Safe and reliable water supplies are critical for our communities, businesses, and the environment. Droughts, limited traditional water supplies, and increasingly stringent regulations have driven communities to use recycled water to meet non-potable demands and to consider both indirect and direct potable reuse to augment drinking water supplies.
Indirect potable reuse includes an environmental buffer, such as a larger reservoir or groundwater basin, and infrastructure for conveyance, often at a high cost. Direct potable reuse (DPR) augments a drinking water supply upstream of a water treatment plant or directly to the public water system. DPR includes more treatment but requires less infrastructure for conveyance and an environmental buffer, which may offer a more viable option for a utility or water district.
With no federal regulations for DPR, individual states in the West, Southwest, and Southeast, including Texas, are developing their own regulations to keep pace with these new potable reuse water supply options and further the protection of public health.
Texas Takes a Case-by-Case Approach to Direct Potable Reuse Regulation, Reducing Unnecessary Over-Design of Facilities
The Texas Commission on Environmental Quality (TECQ) recently published a guidance manual, “Direct Potable Reuse for Public Water Systems,” to explain the regulatory approval process for Texas communities considering DPR. Consistent with the Safe Drinking Water Act (SDWA), and to accommodate on-going research on DPR, TECQ is regulating DPR through the rule exception process.
In Texas, the source water for a DPR facility is treated wastewater effluent that meets current state discharge permit requirements. This provides a clear delineation between regulatory oversight of the wastewater treatment facility under the Clean Water Act, and the DPR treatment facility under the SDWA. When a public water system proposes DPR, they are required to sample the treated wastewater effluent, similar to the requirement to sample a traditional surface water or groundwater source. The amount of treatment required for a DPR facility is based on the pathogen levels in the project-specific source water. The objective of this approach is to protect public health without unnecessary over-design of the DPR facilities.
Texas DPR Guidance Includes Minimum Levels of Pathogen Reduction
In drinking water treatment, pathogen removal is measured with log removal values (LRVs). A log removal signifies a ten-fold reduction in a pathogen concentration: 1 log = 90% reduction, 2 log = 99% reduction, 3 log = 99.9% reduction, etc. Based on the highest levels of treatment required by the Long Term 2 Enhanced Surface Water Treatment Rule, TECQ has set minimum pathogen LRVs for DPR of: 8-log virus, 6-log Giardia, and 5.5-log Cryptosporidium. Then, based on the project specific source water sampling, additional pathogen LRV treatment requirements may be required for the DPR facility.
To address variable chemical contaminants in the treated wastewater effluent source water, TCEQ also requires DPR plants to include treatment processes that remove or destroy a wide array of chemical contaminants, such as reverse osmosis (RO) and ultraviolet light with advanced oxidation (UVAOP).
Like other states, TCEQ requires a multi-barrier treatment approach to treating drinking water. Proposed DPR facilities in Texas are required to have at least four independent treatment processes, with at least two physical/removal processes and two inactivation or oxidation processes. The pathogen LRV for individual treatment processes are set by the Surface Water Treatment Rule.
Finally, the purified water produced by the DPR treatment process needs to be stabilized so that it does not cause corrosion and so that it has a similar, or better, water quality compared to current drinking water supplies.
Summary of the Texas DPR Approval Process
The process for DRP Facility review and approval by TCEQ through the rule exception process are summarized below:
- Perform one-year wastewater effluent characterization study.
- Submit a pilot study protocol that includes four treatment processes, including RO and/or UVAOP for TCEQ review and approval.
- Conduct the pilot study – typically 6-months or more.
- Submit the pilot study report for TCEQ review and approval.
- Design the DPR Facility based on the pilot study treatment processes.
- Submit the DPR Facility plans and specifications for TCEQ review and approval.
- Construct the DPR Facility.
- Submit disinfection and membrane filter performance test verification data.
- Submit a Full-scale DPR Facility Verification Test protocol.
- Startup the DPR Facility and conduct the Full-scale Facility Verification Test.
- Submit the Full-scale DPR Facility Verification Test report.
The process to evaluate, develop, pilot, design, construct, and startup a potable reuse project – either indirect or direct potable reuse – can take five or more years from concept to producing purified water. The recent TCEQ guidelines on DPR are an important milestone for helping Texas communities evaluate and potentially implement potable reuse projects to improve water supply reliability.
More information regarding the Texas DPR Regulations can be found at the link below:
Keep in mind, of course, that this article is for information purposes only and does not substitute as professional advice for how to handle specific situations that may arise. To get a conversation started with our One Water and Drinking Water teams, CONTACT US TODAY.