Announcing the Final Examination of Nyle Rice for the degree of Master of Science
In recent years, concentrations of nutrients such as nitrogen and phosphorus have increased in surface and groundwater resources, due in part to non-point source pollution associated with stormwater runoff. The elevated nutrient concentrations found in stormwater runoff have prompted the design of best management practices (BMP's) to mitigate the problem. The overall objective of this thesis is to analyze the hydrologic performance of innovative surface BMPs and investigate connections between the BMPs and groundwater flows to freshwater springs within a karst environment. The hydrologic performance of two novel stormwater BMPs, blanket filters and vertical reactors containing Bio-sorption Activated Media (BAM), are assessed in terms of capture efficiency and hydraulic retention time. The blanket filters are able to treat over 90% of the stormwater runoff entering a stormwater basin over a monitoring period of one year. Water content monitoring indicates that BAM has a maximum hydraulic retention time of 35 days. Capture efficiency of vertical reactors is less than 1% of runoff, suggesting they are more appropriate technologies for small contributing areas.
Tracking a conservative tracer from an injection point within a stormwater basin to nearby Silver Springs reveals several unique flowpaths and velocities of groundwater. Subsurface velocities observed in the basin ranged from 0.1 m/d to 1.4 m/d, while velocities from the injection well to the spring vary from 2.3 m/d to 13.5 m/d. The fastest travel times observed in the spring may represent flowpaths that include macropore/conduit flow through karst features, while the slower peaks may represent matrix flow. Natural soil matrix plays a vital role in nutrient transformations because nutrient reactions proceed at different rates due to the long contact times, in characteristic aquifers, before it is discharged. Conduits in karst aquifers reduce subsurface contact times, therefore nutrient transformations cannot occur causing elevated nutrient concentrations at the springs.
Committee in Charge: Kelly Kibler (Chair), Ni-Bin Chang (Co-Chair), Dingbao Wang
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