Factors affecting groundwater quality in the Valley and Ridge aquifers, eastern United States, 1993-2002

Abstract

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The quality of our nation's waters: water quality in the Principal Aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions, eastern United States, 1993-2009

“…In the Valley and Ridge aquifers, the relative location of the well on the landscape-its topographic position-is important because it indicates the position on the flow path and therefore groundwater age. (22) The topographic position is the location of the well with respect to the highest point in the watershed and the major stream draining the valley ( fig. 4-5) and can indicate geochemical conditions.…”

“…(22) In the area close to the ridge, groundwater is oxic, making denitrification unlikely, but nitrate concentrations are low because few nitrogen sources are associated with the forested land use overlying that part of the aquifer. Midway between the ridge and stream, the nitrate concentrations are higher because the water is oxic, and agricultural activity provides nitrogen sources.…”

“…Higher concentrations of dieldrin, a pesticide that was used in urban areas and is now banned, were detected in areas with a larger percentage of urban land surrounding a well. (8,22) Simazine, prometon, and tebuthiuron are general-use herbicides that have both agricultural and urban uses-these pesticides were detected most frequently in samples from urban areas in the carbonate-rock aquifers. Pesticides with highest use-atrazine and metolachlor-were among the most frequently detected pesticides in domestic and public-supply wells ( fig.…”

Evaluating Changes in Matrix-Based, Recovery-Adjusted Concentrations in Paired Data for Pesticides in Groundwater

“…Pesticides detected in rivers draining agricultural areas (Liu et al, 2002;McConnell et al, 2007) are oft en the same as those detected in groundwater. Th e prevalence of these pesticides in the environment refl ects a combination of climatic, agronomic, pedologic, and geologic factors that determine the rate, period, and spatial extent of application, the inherent susceptibility of the aquifer, and the persistence of compounds once they are in the hydrologic system (Lindsey and Bickford, 1999;Barbash and Resek, 1996;Johnson et al, 2001;Gilliom et al, 2006;Hancock et al, 2008;G.C. Johnson et al, 2011).…”

“…Th e leaching potential of a pesticide compound can be evaluated by assessing the mobility of the pesticide through the soil and the persistence of the pesticide. Th e pesticides with the greatest potential for transport are those that are highly soluble in water (i.e., they do not readily adhere to soil particles) as indicated by low soil adsorption coeffi cients (K oc ) and that are relatively persistent in the environment, as indicated by low rates of decay (long soil half-lives) (Lindsey and Bickford, 1999;G.C. Johnson et al, 2011).…”