A River Runs Through It - Capturing Trash and Pollutants in Los Angeles
Public agencies in California’s Los Angeles basin have been stepping up their game to limit what enters the street stormwater system to nothing more than water. This includes deployment of full- and partial-protection devices installed within curb inlets, catch basins, and the adjacent stormwater infrastructure to screen incoming water fl ow for trash and additional pollutants, including nitrogen, phosphorous, heavy metals, pesticides, PCBs, and bacteria. In some areas where pollutants cannot be intercepted at the curb, municipalities use inline devices downstream.
One Million Gallons of Trash Four million people spread out over 503 square miles produce considerable incidental trash that collects in streets, open spaces, and waterways. Preventing that trash from fully navigating the storm drain system and reaching the Pacific Ocean is a massive undertaking. Alfredo Magallanes, assistant division manager of the Los Angeles Bureau of Sanitation’s Water Protection Program, his program team, and their counterparts across other city departments, achieved 100% trash control last year, as mandated by the 2001 Ballona Creek and Los Angeles River Trash TMDLs and subsequent amendments. In other words, the city must keep every bit of its typical street trash volume—estimated at 1,374,845 uncompressed gallons in 2012—from reaching its drainages.
A combination of partial-capture devices or catch basin inlet screens; full-capture devices including catch basin insert screens, netting systems, and hydrodynamic separators; and institutional controls like public education, street sweeping, and catch basin cleaning brought Los Angeles into full compliance. “Roughly three-quarters of the city uses partial capture and one-quarter uses full capture,” says Magallanes. “We have five hydrodynamic devices and about 13 netting systems on strategic full-capture locations.” The City’s cumulative institutional controls equaled roughly 12% of total trash TMDL compliance.
Over the years, both the City and Los Angeles County have developed their respective lists of capture devices approved for installation within their jurisdictions. As manufacturers create new devices or modify existing device designs, they may submit them to Magallanes and the Bureau of Sanitation for a one-year performance evaluation that can lead to acceptance by the City as an approved device. “We have a designated area where we test products under real-time conditions, including two wet seasons,” says Magallanes. “We have installed a full-capture hydrodynamic device downstream of the area to catch anything that escapes the test screen so we can calculate removal percentage.”
The Hydra automatic retractable screen (ARS) has recently joined the ranks of city-approved partial-capture devices. Manufactured with polymer instead of the stainless steel typical of most curb inlet screens, the Hydra uses a collection of individual, vertically aligned fingers that hang side by side from a top mounting bar and yield under water flow. A tensioner wheel controls the amount of pressure required to push open the fingers—also called blades by the manufacturer Hydra TMDL.
“Stainless steel screens are rated 86% effective at keeping trash out, but the Hydra is 93%,” says Magallanes. “When it rained, it didn’t obstruct the flow as much as the steel version, and let more flow into the catch basin.” The Hydra design opens only the blades receiving the greatest volume of water, keeping the others closed unless needed. This seems to increase its effectiveness by moving trash away from the drain opening, and keeping it on the street for removal by sweepers.
The lightweight polymer material also permits greater sizing flexibility and easy customization for each curb inlet—ideal for municipalities like Los Angeles that have a range of inlet heights from 4–16 inches. The cheaper polymer material also helps in budgeting. “If you’re looking at a fourteen-inch-tall opening, seven or ten feet wide, that’s a very expensive screen,” says Magallanes. “The new Hydra is about $200 cheaper than a typical stainless steel version.” The polymer screens are also less susceptible to theft by scrap metal harvesters interested in the nickel content of stainless steel screens. “We learned [about theft] the hard way when we started. The nickel price rose, and we had a lot of thefts from crews going down streets and taking them out for the salvage value.”
After 16 years of testing and deploying curb inlet devices, Magallanes has learned a few things, such as which device is best suited to certain niches. He believes the Hydra’s polymer content will keep theft at a minimum, but because it doesn’t have a locking mechanism like typical stainless steel screens, it may be subject to tampering and vandalism. Although he thinks the Hydra will work anywhere it’s deployed, he has decided to install it only in residential and hillside areas where vandalism typically occurs less and the water flow often cannot exceed the force required to unlock a stainless steel device gate. “Here in the city, we have to be strategic on where we place devices, and in areas susceptible to theft or vandalism, we’ll stick with stainless steel,” he explains. In areas with the heaviest theft and vandalism, such as an area where the city’s core homeless population congregates, a mainline full-capture device was installed instead of curb inlet screens.
The Hydra’s simple design and materials also make maintenance by city personnel safer and easier. “It’s safer for our guys, with fewer opportunity for cuts and scratches,” says Magallanes. He explains that the city keeps a limited number of devices on the city-approved list to simplify maintenance. “You want a standardized product with standard tools, not 50 different products and a warehouse full of different equipment or tools. There are close to 55,000 catch basins in the city, and [the maintenance crews] have to move fast.”
