We live in a world of acronyms and equations. A world where letters are used for numbers and WOW upside-down is good old MOM. For instance, if the QSP or PE recommends HERO, he may inform the LRP. And that’s just the tip of the iceberg in the world of engineering-whether civil or environmental. It often sounds like teenagers’ secret language.
One crucial acronym for many in the industry is USLE, the universal soil-loss equation-the result of decades of research and data, some of which dates back to the 1920s. Soil specialists have used USLE to establish predicted long-term soil losses. It does not, however, consider losses from gully, wind, or tillage erosion. It predicts patterns of soil loss from sheet or rill erosion on a given slope, but USLE factors can very widely with weather conditions. Later research led to a revised version, RUSLE. And finally, with the need to handle more complex parameters, that equation was further enhanced to become RUSLE2.
The equation as it was developed, says that the soil loss prediction, expressed in metric tons per hectare per year includes:
R = rainfall or runoff
K = soil erodibility
L = slope length
S = slope gradient or steepness
C = cover and vegetation management
P = erosion control practices
We may not be able to alter environmental elements like the amount of rainfall a site gets, or its soil structure, but in areas where soil is exposed, we can minimize runoff and the subsequent erosion and sedimentation that follow. Well thought out and precisely placed BMPs can make the difference between soil runoff that can be swept up and runoff that results in deeply carved gullies.
Going to the Neighborhood Coffee Shop
When Todd Hudson, project manager and estimator for SWIMS (Stormwater Inspection and Maintenance Services Inc.) began work on a Wal-Mart site in Rohnert Park, CA, the first thing he looked at was the catch basins.
“There was an existing building being turned into a Wal-Mart neighborhood market,” he explains. “The first thing we did was to install catch basin protection. But at this site they were small, so they had to be modified. We didn’t even need to put gravel bags down.”
The Catch Basin Protectors used were a SWIMS product. For perimeter control, Hudson knew he wanted the Heavyweight DuraWattle from WTB Inc.
At the site, Wal-Mart was heavily invested in the neighborhood and public relations. The back side of the large industrial site is used as a community short cut, so installing most sediment control products would have resulted in some costly maintenance or replacements. Hudson chose the DuraWattles, because they’re easy to install on the hard asphalt surface and because he did not have to worry about interrupting the flow of traffic. It was an important factor on this job site.
“During installation, when the construction fence wasn’t up yet, cars came flying through there,” he laughs. “But they can run right over that DuraWattle, and it just springs right back up. Although the traffic slowed a bit after the signs went up and construction activity got under way, people still used the area as a thoroughfare, especially early in the morning. The neighborhood has a Starbucks back there and a muffin shop. So traffic still drives straight on through.”
The Heavyweight DuraWattle was designed as a flexible barrier for use in dewatering and as a sediment barrier. Richard Quinley, owner of WTB Inc., notes that ASTMD 7351 tests show the wattle has 96.6% sediment retention and 58% turbidity reduction. It is also reusable over multiple job sites.
“This was particularly good for this project, which had that older asphalt parking lot,” says Hudson. “DuraWattle didn’t have to be glued in place. It’s easy to install with 1- by 4-inch wood planks and concrete anchoring screws every 4 feet. And it’s like a big foam fiber roll; it bounces right back, as opposed to straw, which squishes down and deteriorates.” To date, none of the wattles installed at the site have needed to be replaced.
When a River Runs Through It
The main reason to restrict sediment runoff at construction sites is to protect our rivers, lakes, and other waterways. But what happens when you have a river running through the site itself? That’s what James Harris, project engineer with Dement Construction, found on a recent Tennessee Department of Transportation (TDOT) project in Waynesboro, TN.
“We are widening US 64/SR 15 from a two-lane highway,” Harris says. “There is a stream-Stream 8-that is located in the roadside ditch of the existing road. The stream flowed west and went into a pipe with an additional stream-Stream 9-and flowed under the existing road.
“I really looked at it and asked myself, “˜What’s keeping the debris from the old part from washing into the new part of that stream?’ In the state of Tennessee, you can’t get as much as a stone in a stream, because its considered to be a sediment release.”
James explained the new site design. “The new construction has a box culvert going under all four lanes of the new road. The design has Stream 8 going into a 24-inch perforated pipe and connecting to a new box culvert. After installing the perforated pipe, we were left trying to figure out a permanent solution to keep any gravel bits from getting into the pipe end after we backfilled it with stone.”
