Demanding Stormwater Controls in Louisville
The Germantown Mill Lofts project in Louisville, KY, involves extensive renovation of an entire city block in the middle of town. Previously, the site was the location of a cotton mill, dating to 1889. The property now consists of more than 250,000 square feet of apartments, multiuse facilities, and other buildings spread over nearly 8 acres.
Because of a variety of factors, stormwater management had to be very precise. For one, the local stormwater agency, the Louisville-Jefferson County Metropolitan Sewer District, is operating under a federal consent decree due to discharges of wastewater and sewage into the Ohio River and local streams.
“This resulted in a requirement to detain the post-100-year flows down to the predeveloped 10-year flows. That’s why we ended up going with the underground detention,” explains Eric Senn, engineering manager with Land Design and Development, the engineering firm for the Germantown Mill Lofts project. “We actually had to over-detain.”
Another issue was ground contaminants onsite, ruling out infiltration. According to Senn, HDPE pipe also wasn’t an option for stormwater control. “HDPE pipe just isn’t large enough for what we needed,” he says. “That’s why we went with a metal pipe.
“We ended up going with a closed system for a number of reasons. Because of the contaminants, we couldn’t have infiltration, and because the area uses a combined sewer system, they didn’t want the possibility of having wastewater backing up into the facility.”
Furthermore, the site location was challenging, with a very tight footprint that was locked on all four sides.
Ultimately, the engineers selected a detention system from Contech Engineered Solutions. It consists of 955 linear feet of 78-inch-diameter aluminized steel corrugated metal pipe that provides over 237,000 gallons of water storage.
Among the water-quality units that Contech provided is a Vortechs stormwater treatment system. This hydrodynamic separator works to keep trash, debris, sediment, and hydrocarbons from entering the detention area.
Installation took place over a two-week period in the fall of 2014, using excavators with straps to place the pipe, gaskets and steel bands for the joints, and a rock thrower to backfill around and between the pipe barrels.
Senn notes that since the installation, a number of large storm events have passed through the area, including some that have caused flooding, but the detention system has been working according to plan, without any unpleasant surprises.
Culvert Solutions Save Money
White County, AR, located in the northwest corner of the state, was facing a problem with existing culverts that were past their designed life expectancy. They were beginning to rust and deteriorate, causing void areas to occur outside the pipe.
Scott Brignac of ISCO Industries explains that at a trade show in 2013, a White County judge had seen ISCO’s Snap-Tite product and remembered it. “The judge was having some problems in these stormwater areas, and had seen our product the year before, so he gave us a call.”
Brignac offered to come in person to see the problem areas so he could offer a proper solution, and the judge, responsible for deciding how to proceed, accepted his offer.
“I went and did a presentation. What he originally was concerned with was a road called Fisher Hill Road. This road had five culverts, 60-inch diameter, about 30 feet long each. It served as a bridge structure.
“Some voids had been caused because of the deteriorated culverts, and part of one end of the road actually caved in. The void had washed out so badly that there was nothing holding the concrete any more in that area. It just fell in.
“After the presentation, it prompted him to start thinking about other areas that they really hadn’t been thinking about. That’s when the Lakeview Estates project came to mind. He told us that they had just repaved the road in question about a year ago, and he made it clear that he was not going to tear up that road to go fix the culverts under the road. He was thinking that the culverts should have been fixed at the same time that the road was repaved.
Repaired culverts at Lakeview Estates
“We went to look at Fisher Hill Road, and the other road in Lakeview Estates. The Lakeview Estates road was in a subdivision with only one way in and one way out. We come across that scenario a lot. The problem is that you cannot shut down the street for any amount of time, because of emergency issues.
“The judge asked for three separate quotes. The first quote was for Lakeview Estates, but only for four of the nine culverts in the road. These four were obviously deteriorating, causing voids. But I told him that if we are going to be here doing these four culverts, you might as well do the rest of them. Although they weren’t showing immediate signs of failing, they are going to fail sooner or later. Either you’ll have to dig them up, or you’ll have to call us to come out and replace them, and you’re going to have to spend more money.
“He then asked for a separate quote on doing those other culverts, and he also wanted a quote for taking care of the culverts on Fisher Hill Road.
