Theoretical and Empirical Implications of Increasing Block Rates

Frasier, Marshall; Conradie, Beatrice; Hoag, Dana; ,

Theoretical and Empirical Implications of Increasing Block Rates

by Marshall Frasier,
Beatrice Conradie,
Dana Hoag,

Document Type: Proceeding Paper

Part of: WRPMD'99: Preparing for the 21st Century

Abstract:

(No paper) The U.S. Army disposed chemical agents, laboratory materials, and unexploded ordnance at the O-Field landfill from before World War II until at least the 1950s. Soil, ground water, surface water, and wetland sediments in the O-Field area were contaminated from the disposal activity. The site is located in the Atlantic Coastal Plain and is underlain by a complex series of Pleistocene and Holocene age sediments formed in various fluvial, estuarine and marginal marine hydrogeologic environments. A transient finite-difference ground-water-flow model was used to simulate flow as well as the effects of a pump-and-treat remediation system designed to capture contaminated ground water from the water-table aquifer before it reaches an adjacent estuary, a tributary to the Chesapeake Bay. The remediation system consists of 14 extraction wells located downgradient of the landfill and upgradient of the estuary. Linear programming techniques were applied to the ground-water-flow model in order to determine optimal pumping scenarios for the well field. The objective function involves varying pumping rates and frequencies to maximize capture of ground water from the water-table aquifer. At the same time, the amount of water extracted and needing treatment is minimized. The constraints placed on the system insure that only ground water from the landfill is extracted and treated. To do this, a downward gradient from the disposal area toward the extraction wells must be maintained. Similarly, the wells can not be pumped to the extent that they cause a downward gradient from the estuary to the well field. The total volume of water extracted must not exceed the treatment plants maximum capacity, nor can any well be pumped beyond its recharge capacity. Finally, a well can not be pumped so that the water level is drawn down below the midpoint of the well screen. Initial efforts using generalized constraints indicate that the objective function can be met by pumping all the wells at rates between 1.9 and 5.5 gallons per minute.

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