That seems to be the definitive factor in municipalities and commercial entities deciding on a particular type of stormwater treatment. Sometimes, location suggests a nontraditional method such as ozone, ultraviolet, or electrocoagulation.
Ozone for Dry-Weather Runoff
Dry-weather runoff is a typical bacteria source in coastal California and often was cited as the culprit for the frequent beach closings at Salt Creek and South Monarch beaches in south Orange County, where bacteria levels had exceeded state standards and the federal Beaches Environmental Assessment and Coastal Health Act.
Salt Creek, an urbanized creek that drains significant portions of the cities of Dana Point and Laguna Niguel, has been the source of bacteria through its conveyance of an urban pollution soup that included fertilizers, animal waste, and detergents.
Despite Dana Point’s aggressive urban runoff programs–launching public information water-quality campaigns, installing filtration devices in catch basins, and requiring various best management practices (BMPs) for new developments–there had been no noticeable impact on beach closings.
Several alternatives were considered. Diverting the dry-season flow to the existing wastewater treatment plant was not feasible because of the system’s 1,000-gallon-per-minute maximum flow rate capacity. City officials then decided a new plant needed to be constructed to deal with the runoff.
Chlorination and dechlorination were rejected for safety reasons, given the plant’s proximity to residential and beach areas, as well as limited access for chemical deliveries.
Ultraviolet (UV) technology and ozone were considered. City officials chose ozone because they believed it would be most reliable and cost-effective in achieving disinfection. The creek has a low UV transmission rate and high levels of turbidity, total suspended solids, iron, and manganese, making it a less-than-ideal candidate for effective UV treatment.
The $6.7 million Salt Creek Urban Runoff Treatment Facility (URTF) was built in November 2005 as an advanced stormwater treatment facility to withdraw, treat, and return up to 1,000 gallons per minute of dry-season creek flow.
The system operates eight to 10 months each year during dry-weather periods with flows from 200 to 1,000 gallons per minute. It is deactivated during wet winter months and prepared for the following season.
Designed to treat up to 1.5 million gallons per day of urban runoff during non-storm events year-round, the system was manufactured by Ozone Water Systems.
The fully automated, 1,700-square-foot system automatically shuts down in response to sustained flows; South Coast Water District operators determine whether it needs to be started manually. The programmable controller allows for continuous and unattended operation.
The four-stage treatment system works as such: An intake grate in the bottom of a concrete flood control culvert discharge apron at the beach takes in dry-season flows up to 1,000 gallons per minute from Salt Creek. A continuous deflective screening device screens coarse debris and floatables from the influent, which then is pumped 800 feet to the treatment facility. The influent also enters basket strainers, which remove smaller debris, and then passes through six horizontal media filters located at the facility. Backwash wastewater is discharged to the sanitary sewer.
When the runoff has been filtered, it enters the ozone contact chambers, where it’s in contact with ozone to kill bacteria and potential viruses. The ozone is produced by one of two generators through a corona discharge method from prepared atmospheric air and is injected through diffuser stones. The plant can produce up to 100 pounds of ozone each day.
The dosage is based on the oxidation reduction potential, which measures the ability of the water to oxidize contaminants. Off-gas runs through a destruct unit, and the final product is discharged through a roof vent.
Treated effluent flows by gravity downstream and is discharged back to Salt Lake, where it enters the ocean. The effluent is monitored for its bacteria levels and to ensure the effectiveness of other BMPs within the watershed.
In low-demand periods, generators go into a “soft start” mode when no ozone is produced. The system also buffers peak ozone demand periods. Plant shutdown procedures protect the facility from first-flush stormwater high-solids loadings.
California officials point out that while BMPs, watershed planning, source controls, and public education have been avenues pursued for National Pollutant Discharge Elimination System (NPDES) compliance, such measures may not address short-term needs in watersheds that may not enjoy optimal health. Advanced runoff treatment is thus necessary, they say.
City officials intend to augment the URTF with other stormwater treatment methods, such as a “vigorous” street sweeping program and the maintenance of catch basin filters in the storm drain inlets, as well as working with community-based organizations such as the Dana Point Earth/Ocean Society.