“After talking to the installation contractor, I gave the judge an estimate for doing a turnkey job, and I explained to him that if he did all three jobs at one time, we could save him about $10,000. This is in addition to the savings he has from using our Snap-Tite liner rather than digging up and replacing his culverts.”
Brignac got the complete job.
On Fisher Hill Road job, there were five existing culverts, each 60 inches in diameter and 30 feet long.
“On this project, we sent them 24-foot lay lengths of the Snap-Tite HDPE pipe. That’s the standard size they come in. But we can make sections from two-foot pieces to 50-foot pieces.
“The pieces have male and female ends, and they just snap together using some chains and come-alongs, and you ratchet them in place.”
Brignac says weather played a factor in the project. “On Fisher Hill Road, the bridge crossed over a good-sized creek. This creek is steadily flowing all the time, but there had been a lot of rainfall during the project that prevented the work crews from doing anything, so we had to dam off the inlet side to stop the water from flowing so we could get the pipes in there and do our grouting. Once we got the pipes in place and applied the grout, it only took a couple of days.
“When we insert our pipe into the existing culvert, we build concrete bulkheads on both ends of the pipe, on the inlet and the outlet. That serves to hold the pipe in place. When we pump in our grout, to fill in the annular space between the two pipes, it keeps that grout from coming out. It fills in that whole void.
“When we pump in the grout,” he continues, “it’s not only filling in the annular space between the two pipes, it’s also filling in all the void areas that have been caused by the deteriorating pipe. For example, with that road that failed, we pumped grout in that whole area, and essentially built them a new concrete bridge for that part of the road.
The Lakeview Estates portion of the job involved five oval-shaped, 40-foot-long culverts measuring 29 by 42 inches. These were relined with 24-inch round Snap-Tite pipes. For another two oval culverts, each 20 by 28 inches and 50 feet long, and for one 40-foot-long, 24-inch-diameter round culvert, 18-inch round Snap-Tite pipes were used. A 40-foot-long, 36-inch-diameter round culvert was relined with a 28-inch round Snap-Tite pipe.
According to the White County judge, this relining solution cost perhaps a fifth of what it would have cost to dig up and replace the culverts. In addition, with the pipe liners, there was no interruption to traffic on the only road serving the Lakeview Estates subdivision. Digging up the culverts likely would have closed the road for at least three days.
Brignac explains why the county judge was the person with the responsibility of deciding how best to deal with the failing culverts.
“In Arkansas, the county judge is the decision maker. I cover four states—Louisiana, Arkansas, Oklahoma, and Texas—and all of them are different. In Oklahoma, it’s the county commissioners that make the decisions. Here in Louisiana, it’s totally different. We have parishes here, not counties.
“Some of these parishes have a form of government with a parish president, a council, a public works director, a streets director, a drainage director, and so on. The decision maker is different for every parish.”
Boots in Washington
A large facility known as St. Elizabeth’s in Washington DC is being built, together with its own stormwater system.
Patrick Rodgers of Winchester Building Supply explains that the new stormwater system is independent, with its own outlet, not entering the standard DC system. According to Rodgers, all stormwater runoff in the region now has to be treated before it enters the Chesapeake Bay or one of its tributaries, and this project is no exception.
“This is a big facility,” he says, “and it already has a lot of stormwater systems built that are operating and fully functional. It’s like a residential subdivision—you have a first phase, and a second phase, and they keep building and adding on until the whole neighborhood is complete.
“Each new section ties into the earlier sections. What we’re doing is phase 20 of the subdivision. They’ve been building there for five years already.”
An important part of the system that Rodgers has been involved with is the assortment of “stormwater boots,” otherwise known as resilient connectors. More specifically, Rodgers has been tasked with installing Press-Seal Gasket boots, which are watertight, flexible pipe-to-manhole connectors. His company also is supplying all of the manholes, catch basins, and drop inlets for this portion of the project.
Because of the watertight requirement for the job, Rodgers wanted the Press-Seal Gasket product.
