ASTM_D_6771_-_02.pdf

Designation:D 6771 02Standard Practice forLow-Flow Purging and Sampling for Wells and DevicesUsed for Ground-Water Quality Investigations1This standard is issued under the fixed designation D 6771;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers the method for purging and sam-pling wells and devices used for ground-water quality investi-gations and monitoring programs known as low-flow purgingand sampling.This method is also known by the terms minimaldrawdown purging or low-stress purging.This method couldbe used for other types of ground-water sampling programs butthese uses are not specifically addressed in this practice.1.2 This practice applies only to wells sampled at thewellhead.1.3 This practice does not address sampling of wells con-taining either light or dense non-aqueous-phase liquids(LNA-PLs or DNAPLs).1.4 This practice offers a set of instructions for performingone or more specific operations.This document cannot replaceeducation or experience and should be used in conjunction withprofessional judgment.Not all aspects of this practice may beapplicable in all circumstances.This ASTM standard is notintended to represent or replace the standard of care by whichthe adequacy of a given professional service must be judged,nor should this document be applied without consideration ofa projects many unique aspects.The word“standard”in thetitle means that the document has been approved through theASTM consensus process.1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:D 4750 Test Method for Determining Subsurface LiquidLevels in a Borehole or Monitoring Well(ObservationWell)2D 5088 Practice for Decontamination of Field EquipmentUsed at Non-Radioactive Waste Sites2D 5092 Practice for Design and Installation of Ground-Water Monitoring Wells in Aquifers2D 5521 Guide for Development of Ground-Water Monitor-ing Wells in Granular Aquifers2D 5903 Guide for Planning and Preparing for a Ground-Water Sampling Event3D 6026 Practice for Using Significant Digits in Geotechni-cal Data3D 6089 Guide for Documenting a Ground-Water SamplingEvent3D 6452 Guide for Purging Methods for Wells Used forGround-Water Quality Investigations3D 6517 Guide for Field Preservation of Ground-WaterSamples3D 6564 Guide for Field Filtration of Ground-WaterSamples3D 6634 Guide for the Selection of Purging and SamplingDevices for Ground-Water Monitoring Wells33.Terminology3.1 drawdown(low-flowpurgingandsampling),nlowering of the water level in a well caused by pumping thewell.3.2 entrance velocity,nthe velocity with which formationpore water passes through a well screen during pumping of thewell.This velocity should be controlled(held to less than 0.10ft/s or 3.0 cm/s)to avoid turbulent flow through the screen andto minimize or eliminate deleterious effects on water chemistryand on well construction materials.3.3 low flow,nrefers to the velocity that is impartedduring pumping to the formation pore water adjacent to thewell screen.It does not necessarily refer to the flow rate ofwater discharged by a pump at the surface.4.Summary of Practice4.1 Low-flow purging and sampling is a method of collect-ing samples from a well that,unlike traditional purgingmethods,does not require the removal of large volumes ofwater from the well.Low-flow purging differs from traditionalmethods of purging(as described in Guide D 6452)in that itsuse is based on the observations of many researchers that watermoving through the formation also moves through the well1This practice is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.21 on Ground-Water andVadose Zone Investigations.Current edition approved Feb.10,2002.Published March 2002.2Annual Book of ASTM Standards,Vol 04.08.3Annual Book of ASTM Standards,Vol 04.09.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.screen.Thus,the water in the screen is representative of theformation water surrounding the screen.This assumes that thewell has been properly designed,constructed,and developed asdescribed in Practice D 5092 and Guide D 5521.In wells inwhich the flow through the screen or intake zone is limited byhydraulic conductivity contrasts(for example,borehole smear-ing,residual filter cake,filter pack grain size,or well screenopen area),the head difference induced by low-flow pumpingprovides an exchange of water between the formation and thewell.Low-flow