Time Domain Reflectometry Surface Reflections for Dielectric Constant in Highly Conductive Soils

This paper presents a model-based approach to determine dielectric constants from time domain reflectometry (TDR) measurement in highly conductive soils. It makes use of information contained in the TDR signal from the reflection at the surface of the soil rather than the reflection from the end of the probe. The TDR method is widely used to determine the volumetric water content of soils. Commonly used information from the TDR signals includes the apparent dielectric constant and the electrical conductivity. The apparent dielectric constant is generally measured by analyzing the travel time of electromagnetic waves reflected from the end of the soil probe. In soils with high electrical conductivities, the attenuation of the signal can eliminate the reflection from the end of the probe, which limits the application of TDR to these materials. A simplified frequency-independent dielectric model is utilized to invert the dielectric constant from the reflected signals at the soil surface. Results indicate that the dielectric constant can be determined with reasonable accuracy by the proposed approach for soils with high electrical conductivity, where the conventional travel time analysis fails due to significant signal attenuation.     

Intrusion within a Simulated Water Distribution System due to Hydraulic Transients. II: Volumetric Method and Comparison of Results

A pilot-scale test rig was used to simulate intrusion behavior associated with hydraulic transient initiated by rapid valve closure in a water distribution system. In Part I, the test rig apparatus and operating conditions were described and intrusion volumes were reported based on a chemical tracer and mass balance calculations. In this paper, the experimental study is extended to determine intrusion volumes by a volumetric method that used video recordings of water fluctuations in the observation column. The results obtained using the volumetric and chemical tracer methods were compared to theoretical calculations. Intrusion volumes associated with a 12.7-mm (1/2-in.) diam orifice were evaluated in addition to 3.2 (1/8-in.) and 6.4-mm (1/4-in.) orifices. The impact of the external head on the intrusion volume was also assessed by comparing results using 0.91 (3 ft) versus 1.37 m (4.5 ft) of external head. The average intrusion volumes obtained using the volumetric approach ranged from 47.3 to 550.2 mL. These volumes were 64–298% greater than intrusion volumes determined by the chemical tracer method reported in Part I. However, the theoretical calculations indicate that the volumetric approach could underestimate intrusion volumes by as much as 50%.     

Spatial Variation of Sediment Sulfate Reduction Rates in a Saline Lake

Devils Lake in North Dakota is a terminal, multibasin, saline lake with an overall surface area that is currently approximately 44,520?ha (110,000?acres). Lake elevation has increased by more than 7?m within 10?years, and vast areas of prairie and cropland have been flooded. The lake is rich in sulfate, and water column sulfate concentrations are relatively uniform within each of the five major basins, but increase from 3.1?mM (300?mg/L) in West Bay to 31?mM (3,000?mg/L) in East Devils Lake. Sediment cores were collected from three of the basins at different water depths, and used in laboratory studies to evaluate the spatial distribution of sulfate-reducing bacteria (SRB) activity in the lake sediments. The high sulfate concentrations within the experimental sediment cores suggest that the activity of SRB is limited by the availability of suitable electron donors rather than by the availability of sulfate and that SRB activity can be defined by a zero-order volumetric rate constant (K0). Experimentally determined K0 values ranged from 11?to?88?mmol SO42? m?3?day?1. The water depths from which sediment cores were collected in Devils Lake are related to the elapsed time since inundation by the rising lake level. It was found that time since inundation influences the observed K0 value. Mean K0 values for cores from an average depth of 4.8?m (submergence time of about 5?years), and 9.4?m (submergence time of about 28?years) were 62 and 17?mmol SO42? m?3?day?1, respectively. The significant difference (two-tailed t-test, p<0.05) suggests that SRB activities in the Devils Lake sediments change with submergence times. A uniform sulfate reduction rate applied to all Devils Lake sediments is therefore only a crude approximation of reality.     

