Degradation of aquatic habitat. Smothering of benthic organisms. Visual blight. Leaching of harmful pollutants. Unpleasant odors. Heavy metals in bedload. Reduction in hydraulic capacity. Increased maintenance expenses.
Such are the effects of gross pollutants cited by one expert on water quality as agencies and academics scramble to determine the most effective way of addressing this sector of overall water-quality concerns.
The “Petri dish,” as it were, is in California, where total maximum daily loads (TMDLs) have been put into effect for gross pollutants–the large debris in runoff, consisting of everything from Styrofoam cups to cigarette butts to construction debris as well as leaves, branches, and other greenwaste. The Los Angeles River “Trash TMDL” in 2002 established a 10-year plan for reducing the amount of trash discharged to the river to zero. A similar TMDL was approved for Ballona Creek, with enforcement of the TMDLs in the hands of the Los Angeles Regional Water Quality Control Board through National Pollutant Discharge Elimination System (NPDES) permits of tributary permit holders, including the California Department of Transportation (Caltrans) and 84 co-permittees of the Los Angeles County Municipal Storm Water Permit.
Bill Selbig is a hydrologist with the US Geological Survey in the Wisconsin Water Science Center, specializing in urban hydrology and water-quality studies with an emphasis on best management practice (BMP) evaluation. He points out that gross pollutants are often overlooked when considering degrading effects to receiving water bodies.
“In order to fully understand the ability of innovative BMPs at trapping and separating gross pollutants from urban runoff, it is essential to characterize what is being transported in runoff both prior to and after a BMP,” he says. “Traditional sampling methods tend to ignore the trash, litter, and large coarse material in the flow stream. New guidelines are being developed by a team of researchers in the American Society of Civil Engineers [ASCE] Gross Solids Technical Committee to address the sampling issues. The committee’s goal is to provide a sampling protocol for field testing of gross pollutants so future evaluation studies have a better understanding of pollutant removal capabilities of a BMP.”
David Smith is a team leader for the USEPA’s Region 9, encompassing Arizona, California, Hawaii, Nevada, the Pacific Islands subject to US law, and some 140 tribal nations. There has been much litigation associated with the Los Angeles trash TMDL, which has been largely resolved, Smith says. In the meantime, a number of municipalities have spent significant funds to invest in BMP upgrades, he notes.
Another step ahead: In November 2004, Los Angeles–area voters passed a $500 million bond issue aimed in part at implementing improved controls to address trash and bacteria issues as they affect beaches and other waterways. “There have been huge public investments in trying to improve water quality in the area,” Smith says, adding that efforts are under way to design and size BMPs to apply to the highest-priority spots.
Smith acknowledges, however, that there are not many TMDL listings for trash because “it’s hard to tell what is meant by debris.” “Debris” is not the way water-quality professionals think of pollutants, he says, adding that gross pollutants are more likely to be regarded as “solid waste” and therefore considered to fall under other agencies’ jurisdictions.
Gordon England, a former lead engineer for the Brevard County (Florida) Stormwater Utility and currently the senior engineer for the Bahamian Ministry of Works in Nassau, notes that more attention is being paid to gross solids these days. But, he says, although the EPA has made “noises” about establishing nationally recognized standards for monitoring large sediment particles, trash, and debris, he knows of no advances in this area. “It will be painful for them to change their ways,” he says. “They have invested heavily to go down the road without gross solids.”
Meanwhile, experts wonder if the Los Angeles River TMDL’s goal of attaining 100% treatment of all particles greater than 5 millimeters is too lofty.
“You can never achieve 100% treatment of any pollutant,” England asserts. “Look at the clips of the floods and tell me how you would filter all of that water. Legal beagles made the agreement with environmentalists without advice from engineers as to practicality.”
Jim Sullivan, an engineer with Metcalf & Eddy in Orange, CA, agrees that the 100% pollutant treatment goal may be challenging to accomplish. “There is the 90% rule: The effort it takes to accomplish 90% of an objective is equivalent to the effort it takes to accomplish the other 10%,” he says. “Accomplishing 90% removal of a constituent takes a certain level of effort, and the level of effort associated with accomplishing 98% removal is not 8% higher. It’s some significant amount more, and so that effort grows exponentially the greater percent removal you are targeting.
