Expanding Technical Evaluation of Local Limits and Ordinance Revision Considerations for Potable Reuse Facilities

BACKGROUND AND OBJECTIVEWater Resource Recovery Facilities (WRRF)s include direct and indirect potable reuse facilities which use a multi-barrier approach to control water quality. All of the barriers are technology driven with the exception of one, source control, which uses regulation to control water quality. A key regulatory component of source control is the sewer use ordinance.The sewer use ordinance:is a legal mechanism implemented by the Water Resource Recovery Facility (WRRF) that sets the requirements for the discharge of pollutants into the WRRF’s collection system, reclamation and treatment facilities;ensures that the WRRF has adequate legal authority to effectively implement its local Pretreatment Program; andcontains Local Limits controlling discharge of pollutants that Users of the WRRF’s sewer collection systems must satisfy.WRRFs are also required to have a Pretreatment Program that is approved by the EPA. As part of this requirement, WRRFs must periodically review its Local Limits. Specifically, EPA regulations require that Publicly Owned Treatment Works (POTW)s with approved Pretreatment Programs must “provide a written technical evaluation of the need to revise Local Limits under 40 CFR 403.5(c)(1), following National Pollution Discharge Elimination System (NPDES) permit issuance or reissuance” [40 CFR 122.44(j)(2)(ii)].For the first time, the Orange County Sanitation District (OCSD), in partnership with the Orange County Water District (OCWD), is expanding its Local Limits and Sewer Use Ordinance to include consideration of the Groundwater Replenishment System (GWRS) and water reuse. The Groundwater Replenishment System is one of the largest indirect potable reuse systems in the world and produces up to 100 million gallons per day of high quality water using full advanced treatment. Applicability and demonstrated results of the Technical Evaluation of Local Limits and regulatory considerations for the Sewer Use Ordinance are described herein.TECHNICAL EVALUATION OF LOCAL LIMITSRegulated Constituents ListAn initial step of a technical evaluation of local limits includes establishing a list of regulated constituents. For facilities which do not produce potable drinking water, the list of regulated constituents typically includes pollutants regulated under the Clean Water Act (CWA). These pollutants are priority pollutants, including various toxic pollutants; conventional pollutants, such as biochemical oxygen demand, total suspended solids, fecal coliform, oil and grease, and pH; and non-conventional pollutants, including any pollutant not identified as either conventional or priority.In consideration of potable reuse, the constituent list is expanded to include pollutants regulated under the Safe Drinking Water Act (SDWA). These constituents are the pollutants listed under the National Primary Drinking Water Regulations (NPDWRs); Secondary Drinking Water Regulations; Contaminant Candidate List (CCL) and regulatory determination; Unregulated Contaminant Monitoring (UCM) program; and the National Recommended Water Quality Criteria. State, regional, and local regulations for potable reuse also need to be considered. In California, for example, Titles 22 and 17 of the California Code of Regulations adds regulations related to recycled water. The National Pollution Discharge Elimination System and Waste Discharge Requirements permits may also add additional pollutants.From this list, numerical limits and standards are added or derived from ambient criteria based on dilution. The most stringent numeric limit of standard is adopted for each constituent. Once developed, the list serves twofold: 1) as a starting point for the monitoring and reporting program; and 2) as numerical starting criteria for water-side mass balance or measured and theoretical removal efficiency calculations.Monitoring and ReportingThe EPA’s Local Limits Development Guidance offers a minimum number of sample days and frequency based on the pollutant, sample point, and the flow capacity of the WRRF. The Appendix of the same guidance document offers methods for determining the number of samples which sets the resource requirements at the expanded sampling points for water reuse. For the GWRS, sampling points were added at the influent to the GWRS and at the product water sample point. This was important to establish the removal efficiencies, both measured and theoretical across the GWRS which allows setting levels of service objectives across the wastewater side of treatment. Some regulatory critical control points can also be set at the influent as a buffer for operator response for direct potable reuse systems.Domestic sampling also needs to be expanded to include the expanded regulated constituent list. Domestic or residential monitoring also needs to consider rapid changes in the consumer product market.Before monitoring is initiated, it is also important to establish method detection limits or reporting limits. The reason why is because the level of environmental occurrence of SDWA water constituents may be much different than CWA as the limits are also much different.The analytical method used on the wastewater treatment side may differ from the method used on the advanced treatment side. This is due to the difference in CWA and SDWA methods and difficulties that come with inferences inherent with the wastewater matrix.Another key factor affecting sampling includes the hydraulic detention time across the wastewater treatment and advanced treatment systems such that the same volume of water is measured at each sample point.Water-Side Mass BalanceThe water-side mass balance for technical evaluation of local limits, in consideration of water reuse, is more complex. In addition to the obvious product water quality, influent quality may also be constrained, and therefore two conditions would need to be evaluated for the most stringent condition.Accuracies and propagation errors may limit closing the water-side mass balance, in which case, experience is essential to make best professional judgements regarding the value of considering smaller wastewater streams. Establishing a flow balance can help in evaluation of the mass balance.SEWER USE ORDINANCEThe Sewer Use Ordinance (SUO) includes a table of the maximum allowable local discharge limits developed from the Technical Evaluation of Local Limits. Recall that limits established for potable drinking water are included. In some cases, as narrative limits can be developed to protect the potable drinking water system.The SUO can also be expanded to include prohibited discharges to protect the potable drinking water system. Care has to be taken when adopting prohibitions as a pharmaceutical prohibition would require a program to mitigate the discharge. For example, if discharges of household pharmaceuticals are prohibited, then public outreach programs such as public awareness campaigns or drug take back promotions are implementations that speak to the prohibition.RESULTS AND CONCLUSIONSIn the multi-barrier approach to potable water reuse, the Technical Evaluation of Local Limits and SUO can be expanded for enhanced source control. Both are protective of the reuse water quality and complementary of the technical barriers for long term regulatory compliance.