Disinfection By-Product Formation during Long-Term Water Storage in Alaska

In many areas of Northern and Western Alaska, small streams and shallow lakes serve as community raw water supplies. These water supplies freeze completely during winter. In order to supply drinking water during the 6–9 month winter, communities store water that was treated during summer. A chlorine residual is maintained in the stored water. Raw water sources derived from surface water may be heavily laden with dissolved organic matter. At utilities where organic matter escapes treatment, the potential for accumulation of disinfection by-products (DBPs) during storage is a significant health concern. The following study was performed to evaluate this potential threat. Water was collected from five operating utilities, four that normally store water for 6–9 months and one that produces drinking water year-round. Raw, filtered (i.e., unchlorinated) and “finished” (i.e., filtered and chlorinated) water samples were collected during the summer pumping season and stored in the laboratory for 8 months. In order to mimic practice in the field, the chlorine residual was maintained in the finished water for the full storage period. While the concentration of DBPs in the finished water varied over the study period, there was not a statistically significant trend from the third to the eighth month of storage. The observed DBP values were strongly a function of the type of treatment system used. Those systems passing more organic matter had higher DBP values throughout the storage period. The ultraviolet absorbance at 254 nanometers ?start(UV254)end? decreased continuously in the finished water coincident with chlorine consumption. ?startUV254end?, often used as a surrogate for DBPs, remained constant during the entire storage periodin raw and filtered water samples. Filtered water that was stored prior to chlorination accumulated fewer DBPs than finished water that was continuously chlorinated during the storage period. This result suggests that storing filtered water instead of finished water for long periods would limit DBP exposure to consumers. This conclusion was based on a comparison of DBP formation potentials (i.e., raw and filtered water) to DBPs (i.e., finished water). It is important to note that DBP formation potentials are based on a ?start24?hend?chlorine contact time. If long term storage were provided for filtered water, a smaller volume of secondary storage would still be needed to provide contact time for disinfection.     

Postconstruction Changes in the Hydraulic Properties of Water Balance Cover Soils

Hydraulic properties of soils used for water balance covers measured at the time of construction and one to four years after construction are compared to assess how the hydraulic properties of cover soils change over time as a result of exposure to field conditions. Data are evaluated from ten field sites in the United States that represent a broad range of environmental conditions. The comparison shows that the saturated hydraulic conductivity (Ks) can increase by a factor of 10,000, saturated volumetric water content (θs) by a factor of 2.0, van Genuchten’s α parameter by a factor of 100, and van Genuchten’s n parameter can decrease by a factor of 1.4. Larger changes occur for denser or more plastic fine-textured soils that have lower as-built Ks, α, and θs and higher as-built n, resulting in a reduction in the variation in hydraulic properties that can be attributed to compaction. After two to four years, many water balance cover soils can be assumed to have Ks between 10?5 and 10?3?cm/s, θs between 0.36 and 0.40, α between 0.002 and 0.2?kPa?1, and n between 1.2 and 1.5. The data may be used to estimate changes in hydraulic properties for applications such as waste containment, where long-term maintenance of hydraulic properties in shallow engineered soil layers is important.     

Retention and Removal of Suspended Solids and Total Phosphorus from Water by Riparian Reeds

Riparian reeds in rivers may be able to remove contaminants such as phosphorus. In this study, a selected river section was surveyed to investigate the effects of riparian reeds on the suspended solids (SS) and total phosphorus (TP) in the water. Six observation periods over two years showed that in the reed zone (the upstream 8.1?km of the river), the SS deposition rates per unit of concentration were between 0.025 and 0.031 1/km, and the TP concentration was decreased from 0.28–0.62?to?0.165–0.31?mg/L with decreasing rate of 41–50%, while in the nonreed zone (the downstream 8.1?km), the SS deposition rates were only between 0.0073 and 0.0092 1/km and the TP concentration was reduced from 0.15–0.30?to?0.12–0.24?mg/L with decreasing rate of 20% or so. The presence of riparian reeds could result in a SS deposition rate four times higher than that in a reed-free area, and the TP removal rate for the nonreed zone was only 40–48.78% of that for the reed zone. Water SS content was significantly lower in the reed zone than the surrounding water area. For the reed zone, water TP concentration was positively correlated to water SS content, but this relation disappeared in the nonreed zone. In both reed and nonreed zones, water dissolved reactive phosphorus concentration showed a significant negative relation to water SS content. Furthermore, water SS content and TP concentration appeared to be linked to reed density, and high reed density reduced the water flow velocity, resulting in lower water SS content and TP concentration.     

