Stormwater | Options for Urban Stormwater Treatment

Options for Urban Stormwater Treatment

Separation devices and catch basin inserts offer options for limited spaces and sensitive environments.

By Carol Brzozowski

Due to Phase II of the National Pollutant Discharge Elimination System (NPDES), many smaller communities and their developers are being asked to take more aggressive action to prevent pollutants from their property from entering waterways. In addition to relying on nonproprietary means, they're turning to manufactured products.

Detention and retention ponds, vegetated bioswales, sand filters, and other structural best management practices (BMPs) have been traditional methods of dealing with runoff. Developers may use various temporary measures for runoff control at construction sites, but Phase II also requires permanent control after construction.

Both underground hydrodynamic separators and catch basin inserts meet those needs in such a fashion that pollutant-control can be out of sight yet still provide ease of mind. As opposed to detention ponds or other aboveground BMPs, these devices take up little space and are favored in areas where undeveloped real estate is rare or in retrofit situations where there is insufficient room for aboveground BMPs.

Underground hydrodynamic separators use various technologies to remove debris and pollutants from stormwater runoff. One such technology has swirling water that forces floating debris into a separate chamber; most include different media through which water is filtered and, compared to other methods, can cost more and require frequent maintenance.

Catch basin inserts allow water to pass through but filter debris and silt through a screen that fits directly inside the catch basin or within a storm drain. They also must be periodically maintained to prevent clogging, and some have filter media, such as absorbent "pillows," that can be added to capture oil, grease, or other pollutants.

Catch basin inserts can also be used to pretreat water that will infiltrate into the ground. Their removal of pollutants and debris helps avoid groundwater contamination - especially in places with high water tables and where infiltrated water doesn't have much sand to go through - or it can be routed to a hydrodynamic separator.

Netting systems, such as those offered by the P.J. Hannah Company, control floating debris after a first-flush storm event. They have been used in Baltimore, MD; Bluff City, TN; Indianapolis, IN; Elizabeth, NJ; Onondaga County, NY; and Pitt Meadows, BC. In many cases, a developer or a community chooses to use "treatment trains," a combination of BMPs.

Elkhart River Walk
For the Elkhart River Walk project in Elkhart, IN, the engineering firm of Whightman Petrie chose a BaySaver Separation System with a treatment capacity of 21.8 cfs. The project is an expansion of the existing River Walk, and the city needs to treat a large volume of discharge in a high-impact location in public view. Among the pollutants with which Elkhart is concerned are sediments, oils, greases, and floatables.

The particular area being redeveloped includes public walking paths and other access points to the river, explains Dustin Sailor, the design engineer for Whightman Petrie. Parcels adjacent to the River Walk portion have been designated for new development.

"The discharge pipe for the storm system currently discharges into what was an old turbine room, and there used to be a canal that went through the area. They used the water power to operate the machinery. The turbine-room structure is still in place, and they started developing the River Walk around the turbine room," Sailor explains. "The intent is to keep debris from the storm system from ending up in that room, which is going to be a point of high contact with the people in that area. They've placed bridges and other things over the turbine room, and it's going to become a centerpiece for the River Walk."

Working with the city, Sailor's job is to design a system that will minimize the amount of large solids, such as trash debris, that will end up in the turbine-room area. The plan is to install the BaySaver at the effluent point.

"Our portion of development of this storm system also takes in multiple blocks of the city," Sailor says. "It's not just this development, but it's additional developments for which we're actually rerouting the storm sewer."

The city will be responsible for maintaining the device. Mike Machlan is a network engineer in charge of water and sewer systems for Elkhart. "I'm anxious to see how [the BaySaver] performs because we have around 40 combined sewer overflows [CSOs] in the community, and CSO treatment is always an issue," he says. "If that effluent is clean enough that a reasonable UV system can be put in, it might save us a lot of money. It would be easier to treat at source for CSO discharges than try to store it and pump it all back to the treatment plant. That's a side benefit to using this product at this time."

The city will be testing the runoff to determine how well the product works. "If it doesn't really produce what we need for a disinfection process on visual inspection, then we probably wouldn't go to the next step. But all of that is really a dream right now," says Machlan. "We just thought, ‘Hey, it would be kind of cool if we could do this as well.' Especially on our smaller CSOs - we have some that are only an 8-inch line or 12-inch line that flows into the river. At sites like that, a small treatment system might be fairly economical compared to our deep-tunnel process."

It's all part of a BMP plan for Elkhart. The city has done NPDES mapping with geographic information systems and now knows where nearly all of the sewers exist.

