Communities of all sizes across the country are required to keep close tabs on their chloride discharge numbers and ensure programs are in place to meet water quality standards. Successful programs not only meet permit compliance but also help protect their region’s surface waters, groundwater, and the sustainable health of the greater aquatic environment.
Most municipal and industrial National Pollutant Discharge Elimination System (NPDES) permit holders are familiar with effluent chloride limits. However, in recent years, discussions about compliance have seemed to ramp up. Much of this is due to changing requirements that come along with receiving a variance. The EPA (and state environmental agencies) are expecting permittees to establish an effective program for minimizing chloride discharge, and holding them accountable for implementation.
As with all permit limits, the genesis of chloride regulation primarily dates back to the Clean Water Act of 1972 and major amendments made to it in 1977. Section 304(a) requires the EPA to publish updated water quality criteria (WQC) that reflect the latest scientific knowledge on the effects pollutants may have on area waters and associated aquatic environments.
In the case of chloride, scientific studies throughout the 1970s and 1980s indicated that, at higher concentrations, chloride adversely affects the life and reproduction of various freshwater plants and animals. Subsequently, in 1988, the EPA published Water Quality Criteria (WQC) specifically for chloride. Individual states, as administrators of the Clean Water Act, must utilize the federal WQC as guidance to develop water quality standards (WQS) specific to their state and implement enforceable effluent limitations. In the decades since, state environmental agencies have implemented their own WQS and implemented them through their NPDES permit programs.
What is chloride and where does it come from?
Chloride is a negatively charged ion, or “anion.” It is generally highly soluble and most often found in a dissolved state, resulting in what is casually referred to as “salty water.” In many wastewater systems, the largest contribution is from water softener discharges. This is particularly an issue in areas of the country with hard water where large percentages of residential, commercial, and industrial users utilize a softener continually. From a treatment perspective, traditional secondary treatment cannot remove chloride from the waste stream. Reverse Osmosis (RO), or a similar type of membrane tertiary treatment, is necessary, however extremely costly. In addition to the significant capital and operating costs associated with RO, these systems produce a large amount of concentrated reject water that also requires disposal.
Requirements of a chloride variance
Because wastewater treatment to reduce chloride concentrations can be both physically and economically challenging, the regulatory agencies have established a process for obtaining a chloride variance. The specifics in each state is different, but the main requirement of the variance is that the permittee implement source reduction efforts to minimize the discharge of chloride. This is done to comply with changes to the regulatory structure implemented in 2015, when the EPA finalized updates to WQS regulations. The updates dictate that permit holders must show progress towards attaining the established water quality criteria for the intended body of water and conduct a “good faith” effort to meet the “Highest Attainable Condition” possible using the resources both available and affordable to them. As part of the variance process, it is necessary to identify, implement, document, and report all source reduction efforts during the term of the permit. Therefore, working with an engineer to create a well-developed and implemented Pollutant Minimization Plan (PMP) is essential.
Pollution Minimization Plan
In development of a PMP, it is important to understand the regulators’ expectations for your individual state. The State of Wisconsin, for instance, provides a guidance document: DNR’s Recommendation for PMPs and SRMs for Arsenic, Chloride, Copper, and Mercury Variances, 2014. The goal of the PMP is to meet the water quality standard and improve systems in order to avoid the need for a variance in the next permit term. The chloride variance will include a requirement for annual reports to document chloride source reduction measures and the effectiveness of those measures.
The State of Wisconsin has developed a helpful three-tiered approach to source reduction measures in ascending order of effort, cost and degree of enforcement. Specifics will vary from state to state, but the overall approach is generally the same.
Step 1 – Identify, quantify and educate
The difficulty with source reduction of chlorides is that there are many sources of chloride in the collection system, tied to a variety of residential, commercial, industrial and public inputs. Step 1 should be to identify the sources of chloride through surveying sewer users and conducting a sampling program to narrow your investigation.
