Stephen L. Harden

Effect of land-applied biosolids on surface-water nutrient yields and groundwater quality in Orange County, North Carolina

Land application of municipal wastewater biosolids is the most common method of biosolids management used in North Carolina and the United States. Biosolids have characteristics that may be beneficial to soil and plants. Land application can take advantage of these beneficial qualities, whereas disposal in landfills or incineration poses no beneficial use of the waste. Some independent studies and laboratory analysis, however, have shown that land-applied biosolids can pose a threat to human health and surface-water and groundwater quality. The effect of municipal biosolids applied to agriculture fields is largely unknown in relation to the delivery of nutrients, bacteria, metals, and contaminants of emerging concern to surface-water and groundwater resources. Therefore, the North Carolina Department of Environment and Natural Resources (NCDENR) collaborated with the U.S. Geological Survey (USGS) through the 319 Nonpoint Source Program to better understand the transport of nutrients and bacteria from biosolids application fields to groundwater and surface water and to provide a scientific basis for evaluating the effectiveness of the current regulations. The USGS conducted a paired agricultural watershed study in the Collins Creek and Cane Creek Reservoir watersheds in Orange County, North Carolina. Field activities were conducted from March 2011 through May 2013 at two field study sites, including biosolids field application sites owned by Orange County Water and Sewer Authority (OWASA) in the Collins Creek watershed and a background study site in the Cane Creek watershed that has no fields receiving biosolids applications. Samples of biosolids source material and soil were collected from the land-application fields for laboratory analyses. Soil samples were also collected from a background agricultural field in the Cane Creek watershed that has never received land-applied municipal biosolids. Shallow groundwater samples were collected quarterly from new monitoring wells installed by NCDENR along the edge of the biosolids land-application fields and a background agricultural field for laboratory analyses. Two surface-water monitoring sites were established on Collins Creek to compute continuous streamflow and collect discrete baseflow and stormwater runoff water-quality data upstream and downstream from the biosolids land-application fields. Surface waterquality samples were also collected for baseflow and stormwater runoff conditions at an existing USGS streamgage on Cane Creek to monitor water-quality conditions in the background study watershed. The study primarily focused on nutrients and bacteria; however, data for field properties and water-quality constituents, including metals, major ions, and contaminants of emerging concern (household-, industrial-, and agricultural-use compounds, pharmaceutical compounds, hormones, and antibiotics) also were collected and used in the analyses. There were no exceedances of the 10 elements with designated U.S. Environmental Protection Agency (EPA) ceiling concentrations for land-applied biosolids in any of the biosolids samples. Treatment processes and storage techniques used by OWASA are effective in eliminating Escherichia coli and fecal coliform bacteria from biosolids. Copper, molybdenum, total Kjeldahl nitrogen, and total phosphorus were elevated in the soil from biosolids land-application fields relative to the background field. The relative richness of these constituents in the biosolids land-application fields is consistent with biosolids being the source of the elevated concentrations given the relatively high concentrations of these constituents in the biosolids samples that were collected. Shallow groundwater in the transitional zone wells, which were located adjacent to and topographically downgradient from all the biosolids land-application fields, were found to be statistically different and had higher nitrate concentrations (medians greater than 12 milligrams per liter) than all the other wells sampled as part of the study. Surface-water nutrient concentrations and yields, primarily nitrate, were higher at the 1U.S. Geological Survey. 2Clarkson University. 