As stormwater regulations tighten, many options are available to treat runoff.

By Roberta Baxter

"It's raining, it's pouring, pollutants are flowing" might be the refrain for stormwater managers these days. Developers, owners, and governmental stormwater managers seek ways to control runoff as Phase II of the National Pollutant Discharge Elimination System (NPDES) tightens the controls for stormwater management. The United States Environmental Protection Agency requires that the problem of stormwater runoff be mitigated through construction and during the postconstruction stage of new developments that disturb 1 ac. or more of land. Redevelopment projects also must be retrofitted for stormwater management.

Despite all efforts to reduce the amount of runoff, we still must handle the pollution that comes from the runoff that does occur. Choosing a permanent stormwater best management practice (BMP) for a project requires research, knowing your area and climate, and considering factors such as space, cost, and maintenance. Many companies offer solutions, and stormwater managers and erosion control specialists can be inundated with choices.

In many projects on both old and new developments, space is at a premium. Aboveground BMPs such as detention ponds and wetlands can add to the aesthetic quality of a site, but they take up a large amount of space. Underground structures save space but often cost more, so a balance must be achieved. The cost of permanent BMPs can range from $800-$1,000 for a catch basin insert up to a couple of hundred thousand for a huge underground unit. The amount of maintenance also must be considered in the total cost.

"These systems have to be maintained," emphasizes Steve Chafin, senior environmental scientist and vice president of field operations for Eco-Systems Inc. in Bloomington, IN. In many places, developers install the systems and then turn maintenance over to city or county agencies. This results in overworked public works departments contracting with private companies to perform the maintenance tasks. Because performance can be compromised by poor maintenance, it is a crucial consideration for meeting total maximum daily loads and NPDES regulations.

This article focuses on manufactured systems for permanent stormwater runoff BMPs. The general category of swales, detention ponds, and wetlands is considered part of a treatment train.

Hydrodynamic separators force stormwater passing through the BMP unit to slow down, allowing debris and pollutants to separate out. Heavier particles settle into the sump, where they can be removed by regular maintenance. Floatable pollutants are skimmed out of the stormwater. Some of the separator systems have components that cause the water to swirl, increasing the amount of settling particles. Because these units are installed in underground vaults, they require less space than aboveground detention ponds.

Most systems capture virtually all solids. If the unit is installed in a very dirty basin, the sump might be increased to handle the bigger load. Otherwise maintenance needs to be performed three to four times a year. The amount of sediment and debris in the grit chamber is determined with a measuring stick. If the chamber is two-thirds full, cleanout is needed. A vacuum truck is used to clean out the sump. The area is large, making for good accessibility, and the cleanout takes about 30 minutes to a couple of hours, depending on the size of the unit and the load of debris.

Chris Landt, regional manager for engineering services of CDS Technologies, states that CDS has one type of treatment device available in various sizes for different sized outflows. "The Phase II requirements are driving most of our business," he notes. Municipalities are requiring BMPs for new developments and retrofitting for older sections.

The CDS systems range from 0.7 cubic feet per second (cfs) up to 64 cfs in the precast concrete models. The treatment rate can range up to 1,000 cfs with the bypass. Landt states that the cost is from $10,000 for small units up to $200,000 for the largest precast. The systems combine a nonblocking screen with swirl separation of solids and floatable materials. A vacuum truck performs maintenance.

Temple Terrace, FL, has installed the largest CDS unit in the southeast part of the city. Joe Motta, city engineer, says the unit was shipped in three pieces from California and assembled on-site. The project was a cooperative effort between the city of Temple Terrace and the Southwest Florida Water Management District (SWFWMD). The 132-ac. drainage basin flows into the CDS unit, then into a 2-ac. wetland, and eventually into the Hillsborough River, which provides drinking water for the city of Tampa. As Motta describes it, the area was just a big ugly ditch, but now it has been transformed into a beautiful wetland area.

"It looks like it's working," Motta remarks of the CDS unit, which SWFWMD is monitoring. SWFWMD has cleaned out the unit with a vacuum truck and measured the amount of debris in addition to measuring the amount of pollutants, such as nitrogen and phosphates, left in the water. From the monitoring, the district hopes to plan a maintenance schedule. Motta expects that maintenance requirements will be every few months, especially during the heavier precipitation months from June to September.

After the success of the huge CDS unit, Temple Terrace is in the process of applying for grants to install three smaller systems. The Department of Transportation also installed a unit on the other side of a highway from the one placed by Temple Terrace and hired the city to provide maintenance for its unit.

California municipalities also are using CDS units. The City of Santa Monica installed a unit on the Santa Monica Pier storm drain watershed, covering about 82 ac. within the downtown commercial district. The Civil Engineering and Architecture Division placed the unit, which is maintained by the Wastewater Department. During the rainy season, inspection is performed after each major rain, and in the dry season, maintenance is performed quarterly. If cleanout is needed, a city vacuum truck is used.

