ABSTRACT

Analyses of ground water from 68 monitoring wells installed downgradient from the eastern boundary of the Defense General Supply Center indicate that volatile-organic compounds are present in both the upper unconfined aquifer and the lower confined aquifer. The principal contaminants in the aquifers are trichloroethene and 1,2-trans-dichloroethene. Chemical analyses and water-level data indicate that the unnamed creek flowing along the eastern boundary of the Federal property acts as a hydrologic discharge boundary and prevents eastward movement of contaminated ground water beyond the creek in the upper aquifer. Analyses of water in lower aquifer wells during 1985-89 indicated that contaminants in the lower aquifer had moved downgradient about 200 feet beyond the boundary of the Federal property. Subsequent analyses during 1989-90 indicate that contaminants have moved as much as 400 feet beyond the boundary of the property in the lower aquifer.

The rate of movement of contaminated ground water in the lower aquifer cannot be determined accurately because of natural degradation processes that deter the downgradient migration of the plume; in addition, precise locations and dates of disposals and spills are not available. Aquifer-test data indicate that ground water flows at about 90 feet per year in the upper aquifer and at about 200 feet per year in the lower aquifer. On the basis of the distance the contaminants have moved from their possible sources, contaminant migration is about 80 percent slower than ground-water flow, indicating that the contaminants are being degraded by natural processes.


Powell, J.D., Wright, W.G., Nelms, D.L., and Ahlin, R.J., 1990, Ground-water contamination and movement at the Defense General Supply Center, Richmond, Virginia: USGS Water-Resources Investigations Report 90-4113, 36 p.


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