Stormwater management system safeguards watershed and cools runoff to protect fish
The new Currwood Logistics Park, like many other developments, added a stormwater detention system that would take care of runoff and meet all local, state and national regulations. But at this warehouse site, not only was water quality important, so was the temperature of discharged water.
Frederick, Seibert and Associates, Inc. (FSA) created an underground system with an 800,000-gallon capacity using large diameter thermoplastic pipe that would hold and cool the water. This would enable the water to flow at a controlled rate into nearby Antietam Creek without raising the water temperature to help protect the creek’s fish. Stocked with Rainbow and Brown Trout, the creek also has smallmouth bass, largemouth bass, catfish, walleye plus other species. A 42-mile-long tributary of the Potomac River located primarily in Washington County, Maryland, the creek was the focal point of the Battle of Antietam during the American Civil War.
“The Currwood site is bordered by the Antietam Creek,” said Trevor M. Frederick, P.E., vice president, FSA. “It's a put-and-take trout stream within Washington County, and the Maryland Department of Environment wanted us to find a way to control the water temperature for the release of the stormwater. An underground pipe system would allow the water to stay cooler than what it would've been in an above-ground system.”
The city’s stormwater management program seeks to not only limit flooding and runoff-related damage but also to improve the quality of the water in the Chesapeake Bay, the Potomac River, and all the tributary streams in Washington County. The city’s stormwater management ordinance establishes the stormwater quality and quantity requirements for both new (“greenfield”) developments, as well as previously constructed sites that are being redeveloped. The city has also developed a program to comply with its National Pollutant Discharge Elimination System (NPDES) permit issued by the U.S. Environmental Protection Agency (EPA).
Currwood Logistics Park stormwater project
Completed in late 2023, the Currwood Logistics Park has two buildings with nearly 2 million square feet of industrial and warehouse space plus offices on a 134-acre site.
The underground stormwater management system has two separate units, both constructed using 60-inch diameter thermoplastic pipes. Detention Unit #1 with a capacity of 46,435 cubic feet used 2,460 feet of the pipe in a 60 x 350 x 7-foot pit, while Detention Unit #2, with a capacity of 61,245 cubic feet, used 3,160 feet in a 60 x 450 x 7-foot pit. A parking area for trucks is on top of the units. The pipe was HP Storm from Advanced Drainage Systems, Inc. (ADS). More than 17,000 feet of HP Storm in additional diameters ranging from 15 to 48 inches were used for connections and to carry runoff. Both systems drain into water quality filters downstream prior to leaving the site.
“We went with the submerged gravel wetland BMP,” Frederick said. “It's the Chapter 5 micro-scale practice within the Maryland Stormwater Manual. The regulations we were meeting were for two and 10-year storm events. Since we were able to discharge directly to the 100-year map floodplain, we did not have to detain up to the 100-year event. This was one of the largest single properties left within the City of Hagerstown limits that was undeveloped,” Frederick said. Frederick continued that there they dealt with a lot of topography when laying out the site and had to make adjustments for the plan to work. He said the site did not allow for as much surface stormwater containment as typical, so the team had to go underground for both quantity and quality control to address the stormwater regulations.
“With the topography that we dealt with on this site, we had upwards of six retaining walls, the largest wall being 22 feet in height,” he said. “This need also reduced the amount of above-ground area we could develop. That's why we had to go underground with these pipe systems. We did as many ponds as we could on the property, but there were a number of restrictive easements, flood plains, forest easements, utility easements, that prohibited us from putting everything above ground. That's why we wanted these underground systems to retain and slowly release the storm water. We had to look at temperature control and how the underground pipe system would allow the water to stay cooler than what it would've been in an above-ground system. The allowable water temp discharging to the Antietam creek (recreational trout water) is 75 degrees.”
Unit One has a 10-year inflow of 30.18 cfs and a 10-year outflow of 6.03 cfs, controlled by a Weir wall within an outlet box with a four-inch low flow orifice. Unit Two has 10-year inflow rate of 40.61 cfs and a 10-year outflow of 9.25 cfs, controlled by a Weir wall in an outlet box with a 5-inch low flow orifice.
“We chose to go with the ADS pipe product because we have used it on previous projects,and we were comfortable with the results we received on those projects,” Frederick said.
