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FACILITATED TRANSPORT OF INORGANIC CONTAMINANTS IN GROUNDWATER: PART II. COLLOIDAL TRANSPORT
Citation:
Puls*, R W., D. A. Clark*, R. M. Powell, AND C J. Paul*. FACILITATED TRANSPORT OF INORGANIC CONTAMINANTS IN GROUNDWATER: PART II. COLLOIDAL TRANSPORT. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/M-91/040 (NTIS 92-114503), 1991.
Impact/Purpose:
information
Description:
This project consisted of both field and laboratory components. Field studies evaluated routine sampling procedures for determination of aqueous inorganicgeochemistry and assessment of contaminant transport by colloidal mobility. Research at three different metal-contaminated sites has shown that 0.45 u.m filtration has not removed potentially mobile colloids, when samples have been collected using low pumping flow rates (-0.2-0.3 LJ mm). However, when pumping velocities greatly exceeded formation ground-waterflow velocities, large differences between filtered and unfiltered samples were observed, and neither were representative of values obtained with the low flow-rate pumped samples. There was a strong inverse correlation between turbidity and representativeness of samples. Several different sampling devices were evaluated in wells (PVC) ranging in depths from 10 to 160 ft. Those devices which caused the least disturbance (i.e., turbidity) also produced the most reproducible samples irrespective of filtration. The following water quality indicators were monitored during well purging: dissolved O2, pH, Eh, temperature, specific conductance, and turbidity. Sampling was not initiated until all indicators had reached steady-state (usually ~ 2 to 3 casing volumes). In all cases turbidity was slowest to reach steady-state values, followed by dissolved oxygen and redox potential. Temperature, specific conductance, and pH results were generally insensitive to well purging variations.