March 15, 2017 03:22

The Last Line of Defense

inlet protection
Reducing sediment runoff at the inlet

In the first song of the broadway smash-hit Hamilton, James Madison describes how a young Alexander Hamilton realizes that opportunity lies just beyond his grasp. “Our man sees his future, drip, dripping down the drain,” says Madison. His description resonates, because going ‘down the drain’ is a universally recognized symbol of a loss that cannot be recovered.

If you’ve written a Stormwater Pollution Prevention Plan (SWPPP) for an urban or suburban property, you can probably relate to that sentiment. Keeping soil at a construction site from going down the drain is exactly what a SWPPP is designed to do, and it is no easy task.

Because once plant life on a property has been removed, the topsoil it kept in place is just waiting to be swept away. At the first drop of rain, or the first gust of wind, soil that isn’t held down will be going places. If the site isn’t rural, then the last stop for any sediment on a property is the nearest storm drain, and it’s up to erosion-control contractors to cut off that avenue of escape.

There are a number of ways in which we can do this, and before we go any further, it’s important to note that an inlet-protection device is ideally not the only line of defense against sediment runoff. Silt fences, erosion-control blankets, filter socks and hydroseeding applications are just a few of the measures that exist to help keep soil in its place on a construction site.

However, it’s a risky proposition to rely on those measures alone to keep soil from migrating. Employees make mistakes, accidents happen, and sometimes a big thunderstorm rolls in with little or no warning and drops three inches of rain overnight. In those cases, you’ll be glad you had a backup option, a last line of defense.

So what do you put in place when the plans just say ‘inlet protection,’ but do not specify a type? Some still choose the simple expediency of surrounding an inlet with rock-filled bags, or hay bales, but that approach is falling out of fashion, according to Ryan Joyce, Certified Erosion, Sediment and StormWater Inspector (CESSWI), and restoration specialist with SWCA Environmental Consultants, Inc., in Amherst, Massachusetts.

“Those low-tech approaches are becoming more and more obsolete, because they’re hard to maintain,” he said. “Usually, you’ll want to have somebody who’ll be able to check on those key drains every day, especially the ones that are off-site, to make sure that they aren’t being over capacitated with material.”

The difficulty of maintenance isn’t the only downside to a lowtech approach. You’ve also got to consider the hidden costs of installation. Let’s say you’re trying to protect six inlets on a site with rock bags. Yes, your materials are inexpensive, but they’re also very heavy, so they’re labor intensive to install. On six inlets, that’s a relatively small difference, but over 60 inlets, the number of employee hours dedicated to laying down rock bags will be significant.

Hay bales are also increasingly under scrutiny from municipalities, for a number of reasons. They are prone to rot, and even when dry, they shed over time, as loose bits of straw get pulled free by the wind. However, municipalities are chiefly concerned with their ability to spread invasive plants. Hay carries seeds of all sorts, so if it wasn’t sourced locally, it might be carrying the seeds of non-native, potentially invasive plant species. That’s the kind of environmental trouble that BMPs are supposed to prevent.

In northern climes with wet, cold weather, a bale can also freeze solid. Frozen hay bales pose a serious hazard to snow plows, drivers and your own employees. They are heavy and solid enough to damage plows and cars, and pose a serious road hazard.

Another quick and easy answer that some contractors choose for inlet protection is to cut a square of geotextile fabric (typically, whatever they use for silt fencing) and slip that under the grate. It makes a certain amount of intuitive sense: silt fences are designed to hold back soil and allow water to pass through, so the fabric should work well on a storm drain.

However, storm drains come under more concentrated flow than most areas of silt fencing, and that changes the equation. The fabric can quickly fill with sediment and become plugged up. Then the next flow will begin to pond above the grate, or tear through and allow everything to fall past. A single sheet of geotextile fabric laid flat under a grate is likely to be an accident waiting to happen, rather than an inlet-protection device.

Thankfully, there are a number of companies offering geotextile products that are designed to go under storm grates. These filter bags, which are considerably more resilient against bursting than a simple, flat piece of fabric, come in both woven and non-woven geotextile fabrics. Woven geotextiles are typically stronger, but with a lower flow rate, where non-wovens are typically a little cheaper, a little more prone to getting plugged up with fine sediment, but have a higher flow rate.

