Owners and vendors talk about how to keep stormwater systems working

By Carol Brzozowski

For capturing pollutants in stormwater runoff, many options are available, and a variety of underground separation and filtration systems on the market offer municipalities new options when it comes to retrofitting existing areas with stormwater treatment or building in small spaces. As with any BMP, regular maintenance is a key to optimal performance. As more cities opt for these manufactured stormwater systems, they're learning how to schedule and perform maintenance activities, and in some cases are basing their choices on the type of long-term maintenance that will be required.

Protecting Lake Maxinkukee

Well before local stormwater ordinances had been enacted, the Lake Maxinkukee Environmental Council in Culver, IN, had received a grant for the installation of four water quality treatment units in 2000.

"It was considered a demonstration project, and part of what we had to do was promote it so that people understood there was this technology available and how it's used," explains Tina Hissong, executive director of the council, which partners with Culver in the effort to keep local waterways clean. Four CDS (continuous deflective separation) units were installed. "When we approached the town council on this, they agreed to do the maintenance if we administered the grant," says Hissong.

She notes that watershed studies have shown that the water quality in the bay where the town of Culver borders it was affected by pollutants. "We knew we needed to do something to deal with the stormwater runoff," she says. "The sediment was accumulating phosphorus at a rate 10 times greater than that at the center of the lake [Maxinkukee]."

Because Culver had been a developed community for quite some time, the council chose a retrofit system, the CDS system from CDS Technologies Inc. Culver already owned a vacuum truck; Hissong notes that cleaning has been fairly simple with that.

"That was one of the reasons we chose it - because we knew that they already had the equipment to maintain it," Hissong says. "That was a big decision in choosing these because we knew that they could be maintained and the town was willing to do it."

This method of maintenance is the most common for the units, says Chris Landt, regional manager of engineering services for CDS Technologies in Winter Park, FL. He notes that more than 95% of all of the CDS units that have been installed have been maintained with a vacuum truck.

Jeff Sheridan, town manager, says the matter removed from the units is not considered hazardous waste. There is a pad in the wastewater treatment plant where the town dumps the matter to let it dry out, and then it is disposed of in the landfill.

Sheridan estimates the town spends between $1,000 and $1,500 per year to clean out the units twice a year with a vacuum truck and two employees.

Hissong had the opportunity to see a unit as it was being installed. "We had a rainstorm. They didn't have the lid on, and it was amazing what it immediately picked up - all of the tree buds, sticks, cigarette cartons, sand and such," she says. "It really does hold it in there. But if you don't clean them out, it's not happening."

Now that the units have been in-ground for a couple of years, the cleaning is dependent upon the time of the year, especially when the rainfall is at its heaviest. "The first years are mostly experimental," Hissong notes. "What's interesting is different units collect different things. With some units, it's primarily organic matter. Some units are mostly sand and grit."

Originally planning on a three-month cleaning schedule, the council discovered that not much accumulated in the units during periods of little rainfall. "But in the spring, they fill up very quickly early on," Hissong notes. "Depending on what the summer is like, and the fall - with lots of leaves and the rain - they have to site-check them, because there is no given schedule for when they need to be cleaned out. They could go six months - through the summer - without needing to be cleaned, but there are certain times of the year when they need to be cleaned more often, even a couple of times a season," she says.

Along the Connecticut River

In Middletown, CT, Vortechnics' hydrodynamic separators, the Vortechs System, are used as a stormwater BMP in conjunction with catch basins. Robert Dobmeier, assistant chief engineer for Middletown Public Works Department, says the town cleans the units every spring after winter's end, after the units have collected sand and other matter that is placed on the roadway during the winter to make the roads safe for driving.

"A lot of runoff from the spring gets in the catch basins, and we do most of our sump cleaning and Vortechs cleaning in the springtime," Dobmeier notes. Three of the city's employees are dedicated to doing the work, using a vacuum truck to remove the sediment from the catch basins.