Airborne Acoustic Method to Determine the Volumetric Water Content of Unsaturated Sands

This paper presents an innovative experimental approach for simultaneous measurements of the suction head, volumetric water content, and the acoustic admittance of unsaturated sands. Samples of unsaturated sands are tested under controlled laboratory conditions. Several types of uniform sand with a wide range of particle sizes are investigated. The reported experiments are based on a standard Buchner funnel setup and a standard acoustic impedance tube. It is a novel, nondestructive, and noninvasive technique that relates the key geotechnical parameters of sands such as volumetric water content, density, and grain-size distribution to the acoustic admittance and attenuation. The results show a very sensitive dependence of the acoustic admittance on the volumetric water content controlled by the value of suction head applied. Analysis of the obtained data demonstrates that the relationship between the volumetric water content and the real part of the surface admittance in the frequency range of 400–1,200 Hz can be represented using a logarithmic equation. It is found that the coefficients in the proposed equation are directly related to the uniformity coefficient and the acoustic admittance of the dry sample, which can easily be measured or predicted for a broad range of sands. A validation exercise is conducted to examine the accuracy of the proposed equation using a sand sample with markedly different properties. The results of the validation exercise demonstrate that the proposed relations can be used to determine very accurately the volumetric water content within the porous specimen from the acoustical data. The error in the acoustically measured volumetric water content is found to be ±2.0% over the full range of volumetric water contents (0 ≤ θ ≤ n, where n is the sample porosity).     

Soil Water Retention and Conductivity When Vapor Flow Is Important

Models of soil water transport often calculate conductivity K from the water retention curve (WRC). Residual water content (θr) has been defined as θ where K = 0. When nonisothermal, coupled vapor and liquid water transport are considered, θr>0 fails because vapor transport often reduces θ to near zero. The author’s objective was to test a model that used unsaturated K(θ) with θ dependence typical of θr>0, while a WRC with θr = 0 was used elsewhere in the model. The system was a closed column of steady state, unsaturated, nonisothermal fine quartz sand with temperature (T) ranging from 5 to 40°C. Soil parameters were adjusted to simulate replicated experimental data from one initial θ condition. The model predicted θ and T within the range of the experimental data and reproduced the sharp drying front. It also satisfactorily modeled experiments with several different initial θ. Model heat flux predictions averaged 11% more than measured values. Experiments performed with two soil column lengths were not substantially different.     

BTEX Removal from Produced Water Using Surfactant-Modified Zeolite

Produced water (water generated during recovery of petroleum) contains large amounts of various hazardous organic compounds such as benzene, toluene, ethylbenzene, and xylenes (BTEX). With increasing regulations governing disposal of this water, low-cost treatment options are necessary. This study evaluated the effectiveness of surfactant-modified zeolite (SMZ) for removal of BTEX from produced water. The long-term effectiveness of SMZ for BTEX removal was investigated along with changes in sorption properties with long-term use. The results of these investigations show that SMZ completely removes BTEX from produced water up to a compound-specific capacity, and that SMZ can be regenerated via air sparging without loss of sorption capacity. The BTEX mobility in laboratory columns of SMZ was in the order of decreasing water solubility and increasing Kow. The most soluble compound, benzene, began to elute at 8 pore volumes (PV), while the least soluble compounds, ethylbenzene and xylenes, began to elute at 50 PV. After treating 4,500 PVs of water in the column system over 10 sorption/regeneration cycles, no significant reduction in sorption capacity of the SMZ for BTEX was observed. The mean Kds determined in these column experiments ranged from 18.3?L/kg for benzene to 95.0?L/kg for p- and m-xylene. Laboratory columns were upscaled to create a field-scale SMZ treatment system. The field-scale system was tested at a natural gas produced-water treatment facility near Wamsutter, Wyo. We observed even greater sorption of BTEX in the field column than predicted from the laboratory results. In the field column, initial benzene breakthrough occurred at 10 PV and toluene breakthrough began at 15 PV, and no breakthrough of ethylbenzene or xylenes occurred throughout the 80 PV experiment. The field and laboratory results, along with the low price of SMZ (about $460?per?metric?t), suggest that SMZ has a potential role in a cost-effective produced water treatment system.     

