Article

Evaluating Nitrate Management in the Volusia Blue Springshed

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Abstract

This investigation evaluated five hypothetical scenarios relating nitrate sources in the recharge of the Volusia Blue Spring to eutrophication in the St. Johns River. In the Volusia Blue recharge area of Florida, decades of nitrate loadings have impacted the quality of springwater discharged from the confined Floridan aquifer. Simulators and field observations were used to develop and define a procedure for the first time by which local and Florida state agencies can better manage nitrate pollution. The simulations were based on population growth projections and nitrogen loads from treated wastewater discharges, septic tanks, and fertilized areas. A one-tailed t-test comparing observed with simulated nitrate values in spring discharge indicates that there is insufficient evidence of discrepancies between observed and simulated results. Results from the simulation of five nitrate management scenarios were used to estimate probable construction costs that were compared with mg L-1 of nitrate removed. Constructed wetlands and targeted septic tank removal were the two most cost-effective nitrate management approaches. However, septic tank removal resulted in the greatest benefit with a 36% nitrate decrease in a 39-year projection of springwater quality.

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... Over the past few decades, the nitrate-N concentrations in Florida's springs have significantly exceeded the 0.35 mg/L standard as a result of human activities (Katz et al., 2009) such as, over fertilization of agricultural lands and lawns, leakage from septic tanks, polluted stormwater runoff from transportation corridors, and contamination from wastewater effluent (Reed et al., 2018). An analysis of 328 private drinking water wells in Florida revealed that 66% of the wells were heavily contaminated by nitrate (FDEP, 2012). ...
Article
Understanding the effects of best management practices (BMPs) on nitrate reduction in karst aquifers is critical for spring restoration. In this study, Conduit Flow Process (CFPv2) and Conduit Mass Three-Dimensional (CMT3D) models were applied to evaluate nitrate removal for Silver Springs in Florida using blanket filters composed of biosorption-activated media (BAM). As the inputs of the model, the spatial and temporal variability of nitrate-N concentration in groundwater recharge was estimated as a function of population and land use, reflecting both point and non-point sources of nitrate. Additionally, the spatial heterogeneity of nitrate removal efficiency in the soil was considered in the evaluation. The model estimates that conduit flow accounts for 48% of spring discharge and 47% of nitrate-N mass transport on average, and the contributions of conduit to flow and nitrate mass transport are higher during wet years. The net effect of nitrate reduction in spring discharge was evaluated for two BMP scenarios, i.e., implementing BAM-based blanket filters in 26 stormwater retention basins and 50% of the urban area. The net effect of the BMP on nitrate reduction for Scenario 1 is limited; whereas, for Scenario 2, the nitrate-N concentration will be reduced to 1.08 mg/L in 2026 for a nitrate removal efficiency of 74% (i.e., a 4.9% reduction relative to the baseline condition). This study suggests that the BAM-based blanket filters benefit is likely to scale with penetration (i.e. greater water quality benefits can be expected with greater BMP implementation). Further, this study shows that whether BAM-based blanket filters leads to net water quality improvements or degradation depends on whether BAM removes more or less nutrients from stormwater than the unaltered soil profile. The simulated effects of the BMP on nitrate reduction may serve as an additional guidance for water resources managers to make decisions on investments in nutrient reduction technologies for spring restorations in karst systems.
... A water-balance model for a karstic aquifer in Okinawa, Japan simulated nitrate concentrations at the sub-basin scale to assess the impact of dam construction (Yoshimoto et al., 2011). MODFLOW and the Modular 3-Dimentional Transport Multi-Species (MT3DMS) contaminant transport model were used to assess nitrogen management strategies in the Volusia Blue spring area of the Floridan aquifer in Florida, USA (Reed et al., 2018). Similarly, MODFLOW and MT3DMS models were part of a hydro-economic model assessing fertilizer standards in a portion of Spain to lower nitrate values in the groundwater of the Mancha Oriental system (Peña-Haro et al., 2010). ...