2 Effect of Land-Applied Biosolids on Surface-Water Nutrient Yields and Groundwater Quality in Orange County, North Carolina monitoring site on Collins Creek downstream from the biosolids land-application fields than the other study sites that drained watersheds without biosolids land application. The largest differences in concentrations between sites were measured at baseflow conditions, which indicate that the main cause of these differences, particularly between Cane Creek and the Collins Creek site downstream from the OWASA application fields, is related to nitrate contribution from the shallow groundwater. Contaminants of emerging concern were detected in approximately 40 percent of the laboratory analyses of the biosolids samples and more frequently in soil samples from the biosolids land-application fields (approximately 40 percent of laboratory analyses) relative to the soil samples from the background field (approximately 12 percent of laboratory analyses). However, contaminants of emerging concern detected in the laboratory analysis for this study do not appear to be good indicators of human-waste contaminants derived from landapplied biosolids in groundwater or surface-water because the number of detections and concentrations at the background wells and surface-water monitoring sites are similar to or higher than those at wells and monitoring sites adjacent to or downstream from the biosolids land-application fields. The data, analysis, and conclusions associated with this study can be used by regulatory agencies, resource managers, and wastewater-treatment operators to (1) better understand the quantity and characteristics of nutrients, bacteria, metals, and contaminants of emerging concern that are transported away from biosolids land-application fields to surface water and groundwater under current regulations for the purposes of establishing effective total maximum daily loads (TMDLs) and restoring impaired water resources, (2) assess how well existing regulations protect waters of the State and potentially recommend effective changes to regulations or land-application procedures, and (3) establish a framework for developing guidance on effective techniques for monitoring and regulatory enforcement of permitted biosolids land-application fields. Introduction Biosolids are defined as any solid, semi-solid, or liquid waste, other than raw effluent or residues from agricultural products and processing, generated from a wastewater-treatment facility, water-supply treatment facility, or air pollution control facility permitted under the authority of the North Carolina Environmental Management Commission (EMC). Depending on the level of treatment that the biosolids receive, the biosolids may be applied to land for fertilizer or disposed of in a surface disposal unit (such as a land fill or incineration). As of December 2009, a total of 260 facilities in North Carolina were permitted to apply biosolids to land and only 15 facilities were permitted for surface disposal. Land application of municipal wastewater biosolids is the most common method of biosolids management used in North Carolina and the United States (National Research Council of the National Academy of Sciences, 2002). Biosolids have characteristics that may be beneficial to soil and plants. Land application can take advantage of these beneficial qualities, whereas disposal in landfills or incineration poses no beneficial use of the waste (National Research Council of the National Academy of Sciences, 2002; Lu and others, 2012). For these reasons, the State of North Carolina and the U.S. Environmental Protection Agency (EPA) consider controlled land application a “beneficial use” of biosolids. However, some independent studies and laboratory analyses (National Research Council of the National Academy of Sciences, 2002; Rudo, 2005; U.S. Environmental Protection Agency, 2009) have shown that biosolids can pose a threat to human health as well as surface-water and groundwater quality. Hence, biosolids are defined as waste under North Carolina General Statute (NCGS) 142–213, and any system that collects, treats, or disposes of waste cannot be constructed or operated without a permit (NCGS 143–215.1(a)). The statute (NCGS 143–215.1(a)) authorizes the EMC and the North Carolina Department of Environment and Natural Resources (NCDENR) to develop and implement State regulations and to issue permits for the generation and disposal of residual biosolids; however, only NCDENR’s Division of Water Resources (DWR) carries out these functions. The North Carolina rules (15A NCAC 02T.1109) for biosolids management meet or exceed the Title 40 Code of Federal Regulations part 503 (40 CFR 503) standards for the use or disposal of sewage sludge. The permitting request and approval process implemented by DWR is designed to provide relevant information to concerned parties before, during, and after the application of biosolids in an attempt to assure that land applications of biosolids are managed safely and effectively. The DWR conducts reviews of all permit applications, performs site visits to proposed application fields to verify site conditions, and works with county managers and health departments to address local concerns with proposed biosolids land-application activities. Permit holders are required to provide DWR with annual reports that summarize the past year’s activities and document that biosolids quality and nutrient management requirements were met. Permit holders also are responsible for meeting the requirements of their permit and for reporting any permit violations. Monitoring and enforcement of permit requirements is challenging and relies primarily on self-reporting of permittees (supplier of the biosolids) and citizen complaints