LOW-FLOW PURGING AND SAMPLING OF GROUND-WATER MONITORING WELLS WITH DEDICATED SYSTEMS

A field study was conducted to assess purging requirements for dedicat ed sampling systems in conventional monitoring wells and for pumps enc ased in short screens and buried within a shallow sandy aquifer. Low-f low purging methods were used, and wells were purged until water quali ty indicator parameters (dissolved oxygen, specific conductance, turbi dity) and contaminant concentrations (chromate, trichloroethylene, dic hloroethylene) reached equilibrium. Eight wells, varying in depth from 4.6 to 15.2 m below ground surface, were studied. The data show that purge volumes were independent of well depth or casing volumes. Contam inant concentrations equilibrated with less than 7.5 L of purge volume in all wells. Initial contaminant concentration values were generally within 20 percent of final values. Water quality parameters equilibra ted in less than 10 L in all wells and were conservative measures for indicating the presence of adjacent formation water. Water quality par ameters equilibrated faster in dedicated sampling systems than in port able systems and initial turbidity levels were lower.