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Protecting karst aquifers from nitrate contamination is an issue of global concern due to the inherent vulnerability of karst aquifers to contamination and the negative health effects of elevated nitrate levels. Hydrological and transport models were developed to assess nitrate transport within a karstic aquifer located in an area with both semi-arid and sub-humid climate conditions. Groundwater flow through the aquifer matrix and conduits was simulated with CFPv2, an experimental version of the Conduit Flow Process (CFP) version of the MODular FLOW (MODFLOW) groundwater model. Nitrate transport was simulated with the experimental Conduit Mass Transport Three-Dimensional Model (CMT3D). The hydrologic calibration of the steady-state model was successful based on a scaled Root Mean Squared Error (RMSE) of 4.9 % for hydraulic heads and percent errors of 3.0 % and 6.6 % for the two major springs in the area. Performance of the transient hydrologic model exceeded the performance of the existing Equivalent Porous Media (EPM) model with a scaled RMSE of 2.2 % and springflow errors of 1.5 % and 2.8 % for the major springs. Similarly, nitrate calibration was successful with all Percent Bias (PBIAS) values between ±25 %. Additional calibration statistics including a two-tailed t-test indicated successful calibration. The CMT3D model corroborates prior research findings that anthropogenic sources as well as biogenic wastes are important sources of nitrate to the aquifer. The methodology used in this study represents an additional tool for watershed managers to address nitrate contamination within karst aquifers.
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Agriculture is the most extensive source of nitrate to water resources. A high concentration of nitrate contamination in drinking water is a significant risk to human health. The aim of this study was to select the appropriate combination of organic substrates and zero-valent iron (ZVI) to use as an electron donor for denitrification in a permeable reactive barrier. From the results, a nitrate-removal efficiency of more than 85% was achieved for all the tested organic substrates at ambient temperature (25±5°C), neutral pH, and under anaerobic conditions. The initial nitrate concentration of 150 mg L-1 and the organic substrates (50 g L-1 concentration) were tested in this study. Different dosages for ZVI (10, 30, 50, and 70 g L-1) were also investigated. Using a mixture of rice husk and rice straw as an electron donor led to the highest nitrate-removal efficiency (93.3%). Using ZVI as an electron donor yielded a lower nitrate-removal efficiency than using the same amount of the organic substrate. However, the use of ZVI coupled with the organic mixture resulted in a higher nitrate-removal rate than when only the organic mixture was used. The nitrate-removal rate increased up to threefold when using ZVI wire, a type of waste from a lathe factory, mixed with the organic mixture as an electron donor.
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Most of earth’s population depends on onsite sewage systems to dispose of their wastewater to the environment. Samples used to estimate contaminant transport in the environment have typically been collected from nitrogen loads external to the septic tank. Here we characterize the isotopes of boron, nitrate–nitrogen and nitrate–oxygen in partially clarified liquid collected directly from within septic tanks located in Florida. Among other parameters, total Kjeldahl nitrogen (TKN) and total boron were also evaluated. Nitrate–nitrogen isotopes from three samples ranged from +1.25 to +10.00‰, and boron isotopes from five samples ranged from +8.8 to +31.3‰. Nitrate–oxygen isotopes ranged from −3.23 to +19.96‰ and were indicative of an anoxic environment. On average, residential septic tanks were found to contain 96 µg L⁻¹ total boron and 63 mg L⁻¹ TKN. Utilizing isotopes of boron, among other parameters, our findings show that the partially clarified liquid in septic tanks contains a distinguishable δ¹¹B signature.
Article
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Wetlands, as active riparian areas in denitrification processes, are largely dependent on the environment. The main objective of this paper is to evaluate changes in the denitrification potential of wetland soils at laboratory scale promoted by climatic and seasonal influences. Several batch denitrification tests were performed with fresh wetland soil (peat) from Brynemade (Denmark) under: three different temperatures (20, 10, and 5°C), drought period, and freeze-thaw event. Results show that nitrate was eliminated in all the experiments in percentages over 90%. However, not all the nitrate removed was reduced to nitrogen gas via the denitrification process; dissimilatory nitrate reduction to ammonium (DNRA) was also present. In fact, the percentage of total nitrogen eliminated at the end of the tests was: 79.7% at 20°C, 84.1% at 10°C, 82.9% at 5°C, 41.0% in the dried soil, and 57.0% in the frozen soil. Thus, it can be concluded that the drying and freezing of the soil favor the DNRA process. Furthermore, in these conditions, nitrite increased sharply and was also accumulated possibly, as a DNRA or denitrification intermediate. Nitrate removal was fitted to a zero-order model, and an increase of the denitrification rates with the temperature was observed (3.8 mg L−1 d−1 at 20°C, 3.0 mg L−1 d−1 at 10°C, and 2.9 mg L−1 d−1 at 5°C). These overall rates were modeled as a function of temperature by the Arrhenius equation and activation energy of 12.88 kJ mol−1 was determined. The fact that the activation energy is low in this work (unstirred batches) compared to previous publications (stirred batches) could be the result of a strong restriction on the nitrate mass transfer in the soil vs. reaction kinetics, which masks kinetic regulating factors of the denitrification rate. Thus, the variation of the denitrification rate with temperature is possibly the result of a combination of changes in mass transfer (diffusive transport) and kinetic constant variation, successfully modeled by the Arrhenius equation.
