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within a large culvert, about 3 feet in diameter, which drains about 1,000 feet of highway.” Heath explains that measuring con-ductivity is an indirect method of ob-taining sodium chloride levels, which is one of the primary goals of the EPA study. “Conductivity is the measure-ment of the ability of water to conduct electricity. The more ions you have in the water, such as salt or other ions, the lower the resistance and the higher the conductivity of the water. It’s a bulk in-dication of pollution. Of course, salt is a very strong set of ions, with sodium and chloride ions, so you’ll get pronounced peaks of salty water that these devices pick up during thawing events after salt has been applied to pavement.” “What is happening in general over the last several years is we keep add-ing more salt to the roads to keep them safe in the winter time, and the salt level keeps going up in our groundwa-ter,” says Tom Faber, project coordina-tor with EPA Region 1. “It’s getting into our streams. Not only is it hurtful for the aquatic life, but when it gets into our drinking water supply, it’s a health issue as well for us.” Indeed, according to a paper by Heath and fellow hydrogeologist Marcel Belaval, chloride levels at the Brown’s Crossing Wellﬁ eld are currently in ex-cess of 20 times the level measured prior to 1960, when I-93 was opened. Faber explains that EPA has set up the YSI telemetry station using YSI 600OMS probes, and the YSI EcoNet service. Heath also utilizes a number of Onset HOBO data loggers to measure temperature and conductance. “These YSI samplers have probes,” says Faber. “There’s a temperature and conductivity probe out and we can go to the website and pull up the data. It’s logging data every 15 minutes. If there’s a storm event, and we want to see what the loading to the stream is, we can pull that up. If we need to go out and take conﬁ rmation samples, which help us correlate the chloride levels with our probe reading, we can go out and measure the high reading, depending on how the salt is melting and how it is applied.” Heath explains that the HOBO data loggers are much smaller than the YSI units, about 1 inch in diameter and 6 inches long. “They are also calibrated differently than the YSI units,” he says. “With the YSI units, you can actually put in calibration corrections, while im-mersing the datasonde into a standard. With the HOBOs, they are factory cali-brated, but you can make adjustments on the data after you download them, based on measurements taken with ﬁ eld meters, both before and after. So those are the major differences.” He appreciates the convenience of the system. “I can sit at my home computer or in the ofﬁ ce and just dial up the information to see what’s going on. The advantage to this is that I’ll be able to monitor peaks of stormwater runoff during freezing rain or thawing events.” When such events occur, Heath ex-plains, “That’s going to free up all the residual salt that’s lying out there on pavements and in snow piles. That’s all June 2012 www.stormh2o.com 11

Stormwater June 2012 : Page 11

Imbrium