Storms happen regularly, and they are not always catastrophic. Municipalities and other landowners can prepare for different levels of anticipated storms – with those that strike once in a hundred years being the most difficult to forecast and manage – without panic or budget-wrecking costs. Almost all public employees, manufacturers, and engineers with whom we have discussed stormwater management agree that affordable preventive measures can save a community significant remedial expenses after the inevitable storm event. Regular storms are sometimes alluded to as “initial” storms, and it is for these events that we prepare drainage systems that keep down the cost of street maintenance and allow any unusual amounts of water to drain to acceptable locations.
Where the percolation is good, open ponds have been popular because they offer the maximum amount of storage for the amount of land used. Experienced engineers tell us that open ponds should be a minimum of 18 in. deep and should be constructed at least 2 yd. from adjacent property lines and more than that from any structure. A source of practical information about ponds and related topics is the Natural Resources Conservation Service (NRCS). With more than 3,000 conservation districts, the NRCS offers information that can be helpful specific to your particular community and point you in the right direction. The NRCS lists more than federal, state, and local governments among its customers; it also offers guidance to individuals such as ranchers, farmers, and contractors – in all, to more than a million entities last year.
Runoff from outside the area under consideration for new drainage systems is important but easy to overlook. The storm runoff from areas already developed might be simple to analyze, but you should also consider anticipated future use of undeveloped land that could be a source of runoff. If future use is undecided or unknown, then the flow calculations will probably be based on such existing features as slopes and natural drainage routes. One aspect of drainage systems that caught our attention among the specifications from some engineering consultants – it seems obvious when you read it, but might not be so obvious before doing so – is that any new drainage system should not simply transfer problems from one location to another. An example of what not to plan is outfalls that cause runoff to enter irrigation canals and threaten them with flooding. “The more permanent the solution, the better the drainage system” is an often-repeated caveat.
It’s no surprise that regulatory authorities require information about proposed drainage systems in a community, especially for new structures and residences. You’ll need to provide information on such local details as property lines; streets; right-of-way limits with names and grades; the types of gutters and curbs proposed for the streets and the flow direction of the streets; proposed manholes, culverts, inlets, storm drains – all the aspects of drainage control; the proposed locations of outfalls and infalls; elevation of affected buildings; and a map that shows all the information requested. It sounds overwhelming but makes good sense, and experienced help with the necessary calculations and paperwork is often available locally. Gathering this information now will also extend to the future. The specifications of any new drainage system introduced after yours will be checked for compatibility and quality of control.
Some individuals and public authorities see programs such as the National Pollutant Discharge Elimination System (NPDES) Phase II as further unfunded intrusions into local affairs, but Jim Frei of Stormwater Services Group (SSG) in North Carolina makes a positive point: “There has been a significant and publicly appreciated improvement in wastewater treatment since the government pressure back in the ’70s. These advances concerning stormwater are the same. They will bring benefits to communities, and the funding challenge is to convince people that the benefits are a good investment.” Concerning the question of prevention or cure, Frei (and almost all the people with whom we spoke) suggests that removing pollutants at the source is better than waiting until after the storm event, especially when pumping systems might not remove enough.
Writing stormwater pollution prevention plans (SWPPPs) – documents that are required for each facility that has been issued an NPDES stormwater discharge permit – is one service that SSG provides. For Weyerhaeuser’s Greenville Lumber Mill in North Carolina, notes the company’s Charles Daughtery, “Mr. Frei helped support NPDES permit number NC0073229 by inspecting the site for potential pollutant services, selecting appropriate best management practices, investigating illicit connections, and writing the original SWPPP for this mill.” At manufacturing facilities, it is also important that all employees (not just those involved by definition of their jobs) are aware of regulations and conduct to comply with them. “Apart from site investigation and other services, he gave our employees training on environmental topics,” says Terry Wilder for Crocker’s Marine, a boat builder at Wrightsville Beach, NC.
“A workshop on stormwater permitting and pollution prevention was helpful to our employees – about 150 of them,” comments Tammy Parker for Consolidate Diesel Company in Whitakers, NC. “We suggest the SWPPP be updated every few years,” adds Frei. “This will reflect changes at a facility, and many states require certification at renewal time that an SWPPP has been written.”
Catching the Fugitive Pollutants
Many problems associated with stormwater come from moving water’s ability to transport sediment. The amount carried will relate to the depth of the flow and its speed and temperature. The amount of sediment carried by the water will also depend on how much sediment there is at a particular site. The same water that can carry soil sediment quickly and in great quantity also carries the debris of modern living in the guise of drink containers, food packaging, newspapers, and all the other bits and pieces of waste we have become accustomed to perceiving as normal but unwelcome residents of streets and gutters.
The thought and touch of oil and grease make many people pull wry faces, but these substances are even more offensive when included in water that is possibly destined for treatment and reuse as drinking water. Contractors, public works departments, garages, bus stations, and parking lots can all leave hydrocarbons (fuel, lubricants, and oil) where they are not wanted. One method of managing this common problem is the use of a hydrophobic material, one that dislikes water but which will absorb oil. AbTech Industries of Scottsdale, AZ, makes Ultra Urban Filters (UUFs), which trap the oil and grease from runoff water by absorbing them with a sponge and catch other trash and debris in a basket. The absorbent can be recycled once its job is done. The UUF can also serve as a retrofit for existing storm drains and catch basins. Drop-in units are used for basins where the water flows in from the top. For curb-opening drains, modular filters of varying sizes can be installed in about 20 minutes to a mounting bracket inside the storm drain.
