Sampling Colloids and Colloid‐Associated Contaminants in Ground Water

Backhus, Debera A.; Ryan, Joseph N.; Groher, Daniel; MacFarlane, John K.; Gschwend, Philip M.

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

Cited by 111 publications

(67 citation statements)

References 22 publications

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“…The sample was taken directly from a stainless steel sampling tap on the rising-main of the borehole. Appropriate protocols were followed to minimise the risk of artificially creating or mobilising colloids during sampling (Backhus et al, 1993). Two sterile 50L stainless steel sample containers, (Ucon Containersysteme AG, Germany) with stainless steel plugs and PTFE seals, were used to collect and store the groundwater.…”

Section: Groundwater Samplingmentioning

confidence: 99%

The significance of colloids in the transport of pesticides through Chalk

Gooddy

Mathias

Harrison

et al. 2007

Science of The Total Environment

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Agrochemical contamination in groundwater poses a significant long term threat to water quality and is of concern for legislators, water utilities and consumers alike. In the dual porosity, dual permeability aquifers such as the Chalk aquifer, movement of pesticides and their metabolites through the unsaturated zone to groundwater is generally considered to be through one of two pathways; a rapid by-pass flow and a slower 'piston-flow' route via the rock matrix. However, the dissolved form or 'colloidal species' in which pesticides move within the water body is poorly understood. Following heavy rainfall, very high peaks in pesticide concentration have been observed in shallow Chalk aquifers. These concentrations might be well explained by colloidal transport of pesticides. We have sampled a Chalk groundwater beneath a deep (30 m) unsaturated zone known to be contaminated with the pesticide diuron. Using a tangential flow filtration technique we have produced colloidal fractions from 0.45µm to 1kDa. In addition, we have applied agricultural grade diuron to a typical chalk soil and created a soil water suspension which was also subsequently fractionated using the same filtration system. The deep groundwater sample showed no evidence of association between colloidal material and pesticide concentration. In comparison, despite some evidence of particle trapping or sorption to the filters, the soil water clearly showed an association between the <0.45µm and <0.1µm colloidal fractions which displayed significantly higher pesticide concentrations than the unfiltered sample.Degradation products were also observed and found to behave in a similar manner to the parent compound. Although relatively large colloids can be generated in the Chalk soil zone, 2 it appears transport to depth in a colloidal-bound form does not occur. Comparison with other field and monitoring studies suggests that rapid by-pass flow is unlikely to occur beneath 4-5 m. Therefore, shallow groundwaters are most at risk from rapid transport of high concentrations of pesticide-colloidal complexes. The presence of a deep unsaturated zone will mean that most of the colloidal-complexes will be filtered by the narrow chalk pores and the majority of pesticide transport will occur in a 'dissolved' form through the more gradual 'piston-flow' route.

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Section: Groundwater Samplingmentioning

confidence: 99%

The significance of colloids in the transport of pesticides through Chalk

Gooddy

Mathias

Harrison

et al. 2007

Science of The Total Environment

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“…Colloid nutrient transport also can play a significant role in organic and inorganic nutrients migrating to stream and lake ecosystems (Ryan and Gschwend 1990;Chin and Gschwend 1991;Qualls and Haines 1991;Backhus et al 1993;Rhea et al 1996). Lake Tahoe research in this regard is in its infancy.…”

Section: Colloids and Their Potential Importance To Nutrient Water Chmentioning

confidence: 99%

Lake Tahoe watershed assessment: volume I

Murphy¹,

Knopp²

2000

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The United States Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation and marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) This watershed assessment of the Lake Tahoe basin in northern California and Nevada is the first attempt to collate, synthesize, and interpret available scientific information with a comprehensive view toward management and policy outcomes. The seven-chapter report presents new and existing information in subject areas pertinent to policy development and land and resource management in the basin, including environmental history, air quality, watershed dynamics and water quality, biological integrity, and socioeconomic conditions. Key findings report the extent of recent climatic changes, historic accounts of past environmental disturbances, state of our understanding of why the Lake's clarity is declining, significant role that air quality plays in the decline, and an initial nutrient budget for nitrogen and phosphorous that are believed to fuel algae growth. In addition, important new work related to old-growth forests, the risk of wildfire and the conservation of biological diversity in the basin have helped to broaden our perspective of the interrelated nature of the environmental challenge facing the basin. A detailed analysis of institutional arrangements and capacities in the Lake Tahoe basin is presented in the context of environmental decision-making.

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Section: Colloids In Natural Systemsmentioning

confidence: 99%

“…There is considerable debate on whether colloids sampled from natural systems are mobilized due to the sampling technique. The reader interested in this topic is referred to Backhus et al (1993), Puls et al (1992), and Puls (1990).Perturbations in solution chemistry, aquifer hydraulics, and rainfall infiltration can generate colloids (Ryan and Elimelech 1996). At a site in the southwestern United States, changes in solution chemistry due to water infiltration through a coal-ash disposal site increased the number of silicate colloids, which was not observed in adjacent wells ).…”

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confidence: 99%

Colloid suspension stability and transport through unsaturated porous media

McGraw¹,

Kaplan²

1997

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Executive SummaryContaminant transport is traditionally modeled in a two-phase system: a mobile aqueous phase and an immobile solid phase. Over the last 15 years, there has been an increasing awareness of a third, mobile solid phase. This mobile solid phase, or mobile colloids, are organic or inorganic submicron-sized particles that move with groundwater flow. When colloids are present, the net effect on radionuclide transport is that radionuclides can move faster through the system. It is not known whether mobile colloids exist in the subsurface environment of the Hanford Site. Furthermore, it is not known if mobile colloids would likely exist in a plume emanating from a Low Level Waste (LLW) disposal site. No attempt was made in this study to ascertain whether colloids would form. Instead, experiments and calculations were conducted to evaluate the likelihood that colloids, if formed, would remain in suspension and move through saturated and unsaturated sediments.The objectives of this study were to evaluate three aspects of colloid-facilitated transport of radionuclides as they specifically relate to the LLW Performance Assessment. These objectives were: 1) determine if the chemical conditions likely to exist in the near and far field of the proposed disposal site are prone to induce flocculation (settling of colloids from suspension) or dispersion of naturally occurring Hanford colloids, 2) identify the important mechanisms likely involved in the removal of colloids from a Hanford sediment, and 3) determine if colloids can move through unsaturated porous media.Mobile colloid formation is commonly described as a three-step process: genesis, stabilization, and transport. Colloid genesis describes how the micron-sized particles are formed in groundwater. Stabilization describes how the colloids are brought into suspension, which is a function of the colloid and groundwater chemical composition and water flow (kinetic) forces. Transport describes how the suspended colloid move through the porous media or are retained by the porous media by physical forces (such as diffusion, straining, or gravitation settling) or physicochemical attraction of the colloid to the matrix.As the second step in mobile colloid formation indicates, colloids must remain in suspension, i.e., not flocculate, in order to be transported with groundwater flow. A series of batch experiments was conducted to identify the chemical conditions where dispersion and flocculation (settling out of suspension) of Hanford sediment colloids (

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Sampling Colloids and Colloid‐Associated Contaminants in Ground Water

Cited by 111 publications

References 22 publications

The significance of colloids in the transport of pesticides through Chalk

The significance of colloids in the transport of pesticides through Chalk

Lake Tahoe watershed assessment: volume I

Colloid suspension stability and transport through unsaturated porous media

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