Date of Award

8-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Duke Ophori

Committee Member

Matthew Gorring

Committee Member

Joshua Galster

Abstract

When little groundwater level data is available, the potential energy gradients reflected in the topography, assumed to be saturated to the surface, can be used to estimate the directions and relative rates of groundwater flow (flow systems). Darcy’s law conveniently relates groundwater water levels to the rate of groundwater flow. Toth (1963) related topography to groundwater flow systems. Flow systems can transport surface contamination, if present, to wells. The topography and likely contamination point source surface locations were used to create and contrast the flow systems impacting two wells in order to assess contamination risk. The two wells, Canoe Brook well no. 1 (CB-1) and Canoe Brook no. 3 (CB-3) are in the East Orange Water Reserve (EOWR). Only well CB-3 has high chloride ion concentrations. Both wells are completed in the EOWR’s sand and gravel aquifer, which is overlain by low permeability clay-rich till and underlain by a fractured bedrock aquifer (Towaco and Preakness Basalt Formations). The distribution of groundwater flow (flow systems), well capture zones and recharge zones were characterized using MODFLOW. Features of the topography, geology, flow systems, capture zones and recharge zones which might relate to contamination risk for each well were compared. The Canoe Brook well field was conceptualized as a 10,667 ft. by 8,888 ft. by 400 ft. deep drainage basin- with the Livingston half-basin on Canoe Brook’s west bank and the Millbum-South Mountain half-basin on its east bank. Maximum elevations in the Millbum-South Mountain halfbasin were double those in the Livingston half-basin. The domain’s three layers were represented using hydraulic conductivities typical for silty clay, sandy gravel and fractured bedrock, respectively. Consistent with Tôth s (1963) findings, high magnitude relief generated deeper surface-influenced groundwater flow (local flow systems). Well CB-3 was in high relief topography with low overall basin slope. The local flow systems were the dominant flow systems at CB-3. More relief features and lower basin slope meant more recharge starting points on the surface area, which caused more drainage over a wider area. There was no deep groundwater flow at CB-3. Well capture zones show the recharge starting points and flow path of the majority of the groundwater supplying a well. The well CB-3 capture zone directly received bulk transport from scattered recharges resulting in a capture zone with less integrity. Many recharges are overlain by roads. In addition, chloride dispersion downward could occur most easily into the CB-3 capture zone based on its shallow subsurface position, long length and flat shape. Simulated aquifer recharge was occurring directly above CB-3; chloride could disperse into the well itself. Geology also predisposed well CB-3 to contamination. The protective clay-rich till layer at CB-3 was the thinnest. The hydraulic and geological features of the well CB-1 were opposite to CB-3. Topographically, the basin slope was high and relief was low. The groundwater flow at CB-1 was marked by a deep intermediate flow system. The CB-1 capture zone had no recharges under roads. Its structure was deep, squat and fast flowing. No aquifer recharge occurred above the well. The protective clay layer at CB-1 was the thickest. In light of Toth’s topography-flow system relationships and Darcy’s law, the results of the simulation predict the long term impact of the development over regional recharges. With the loss of regional recharges, regional flow systems are replaced by local flow systems. High relief areas become more strongly influenced by surface-associated local flow systems. As a result, with regional development, high relief areas may become more prone to contamination from the surface.

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