Date of Award

2006

Document Type

Senior Project

Degree Name

Bachelor of Science (BS)

Department

Geological Engineering

First Advisor

Dr. Scott F. Korom

Abstract

Nitrate concentrations in the Karlsruhe aquifer (23,070 acres), located in north central McHenry County, North Dakota have been monitored by the North Dakota State Water Commission since 2001. The average nitrate-N concentration in the top ten feet of the aquifer was determined to be about 14.0 mg/L. The objective of this engineering design was to determine the location of shallow areas in the Karlsruhe aquifer where phytoremediation would be most suitable and to evaluate the effect of phytoremediation on attenuating nitrate-N concentrations. The determination of areas in the Karlsruhe aquifer where phytoremediation would be most effective was carried out through analysis of the average depth to water table in the spring and fall, and land use for that region. The potential phytoremediation areas were narrowed down further by accessing the location of primary discharge points in the aquifer. Cross-sections and flownets were utilized to gain a general understanding of groundwater flow beneath these areas. Calculations of nitrate-N loss were based on the hydraulic conductivity, porosity, hydraulic gradient, and the average nitrate-N concentration in the aquifer as well as the hybrid poplar’s nitrogen uptake ability. Overall, the influence of phytoremediation on nitrate-N concentrations in aquifer discharge was variable. The 66 ft long buffer was able to decrease the average concentration of 14 mg/L by about 50% to a value below the EPA-MCL when the hydraulic conductivity was 20 ft/day. The 30 ft long buffer decreased the initial nitrate-N concentration by only 20% when the hydraulic conductivity was 20 ft/day. Both riparian buffers had negligible effects on nitrate-N concentrations at maximum hydraulic conductivity. The geologic material comprising the Karlsruhe aquifer appears to have the greatest influence on the hybrid poplar’s ability to remove nitrate from the subsurface. The high hydraulic conductivity values for the aquifer create groundwater flow conditions in which the interaction between nitrate and the root zone is limited. However, it was recommended that a 66 ft long buffer be implemented along the Wintering River because the average nitrate-N concentration in the upper portion of the aquifer is above the EPA-MCL and a riparian buffer has the potential to decrease the concentrations to a suitable level.

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