Water

Managing Trash and Contaminants With Screens and Storage

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Credit: Oldcastle
Installing the StormCapture vault system in Santa Monica
Every year, Heal the Bay, a nonprofit advocating for coastal water quality in the Los Angeles region, lists all the beaches in Los Angeles County and grades them based on visual experiences, the quality of the water, the quality of the beach, and its cleanliness. Each year the annual report lists some of those beaches on its Beach Bummer List—a compendium of the dirtiest, least desirable, and most inhospitable attractions on the Los Angeles coastline. For several years, the beach surrounding Santa Monica Pier, a recreational attraction that hosts over 6 million visitors every year, has had the dubious distinction of holding a prominent position on that list. “Many factors contribute to that,” says Selim Eren, an engineer with the city of Santa Monica. “Having restaurants on the pier and having an open timber structure and a dark and moist environment under the pier doesn’t help, overall, the situation there.”

He adds, “There have been many studies that the city has done, including DNA traces to discover the sources of bacterial pollution, to determine whether it’s human related or animal related. There have been studies on bird control for pigeons or other birds around the pier. Other projects have concentrated on getting the trash out of parts of the public space. We’re also doing beach cleanups and managing the beach in coordination with LA County.”

More specifically, he says, one of the main contributors to beach water-quality degradation has been stormwater. “It comes in two forms, one of which is urban runoff that would include dry-weather flows, and stormwater itself.”

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The watershed lacks natural features that could mitigate stormwater pollution. “In such an urban congested area, there is no infiltration, so any car wash or anything that gets onto the street ends up going into the ocean through the storm drain channels. Usually, the first flush is the dirtiest time; all the dirt, dust, and metals from car tires and oils that have accumulated for a long duration wash into the drain.”

Eren is the project engineer for the Santa Monica Pier Stormwater Harvesting System, an innovative water-quality project designed to improve water quality and visitors’ experience at the Santa Monica Pier beach by countering the spike in pollutants during the first flush. The system is designed to capture stormwater falling on the urban watershed and sequester it for storage, treatment, and use. A cornerstone of the City of Santa Monica’s Clean Beaches Program, the stormwater harvesting project comprises a 1.6 million-gallon stormwater cistern to capture dry-weather and wet-weather runoff of up to the 85th percentile storm in the drainage area.

The Clean Beaches Program goals are simple and direct, Eren notes: “To prevent any of the polluted stormwater from the city from contributing to degrading the quality of the water on Santa Monica beaches.” And the means to achieve that goal for the Santa Monica Pier watershed, he says, “is to eliminate most of the runoff and stormwater from reaching the ocean.”

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A Single Pipe Runs Through It
According to Eren, a single outfall pipe drains the entire Santa Monica Pier watershed, paving the way for a straightforward solution. “We have seen in the region, state, and many other places that an end-of-pipe solution is the most effective way of eliminating stormwater pollution into the waters of the United States,” he says. He notes that Santa Monica Pier presents an almost ideal opportunity to deploy end-of-pipe techniques. “The reason that we can do this and fully be in compliance for this watershed is that the watershed is fairly small,” he says. It consists of 106 acres, bounded by Wilshire Avenue to 4th Street on the south, by Colorado Avenue on the north, and by the beach on the west. “We can actually have just one mitigation structure to address the whole watershed,” says Eren.

The project will direct all of the runoff from the existing outfall through a CDS hydrodynamic separator manufactured by Contech, then to the new Santa Monica Clean Beaches Cistern, preventing it from reaching the ocean in a polluted condition. The location for the cistern historically housed the Deauville Beach Club until it was destroyed by fire decades ago. Now mostly vacant and underutilized, the plot, which is now owned by the city, has more recently served as a depot for beach maintenance operations. However, as an additional benefit of the project, after installation of the cistern underground, there are plans to top off the project site with landscaping and parking, enhancing free and clear coastal access for visitors.

Letting Gravity Do the Lifting
To reduce the project’s energy footprint, rather than installing pumps that require both maintenance and fuel, the project relies on gravity to transfer water from the pier outfall out to the 1.6 million-gallon cistern. However, that meant placing the cistern well below grade.

“In our case, we were going extremely deep; there would not only be traffic loading from the top, but heavy soil pressure, as well as water table pressure and buoyancy from the shallow water table that is kind of acting against it. We really needed to have a specially designed system,” says Eren. “During design, we were deciding whether the structure should be precast or cast in place. The ground level is at the beach level, and the water table is very shallow. It varies seasonally, changing between 5 and 10 feet and depending on the tides as well. Also, the footprint of the site is very small, so there is no way to cut and slope the edges of the excavation that would be needed to get approximately 30 feet below the surface.”