One of the goals of Dana Point and South Coast Water District officials is to develop an optimized ozone dosage protocol to apply the minimum required ozone dosage to achieve effective bacteria treatment in an effort to conserve energy costs that result from greater ozone generation.
Another goal is to investigate the feasibility of recycling treated urban runoff for irrigation.
Lisa Zawaski, water-quality engineer for Dana Point, says bacteria levels have continued to improve significantly as a result of the URTF. Although beach closings were necessary while the plant was down for operation and maintenance issues during its first year, results have otherwise been “superior,” she says.
“The water quality at the beaches has improved so much that the beaches are eligible for removal from the state’s 2008 303(d) list of impaired water bodies for bacteria,” Zawaski says.
Additionally, the project complies with total maximum daily load (TMDL) requirements currently in development.
The Dana Point URTF was featured at the International Ozone Association’s World Congress on Ozone and Ultraviolet Technologies meeting in Los Angeles in August.
In a final report Dana Point released in March 2007, prepared by the Public Works and Engineering Department, officials declared the approach a success. The report outlines a number of keys to the project’s success:
- Engaging operations staff and wastewater and stormwater professionals in design and planning
- Carefully evaluating water quality to ensure process selection
Allowing design flexibility to accommodate variable surface-water conditions - Considering short-term and long-term monitoring plans and costs
- Relying on experienced operations personnel as troubleshooters, and properly training staff in the design and function elements of the plant
- Keeping careful, comprehensive, and accurate records
- Obtaining community support
Additionally, Dana Point public works officials cite a number of lessons learned from the project. Among them:
- Include features for an automated data-retrieval system, important for reporting requirements and continued operations evaluations.
- Consider filtration system design and construction and development of backwash protocols in recognition of the dynamics of urban runoff water quality.
- Acknowledge that there are materials and equipment not subject to ozone under normal operating conditions but that may be exposed under specific circumstances; thus, evaluate and consider ozone-resistant materials where appropriate.
- Ensure adequate access for maintenance; consult with future operators in design phase details. Consider that highly specialized equipment repairs may take longer than anticipated.
- Ensure coordination between the electrical engineer and operations staff to ensure ease of access and the implementation of efficient lock-out/tag-out procedures.
UV Treatment for Bacteria
Elsewhere in California, ultraviolet treatment was the choice when officials in Encinitas had to confront a problem with Cottonwood Creek.
Much of Cottonwood Creek–which runs through the center of town and has historic significance as a water supply in the early 1900s–flows under impervious cover, such as Encinitas Boulevard.
Cottonwood Creek watershed drains to the creek and into the Pacific Ocean at Moonlight Beach through large culverts. Bacterial pollution from urban runoff has long plagued the coast of Moonlight Beach, with the beach having received failing grades from the Heal the Bay watchdog group. It was frequently subject to closures.
Over the years, the quality of the water of Cottonwood Creek significantly degraded.
“When the county does its testing, it routinely comes up exceeding the bacteria standards for many, many years at pretty high levels,” notes Kathy Weldon, stormwater program manager for Encinitas. The city consequently engaged in many studies and inspections of those areas directly connected to the storm drain system.
“We had to go to some mechanical means to get those numbers down,” Weldon says. “The waters were on the 303(d) list due to excessive fecal coliform levels, so we knew eventually this was going to be a TMDL site, which it is right now.”
In considering the options for a structural BMP, city officials pared the choices down and eventually settled on UV treatment; Weldon cites water-quality concerns as the reason. The system was supplied by Clear Creek Systems of Fresno, CA, in 2002.
Five years down the road, Encinitas officials are pleased with the results. Coliform bacteria have been reduced by 99.9%.
“We’re always getting very good kill rates for water quality coming out of the treatment facility,” says Weldon.
The primary concern with UV treatment facilities is getting the turbidity out, Weldon notes. “The good thing about this creek is it doesn’t typically have high turbidity to start with,” she says. “We wanted to make sure we get everything out before it even hits the UV treatment area in order to get the right ultraviolet kill.”
Weldon says the municipality has put in so much treatment ahead of time that most of the pollutants–including viruses and bacteria–are killed before the influent reaches the UV treatment.
