Effects of Land-Applied Biosolids on Water Quality in the Jordan Lake Watershed, North Carolina

Science Center Objects

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.

However, recent studies have shown that biosolids can pose a threat to human and environmental health. The impact of land applied municipal biosolids to agricultural fields on delivery of nutrients, bacteria, metals and emerging contaminants to surface water and groundwater resources is largely unknown. The U.S. Geological Survey (USGS) conducted a paired agricultural watershed study in the Collins Creek and Cane Creek Reservoir watersheds in Orange County, North Carolina to determine the effect of land-applied biosolids on surface-water and groundwater quality.

Background:

Biosolids are defined as any solid, semi-solid, or liquid waste, other than 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 Environmental Management Commission (EMC). Depending upon the level of treatment that the biosolids receive, the generator may land apply the biosolids for livestock feed or dispose of the biosolids in a surface disposal unit (i.e. land fill, incineration). The practice of applying biosolids from municipal wastewater treatment plants to agriculture fields is becoming commonplace across much of the Piedmont and Coastal Plain of North Carolina. As of December, 2009 a total of 260 facilities (5,145 fields comprising 107,200 acres) were permitted to land apply biosolids in North Carolina and 15 facilities were permitted for surface disposal.

Image of a biosolid application field in Orange County, North Carolina
Biosolid application field in Orange County, North Carolina

Land application of municipal wastewater biosolids is the most common method of biosolids management used in North Carolina and in the United States. Biosolids have some characteristics that can be beneficial to soil and plants, and thus land application can take advantage of the beneficial qualities; whereas disposal in landfills or incineration poses no benefits or use of the waste. 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 (U.S. Environmental Protection Agency, 2009; National Research Council of the National Academy of Sciences, 2002; and Rudo, 2005) have shown that biosolids can pose a threat to human health as well as surface-water and groundwater quality. Hence, under North Carolina General Statue (NCGS) biosolids are defined as waste (NGCS 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 authorizes the EMC and the Department of Environment and Natural Resources (DENR) to develop and implement state regulations and issue permits for the generation and disposal of residuals, however only DENR's Division of Water Quality (DWQ) carries out these functions. The North Carolina rules for biosolids management meet or exceed the Federal 40 Code of Federal Regulations (CFR) 503 standards for the use or disposal of biosolids.

NC Division of Water Quality (DWQ) implements a permitting strategy that is designed to assure that relevant information is available to concerned parties before, during and after application of biosolids in an attempt to assure that land applications of biosolids are managed safely and effectively. DWQ conducts regional and central office reviews of all permit applications and conducts site visits to proposed fields to verify conditions and works with County Managers and County Health Departments to address local concerns with proposed land application activities. Permit holders are required to submit an annual report summarizing the past years activities and documenting that biosolids quality and nutrient management requirements were met. Permit holders are responsible for meeting the requirements of their permit and to report any violations. Monitoring and enforcement of permit requirements is challenging and relies primarily on citizen complaints and self reporting of permittees. There are no consistent guidelines on groundwater and surface water monitoring at biosolids land-application sites before problems arise. Many monitoring requirements are the result of complaints or evidence of impacts to waters of the State after contamination has occurred. A better understanding of the quantity and characteristics of nutrients, bacteria, metals and emerging contaminants that are transported away from biosolids fields to surface water and groundwater resources would provide the framework for developing guidance on effective techniques for monitoring and regulatory enforcement of permitted biosolids land application fields.

Objective:

The primary objective of this investigation is to initiate a paired agricultural watershed study designed to better understand transport of nutrients and bacteria from biosolids application fields to groundwater and surface water. Results will be useful for developing and implementing Total Maximum Daily Loads(TMDLs) for nutrient-impaired watersheds and to provide a scientific basis for evaluating the effectiveness of the current regulations. The proposed study primarily focuses on nutrients and bacteria because these are priority constituents for the 319 Program and because the study area is included in a nutrient TMDL. Data for other water-quality constituents including field parameters, metals, major ions, and organic wastewater compounds, will be collected and used to characterize the potential impact of land applied biosolids to groundwater and surface water.

The objectives for this investigation are as follows:

  1. Assess the offsite transport of nutrients and bacteria in groundwater and overland runoff from the biosolids application fields to receiving streams;
  2. Compute and compare surface water nutrient and bacteria loads for both a watershed with biosolids land application and a nearby watershed without biosolids application;
  3. Perform preliminary evaluation of organic wastewater compounds as potential indicator of Wastewater Treatment Plant (WWTP) residual biosolids derived constituents in surface water and groundwater; and
  4. Analyze and summarize the data to characterize impact of land applied biosolids on groundwater and receiving surface water.

