Nov. 17, 2015 10:43

Down the Storm Drain

downthedrain

For most people, the sight of a storm drain does little more than make them grip their keys just that little bit tighter. Any engineer or contractor assessing a jobsite, however, will have a different train of thought. To them, a storm drain is not a point of no return as much as it is a point of great expense. Dropping a hand tool down an inlet is the least of their concerns, compared with the almighty headache caused by some other things that can spill through that grate.

According to the EPA, construction efforts that disturb one or more acres of land require a Stormwater Pollution Prevention Plan (SWPPP). These plans require that the contractor protect any nearby inlets that might be affected by the construction. Without proper protections, trash, grass clippings, leaves and sediment can all go directly down the drain, and the contractor would be subject to fines. They may even be subject to liability related to any flooding that may occur.

The most common treatment for a clogged storm sewer is a vacuum truck. Given that even a bargainbasement vac-truck costs upwards of $80,000, it should come as no surprise that flood prevention is generally preferable to remediation.

For many, inlet armor takes the form of a bunch of geotextile sacks filled with rocks. While ringing an inlet with these bags may seem like an easy answer to a simple problem, there’s more to it than that.

Although the materials involved are quite cheap, this method is labor-intensive. The work-hours involved in installing and removing these heavy sacks can more than make up for the low cost of gravel and fabric. Furthermore, this method has a large footprint, and can pose a hazard to the tires of passing vehicles, including a contractor’s own equipment.

In other locations, hay bales have been a commonplace erosioncontrol solution. However, while they are cheap, and effective at limiting soil, many municipalities are finding that they cause at least as many problems as they solve.

“Hay bales rot in 30 days or less,” said Elliott Davis, who does marketing for GEI Works in Sebastian, Florida. “Typically, a hay bale doesn’t bind the straw together really well, so you get a lot of hay going down the drain.” Not only does that bring its own clogging risk, but the straw can also carry the seeds of invasive plant species with them. Although bales can get certified by their states as weed-free, what is native to one state may be considered a weed in another.

Finally, not only is neither method as cost-effective or efficient as they seem, but they aren’t reusable either. Once the construction is completed, the bags and the bales are loaded into trucks and disposed of. Fortunately, these aren’t the only options. For both pre- and post-construction measures, there are a vast range of storm-drain protection devices that a contractor can install which are reusable, effective and economical.

There are a number of companies that sell devices designed to sit atop the grate and prevent sediment and trash from entering the system. Probably the simplest of these are mats made of coir, the fibrous husk of the coconut. Formed into the shape of a carpet, coir naturally filters out sediment quite easily, and is tough enough to move to the next job site when it’s done.

However, at least one municipality is discouraging coir use, though even they admit it filters really well. According to Wes Rood, stormwater specialist for the city of Westfield, Indiana, they encountered too many problems with flooding. The devices were often poorly maintained, and when flooding inevitably occurred, the resultant problem-solving took a rough-and-ready approach.

“What happened was that instead of trying to scrape the top of this fiber mat with a flat shovel, to allow the water to start draining again, they simply poked a hole in it,” he said. “Then you have no inlet protection and a direct discharge of sediment into the stormwater system.” Now the city’s standards are more stringent, and require a geotextile bag with a metal frame and overflow ports. A number of inlet protection companies make such a product to fit a variety of grate styles and dimensions.

The feature that contractors probably look at the most in distinguishing between these products is how the geotextile fabric is made. Some bags are made of woven synthetic fibers, which tend to offer a high tensile strength, making them more resistant to bursting, but they may not have a high enough flow rate.

Other bags are made of nonwoven fibers, extruded from a machine and compressed into a sheet. The sheet is then punched through with barbed needles, and when the needles come back through, the barbs interlock the fibers. Non-woven fabrics tend to be a little cheaper and offer higher flow rates, but the material can be unevenly distributed through the fabric. This makes the fabric more prone to blinding, which means it will dam up faster, and is more likely to rupture.

Whatever fabric a filtration bag is made from, the most important part of implementing this component of an SWPPP is maintenance. The EPA guidelines are deliberately vague, requiring inlet inspection “frequently, and after every rainfall.” Maintenance requirements can be hard to pin down, as they vary from product to product.

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In many ways, we are fortunate that, in our chosen profession, we are able to help people when certain disasters occur: the tornadoes in Missouri, Oklahoma, Louisiana and Georgia, the flooding in Louisiana, the snows in the northeastern part of the country, the rain in California, and the snow in Colorado....

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