DNAPLs, as well <br /> as the procedures to be used for detecting and sampling these contaminants <br /> LNAPL Detection Collection <br />' RPs should specify in the SAP the following procedures for detecting the presence <br /> of LNAPLs These procedures should be followed before the well is evacuated <br /> for conventional sampling <br /> 4 <br />