"I can't say we clean all of them every year, but there are certain ones that are in a low point of a roadway, in a sag somewhere, that we know get more sediment than in other catch basins. We generally try to get those every spring," Dobmeier says.

Vaikko Allen, technical manager for Vortechnics, notes proper maintenance starts with inspection. "We recommend that the systems are inspected quarterly during the first year of installation just to establish rates of accumulation - solids, fluid, and debris, as well as oil and grease. Based on what we find during those inspections, we can schedule maintenance," he says.

Typically, the system will fill up about every one to two years and will have to be evacuated. "The way you can tell if it needs to be maintained or not is by opening up the mantle cover and the grid chamber is easily accessible, so you could take a rod and just stick it in the top of the water surface, stick it down a little further until you come to the top of the grid pile, and if the distance there is any less than about 6 inches through the two measurements, then it should definitely be cleaned out," Allen says, adding that the systems are typically maintained with a vacuum truck.

Allen says there are no seasonal variations when it comes to maintenance. "That's one of the benefits of the four-tank system over another proprietary below-grade system - there really is no biological component to be concerned with," he says. "It's important not only for consistent performance, but also you can maintain these things any time of the year. You want to make sure it's not raining at the time you do it, or you will have a lot more water to pump out than you would otherwise."

Kim West of Vortechnics adds that many municipalities in cold-weather climates opt to evacuate or clean out the system after the sanding season, rather than in the middle of it or right before it starts. "If you do have a heavy sanding area in a cold climate, that could be one seasonal difference," she says.

The matter that Middletown collects from the catch basins is treated as hazardous waste and disposed of at a landfill that is no longer active for garbage but has the capacity for the catch basin material, Dobmeier says.

On occasion, Dobmeier says, the local health department uses pesticides to address disease vectors such as mosquitoes. The department used tablets into the catch basins about three years ago, but there is no regular program in place. There is concern from some, including public health officials specializing in vector-borne diseases, that the relatively still, often stagnant, water in underground stormwater filtration and treatment units, as well as in nonmanufactured BMPs such as detention ponds, can provide mosquito habitat.

"I've heard both ways, that they don't breed in catch basins," Dobmeier says. "In the town I live, they actively put the tablets in the catch basins. It's preventative. It can't hurt."

Pathogens present another concern. Bacterial counts inside treatment units can get high, and contaminated water washed out into receiving waters. With respect to the pathogens, Vortechnics does testing, taking samples of inflow versus outflow in some of the town's systems, "but we're more concerned about sediment and how that could impact downstream water bodies and wetlands," Dobmeier says.

Those bodies of water that the town is protecting include the Connecticut River and a sensitive recreational area. "We put a Vortechs unit upstream from that area," says Dobmeier. "Now we have about five of them and we've used them in other sensitive areas. The Connecticut River was the first one we used it at." That installment took place in 1995.

High Real Estate Prices in Oregon

Orenco Station is a 190 ac. neotraditional community of 450 residences, a 6 ac. town center, and a 50 ac. shopping center that is 70% developed. With high land costs, the developer sought to maximize development density when starting the community five years ago.

As part of the underground infrastructure for the development, three underground precast and cast-in-place vaults containing 140 radial flow cartridges treating a water quality flow of 4.7 cfs were installed to meet water quality requirements set by the City of Hillsboro, OR. The StormFilter from Stormwater Management is a passive flow-through stormwater filtration system consisting of vaults that house rechargeable cartridges filled with a variety of filter media.

The filter systems are installed in-line with the storm drains. As stormwater passes through the cartridges, the filters trap particulates and absorb materials such as dissolved metals and hydrocarbons. Treated stormwater flows into a collection pipe or discharges into an open channel drainageway.

