As natural areas have urbanized and turned into parking lots, driveways, and housing developments, more impervious surfaces have been created, generating increased amounts of polluted runoff. And, according to the Delaware Nonpoint Education for Municipal Officials (NEMO), this increased volume of runoff has entered streams at a much faster rate than it did previously.

In a natural setting, said NEMO, rain falls on vegetation and is either captured by plants or infiltrated into the soil. In a developed community, however, stormwater runoff can cause flooding that is known to scour streambanks and cause erosion. It collects and deposits pollutants such as oil, sediment, fertilizers, trash, debris, and chemicals into nearby waterways.

Supervising stormwater to prevent pollution and flooding is a key aspect of most development projects, said NEMO. Moreover, “stormwater management is the science of controlling stormwater runoff to prevent adverse impacts on the environment.” The goal is to protect water quality in the process.

The primary method to control stormwater discharges is the use of best management practices (BMPs). Additionally, most stormwater discharges are considered point sources and require coverage under a National Pollutant Discharge Elimination System (NPDES) permit. According to the U.S. Environmental Protection Agency (EPA), the NPDES program regulates stormwater discharges from three potential sources: municipal separate storm sewer systems (MS4s), construction activities, and industrial activities.

Most stormwater discharges, said the EPA, are considered point sources, and operators of these sources may be required to receive an NPDES permit before they can discharge. This permitting mechanism “is designed to prevent stormwater runoff from washing harmful pollutants into local surface waters such as streams, rivers, lakes, or coastal waters.”

A DuroMaxx rainwater harvesting system, from CONTECH Construction Products, is installed in Tucson, Ariz. With 15-psi-rated joints, DuroMaxx, a steel-reinforced HDPE pipe, makes an excellent cistern, the company said. Advanced Drainage Systems’ development focus on stormwater treatment systems includes extending the maintenance cycle and improving efficiencies at higher flow rates.

Quality shift
Vaikko Allen, CPSWQ, LEED-AP, regulatory manager for CONTECH Construction Products Inc., said there has been a major shift to managing runoff volumes as a means of addressing water quality.

“It’s an intuitive shift that favors those technologies with infiltration, evapotranspiration, or rainwater harvest capabilities,” Vaikko said. “For example, the EPA is targeting a 2012 release for new rules that would limit the rate and volume of discharge from new developments. The agency also recently released stormwater mitigation guidance for Section 438 of the Energy Independence and Security Act which requires new federal facilities to retain the 95th percentile design storm on site where feasible.”

At the same time, Vaikko said, treatment requirements are generally becoming more stringent, and the connection between stormwater runoff and water supply and energy issues is more widely appreciated. “The role of separators and filters is shifting from stand-alone use to integration in treatment trains including landscape-based BMPs, infiltration, and rainwater harvest,” Vaikko said.

As regulations become more focused on maintenance and minimum discharge levels, it is more incumbent on manufacturers to plan for not only removal of pollutants, but also the ability to maintain devices, said Kevin Miller, P.E., market manager for Advance Drainage Systems (ADS). “Extending the life of separators and filters through the use of treatment trains and targeted pollutant removal, as well as planned maintenance intervals without causing undue cost for the owner, are all factors that are influencing design and manufacture of these devices,” he said.

Filterra’s Roofdrain can treat rooftop runoff at ground level with a piped-in-flow from rooftop drainage areas, and be used for new construction, retrofits, commercial, or residential applications. High flows bypass the system internally.