That was when Harris called on one of his suppliers, Kirk England of England Erosion, Seed & Supply of Nashville, TN. England was enthusiastic about a new product that has just come out and said it would be ideal to solve the problem: the Silt-Saver Pipe Stopper developed by Roger Singleton, president of Silt-Saver Inc. in Conyers, GA. England brought the Pipe Stopper to the site, and after some measuring and discussion of objectives, James chose the open mesh design, designed to allow water to pass through easily but also to keep larger particles from entering the stream.
“The other slip-cover had a filter cloth on the bottom half to filter any sediment from entering,” Harris describes. “After we installed the perforated pipe, the Pipe Stopper just shoved right in the end of the pipe with a really snug fit.”
From what began as a rather puzzling TDOT construction project, James says he has become a rather enthusiastic user of the Pipe Stopper. “If we had used plywood, it would have rotted out at some point. If we had placed a large rock or boulder of some kind at the end of the pipe, it would have either restricted the flow or had voids to allow smaller stones to enter the stream. After using this product one time, it has made me a huge fan. I am looking to get more to have on hand in the warehouse for jobs in the future.”
The Pipe Stopper is a sediment control device designed for horizontal pipe applications. It’s specifically designed to prevent or reduce the movement of sediment into stormwater pipes during construction, according to Singleton. It has an HDPE reusable frame with “friction fingers” for attachments. Providing a snug fit, it is easily snapped in and out of a pipe opening, and the design allows it to stay in place during inlet construction, holding back sediment while allowing stormwater to pass through the filter, which was exactly what James was looking for. The filter cover, much like a shower cap, fits over the HDPE frame and helps reduce costs that are associated with pipe cleanouts.
The Legacy Act and the Grand Calumet River
A project under way on the Grand Calumet River is being partially financed with funds from the Great Lakes Legacy Act. The majority of the Grand Calumet River drains into Lake Michigan, with approximately a billion gallons a day making its way from the east end of Gary, IN. From there, it courses some 13 miles past the industrialized cities of Gary, East Chicago, and Hammond. Just south of downtown Chicago is the portion of the river referred to as the AOC, or area of concern. That’s because much of the river’s flow actually begins as municipal and industrial effluent, cooling and process water, and urban stormwater runoff. And although the discharges have lessened, contaminants still impair the AOC.
Efforts along the river include a 1.8-mile length to be restored between Indianapolis Boulevard and Hohman Avenue. Because most of the pollutants are tied up in the sediment that lies at the bottom of the Grand Calumet River, massive dredging operations are taking place. There are some 5 million to 10 million cubic yards of sediment contaminated with PCBs, PAHs, and heavy metals like mercury and lead, referred to as “legacy pollutants.”
“Because of the size of the site, there are multiple BMPs being used,” says Joe Moore, vice president with Moore & Moore Erosion Control & Siltworm in Crown Point, IN. “Most of our involvement was at the site in Gary, but we have our product at multiple locations. Our company supplied and installed Siltworm as a perimeter control at the very beginning of construction.”
Moore & Moore Erosion Control manufactures Siltworm, a very large perimeter control device similar to a long, absorbent snake. Although it looks like it can literally surround several blocks, Moore explains that 90% of the company’s orders are for 8-foot sections that can be installed at a site with about a 6-inch overlap connecting them. The Siltworm is 9 inches in diameter, and each section weighs approximately 80 pounds when saturated. Moore points out that the segments are filled at the manufacturing plant, to achieve consistent quality.
In 1991, the Citizen’s Advisory for the Remediation of the Environment Committee (CARE) began working in an active role with the Department of Environmental Management (DEM) to help implement the Remedial Action Plan (RAP) and make future updates in the AOC. (That should provide anyone with his or her daily dose of acronyms.) It is estimated that 350,000 cubic yards of sediment will be dredged and capped. As one section is dredged and completed, another section will be dredged until the area is restored. In 2016, once dredging is complete, wetlands are slated to be restored and planted with native plants.
“Siltworm is there for the duration of the project,” Moore says. “With its very low maintenance, availability to be placed in a wetland, and ability to separate contaminants from stormwater, it was a perfect fit. As a manufacturer and supplier of Siltworm, it was a great place to showcase our technology, which-being less than 10 years old-is often not known as an option to engineers who do design work. Our real work is educating engineers and municipalities.”