Complicating matters, Eren says, the Santa Monica Pier “is actually busy all year, with some of the busiest days right around Christmas time.” For construction purposes, he notes, “We needed to stay outside of the summer season as much as possible.” Therefore, building a form and then casting the structure in place would have added an unacceptable duration to the construction schedule. “We decided to use the StormCapture PV panel vault system from Oldcastle,” he says.

After excavation was completed, says Eren, contractors installed a cast-in-place slab. About 180 straight-wall panels of a specially designed thickness make up the skeletal structure of the storage cells, building out the facility “very close to the size of a football field.” The top slab is designed to weight specifications and thicknesses to keep the structure in the ground “and to work against buoyancy forces on the site.”

Importantly, he notes, it also had to be designed to handle seismic loading. “When it contains water, in a seismic event, that water moves. So the walls have to be calculated and the connections have to be calculated to keep the structure in place in a worst-case event.”

Furthermore, he says, “We needed to build the tank and to do a leak test before it was backfilled.” That meant that the tank needed to be designed to withstand seismic loading when standing by itself, when not surrounded with backfill earth. “In a worst-case scenario, if there is a seismic event when the tank is full and it’s not backfilled, you need to mitigate for all the scenarios and forces that the structure would take, so it’s very robust.”

To complete the leak test, groundwater, plentiful in the coastal environs, was pumped in to completely fill the tank. Measurements were taken two days later to document any water loss. “With this type of structure some water loss is expected,” says Eren; however the tank met the acceptable limit of losing no more than 0.01% of the water. “That would amount to half an inch from the whole 1.6 million-gallon tank,” he explains. After the structure passed the leak test, the water it had held was retained for use during ongoing construction tasks, such as preparing the backfill for compaction.

Credit: Oldcastle

Applying Concept to Visions
Eren says that large-scale stormwater cisterns are great in concept and could play a valuable role protecting beaches in many coastal regions, except for one catch: What to do with the huge volumes of polluted stormwater potentially gathered and stored between rain events?

Typically, he notes, stormwater detention projects are paired with infiltration projects. “You have this large amount of water that you’d like to prevent from reaching the beach or the lakes or some other body of water. So the first immediate solution is infiltration.” However, the Santa Monica area is not a prime candidate for deploying an infiltration pit. Aside from the high-density development in the area that makes land-hungry infiltration facilities less-than-ideal solutions, he says, “the types of soil and geology in the region prevent infiltration in a short time for large volumes.”

What makes things interesting in the case of the Santa Monica Pier project, Eren says, is that Southern California has a history of viewing water as a highly prized commodity, and this has inspired innovation on a number of fronts. As far back as 2001, he says, “Visionaries of the city built a stormwater treatment facility in the vicinity of the pier that is called the SMURRF,” or Santa Monica Urban Runoff Recycling Facility. For almost two decades, this facility has been conserving water by treating dry-weather flows from the city’s stormwater sewers and distributing the treated water for nonpotable use. With the completion of the new harvesting system, says Eren, “When we capture wet-weather flows we’ll be pumping all the water to the SMURRF and we’ll have a chance to treat it for nonpotable uses such as irrigation and toilet flushing.”

Photos: Storm Capture installation

According to Eren, while the majority of the water the SMURRF currently supplies is used for the city’s parks and irrigation, SMURRF also “has a couple of commercial customers that use some of its water in their buildings for toilet flushing.” Currently equipped with filtration and ultraviolet (UV) disinfection systems, as well as oil and grease separators, the SMURRF will be undergoing upgrades in the next few months. “We will be upgrading with a reverse osmosis membrane filter, similar to those used for drinking water treatment, and desalination that will enable the facility to treat slightly salty water.” And that highlights another clever innovation facilitated by the new stormwater harvesting system’s design.

With the cistern buried deep underground to take advantage of gravity to feed the tank from the beach outfall, the structure will rest perennially surrounded by the brackish groundwater endemic to the shallow water table typical of the coastal hydrology. “We took advantage of the situation and built a perforated pipe drainage system under the tank that would collect that local brackish groundwater. Not nearly as salty as seawater, but not as good as fresh groundwater, in this project we’ll be collecting it during the non-storm events, when the structure is underutilized. We’ll be able to collect brackish groundwater by pumping in the water surrounding the tank. This brackish groundwater will be routed to the stormwater treatment facility, providing a continuous influx of water to the treatment system even when there are minimal storm flows, connecting the harvesting project as a dry-weather lifeline for the SMURRF.”

