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A Protocol for Estimating Potential Water Quality Impacts of Recycled Projects

Project: 04-16
Type: Decision Making Tool
Year: 2009

Program: Principal
Funding Partner: Bureau of Reclamation
Total Investment: $244,325 (Cash)

Principal Investigator: David W. Smith, Ph.D., Merritt Smith Consulting


The use of recycled water is regulated by multiple agencies, each of which has specific areas of jurisdiction, especially in California. These regulations have led to project permitting structures that are prohibitively complex, especially for small, low-flow wastewater systems, to the point of discouraging the development of recycled water projects even though recycled projects have been demonstrated to offer substantial benefits. Establishment of a decision-making framework and assessment tools will facilitate efficient and comprehensive evaluation of recycled water use by project proponents and help streamline the permitting process by California regulators.

Goals and Objectives

The project developed a standardized process, or framework, with associated analytical tools, for evaluating potential groundwater quality impacts that could result from incidental recharge by recycled water beneficially used for irrigation or stored in ponds.

Research Approach

Development of the framework included a review of the literature to identify tools from several scientific disciplines that could be applied to the assessment of groundwater quality impacts from incidental recharge by wastewater effluent meeting disinfected tertiary treatment standards. Those tools were then assembled into a two-tiered, decision-making process to first screen effluent quality by identifying constituents of potential concern relative to groundwater and then further estimate the risk of potential impact using site specific data. A pilot test was conducted using a small wastewater treatment system that employed MBR technology to generate effluent meeting disinfected tertiary criteria. Data from the pilot test was evaluated to assess 1.) MBR plant performance relative to conventional treatment by extended aeration 2.) Evaluate key operational differences between small MBR and conventional wastewater treatment systems and 3.) Provide data to subject to analysis using the Framework.

Findings and Conclusions

The pilot study confirmed the documented fact that MBR systems produce effluent of superior quality over more traditional wastewater systems. The study also found that proper sizing of the MBR system was critical in obtaining operational efficiencies for small treatment systems (less than 10,000 gallons/day). The Framework was extremely useful in evaluating potential groundwater quality impacts. The Framework consists of two steps; a preliminary screening and a detailed site screening to identify water quality constituents of concerns in effluent relative to the quality of the groundwater in the area where the recycled water will be beneficially reused for irrigation or stored. The preliminary steps compare the anticipated recycled water quality to groundwater quality relative to applicable federal and California regulatory standards and guidance. A list of constituents of potential concerns are developed and then subjected to further analysis using more site specific data. Tools to evaluate the fate of nutrients, salts, metals and organic carbon are provided. These tools are used to estimate the interaction of these constituents in effluent migrating through site soils prior to reaching groundwater. The tools are particularly useful in estimating effluent organic matter attenuation and the potential for formation of disinfection by-products in groundwater. Furthermore, the tools allow the project proponent to estimate the impact of nutrient, salt, and metal build-up in soils and their affects of recycled water use over time.

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