The first maintenance at Orenco Station, performed in 1999, a year following the installation, required the removal of substantial volumes of sediment from the construction activity occurring on the site. During the second year of operation, sediments removed from the floor of the vault totaled about 3.5 yd3, and an estimated 2 yd3 were contained within the filter media pores.

Maintenance procedures include confined-space entry procedures, cleaning of pretreatment forebays, removing the used cartridges, cleaning sediments from floors (a vacuum truck is used for heavy loads), inspecting and repairing joints and seals inside the vault, and installing new cartridges. Used cartridges are emptied at a maintenance yard or landfill, then cleaned and refilled with filter media for use elsewhere. Residuals are tested for TPH and metals. The total disposal volume, including media, is 15 yd3, with disposal costing about $65/yd3

The maintenance takes three crew members for a total of 63 hours, a Ford F-800 with 4004EH Autocrane and cartridge cradle, hand tools, an industrial drum-mounted wet vac, and drums for sediment disposal.

Matt Stiller, director of operations for Stormwater Management, says the company offers an array of maintenance services. "We supply cartridges in exchange for the original cartridges removed from the vault," he says. "We are essentially getting back what we call the basket, or just the core of the cartridge, without the media. At that point, we recommend the system owner utilize their subcontractor who is already servicing their catch basins on their site."

Stiller says Stormwater Management provides maintenance training with a video, or, if necessary, hands-on help. "We like to do that on a one-time basis," Stiller says. "That's one end of our service program; the other is we accomplish the entire maintenance."

The company services about 90% of the installed systems that are maintained. But for those who maintain their own systems, Stiller says they should be maintained annually. "That's based on expected pollutant loading and impervious area and water quality regulations for the jurisdiction," Stiller says. "There will be some rare exceptions to annual maintenance, where either there's not enough room to install a large enough system to handle the pollutant loading for a full year, or in an industrial application, where there is an extremely high loading of sediment and we may intentionally design for more frequent maintenance."

Brian Long, of Wiitala Property Management, a division of PacTrust in Portland, OR, and the company that manages Orenco Station, reports that since the first maintenance, the development has been in compliance with the United Sewer Agency in Hillsboro.

Long likes that Stormwater Management takes care of the turnkey maintenance and that he does not have to worry about it. He gets a report from the company after each annual maintenance.

"When we built out there, we would have probably had to put about an acre pond in to have the water percolate down through the soil," he says. "That acre is expensive land in this area.

"This is an alternative that I think does a better job. It catches all of the oil and grease from the runoff in the parking lot. It filters out everything before we dump it into the environment. It's definitely not unsightly. It's all underground, and to date, there have been no problems with it."

Long witnessed the first maintenance.

"I believe they are the only ones who can really service," he says. "The operation is quite extensive. I wouldn't want to put my crews on it. It would cost me more time and trouble flushing them out and disposing of the matter. These guys are set up to service their own equipment and do it quite efficiently."

Stiller says it takes about three people to maintain the system, including a confined-entry worker, a vactor-truck operator, and a third person to assist.

"The maintenance cost varies quite a bit, as we have some fixed mobilization costs, so a two-cartridge system - one of our smaller systems - is going to cost close to $200 per cartridge," Stiller says. "Our largest system is more than 200 cartridges, and then our per-cartridge cost - we obviously spread those mobilization costs out - is $100 or less per cartridge."

In terms of improper maintenance, Stiller says the Stormwater Management systems are designed with an internal bypass so that parking lots, for example, will not be flooded.

"Obviously, their treatment rate is going to decrease greatly," Stiller says. "It is possible for the cartridges to be entirely occluded in extreme cases where maintenance has been neglected and for water to be passing through the overflow."

Disposal Issues: Is It Hazardous Waste?

Landt and Allen agree that the matter removed from the units is generally not treated as hazardous waste, but that often depends on local policies. "What we find most often happens is that it's picked up by a septic hauler and either dropped off in a wastewater treatment plant or brought to a landfill," Allen says. "In some cases, there could be a lot of oil that accumulates, and there are ways to remove that. You could remove it with ascorbic pads or a skimmer. You may have to dispose of that in some other place besides a wastewater treatment plant or landfill."