According to Weldon, all intake and return facilities are located in a double box culvert measuring 6 feet wide by 4 feet high within a city right of way to an existing street. A 12-inch-high removable wood weir at the upper end of the south box culvert diverts dry-season flows to the north box culvert, where flow then is diverted to the wet-well pump station.
A second 12-inch removable wood weir creates a pool at the downstream end of the north culvert. A notch cut into the south culvert weir was designed to discharge approximately 15% of the flow to the culvert to provide the required bypass. The weirs can be secured in place during operation and removed during wet periods to minimize debris collection.
Diverted flow is moved by pumps that handle submersible solids to the treatment facility enclosure. The flow passes through two basket strainers and then flows through two multimedia filters before passing through two UV-light disinfection chambers. To avoid retreatment, the flow is returned downstream of the diversion weir in the south box culvert.
The diversion weirs were sized for a maximum flow of 150 gallons per minute. If higher flows are experienced and the level in the wet well rises above normal operating conditions, an alarm is activated. If the water level in the wet well continues to rise, the system will shut off. Flow contained in the wet well then can return to the creek via a return line.
During anticipated heavy rainfall periods, the system is shut off manually and the diversion weirs are removed. This allows the box culverts to pass flow down the creek.
Instrumentation and controls include a flow meter, a turbidity meter, and UV bulb monitors.
Automated wipers remove scale buildup in the UV chamber to reduce maintenance and cleaning requirements. Extremely low or high water levels in the influent pump station or influent turbidities in excess of 20 nephelometric turbidity units cause the facility to shut down automatically. An alarm is sent via telemetry to the operations center of the San Elijo Joint Powers Authority, which monitors and maintains the treatment facility.
As for the footprint, the system was placed by an existing sewer pump station and utilizes a box culvert for discharges.
There was hardly a learning curve for the UV, Weldon says.
“The learning curve is learning the process of how everything works and keeping it functioning,” she says. “The UV is pretty much a light bulb. There haven’t been many problems with it. It’s just changing it out from time to time.”
The biggest costs for the city are water and energy, because the cities do eight to 10 hours of backflushing, says Weldon.
Noting that although the city has met its goal by eliminating the risk of a public health threat and opening up the beaches after getting numbers down on pollutants, Weldon points out there still remain some concerns.
“We’re still one block from the beach,” she says. “And you still have the chance of regrowth because it’s still a natural channel. We have other issues at the beach. There is a high-tide influence with the trash line at the beach. Other things are causing the counts to come up–not necessarily what was coming down the creek to start with.
“We’re receiving other influences now that we’ve eliminated the biggest one. Whether or not they’re pathogens or just a nuisance factor is the question.”
She says other municipalities in similar situations should consider being as close to the compliance point as possible before discharging back, “so when you take another sample down the stream, you aren’t alarmed that your counts have come up. Location is a big key. Pretreatment is another big key. Make sure you get as much of the turbidity out before you do the UV to keep the function at the optimal level. Be prepared for backflushing. Try backflushing with some other type of water than a drinking-water line.”
Weldon says while there may have been a different type of treatment that could have been used, such as wet ponds, “It may have not been good enough for this location.”
Electrocoagulation and Stormwater
Giving water an “electric shock” is another nontraditional stormwater treatment method being utilized.
Among the companies providing electrocoagulation equipment is Water Tectonics in Everett, WA. Operated by Jim and Jason Mothersbaugh, the company makes Wave Ionics, an electrocoagulation system that is being used as an effective means to treat stormwater.
The company describes electrocoagulation (EC) as “an electrical process that has the capacity to destabilize emulsified oils, contaminants, metals, and sub-micron particles. When contaminated water passes through the EC cells, the primarily negatively charged particles combine with a positive charge from the cell plates, which initiates the coagulation process.
“The particles agglomerate into larger particles, no longer being suspended in the water column. Depending on the type of contaminant being removed, the agglomerated particles either rise to the top [oils] or settle to the bottom [sediment] of the water column.”
Jim Mothersbaugh explains that electrocoagulation originally was used for the de-emulsification of emulsified oil and for the precipitation for heavy metals.
