Brian L. Benham

MODELING BACTERIA FATE AND TRANSPORT IN WATERSHEDS TO SUPPORT TMDLS

Fecal contamination of surface waters is a critical water-quality issue, leading to human illnesses and deaths. Total Maximum Daily Loads (TMDLs), which set pollutant limits, are being developed to address fecal bacteria impairments. Watershed models are widely used to support TMDLs, although their use for simulating in-stream fecal bacteria concentrations is somewhat rudimentary. This article provides an overview of fecal microorganism fate and transport within watersheds, describes current watershed models used to simulate microbial transport, and presents case studies demonstrating model use. Bacterial modeling capabilities and limitations for setting TMDL limits are described for two widely used watershed models (HSPF and SWAT) and for the load-duration method. Both HSPF and SWAT permit the user to discretize a watershed spatially and bacteria loads temporally. However, the options and flexibilities are limited. The models are also limited in their ability to describe bacterial life cycles and in their ability to adequately simulate bacteria concentrations during extreme climatic conditions. The load-duration method for developing TMDLs provides a good representation of overall water quality and needed water quality improvement, but intra-watershed contributions must be determined through supplemental sampling or through subsequent modeling that relates land use and hydrologic response to bacterial concentrations. Identified research needs include improved bacteria source characterization procedures, data to support such procedures, and modeling advances including better representation of bacteria life cycles, inclusion of more appropriate fate and transport processes, improved simulation of catastrophic conditions, and creation of a decision support tool to aid users in selecting an appropriate model or method for TMDL development.

Comparison of hydrologic calibration of HSPF using automatic and manual methods

The automatic calibration software Parameter Estimation (PEST) was used in the hydrologic calibration of Hydrological Simulation Program-Fortran (HSPF), and the results were compared with a manual calibration assisted by the Expert System for the Calibration of HSPF (HSPEXP). In this study, multiobjective functions based on the HSPEXP model performance criteria were developed for use in PEST, which allowed for the comparison of the calibration results of the two methods. The calibrated results of both methods were compared in terms of HSPEXP model performance criteria, goodness-of-fit measures (R-2, E, and RMSE), and base flow index. The automatic calibration results satisfied most of the HSPEXP model performance criteria and performed better with respect to R2, E, RMSE, and base flow index than manual calibration results. The results of the comparison with the manual calibration suggest that the automatic method using PEST may be a suitable alternative to manual method assisted by HSPEXP for calibration of hydrologic parameters for HSPF. However, further research of the weights used in the objective functions is necessary to provide guidance when applying PEST to surface water modeling.

Evaluating, interpreting, and communicating performance of hydrologic/water quality models considering intended use: A review and recommendations ☆

Abstract Previous publications have outlined recommended practices for hydrologic and water quality (H/WQ) modeling, but limited guidance has been published on how to consider the projects purpose or models intended use, especially for the final stage of modeling applications – namely evaluation, interpretation, and communication of model results. Such guidance is needed to more effectively evaluate and interpret model performance and more accurately communicate that performance to decision-makers and other modeling stakeholders. Thus, we formulated a methodology for evaluation, interpretation, and communication of H/WQ model results. The recommended methodology focuses on interpretation and communication of results, not on model development or initial calibration and validation, and as such it applies to the modeling process following initial calibration. The methodology recommends the following steps: 1) evaluate initial model performance; 2) evaluate outliers and extremes in observed values and bias in predicted values; 3) estimate uncertainty in observed data and predicted values; 4) re-evaluate model performance considering accuracy, precision, and hypothesis testing; 5) interpret model results considering intended use; and 6) communicate model performance. A flowchart and tables were developed to guide model interpretation, refinement, and proper application considering intended model uses (i.e., Exploratory, Planning, and Regulatory/Legal). The methodology was designed to enhance application of H/WQ models through conscientious evaluation, interpretation, and communication of model performance to decision-makers and other stakeholders; it is not meant to be a definitive standard or a required protocol, but together with recent recommendations and published best practices serve as guidelines for enhanced model application emphasizing the importance of the models intended use.

