Guardians at the Grate

Inlet protection devices keep trash, pollutants —and sometimes alligators—out of the system.

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Located in the South Bay area of Los Angeles County, CA, Machado Lake once was known as a prime bird-watching location but has suffered numerous indignities in recent years. It has become a dumping ground for unwanted snakes and a variety of trash, as well as a repository for pesticides. It even became notorious for an alligator that mysteriously appeared and resisted all attempts at capture for many years, managing to famed “Crocodile Hunter” Steve Irwin, who was brought in to try to bring relief to worried neighbors.

But now six cities around the lake have joined together in what Terry Flury refers to as the Machado Lake Project. Flury, who is with United Storm Water in southern California, explains that this initial phase is to prevent trash from entering the lake. Subsequently, pollution reduction will also be addressed.

“We’re putting in mass BMP devices–we’re actually putting in what we call an automated retractable screen (ARS),” he says. “We’re installing ARS units all over those six cities surrounding the lake.” The cities are Torrance, Lomita, Rancho Palos Verdes, Palos Verdes Estates, Rolling Hills Estates, and Carson.

Photo: United Storm WaterAn automated retractable screen unit
Photo: United Storm Water
An automated retractable screen unit

“We’re putting in those devices, as well as our connector pipe screen, what we call CPS inserts,” he says. “These CPS inserts are five-millimeter screens that go inside the catch basins, over the storm drain outlet pipe. This is considered a full-capture device, which prevents items as small as cigarette butts from entering the storm drains. This is joined with the ARS units, which keep out large debris, like bottles, cans, diapers, and the like.”

During a large storm, when stormwater reaches about half of the curb height the ARS opens to prevent street flooding, allowing everything–water and debris–into the storm drain. “However, whatever it lets in is still prevented by the CPS unit from getting into the storm drain system,” he notes.

The system is being used throughout California. “We’re putting in these devices up in the San Francisco Bay area, and we put in around 10,000 of the screens for the county of Los Angeles alone. It’s been an ongoing project for us the last couple years.

“It’s sort of been like inventing the wheel, then improving it. For the last seven or eight years, these automatic retractable screens have been around, but they really haven’t worked very well. So recently we’ve come up with a device that is simple, but has been very effective, and it works really well with trash.”

Flury says Los Angeles County requires that all BMP stormwater products undergo testing in order to be approved. The county maintains a testing facility at San Gabriel Dam, where it runs hydraulic tests on various products to verify that they are functional.

“You have to pass muster through the engineering department of the county of Los Angeles before you can put any devices in, for any city within the county boundaries,” says Flury.

“When the county tests these devices at the San Gabriel Dam, they have a very neat system. They have a double catch basin, and they have a 6% grade with the curb that they set up with a big 2.5-foot-diameter pipe coming from a pump system, from the lake. They are able to generate whatever cubic-feet-per-minute flow they want down that grade into the catch basin. In behind the catch basin they have a weir, and the weir is marked per foot, so they can measure water flow.

“Say we put in our screen in the catch basin that’s in front of the weir. With the water flow that enters our screen, we are able to tell when it goes into the next basin, the bypass, how much water actually goes into our screen, and thus give them a mark of how many cubic feet per second they can handle.

“The only problem is that they have been doing this for the past five or six years, but they don’t test it with trash,” he continues. “During a first-flush event, you get anything and everything going down that curb system. You get leaves and twigs and branches and paper bags, and they don’t test for that. That’s been the real killer of these screens.

“So we’ve done our own homework on that, and we have a catch basin next to our facility that we use to test, and we’ve come up with a device that works well with trash.”

Flury notes one result of the county’s failure to fully test these stormwater BMP devices. “There was a company that recently went out of business that was a competitor of ours. They sold the city of Los Angeles an ARS screen that was well thought out. It was a very nice looking screen, probably one of the better-looking screens that I’ve ever seen.