"We have them distinguished by whether it's a storm sewer, a sanitary-only sewer, a combined sewer, or a separate sewer going into a combined area or a totally separate area. We're making sure that we actually have all of the outfalls located," Machlan says. "We have two rivers going through Elkhart, so a lot of neighborhoods have two catch basins going through a 10-foot easement out to the river. Those are some of the things that we're trying to make sure we've got tied down really well."

Additionally, the city is moving forward with its BMPs. "Some of it is pretty simple, but [if] you think about it, it helps the public," Machlan says. "We use a symbol indicating where all of our catch basins go to the river. For a number of years, we've stenciled on some of the inner-city areas on the curb, ‘This inlet goes directly to the river; anything that gets poured in here will go to the river.' We try to educate the public."

Leaves in Winter Park
Being a designated "City of Trees" is a source of pride for residents in Winter Park, FL. But those leaves are also one of the city's main sources of storm-sewer problems.

"We get an awful lot of leaf debris," says Bruce Lomberk, a design engineer with the public utilities division of Winter Park. "CDS [continuous deflective separation] Technologies' structures are fabulous for removing it and also excellent in the fact that they will bypass it if they become full. We've also used one of their devices not so much as a solids-removal device but more as a containment device for petroleum overspill on a fueling facility that we've just put into our public safety facility."

During the last three years, Winter Park has installed CDS units at three locales in the community: a CDS PMSU 30-28 unit with a treatment capacity of 3 cfs on Elizabeth Dr., a CDS Model PMSU 30-30 unit with a treatment capacity of 3 cfs on the Lake Wood Dr. cul-de-sac, and a CDS Model PSW 30-28 with a treatment capacity of 3 cfs on Park Ave. All of the projects were retrofits of older developments.

Lomberk says the challenges involved in the jobs centered around existing utilities and utility coordination because of the depth and amount of excavation required to install the separation devices. All of the sites had space constraints. Roads had to be closed for installation, and there was a time limit on how long the road could be closed. "In retrospect, it was an easy job," Lomberk says of the city's installation of the systems.

omberk reports that the city does regular checks on the lake's water quality but nothing specific to the performance of the separation devices. "Our calculations on the performance of the structures is done by solids-removal assessment, and that's just gotten underway."

He says Winter Park decided to go with CDS devices because of land values and site constraints. "It's a vertical installation. If we can find a 20-foot-diameter hole that we can poke way down in the ground, it's a better system." The city maintains the system.

Dana Point Catch Basins
In Dana Point, CA, the use of Fossil Filter Flo-Gard catch basin inserts enabled the municipality not only to stop contaminants from entering local waters but also to identify and address specific contaminants that were being generated at certain points throughout the region.

Each insert contains a filtering medium - a sorbent - and a silt and debris containment area directly under the catch basin grates. Pollutants are

removed from the runoff before they enter the drainage system, through which they might go underground and become saturated or emulsified.

The water runoff flows through the filter into the inlet and the drainage system while contaminants, sediment, and debris are trapped in the insert or by the sorbent for removal.

KriStar Enterprises' Flo-Gard Plus is a multipurpose catch basin insert designed to capture sediment, debris, trash, oils, and grease from low (first-flush) flows. It operates as a BMP for the removal of petroleum hydrocarbons, silt, and debris from stormwater runoff. A dual high-flow bypass allows flows to retain sediment and larger floatables, such as debris and trash, and allows for sustained maximum design flows under extreme weather conditions. The systems include a wall-mount combination unit, a frame-mount flat-graded unit, and a catch basin insert in a curb-opening style.

Bill Roseberry, a stormwater specialist in Escondido, CA, was involved with the installation of 150 Flo-Gard filters in Dana Point in 2001. Receiving waters of concern include Aliso Creek, Dana Harbor, and the Pacific Ocean.

The filters performed successfully. Other types of BMP filters in the storm sewer system were also tested. KriStar also monitored the filters to assess their performance and generate information on the way waste accumulates in cities and how effective filters are in trapping it.

"I thought we're not going to be getting a whole bunch of debris in these, and we'd do a quarterly cleaning," Roseberry says. "It didn't matter if it was summer, winter, rain - every time we went out, the filters were almost full. This is a community that is built out, so there isn't a lot of construction going on. That really surprised me."

Roseberry was surprised as well by how much debris was still getting into the street, and he noted different patterns occurring in various neighborhoods. "You can tell when somebody's doing remodeling. You will start to find some debris, whether it be concrete or paint, from a remodeling project. You can tell when the landscaping was done because you find a lot of grass clippings and weeds getting washed down in there.

"We also had some filters that were always full of trash, even when I would do an inspection after a month. I wondered, where is the trash coming from? Then I started looking at the area and discovered it was near a bus stop next to a fast-food market." When the trash can near the bus stop was full, people would put their trash on the street next to the can, and it would be blown into the street and into the filter.

