Erosion Control March/April 2017 : Page 50

Singleton, owner of Silt-Saver, had contacted him to request a third-party evaluation of a product Singleton had developed. Spotts says he is always interested in developing new BMPs. They visited a cul-de-sac on a con-struction site Singleton owned that had a drain in the middle of it, a road that wrapped around it, and a fire hydrant nearby. They set up a typical BMP nor-mally used around inlets: four stakes wrapped with silt fence. They raked soil around the outside of the silt fence material. Spotts stood in a hole where the drain was located, preparing to take water samples from water that would leak through the silt fence as Singleton activated the fire hydrant. Spotts looked up to note that the sides of the silt fence between the posts were beginning to cave inward and rapidly climbed out of the hole as the stakes collapsed. “I was concerned about the effective-ness of it, particularly since the water was not very high on the side of the silt fence—maybe 10 inches, which wasn’t much,” he says. They agreed to repeat the field test the next day with the Frame and Filter Assemby BMP Singleton had designed. “He had a black frame with a piece of geotextile material wrapped around it like an inverted ice cream cone,” notes Spotts. “We put some gravel around the bottom of it so the water wouldn’t escape underneath around the lower lip of it. He turned on the water. I waited and waited for the thing to collapse. Surprising to me and everyone else, it did not collapse; the water rose up to the very top of the container itself with no collapse. “I was very impressed with it,” he says. “Structurally, the round circle around the drop end attempted to go into compressions as water exerts pres-sure equally on all sides, so there’s no chance of it collapsing inward like the one we did with the four stakes and silt fence. That’s very important.” The second factor was that the fabric slowed the water down enough so that much of the sediment collected on the For related articles: www.erosioncontrol.com 50 EROSION CONTROL outside and allowed clearer water to pass on through, which was the water Spotts had sampled. Spotts says the Silt-Saver devices have “caught on very well here in Geor-gia. They’re used extensively by the DOT as well as construction—private practice, commercial, and industrial. They’re very popular, and I can say they do a very fine job.” Spotts points out that drain and inlet protection is just one BMP that must be employed on a site where there’s going to be potential for erosion and sedimentation. “To say that by itself it is sufficient is certainly misleading, and it is not to be construed to be the all-in-one answer,” he says. “As with all BMPs, there also is a certain amount of maintenance required. Once the pores in the filter clog up, it then becomes a dam rather than a filter and you need to replace the filter fabric on the outside.” An approach used by some is to let the fabric dry, “beat” the clay sediment off with a board, and put the fabric back on again. “That’s considered a less expensive way of doing it,” says Spotts. “I don’t know that it lasts a lot longer. It might be easier just to replace the entire thing in terms of saving time and money.” Maintenance or replacement should be performed when the sediment rises halfway up the height of the fabric, says Spotts. Silt-Saver offers a two-stage filter for its Frame and Filter Assembly. The staged-release woven fabric with differ-ent sieves in each of the stages produces different efficiencies along with differ-ent flow rates. The first 12 inches verti-cal starting at ground level offers 98% efficiency with 180 gallons per minute, per square foot flow rate, says Single-ton. The next 12 inches offers a higher 1,350-flow rate. “This two-stage concept limits flooding with the controlled release of stormwater,” says Singleton. “Sediment is transported by stormwater. To only address the efficiency of a practice without addressing the stormwater is a setup for failure.” Silt-Saver also has incorporated the staged-release concept into two of its woven silt fences, addressing the controlled release of the impounded stormwater and reducing the hydro-static pressure behind the fence that can lead to undermining of the fence or total system failure, says Singleton. Although this type of BMP is often used in conjunction with others for comprehensive erosion control and stormwater mitigation, what would not necessarily work well with it is the use of polymers, says Spotts. “The polymers would cause the clay part with the fines to quickly clog up the pores, making it turn into a dam rather than into a filter,” he says. “I would use something like this to get out the coarse material for the sands and silts as quickly as possible and then later on use polymers as necessary. Polymers are much more effective on the finer-clay sized particles than they are on the sands and silts.” While not everyone ascertains the effectiveness of the BMP through monitoring influent and effluent, Spotts points out that is exactly what his company does, in keeping with a Georgia requirement to monitor for the quality of water being discharged from a construction site. “It’s part of the NPDES stormwater program,” he adds. “We monitor water coming in and water coming out. We have criteria that say the water going off of a site may not exceed more than 25 NTUs [nephelometric turbidity units] above what the water is coming into the site. If you have an upstream site with 100, your allowable discharge off the site is 125.” For more pristine environ-ments, such as a trout stream, discharge cannot be more than 10 NTUs above background, “so in that case, it would only be 110,” he says. “You can see 125 in the water, and 110 doesn’t look a whole lot better,” he notes. “In terms the ecosystem, there’s a real significant impact. We want to keep our waters clean. Water is the most important resource that the state of Georgia has.” In addition to being a consultant for private contractors, Spotts is also a code enforcement officer for the city of Chamblee, a bedroom community outside Atlanta. “I issue stop-work orders and cita-tions for sites that have discharge of water off the site or have the silt fences down,” he says. “Whatever the BMP WWW.EROSIONCONTROL.COM

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