Another manufacturer of hydrodynamic separators is Vortechnics Inc. of Scarborough, ME. The Vortechs System includes baffles that cause the water to swirl inside the unit to increase precipitation of solid materials and to prevent resuspension. An oil chamber captures hydrocarbon pollutants. Fran Tighe, vice president of Vortechnics, points out, "One of the strengths of our system is the ability to handle high flow rates, not just the first flush. Systems that bypass with heavier flows might miss too many of the pollutants you are trying to remove. The Vortechs System is easy to maintain and very efficient and can be used as a standalone or as part of a treatment train."

In the city of Worcester, MA, Vortechs units are in use to capture pollutants before they reach a local lake. Beta Engineering of Norwood, MA, chose the Vortechs System to intercept pollutants from an existing 42-in. storm sewer before it drained into Lake Quinsigamond. In two years, the Vortechs System captured approximately 14 tons of sediment.

The Village of Lake George, NY, also chose the Vortechs System. Lake George is the largest body of water in the Adirondack Park. A Vortechs model 11000 was installed at Canada Street and monitored over two years. Sediment collected in the grit chamber was predominantly sand-size. For each storm event, the unit captured between 68% and 88% of the particulate material. Lake George is considering installing other units.

Dennis Daniel of Daniel Engineering in Ventura County, CA, has used both the Vortechs and BaySaver systems. Two large Vortechs models were installed on a 50-ac. industrial complex about five years ago. Daniel says they were chosen because of their ability to handle large flows and their ease of maintenance. The units were adapted to an existing system, and their profile made it possible to avoid the shallow groundwater level.

Consisting of two manholes and a separator unit, the BaySaver Separation System separates both sediment and oily residue. Recently Daniel worked on a project that used two BaySaver units on an 8-ac. shopping complex site. He notes that these units are able to handle large outflows, are easy to maintain, and fit under a standard manhole. "So far they are working great," he reports. Maintenance of the BaySaver system is performed with a standard vacuum truck through the manhole covers.

At one time, city and county governments accepted the word of owners that maintenance of stormwater BMPs was performed as required. Now, Daniel states, governments are requiring the maintenance schedules to be recorded in public documents. "Each city or town has different regulations, so it's hard to keep up."

Bryan Parker of Elgin Surveying and Engineering, recently installed a BaySaver model at the Rolla, MO, Health and Rec Center. The runoff from the service area with vehicle traffic and trash cans flows into a lake. This was the first time that Parker installed a BaySaver, but he and the contractor maintain that the unit was easily installed. After two months of operation, the unit has handled a couple of heavy storms and seems to be working well.

Stormceptor units, manufactured by Rinker Materials Corporation, come in submerged, inlet, and inline systems, ranging in size from 72- to 144-in. diameters. They also use gravity to separate heavy particles without allowing resuspension and floatable pollutants. The bypass diverts extra heavy flows.

James Sharp, superintendent of streets and fleet in Fountain Valley, CA, is "more than pleased" with the Stormceptor installed at the city vehicle yard. The new 3-ac. yard supports about 180 vehicles, from police cars to heavy equipment. All runoff is diverted into the Stormceptor system. After approximately 18 months in use, the units soon will have their first cleaning. Sharp says the city has been monitoring the sediment load through several rainstorms. He adds that the system has done an excellent job of capturing hydrocarbons. "We run a clean yard, but we chose a system with good oil-spill capture, just in case."

Stormceptor units also are in use in Irvine, CA. Skip Tracy, public works superintendent, states that the city chose to install two Stormceptor units to meet permit requirements. Because NPDES and the regional water board have set no specific criteria, Tracy says it's hard to decide what water-quality methods to use. He believes that the Stormceptor system will more than meet the regulations handed down, so it is the best way to start meeting standards now. The city has 3,300 catch basins, and he notes that placing and maintaining inserts would be very costly and labor-intensive. The city storm sewers drain into the major channel of San Diego Creek and then into Newport Back Bay, which has been an environmental problem for years. Intensive work by cities near the bay is resulting in a much cleaner bay and ocean.

The first unit in Irvine has been in place for about a year and a half at the corporation yard, which services all types of vehicles. Tracy maintains that it easily handles the first flush and the flow after that as well. Maintenance has been easy, "just like opening up a manhole and vacuuming it up." Because of the climate, the city finds that the units require more frequent cleanings through the winter and perhaps only one in the summer.

In summer 2002, the city installed a second small Stormceptor at the local "bark park," a place where residents walk their dogs. At the end of the summer, they plan to install two units at the city hall/civic center to treat runoff from parking areas.