CDS instructs municipalities that whoever is regulating material cleaned out of catch basins with vacuum truck operations will specify what to do with the contents. "In a contaminated basin where you have a lot of oil coming down the pipe, there might be a regulatory agency that wants to treat the CDS unit contents as a hazardous material and require special disposal requirements, and unfortunately, sometimes cities might shy away from putting in a structural BMP for that reason," Landt says. "They might say, 'These special disposal requirements are not something our maintenance department wants to deal with, and therefore we are going to look at other options.' I would say to the regulatory agency, 'Would you rather have that material going down into a stream or lake if it is hazardous waste, or would you rather capture it and put it in a regular municipal landfill that probably receives a lot worse stuff anyway? Why should you bother to regulate it as hazardous waste when it's really not causing any problems to the landfill and the net gain is huge?'

"Discharging that type of material into receiving water causes a serious impact to water quality. Taking that material out of the stormwater and putting it into a municipal landfill has no detrimental impact. It should not be treated as hazardous waste."

The Mosquito Question

With the spread of West Nile virus in the United States, concerns about standing water providing a breeding ground for mosquitoes and other disease vectors has become widespread (see "The Dark Side of Stormwater Runoff Management: Disease Vectors Associated With Structural BMPs" in March/April 2002 Stormwater www.stormh2o.com/sw_0203_dark.html. Manufacturers are addressing the issue.

"We have come up with varying options to either keep mosquito larvae from having a route out of the CDS unit or keep mosquitoes from being able to get in easily," says Landt. For example, airtight hatches can be used, as well as measures that can be implemented within the pipes to minimize vector movement. Units can also be flushed out periodically to avoid standing water.

Vortechnics has a mechanism to address the issue as well: an insert that fits underneath the manhole cover. "One of the ways mosquitoes can get into the system in the first place is through the pick holes in the manhole covers," says Allen. "When requested, we can provide these inserts, which basically are a small mosquito-proof screen of a size that prevents mosquitoes from going back and forth."

Mosquitoes generally do not breed in the grit chamber or anywhere previous to the baffle wall of the system (the first two chambers), Allen says, because typically these chambers contain oil. "A small concentration of oil will create a sheen on top of the water and make it harder for mosquito larvae to respire, so even if they can pass through in and out of the system, it would take a relatively clean system for them to have an environment where they can reproduce freely," he says.

"In Florida, you've got so much standing water anyway, including down in your pipe systems," Landt notes. "Stagnant water can create more problems, but you always have numerous catch basins that always have a little bit of water in them. Draining [underground treatment units] of all of their water is not going to make much of a difference. You've got all of this standing water in the pipe system that is a potential mosquito breeding ground, so picking one particular structure and making it be drained is not having an overall effect, in my opinion."

An associated issue is pathogens in stormwater treatment systems, although Landt says this is an issue that has not received as much evaluation, except in cases where there are combined sanitary and storm sewer systems.

"We have a very large combined sewer overflow facility in Louisville where we are actually disinfecting downstream, but that's because it's raw sewerage," he says. "When storm events come, they are discharging some raw sewerage from [combined sewer] overflows into creeks and streams, which is obviously a pathogen problem, with E. coli and a number of other things.

"In that facility, we are using a CDS unit to reduce the turbidity enough that we can UV-disinfect the effluent from the unit before it discharges into the stream. The CDS system serves to allow for disinfection," he says.

For stormwater, however, such measures are rarely taken "because people are generally not used to designing disinfection systems in the stormwater systems," he notes. "You can't chemically disinfect stormwater, because you don't want to discharge chlorine or any of those types of chemicals to natural water bodies, and UV disinfection would be fairly expensive." However, he notes that the CDS or other underground stormwater treatment units are not contributors to the pathogen problem. "In the monitoring process they will sometimes learn there's an E. coli problem in the system and they'll try to identify the source and eliminate it. It could be septic tanks. There are all kinds of things that might contribute to it," he says.