“They have what is called a Direct Drive, which means that there is a steel band that we tighten up,” he explains. “There’s a hole or penetration in the manhole for the pipe to sit in, and the band that makes the pipe stay in the hole expands outward and tightens up to make things watertight and to hold it in place. This is done with a torque wrench; you just tighten it in. Once it’s in, it stays.
“Some of the other connectors that are out there—and we use some of them—haven’t quite gotten up to this level. Up until they created Direct Drive at Press-Seal, we used other boots. But when somebody creates the better car, everybody jumps to the better car for a little while, until the rest of the market can catch up.”
On this project, the manholes are all made of precast concrete, and the majority of the pipe is concrete as well. There are also small runs of HDPE pipe, however.
Rodgers quickly ran into a problem that had to be resolved. “What was called for on this project are the standard field inlets for DC. This standard field inlet is a rectangular box, an opening of 20 by 28 inches.
“That opening in the catch basin is rather small, and you can’t put boots—resilient connectors—in a box when you have odd angles of pipe coming in. You have to use a round structure. You can only use a boot in a square box if it comes in flat with the wall, or straight in with the wall.
“So what I did was to convert that field inlet. I kept the same grate on the top, but I converted the structures to round manholes. We then used a flat top to reduce the size for the grate to sit on. So there’s a 28- by 28-inch opening in the flat top.
“This way, we were able to use resilient connectors. And these structures are very deep. They have a narrow box that is barely more than two feet by two feet, and 15 to 18 feet deep. There would be no way you could ever get down inside of one of those.
“With the depth of this project, and the requirement for resilient connectors specified by the engineers, we had to come up with a little different way of doing things rather than using the traditional inlet box.” Converting to round manholes, he says, will allow a person to get in to clean the pipe or deal with a clog.
Rodgers also stresses the need to properly understand the regulations relevant to the project. “We are now subject to the Chesapeake Bay [total maximum daily load] regulations—everything that goes on in terms of storm runoff, and that specifically means every type of construction. When I use that first bulldozer, when I hit that first blade of grass, or I cut down that first tree, these regulations kick in.
“There are books now on everything that we do, regarding construction in the northern Virginia and southern Maryland areas, anywhere in the Chesapeake runoff area. It’s highly regulated. Once we expose the dirt, it’s regulated on how much can be exposed, what we have to do with the runoff, and how we treat and store that runoff. It’s no longer a case of simply putting up a little silt fence. Everything that runs off gets treated. Somewhere, some way, that water is taken care of, or it is highly monitored to make sure that if it is just running off, that it meets standards. It doesn’t mean that you always have to treat it, but you have to make sure it’s not contaminated.
“Certainly, if there is silt runoff, or any type of soil runoff or erosion, then it has to be contained.”
For this project, a 16-cartridge contact filter system is being put in place to treat runoff. Discharge time is calculated at 2.15 hours, for maximum flow to move through the system. There is an impervious building area of 1.6 acres, and the parking and roadway areas will take up another 1.6 acres.
“The nice thing is that this is going to be a storm system that’s going to be completely watertight,” says Rodgers. “The manhole joists and the concrete joints are going to be sealed with gaskets. We’re basically following sanitary specifications for a storm line, in terms of being 100% watertight.”
Space-Saving Detention in Delaware
Adding a large-volume filtration structure to each of the two underground retention/detention systems for a new hotel in New Castle, DE, enhanced the ability to control pollutants from stormwater runoff.
The stormwater management systems are large, and space was at a premium, so they were put under the parking lot, which maximized the use of the property. The system needed to comply with the Delaware water code and be able to remove any suspended solids because of the pollutants attached to those solids.
The systems were designed to withstand freeze/thaw cycles, plus the weight of vehicles parked overhead. Buried under the parking lot of the new 140-room hotel, near creeks and tributaries that eventually lead to the Delaware River, is the filtration structure.
Each retention/detention system is more than 200 feet long by 40 feet wide, using a total of 2,530 linear feet of 42-inch-diameter HDPE corrugated pipe. The filtration structure is made up of 30 domed chambers wrapped in geotextile fabric. The systems are buried 12 inches deep for non-traffic areas, 18 inches for traffic areas, and up to a maximum of 96 inches in other areas.
Originally, corrugated metal pipe was specified for the job, but this later changed to HDPE pipe due to its watertight seals and 100-year rated service life.