“But it had a major flaw, and that flaw was that it would open up beautifully with fresh water coming at the curb, but the moment that trash hit it, it didn’t open at all. They put in maybe 15,000 of these screens all over the city of Los Angeles, and they had nothing but problems with them.

“There were a lot of issues,” he adds. “They had flooding; they had accidents during the flooding, major lawsuits–and all of this because of the trash. Yet this device went through the testing program and passed.”

According to Flury, United Storm Water has tried to assist the county in upgrading its processes.

“We’ve even had the county come over to our facility when we conduct our testing,” he says. “We put every type of trash that you would find in a first-flush event down the curb. Then we run our vacuum truck upstream and let the water come down naturally. We showed the county that this is the way we think all these screens should be tested. They took that to heart, and they’re currently trying to come up with a system to do that. Their concern is that with the dam, they have to have a trap system to prevent all that trash from getting into the dam. To me that is no problem; you just plug it off or have a filter system down below. But it’s definitely something that they’re working on.”

Not a lot of maintenance is required with these capture devices. “United Storm Water is known for cleaning catch basins,” says Flury. “We do an annual contract with the county where we clean out about 8,500 storm drains four times a year. So we’re constantly doing that.

“The county has told the cities within its borders it’s generally best that if these devices are put in the catch basins, they should be cleaned four times a year. But a lot of the cities that don’t have the flora and fauna all over the place, and they can get away with three times a year easily, with no problem. The cities that have major tree-lined streets are the ones that have to be done quite often.”

Now, About That Alligator…
“Somebody had him as a pet, and it grew and grew and grew, and the next thing you know, some people were at the park where the lake is, and they saw an alligator come out and grab a duck out of the water.

“Then they called the alligator guy from Australia, because nobody could get the alligator out. And he couldn’t either. A couple years after he left, the alligator vanished somewhere, and nobody saw it for a while.

“To make a long story short, they finally saw it and were able to capture it, and it was taken to the zoo.”

Indeed, Machado Lake is now on its way to being both cleaner and safer.

The Benefits of Baskets
“Each year, thousands of pounds of nutrient-rich sediments, leaves, and trash debris are transported directly into many of our local lakes from untreated stormwater associated with impervious streets, parking lots, and driveways,” commented Sergio Duarte, senior environmental specialist in the Environmental Protection Division (EPD) in Orange County, FL, at a 2013 North American Lake Management Society conference. “These pollutants negatively impact the water quality, use, and enjoyment of the local lakes. That is why stormwater catch basin insert filter baskets (CBI) have become a useful option for Orange County’s Lake Management Program. The CBIs are installed directly into the existing stormwater curb or grate inlet infrastructure and capture debris such as sand, leaves, and trash while allowing the water to drain into the stormwater system.”

Photo: Orange County Environmental Protection DivisionCleaning the baskets
Photo: Orange County Environmental Protection Division
Cleaning the baskets

In a recent interview, Duarte notes that Orange County–which includes the city of Orlando and a dozen nearby communities–has contracted with Suntree Technologies since 2008, and in 2014 currently has more than 600 filter baskets in 16 lake basins. “Orange County plans to install an average of 200 filter baskets per year for the next three years to cover additional lake basins,” he adds.

“We originally went with the baskets with the idea that they were going to supplement the street sweeping program. At that time, all we had in mind was to have a secondary device to help us trap the debris that the street sweepers were missing. Over time, we evolved with the baskets, and we did realize that the baskets were really useful to also protect existing stormwater systems of any type.

“This includes, for example, inlets that are connected to retention ponds, or a structure that has a direct outfall to a lake,” he says. “We found that just having a basket there was reducing the flow of sediment to those stormwater treatment areas. In other words, what the baskets were doing is extending the life, or maintaining the performance, of those ponds or outfall pipes.

