One of the hazards associated with development, whether in crowded coastal areas or empty spaces out West, is the impact it makes in the quantity and quality of runoff. Nobody wants to be part of a negative headline. Fortunately, a number of pipe products are designed to meet the challenge of even a 100-year storm. Still, whoever has charge of the landscape, whether a single home, commercial, industrial, or public site, has to decide which is the most cost-effective solution for a given site condition.A Solid Look at ConcreteOne challenge is ensuring that the onsite solution doesn’t bring on problems downstream. “Whatever is used, it’s important to look at not only where the water is coming from but also where it’s going,” explains Nick Domenico, sales manager for Kerr Concrete Pipe. “Even on a flat grade, you want to move the water from the backed-up area safely. Baffle systems help slow the flow and prevent downstream flooding.” Domenico reports that his firm, with manufacturing plants in Hammonton and Farmingdale, NJ, distributes 12- to 120-in. round and 18- to 108-in. elliptical reinforced concrete pipe (RCP) throughout all of New Jersey and an ever-spreading market in New York. (Kerr’s sister company, Cayuga, markets in the state of Pennsylvania.)
“Because concrete is fuel- and fire-resistant, we do a lot of airports. Concrete will take a heavy load and is warranted for use under taxiways and parking garages. Airports tend to evolve; an area used for parking may become a taxiway, which means heavier loads. The need is to design pipe installation in such a way that it anticipates new uses. There are lines in use today where the pipe is over 100 years old–not surprising since concrete grows in strength as it ages. It lasts longer than other lighter materials.” What about the weight challenge presented by concrete? Relates Domenico, “It’s ideal for areas where pipe depth will be rather shallow, yet it can handle burials of 100 feet or more without deflecting or collapsing. Furthermore, not only is RCP strong enough to handle traffic with minimal cover but, since it’s available in gasketed or mortared joints, concrete pipe can be soil-tight and silt-tight. Regardless of how well manufacturers build a product, the operation of the storm line depends on the contractor’s installation, and RCP is the most foolproof product to install. Inspection when laying each section of pipe is not crucial when concrete is used because there is such a large safety factor in design. When you use RCP you get 90% of the strength delivered on the truck. When installing flexible pipe, the bedding and backfill play a larger role in creating the strength of the line.”Domenico also reports that stormwater trends in this highly populated state include putting retention ponds underground. Underground systems present fewer public hazards than open ponds, don’t need mosquito abatement programs, don’t present aesthetic challenges, and don’t compete for surface acreage.Middlesex Trenching Company of Metuchen, NJ, has been doing site-preparation work since 1952 and includes underground retention systems in its repertoire of services. “One of our more recent projects for Adams Bickel Associates involved the site work for Commerce Bank’s regional headquarters 12 miles away in Bridgewater,” explains William Gulya, president. He adds that site preparation for this current project totaled nearly $1 million, with the 107- x 130-ft. retention basin accounting for 30% of the bid.“Basically it’s a series of 48-inch RCP connected with specially fabricated concrete tees. Stormwater is collected through a series of catch basins and manholes from the finished parking lot, then routed into this underground storage facility. When completed, the top of the retention pipes were 5 feet from the surface, which will be used as the major street access to the bank and for parking. We’ve put in all types, but RCP was called for in this one because it was more economical, and we didn’t need to go nearly as deep as we would have with other products.” This also reduced the risk of groundwater intrusion, a factor in this coastal state.With just 12 working days permitted for installation, the 26 concrete tees joining the 15 lines of piping posed a particular challenge to the crew of five because of the awkwardness of slinging them into place. Gulya explains, “We worked closely with Kerr Concrete Pipe to be able to lift them safely and efficiently and put them right into place with a minimum chance of damaging the pipe. Basically we located 3-inch cored holes, about a foot from each end of the tee, and used tapered steel cones that slipped into the holes when the tee was lifted, keeping the tee level. It made installation a piece of cake.” After backfilling to subgrade with 2.5-in. clean stone, it was a matter of paving to grade, and the retention basin was ready for use.Mike Saubert, director of marketing for the American Concrete Pipe Association (ACPA) in Irving, TX, points out, “Stormwater transport and detention has certainly become a more critical topic in the last couple of years as a result of federal legislation and state and local governmental actions. That’s why ACPA, in conjunction with the Illinois Concrete Pipe Association, has issued DASH–Detention and Sewer Hydraulics–software to enable engineers and pipe specifiers to develop stormwater detention systems utilizing precast concrete pipe. We’re also seeing a lot of interest from our membership with stormwater separator systems, which isolate waste