"The simple solution was to put another trash can at the site. There are little things like that we can track and see what's going on and come up with solutions," Roseberry says.

The area the catch basin inserts serviced is a low-flow study area, Roseberry explains. "What they're concerned with are the periodic low-rain events and the hydrocarbons that come up after a quarter-inch of rain gets captured. They're not really concerned with the deluge that might come the third or fourth day of a big storm because most of the debris and waste products are going to be flushed off the street with the first flush."

"If there was a 9-foot catch basin or a curb inlet, we would only put the filter at the first 4 feet of that because if it started really raining, most of that stuff would get washed through anyway or would already be captured. Dana Point isn't doing a full-face capture - they're doing a partial, low-flush capture. It's more economical for a city to do that."

Dana Point, an NPDES Phase II community, was among the first in California to install catch basin inserts. "It's probably one of the best programs I've seen put together as far as monitoring it to see how effective it is and what the benefits are," says Roseberry. "I know a lot of other cities in Orange County were looking at it, so instead of having to go through the same study, they waited for the results and made their own recommendations based on those."

Roseberry favors the construction of the Flo-Gard catch basin inserts based on more than eight years of design concepts and improvements. The stainless steel construction eliminates rusting.

"They do take into account a lot of different things, such as what you're trying to capture," he says. "It's mainly the silt, sediment, hydrocarbons, and trash. It's hard to capture anything in the dissolved state anyway because once it's in the water, it's hard to get back out without chemicals."

Roseberry says the initial installation cost might be higher, but they are anticipated to last a long time, necessitating little replacement and low maintenance. The Dana Point project cost $41,000 in materials and installation, and cleaning the catch basins four times a year costs $30,000.

"We maintain, we do the reports and give them to the city, and they're able to keep a running log of what's out there. We make notes when we see something like food grease at a restaurant, which is a big bacteria breeder. The city is able to go back and address that concern."

Petroleum Coke at the Port of Wilmington
According to Michael Sharpless, vice president of Stormdrain Solutions in Devon, PA, the advantage of proprietary (manufactured) systems versus such methods as detention ponds, bioswales, and sand filters is "like washing a car with soap and water versus washing it with just water. Systems that were specified 10 years ago are no longer a viable means to treat stormwater effectively." Stormdrain Solutions' Inceptor can effectively treat runoff because it does not require excavation or the utilization of valuable land resources, Sharpless says.

"[These types of systems] also promote better awareness of the problem and establish a regimented maintenance plan for municipalities, landowners, and developers to follow," he points out, adding that, as opposed to a detention pond where a contractor cuts the grass, maintenance with proprietary systems involves a visual monitoring process through which inspections and filter replacements are made.

The return on the initial investment "boils down to the effectiveness of the technology as a whole," Sharpless says. "Effectiveness includes the performance of the filter, the longevity of the components, and the maintenance plan necessary to ensure proper performance. There are other structural BMPs out there, but they require a higher frequency of maintenance." That might include vacuum cleaning and waste disposal.

The Inceptor is retrofitted to various types of catch basin or curb inlets. The peaked top allows the floatable debris to be shed, thus decreasing the maintenance frequency and manpower costs. Each of the three Inceptor designs houses the company's patented PolyDak filter, which passively treats all stormwater runoff at the point of inception, the catch basin.

One example of its use is at the Port of Wilmington in Wilmington, DE. The marine terminal accommodates more than 400 ships that load and unload nearly 5 million tons of cargo each year. It's the leading North American port for fresh fruits such as bananas; cargo also includes chrome ore and petroleum coke, a black, gritty substance that is exported to Europe for use as fuel.
Kysa Skinner, project engineer for the Port of Wilmington, says previous approaches had not addressed adequately the large amounts of petroleum coke that entered the port's storm drains each time there was a wet-weather event.

"We used rolled-up burlap, hay bales, and other things that didn't work," Skinner says. "We tried to put slates over our catch basins and vacuum up after the ships were loaded or unloaded, and that wasn't effective either.

"We knew we'd have to protect the port because of the Clean Water Act, but just the fact that we know these materials shouldn't hit our waterways was motivation for us. [Stormdrain Solutions] said they'd do a demonstration for us, so they built an Inceptor and left it in for a month to show us what it would do." Inceptors were eventually installed in all of the storm drains around the port's docks and bulk transfer facilities.

Pu'uhonua O Honaunau parking lot

Sea turtle

Protecting Wildlife in Hawaii
In some cases of runoff management, creative solutions must be found. Such is the case at a site on the island of Hawaii. Stormwater runoff from the Pu‘uhonua O Honaunau National Historical Park parking lot in Honaunau drains directly into surrounding waters that turtles, tropical birds, and other wildlife call home. Contaminants such as oil, grease, and sediment called for effective water-treatment measures to protect this sensitive habitat.

