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.

Development of total maximum daily loads for bacteria impaired watershed using the comprehensive hydrology and water quality simulation model.

The objective of this study was to develop bacteria total maximum daily loads (TMDLs) for the Hardware River watershed in the Commonwealth of Virginia, USA. The TMDL program is an integrated watershed management approach required by the Clean Water Act. The TMDLs were developed to meet Virginia's water quality standard for bacteria at the time, which stated that the calendar-month geometric mean concentration of Escherichia coli should not exceed 126 cfu/100 mL, and that no single sample should exceed a concentration of 235 cfu/100 mL. The bacteria impairment TMDLs were developed using the Hydrological Simulation Program-FORTRAN (HSPF). The hydrology and water quality components of HSPF were calibrated and validated using data from the Hardware River watershed to ensure that the model adequately simulated runoff and bacteria concentrations. The calibrated and validated HSPF model was used to estimate the contributions from the various bacteria sources in the Hardware River watershed to the in-stream concentration. Bacteria loads were estimated through an extensive source characterization process. Simulation results for existing conditions indicated that the majority of the bacteria came from livestock and wildlife direct deposits and pervious lands. Different source reduction scenarios were evaluated to identify scenarios that meet both the geometric mean and single sample maximum E. coli criteria with zero violations. The resulting scenarios required extreme and impractical reductions from livestock and wildlife sources. Results from studies similar to this across Virginia partially contributed to a reconsideration of the standard's applicability to TMDL development.

Risk-based decision making to evaluate pollutant reduction scenarios.

A total maximum daily load (TMDL) is required for water bodies in the U.S. that do not meet applicable water quality standards. Computational watershed models are often used to develop TMDL pollutant reduction scenarios. Uncertainty is inherent in the modeling process. An explicit uncertainty analysis would improve model performance and result in more robust decision making when comparing alternative pollutant reduction scenarios. This paper presents a risk-based framework for evaluating alternative pollutant allocation scenarios considering reliability in achieving water quality goals. We demonstrate a generic routine for the application of Generalized Likelihood Uncertainty Estimation (GLUE) to Hydrological Simulation Program-FORTRAN (HSPF) using existing softwares to evaluate two bacteria reduction scenarios from a recently developed TMDL that addressed a bacterial impairment in a mixed land use watershed in Virginia, U.S. Our probabilistic analysis showed that for reliability levels <25%, the recommended TMDL bacterial load reduction scenario had the same exceedance rate as the full reduction scenario (fully reducing all bacterial loads except wildlife), while for reliability levels between 25% and 50%, the exceedance rates for the two pollutant reduction scenarios were similar, with the TMDL recommended scenario violating the water quality criteria only slightly more often. The full reduction scenario performed better in higher reliability levels, although it could not meet the water quality criteria. Our results indicated that, in this case, achieving water quality goals with very high reliability was not possible, even with extreme levels of pollutant reduction. The risk-based framework presented here illustrates a method to propagate watershed model uncertainty and assess performance of alternative pollutant reduction scenarios using existing tools, thereby enabling decision makers to understand the reliability of a given scenario in achieving water quality goals.

Scale-dependent impacts of urban and agricultural land use on nutrients, sediment, and runoff.

We coupled a spatially-explicit land use/land cover (LULC) change model, Dinamica EGO, (Environment for Geoprocessing Objects), with the Chesapeake Bay Watershed Model (CBWM) to project the impact of future LULC change on loading of total nitrogen (TN), total phosphorous (TP) and total suspended solids (TSS) as well as runoff volume in the watersheds surrounding Virginia's Shenandoah National Park in the eastern United States. We allowed for the dynamic transition of four LULC classes, Developed, Forest, Grasses (including both pasture and hayfields) and Crops. Using 2011 as a baseline scenario and observed differences in LULC between 2001 and 2011, we estimated the temporal and spatial patterns of LULC change as influenced by physiographic and socio-economic drivers 50 years in the future (2061). Between transitions of the four LULC classes, the greatest absolute change occurred between the gain in total Developed land and loss in total Forest. New Developed land was driven primarily by distance to existing Developed land and population density. Major findings on the effect of LULC change on watershed model outputs were that: the impact of LULC change on pollutant loading and runoff volume is more pronounced at finer spatial scales; increases in the area of Grasses produced the greatest increase in TP loading, while loss of Forest increased TN, TSS, and runoff volume the most; and land-river segments with a greater proportion of Developed or a smaller proportion of Forest in the 2011 scenario experienced a greater change in runoff than other land-river segments. Results of this study illustrate the potential impact of projected LULC change on nutrient and sediment loads which can adversely impact water quality. Studies like this contribute to a broader understanding of how ecosystem services such as fresh water respond to LULC change, information relevant to those in planning and watershed management.

Development of bacteria and benthic total maximum daily loads: a case study, Linville Creek, Virginia.

Two total maximum daily load (TMDL) studies were performed for Linville Creek in Rockingham County, Virginia, to address bacterial and benthic impairments. The TMDL program is an integrated watershed management approach required by the Clean Water Act. This paper describes the procedures used by the Center for TMDL and Watershed Studies at Virginia Tech to develop the Linville Creek TMDLs and discusses the key lessons learned from and the ramifications of the procedures used in these and other similar TMDL studies. The bacterial impairment TMDL was developed using the Hydrological Simulation Program-Fortran (HSPF). Fecal coliform loads were estimated through an intensive source characterization process. The benthic impairment TMDL was developed using the Generalized Watershed Loading Function (GWLF) model and the reference watershed approach. The bacterial TMDL allocation scenario requires a 100% reduction in cattle manure direct-deposits to the stream, a 96% reduction in nonpoint-source loadings to the land surface, and a 95% reduction in wildlife direct-deposits to the stream. Sediment was identified as the primary benthic stressor. The TMDL allocation scenario for the benthic impairment requires an overall reduction of 12.3% of the existing sediment loads. Despite the many drawbacks associated with using watershed-scale models like HSPF and GWLF to develop TMDLs, the detailed watershed and pollutant-source characterization required to use these and similar models creates information that stakeholders need to select appropriate corrective measures to address the cause of the water quality impairment when implementing the TMDL.

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.