Technical Report
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GeoHydros was originally contracted by Ginnie Springs Outdoors, Inc. to evaluate a regional-scale steady-state equivalent porous media groundwater flow model of north Florida that was developed for the Suwannee River Water Management District (SRWMD) in 2008 by the SDII Global Corporation (NFM-08) and compare the results of that model to the results of a sub-regional scale steady-state hybrid groundwater flow model of the western Santa Fe River basin that GeoHydros had previously completed for Coca-Cola North America in 2008 (WSFM-08). The stated purpose of the NFM-08 is for use in the evaluation of “the effects of existing and proposed groundwater withdrawals on the aquifers … of the District” primarily to support the evaluation of impacts associated with consumptive use permit applications, and the designation and management of Minimum Flows and Levels. The goal of the WSFM-08 was to accurately simulate karstic groundwater flow patterns to the 1st and 2nd magnitude springs on the Santa Fe River under both low water and high water conditions. The purpose of GeoHydros’ investigation was three-fold: 1) to identify any design issues that would be reasonably expected to diminish the reliability of the model’s assessments of impacts to spring and river flows associated with cumulative groundwater pumping in and surrounding the SRWMD; 2) to evaluate the efficacy of the equivalent porous media approach through a comparison of the SDII model results in the western Santa Fe River basin to results obtained from the hybrid model; and 3) to describe the key groundwater modeling processes, reasonable expectations for model quality and disclosure, and the degree to which the NFM-08 meets these expectations. The NFM-08 was evaluated on the basis of three broadly accepted criteria for quality of a groundwater flow model: 1) the degree to which simulated groundwater levels and flows match real-world conditions; 2) the degree to which the framework of model parameters adheres to a reasonable conceptualization of the hydrogeologic conditions being simulated; and 3) the appropriateness of the mathematical representation of the flow processes. In addition, the supporting documentation was evaluated to determine the degree to which it provides the reader with a complete and transparent understanding of the model development process, all underpinning assumptions, and any limitations that have bearing on the model’s intended applications. The Upper Floridan Aquifer is represented in the NFM-08 as an equivalent porous media, homogenous within 5,000 x 5,000 foot grid blocks, that does not contain conduits though conduits are known to be ubiquitous throughout much of the model domain and to have evolved as a consequence of karstification. Because the model does not address conduit flow, it relies on implausible parameter values to force the porous media groundwater flow equations to simulate observed spring flows and river gains. As a result, the simulated groundwater surface poorly represents observed groundwater levels and local hydraulic gradients. The NFM-08 was intended to calibrate to average groundwater levels and spring flows occurring between June 1, 2001 and May 31, 2002, however it represents both poorly. SDII defined the model’s calibration target as +/- 5% of the total change in observed Upper Floridan Aquifer groundwater levels as measured in 676 wells across the model domain. The NFM-08 Model domain spans the width of the Florida peninsula from South Georgia to southern Marion County. The calibration criterion of +/- 5 feet was only applied to the average of the absolute differences between simulated and observed values at the 676 wells. The resulting criterion is broad relative to the observed variation in groundwater levels during the calibration period, during which groundwater levels in more than 50% of the wells in the SRWMD having at least monthly measurements varied by less than 3 feet. Application of the chosen calibration criterion allowed widespread and large magnitude differences between observed and simulated groundwater levels across the model domain. Differences at 147 of 534 wells (~28%) within the SRWMD were larger than the 5-foot criterion. Differences at more than 10% of those wells distributed throughout the central Suwannee River and Santa Fe River basins were greater than 10 feet. Where such large-magnitude errors exist, the model cannot reliably predict groundwater level fluctuations and the widespread distribution of large-magnitude errors significantly undermines the reliability of the predictions throughout the model domain. The model cannot simulate flow to discrete springs as is implied in the SDII report because the resolution of the model is predicated on the use of 5,000 X 5,000 foot grid cells and many of the springs described as correctly simulated fall within a single grid cell. Individual spring flows within a single grid cell were accounted for through the use of multiple conductance terms associated with Drain and River assignments to the grid cells. The conductance terms describe the ability of the streambed at the respective locations to transmit water from the aquifer to the river thereby acting