Date of Award
Master of Science (MS)
The McVille, North Dakota, Municipal Waste Stabilization Lagoon is situated above the McVille Aquifer, an unconfined glaciofluvial aquifer capable of significant water yields. The site contains a 3-D network of 29 monitoring wells. Standing waste-water is maintained in the clay-lined, primary-operating cell. Operating practices at the site entail periodic discharges of waste-water from the lined cell to an unlined cell, a procedure which results in rapid infiltration.
The shape and extent of the groundwater contaminant plume caused by the waste-stabilization process is best delineated by the distribution of chloride. Background wells contain less than 10 mg/L chloride. The area up to 60 m downgradient of the lined cell contains chloride levels at the waste water mean concentration of 256 mg/L. Further downgradient, the chloride levels decrease gradually to 130 mg/L, at a distance of 220 m from the lined cell. Contoured concentrations of total dissolved solids and electrical conductivity display a similar subelliptical plume shape. These three parameters are essentially nonreactive and appear to be attenuated by hydrodynamic dispersion.
Water-table elevations, redox potential and water chemistry, which were determined before and after discharge of waste water into the unlined cell, did not demonstrate a distinct effect resulting from this event. A slight rise in the water table elevations was detected 3 days after the discharge.
The most important hydrogeochemical interactions are a result of redox processes controlled by anaerobic bacteria. The infiltrating waste~water contains high disorganic carbon (DOC) concentrations. Oxidation of DOC I the aquifer results in lowering of the redox potential. Sulfate concentrations decrease beneath and shortly downgradient of the lined cell, as sulfate is reduced to sulfite, Elevated Fe and Mn levels immediately downgradient of the lined and unlined cells indicate reduction and dissolution of solid phases. Arsenic concentrations in this same area, where adsorbed ions are liberated as t e iron phase dissolves. The abrupt downgradient detion decrease in Fe, Mn and As suggests precipitation or adsorpelements. Field measured redox potentials extent of a plume of reducing water, along with the afore-mentioned inorganic constituents. The measured pe gradually increases, approaching background levels at the extreme downgradient edge of the site.
High ammonium values, up to four times the level within the waste-water, are present within the plume of reducing groundwater. High nitrate waters are contributed upgradient of the lagoon. Beneath and downgradient of the lagoon, the dissimilatory reduction of nitrate by anoxic Bactria forms ammonium. Ammonium is attenuated by adsorption and ion exchange. For Ca and Mg.
Bulger, Paul R., "Evaluation of the interaction between seepage from a municipal waste stabilization lagoon, McVille, North Dakota, and a shallow unconfined aquifer" (1987). Theses and Dissertations. 40.