Siltworm is filled with a proprietary blend of bark-free, kiln-dried hardwood mulch. The filler can act as compost. Because the mulch filler is kiln-dried, it acts as a sponge when it gets wet, providing filtration.
As of last year, the Legacy Act project had removed 580,000 cubic yards of sediment in the second dredging on the West Branch of the Grand Calumet River. Cleanup efforts in the Roxana Marsh Branch of the river were completed in 2011 at a cost of $31.1 million, with 50,000 cubic yards of sediment dredged. Fish and other aquatic species have improved, and restrictions on drinking water were lifted after US Steel completed numerous projects that included removal of 800,000 cubic yards of sediment, thereby reducing harmful contaminants in the Grand Calumet River.
Twelve Lanes Across the Bridge
Todd Felts, distributor and project manager with England Erosion, Seed & Supply in Nashville, works on many TDOT highway and bridge construction projects. He has been trying a new product, Staged Release Silt Fence (SRSF), manufactured by Silt-Saver.
“Roger [Singleton] came up with the first geotextile designed specifically for vertical placement to control silt and sediment using different sieve-sized geotextiles all made up into one roll,” Felts explains. “It holds the solids to be retained while allowing for the release of stormwater runoff. We have this new SRSF on three different TDOT projects in Tennessee right now.”
One Bedford County TDOT project calls for construction of a concrete I-beam bridge. This was a project, Todd says, where the SRSF especially made difference.
“All silt fence is placed to retain sediment, but what is unique about this product is that, as the amount of water or depth of the runoff increases, the speed of water passing through the fence increases. And this decreases the likelihood of the system being knocked down from the pressure of the water against it or failing resulting in a sediment release.”
All three of the TDOT highway projects where the SRSF are installed are located in middle Tennessee counties. In addition to the Bedford County project, Felts and Christopher Karper, CPESC, a senior engineer with Lochner Engineering, installed the SRSF on sites located in Montgomery and Williamson Counties as well. And in an area where a good rainstorm can come up at any time, it’s good to know the fence has been installed and is ready.
The Williamson County site, which Karper oversees, consists of widening Highway I-65 to help relieve high traffic congestion and improve public safety. In addition to other construction, a bridge over I-65 that will be widened from two lanes to 10 12-foot lanes. The work will be completed in stages to accommodate the traffic flows. An additional two bridges will be constructed, also in stages. Highway lanes will provide access to a new subdivision, and new power poles and water and sewer lines will be installed. Comcast and AT&T fiber optics will also be relocated.
“I assist with scheduling inspection assignments with the contractors’ activities project wide,” explains Karper. “We have used a combination of rock check dams, enhanced rock check dams, sand bags, sediment filter bags, Type A catch basins, geotextile, temporary sediment tubes, and temporary mulch, bales, silt fence, and other silt fence with backing.”
The SRSF has been installed, and to evaluate its performance Karper says he’s just waiting for a “good rain event” to see how it stands up to pressure. He adds that on
a site this large, erosion and sediment control is a daily issue. “We started with 110 outfalls, and I have added an additional four or so. You have to know how the stormwater runoff affects each outfall and adjust your erosion control measures accordingly. Also, as the project is constructed, runoff is affected and additional adjustments are needed in many areas.”
Silt-Saver president and owner Roger Singleton says these types of variables are what the SRSF was designed to accommodate. He explains that the SRSF is designed to release excessive amounts of stormwater before the point of being overtopped. The fence includes belts woven within the fabric, between each individual flow stage, for attachment and to provide additional linear strength. The belts provide the structural integrity to support the linear pressure of the stormwater without the need for wire. This reduces undermining or total system knockdown due to the hydrostatic pressure created by impoundment.
On large highway projects like these, Felts points out, several companies are working onsite all at once, in addition to the highway traffic. On congested sites like this, the Silt-Saver product really shines-literally. “Bright green is the signature color of Silt-Saver, and each band is that bright green, as well as the top section of geotextile. So you get the added benefit of delineation,” he explains. “Silt fences are run over all the time by machinery because it is sometimes hard to see or gets lost from the operator’s position. This product accomplishes both purposes on the construction site, without duplicating resources, material, and man hours.“In my book, this helps to decrease the cost of overall construction and shows the public that our industry is responding to the real concerns about the rising costs of environmentally conscious construction practices.”