as confining material that separates the springs and rivers from the Upper Floridan Aquifer. The use of the streambed conductance terms is inconsistent with well-established unconfined conditions of the Upper Floridan Aquifer existing at the majority of the simulated springs. The values assigned during the calibration process are implausible because they equate to the presence of substantial confining material where confining material does not exist. As a consequence and in almost all instances, the match between simulated and observed spring and river flows was achieved at the expense of realistic simulations of groundwater levels at the rivers. The simulated levels deviate from observed values by more than 10 feet along much of the central Suwannee and western Santa Fe Rivers. These deviations were not discussed or disclosed in the report accompanying the NFM-08. Discrepancies between observed and simulated groundwater levels at the rivers exceeded the 5-foot criterion for matching groundwater levels at more than 50% of the assignments, some exceeding 20 feet. Considering that river stage is known to match the groundwater level in the unconfined portion of the Upper Floridan Aquifer where the rivers flow directly on Upper Floridan Aquifer limestones, these discrepancies raise the average difference between observed and simulated groundwater levels in the SRWMD to 5.6 feet, which violates SDII’s criterion for model calibration. The absence of conduits from the model design required the calibration effort to rely on implausible hydraulic conductivity, recharge, and streambed conductance assignments in order to force the model to approximate hydrogeologic conditions that the underlying mathematical equations were not intended to represent. Hydraulic conductivities deviate from values derived from aquifer performance tests and reported by the US Geological Survey (USGS) by 0.5 to 2.6 orders of magnitude across much of the model domain. Assigned recharge distributions fail to correlate to precipitation or documented land use. The magnitude of assigned recharge results in simulated groundwater discharge to rivers and streams that flow to the Gulf of Mexico that exceeds measured values by between 300 and 950 cfs, or when compared to sub-watershed scale discharge, exceeds measured values by between 231 and 750 cfs. The streambed conductance terms imply the existence of confining material in the unconfined part of the aquifer that does not exist. As a consequence of implausible parameter values, the model violates the assumptions underpinning the groundwater flow equations with which it was constructed throughout approximately half of the model domain including much of the Suwannee River basin. The model under-estimates the measured impacts to Upper Floridan Aquifer groundwater levels from municipal groundwater pumping at two locations evaluated, the City of Gainesville and Fernandina Beach, by more than 30 feet in both cases. The model under-estimates the capture zone for City of Gainesville’s well field by more than 100 square miles, and it fails to accurately simulate documented groundwater flow paths to the Santa Fe and Ichetucknee Rivers. Model boundaries were not designed or assigned according to standard practices that focus on limiting the degree to which simulated pumping is derived directly from external model boundaries. Approximately 38% of the simulated flow through the UFA is to external model boundaries (24% to the general head nodes defining the southern model boundary, and 14% to the constant head nodes defining the Gulf of Mexico boundary). Removing the assigned pumping (not including wells used to represent river siphons) revealed that the boundary conditions permit more than 40% of the simulated well extractions to intercept flow that would otherwise be to the external boundaries (35.5% to the general head nodes representing the southern boundary, and 5.1% to the constant head nodes representing the Gulf of Mexico). These boundary condition effects are not disclosed in the NFM-08 report and the associated limitations on the model’s ability to reliably predict impacts to groundwater levels or flows have therefore not been disclosed to readers or model users. These problems reveal that the NFM-08 is poorly constructed and not reliable for its stated purpose. Furthermore, the model report is misleading because it does not disclose the necessary information for readers or model users to indentify the degree to which the model fails to meet these criteria. With respect to the technical practicability of improving on these model limitations, comparisons of the NFM-08 (equivalent porous media model) to the WSFM-08 (hybrid model that includes conduits) reveal substantial differences that are consequential to groundwater resource management decisions. The hybrid model, in which the UFA was simulated as a dual-permeability framework consisting of conduits embedded in a porous media, achieved substantially better matches to observed groundwater levels and spring flows under both low-water and high-water conditions where the improvement stemmed from significantly different simulations of groundwater flow patterns and velocities. Where the NFM-08 failed to simulate tracer defined groundwater