Master of Science / Department of Biological & Agricultural Engineering / Stacy L. Hutchinson / A field study was conducted at Fort Riley, Kansas from late spring to early winter of 2007 to investigate the ability of vegetated filter strips (VFS) to attenuate pollutants resulting from military activities, the impact of different management practices (i.e. burning and mowing) on VFS performance, and the effects of vegetation on hydrological components of VFS, especially infiltration and runoff. Two native tallgrass VFS sites, each comprising three plots, located in the military training area of Fort Riley were used for this study. Fifteen rainfall events were simulated on each site along with overland application of water containing nitrogen (N), phosphorous (P) and sediment. At the end of the season both VFS were managed by mowing or burning and a final rainfall simulation was done. Variables including rainfall, infiltration, runon, runoff, above ground biomass density, pollutant concentrations of runon and runoff, and soil moisture were measured and used in the data analysis. Hydrograph development, water balance, and mass balance calculations were carried out in order to calculate the pollutant trapping efficiencies (PTE) of the VFS. Statistical analysis was done by fitting several regression models. Mean comparisons were also done for variables and variance was decomposed into time, plot and site effects at an alpha = 0.05. Results showed that on average the VFS attenuated 84 % of total nitrogen, 24 % of total phosphorous and 95 % of sediments. Regression models showed that infiltration percentage and biomass density have a positive correlation with PTE. Runoff volume and PTE were negatively correlated. Soil moisture was negatively correlated with infiltration and time to runoff. With increasing biomass density, percentage of water infiltrating and time of concentration increased. Management practices, especially burning, tended to reduce PTE. Also, both management practices reduced infiltration percentage and time of concentration. PTE reduced with intensifying rainfall and increased when rainfall faded off. Phosphorous was the most sensitive pollutant for intense storm conditions followed by nitrogen, while sediment was comparatively insensitive.

Increases in reactive nitrogen from human actions have led to negative impacts on surface water (SW) and groundwater (GW) quality, and it is important to better understand denitrification processes in aquatic systems. The hyporheic zone has unique biogeochemical conditions, and is known to attenuate contaminants originating from SW and traveling through the hyporheic zone, together with necessary reactants. However, the ability of the hyporheic zone to attenuate contaminants from deeper upwelling GW plumes as they exit to SW is less understood. I used MODFLOW and SEAM3D to simulate hyporheic flow cells induced by riverbed dunes and upwelling GW together with mixing dependent denitrification of an upwelling nitrate (NO3-) plume. My basecase model scenario entailed dissolved organic carbon (DOC) and dissolved oxygen (DO) advecting from SW and DO and NO3- advecting from GW, which is typical of water in agricultural land uses. I conducted a sensitivity analysis to determine controls on mixing dependent denitrification. Mixing dependent denitrification increased with increasing hydraulic conductivity, decreasing lower bottom flux, as well as increasing DOC in SW and NO3- in GW. Non-mixing dependent denitrification also occurred when there was SW NO3-, and I found its magnitude was much greater than mixing dependent denitrification. Nevertheless, potential for hyporheic zones to attenuate upwelling NO3- plumes seems to be substantial, though highly variable depending on biogeochemical reaction rates as well as geomorphic, hydraulic and biogeochemical conditions. Stream and river restoration efforts may be able to increase both mixing and non-mixing dependent reactions by increasing hyporheic zone residence times. / Master of Science

The pollution of streams and rivers is a growing concern, and environmental guidance increasingly suggests stream restoration to improve water quality. �Solute retention in off channel storage zones such as hyporheic zones and floodplains is typically necessary for significant reaction to occur. �Yet the effects of two common restoration techniques, in stream structures and inset floodplains, on solute retention have not been rigorously compared. �We used MIKE SHE to model hydraulics and solute transport in the channel, inset floodplain, and hyporheic zone of a 2nd order stream. �We varied hydraulic conditions (winter baseflow, summer baseflow, and storm flow), geology (hydraulic conductivity), and stream restoration design parameters (inset floodplain length, and presence of in stream structures). �In stream structures induced hyporheic exchange during summer baseflow with a low groundwater table (~20% of the year), while floodplains only retained solutes during storm flow conditions (~1% of the year). �Flow through the hyporheic zone increased linearly with hydraulic conductivity, while residence times decreased linearly. �Flow through inset floodplains and residence times in both the channel and floodplains increased non linearly with the fraction of bank with floodplains installed. �The fraction of stream flow that entered inset floodplains was one to three orders of magnitude higher than that through the hyporheic zone, while the residence time and mass storage in the hyporheic zone was one to five orders of magnitude larger than that in floodplain segments. �Our model results suggest that in stream structures and inset floodplains are complementary practices. / Master of Science