Centrifuge Permeameter for Unsaturated Soils. II: Measurement of the Hydraulic Characteristics of an Unsaturated Clay

This paper presents the hydraulic characteristics of an unsaturated, compacted clay, including its soil-water retention curve (SWRC) and hydraulic conductivity function (K function), determined using a new centrifuge permeameter developed at the University of Texas at Austin. A companion paper describes the apparatus, its instrumentation layout, and data reduction procedures. Three approaches are evaluated in this study to define the SWRC and K function of the compacted clay under both drying and wetting paths, by varying the inflow rate, the g level, or both. For imposed inflow rates ranging from 20 to 0.1 mL/h and g levels ranging from 10 to 100 g, the measured matric suction ranged from 5 to 70 kPa, the average volumetric water content ranged from 23 to 33%, and the hydraulic conductivity ranged from 2×10?7 to 8×10?11?m/s. The SWRCs and K functions obtained using the three different testing approaches were very consistent, and yielded suitable information for direct determination of the hydraulic characteristics. The approaches differed in the time required to complete a testing stage and in the range of measured hydraulic conductivity values. The g level had a negligible effect on the measured hydraulic characteristics of the compacted clay. The SWRCs and K functions defined using the centrifuge permeameter are consistent with those obtained using pressure chamber and column infiltration tests. The K functions defined using the centrifuge permeameter follow the same shape as those obtained from predictive relationships, although the measured and predicted K functions differ by two orders of magnitude at the lower end of the volumetric water content range.     

Nonequilibrium Nonaqueous Phase Liquid Mass Transfer Model for Soil Vapor Extraction Systems

Soil vapor extraction is a popular soil remediation technology that is hampered by less than optimal performance in the field due to mass transfer limitations. Therefore, laboratory column venting experiments were completed to quantify mass transfer limitations for the removal of multicomponent nonaqueous phase liquid (NAPL) contaminants from a silt loam soil at three water contents. The observed mass transfer limitations were quantified using a four phase multicomponent, nonequilibrium contaminant transport model based on first-order mass transfer kinetics. The overall mass transfer coefficient Kga was treated as a variable and modeled as a linear function of the NAPL volumetric fraction using two adjustable parameters (m, the slope parameter and Kgamin, the intercept). Both were back calculated from column venting data. The agreement between the calibrated model and experimental results were favorable for the removal of single and binary contaminants under conditions ranging from near equilibrium to severe mass transfer limitations and extended tailing. A strong dependency of Kga on water content was evident by the differences in Kgamin and to a lesser extent, m, at the three water contents investigated. A single expression Kga captured the performance of both components in the binary mixture. For the quaternary venting experiments a single expression for Kga captured the performance of all four components well under air dry conditions. However, the agreement between the hexane model versus the experimental result deteriorated significantly as the water content increased. This difference is attributed to hexane’s lower affinity for the water phase relative to the other three components in the mixture.     

Multidimensional Infiltration with Arbitrary Surface Fluxes

A new solution to the multidimensional linearized Richards equation was derived using a Fourier integral transform. Exponential functional forms k = kseαψ and θ = θr + (θs ? θr)eαψ were used to represent the hydraulic conductivity and pressure relation and the soil water release curve. The analytical solutions consider the conditions of time dependence and nonuniform distribution of rainfall intensity and arbitrary initial water content distribution with a water table. The analytical solutions can be used to predict the ponding time and to obtain the volumetric water content distribution over time and space.     

Modeling Arsenite Adsorption on Rusting Metallic Iron

Experimental data on As(III) adsorption by rusted zero valent iron (ZVI) could be modeled using a simple Langmuir isotherm model. However, the adsorption equilibrium was observed to shift with time, as continued rusting produced additional sites on the rusted ZVI surface for potential arsenic adsorption. A modified Langmuir isotherm model was formulated taking into consideration the temporal variation in the site concentration for potential arsenic adsorption on the rusted ZVI surface. This model simulated the long-term experimental data on As(III) adsorption quite well. The model was further refined by apportioning the arsenic adsorbed on the rusted ZVI surface into labile and irreversibly adsorbed fractions. Finally, the developed model was used to simulate the performance of an adsorption column. The simulation results indicate that an adsorption column of length 0.4 m and diameter 0.056 m, i.e., containing 0.001?m3 of rusted ZVI weighing 4.76 kg, and operated at an empty bed contact time of 12 min, can treat 2,375–2,525 L of water containing 100?μg?L?1 of As(III) such that the effluent As(III) concentration from the column is less than 10?μg?L?1.     