“Caltrans’ studies show they can get to the 100% removal,” he notes, “but it is 100% removal of particles greater than 5 millimeters and nominal diameter during a specific storm event.”
For many reasons, it’s not possible to achieve 100% removal of manmade trash that makes its way to the Los Angeles River, Sullivan asserts. Chief among them is that much of the trash deposited in the river doesn’t even come into contact with the drainage system an approved device could handle.
Yet the concerns about water quality underscore efforts to find the best approach.
The primary problem with trash and gross pollutants is that they are breeding grounds for bacteria that could pose a human health risk, Smith notes. “Secondly, it’s offensive,” he says. “Who wants to swim in a trash-streamed beach, river, or lake?”
Additionally, Smith cites adverse affects of trash on aquatic life. “Marine mammals, fish, and marine birds have been injured or killed by ingesting nurdles [bits of plastic] and other kinds of trash,” he points out.
Trash fouls up animal habitats along shorelines. It can be responsible for a reduction in dissolved oxygen in the water, which is bad news for fish species. Birds ingesting trash can get strangled by it. In addition, there’s a tremendous aesthetic problem with the Los Angeles River, Smith points out. He attended a conference addressing the problem of plastics being washed out to sea and becoming part of a circular pattern that remains and builds up. “If you were testing for particles and looking at whether fish species have plastic debris in their stomachs, the studies have portrayed that this activity has been increasing,” he says, adding it’s become the primary problem.
Another major source of the trash stream: materials generated by the fast-food industry. However, Smith says, “We feel pretty positive that real work is happening to address the issue.”
Selbig cautions that inadequate characterization and sampling of gross pollutants can positively and negatively bias the overall performance of urban BMPs. “Environmental managers rely on quality data when evaluating a device that claims to operate at a certain performance level,” he says. “If influent/effluent concentration data are determined from samples that preclude particles greater than a certain size, then the ability of a device to remove those particles may be underestimated.”
Similarly, if a sample intake is placed in a zone of concentrated particle transport, then the sample might become enriched and could lead to overestimation of the removal capabilities of a device, he adds.
“Currently, there is no single, proven water sampler that can collect the range of particle sizes associated with urban runoff,” Selbig says. “However, most BMPs are designed to capture sand-sized particles and larger and in some cases, fine particles as well. Therefore, it is important to provide instrumentation guidelines to anyone evaluating a BMP so that adequate sampling techniques are employed to ensure fair and representative data quality.”
The researchers are hard at work on the issue, such as the ASCE’s Gross Solids Technical Committee, formed to provide municipal officials with a consistent methodology for testing and evaluating BMPs and to give vendors a target to use in developing new products. Researchers point out the need for TMDLs to be revisited by regulatory agencies and for the need to add a new parameter for gross solids to the pollutant lists.
Betty Rushton, an environmental scientist retired from the Southwest Florida Water Management District, now works with the University of Florida studying low-impact development, and she also chairs the Gross Solids Technical Committee. Her focus of study has been the Continuous Deflective Separation (CDS) unit. In a study that was completed in November 2005, a major storm drain pipe in a 132-acre drainage basin in Tampa was retrofitted with a CDS unit and linear pond to help treat stormwater discharge. The site is upstream from a commercial development with a parking lot.
The CDS technology is designed to remove large-sized particles such as litter, leaves, twigs, sand, and paving residue from storm runoff. The study concluded that the technology performs well in this arena, but Rushton notes that it does not remove the dissolved and suspended particles present in the water column.
The CDS unit did remove levels of polycyclic aromatic hydrocarbons (PAHs) at concentrations many times higher than levels considered toxic to benthic organisms. Rushton attributes the presence of PAHs to nearby commercial development. Because PAHs do not easily dissolve in water, they are rarely measured in water-quality studies, but they are considered a serious problem in sediments in portions of Tampa Bay.
Another conclusion of the study was that no apparent differences were measured for nutrients before and after water flowed through the CDS unit, suggesting that decomposing leaves in the unit were not increasing nutrient concentrations in the water column.
The study concluded that if litter and large-sized particles are the pollutants of concern in a drainage basin, a CDS unit is a good solution, but if the problem is dissolved or suspended particles–especially nutrients–the unit will not reduce those pollutants. Therefore, it recommended that a CDS unit is best suited as the first element in a series of stormwater treatment methods.