Capable of treating 500,000 gallons per day, the SMURRF had been treating in the range of from 150,000 to 250,000 gallons per day depending on the season. Meanwhile, demand for nonpotable water has varied between 250,000 and 280,000 gallons. “There have been times we’ve had to supplement SMURRF water with potable water to meet customer demand. And we couldn’t take on more customers; we could only handle so much because dry-weather runoff was very limited.” With the combination of the projects and their mutually beneficial capabilities, says Eren, “we’re going to have virtually unlimited water supply by using primarily stormwater, but also brackish water when stormwater is unavailable.” Thinking about the past need for purchasing potable water to supplement customer demand for reuse water, Eren notes that with the new system in place, “We will never have to supplement anymore.”

Credit: iStock/EXTREME-PHOTOGRAPHER

The Key to Keeping Out Trash
Alex Wykoff, environmental specialist with the City of Cupertino, CA, has been engaged in a pilot project to test 10 curb screen devices from Hydra TMDL. “We have very aggressive trash reduction requirements in California. We want to see if we can replicate full-capture performance by having a street sweeper and a robust curb screen that when used in combination are equivalent to a full-capture device. That gives us options,” he says.

“There are several different types of curb inlet screens,” explains Wykoff. “The auto-retractable Hydra is unique. It has vertical keys like a piano.” A wire behind them holds them with just enough tension to keep the aperture between the keys closed during dry weather to exclude trash, opening only when the pressure of flowing water pushes them open during a storm.

Wykoff notes there are a number of objectives that he hopes to achieve during the pilot project. Along with evaluating the Hydra TMDL devices’ performance during storm events, he also hopes to assess their durability holding up to local conditions and municipal operations such as street sweeping. So far, he says, the results have been promising. Visual inspections he has performed on the 10 installed units during dry weather show they successfully keep litter and materials out of the storm drain inlets and “even manage to exclude some sediments.”

The debris exclusion keys of the Hydra TMDL Automatic Retractable Screens are made of durable black marine-grade acrylonitrile styrene acrylate (ASA) plastic with a UV inhibitor added. Wykoff says the keys have held up well to sunlight exposure with no evidence of photodegradation. Furthermore, during the study period, he has observed no damage from wire brushes of street sweepers regularly deployed to clear the materials the keys have blocked from entering the city’s catch basins.

The keys of the Hydra ARS units open to a 5-millimeter maximum aperture, providing 93% capture, allowing water through, but keeping contaminating materials and litter out. These contaminants can then be picked up by roadside street sweepers. According to Wykoff, they have minimal maintenance requirements. By contrast, full-capture devices that fit within catch basins, he says, are more expensive and present more of “a challenge keeping them clean.”

Smoke Out
Wykoff says a major concern that his program would like to address is water-quality degradation caused by the haphazard disposal of tobacco products. Cigarette butts have been pegged as contributing up to 30% or more of the individual pieces of trash refuse contaminating stormwater. Wykoff recently attended a seminar offered by a local countywide environmental advocacy group in consort with the Department of Health and Human Services. “They talked about the fact that the toxins get concentrated in the filters of the cigarette butts and that the plastic filters themselves are major sources of pollution.”

He says, “We’re looking at cigarette butts as one of the major contributors to water-quality degradation. The 5-millimeter screen will be appropriate to stop cigarette butts from getting into the catch basin.”

Overall in Cupertino, he says, “The amount of trash loading observed is dependent on what area of the city you’re talking about. In a residential area there would be a higher proportion of organic waste, such as yard waste or leaves; in the downtown area there would be more packaging waste.” Although in general Cupertino is pretty clean, “the type of packaging that would be found in more commercialized districts includes disposable cups, chip wrappers, and cellophane, while batteries are common to find in residential areas,” he says, speculating that they might be the result of toppled electronics recycling bins not being properly cleaned up.

Although Wykoff has not had the chance to observe the performance of the Hydra ARS units during an actual storm event, as the region has been relatively dry since installation, he does have plans to do so. “We’ve only had one rain event since they were installed and that was on my day off, so I didn’t get to see them in operation.”

For the next storm, however, he has made provisions to make instant observations. “We’ve got one device installed right outside the office at City Hall, so we can go out and monitor it visually when it rains. The other nine are on an arterial roadway with mixed uses over a span of two miles on a row of untreated catch basins,” to provide an overview of how the devices respond under a range of conditions along the route.