flow paths, the hybrid model accurately did so. Where the NFM-08 failed to match tracer-defined groundwater velocities, the hybrid model accurately did so. And, where the NFM-08 used unrealistically high hydraulic conductivities, resulting in an inability to simulate observed impacts to groundwater levels derived from municipal groundwater pumping in areas such as Fernandina Beach and the Gainesville municipal well field, the substantially lower hydraulic conductivity values used in the hybrid model support the simulation of much larger simulated drawdowns in the aquifer matrix that are more consistent with observed conditions. These discrepancies demonstrate that the equivalent porous media approach is incapable of adequately simulating the patterns of groundwater flow to springs and therefore the impacts of groundwater pumping on those flow patterns. Moreover, the fact that the hybrid model was constructed with commercially available, widely used software as well as publically available datasets demonstrates that the decision to use and rely on equivalent porous media assumptions and methods cannot be argued to be based on technological impracticability. In summary, the flaws in the NFM-08 and the manner in which it is being used by the SRWMD identified through this investigation impart substantial limitations on the model’s assessments of the magnitude and spatial distribution of impacts to spring and river flows associated with current and future groundwater extractions. The limitations have direct bearing on water management district consumptive use permit application review processes and Minimum Flows and Levels programs. The most relevant conclusions in this regard are: 1) the NFM-08 is poorly constructed and fails to meet broadly accepted measures of quality, and therefore cannot be reliably used to simulate or predict impacts to groundwater flows and levels created by groundwater extractions within or surrounding the SRWMD; 2) the approach and software used for the NFM-08 do not represent the best available technology; 3) alternative methods and software could be, and could have been leveraged to build a better model that provides substantially more reliable predictions; and 4) by using the NFM-08, the SRWMD is not pursuing a reasonably conservative approach to the characterization and mitigation of impacts to spring and river flows associated with groundwater withdrawals.
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The aquifer can be subdivided into an upper 10- to 15-m thick oxic zone that contains O2 and NO3-, and a lower anoxic zone characterized by Fe2+-rich waters. The redox boundary is very sharp, which suggests that reduction processes of O2 and NO3- occur at rates that are fast compared to the rate of downward water transport. Nitrate-contaminated groundwater contains total contents of dissolved ions that are two to four times higher than in groundwater derived from the forested area. The persistence of the high content of total dissolved ions in the NO3--free anoxic zone indicates the downward migration of contaminants and that active nitrate reduction is taking place. Nitrate is apparently reduced to N2 because both nitrate and ammonia are absent or found at very low concentrations. Possible electron donors in the reduced zone of the aquifer are organic matter, present as reworked brown coal fragments from the underlying Miocene, and small amounts of pyrite at an average concentration of 3.6 mmol/kg. Electron balances across the redoxcline, based on concentrations of O2, NO3-, SO42- and total inorganic carbon (TIC), indicate that pyrite is by far the dominant electron donor even though organic matter is much more abundant. Groundwater transport and chemical reactions were modeled using the code PHREEQM, which combines a chemical equilibrium model with a one-dimensional mixing cell transport model. -from Authors
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Groundwater chemistry and tracer-based age data were used to assess contaminant movement and geochemical processes in the middle Claiborne aquifer (MCA) of the Mississippi embayment aquifer system. Water samples were collected from 30 drinking-water wells (mostly domestic and public supply) and analyzed for nutrients, major ions, pesticides, volatile organic compounds (VOCs), and transient age tracers (chlorofluorocarbons, tritium and helium-3, and sulfur hexafluoride). Redox conditions are highly variable throughout the MCA. However, mostly oxic groundwater with low dissolved solids is more vulnerable to nitrate contamination in the outcrop areas east of the Mississippi River in Mississippi and west Tennessee than in mostly anoxic groundwater in downgradient areas in western parts of the study area. Groundwater in the outcrop area was relatively young (apparent age of less than 40 years) with significantly (p 50 m depth) indicated contaminant movement from shallow parts of the aquifer into deeper oxic zones. Given the persistence of nitrate in young oxic groundwater that was recharged several decades ago, and the lack of a confining unit, the downward movement of young contaminated water may result in higher nitrate concentrations over time in deeper parts of the aquifer containing older oxic water.