Sensitivity Analysis of Soil Hydraulic Properties on Subsurface Water Flow in Furrows

Knowledge of the sensitivity of various soil hydraulic properties is beneficial for model development and application purposes. It can lead to better estimated values, better understanding, and thus reduced uncertainty. In the present study, an extensive sensitivity analysis was performed to investigate the effects that various soil hydraulic properties have on subsurface water flow below furrows during two successive irrigation events to see which irrigation event was more sensitive and to analyze the effect of spatial variations in the initial soil water contents within the soil profile. Testing the sensitivity of the various soil hydraulic parameters in the van Genuchten-Mualem expression was carried out using the HYDRUS-2D model for two irrigation events 10?days apart. Results showed that the first irrigation event was clearly more sensitive than the second one. The latter event was mainly associated with the nonuniformity of the initial soil water contents within the soil profile. Pressure heads in the soil profile were more sensitive than cumulative outlet fluxes and soil water contents. Sensitivity analysis results for pressure heads, cumulative fluxes, and water contents indicated that in every case the most sensitive parameter was the hydraulic property shape factor (n) followed by the saturated water content (θs), the saturated hydraulic conductivity (Ks), the residual water content (θr), and the shape factor in the soil water retention curve (α), with the pore-connectivity parameter (l) the least sensitive parameter during both irrigation events. Pressure head sensitivity analysis for all parameters studied showed that the least sensitivity was linked with the wetting front as it gradually moved deeper with time, and the highest sensitivity was observed in those regions where the initial soil water contents were lower. Similarly, for water contents, higher sensitivity occurred in the drier regions during the first irrigation event and near the moisture front in the second irrigation event. Both pressure heads and water contents showed some sensitivity near the soil surface during both irrigation events, suggesting the importance of evaporation from the soil surface.     

Preliminary Evaluation of Microbially Mediated Precipitation of Cadmium, Chromium, and Nickel by Rhizosphere Consortium

Elevated heavy metal soils and water contamination have been shown to impose toxic effects on plants, animals, and human health. The extent of toxicity depends on the nature of the metals, soil and aquatic system characteristics, and the complex interactions between metals and the environment. Recent studies have shown that metal–microbe interactions may be effective for the remediation of contaminated media. This study investigated the effectiveness of an isolated rhizosphere bacterial consortium for treating an aqueous solution containing 600 mg/L of Cd, Cr, and Ni. The consortium was resistant to the metal toxicity as evidenced by an increase of population density of more than 6×1011?cfu/mL. The microbial activity facilitated a reduction in aqueous metal concentration with a metal precipitation selectivity of Cr?Cd>Ni.     

Arsenic Removal by a Colloidal Iron Oxide Coated Sand

A novel treatment process for arsenic removal from contaminated groundwater has been developed for use as a reactive barrier or a small drinking water treatment unit. In this study, modified porous media was made by the deposition of colloidal iron oxide onto sand grains at intermediate pH and ionic strength. Kd values from column experiments were 0.016–0.37?L/kg for As(III) and 0.023–0.85?L/kg for As(V), being lower than those of batch experiments (0.50 and 1.30?L/kg for As(III) and As(V), respectively) due to lower availability of surface adsorption sites in the packed column. Media-independent Kd values reflect the enhancement of arsenic adsorption with an increase of colloidal iron oxide coated sand fraction, apparently due to adsorption equilibration during arsenic transport under the same flow column conditions. The heterogeneous composition of two groundwater samples also reduced arsenic adsorption. Therefore, arsenic elution near the initial breakthrough was regulated by available adsorption surface in a porous coated sand media as well as the effects of competing oxyanions. The exhaustion of adsorption capacity near the critical contamination level is sensitive to geochemical and remedial properties of the contaminants.     

Removal of 17β Estradiol and Fluoranthene by Nanofiltration and Ultrafiltration

With the recent emergence of endocrine disrupting compounds as an important potable drinking water and reclaimed wastewater quality issue, the removal of two estrogenic compounds (17β-estradiol and fluoranthene) by nanofiltration and ultrafiltration membranes was investigated. A less hydrophobic organic compound model species [parachlorobenzoic acid (PCBA)] was tested. 17β-estradiol (E2), fluoranthene, and PCBA were applied to the membrane in the presence and absence of natural organic matter (NOM). Both batch adsorption and dead-end stirred-cell filtration experiments indicated that adsorption is an important mechanism for transport/removal of relatively hydrophobic compounds, and is related to the octanol-water partition coefficient (KOW) values. All filtration measurements were performed approximately the same permeate flow rate in order to minimize artifacts from concentration polarization varied with different hydrodynamic operating conditions at the membrane interface. The percent removal by dead-end stirred-cell filtration ranged from 10 to >95% depending upon membrane pore size/hydrophobicity and presence/absence of NOM at an initial concentration ranging from 0.1 to 0.5 μM. Additional batch adsorption experiments with radio-label (3H) E2 at lower concentrations ranging 0.025 to 5 nM showed that E2 removal due to adsorption was independent of its initial concentration. Adsorption occurs both on the membrane surface and interior membrane pore surfaces. However, adsorption was insignificant for PCBA (log?KOW = 2.7), but removal presumably occurred due to electrostatic exclusion. Partition coefficients (log?K) of 0.44 to 4.86 measured in this study increased with log?KOW and membrane pore size.     