Residential: It is not uncommon, especially in more rural communities, for higher chloride loads to come from homes with ion exchange water softeners. Consider sending a questionnaire to households to assist in taking inventory of the quantity, age and type of softeners in use, with education about system tune-ups and replacement or upgrades.
Commercial/Industrial: These facilities will have defined discharge points to the sewer system. Pinpoint industries that utilize salt directly in their processes, use softened cooling water or wash water. The largest water users will provide the biggest opportunities for source minimization. This is where implementation of a sampling program can be helpful. Municipalities may also employ a centralized ion exchange softening system on the potable water system for hardness and/or radium reduction.
Highway & Public Works Departments: Road salt may also be a significant source of chloride in wastewater. What is recognized as an excellent way to provide safer roads for motorists in the winter, excessive use of road salt can impact water wells, resulting in elevated sodium and chloride levels in the water supply and resulting in higher chloride levels in wastewater.
Step 2 – Optimize and encourage progress
Next, take the data and information gathered and work with the identified contributors to optimize operations and/or encourage replacement of older softening systems. In parallel, sampling may be continued, perhaps on a more frequent basis than required in the WPDES permit, to monitor the effectiveness of changes.
Residential: Consider working with local plumbers and softener suppliers to initiate a softener tune-up program or provide funding to complete the inspections. A targeted Madison Metropolitan Sewage District (MMSD) pilot study found a 27% chloride mass reduction from residential softeners after optimization efforts. Further targeted study suggested a 47% reduction in chloride discharge when softeners were upgraded to a higher efficiency, demand-based system. The key to an effective softener replacement program is providing the necessary public education regarding the cost savings that will be achieved through reduced salt use.
Commercial/Industrial: These users may have a greater financial incentive to limit salt usage and the financial resources to implement more efficient softening systems. Simple changes like reducing the frequency of regeneration or increasing the portion of water that bypasses the softener can result in significant reductions. For those that soften a large amount of water, encourage recycling the portion of the brine produced near the end of the rinse cycle for use in the next regeneration. Those that use a single-pass cooling water system may be able to recycle cooling water or even upgrade to a closed-loop system. Each industry is different, so there may be additional optimization and minimization activities available.
Highway Departments: Road salt application methods and technologies have made great advancements in recent years. Many highway departments are now proactively applying a brine spray to roadways, rather than reactively treating snow and ice after the fact. This method is more effective and results in a significant reduction in salt usage. Many states now offer specific training and certification programs that address safe, effective road salt use and education about alternatives. The Department of Transportation, Pollution Control Agency and Department of Environmental Services are all good places to start.
Step 3 – Ordinances and required improvements
The final step is enforcing ordinances or user agreements with large water users to limit the chloride concentration (or mass) in wastewater, and/or to require replacement of inefficient equipment.
Residential: This might mean requiring all softeners installed in new construction housing to be high-efficiency units with a minimum efficiency rating (e.g. 4,000 grains of hardness removed per pound of salt used). Or, mandating that residents replace inefficient timer-based systems by a certain date. Some municipalities have developed rebate programs to further incentivize action. A municipality could also prohibit exterior faucets and hose bibs from receiving soft water, therefore reducing the frequency of softener regeneration.
Commercial/Industrial: For larger individual, industrial or commercial users, create or modify a wastewater service agreement with an established maximum effluent chloride concentration and/or mass. This type of program would likely require a sampling station on the customer’s property for regular composite sampling.
Since the EPA established a Highest Attainable Condition criteria for variances to effluent wastewater limits in 2015, obtaining a chloride variance requires implementation of an ongoing Pollutant Minimization Plan that provides a concrete plan for reducing effluent chloride. Variance holders are expected to make a “good faith” effort, and be held accountable for effectively implementing the plan. Working with residents, commercial and industrial customers to identify, educate and implement cost-effective changes will be key to a successful plan. And, key to a higher quality of water within your community now, and for generations to come.