“It’s an applied current to a metallic plate that releases an inorganic metal that forms electrocoagulation,” he says. “It’s an advanced form of aluminum sulphate treatment and ferric chloride treatment.”
He says EC’s biggest advantage over such methods as polymer treatment is that “it automatically adjusts to the conductivity of the influent water because it is an electrical process. It instantaneously adjusts its dosage based on the level of contaminants coming into the system.
“Any other operation, such as drinking water, for instance, has a fairly even character. Stormwater has no even characters–it’s all over the place and extremely heavy, and then it’s nothing.
“Unless you have an operator on hand who can instantaneously adjust to the level of contaminants in the incoming stormwater, you’re either going to be applying too much or too little polymer or chemical. The advantage of electrocoagulation is that it senses the conductivity and adjusts its dosage automatically based on that conductivity.”
Water Tectonics’s EC units enable a 99% reduction in suspended solids, emulsified oils, metals, copper, nickel, and zinc.
“Up until this point, the industry would take advantage of very easily removed large particles and say they were doing 99% removal,” Jim Mothersbaugh points out. “It is getting to be more of a norm in the industry that instead of always going by 99%, we instead look at parts removal: We have a 99% removal on copper from a raw ppm [parts per million] of 38 to 0.48 for EC-treated water; 99% removal of nickel, from a raw 24 ppm to an EC-treated ppm of 0.01; and a 99% removal on zinc, from a raw 221 ppm to an EC-treated ppm of 0.41.”
To date, the company has been focusing on the construction market, because it has a requirement to control its discharges and the finances to do so, Jim Mothersbaugh notes.
“The main contaminators or places of pollutants in the country are not really from construction people–they’re from the scrap metal yards, the steel fabricating facilities, the food processing industry, the poultry industry, the fish processing industry, and the meat processing industry, so when stormwater and processed water come into play in those industries, that’s where we there is a large outfall of pollutants,” he says.
“Those industries also are the ones located on our primary rivers, oceanfront, and harbors. That is where the importance of this market is going. The State of Washington is leading the way by going after the main sources of pollution. That is a significant move.”
The oil and gas industry is another that has come onto the radar for its pollutants contribution, Jason Mothersbaugh notes. “They have traditionally taken their processed water and injected it into a Class 5 injection well and disposed of it in a deep well. The US Environmental Protection Agency is starting to close that loophole. They’ve determined the Class 5 injection well is dry and the water they are pushing into that well is leaking out into major aquifers and streams.
“Electrocoagulation works well in those applications, not only to reduce the amount of water for recycled reuse but also the contaminant loading required for disposal.”
The nontraditional stormwater treatment market is undergoing rapid growth, notes Jim Mothersbaugh, with the fastest-emerging markets for EC technology being in the industrial sector: “ports, marinas, scrap metal yards, wood treaters, and oil and gas.”
The system consists of an input pump, a treatment section, sand filters, and discharge for the effluent. EC is effective in conjunction with other systems, removing up to 90% of pollutants and allowing other methods, such as ozone or UV, to improve in performance, Jim Mothersbaugh says.
As for the cost of EC compared to other methods, Jim Mothersbaugh says as far as a standard 300- or 400-gallon-per-minute system, there’s an initial capital cost of about $400,000.
“What you are not going to be seeing is a full-time operator 24 hours a day, because everything we are building is computer-operated and is also the only system approved in the state of Washington that does not require an operator,” he says.
“Everyone has gone with full-time operators; we have gone “˜operator-less.’ Where we see that as critical in the industrial market is that the industrial market is a 24/7 market. They can’t afford to have a three-man crew or a six-man crew running 24/7, so there is a labor savings.”
For now, Water Tectonics’s EC system is being used primarily in the state of Washington but is starting to expand into the Midwest as well as Georgia.
Maintenance on EC systems is minimal, Jim Mothersbaugh says. “All of these new systems are built with so many multiple safeguards for temperature, pressure, flow, lack of flow, and operating ranges that if we start to see something going, we can easily respond to it by a wireless alert,” he says. “It probably costs about $0.25 per 1,000 gallons on maintenance, including electrical and consumables.”
