Sampling Colloids and Colloid-Associated Contaminants in Ground Water

doi:10.1111/j.1745-6584.1993.tb01849.x

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Wiley InterScience

Ground Water

Volume 31 Issue 3, Pages 466 - 479

Published Online: 4 Aug 2005

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Sampling Colloids and Colloid-Associated Contaminants in Ground Water

Debera A. Backhus ^a , Joseph N. Ryan ^b , Daniel M. Groher ^c , John K. MacFarlane ^d Philip M. Gschwend ^d

^a School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405. ^b Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Campus Box 428, Boulder, Colorado 80309-0428. ^c ABB Environmental Services, Corporate Place 128, 107 Audubon Rd., Suite 25, Wakefield, Massachusetts 01880. ^d Water Resources and Environmental Engineering Division, Civil and Environmental Engineering Department, Massachusetts Institute of Technology 48-415, Cambridge, Massachusetts 02139.

Discussion open until November 1, 1993.

ABSTRACT

It has recently been recognized that mobile colloids may affect the transport of contaminants in ground water. To determine the significance of this process, knowledge of both the total mobile load (dissolved + colloid-associated) and the dissolved concentration of a ground-water contaminant must be obtained. Additional information regarding mobile colloid characteristics and concentrations are required to predict accurately the fate and effects of contaminants at sites where significant quantities of colloids are found. To obtain this information, a sampling scheme has been designed and refined to collect mobile colloids while avoiding the inclusion of normally immobile subsurface and well-derived solids. The effectiveness of this sampling protocol was evaluated at a number of contaminated and pristine sites.

The sampling results indicated that slow, prolonged pumping of ground water is much more effective at obtaining ground-water samples that represent in situ colloid populations than bailing. Bailed samples from a coal tar-contaminated site contained 10–100 times greater colloid concentrations and up to 750 times greater polycyclic aromatic hydrocarbon concentrations as were detected in slowly pumped samples. The sampling results also indicated that ground-water colloid concentrations should be monitored in the field to determine the adequacy of purging if colloid and colloid-associated contaminants are of interest. To avoid changes in the natural ground-water colloid population through precipitation or coagulation, in situ ground-water chemistry conditions must be preserved during sampling and storage. Samples collected for determination of the total mobile load of colloids and low-solubility contaminants must not be filtered because some mobile colloids are removed by this process. Finally, suggestions that mobile colloids are present in ground water at any particular site should be corroborated with auxiliary data, such as colloid levels in "background" wells, colloid-size distributions, ground-water geochemistry, and colloid surface characteristics.

Received November 1991, revised December 1992, accepted December 1992.

DIGITAL OBJECT IDENTIFIER (DOI)

10.1111/j.1745-6584.1993.tb01849.x About DOI