“The baskets are primarily used for two simple reasons. One is to trap sediment during the rainy season. In Florida, we get a lot of heavy rains. The other purpose is to trap leaves during the fall. Those are the two main materials that we are trapping.”

He adds, “Sediment is the killer of retention ponds, because they will fill over time, and they will then not perform as expected. So the baskets proved to be a way to extend the life of these systems, or a way to minimize the maintenance frequency of those ponds. We have ponds that we used to have to clean every five years or so, but with the baskets, we have seen that the ponds can go longer without that type of cleaning or maintenance.

“We noticed the same thing with outfall pipes. We used to have a lot of sediment accumulation in the outfall pipes, and with the baskets we don’t have sediment buildup at the same rate. So we have been really happy with this added best management practice.

“The other thing is that the baskets are also good for BMP treatment trains. We have second-generation baffle boxes, and in many areas we install inlet baskets in the system immediately upstream. So the baskets help us to trap a portion of the sediment, thereby having less sediment going into the baffle boxes.”

He notes that it’s easier to clean a basket than a baffle box. “When you’re cleaning a baffle box, you actually need to bring a vacuum truck, and you have to do pumping. There is a lot of work to do. But with the baskets as part of a treatment train, they are very cost effective and can be readily cleaned by a team of two in a matter of minutes.”

Duarte says the county has 36 lake taxing districts, which provide most of the funding for this ongoing catch basin project. “We have close to 700 water bodies in Orange County, distributed among 12 drainage basins. But we have just a handful of lakes covered with baskets. This is why we are continuing the program of adding as many as 200 each year.”

Encompassing 99 square miles, the various bodies of water make up about 10% of the area of the county. Lake Holden, Lake Conway, Lake Jessamine, Lake Tibet, and Lake Lawne are a few of the lakes currently serviced with a variety of curb inlet and grate inlet baskets.

Although the baskets were originally envisioned primarily to assist the street sweeping program in keeping trash out of the storm drains, they have also served to reduce organic and sediment loads to stormwater ponds, and have been responsible for significantly reducing the amounts of total phosphorus and total nitrogen in the system.

According to research done by Orange County EPD in 2013, catch basin inserts with monthly cleanings have averaged removal of 0.44 pound per month of total nitrogen and 0.11 pound per month of total phosphorus. However, Duarte says further research is needed to test catch basin insert removal rates based on existing pollutant pre-loads and the size of the inlet or catch basin insert micro-basins (the drainage area associated with each such inlet).

“Compared to other baskets,” he says, “Suntree baskets have a multi-stage filtration based on three different types of mesh sizes. The smallest mesh in the bottom of the basket can trap fine sediment, compared to other baskets in the market. With some of the other baskets, you don’t get that kind of ability.

“So we’ve been attracted to that fact, that they are useful to us during Florida’s rainy season to trap sediments, as well as during the fall, winter, and spring months when we get a lot of leaf and oak tree acorn litter loads in residential areas.”

He adds that all of the county’s Suntree baskets are custom made. “I’ve been so grateful that Suntree has been able to work with us in that sense. We have different types of drains–we have grate and curb inlets. Some are old-fashioned shallow inlets, and we’ve had to struggle with those.

“We also developed, with Suntree, a procedure where the baskets are uniquely labeled, secured with locks and tethers, and installed without causing street flooding during the rainy season. Over the years we have worked with them, determining where these baskets will work and where they will not. We have been learning a lot.”

He continues, “We had some shallow baskets, and then we learned later that this probably wasn’t the best way to go, because they were too shallow. In some cases, they were blocking more than one-third of the pipe opening and inducing flooding.”

Duarte says that the baskets are generally cleaned out on a monthly basis. “In some areas, though, we have increased the sweeping frequency, to help the baskets. It’s easier to adjust the sweeping frequency than the cleaning frequency of the baskets, in most cases.”