A Pilot Study in Los Angeles
During six weeks in late 2004, the Los Angeles Department of Water and Power’s Western District Headquarters installed an electrocoagulation system from Powell Water Systems as part of a pilot study for treating heavy metals and bacterial pollution from dry-weather runoff in Ballona Creek. The EC unit is completely self-contained and skid-mounted.
“The only thing you’d need after electrocoagulation is some type of filtration,” says Rodney Van Johnson, a project manager with Powell. “With electrocoagulation, we take out everything in there. The beauty of it is that the solids are non-toxic, so you have a sludge that’s not hazardous and can be used for fertilizers. When you’re dealing with polymers and other chemicals, there are still bacteria in there that can grow.”
Pretreatment also is used with EC to reduce energy costs, Van Johnson notes.
Because of the heavy metal and bacterial pollution, Ballona Creek has been on the EPA’s 303(d) list and has TMDLs being developed. Anticipating numerical standards necessary to establish the TMDLs, electrocoagulation was chosen.
A spot near Fairfax Avenue along Ballona Creek was chosen for the installation because it provided continuous dry-weather runoff and was located next to a city municipal yard where the unit could be placed.
Ballona Creek takes in water from a 128-square-mile area with a typical dry-weather flow of 11 million gallons per day. In the pilot study, an EC unit designed to treat 1.5 gallons per minute was installed, and the unit ran six to eight hours a day.
Flow from a channel near Fairfax Avenue along Ballona Creek was pumped into the system, with water-quality samples analyzed. There was a 99% removal of total coliform, E. coli, and Enterococci bacteria, with high removal efficiencies for chromium (more than 98%), copper (more than 96%), and lead (more than 98%).
“We’re pretty excited about the test results and the capabilities of what we’re able to do,” notes Van Johnson.
The placement of treatment system equipment is contingent on identifying critical source areas and the major drains with poor-water-quality discharges. Each unit needs to be sized based on the storm drain flow and typically is placed near the storm drain outlet. Dry-weather runoff usually is screened and routed or pumped to the treatment system, where it undergoes electrocoagulation and filtration.
Typical operation and maintenance costs range from $0.25 to $0.50 per 1,000 treated gallons, with capital costs dependent on the water’s constituents and necessary standards. In the Los Angeles pilot project, the per-gallon cost was $0.33, with electrical costs as 4 kilowatts, Van Johnson says.
While the pilot study at Ballona Creek was successful, the bacterial pollution returned after the study was terminated and beach closures resumed, Van Johnson says. But he notes that California recently approved the use of EC for turbidity in construction runoff, adding that in order to accept the technology, pilot tests such as the one conducted in Los Angeles had to be completed first.
It takes that approval–as well as more review and more research–for the methodology to move forward.
“Our EC systems are different from others because you can have a larger volume of water,” says Van Johnson. “We have our chambers set up so the water flows in and right up to the top, the electrodes are treating the water, and then the water flows out. The blades can last up to nine months a year before they have to be changed.”
Los Angeles’s stormwater manager, Shahram Kharaghani, was impressed with electrocoagulation, saying his experience with it was “positive.
“We are identifying a specific location where we can potentially use that technology, but there are no specific projects that I have in my mind that I’d say yes or no.
“All of these BMPs have a specific usage. I would use it if the need comes for that specific use for specific site conditions. We do a lot of pilot studies when the opportunity arises, because the water should have some type of turbidity,” he explains.
The Los Angeles area has a great deal of surface water that flows during dry and wet weather, and the EC pilot project was conducted with a small amount of water, Kharaghani says.
“When you do a pilot project, you do it on a small scale,” he adds. “Not all the time when you do a larger-scale test are you going to have the same results. Those are the scientific considerations; I’ve asked my scientists to make sure that if it were a larger project, it would be successful.”
Electrical power is another consideration with this type of BMP, notes Kharaghani. “You also have to worry about the power and how much electricity it’s going to use,” he says. “This is in competition with other best management practices that may not use electricity.
“Each of the BMPs has its own issues. Some need a lot of land; some need electricity. But this would be a tool in our toolbox to eliminate the pollutants in the water. The more tools we have in our box, the better equipped we are to deal with the pollutants that we find in the waters in the city of Los Angeles.”