Users and manufacturers alike emphasize the need for maintenance of all protective devices. The AbTech filter devices used by the City of Springfield, MA, were laboratory tested 11 weeks after installation. Among the goals were measuring the devices’ effectiveness and assessing their condition after more than 60 days of collecting trash, sediment, and debris. “It is important to maintain the boxes by vacuuming them out in place prior to the winter season,” notes laboratory representative Alfred A. Reigins. “Such maintenance allows removal of the fall-season debris, which in one box exceeded 95 lb. The box, already designed to handle temperatures to -40ºF, will be modified to use a strap made of seat beltlike material to give it more flexibility.” The laboratory’s report to the city noted that the filters exceeded expectations in all cases, collecting or containing more than 89% of the carbons flowing through in liquids. “The debris contained significant quantitative and qualitative characteristics,” continues the report. “The average amount of debris approached 40 pounds per UUF. Assuming this represented one third of an annualized figure and further assuming that 40,000 UUFs were deployed in the city, this implies that 4.8 million pounds of debris, trash and sediment might be vacuumed out of the system prior to reaching the sewage treatment plant. With significant levels of lead, zinc and copper involved, the cost savings could be significant, too.”
The new pharmacy planned by Rite Aid Corporation in Manchester, ME, faced especially strict local standards related to phosphorus runoff (a prime pollutant responsible for algae blooms in lakes and ponds) because nearby Cobbossecontee Lake is considered one of the most polluted lakes in Maine. “We worked closely with town officials and representatives of the Cobbossee Watershed District to develop a stormwater management plan,” states Patrick Clark, P.E., with Land Use Consultants of Portland, ME, engineering consultants to Rite Aid. After several unsuccessful, conventional stormwater treatment methods were evaluated, the choice was Stormtreat Systems. “The final design comprised a conventional stormwater collection system of catch basins, swales, and piping,” says Clark. “The most polluted first flush of runoff goes to an underground storage vault connected to five Stormtreat modules in parallel. After that, an underdrain system collects the treated effluent and discharges it to a highway storm drain.”
A Stormtreat System will guide stormwater through a multistage system to remove the total suspended solids before infiltration. There is a grit filter bag that traps the bigger floatables trying to work their way past the catch basin, then a series of sedimentation chambers fitted with skimmers and a gravel filter that acts as a substrate for a constructed wetland. The sedimentation chambers trap the particulates of larger diameter while the smaller particles in the size range of silt and clay are filtered in the gravel wetland substrate. Because they are mostly organic, the smaller particles can be decomposed by bacteria residing in the wetland plant root zone. Treated stormwater then infiltrates the stone (about 0.75-in. size) used as backfill in the excavation under and around the tanks. The highly permeable stone transmits the treated water downward until it encounters the parent soils. During peak flow periods, it is possible that the infiltration rate will exceed the permeability of the parent soils. In this instance, the stone backfill area serves as a temporary reservoir, and as it fills with water, the treated stormwater meets a much larger leaching surface. The Stormtreat System has been used successfully in industrial and municipal applications, as well as at sites for the protection of coastal waters.
Petroleum hydrocarbons include most, if not all, oil-based products generated by motor vehicles powered by fossil fuels or lubricated with any of the byproducts. Those include oil, grease, gasoline, and some antifreeze. You can imagine that they are common visitors to Main Street and construction sites. A common method for separating oil from water runoff employs big underground oil/water separators (usually of precast concrete). Although effective, they are expensive to purchase and install, and they sometimes have another disadvantage: being underground, they are difficult to inspect and maintain. Too often, because they are difficult to service, they’re neglected. “Many of them became expensive planter boxes,” comments Debra Allard, president of KriStar Enterprises in Santa Rosa, CA. “No matter how efficient a device may be, it has to be serviced periodically or it becomes worthless.” The collected contaminants in untended systems can be washed back into drainage systems by heavy rains. For some locations, a less expensive and easier-to-install alternative is an inlet protector such as KriStar’s patented Fossil Filter, available for rectangular, square, round, and curb inlets and for trench drains. The FloGard Fossil Filter is a replaceable catch-basin insert that comprises a woven geotextile fabric for collecting debris, silt, oils, and greases. It effectively filters at low flows and – because of the built-in, high-flow bypass – will not hinder high flows through the system. Filters of this type can be used in main and side streets, truck yards, bus depots, and parking lots and at airports.
By the very nature of the work and the equipment and materials used, construction generates waste and debris, and many inlet protection devices are intended for catching construction-site soil and debris before they reach nearby storm drains. Some of these solutions are temporary, unlike large underground treatment systems, and many are reusable.