Increased reactive nitrogen from human activities negatively affects surface water (SW) quality. The hyporheic zone, where SW and groundwater interact, possesses unique biogeochemical conditions that can attenuate contaminants (e.g., denitrification), including mixing-dependent reactions that require components from both water sources. Previous research has explored mixing-dependent denitrification in the hyporheic zone but did not address the effects of varying SW depth as would occur from storms, tides, dam operation, and varying seasons. We simulated steady and unsteady hyporheic flow and transport through a riverbed dune using MODFLOW and SEAM3D, and varied SW depth, degree of sediment heterogeneity, amplitude and frequency of sinusoidal fluctuations, among others to determine these effects. We found that increasing steady state surface water depth from 0.1 to 1.0 m increased non-mixing dependent aerobic respiration by 270% and mixing-dependent denitrification by 78% in homogeneous sediment. Heterogeneous hydraulic conductivity fields yielded similar results, with increases in consumption due to variation in correlation length and variance of less than 5%. Daily SW fluctuation, including variation of amplitude, period, and sinusoidal versus instantaneous changes had significantly less impact than longer-term trends in SW depth. There is potential for the hyporheic zone to attenuate NO3- in upwelling groundwater plumes. Restoration efforts may be able to maximize the potential for mixing-dependent reactions in the hyporheic zone by increasing residence times. / Master of Science / Increased nitrogen in runoff from human activities negatively affects surface water quality. The hyporheic zone is where surface water and groundwater interact, and the mixing between the waters can help to this nitrogen to undergo reaction (denitrification), potentially stopping the contaminant from spreading. Previous research has explored this idea, but has not addressed the impact of varying surface water depth, as would realistically occur due to storms, tides, dam operation, and varying seasons. We simulated both constant and fluctuating surface water conditions on a riverbed dune to see the effects on hyporheic flow and denitrification. Test variables included the surface water depth, the degree of sediment heterogeneity, the amplitude and frequency of surface water fluctuations. We found that increasing the steady-state surface water depth had the most dramatic increase on the amount of reaction undergone. This trend was also seen in heterogeneous sediment. Any daily-scale surface water fluctuations, including runs that varied the amplitude, period, and sinusoidal vs instantaneous changes in surface water depth, had significantly less impact than longer-term trends in surface water depth.

Diesel #2 is used to heat nearly 400,000 dwellings in Virginia. Home heating oil released from leaking underground tanks located adjacent to homes and residing in unsaturated soil adjacent to houses poses a potentially serious health risk. Specifically, the migration of hazardous vapors into buildings, known as vapor intrusion, can negatively impact indoor air quality in homes and public buildings (USEPA 2015). In this look-back study, we assessed the potential for petroleum vapor intrusion by sampling soil vapor at 25 previously remediated spill sites. Residual contaminants, in particular total petroleum hydrocarbons (TPH) and naphthalene, were detected in approximately 1/3 of the samples. Concentration levels were correlated to site variables (building type, remediation time, physiographic region) including previous abatement measures. Spill category as assigned by the remediation contractor was investigated in conjunction with these three site variables. Remediation time was the most promising predictive site variable, with visible trends downward in DEQ Category 2 sites with increased remediation time. Higher contaminant concentrations were found near basement-style dwellings, which we hypothesize is due to the wall of the basement blocking horizontal migration of contaminants and the flow of oxygen to the release source zone. We found that many sites exceeded the sub-slab risk target threshold in naphthalene concentration, which has negative implications on previous abatement strategy efficacy. / Master of Science / Diesel is used to heat nearly 400,000 residences in Virginia. Diesel released from leaking underground tanks located adjacent to homes and residing in soil adjacent to houses poses a potentially serious health risk. Specifically, the migration of hazardous vapors into buildings can negatively impact indoor air quality in homes and public buildings (USEPA 2015). In this study, we assessed the potential for vapor migration by sampling soil vapor at 25 previously remediated spill sites. Residual contaminants were detected in approximately 1/3 of the samples. Concentration levels were compared to site variables (building type, time since spill, soil type) including previous remediation activity. Spill category as assigned by the remediation contractor was investigated in conjunction with these three site variables. Remediation time was the most promising as a predictive site variable. Higher contaminant concentrations were found near dwellings with basements, which we hypothesize is due to the wall of the basement blocking horizontal migration of vapors. We found that many sites exceeded the target threshold in naphthalene concentration, which has negative implications on previous remediation effectiveness.