Access for Maintenance

While maintenance for the larger StormFilter units involves physical entry into the unit, where cartridges can be changed and inspection can be performed at close range, some other units do not allow for entry, and the vantage point for visual inspections varies. 

 "We try to make our designs as easy as possible to maintain, and that means one access point for cleanout versus multiple access points," Landt says. "The more access - visibility and physical access - you've got inside any treatment unit, the easier it is to maintain. We try to maintain good diameter access and good-sized diameter chambers all the way down into the sump, so you can get visual verification from the surface that you have removed what you've captured, and you don't ever have to have any kind of physical entry."

CDS employees prefer meeting with municipal maintenance personnel to ensure that maintenance is as easy as possible. "We know if we design a CDS unit with a 12-inch access, they would complain because it would be very hard to verify whether or not they were removing anything," he says. "They wouldn't know what it is capturing, and they wouldn't know when they were done maintaining the unit because they wouldn't be able to tell if they've only cleaned out half of what is down there. So we've tried to make our systems open, easy to access, easy to look at, and offer different cleanout options using vacuum trucks or baskets to make it the best possible world for maintenance people to perform."

CDS provides an optional sump basket that can be used in the shafts so that a basket that functions like a pool skimmer basket can be pulled and materials can be dumped into a disposal vehicle, "which is a little bit easier than vacuum trucks in some cases because you don't have to draw down a water volume. Rather, you physically remove the solids," Landt says.

Maintenance costs vary according to the shaft that is being maintained and the basin size, he says. "We have CDS shafts that will treat flow rates as small as 0.7 cubic feet per second, and you might treat less than an acre with one of those units," Landt says. "They are small enough for a vacuum truck to completely suck it out and be done with maintenance in 10 minutes from the time the hatch is first opened. A one-man vacuum truck crew could handle that without any problem, and they frequently do.

"Then we go up to units designed to treat 64 cubic feet per second. You could treat a few hundred acres with one of those, and they may take a half a day to clean out, depending on the volume in there."

There is such a unit used in Orlando, FL, that routinely gets about 20 yd3 removed from it each time it is maintained. "Picture a couple of average-sized dump trucks full of material and you're sucking that out with a vacuum truck or moving it with a clam shell. In that case, it would probably take a crew of about three people and the vacuum truck. We have everything in between," Landt says.

Operation Depends on Maintenance

Manufacturers agree that maintenance is critical to proper operation of the systems, and they emphasize this to their municipal customers who are performing maintenance themselves or contracting to have it done.

Allen points out that like any other system, if the Vortechnics system is not maintained properly, it's not going to work. "If it fills up, your removal efficiencies are going to drop right off to the point where you're not removing much of anything," he says.

"The sediment and grit builds up in sort of a conical pile because of the way the vortex motion swirls," West explains. "We've monitored some of the systems ourselves. We've had former customers who haven't cleaned them out, and if they get really high and the water flows through, it will scour off the very top of that. It's not going to wash out everything it's collecting if it's not maintained, but it will stop treating new amounts if it is not maintained."

Landt says that if not properly maintained, the CDS units will fill up with debris to the point where they are no longer passing flow. "We always have a full bypass system in all units so if you never did maintain them, they are not impeding flow, but there may not be flow being treated anymore. Then as soon as you go clean out the unit, it's treating again.

"You've got to clean CDS units out for them to operate effectively," Landt says. "It fills up its sump and it's still operating as effectively as it ever did, but as you build up debris and sediments in the actual screening chamber, it starts to become less effective because it is processing less and less flow. It's really a function of flow rate process as to the effectiveness of the unit. When you start limiting the flow rate, you are obviously treating less water, taking out less pollutants."