“I also studied some drop boxes and got totally different results,” Rushton says. “There are a lot of different processes going on, and perhaps we need to start looking at units that do more specific things. If you are really concerned about removing leaves, you might want something different than if your big problem is sediment or litter.” She notes that one advantage of drop boxes, baffle boxes, and hydrodynamic separators is that they are underground, so they don’t take up valuable land area.
On the other side of the country in California, testing also has been ongoing. Caltrans’ Gross Solids Removal Devices (GSRD, pronounced “gizzard”) pilot program outlined six objectives each device or system had to meet:
- Capture all particles retained by a 5-millimeter mesh screen from all runoff generated from a one-year, one-hour storm.
- Be designed to prevent plugging or blockage of the screening module.
- Pass the design flow as specified in the Caltrans Highway Design Manual.
- Drain within 72 hours to avoid vector breeding.
- Hold the estimated annual load of gross solids, based on one cleaning per year.
- Require no maintenance other than inspections through the storm season.
A variety of devices were tested. Some worked well; others did not. Those that met the six criteria were characterized as approved devices. Metcalf & Eddy then created standard details and guidelines for the approved devices.
Two devices are now approved: a linear radial screen and an incline screen. The linear radial screen is a water well screen with 5-millimeter slotted openings on the side that’s installed in a concrete vault. Stormwater carrying debris flows through a casing pipe, with water flowing out through the screen and the debris remaining inside the vault. A maintenance crew typically vacuums the solid material annually.
The incline screen comes in two types. One type is a curved wedge-wire screen design with 5-millimeter spacing. Stormwater carrying debris flows into a distribution chamber, over a flow distribution weir, and onto the face of the curved screen. The debris is housed in a concrete vault, while the water flows through the screen into a collection channel.
The second type is similar but sloped. Stormwater carrying debris flows onto an energy-dissipating slab and over the sloped screen. The debris is housed in a concrete vault; the water flows through the screen to the outlet sewer.
“There are a variety of different sizes and shapes for each of the types, but the mechanism of the screening process itself is similar,” Sullivan says. “The concept of the device is that it doesn’t require any mechanical action. Water will flow through the device, which will retain the gross solids, and the stormwater–free of gross solids–will then bypass and go to the LA River.”
Nylon mesh bags secured to the ends of outlet pipes are another type of device being used to meet the TMDL. Brown and Caldwell, an environmental engineer and consulting company with offices in Walnut Creek, CA, works with municipal clients in addressing water-quality issues associated with NPDES permitting requirements for stormwater as well as industrial and municipal wastewater, total maximum daily load requirements, and other client needs. The company designed the bags to collect litter from first-flush runoff. The bags are secured with a metal brace around the outlet of a storm drain so they won’t fly off with high water volumes but can capture debris, leaves, glass, plastics, metals, and other particles coming down the line.
Caltrans is now using the solid waste removal bags as a BMP. “The issue is what’s the most cost-effective design that’s not going to cause any flooding and is relatively easy to maintain,” says Nancy Gardiner, a water resources division manager for Brown and Caldwell.
As a streets and stormwater assistant division manager for the City of Orlando, FL, Kevin McCann would agree. A major tourist destination, Orlando and its surrounding areas cannot afford to look bad. Even though Orlando does not have a TMDL for gross pollutants, the municipality has tried some innovative ways to collect them.
“Our crews spent a tremendous amount of time picking up garbage and trash along the shorelines of lakes, so we’re trying to keep it from getting in the lakes,” McCann notes, adding that residents around the lakes have lodged complaints because of trash.
The city also is trying to reduce pollutant loadings that occur as a result of leaves and grass clippings. To that end, Orlando is using CDS units in locations where there are high flows, as well as baffle boxes with screens, specifically those manufactured by Suntree Technologies. “Those seem to be good for capturing gross pollutants,” McCann says. “We are also putting inlet filters in our catch basins, trying to capture them at the outfall.” The types of pollutants Orlando is capturing primarily include Styrofoam products, paper, cans, leaves, some sediments, tree limbs, and twigs.
McCann notes there are more than 100 lakes in Orlando, which all are impacted to some degree by gross pollutants. In particular, those such as Clear Lake border large areas of commercialized land with massive impervious areas and heavy traffic. Other lakes, adjacent to oak canopy, would practically be covered with leaves, in addition to trash from adjacent highways.
