Date of Award

2008

Document Type

Senior Project

Degree Name

Bachelor of Science (BS)

Department

Geological Engineering

First Advisor

Dr. Scott F. Korom

Abstract

A rural electric cooperative (REC) proposes to build a 700 megawatt (MW) coal fired base load electrical generating station in north-central South Dakota. The plant would consist of a supercritical pulverized coal boiler and a steam turbine generator. Solid wastes generated through the operation of the boiler and associated plant air pollution control systems would be disposed at an onsite landfill. A 202-acre landfill with 10 percent slopes is proposed to manage approximately 685 tons of waste each day; a design capacity of 15,000,000 yd3 is required for the anticipated 50-year life of the facility. The objective of this report is to provide an engineering design for a solid waste landfill that is environmentally sound and economically feasible.

The design considers project site background information (soil, geology, and climate) and the regulatory requirements set forth in the State of South Dakota solid waste management rules. A variety of landfill liner, leachate collection, and cover system options were evaluated using the US EPA Hydrologic Evaluation of Landfill Performance (HELP) model. The HELP computer program is a hydrologic model of water movement across, into, through and out of landfills. A 24 in. thick compacted clay liner (CCL), a 48 in. thick CCL, and a composite liner consisting of a 60 mil high density polyethylene (HDPE) geomembrane overlying a compacted soil layer were evaluated with and without a leachate collection system. Two cover systems were evaluated to predict the performance of the closed landfill. Again, the HELP model was used to determine the predicted seepage rate through both 36 in. thick and 48 in. thick landfill cover systems and through the entire landfill. An economic evaluation of the various design options is also provided. The recommended design includes a 48 in. thick composite cover system and a 24 in. thick CCL bottom liner at a total estimated cost of $41,301 per acre.

At present, no site specific hydrogeologic information is available; important characteristics such as hydraulic conductivity and hydraulic gradient are not known. Calculations using a range of aquifer parameters and the gradients were completed to provide an envelope of contaminant travel time values. The US EPA Optimal Well Locator (OWL) program was used to account for the effects of dispersion in determining the lateral spacing of wells.

Based on the hypothetical landfill layout and groundwater flow regime depicted in this design study, the recommended monitoring network for the 202-acre site consists of 16 wells. Six wells would be either up- or side-gradient, while ten wells would be positioned downgradient. Downgradient wells would have a lateral spacing of approximately 70 m and would be located a maximum of 25 m from the landfill boundary. Calcium, sodium, boron, sulfate, bicarbonate and chloride are recommended as "indicator" parameters for the long-term monitoring of groundwater at the facility.

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