Magallanes notes that the only post-approval question remaining for the Hydra involves long-term performance of the polymer blades and their degradation over time. This year, with plenty of existing devices reaching the 15-year mark since installation, the Bureau of Sanitation began its replacement program. Magallanes’ team maintains a database containing statistics on every catch basin inlet screen, including when they were “born.” To maintain compliance with the trash TMDLs, they’ll need to annually replace roughly 2,600 devices at the cost of $4 million to $5 million.
El Monte Juggles Multiple TMDLs
Just east of the City of Los Angeles is the smaller municipality of El Monte, also within the Los Angeles River watershed and subject to its multi-pollutant TMDLs. Although its baseline trash contribution at 42,208 uncompressed gallons is much smaller compared to its larger western neighbor, the requirement for 100% reduction still applies. In addition, El Monte must also comply with a separate trash-only TMDL for nearby Legg Lake, which receives drainage from the municipality, and the Los Angeles Area Lake TMDL governing trash, nitrogen, phosphorous, mercury, organochlorine pesticides, and PCBs. With dueling TMDLs, El Monte tackles compliance in part through street-level devices—partial-capture automatic retractable screens installed at the curb inlet and full-capture connector pipe screens installed inside catch basins—depending upon the location, jurisdiction, and presiding TMDL.
“The city has done its due diligence and installed both trash and nutrient filters,” says Robin Rickman, project engineer with Pacifica Services, contracted consultant to the city for oversight of device installation. In August, United Storm Water Inc. installed a handful of its Wing-Gate ARS devices—some with AbTech Industries’ Ultra Urban Filters and some without—within the city. “Currently, we’re about 34% complete with the current batch,” says Rickman, “but we’ll be remobilizing to finish up the larger project by installing about 1,500 more devices, including the remaining storm lines down to Legg Lake. It’s a big push.”
Made from stainless steel, the Wing-Gate ARS stays closed during dry or low-flow conditions to keep trash on the street for collection by street sweepers. It swings open from a spring-loaded vertical hinge during higher flows when greater volume must pass through. The gate has 3/4-inch perforations for flow-through and fits into the inlet opening such that it leaves 1 or 2 inches completely open for a high-water bypass. The gate tension can be adjusted to open with more or less resistance. The device fits inlets with a minimum 4-inch height and 6-inch depth.
After stormwater flows through the Wing-Gate ARS and into the catch basin, it passes through AbTech’s Ultra Urban Filter loaded with Smart Sponge HM media on those structures where they’ve been included. Each Ultra Urban Filter can handle a flow rate up to 190 gallons per minute and removes more than 80% of total suspended solids and oil and grease. AbTech expects the Ultra Urban Filter with HM media to last three to five years, due to the efficiency of the Wing-Gate ARS at keeping trash and debris out of the catch basin. Weighing 6 to 7 pounds, a Smart Sponge can be used to fuel waste-to-energy facilities or cement kilns, or can be disposed of as solid waste at landfills.
Rickman keeps tabs on United Storm Water and updates El Monte staff as appropriate. Because United Storm Water originally worked with the city to map out each device location, type, and documentation, the company is well versed on how and where things need to happen. “United does a great job, and they’re quite efficient,” says Rickman. “Occasionally, normal issues pop up like trash or cars blocking access. It’s all part of the process, and you just have to come back another day.”
Rickman and Pacifica also coordinated access permitting with the County of Los Angeles for inlets located within El Monte but owned by the county. After submitting the required worksheet demonstrating which catch basins require access and installation of protection devices, the county indicates which device type it recommends for each location. Assuming the permittee accepts, they provide approval to access and issue appropriate permits, and later provide a county inspector to verify the installation.
Like the City of Los Angeles, El Monte must monitor and maintain its protection devices in perpetuity.
Embarking on TMDL Compliance Backed by years of experience, Magallanes has plenty of thoughts for any municipalities just beginning TMDL compliance efforts. “They need to be aware of what curb inlet structures are in their streets before looking at what products are on the market,” he advises. “The inlets—do they vary in size and capacity?” He also reminds that inserting anything in an existing system means introducing a flow obstruction, potentially leaving more stormwater on the street and setting the municipality up for additional claims each year. “You need to consider impacts like having water on your streets for a longer time. Is that a risk you want to take? Is your street sweeping program ready to get the additional trash being blocked and left behind?”
Magallanes stresses the need to inform the public from the very beginning, and notes that consulting retained legal counsel in doing so would be helpful. “In some areas, we didn’t notify the residents of our plans, and at some times we were installing thousands of catch basins per month,” he explains. “We were getting a whole bunch of calls that were not very nice. You need good public relations to inform them of the benefits to them.”
His third tip also includes communication, this time with the fire department who typically is a first responder to flooding. “They want to clear the flooding, and if they don’t know what’s in the street, they’ll destroy it.” This can be especially true If the installed devices have locking mechanisms and the fire department is not equipped with the ability to unlock it as designed. “Their job is to clear the water, make sure it flows, and the public is safe.”