To provide the watertight requirement, the N-12 pipe manufactured by Advanced Drainage Systems (ADS) has a gasketed bell and spigot. In some pipe systems, freeze/thaw cycles will destroy the joints or the grout used as a seal. Silt and sediment will then infiltrate the system and be carried to nearby streams.
Incorporated into the runs of the HDPE pipe is a filtration unit, known as a StormTech Isolator Row, with weirs at each end of each system. The Isolator Row is typically designed to capture the first flush of sediment and pollutants.
The first system, located on the south side of the property, uses six rows of 198 linear feet of N-12 pipe with the Isolator Row incorporating 18 StormTech chambers making up the last, horizontal row. The second system, on the north end of the property, also consists of six rows of HDPE pipe and 12 StormTech chambers for the Isolator Row in the center.
The Isolator Row is a series of StormTech chambers surrounded with filter fabric and connected to a closely located manhole for easy access. The fabric-wrapped chambers provide for settling and filtration of sediment as stormwater rises in the Isolator Row and ultimately passes through the filter fabric. The open-bottom chambers and perforated sidewalls allow stormwater to flow both vertically and horizontally out of the chambers. Sediment is captured in the Isolator Row, protecting the storage areas of the adjacent stone and chambers from sediment accumulation.
The Isolator Row incorporates an upstream, standard manhole, which not only provides access to the Isolator Row but also typically includes a high-flow weir so that stormwater flow rates or volumes that exceed the capacity of the Isolator Row overtop the overflow weir and discharge through a manifold to the other chambers.
For this project, the Isolator Row is between two catch basins, according to Mike Holt, regional representative with ADS. “To actually get everything into the Isolator Row, there are weirs in those catch basins with grates on the Isolator Row side of the weir, so anything that comes into the grates on top comes down on the Isolator Row and not just into the HDPE pipe. Most of the time you get small rain events and everything will go into the Isolator Row and not even top over the weir.”
Ron Vitarelli of ADS explains, “By putting the systems under the parking lot, you gain parking space, which is at a premium for any building, especially a hotel. Otherwise you have to have a pond, which can draw geese and mosquitoes, which are a nuisance and can transmit pathogens such as West Nile virus. An underground system with a proper filtration and storage system is a best management practice.”
Maintainable Subsurface Detention
Additional parking lots were being added to a large business location in Greenville, SC, and the challenge was to incorporate enough stormwater storage underneath the parking lots and still be able to tie into the existing stormwater system.
“This created a lot of invert parameters that most detention systems couldn’t meet,” notes Ben Aulick, regional specification manager for ACO Polymer. “When I went in to meet with these guys, they were ready to bash their heads into the walls.
“The problem is that there is existing piping going into the system that has been there for a while. They had an aboveground detention pond. These ponds had piping going into them. In order to be able to tie into all of the existing systems, the only option to expand was to go below ground.
“Since the existing system wasn’t designed for that, it was challenging to stay shallow enough to tie into the existing system, and also to provide the storage they needed. They were considering a chamber and stone detention, but with this the engineers have to use a void of about 40%, which means they would have to go much deeper and much wider than the site would allow. Instead, our modular system has a 95% void, so we were able to do a lot of single-layer work while still getting the storage they need.”
The system used is ACO Polymer’s Stormbrixx geocellular stormwater management system. This project involved a 12,000-cubic-foot installation of the HDPE material.
The Stormbrixx system doesn’t replace the aboveground detention pond. Instead, it accommodates the stormwater runoff from the additional parking lots.
Aulick believes that the Stormbrixx system was selected for this installation because of its ability to be maintained after it is put into place. “You can get in and inspect the whole system, from the inlet to the outlet,” he says. “Most systems require a separate structure to maintain the system free of debris. It’s already designed within our system.”
According to Aulick, many municipalities won’t allow subsurface detention unless it involves a concrete vault that has a removable top. “Subsurface detention has traditionally been a challenge, especially in previous years, because it wasn’t really regulated from a maintenance standpoint. These things will silt up, and they will get stuff in them if they’re not cleaned out. They’ll fill up to capacity, and with some of those systems, you simply can’t clean them out.
