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Tools for Surface Water Nutrient Loading Attributable to Reclaimed Water

Project:13-11
Estimated Release: 2016
Type: Report

Program: Tailored Collaboration
Funding Partner: NA
Total Investment: $479,666 (Cash: $100,000, In-Kind Cash and Service: $379,666)

Principal Investigator: Joan Oppenheimber, MWH Americas

Background

The study builds upon the accomplishments of an initial Foundation sponsored study conducted by the same project team and published in 2012. The study established an empirical approach for distinguishing the volumetric load from wastewater sources to nutrient impaired water bodies through the use of sucralose, a conservative marker only present in wastewater sources (Oppenheimer et al., 2012; Jacangelo et al., 2012). As a result of this study, FDEP and many utilities are incorporating this compound into their water quality monitoring regimes. Knowledge of the nutrient concentration in the regionally applied reuse water then provides a worst-case estimation of the nutrient loading to the impaired water body from reuse water runoff or overspray. It is worst-case because it represents a maximum value that does not account for nutrient attenuation from best management practices such as engineered detention basins or naturally occurring attenuation prior to final discharge. It is also worst-case because it is confounded by any wastewater loads from leaking septic systems present in the watershed.

So although sucralose has been demonstrated as a suitable indicator compound of wastewater loading to surface waters (Oppenheimer et al., 2011) there is still a need to develop additional markers in order to distinguish reuse from septic system loads. The initial study evaluated carbamazepine and Gd anomaly, compounds consistently present in urban reuse effluent but less unlikely to be present in the smaller population base of septic systems because of the smaller populations served. Both provide valuable information, but do have some limitations. Carbamazepine is attenuated by photolysis and Gd anomaly has marginal sensitivity which means that their absence will not definitively rule out reuse source loading (Jacangelo et al., 2012). In addition to development of these source specific markers, it is also desirable to develop marker ratios that may differ between source and load that may indicate certain attenuation processes during surface transport through wetlands and ponds or groundwater transport through anoxic pockets within the vadose zone.

Goals and Objectives

The project will:

  • Obtain a better understanding of nutrient fate and transport processes relevant to water reuse loading conditions in order to develop a nutrient tool that can convert site specific water reuse volumetric loading assessments to corresponding water reuse nutrient loading assessments;
  • Expand the list of wastewater markers developed in the first phase of the study so that water reuse loads can be distinguished from leaking septic system loads.
  • Integrate the monitoring approaches and data interpretation schemes developed from the current and earlier study within the framework of existing FDEP BMAP programs and tools.

These objectives are necessary to the development of tools for assessing the role of water reuse applications in contributing nutrients to impaired receiving waters. Water reuse plays a critical role in the maintenance of adequate water supplies, as much of the world continues to address water shortages. Reuse applications must not be curtailed or burdened with high energy nutrient reduction technologies unless there is a clear demonstration that these approaches are warranted.

Research Approach

Task 1 will consist of a Literature Review and State and Local Agency Database Review in order to provide the necessary background information that is needed to perform the Task 2 bench-scale experimentation and Task 3 field reconnaissance sampling. The objective of Task 1 is to: (1) propose an updated target list of markers based on the latest literature on the use of sweeteners and other trace constituents as markers of wastewater impacts to groundwater and surface water; (2) perform initial analysis of study area wastewater sources (i.e. reuse effluent, well sampling in vicinity of septic) as needed to finalize the proposed target list of markers prior to Task 2 bench-scale experimentation and Task 3 field reconnaissance sampling; (3) identify key environmental variables influencing nutrient and marker transformations during transport from reuse irrigation and OWTS sources to surface water loadings; (4) assess findings of a recent FDEP state-wide sucralose reconnaissance survey and its perceived utility in predicting TMDL nutrient impaired water bodies; (5) review State and local government databases maintained for permitting of reuse and onsite water treatment systems (OWTS) sources in order to glean information relevant to the study site and assess their ability to be integrated within an overall marker monitoring strategy; (6) perform outreach activities for any additional surface and groundwater monitoring programs/data and relevant findings of stakeholder studies performed in the Gordon River watershed; (7) schedule integration of proposed project activities with the BMAP and other relevant regional activities.

Two sets of bench-scale experiments will be performed during Task 2 and this information will address knowledge gaps raised by the Task 1 literature review and help inform the interpretation of the data collected during the Task 3 field reconnaissance sampling program that supports the FDEP BMAP activities. These experiments will aid in: (i) understanding the fraction of nutrient attenuation occurring for overland transport through BMP detention basins that should be specifically attributed to the reuse water fraction co-mingled with stormwater; and (ii) understanding the fraction of nutrient attenuation during surficial aquifer transport that should be attributed to infiltrating reuse water that may be co-mingled with septic leachate.

During Task 3 field reconnaissance sampling, sucralose will be utilized to assess the volumetric fraction of reuse water in several detention basins within the study watershed during wet and dry season sampling. Sucralose is known to be a conservative marker of wastewater volumetric loading based on the previous study findings which demonstrated its absence in rainfall, urban runoff, and detention basins in regions without reuse irrigation. While OWTS is a potential confounding source of sucralose, OWTS should not have any significant input to a properly designed and sited detention basin. The objective of Task 3, in combination with the results obtained during Task 2, is to lay the groundwork from which to develop more definitive tools for distinguishing inputs from OWTS and reuse sources and a better understanding of how different ratios of various markers might be utilized to estimate conditions influencing nutrient attenuation during transport. Such tools will inform Task 3 and future TMDL BMAP efforts so that specified source load reductions can actually fulfill the TMDL requirements.

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