Article
The objective was to collect detailed data on the progress of the N flush to facilitate finding a model to describe the process. Samples of three soils were preincubated, dried, rewetted, and incubated at 30°C for up to 20 d with periodic samplings. Cumulative net N mineralized in undried samples was adequately described by zero-order kinetics. In contrast, describing cumulative net N mineralized in dried and rewetted samples required a model with two N pools, one following zero-order and the other first-order kinetics. Drying and rewetting the soils also significantly increased the background mineralization rate, suggesting transfer of N from a passive pool to the zero-order pool. -from Author
Article
A simplified, quasi-steady-state model has been formulated for groundwater denitrification using immobilized cells. The model takes into account the diffusion-limited penetration of nitrate and nitrite into the immobilized-cell biocatalyst particle, uniform intraparticle cell density, equivalent slab geometry for the spherical particle, zero-order intrinsic reaction kinetics of the immobilized cells, sequential reduction of nitrate to nitrite and nitrite to dinitrogen within the particle, no inhibition of the sequential reactions by either nitrate or nitrite, and ideal plug flow conditions in the bioreactor. As a result, the reaction in the bulk fluid of the plug-flow bioreactor can be described by a half-order kinetics, and the process is characterized by the half-order reaction rate constants for nitrate and nitrite reduction. These constants incorporate the intrinsic reaction kinetics of the immobilized cells, the size and packing density of biocatalyst particles in the reactor, and the effective diffusion coefficients of nitrate and nitrite in the particle matrix.
Article
The roles of NH.-N diffusion, NH.-N oxidation, NO3-N diffusion, and NO3-N reduction in controlling N loss from continuously flooded soil were evaluated in independent ex- periments. Applied NH,-N moved from zones of high NH4-N concentration to the zones of low NH4-N concentration. The average diffusion coefficient (D) for NH.-N in flooded soil ranged from 0.059 to 0.216 cm" day1 for different soils. Dif- fusion coefficients were influenced by soil type and soil-water content. Rate of NH4-N oxidation in the aerobic layer of flooded soil range from 1.2 to 3.5 /tg g'1 day1 in different soils. Nitrate diffusion into the anaerobic soil layer ranged from 0.96 to 1.91 cm2 day1, whereas NO3-N reduction rates were 0.32 to 0.52 day1. The slow rate of NH 4-N diffusion from the anaerobic soil layer to the aerobic soil layer and the slow rate of NH t-N oxidation in the aerobic soil layer indicate that these two processes are limiting steps in controlling N loss. Nitrate diffusion into the anaerobic soil layer and NO3-N reduction in the anaerobic soil layer were found to proceed at a faster rate and are not likely to limit N loss from flooded soil.
Article
A two-dimensional model representing flow and nitrate transport in groundwater was developed and applied to a hillslope of the Kervidy catchment. The objective of the modelling was: (1) to characterize better the flow and nitrate transport in the groundwater and to determine the characteristic times of the system; (2) to explore the consequences of changes in nitrate leaching to groundwater on nitrate concentration in stream water. The finite-difference code MODFLOW was used to simulate the distribution of hydraulic head within the groundwater. Nitrate transport was described by the convection equation solved using MT3D. MODPATH was also used to analyse flow paths and travel times in the groundwater. Four units were considered in the model: (i) the plough layer, (ii) the soil, (iii) the weathered shale and (iv) the fissured shale. Autotrophic denitrification in the shale and partly in the weathered shale was represented, as well as heterotrophic denitrification in the upper horizon of bottom land. A steady-state average flow was assumed with a spatially uniform groundwater recharge of 2 mm day−1, corresponding to the winter mean daily recharge observed in the Kervidy catchment. Nitrate recharge rate was fixed at 100 mg l−1, which is equivalent to a nitrogen flux of 165 kg ha−1 year−1. Six scenarios of nitrate leaching changes were analysed with the model. The first two correspond to spatially uniform decreases of the nitrate recharge rate to 80 and 60 mg l−1, respectively. In the other four scenarios, nitrate recharge rate was spatially distributed along the hillslope so that the average nitrogen flux remained equal to 165 kg ha−1 year−1. Simulated hydraulic heads were similar to observed values along the hillslope, except for the summit. The transport model reproduced the spatial pattern of nitrate concentrations observed in the weathered shale groundwater, a deviation appearing only in the nearest piezometer to the stream. Travel times within the groundwater appeared to be highly variable, from a few days up to 3 years. Scenario analysis showed that a significant decrease of stream nitrate concentration can be expected following a global decrease in nitrate leaching along the hillslope. However, the fall could be very gradual in time. Copyright © 2002 John Wiley & Sons, Ltd.