from stormwater runoff before transporting that water to processing plants.”Increasingly, local authorities are mandating such systems wherever cars gather in great numbers, whether it’s a local filling station, a shopping mall, or a sports complex. Saubert observes, “It keeps our members busy providing solutions for more efficient stormwater storage and transport. More and more, stormwater is being diverted from sanitary systems because you don’t need to process stormwater at the same level you do human waste. This separation is helping municipal treatment plants have a longer life before growth outpaces original capacity.”He continues, “Precast concrete pipe has benefited tremendously from new technology. Pipe design has changed significantly during the past two decades. For example, our members can design and manufacture products for specific applications and installation requirements. Owners may be able to use a lower strength class of pipe where they have good backfill and good native soil, or if they have very weak soils, they can opt for a higher strength class of concrete pipe to achieve design parameters.”ACPA President John J. Duffy, who has been in the industry since 1974, reports that precast concrete pipe is a $1.4 billion- to $1.6 billion-a-year business, with 75–80% used for stormwater and the remainder for sanitary systems and miscellaneous uses. “The principal advantages of concrete pipe are that it is more durable, comes in a wide assortment of classes, and has a proven service life of over 100 years.”Although there can be a concern about shipping issues, Alan Siebenthaler, director of marketing and quality assurance for the National Precast Concrete Association in Indianapolis, comments, “There are precast concrete plants throughout the country, so shipping costs are not the issue faced by manufacturers of other pipe materials. RCP is readily available. When it comes to pipe product, we’ve found that when you include installation and long-term maintenance, overall project costs tend to lean in our favor. Specifiers and contractors must understand the limitations of all types of pipe. RCP comes in a broad range of sizes and with high compressive strength so is therefore ideal for nearly all applications.” However, Siebenthaler notes, “Reasonable care must be taken with job-site storage, handling, and installation of RCP. Good practices can prevent damage in any type of pipe, reducing the number of discarded pieces and overall costs. During installation, use of the proper equipment and safety procedures will reduce the likelihood of damage and injury while improving installation time. Installers must know the best procedures for installing RCP. This information is usually available from the pipe manufacturers and trade associations.”When Flexibility Is Part of the Equation
Just as concrete can use its weight to its advantage, plastic–whether PVC (polyvinyl chloride) or HDPE (high-density polyethylene)–can use its flexibility, notes Bob Walker, executive director for the PVC Pipe Association in Dallas. “Of all the plastic pipe in use, PVC is the most dominant and most used material overall. It has a higher tensile strength and a greater stiffness, compared with other thermal plastics. As a result, it is the most prevalent material for stormwater transmission.”Walker reports that PVC and other thermal plastics enjoy a growing market for stormwater needs, whether piping or ponding the flow. “We think it’s the most durable product out there. PVC can be stretched, bent, or deformed without slitting, cracking, or breaking. In university tests still underway, after 22 years of pipes being deflected as much as 30% to 40%, there is no cracking, breaking, or deterioration of the material.”He points out that while thermal pipes tend to feature smooth interiors for better hydraulic capacity and lower maintenance needs, some products have corrugated outer walls. “Some feature concentric ribs on the outside, while others are helical or spiral in nature like corrugated metal. Other exteriors are shaped like a T, which gives an I-beam effect.”PVC also is seen as user-friendly, as long as the contractor makes sure imbedment material is put in place as needed. “If planned for deep burials or in high-traffic areas with a shallow covering, you need to compact the imbedment at least halfway up the sides of the pipe to maintain the circular configuration,” describes Walker. “Stone dimpling is not as big a problem as with HDPE and other flexible materials. Also, each length of PVC includes a bell and gasket at one end and straight spigot at the other; there are no couplings to buy. The contractor simply pushes the joints together for a watertight seal. Watertight joints eliminate erosion of imbedment or under roadways.”He cites a memo received from the Chippewa County Highway Department in Chippewa Falls, WI, where frost heave is a problem for buried pipe. The department installed about 40 Nyloplast Curb Inlet Structures in various locations through the county, one of them under a county road passing through the town of Jim Falls. In the memo, department member Wayne Krejci reported superior compaction during installation because of the installers’ confidence that compaction equipment would not damage the pipe connection joint. He wrote, “When using concrete structures, the installer may lighten up on the compaction to protect the joint integrity and thus leave an area that allows moisture to collect, freeze, and heave the structure as the soil reacts.”
