Stormwater June 2012 : Page 16
we can change thresholds in real time, we can move sample arms and respond if there’s something that needs to be done immediately.” Once the samples are obtained via the DISA unit, a couple of steps are necessary to obtain particle size dis-tribution readings. “Once we have our water sample in our container, we’ll take it back to our laboratory, to pro-cess it for analytical testing,” explains Selbig. “That can be done in a num-ber of different ways, but typically we’ll use a churn splitter. Say a storm comes through and we’ve sampled it and have about 20 liters of water that we cap-tured. The analytical lab that we use only wants perhaps a liter of water. So we need to pare that 20 down to one. We’ll use a churn splitter, which is basi-cally a large bucket that you pour all your water into, and split off whatever you need. “The DISA is a means to collect the water. It doesn’t store the water itself. It’s simply a metal arm that moves up and down, so that when there’s a pump, it can draw the water from the right spot. Then that pump pulls the water into a regular Isco sampler, which has containers to hold it. So we’ll collect the water after a storm and bring it back to our lab and process it.” At that point, the laboratory uses a Laser In-Situ Scattering and Transmis-sometry (LISST) particle size analyzer from Sequoia Scientifi c. “There are a number of LISST devices,” says Selbig. “I believe that all but two of them are set for stream settings. They’re fairly large, and you just put them in the stream, and they’ll read particle size distribution that way.” For fi eld testing, a LISST-Portable device is currently being used. The same type of device was also used dur-ing lab testing to collect samples from a storm sewer that had been set up in the laboratory. “It was really handy, and we’re very pleased with that product,” says Selbig. “[Sequoia] has been very helpful whenever we would have some complications or technical problems.” The LISST-Portable can be trans-Offering A Proven Solution to Stormwater Runoff for Over 20 Years ECO-OPTILOC ® ECO-PRIORA ® ECO-STONE ® Sustainable, Durable, Beautiful and Economical. UNI ECO-STONE ® FAMILY OF PERMEABLE INTERLOCKING CONCRETE PAVERS • Manages runoff through on-site infiltration -accommodates a variety of stormwater management objectives • Can save money by combining parking AND detention in one cost-effective system • Allows better land-use planning, especially in high-density areas and reduces impacts on combined storm/sewer systems for cost savings • Mitigates runoff volumes and peak flows, reduces pollutants, addresses water quality/quantity • EPA-recommended BMP and qualifies for LEED ® and other green building accreditation • Superior durability under traffic loading -withstands turning movements without surface degredation or raveling, can be installed in any season, and can be used immediately • Call 1-800-872-1864 or visit www.uni-groupusa.org for our free Lockpave Pro software ECOLOC ® ported easily. “It’s a very small unit. It allows us to take it from one site to the next and get nearly instantaneous results.” Selbig explains the practical effects of having accurate particle size distribution readings, free from stratifi cation bias. “This new distribution can be inserted into the model to help the engineers who are designing a wet detention pond, for example. That’s the type of informa-tion that’s very important to them. It ul-timately will determine if a pond is 200 square feet or half an acre in size. That, of course, means money. The more land you need, the more expensive it’s going to be to build the thing. “What we’re hoping is that the data coming from our research will help both engineers and regulators to design stormwater treatment facilities that are not unnecessarily costly.” Another implication of the re-search, he says, involves the Wiscon-sin Department of Natural Resources requirements for new development, which mandate 40% total suspend-ed solids (TSS) removal by 2013. “It may be down to 20% right now,” he says. “Let’s say, for example, that the city of Madison has to put in certain practices, such as street sweeping, de-tention ponds, biofi ltration swales, and grass swales. Each one of these gets prescribed a benefi t of a certain solids reduction. They have to prove to the state that they are going to reduce their overall total suspended solids by 20%. What we’re realizing now is that the data that has been collected to charac-terize how much is actually coming off of these surfaces—streets, parking lots and so on—is wrong. “Our regulator, the DNR, may re-alize that 20% may have to go up to 50%. Who knows where that’s going to go? That’s down the road a bit. But these are the kind of conversations we’ve been having.” Steve Goldberg writes on issues related to erosion control and the environment. UNI-GROUP U.S.A. MANUFACTURING PERMEABLE PAVERS SINCE 1989 Scan here to share this article or read later. Get the app at http://gettag.mobi 16 June 2012 www.stormh2o.com