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High-Permeability Layers for Remediation of Ground Water; Go Wide, Not Deep (2005)

Robertson, W.D. ; Yeung, N. ; VanDriel, P.W. ; [et al.]

Oxford, UK; Malden, USA : Blackwell Science Inc

Ground water 43 (2005), S. 0

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ISSN: 1745-6584

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Notes: A nitrate-reactive porous media layer comprising wood particles with very high hydraulic conductivity (K∼ 1 cm/s) was used to successfully treat nitrate in a shallow sand-and-gravel aquifer in southern Ontario. Nitrate concentrations of 1.3 to 14 mg/L as N in the aquifer were attenuated to 〈0.5 mg/L as N in the reactive layer. Borehole dilution testing indicated that ground water velocities in the reactive layer, although variable, averaged five times higher than in the surrounding aquifer, suggesting that the layer was capturing ground water flow from deeper in the aquifer. The use of high-K reactive media opens up the possibility of installing permeable reactive barriers as horizontal layers in the shallow water table zone that do not necessarily have to penetrate the full depth of a contaminant plume to be effective. Model simulations show that the depth of capture of a high-K layer increases as the layer width in the direction of flow increases. Shallower emplacement could decrease barrier costs at some sites.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1745-6584.2005.0062.x

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Hydrogeology Of An Unconfined Sand Aquifer And Its Effect On The Behavior Of Nitrogen From A Large-Flux Septic System (1992)

Robertson, W.D. ; Cherry, J.A.

Springer

Hydrogeology journal 0 (1992), S. 32-44

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ISSN: 1435-0157

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Detailed monitoring of groundwater in a shallow sand aquifer impacted by a large-flux septic system showed that water quality in the shallow water table zone below the tile bed was similar to that of smaller-flux septic systems in similar hydrologic settings where effluent residency in the unsaturated zone was of similar duration. During residency of about one week in the 4-m thick unsaturated zone, effluent NH+ 4 was largely oxidized to NO− 3, about 75% of DOC was biodegraded, and acidity produced by the above reactions was neutralized by dissolution of calcite. Beneath the tile bed and extending laterally downgradient a distance of 80 m to the Lake Erie shoreline, a distinct plume of impacted groundwater was easily distinguished by elevated levels of electrical conductance, Cl−, NO− 3, HCO− 3, NA+, Ca2+, and K+ and by depressed levels of pH and dissolved oxygen. High NO− 3 levels that occur below the tile bed disappear, however, in the anaerobic plume core zone 10 to 70 m downgradient, apparently as a result of denitrification. The rich reserve of solid-phase organic carbon in the aquifer sediment (2.5%) probably provides much of the organic carbon for heterotrophic denitrification. This condition is in contrast to other septic system plumes in sand aquifers where high NO− 3 levels persist and where aquifer organic carbon values are much lower. Although NO− 3 is attenuated in the plume core, persistence of NO− 3 along the aerobic upper fringe of the plume demonstrates the ability of septic systems to cause significant water-quality degradation of sand aquifers when the conditions favorable for denitrification do not exist. The sharp boundary between the plume water and non-impacted water adjacent to and overlying the plume in the area 50 to 100 m downgradient from the tile bed, and the undiluted nature of non-reactive solutes such as Cl− throughout the core of the plume, demonstrates that dispersion has only a weak influence on the plume. This is consistent with dispersion studies in many other sand aquifers.