Date of Award

8-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

Christophe Darnault, Committee Chair

Committee Member

Lawrence Murdoch

Committee Member

Ronald Falta

Abstract

Wastewater reuse, particularly via the use of spray irrigation of treated effluent, is a common practice worldwide and can help lessen the impact of the overconsumption of water resources. The increased recharge to the subsurface that enhances weathering and erosion during the irrigation application process makes it important to characterize any changes in the land surface over time. The Living Filter at Pennsylvania State University receives on average 1.5 million gallons per day (MGD) of secondary treated wastewater effluent year round. This Living Filter has been in continuous operation in some capacity for the past 55 years without any significant issues related to geomorphologic processes. For over 50 years, nitrate as nitrogen (NO3-N) concentrations in the karstic groundwater system have fluctuated with time due to variations in the application rate of the effluent and concentration within the effluent. Although nitrate concentrations previously exceeded the federal maximum contamination levels (MCL) of 10 parts per million (ppm) in groundwater monitoring wells in and around the living filter, they are now below the MCL of 10 ppm ever since the early 2000's.

The objective of chapter two of this study was to identify and relate any bedrock fracture traces and surface depressions to any surficial or geomorphologic processes currently underway.

The objective of chapter three this study is to (1) model groundwater flow in the karst landscape to examine the hydraulic response of the aquifer to the recharge by wastewater irrigation of the Living Filter and (2) simulate the fate and transport of nitrate in the karst aquifer resulting from wastewater irrigation of the Living Filter site.

For chapter two, a manual process was developed in order to determine the trend and location of several fracture traces within the Astronomy site section of the Living Filter. The Living Filter is underlain by a massive dolomite with fractures trending near N-S that were previously documented using photogrammetry. A semi-automated isolation scheme was next used to identify and correlate closed hillslope depressions to the location of fracture traces in the Living Filter. A predominant but slight NE-SW trend was observed among fractures at N5E in the area north of the Pennsylvania Furnace Anticline. A high occurrence of depressions was noted in the area of fractures compared to non-fractured bedrock. The depressions in this area were found to have a net gain of 8,000 ft2 the result of which was from the net loss of 5,000 ft2 within the agricultural portion of the site and a net gain of 13,000 ft2 within the forested portion of the site. Cross sections of several depressions within cropped areas indicated a lower angle slope corresponding to a V-shape while depressions within forested areas were characterized by a traditional U-shape and previously established steeper slope.

For chapter three, a framework was developed to model the impact of treated wastewater and disposal of large volumes of wastewater for irrigation in agriculture and forestry land uses on groundwater nitrate contamination in a karst landscape of the Spring Creek Watershed, central Pennsylvania, in order to understand the long term contributions of nitrate to the unconfined karst aquifer below the "Living Filter" site. This study uses a numerical simulation model to examine groundwater flow and nitrate fate and transport in the karst landscape of the Spring Creek Watershed, central Pennsylvania, in response to aquifer recharge by wastewater irrigation of the Living Filter site. The simulation of nitrate fate and transport in the aquifer was conducted by developing a groundwater mass transport model using MODFLOW and MT3DMS. A number of predictive simulations for year 2015 and 2035 were carried out to evaluate the impact of treated wastewater and disposal of large volumes of wastewater for irrigation in agriculture and forestry land uses on groundwater nitrate contamination and concentrations. The calibrated groundwater model yielded a Root Mean Square Error of 5.41 for the area of irrigation and 24.67 for the entire modelled area. Results of the water quality model show that the aquifer recharge by wastewater reuse irrigation does not produce nitrate levels above 10 mgL−1 in the karstic landscape of the Spring Creek Watershed, thus meeting the regulatory standards for nitrate in groundwater. Results also demonstrated the sustainability of wastewater reuse irrigation practices for agriculture and forestry land uses.

These results will enhance the current understanding of the different morphologic characteristics of both forested and agricultural depressions in karst topography along with the nitrate dynamics of karstic wastewater effluent recharge systems. The workflows implemented here can be implemented in similar sites that display topographical variances from the bedrock fractures or increased nitrate concentrations from wastewater effluent recharge.

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