But, as new regulations continue to push low-impact development (LID), engineers cannot depend on conventional technologies alone, said Terry Siviter, general manager for Filterra Bioretention Systems. “Rather, innovative LID stormwater treatment technologies are being implemented to meet more stringent water quality requirements,” he said. “Larger LID runoff-reduction designs, such as standard bioretention cells, are a great option for meeting water quality requirements when designed correctly.” Unfortunately, because of inconsistent design criteria and contractor substitutions, performance cannot always be guaranteed for every installation, Siviter said. “Filtration as a unit process has been considered by many experts as the solution for higher removal efficiencies and better effluent quality to meet these emerging, stringent water quality regulations,” Siviter said. “Where space is limited, and runoff-reduction methods are not practicable, packaged stormwater quality treatment systems like Filterra are a great alternative. Filterra also follows strict quality control procedures to ensure that the media within each unit meets flow-rate and pollutant-removal performance claims.”

StormwateRx, which focuses on industrial facilities, said its Aquip filtration system is effective as pretreatment to infiltration, and has been used for purification of stormwater prior to reuse. A StormTrap water quality structure installed in Twin Lakes, Wis., captures sediment in the stormwater before it flows to Elizabeth Lake. The structure is equipped with a trash basket at the inlet to help screen out trash and other floatables.

The most significant current U.S. EPA action is the announcement of its intent to write new regulations, expected to be enacted by 2012, said Craig Beatty, president of KriStar Enterprises, Inc. “While there remains a degree of uncertainty over their final form, two factors seem surely to be a critical component in the future of stormwater treatment and filtration devices — the implementation and accountability for numeric limits on pollutants, and the desire for green solutions,” he said. “This makes it imperative that such devices, and even engineered land-based systems, are designed to be adequately monitored for their effectiveness and long-term sustainability.”

Greater regulation of non-point source pollution by the EPA will mean an increase in the use of stormwater treatment and filtration devices, but also a smarter and more holistic approach to stormwater treatment, said Merideth Burkhart, water quality chemist for StormTrap. “We see this reflected in the increasing popularity of LID where stormwater management and treatment is an integral part of the site development plan from the beginning stages.”

State and federal regulators continue to drive both stormwater flow or volume control, and more effective point-source pollution control through the NPDES stormwater permit renewal processes. Filtration and other treatment BMPs are increasingly encouraged for pretreatment to infiltration, to protect groundwater quality, or for onsite reuse, said Calvin Noling, P.E., president and CEO of StormwateRx LLC.

“Use of chemicals in concert with treatment BMPs is often controlled and discouraged by regulators to prevent addition of other deleterious substances to waterways that might not be measured by the stipulated pollutant monitoring techniques,” he said. “Municipalities are becoming more involved in NPDES stormwater permitting and enforcement of point source pollutant dischargers within their jurisdictions, and in some cases private citizen groups are becoming involved as well.”

Filtration factors
There are several factors to consider for a successful, long-term operation of stormwater treatment and filtration devices. According to Miller, the use of treatment train concepts and maintenance of the systems is vital. “Removal of pollutants by devices designed for them extends the longevity and useful life of all the units in the system,” he said, adding that proper design of the systems and integration with water quantity devices can further enhance the overall system. “Adequate design for loading, backwash, resuspension, and maintenance is all important to a successful system,” Miller said. “Lack of focus on these areas can lead to premature failure of the systems and extended problems for the owners.”

According to Vaikko, the most critical factor is enforcement. “Without enforcement, BMPs can be ignored and valuable lessons regarding the importance of pretreatment and source control, adequate sizing, securing inspection and maintenance access, and budgeting for major maintenance will not be learned. Thankfully some agencies are leading the way in closing the accountability loop,” Vaikko said. “For example, the current San Diego region NPDES Phase I permit requires permittees to report annually on the operational status of BMPs including inspection and maintenance records. Some cities have passed this requirement on to BMP owners, requiring them to certify that their BMPs are in good operational condition.”

According to Siviter, no BMP will be successful in the long term without following a proper maintenance schedule. “Lack of maintenance can reduce both water quality and flow rate performance,” Siviter said.