Based on visual inspection of the basins, Wykoff says a significant proportion of waste material is being kept at street level and can be picked up by street sweepers. He likes that there is a labeling option that can be ordered from Hydra TMDL that reads “Keep Your Butts Out of Here.” “We liked that option; we may draw a few more eyes to pay attention to the issue,” he says.

Credit: United Storm Water
Beverly Hills has installed 500 of these devices on its inlets.

A Full-Capture Combo
Josette Descalzo, environmental compliance and sustainability programs manager for the City of Beverly Hills, CA, explains that Greater Los Angeles County is regulated by the Los Angeles MS4 permit administered by the Los Angeles County Regional Water Quality Control Board. The goal of the permit is to improve stormwater runoff quality. One of the water-quality improvements that cities are required to meet is eliminating trash and reducing other chemical pollutants that are included in urban runoff.

The City of Beverly Hills is part of a watershed management group within the Ballona Creek watershed. Current regulations require the city to manage the trash coming from urban runoff. “One way to manage that is to install full-capture screen devices inside every single catch basin,” says Descalzo. “In the City of Beverly Hills, we have approximately 1,600 catch basins, owned by the city and the county flood control system. The regulation requires each municipality to install full-capture screens in all of the catch basins within the jurisdiction. By the end of this year, we will have installed full-capture devices in all of our catch basins.”

The city deploys two types of devices to eliminate trash from stormwater at the catch basin. “We have a screen in front of the catch basin called an automatic retractable screen, or ARS, that separates the big debris. These were installed by United Storm Water about 10 years ago on around 500 catch basin inlets in the city. They have a screen with three-quarter-inch circular mesh to hold trash on the surface to be picked up by street sweeping, with an opening at the base to allow water to flow underneath into the catch basin.” In addition, inside the catch basins Beverly Hills has deployed full-capture devices placed before the outlet of the catch basin. The catch basin full-capture screens from United Storm Water are regulated to have an aperture of 5 millimeters, so any debris is larger than 5 millimeters is kept within the catch basin. Typically the units are configured with an overflow that is above the 90% capacity line of the catch basin.

A Good Defense
In addition, says Descalzo, the city has an enhanced street sweeping program that serves “as a first line of activity to mitigate trash from entering the catch basin.” As Colonel James Burnley, solid waste manager for the City of Beverly Hills, describes the program, “It consists of six-days-a-week street sweeping in all of our business districts, in addition to servicing street receptacles seven days a week. Typically, in the City of Beverly Hills, we do not see so much of a litter issue curbside because of those services in the business district.” Preserving the city’s public image and reputation, he notes, is a major reason the department focuses so keenly on “keeping the streets looking nice and immaculate.”

“A lot of the issues you talk about concerning trash in the gutter are a result of overflow. When street receptacles are not available, people just throw trash out or dump it curbside wherever they can find. We are also looking to put more receptacles out where we see areas that may be problem areas,” says Burnley.

Keeping trash out of the stormwater system also means keeping an eye on the weather. “We get a forecast before the storm hits. Pre-storm, we have a crew go through those areas where we have high litter—we know our high litter areas. They go through and do pre-storm maintenance.

“To support everything else that we do, we have a catch basin inspection program. We go catch basin to catch basin, physically opening the manhole and inspecting the debris or trash level in each one. When the inspector tags the catch basin as having a high level of debris, we will get them serviced to prevent flooding.”

Installation of the full-capture catch basin inserts began in 2015. Each catch basin is measured to record the depth, the width, and the location of the inlet and the outlet of the catch basin; with these dimensions, United Storm Water is able to design and manufacture a custom full-capture screen that will fit in that specific catch basin, explains Descalzo. “United Storm Water has been great to us; they’ve done this with several other cities within the Los Angeles region. They give us a very thorough report of which catch basins have been installed, so we have the details and data that we can use to import into our GIS asset management system.” As the majority of the city’s 1,600 catch basins have been equipped with the United Storm Water full-capture inserts, Descalzo says the installation process is nearing completion. “As funds are reserved for it, we are completing the project by the end of this year, which meets the regulatory deadline.”

However, even prior to meeting the benchmark of full saturation with full-capture devices, Descalzo says the combined efforts of the City of Beverly Hills other municipalities within the watershed group have successfully met the requirements for compliance with the trash TMDL for Ballona Creek.

“We had a deadline to install these and will have done so by this year.” With the installation of about 200 more units in the next couple of months, says Descalzo, the project will be complete. “After that, for trash, we’ll be pretty much set.”  SW_bug_web

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