The units are designed to have a cell that isolates the captured pollutants from the treatment area. "What happens in some of our competing products is they can capture some debris during a small event, but when a big event comes, they might lose all of that previously captured debris when it gets washed out because of the turbidity in the treatment chamber," he says. "They are basically trying to store pollutants in the same area that they are trying to treat. CDS units are designed to isolate the captured material away from the area being treated that experiences the high-velocity flow rates.

"As you build up material in a unit, the effectiveness is not decreased until you've filled up the sediment storage area completely and have started to build up material in the processing area," he says. "You have to not maintain one for awhile for that to happen."

The average cost of maintaining a unit per year depends on its size, Landt says. "In the city of Winter Park, Florida, I've seen them clean out their 3-cubic-foot-per-second CDS units with a one-man vacuum crew. He pulls up to it, puts his cones out, pulls the hatch, puts his hose in, sucks it out in 15 minutes, and then he's gone again. If that happens even three times a year, the maintenance expense is minimal.

"Then you go up to the 64 cfs­type unit where you are removing 20 cubic yards from it, and it's 30 feet in the ground. Every installation varies. If it is a big installation, it takes longer. You might have a three-worker crew and fill up the vacuum truck a few times before you leave, and it might cost more than $1,000 per cleanout. It depends on the size of the unit and on how much debris that unit is collecting.

 "There is a 64 cfs unit in Orlando that a three-man crew might spend a half day cleaning, but what they used to do is an outfall pipe went into a U-shaped chainlink fence built in the lake," he says. "It was supposed to capture large debris, but after every few events, they had to have the maintenance crew out there to physically pick this debris off the fence or the fence would block flow and it would end up flooding out and they would have to repair the fence. They would go into the outfall locations and dig the sediment that had accumulated out of the lake every few years."

The units also get used as pretreatments for runoff before it reaches wetland systems or underground infiltration basins. "They'll definitely extend the lifespan of an underground infiltration basin," Landt says. "The pervious nature of that underground infiltration basin is extended because it's not accumulating fine sediments; the CDS units actually take those out. When you extend the life span of something like that, instead of digging it up and replacing it in 10 years, you might extend the lifespan to 20 years. That's also a big cost savings."

Another underground system being used in installations around the country is a unit from Advanced Drainage Systems (ADS), which manufactures a product for onsite stormwater treatment. The product is based off of a large-diameter pipe and incorporates weir plates and the use of physics to separate hydrocarbons and heavier-weighted particulates.

The two-chamber product takes in stormwater with particulates settling in on one side of the tank and hydrocarbons carried over to another side of the tank. An outlet at the lower part of the structure ensures that only water goes out and the hydrocarbons are kept in suspension.

Tony Radoszewski of ADS says the unit is sold as part of a complete stormwater management system. The unit needs to be maintained every six months or once a year at the minimum. It is cleaned with a vacuum truck.

"Typically, what you are looking at is urban pollution, which is predominantly going to be hydrocarbons from automobiles and particulate matter from stormwater runoff," Radoszewski says. "Some of these units are also put in commercial applications such as gas stations that have convenience stores because of the fair amount of hydrocarbons that are spilled there."

A town can have the best product possible, but without proper maintenance, it's not going to perform to its capacity, West of Vortechnics points out. "Other companies like us are working so hard to provide these solutions, and if they are not maintained, then the water quality issues are not being met," she says. "And that's what we are all here for: to maintain the water quality." 

Carol Brzozowski is a journalist in Coral Springs, FL.

SW July/August 2004

Home + About + Subscribe + News + Calendar + Glossary
Talk + Images + Advertise + Contact Us + Search + Register + Services

Distributed Energy | Erosion Control Magazine | MSW Management Magazine
Grading & Excavation Contractor | StormCon | ForesterPress | Forester Media

© 2000 - 2004 FORESTER MEDIA, INC.