Modeling Nonpoint Source Pollutant Losses from a Small Watershed Using HSPF Model

Hydrologic models play an important role in the assessment of nonpoint source (NPS) pollution, which is essential for the environmental management of water resources. The present study has been undertaken to evaluate the applicability of a physically based continuous time scale, hydrological, and water quality computer model—Hydrologic Simulation Program-Fortran (HSPF)—in simulating runoff and sediment associated NPS pollutant losses from a small mixed type (land under agriculture, shrubs and forest, rocks, grasses) watershed of the Damodar Valley Corporation, Hazaribagh, India. Water soluble NO3–N, NH4–N, and P were considered as pollutants and their concentrations in the runoff were measured at the outlet of the watershed, randomly for 15 dates during the monsoon season (June–October) of 2000 and 2001. The model calibration and validation results reveal that the seasonal trend of HSPF simulated runoff, sediment yield, and NPS pollutants compared reasonably with their measured counterparts. Although the concentrations of pollutants were generally overpredicted for NO3–N and underpredicted for NH4–N and water-soluble P in the month of June when fertilizers releasing NH4–N and P are applied in rice fields, the differences in the mean concentration were not significantly different at a 95% level of confidence. Variation in the simulated losses of water soluble N and P species between the years occurred largely due to differences in the amount and distribution of rainfall. These results indicate that the HSPF model can be used as a tool for simulating runoff and sediment associated NPS pollution losses from the study area.     

Subsurface Mobility of Organo–Cr(III) Complexes Formed during Biological Reduction of Cr(VI)

Hexavalent chromium [Cr(VI)] contamination of soil and groundwater is a major concern for some industrial sites as well as many United States Department of Energy sites. Bioreduction of Cr(VI) to less toxic and less mobile Cr(III) has received much attention as a viable method of remediation. However, bioreduction of Cr(VI) also produces soluble organo–Cr(III) complexes and little is known about the fate of these complexes in the environment. Cr(VI) was reduced abiotically in the presence of cellular organic compounds (malate, cysteine, and serine) and biotically in the presence of two test organisms (Cellulomonas ES6 and S. oneidensis MR1). The soluble organo–Cr(III) complexes formed were then introduced to soil columns to evaluate their sorption affinity and transport characteristics. The column data indicated that a significant fraction of the biologically derived organo–Cr(III) complexes are both soluble and mobile. Other complexes were observed to have limited mobility, indicating that a heterogeneous mixture of complexes are formed during biological reduction of Cr(VI).     

Dual Discharge Approach to Accessing Assimilative Capacity: Probabilistic Analysis and Management Application

A dual discharge strategy has been proposed for management of the effluent from the Syracuse Metropolitan Treatment Plant (Metro). The approach involves routing the discharge to the Seneca River when assimilative capacity is available there and to Onondaga Lake when it is not. Application of a deterministic modeling approach has demonstrated that the dual discharge strategy is effective in meeting water-quality standards/goals in both the river [dissolved oxygen (DO)] and the lake [total phosphorus (TP)] under summer average conditions of river flow and upstream boundary condition DO. Here, that analysis is extended to include a probabilistic treatment of the impact of natural variability in river flow and DO boundary conditions on the feasibility of this management option. Model simulations, incorporating these key sources of system variability, indicate that the dual discharge strategy will meet the lake management goal for TP ～ 94% of the time, with no attendant violation of river DO standards. Excursions from the lake TP goal, occurring ～ 6% of the time, range from 1–5?μg?L?1, are within the range of uncertainty in indicators applied in identifying trophic status. This novel management option is compared with an in-lake discharge alternative in terms of technical and economic feasibility and public acceptance of resultant water quality. Additional management actions, recommended to accompany implementation of the dual discharge strategy, are discussed.