Enhanced Nitrate and Phosphate Removal in a Denitrifying Bioreactor with Biochar

Denitrifying bioreactors (DNBRs) are an emerging technology used to remove nitrate-nitrogen (NO) from enriched waters by supporting denitrifying microorganisms with organic carbon in an anaerobic environment. Field-scale investigations have established successful removal of NO from agricultural drainage, but the potential for DNBRs to remediate excess phosphorus (P) exported from agricultural systems has not been addressed. We hypothesized that biochar addition to traditional woodchip DNBRs would enhance NO and P removal and reduce nitrous oxide (NO) emissions based on previous research demonstrating reduced leaching of NO and P and lower greenhouse gas production associated with biochar amendment of agricultural soils. Nine laboratory-scale DNBRs, a woodchip control, and eight different woodchip-biochar treatments were used to test the effect of biochar on nutrient removal. The biochar treatments constituted a full factorial design of three factors (biochar source material [feedstock], particle size, and application rate), each with two levels. Statistical analysis by repeated measures ANOVA showed a significant effect of biochar, time, and their interaction on NO and dissolved P removal. Average P removal of 65% was observed in the biochar treatments by 18 h, after which the concentrations remained stable, compared with an 8% increase in the control after 72 h. Biochar addition resulted in average NO removal of 86% after 18 h and 97% after 72 h, compared with only 13% at 18 h and 75% at 72 h in the control. Biochar addition also resulted in significantly lower NO production. These results suggest that biochar can reduce the design residence time by enhancing nutrient removal rates.

Modeling and assessing the impact of reclaimed wastewater irrigation on the nutrient loads from an agricultural watershed containing rice paddy fields

Two models were used in concert to predict nutrient loads in a waterbody receiving irrigation return flows from a rice paddy production system. Two irrigation scenarios were simulated, one using reclaimed wastewater as the irrigation water source, the other using water from a surface reservoir designed to supply irrigation water. Total nitrogen (TN) and total phosphorus (TP) loads in irrigation return flows from the rice paddy fields were simulated using the field-scale water quality model Chemical, Runoff and Erosion from Agricultural Management System model for rice paddy fields (CREAMS-PADDY). The output from CREAMS-PADDY was then used as input data for Hydrological Simulation Program-FORTRAN (HSPF) model. HSPF was used to evaluate TN and TP loads in the receiving waterbody at the watershed-scale. CREAMS-PADDY and HSPF were calibrated for both hydrology and water quality using observed data. Both CREAMS-PADDY and HSPF showed good agreement between the observed and simulated data during the calibration and validation periods. Simulation indicated that TN and TP loads from the study paddy fields increased by 207% and 1022% when reclaimed wastewater was used for irrigation compared to conventional irrigation. Irrigating paddy fields (18.8% of the 385 ha study watershed) with reclaimed wastewater increased the TN load at the watershed outlet by 10.3% and TP by 14.0%. The increase in nutrient loads was the result of the high nutrient concentration in the reclaimed wastewater. The procedures used in this research can be used to develop wastewater reuse strategies that minimize environmental impacts on watershed water quality.

Incidence of waterborne lead in private drinking water systems in Virginia

Although recent studies suggest contamination by bacteria and nitrate in private drinking water systems is of increasing concern, data describing contaminants associated with the corrosion of onsite plumbing are scarce. This study reports on the analysis of 2,146 samples submitted by private system homeowners. Almost 20% of first draw samples submitted contained lead concentrations above the United States Environmental Protection Agency action level of 15 μg/L, suggesting that corrosion may be a significant public health problem. Correlations between lead, copper, and zinc suggested brass components as a likely lead source, and dug/bored wells had significantly higher lead concentrations as compared to drilled wells. A random subset of samples selected to quantify particulate lead indicated that, on average, 47% of lead in the first draws was in the particulate form, although the occurrence was highly variable. While flushing the tap reduced lead below 15 μg/L for most systems, some systems experienced an increase, perhaps attributable to particulate lead or lead-bearing components upstream of the faucet (e.g., valves, pumps). Results suggest that without including a focus on private as well as municipal systems it will be very difficult to meet the existing national public health goal to eliminate elevated blood lead levels in children.