“Nowadays, this is a little less prevalent because we have all the guidelines regarding infiltration upstream of these units, but stuff still gets in them. With the Stormbrixx unit, however, if debris does get in there, you can access it.”
Another issue with subsurface systems involves durability. “Unfortunately, in the US we don’t have a guideline for how these products should be manufactured,” notes Aulick. “That’s why there have been some issues historically.
“If you go to Europe, where they do things much differently than we do here, they’re probably 12 years ahead of us when it comes to the development curve. There’s a code for these systems, basically a guideline on subsurface detention, how to design it and some of the requirements. One of the things you have to test for is life expectancy.
Stormbrixx geocellular stormwater management system
“There is what might be called a 75-year environmental weathering test of modular systems. Realistically, they are going to last longer than 75 years, because HDPE hardly breaks down. But a big part of this is that you have to test for creep. This means that anything under a load starts to relax over time and dips a little bit.
“We test our systems to conform to that [code], but most people in the US don’t do that test. That’s scary, because that’s what ultimately causes these things to fail. After 20 years, for example, it can flex too much, and with soil pressure above them, things start to collapse.”
StormKeeper chambers installed at the Manchester-Boston Regional Airport
Expanding an Airport
The Manchester-Boston Regional Airport, located in Manchester, NH, has been undergoing an expansion of its facilities. To help handle its stormwater needs, the airport is incorporating an underground chamber system, a StormKeeper unit from Lane Enterprises.
“They were going with the chamber system, and the StormKeeper is actually one that meets ASTM standards for chamber manufacturing,” notes Kevin Miller, the lead engineer for the StormKeeper chamber. “It’s probably the most durable and structurally resilient one that’s out there.
“I believe they would have gone with an underground system no matter what, because being an airport, they don’t have a lot of room to put in an aboveground system,” he says.
The StormKeeper is a new product, introduced in April 2015. “It’s an arch-shaped chamber, made out of polypropylene,” explains Miller. “They are modular, so they can be used with as many or as few as you need to store stormwater underground.” Installation involves placing stone, geotextile, and the chambers themselves, “as well as whatever header or additional plumbing or storm drainage you need to be able to get the water into the chambers.
“The primary use of it is for water quantity storage, attenuating your outflow so that you meet predeveloped conditions. But you can also, through the use of what we call sediment strips—a combination of filter fabric or geotextile in a built-up cross section—use it as a water-quality device as well.
“People may have a row of chambers used as a sediment strip, for the water-quality volume that they need to treat, then some type of bypass weir for whatever is over that volume.”
This is indeed what was specified for the Manchester-Boston Regional Airport. Pretreatment was required to remove sediment, and the StormKeeper sediment strip has been approved as a permitted pretreatment technique.
The StormKeeper can be set up with or without an infiltration system. “There are a number of ways to handle it. It’s extremely flexible,” says Miller.
“You can decide that you want to use it as a straight infiltration system. You would allow the water to come in, you plan what your drawdown time would be based on the infiltration rate of your site, then you would design your system to detain that volume of water. You would probably also include some kind of overflow bypass, in case you ended up with too much water from whatever storm event might happen.
“You can also design it so that you infiltrate and remove the water with underdrains that take the water out. Or you can design it another way so that you are not infiltrating any of it, and releasing all of it.”
For this airport project, the StormKeeper system was designed to retain and infiltrate the 10-year storm event. Weirs in the connection manholes and catch basins were sized to pass larger storm events.
As Miller described, the development of this chamber system was a bit unusual.
“We partnered with another storm chamber manufacturer, Prinsco. We came to the agreement that we both needed a chamber, and we wanted multiple chamber sizes. But because we’re both regional manufacturers, we decided that we really didn’t have the demand in each of our regions to support the development of two chambers.
“So we partnered with them and brought the chambers to the market in a partnership agreement. That’s how we were able to come to market and have both sizes of the chambers we have right now.
“They call their system HydroStor. It’s the same product, same design, same molding process. Everything is the same for both chamber lines. We used the abilities of both companies to be able to put this together. The idea was the expertise that we have within both companies will provide us with what we need to get all this developed, and to help distribute that cost.”