Article
This paper presents and implements a framework for modeling the impact of land use practices and protection alternatives on nitrate pollution of groundwater in agricultural watersheds. The framework utilizes the national land cover database (NLCD) of the United State Geological Survey (USGS) grid and a geographic information system (GIS) to account for the spatial distribution of on-ground nitrogen sources and corresponding loadings. The framework employs a soil nitrogen dynamic model to estimate nitrate leaching to groundwater. These estimates were used in developing a groundwater nitrate fate and transport model. The framework considers both point and non-point sources of nitrogen across different land use classes. The methodology was applied for the Sumas–Blaine aquifer of Washington State, US, where heavy dairy industry and berry plantations are concentrated. Simulations were carried out using the developed framework to evaluate the overall impacts of current land use practices and the efficiency of proposed protection alternatives on nitrate pollution in the aquifer.
Article
Recharge and contamination of karst aquifers often occur via the unsaturated zone, but the functioning of this zone has not yet been fully understood. Therefore, irrigation and tracer experiments, along with monitoring of rainfall events, were used to examine water percolation and the transport of solutes, particles, and fecal bacteria between the land surface and a water outlet into a shallow cave. Monitored parameters included discharge, electrical conductivity, temperature, organic carbon, turbidity, particle-size distribution (PSD), fecal indicator bacteria, chloride, bromide, and uranine. Percolation following rainfall or irrigation can be subdivided into a lag phase (no response at the outlet), a piston-flow phase (release of epikarst storage water by pressure transfer), and a mixed-flow phase (increasing contribution of freshly infiltrated water), starting between 20 min and a few hours after the start of recharge event. Concerning particle and bacteria transport, results demonstrate that (1) a first turbidity signal occurs during increasing discharge due to remobilization of particles from fractures (pulse-through turbidity); (2) a second turbidity signal is caused by direct particle transfer from the soil (flow-through turbidity), often accompanied by high levels of fecal indicator bacteria, up to 17,000 Escherichia coli/100 mL; and (3) PSD allows differentiation between the two types of turbidity. A relative increase of fine particles (0.9 to 1.5 microm) coincides with microbial contamination. These findings help quantify water storage and percolation in the epikarst and better understand contaminant transport and attenuation. The use of PSD as "early-warning parameter" for microbial contamination in karst water is confirmed.
Setting capacity charges for water and wastewater systems
  • S L Carroll
Carroll, S. L. (2005). "Setting capacity charges for water and wastewater systems." 〈http://www.frwa.net/uploads/4/2/3/5/42359811 /frwawhitepaper5capacitychargesimpactfees032408.doc〉 (Apr. 1, 2016).
Nutrient TMDL for Blue Spring (Volusia County) and Blue Spring Run (Volusia County), WBIDs 28933 and 28933A
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Florida Department of Health assessment of water quality protection by advanced onsite sewage treatment and disposal systems: Performance, management, monitoring
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Roeder, E., and Ursin, E. (2013). "Florida Department of Health assessment of water quality protection by advanced onsite sewage treatment and disposal systems: Performance, management, monitoring." 〈http://www .floridahealth.gov/environmental-health/onsite-sewage/research/advance dostdsfinalreportdraft.pdf〉 (Jan. 5, 2016).
Costs weighed for sewer retrofit near Wekiwa Springs
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