Assessing the Effects of Climate Change on Waterborne Microorganisms: Implications for EU and U.S. Water Policy

ABSTRACT Despite advances in water treatment, outbreaks of waterborne diseases still occur in developed regions including the United States and Europe Union (EU). Water quality impairments attributable to elevated concentrations of fecal indicator bacteria, and associated with health risk, are also very common. Research suggests that the impact of such microorganisms on public health may be intensified by the effects of climate change. At present, the major regulatory frameworks in these regions (i.e., the US Clean Water Act [CWA] and the EU Water Framework Directive [WFD]), do not explicitly address risks posed by climate change. This article reviews existing U.S. and EU water quality regulatory legislation for robustness to climate change and suggests watershed modeling approaches to inform additional pollution control measures given the likely impacts on microbial fate and transport. Comprehensive analysis of future climate and water quality scenarios may only be achievable through the use of watershed-scale models. Unless adaptation measures are generated and incorporated into water policy, the potential threat posed to humans from exposure to waterborne pathogens may be amplified. Such adaptation measures will assist in achieving the aims of the EU WFD and US CWA and minimize impacts of climate change on microbial water quality.

Quantitative analysis of microbial contamination in private drinking water supply systems

Over one million households rely on private water supplies (e.g. well, spring, cistern) in the Commonwealth of Virginia, USA. The present study tested 538 private wells and springs in 20 Virginia counties for total coliforms (TCs) and Escherichia coli along with a suite of chemical contaminants. A logistic regression analysis was used to investigate potential correlations between TC contamination and chemical parameters (e.g. NO3(-), turbidity), as well as homeowner-provided survey data describing system characteristics and perceived water quality. Of the 538 samples collected, 41% (n = 221) were positive for TCs and 10% (n = 53) for E. coli. Chemical parameters were not statistically predictive of microbial contamination. Well depth, water treatment, and farm location proximate to the water supply were factors in a regression model that predicted presence/absence of TCs with 74% accuracy. Microbial and chemical source tracking techniques (Bacteroides gene Bac32F and HF183 detection via polymerase chain reaction and optical brightener detection via fluorometry) identified four samples as likely contaminated with human wastewater.

Applications of Microbial Source Tracking in the TMDL Process

The US Environmental Protection Agency’s Total Maximum Daily Load (TMDL) program is frequently cited as a primary driver in the development of microbial source tracking (MST) techniques. As MST techniques continue to mature, it is prudent to identify those areas where further MST-related research is most likely to contribute to the efficient development and implementation of bacterial TMDLs. The objectives of this chapter are to review the basic phases in the TMDL process, to describe current applications of MST within these stages, to identify research needed to increase MST application, and to discuss opportunities for the expanded use of MST data within the TMDL process.

Sensitivity of streamflow and microbial water quality to future climate and land use change in the West of Ireland

This study applied catchment modeling to examine the potential effects of climate change and future land management variations on streamflow and microbial transport sensitivities for two locations in the west of Ireland (Black River and Fergus River). Simulations focused on plausible combined scenarios of climate, population and agricultural production variations for the 2041–2060 period and compares resultant impacts to a baseline existing period (1994–2007). The variations in monthly, seasonal and annual streamflow, and the daily microbial load (for E. coli) were used to assess sensitivities. Results indicate that possible future changes in microbial load for both the Fergus and Black catchments typically follow projected seasonal fluctuations in precipitation and streamflow. Increased winter rainfall (intensity and frequency) will cause significant impacts on microbial transport, representing a period of increased risk. An increase in microbial source loads to land, concomitantly with projected changes in climate is likely to exert greater microbial pollutant pressures on surface waters. The simulated scenarios, and resultant microbial load changes, suggest that future variations in land use/management may be as important as the effects of climate change on in-stream microbial pollutant loads. Outcomes from this study can prove useful for informing water resource managers and other decision makers about potential impacts. This information can instigate the development of adaptation measures needed to alleviate increased catchment pollution from microbial contaminants (and other pollutants) in future years.