The Siltsack catch-basin silt filtering system, offered by ACF Environmental of Richmond, VA, is one such inlet protection device. The Siltsack is installed by removing the drain grate, inserting the sack, and replacing the grate to hold the filter in position. It is simple to remove for cleaning and reuse or for disposal and replacement. It is a sediment control device used as both a primary and a secondary control for preventing clogging in drainage systems. The manufacturer has some pertinent advice: Don’t install the device and then leave it forever. “Each Siltsack should be inspected after every major rain event,” advises David Kelley of ACF Environmental. “If there have been no major events like heavy rain or storms, we recommend that the product be inspected every two or three weeks. There is a yellow restraint cord that should be visible at all times. If the cord is covered with sediment, the owner should empty the Siltsack.”
A potential replacement for awkward rock check dams is the Triangular Silt Dike. Workers can install the Silt Dike, which is made of durable but lightweight materials (weighing 7-9 lb. per 7-ft. section), in minutes with U-shaped wire staples. It helps to contain erosive soils on roadsides and at industrial and commercial construction sites. This product has been successful as a temporary ditch liner, for drop inlet protection, as a diversion dike, and also for pond and stream protection. It conforms to the contours and curves of rough terrain and is reusable.
ACF Environmental’s Dirtbag does just as the name implies: bags the dirt. It collects sand, silt, and fines and has been used successfully at construction sites, for pipeline installation, and in highway and utility projects. The user installs it on a slope so that incoming water flows downhill through the product without causing more erosion. The neck of the bag is strapped tightly to the discharge hose. “When the Dirtbag is full, it will no longer efficiently filter sediment or pass water at a reasonable rate,” points out Kelley of ACF. “The flow rates will vary, depending on the size of the bag, the amount of sediment and its type passed into the bag, the type of ground conditions under the bag, and the degree of slope on which it stands. Under most circumstances, it will accommodate flow rates of 1,500 gallons per minute.” Common sense dictates that excessive flow rates and overfilling the bag with sediment can cause ruptures in the material or break away the hose attachment straps. As with all the products mentioned, you don’t want to install them and leave them, just as you wouldn’t leave the dishwasher full and expect it to be ready for the next load after its cleaning cycles.
Some devices are located outside the drain to filter sediment, such as the Verti-Pro from Alpine Stormwater Management Company in Gahanna, OH. “You just clamp it onto the catch basin, and then you can reuse it by just springing it off,” describes Bill Resch, environmental director for New Albany Schools in Franklin County, OH. His environmental team is responsible for ensuring sediment control during construction of the school district’s new $19 million middle school. “For the last 10 years, since development came to our community, we’ve attempted to get developers and contractors to adequately or skillfully install sediment control devices, particularly catch-basin barriers and curb inlet barriers. The revolution, you might say, in the compliance level has been standardized, manufactured products. In the past, some contractors would drape some sediment fence around four survey stakes, and the first wind or the first rain that comes by, it falls in.”
Another outside-the-drain option is the Beaver Dam from Dandy Products in Grove City, OH. “We used the Beaver Dam curb inlet sedimentation filters at several job sites this past construction season,” comments Steven N. Savko, president of Nicholas Savko & Sons Inc. in Columbus, OH. “Each job was in a municipality where sedimentation control was strictly enforced, and in each case the filters worked excellently.” Adds Mark Troilo, senior project manager for Dineen Excavating Company Inc. in Plain City, OH, “I was especially impressed by the simple installation and the fact that it can be easily cleaned of silt without using any equipment. It is practical because it is a one-time purchase per inlet for the entire course of the project.” The Beaver Dam allows suspended solids in stormwater to settle out of the slowed flow. Made of a woven monofilament, the Beaver Dam is available in various diameters, with 3 in. the standard.
The Dandy Bag, also from Dandy Products, is designed for use with flat grates and mountable curbs. Again, simple installation is stressed by the manufacturer (because not every municipal worker or contractor’s laborer is an expert). The user stands the grate on end and places the bag over the grate. After rolling the grate over so that the open end is up, the worker pulls up the sack, tucks in the flap, and presses the Velcro strips together, ensuring that the end of the grate is completely covered by the flap. Then, holding the handles, the worker places the grate with the bag inserted back into the catch-basin frame. Regular inspection and maintenance are essential, of course. Inspection of the inlet can be done by removing the bag with the grate inside. By removing sediment, silt, and debris from the surface and the vicinity of the Dandy Bag – a stiff-bristle broom or a square-point shovel are popular for this – the owner will ensure correct operation of the device. Fine material inside the bag should be removed regularly, and a bag no longer in use should be disposed of at a recycling center or a solid waste facility.
Let’s say it again: Most of the systems described here are intended to prevent problems. “In our opinion, it is better to be proactive and have products in place prior to the stormwater event,” comments Dan L. Cleveland Jr., national product manager for Dandy Products. “That way you can establish prevention and lines of sediment, silt, and oil defense. After the fact, you become reactionary and begin fighting an uphill battle. The only thing one can ascertain after the stormwater event is where you should have had products in place to prevent the runoff and unprotected areas.” Contractors who have had to flush inlets after failing to protect them will plainly tell you how they would rather have spent their money. Noncompliance is very expensive.