Beatty agreed: “It has been often stated that a BMP is not a BMP if it is not maintained,” he said. “The single most important factor, and most often overlooked in the design phase, is the role maintenance plays in the long-term operation of any stormwater treatment and filtration system. Without a regular program of inspections and maintenance, systems can become inoperative and even progress to the point of becoming a net contributor to downstream pollutant loads.”

Regardless of whether it is a proprietary, manufactured device or land-based low-impact system, the filtration paths will become clogged over time, Beatty said. “After all, the sediments and pollutants being removed from the stormwater flow have to go somewhere,” he said. “Failure to clean and maintain the filtration capability of the system will render a stormwater treatment system inoperable for the functionality it was designed.”

It is important that treatment devices be sized correctly in order to function properly on a long-term basis, Burkhart said. “This requires knowledge of the types of pollutants and the pollutant load the device will actually receive,” she said. “But since specific information is rarely available we have to size them based on the best available local data. At the very least, the treatment devices shouldn’t be undersized for the contributing area.”

According to Noling, a treatment BMP must fit the use of the site. “Commercial or residential sites favor natural or underground systems because appearance is of utmost importance,” he said. “Operating industrial facilities favor systems that work well as a retrofit, are easy to access, can be maintained by their own personnel, and do not require operator attendance.”

Treatment trends
Companies are responding to stormwater treatment trends in many ways. For example, many have launched new or upgraded products, or are conducting specific research and development in this area.

ADS and its partner companies are continually working on improving its treatment train approach, said Miller. “This includes our inserts, gravity devices, and filter systems. Focuses include extending the maintenance cycle and improving efficiencies at higher flow rates,” he said. “Products are being developed for segments of the market previously ignored.”

CONTECH recently released the UrbanGreen BioFilter, a hybrid system that incorporates biofiltration and cartridge-based media filtration in one precast structure.

“It can be integrated into a streetscape or other landscaping area to address most common urban pollutants,” Vaikko said. “DuroMaxx is a large-diameter plastic pipe with helical steel rib reinforcement. It has 15-psi-rated joints and makes an excellent cistern. We are seeing more projects integrating these and other CONTECH BMPs into treatment trains that infiltrate, harvest, or detain stormwater.”

Siviter said Filterra has invested heavily in recognized third-party verification protocols and has been TAPE and TARP tested and approved based on high pollutant removal performance by third-party monitoring. To that end, Filterra was recently awarded a General Use Level Designation (GULD) for total suspended solids, heavy metals, and oil and grease by the Washington State Department of Ecology.

What makes Filterra unique, Siviter said, is that it is a sustainable design, incorporating biological, physical, and chemical processes for optimal pollutant removal. “The plant is a critical part to the Filterra system because the root system supports microbial life which consumes or breaks down pollutants into less toxic forms, making them available for plant uptake,” Siviter said. “The media captures the pollutants and the biology breaks them down. The plants uptake pollutants, which make the absorption sites of the media available again for capture of pollutants.”

KriStar Enterprises continues to produce products that address the ever-changing regulatory environment for stormwater treatment, said Beatty. The company’s recently introduced concepts include the Pod Water Management System that combines many of KriStar’s existing treatment technologies with underground stormwater storage systems to create smaller footprints for an integrated LID solution. “In addition, we are underway on a development program to expand upon existing tree box filtration systems research, and enhance the performance of our TreePod Biofilter with the goal of creating a solution for achieving tighter numerical effluent limits on a wider variety of constituents in the future,” Beatty said.

StormwateRx LLC manufactures stormwater treatment BMPs for industrial facilities throughout North America. “Our systems are designed specifically for retrofit applications on operating industrial sites where a high degree of pollutant removal is desirable, or where specific pollutants are targeted,” Noling said. “StormwateRx has an active research and development program focused on improving the performance of our systems, and making them more user-friendly. Our Aquip filtration system is effective as pretreatment to infiltration, and has been used in several cases for purification of stormwater prior to reuse.”

Pamela Accetta Smith is a freelance writer based in Albuquerque, N.M.