Another concern with concrete in that region is corrosion from roadway salts. Some Midwest municipalities are reporting the need to rehab concrete drainage structures on an eight- to 10-year cycle. In this instance, thermoplastics tend to last longer than either metal or concrete.Dave Allison, P.E., applications engineering manager with the Plastics Pipe Institute in Washington, DC, remarks, “We sense that the market is growing for plastic pipe. We have seen a steady improvement in the polyethylene material used for corrugated piping.” He adds that contractor care during installation also affects the line’s life.Looking to resin improvements, Allison comments, “Some of our corporate members are moving into larger sizes, with corrugated manufacturers working on a 60-inch pipe. Our member firms offer smooth interior walls with corrugated exteriors, so you have the best of both camps. They also can supply extremely thick walls, as measured in terms of diameter to wall thickness. A DR-7, for example, is a 14-inch pipe with walls 2 inches thick. That’s a lot of plastic.”Still, thin-wall or HDPE research continues, partly because it’s possible for two workers to manually move an 18-in.-diameter, 20-ft.-long plastic pipe. “This is ideal when dealing with a site where there isn’t room for lifting equipment,” points out Allison. “With HDPE corrugated, you don’t have to round up lifting equipment to load, unload, or help put the pipe in place, yet the pipe can handle loads typical for highway application.”Regarding the chemical resistance factor, Allison maintains, “Aluminum will resist corrosion, and the steel pipe industry has tried galvanizing or [applying] epoxy over corrugated piping, but those are coatings on top of basic material and can be disturbed, while HDPE is rust-free all the way through. HDPE has three to five times the abrasion resistance of steel. It will not corrode, and it can handle high-pH soils because it’s chemically inert.”
He cites the example of an area in Oregon where 2- to 3-in. gravel was washing down into a valley, eroding bottoms out of corrugated steel tubes in three to four years. “Abrasion also is a problem in concrete, but not to the degree it is in steel. But because HDPE will not corrode, it’s becoming the material of choice for underground water detention facilities so owners can make double use of the land.”Concerning installation issues, Allison continues, “As a civil engineer, I like to say all pipe needs to be installed properly, including compaction, [with] no voids under the pipe. No matter what the product, the contractor has to follow the directions to ensure maximum life. As for life, right now we’re very comfortable stating HDPE will last a minimum of 50 years, and we’re continually working to expand that, but it’s difficult when you don’t have a 50-year history, while other products have been around for generations.”Helping Steel Attain a Longer LifeCorrugated steel is another long-term product for piping projects. When it comes to stormwater applications, Brian Roberts, executive director for the National Corrugated Steel Pipe Association, reports, “We have more than 90% of the stormwater detention market, and our members do about $500 million a year in culvert and storm sewer work.”Roberts sees the need for detention to deal not only with peak flows but also with water treatment issues. “When talking about storing large volumes of water, that’s where steel comes into play. We’re a winner there because of cost, strength, durability, and the flexibility to fabricate almost anything. There are three types of control systems: detention, infiltration or groundwater recharge, and filtration. With detention you simply hold the water and control the release rate after a storm event to prevent downstream flooding and erosion issues. With infiltration you’re trying to put water back into the ground, controlling both quantity and quality.” He adds that a sand media typically suffices for quality control and is used as a best management practice commercially, industrially, and publicly.“Most such installations are under parking lots, so structural performance is a very important issue because most are put under minimum cover conditions, even as little as 12 inches from the ground’s surface to the structure.”Roberts explains that while holding-tank diameters tend to start at 48-60 in., it’s not uncommon to see sizes in the 96- to 120-in. range. He notes, “Our industry is driven by the regulatory community, but as the field of stormwater management develops further, we’ll see techniques for dealing with water quality that will improve and become standardized. The types of filtration media, pretreatment methods, et cetera, will improve over time.