Scope:

This work will be conducted in cooperation with NC Division of Water Quality (DWQ) in the Collins Creek and Cane Creek Reservoir watersheds in Orange County, North Carolina. The scope of work for this proposal extends over a 3-year period, beginning in January 2011 and ending in March 2014.

Field data collection activities are being conducted during the first two years. Field activities are being conducted at two field study sites, including biosolids field application sites owned by Orange County Water and Sewer Authority (OWASA) on Collins Creek and a background study site on Cane Creek that has no fields receiving biosolids applications. At the Collins Creek biosolids field application sites, samples of biosolids source material and soil will be collected in the application fields for laboratory analyses. Groundwater samples will be collected for laboratory analyses, from new monitoring wells and(or) drive points installed by NCDENR, along the edge of biosolids application fields. Two surface-water sites (upstream and downstream of the biosolids application fields) were established on Collins Creek to monitor water-quality conditions adjacent to the biosolids application study site. Surface-water samples also will be collected to monitor water-quality conditions at the background study location on Cane Creek. An existing USGS stream gage on Cane Creek (Station number 02096846) will be used to document streamflow at the Cane Creek site. Groundwater samples will also be collected from new monitoring wells and(or) drive points installed by NCDENR along the edge of agricultural fields that have never had land application of biosolids for laboratory analyses.

Samples of source material, soil, surface water and ground water will be analyzed primarily for nutrients, major ions, metals and fecal-coliform bacteria. As part of this 319 project, preliminary sampling of biosolids source material from the application fields and surface water at the Collins Creek upstream and downstream application sites, as well as the Cane Creek background site, will be conducted for analysis of organic wastewater compounds (OWCs), including such things as household, industrial, and agricultural-use (HIA) compounds, pharmaceutical compounds, hormones, and antibiotics. In the final year of the project, the USGS will work collaboratively with NCDENR to develop a final project report that evaluates the study.

Approach:

Task 1. Collection of data to characterize groundwater, surface water and soil associated with agricultural fields with and without land applied biosolids

NCDENR installed 4 monitoring wells along the edge of biosolids application fields adjacent to Collins Creek and 2 monitoring wells along the edge of agricultural fields without biosolids applications adjacent to Cane Creek. Four rounds of groundwater samples are being collected per year during the 2-year monitoring period from each well. Samples are collected approximately every 3 months to represent seasonal differences. The groundwater samples are analyzed primarily for nutrients, total metals and fecal-coliform and E. coli bacteria; select samples are analyzed for major ions, field alkalinity and emerging contaminants. Laboratory analysis of groundwater samples will be used to examine potential groundwater transport of nutrients, metals, and fecal coliform to surface water and compare groundwater beneath fields with and without the application of biosolids.

Image of Collins Creek monitoring station downstream of OWASA biosolids application fields at highway 54 in Orange County, North
Collins Creek monitoring station downstream of OWASA biosolidsapplication fields at highway 54 in Orange County, North Carolina

Surface-water sampling stations will be installed at an upstream site and a downstream site on Collins Creek and at a background site on Cane Creek. Automated water-quality samplers and stage recorders are installed at each location for use in determining concentrations of nutrients, metals and fecal-coliform bacteria in a watershed receiving applications of biosolids and a background watershed with no applications of biosolids, respectively. Routine water-quality samples are collected from surface-water sites approximately every 6 weeks for the 2-year monitoring period (total of approximately 16 samples per site) as flow conditions permit. Samples at these sites are also collected during targeted stormwater-runoff events (approximately 8 per year) over the 2-year monitoring period. The Collins Creek sites will be rated to compute a continuous record of discharge for the determination of instantaneous and annual constituent loads. The sampling strategy will strive to obtain samples covering the range of streamflow conditions encountered during the study period. The surface-water samples will be analyzed primarily for nutrients, total metals, and fecal-coliform and E. coli bacteria; select samples will be analyzed for major ions and emerging contaminants.

As part of the project, laboratory analysis of biosolids source material and soil from the Collins Creek biosolids application fields will be performed to document the amounts of nutrients, metals, and fecal coliform and E. coli found in the biosolids material applied at the site. Soil samples will be collected once before and after the application of biosolids at three fields in the Collins Creek watershed each year. Two soil samples will be collected from the background agricultural field in Cane Creek each year. A total of 3 biosolids source material samples that correspond with the soil samples from biosolids application fields will be collected each year. The biosolids and soil samples will be analyzed primarily for nutrients, total metals, and fecal-coliform and E. coli bacteria.