Sediment bags will need periodic cleanouts, like any inlet-protection device. The inspection and maintenance schedule will vary from site to site, but scheduling a check at least once a week and after any heavy rainstorm is a good start. Defining what makes a rainstorm sufficiently ‘heavy’ can be a bit tricky, depending on what the local weather is prone to do, but one common rule of thumb is that any 24-hour period which sees two or more inches of total rainfall is enough to warrant an inspection.

When in doubt, err on the side of caution. It is almost guaranteed to be easier and less expensive to maintain a BMP a little more often, than to clean up sediment from a ponding event, or a total BMP failure. Lifting a filter bag with 20 pounds of sediment inside is a much simpler task than a fully loaded bag that might require an extra employee, or an extra piece of equipment, to clean safely.

Vince Morris, president and CEO of Ertec Environmental Systems in Alameda, California, says that below-grate systems pose inherent safety risks to contractors. “There are lots of injuries associated with lifting grates,” he said. “They’re very heavy, and they can get stuck, so foot, hand and back injuries are a risk. Sometimes, lifting a grate will require equipment. Always, it requires at least two people.”

That last part, about it requiring two people, is why Russ Daveggio, CESSWI, has switched away from bags. He’s the project and estimating manager for Team EES, an Alameda-based erosion-control company. Instead, they use the abovegrate inlet-protection devices that Ertec sells. “The main benefit is that they’re more cost-effective; they’re lower in total cost,” said Daveggio. “For instance, I can send one guy out in one vehicle, and install 30 or 40 of those in one shift. Before, it would take me three or four guys to install half that many devices.”

Daveggio inspects other companies’ inlet-protection measures from time to time. The main problem he encounters when inspecting sites? “Ineffective product being installed at the lowest cost,” he answered. “Somebody will throw a piece of geotextile fabric underneath a grate, or maybe put a couple of rock bags out there, and they think they’re protected. Then they walk away from it and don’t ever look at it again.”

A stringent maintenance schedule can make cheap materials work, but it may be more cost-effective to spend a few extra dollars on more expensive storm-drain protectors that are less likely to fail and are reusable, like coir mats. Coir is a natural fiber made from coconut husks, and is often used in erosion control because it’s strong and long-lasting, but also biodegradable.

Of course, one of the problems with coir mats is that when they get clogged up, they need to be brushed clean. An employee who doesn’t understand how mats work, and just sees a plugged-up drain, will ‘fix it’ by punching holes in the mat. This highlights another facet of using inlet protection BMPs.

“It’s all about education,” said Daveggio. “What we do with our company is to educate our own employees; we explain to them what we’re putting in and why. It leads to better installations and helps reduce maintenance.” Because they know what to look for, and what to expect the BMPs to do, they know when maintenance is needed, when it isn’t, and how to do it.

Even if you put in high-end storm drain protection devices, and follow all the maintenance instructions, in a big storm, there will still be some sediment making its way into the sewers. This is because inletprotection device designers figure that it’s better to catch most, rather than all of the runoff, if you avoid ponding and flooding by doing so. So inlet-protection devices come with overflows planned in, to allow excessive rain to make it past the device with a minimum of filtration during a big rainfall.

As long as you are following your SWPPP and making a good effort at reducing sediment runoff, an inspector for the local jurisdiction should be understanding about this kind of runoff, according to Kevin Anderson, CESSWI, project manager at R&O Construction in Ogden, Utah. “What I’ve found is that if they come out and inspect, and see that you are actively pursuing the stormwater plan, by and large, they leave you alone.”

Putting in the time to do your homework and choose a sensible inlet-protection device will prove that you’re aware of your responsibility to reduce sediment runoff and take it seriously. Then, even if a BMP fails, an inspector will know that it was in spite of your efforts, not because of them. “If a contractor can build a reputation with a city as someone who takes stormwater seriously, that will go a long way,” Anderson said. “If you’ve worked with a municipality before, it will know what you’re up against and what you’ll do.”

In states around the country, the dry spells are getting drier, and the wet spells are getting wetter. This stands to make erosion more severe, and as cities and counties deal with this, they’re likely to crack down on enforcement. When they come to check your site, you can show them that you’re compliant and up to speed on the latest techniques and options for cutting down on runoff.

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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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