“The [biggest] advancement for us in metal pipe has been the development of various new coatings. These coatings allow us to extend the service life and also use [the pipe] in a wider environmental range. Galvanized is still the standard, but both Aluminized Type 2 and polymer precoated are increasing our market share.” Roberts emphasizes, “The idea is to protect the steel, which provides structural superiority and can be fabricated to any size or shape needed. We’re seeing a resurgence in the demand for our products.”Eric Whitney, stormwater treatment products marketing manager for Contech Construction Products in Middletown, OH, agrees. Phil Perry, supervisor of corrugated metal pipe (CMP) for Contech, reports that the company expects $450 million in sales this year. “Storm sewers are a major part of DOTs [Departments of Transportation], municipalities, counties, and a lot of private commercial work. Every shopping center, subdivision, commercial office, warehouse, new school, and new prison has storm sewers.”Whitney points out, “We make steel, aluminum, and lots of different types of corrugated metal pipe with metallic and nonmetallic coating. We try to match the right corrugated product to the customer’s needs. For example, Florida DOT has a design life requirement such that they use a lot of aluminum pipe and Aluminized Steel Type 2, which gives them a long service life in their harsh environments, which includes saltwater intrusion.”Other areas of the country favor the use of polymeric-coated CMP, which can handle low pH and water, while galvanized works well with high-pH conditions. With aluminum, an appropriate corrugation and thickness can be specified to give the pipe the equivalent strength of steel. Perry says, “A 16-gauge corrugated steel may handle up to 75 feet of cover, whereas 16-gauge aluminum may handle only 25 feet, but 90% of the jobs out there involve less than 10 feet of cover, so it’s really a nonevent.“The number-one problem with any pipe product in the marketplace, whether plastic, concrete, steel, or aluminum, is poor installation by the contractor. The primary problem is using poor backfill materials that don’t compact well.” Another problem involves the minimum cover needed. What may suffice for general traffic after construction might not handle heavy equipment during construction, so temporary berming over the pipes during the construction phase helps all products handle the temporary additional load.Whitney notes that raw prices for metal piping vary across the country, with aluminized costing 10–15% more than galvanized, polymer-coated steel 30–40% more, and aluminum 30% above galvanized CMP. “A new product on the market is bell-and-spigot joint for metal pipe. Contractors can install that pipe similar to concrete or HPDE pipe, no wrench work necessary.”Perry adds that one of the evolving markets for metal is underground stormwater storage because the cost-effectiveness and the larger diameters possible with corrugated metal make it an attractive choice. “This is why the City of Champaign, Illinois, chose corrugated metal pipe for a large stormwater storage project requiring 155,000 cubic feet of storage. Contech supplied 9,000 lineal feet of 132-inch-diameter pipe to meet the needs of the project. With diameters of 6 to 144 inches, metal gives the user a wide range of choices when it comes to specifying a stormwater drainage system.”As manufacturers of concrete, plastic, and metal pipe continue to improve the products they offer for stormwater concerns, the ultimate winner is the user, whether private, commercial, industrial, or public.
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