Orlando has been trying to capture gross pollutants for about 20 years, first using debris-collection devices at the end of pipes akin to fence enclosures. “They weren’t very effective,” McCann says. “They would blow out and get undermined because there was so much flow going through, but we’ve been trying to improve on that.” The city began using CDS units and baffle boxes about six years ago and inlet filters in the last year.
At Lake Rowena, the city is using a rotating bar screen that removes trash from a 96-inch pipe; the flow rates are so high nothing else will work. “It’s like what they use at wastewater plants to clean out big materials in the inflow,” McCann says. “It’s underground; it rotates and drops everything into a large collection basket. We get a lot of material from that one.”
The city has been pleased with the results of its approach, as measured by the amount of material being collected. McCann says more than 100 cubic yards of material are removed monthly. Labor reduction cost savings are realized through the ability to collect more material–some 15 yards–before having to dump it, McCann notes. “It would take 20 people to collect that much in one day manually, whereas now, a two-man crew can do it,” he says.
Device maintenance also is a concern for Orlando, as it is for any community. “When we were using the debris-collection devices at the outfalls, it would require our crews to walk through people’s yards to get to them,” he says, adding crews had to manually clean out the devices. Noting the ineffectiveness of that approach, McCann praises inlet filters for affording the city the opportunity to clean them with a vacuum truck and less manpower.
Although the city does not know the exact correlation between gross pollutants and some local water-quality issues, McCann notes that the number of fish kills in city lakes has dramatically decreased over time and such events are now rare. “Some of that has to do with collecting the large organic material and grass clippings, because that would have an impact on the oxygen levels,” he says.
While testing continues, municipal officials in California and other areas can now decide which BMPs provide the most effective means to address TMDL allocations. For one, the US Geological Survey provides the science necessary for environmental managers to make sound public decisions, says Selbig. England has pioneered the use of some innovative stormwater BMPs and had a hand in writing the ASCE Guide for Best Management Practice Selection in Urban Developed Areas. Rushton says manufacturers are rallying. Suntree Technologies, for example, has developed a baffle box that holds the leaves up above the sediments.
Regarding the Los Angeles River trash TMDL, Sullivan says the testing phase is 80% complete, resulting in devices that meet all the criteria Caltrans established.
“The department is going forward with regular projects to comply with the TMDL to install these devices for a more wide-scale regular use,” Sullivan says. “We are evaluating those projects, because our initial phase was to develop the standard plans.” He notes it takes time to develop a standard plan because Caltrans wants to ensure it is “bulletproof.
“We’re going to evaluate these more wide-scale projects on how they performed, how our standard details were implemented, and how construction went, and then the results of that monitoring will go back into refining the standard details to make them more cost-effective and easy to use, and to make the device easier to build,” Sullivan says.
The department seeks smaller, better-performing, and less expensive methods, “so if a viable pilot is identified that may improve the total life-cycle cost of these devices, they are going to look hard at it and probably do a study on that,” Sullivan says.
He points out that while constituents typically adhere to gross solids, “removing gross solids is the minimum treatment for traditional new development and redevelopment projects. Caltrans is targeting trash because they are going to need to do something at their facilities to address that TMDL.”
Rushton, in Florida, is in favor of more low-impact development designs. “We’ve changed the hydrology even when we put in ponds, because all it does is shave off the peak flow–it doesn’t shave off the volume of water that goes through, and it’s this volume that may be so detrimental to our streams, because now you start having a lot more force and a lot more sedimentation in the stream,” she says. “It’s going to take more than one method to solve our stormwater problem, and looking at these gross solids is going to be one of those methods.”
The eradication of trash–a blight in high-use urban areas–is rooted in this multipronged approach. And while some BMPs are showing promise, there may be adverse effects if they are not properly maintained, causing back-ups in storm drain systems, Smith says. He points out that efforts to head off the problem on the front end–better litter collection and traditional street and sidewalk sweeping before the trash gets into a storm drain–provides some relief.
“It pays to do some careful studies,” Smith says. “It’s expensive to implement technology. Preventative practices are better in the long run. Government’s ability to do maintenance is pretty limited. Once the trash gets into the storm drain system, it’s difficult to deal with it.”