Constituents

A broad range of constituent groups will be analyzed (table 1). Chemical analyses of water, soil and biosolids samples will be conducted at the USGS National Water Quality Laboratory (NWQL) in Denver, Colorado, the NCDENR Water Quality Laboratory and TriTest, Inc. in Raleigh, NC.

Image of water quality constituents table

Task 2. Determine surface-water nutrient and bacteria loads in Collins Creek and Cane Creek

For all surface-water monitoring locations, the streamflow data will be combined with the sample analytical data for determining instantaneous loads of ammonia, nitrate, total nitrogen, total phosphorus, and fecal- coliform bacteria at the times samples were collected. The data from the downstream Collins Creek site and Cane Creek site will be examined to determine if a load versus flow relation can be established for use in determining annual cumulative loads of ammonia, nitrate, total nitrogen, total phosphorus, and fecal coliform bacteria in both Collins and Cane Creeks. Computations of cumulative loads would allow for a more thorough evaluation of nutrient and bacteria transport in these tributaries. Jordan Lake is 303d listed for nutrient over-enrichment and correspondingly, Collins Creek and Cane Creek are classified as Nutrient Sensitive Waters; therefore, trace metals loadings for the study sites are not a major priority for the 319 grant program and will not be computed. However, metals are of concern in biosolids (EPA, 2009; National Research Council of the National Academy of Sciences, 2002; Rudo, K., 2005) and although loadings will not be computed, metals concentrations will be used to characterize the impact of land applied biosolids on groundwater and surface water.

Analytical results for nutrients and bacteria will be compiled and coupled with streamflow data for use in determining in-stream loads with the USGS S-Plus Load Estimator (S-LOADEST; Runkel and others, 2004) program. The in-stream cumulative loads and yields at the downstream Collins Creek site and the background Cane Creek site will be compared to examine potential differences in watersheds with and without field application of biosolids. Instantaneous and cumulative loads and yields computed for the upstream Collins Creek site will be compared to corresponding loads at the downstream site to evaluate the relative nutrient and bacteria contribution of the watershed upstream of the biosolids application fields. To the extent possible, the timing of biosolids applications to fields in the Collins Creek study drainage will be documented for use in evaluating nutrient and bacteria loads.

Task 3. Perform preliminary evaluation of organic wastewater compounds as potential indicators of biosolids derived constituents in surface water and groundwater

A study by Kinney and others (2006) found that various organic wastewater compounds (OWCs) were present in nine different biosolids products produced by municipal wastewater treatment plants in seven different states. Of the 87 OWCs analyzed, 55 of the OWCs were detected in at least one biosolids product. The study indicates that additional information is warranted to better understand the potential for land applied biosolids to serve as nonpoint source of OWCs into the environment. As part of this proposed project, a preliminary round of sampling for OWCs will be conducted on biosolids source material and in groundwater at the Collins Creek application fields and surface water samples at sites, upstream and downstream on Collins Creek, of the application fields and the background site on Cane Creek. The samples will be analyzed as part of the USGS National Toxics program for a suite of OWCs, including such things as personal care products, pharmaceutical compounds, hormones, and antibiotics. The data will be examined to determine if OWCs are present in the biosolids, soils, groundwater and surface water adjacent to the biosolids application field study area on Collins Creek, and if so, can analysis of OWCs be used as potential indicator of human waste contaminants derived from residual biosolids.

Task 4. Analyze and summarize the data to characterize impact of land applied biosolids on groundwater and surface water

The water-quality laboratory results will be used to characterize groundwater and surface water in the study watersheds, with and without, land applied biosolids. Both groundwater constituent concentrations and surface-water metals concentrations and nutrient and bacteria loadings will be used in the characterization. Groundwater constituent concentrations and annual storm event surface water loads (and(or) yields) will be compared at the background and biosolids application fields sites. Concentrations and loadings in the Collins Creek and Cane Creek (background) watersheds will be compared using appropriate statistical procedures. Comparisons of upstream-to-downstream concentration and loading results in Collins Creek will be conducted using matched-pair statistical procedures, such as the Wilcoxon signed rank test and Median Aligned-Ranks ANOVA. Chemical analysis of biosolids source material and soils from fields with and without land applied biosolids will help relate the water quality results to the contributing watersheds. The data will provide insight to: 1) the differences in the amount of monitored constituents that are being delivered to groundwater and surface water from agricultural fields with and without land applied biosolids, and 2) the potential impact of land applied biosolids on water quality.