Of the greatest importance is that the baskets appear to be doing their jobs well. “The value of a BMP is related to its pollutant removal capacity,” he explains, “so we have looked at studies reviewing the performance of those baskets in terms of the type of material that they remove, the weight, and so on. We have also done our own lab samples to examine removal efficiencies in terms of total phosphorus, total nitrogen, and metals.

“We love them, and we have been studying them very closely. For us, they are one of the most inexpensive BMPs. You don’t have to tear apart the existing infrastructure, as with some other BMPs, and you don’t have to get involved with land purchases, as is the case for the construction of stormwater ponds or other type of BMPs.

“This is something with which we can just go to a neighborhood and get it in place. It’s a ready-to-go BMP, and so inexpensive. They are easy to install and maintain, they have a simple bypass technology, and they are durable. They are a good supplement to the street sweeping program, as a BMP treatment train.”

Light Rail in Phoenix
A 3-mile light rail project was underway in Phoenix, AZ, but the portion of the project devoted to inlet protection was not going well.

“The contractor had ordered, originally, a bunch of green fabric, almost like angle-iron curved inlet protection,” describes Cary Winters of UltraTech International. “It was four feet wide, and it had a fabric around it, so it looked like the letter “˜L.’ They wanted to stick that up against a curb inlet, and then nail it in or shoot it in with concrete shot and a piece of wire.

Photo: Ultratech
Photos: Ultratech

“It was a real old-school way of going about things. The problem was that people would drive by, and there wasn’t much support there. It wasn’t fastened in well and it wasn’t flush to the curb, so people would knock off the curb inlet protection. It would end up down the street, so the street was being littered, and they had to constantly put them back in place. It was kind of a nightmare.

“Finally, they got a bunch of steel wire and took concrete shots, and shot each one into the curb to hold it in place. This was time consuming, but an even bigger issue was that a lot of the curbs they were doing were brand new. They were rebuilding the sidewalks and the curbs, and they couldn’t use the concrete shots with the brand new curbs, because it needed to have a finished look when they turned it back over to the state.”

After a few months, the contractor decided there had to be a better solution and purchased about 100 of UltraTech’s 4-foot-wide Gutter Guard Plus units. “These incorporate a little triangular piece of foam,” explains Winters. “Two or three months into the project, they had no issues with those getting taken away with street sweepers and buses. They wedge themselves into the curb inlets extremely well. They are flush against it, so it keeps the sediment and the debris and the trash out of the drain, but it still allows the stormwater to flow through it.”

Gutter Guard Plus units stay in place even with heavy traffic.
Gutter Guard Plus units stay in place even with heavy traffic.

According to Winters, these units permit a flow rate of 456 gallons per minute.

“The SWPPP [stormwater pollution prevention plan] mandates that they have to protect the storm drains, so this product keeps them compliant, and it also prevents hundreds of man hours of headaches. Another nice thing is that when they need to move them, they can just un-wedge them out of the curb inlet. Let’s say they are going to go do the next mile stretch; they don’t have to unfasten all the shots, and they don’t have to move all these big, bulky things around. These are lightweight, with foam and PVC with fabric around them. So they just un-wedge them and take them down the street and put them in another drain.

“They were concerned with rocks and pieces of concrete and gravel and larger pieces of trash coming off the jobsite. With the Gutter Guard Plus unit in place, there’s only about an inch of space, so you can’t get much in there.”

Winters adds that the units are for temporary inlet protection, for the duration of the project. When it is completed, Winters expects the contractor to bring the Gutter Guard Plus devices out to the next jobsite.

“It’s fairly reusable,” he says. “The product is really just a blocker, not a filter that’s going to get saturated. It just stops things from entering the storm drain.”

He notes, however, that the product isn’t limited to temporary construction projects. “You can use this as permanently as you’d like. We have industrial companies that aren’t doing any construction, but constantly get debris in their storm inlets, so they use this product. It can be used as long as you want, as long as the foam doesn’t degrade. It can potentially last years and years.” SW_bug_web

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