The StormFilter system by Stormwater Management Inc. of Portland, OR, has models that operate as catch basin inserts as well as separators. Cartridges with various media filter the stormwater before releasing it.

When Costco Wholesale was constructing a warehouse store on a 22-ac. site in Clackamas, OR, 8 ac. were designated as flood control and wetlands for part of the stormwater plan. To avoid losing more property, engineers chose the StormFilter model as part of the treatment train. Stormwater is directed into a large underground vault and then pumped by lift station through the StormFilter cartridges. Two units, one 8 x 18 ft. and the other 8 x 14 ft., contain up to 24 filters. The amount of flow treated ranges from 0.33 cfs to 0.64 cfs. The discharge flows into wetlands and then into Kelley Creek. Even with traffic of several hundred vehicles a day, the system has performed well and protected the environment.

The area around a historic bridge in Portland, OR, has been fitted with CatchBasin StormFilter units, which contain cartridges filled with perlite. The perlite absorbs hydrocarbons and other pollutants. The company even color-coordinated the units with the bridge to reduce their visibility. The project will enhance the quality of water draining into the Willamette River, as well as preserve the historic quality of the bridge.

The Hydro-Kleen filtration system by Hydro Compliance Management Inc. in Ann Arbor, MI, is designed to fit round or square catch basins and often is used for retrofitting as well as on new sites. Stormwater flows through a sedimentation chamber and then into the filtration side, which is filled with media that capture hydrocarbon pollutants. Overflow protection prevents flooding in heavy rain events. The initial cost of the unit is about $2,000, and filters can be replaced for about $400.

Catch basin inserts are another structural BMP designed to capture sediment before stormwater passes into the drainage system. Usually consisting of a geotextile fabric sack, each insert fits within a catch basin. Adapter skirts are available to fit different-size basins. Pillows or absorbent packs can be added to absorb oil, grease, or hydrocarbons. Because catch basin inserts can be overcome by heavy stormwater flow, they generally are recommended for flows less than 10 gal./min. In addition, sediment caught by the filters can clog them quickly, so they might need to be replaced often in heavy sediment areas.

"Municipalities tend to shy away from catch basin inserts because of the maintenance," observes Steve Chafin of Eco-Systems. Yet he notes that any BMP requires maintenance, and he has found the inserts very effective. "They are very efficient at sediment and hydrocarbon removal and useful in locations where the discharge is directly to a receiving stream."

KriStar Enterprises Inc. of Santa Rosa, CA, manufactures catch basin inserts called Fossil Filters. Surface-water runoff flows through the catch basin insert, where floatable pollutants are captured by a filter medium called Fossil Rock. The woven geotextile monofilament fabric filter grabs sediment. During heavy flows, excess water flows into the bypass. Fossil Filters are constructed to fit industry-standard-size drainage inlets. Maintenance includes inspecting and replacing the Fossil Rock and insert, if necessary.

Locations where Chafin has installed the Fossil Filter systems include condominium complexes, shopping center parking lots, and suburban areas. He reports that, on average, his company cleans 30-50 lb. of dry material out of the inserts at each of the quarterly maintenance periods. His business is about half new construction and half retrofitting.

Chafin recounts one spectacular example of the effectiveness of proper stormwater filtration. A condominium complex contracted his company to clean up a detention pond that also doubled as a water feature. The pond was covered with the scum of blue-green algae, and the catch basins in the complex were unfiltered, adding to the pollutant load in the pond. Eco-Systems mitigated the problem with a two-step method. First, it treated the detention pond, physically removing the biomass from the pond and setting up a biofilter system, including pumping the water through gravel; adding beneficial bacteria, fish, and native ornamental plants; and installing an oxygenating waterfall. The second step was to treat the entire watershed. Much of the biomass in the pond came from landscaping, such as grass clippings and mulch that slid out of flowerbeds. The beds were hemmed in with edging. Some pollutants also came from the condominium parking lots and streets. Installing FloGard inserts and filters with a quarterly maintenance schedule mitigated these problems. Chafin states that the difference in the pond has been amazing. It is now a vibrant, eye-pleasing feature that no longer discharges pollutants into the nearby stream.

The City of South El Monte, CA, is using catch basin inserts to help protect southern California beaches. Water from the city's storm drains eventually runs to the ocean, so cleaning the stormwater is critical. City Engineer Jim Harris says two inserts have been installed and are being monitored to see the effect they have on the water quality.

Stormwater runoff will continue to be a fact of life. As regulations tighten and the public becomes more aware of the problems of runoff, stormwater managers will need choices to mitigate the consequences. Municipalities and developers can choose systems best suited for their situations–amount of runoff, available space, cost, and maintenance schedules.

Frequent contributor Roberta Baxter specializes in science and technology topics.

EC - November/December 2002