What's more, the national park is on the site of an ancient sacred burial ground, protected by regulations limiting excavation depth to 6 ft. below the top grade.

The National Park Service worked with Stormwater Management to come up with a solution. Because of excavation restrictions, it was out of the question to use a StormFilter filtration system in a deep underground vault, so Stormwater Management Inc. engineers designed a custom StormFilter configuration. The system features one standard one-cartridge CatchBasin StormFilter, two two-cartridge CatchBasin StormFilters, and one three-cartridge CatchBasin StormFilter. The contributing drainage area is 2.1 ac., 74% of which is impervious. The water-quality design flow rate is 0.26 cfs, or 120 gpm. The maximum internal bypass flow rate is 1.0 cfs per standard CatchBasin and 3.0 cfs per deep CatchBasin. Cartridges inside the StormFilter units contain various media, depending on the pollutants of concern at the site; in this case, perlite (a porous volcanic ash) was used to address the targeted pollutants of oil, grease, and total suspended solids. The systems were installed in March 2003 at a cost of $22,150.

Ski Run Marina Village StormFilter system

Click here for larger view

Ski Run Marina Village
Sometimes a more traditional installation works. When a retention basin in Ski Run Marina Village in South Lake Tahoe, CA, failed to function properly, city officials sought a better solution to treat runoff from a parking lot carrying phosphorus, oils, grease, nitrogen, soluble metals, and fine sediment of 10–15 microns.
It came in the form of a customized precast Stormwater Management StormFilter, which was installed in 2001 some 50 ft. from the beach of the lake at Ski Run Marina Village. The underground unit addressed the problem while accommodating space constraints - in this case, a need to preserve parking space.

"We were looking for something that would meet the effluent standards of Lake Tahoe, which are extremely strict and in a very tight area with a high water table," says Steve Peck, engineer for South Lake Tahoe.

The area had been redeveloped in the early 1990s. Old hotels were torn down to make way for Ski Run Marina Village, a new hotel, and a new service station.

"We built a retention basin in the vicinity of where the StormFilter now is, but it just wasn't functioning properly," Peck notes. "It was built incorrectly, and it was too small. In our research, we found this and decided to give it a shot."

Perlite and zeolite filtration media were chosen to target the variety of pollutants. The system contains 50 filter media cartridges. The contributing drainage area is approximately 9 ac. The interior vault is 36 ft. long and 10 ft. wide, and the water-quality design flow rate on the system is 1.67 cfs (750 gpm). The maximum internal bypass flow rate is 2.2 cfs. The system was installed at a cost of $68,000. Maintenance is done by the property owner.

Two years later, Peck and his colleagues note that with every rain event, the data are getting better, as is the system efficiency. The runoff is tested to see how well the device is working.

Other Options
To suit particular needs, there are other choices of underground filtration, including oil/water separators and netting systems. Oil/water separators are targeted for such areas as parking lots and airports.

The challenge for the city of Palo Alto, CA, for example, was to upgrade and maintain its oil/water separation process at two of its fire stations. The existing fueling/wash pads had been discharging directly into the sanitary sewer system, and the city's waste program required pretreatment before discharge. In the past, the industrial nonpoint-source discharges had been treated through large-volume modified septic tanks.

Among the oil/water separators chosen was the ecoSep oil/water separator by Royal Environmental Systems. The technology offered a performance of less than 5 ppm effluent-free oil content based on a 5,000-ppm influent concentration. The separator also included a spill-control inlet valve to protect against discharge from catastrophic events. City officials chose the units in hopes of realizing a return on the investment within three to four years.

The ecoSep's below-grade oil/water separation unit has a grit chamber that removes solids from the influent. The grit trap is the first of two concrete tanks in the design. The grit chamber compensates for influent temperature fluctuations and oil-concentration influxes and initiates the separation of light fluids. A perforated 90° outlet tube prevents solids from entering the separation chamber.

The water then goes to a gravity separator through a float-activated shutoff valve in the inlet, and the oil floats on the surface. EcoSep separates light liquids with gravities less than 0.95.

In residual oil media, droplets too fine to be separated solely by gravity accumulate into larger drops that rise to the surface. The coalescing media is made of reticular foam. A venting pipe provides an effluent sampling port. The separated water has a residual contamination of free-petroleum content of less than 5 ppm.

Generally most oil/water separation units work in a similar fashion, though each manufacturer has a variation on the common principles.

Frequent contributor Carol Brzozowski is a journalist in Coral Springs, FL.

SW - January/February 2004

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