Managing the Storm
Storm water management is an issue that affects everyone. Each day, more land is developed for housing and industry. With each new development, more land is sealed by roads, parking lots and roofs. This sealing of the earth disrupts the natural course of storm water. Rather than soaking into the soil, rainfall flows across impermeable surfaces, picking up oil, trash and other pollutants, then quickly flows into low-lying areas, rivers and lakes.
To control the flooding and pollution issues that are inherent in storm water management, the U.S. EPA and other regulatory agencies have developed regulations that require all or a portion of storm water to be managed on site.
Above-ground detention ponds are a common solution, but these usually require a large amount of land, and sometimes pose safety and aesthetic issues. Often, underground structures are a more convenient and economical solution because water can be temporarily stored underground before being released to a storm sewer or back into the surrounding soil to recharge groundwater sources. Arched chamber or corrugated pipe systems provide underground storage; however, they are limited in their size and shape, and require a large amount of stone for storage.
While all of the above solutions work well in many applications, some sites pose unique challenges for storm water management. These challenges can include high water tables, constraining geological features, or simply a limited amount of available land. When designing a storm water management system for these sites, a unique product is needed to meet regulatory requirements.
A flexible solution
Invisible Structures, Inc., based in Golden, Colo., has developed a variety of storm water management products since its inception in 1982. Among these products is Rainstore3 (RS3), a plastic structure introduced in 1998 that can be used for underground detention, retention or water harvesting. With the structure located underground, the land above is made available for other uses.
“RS3 is very unique as a product. There are competing technologies, but there is nothing really like it on the market,” said Dustin Glist, media and information director for Invisible Structures. “It is a stackable, modular system, so you can stack it like legos.”
Each RS3 unit is made from recycled injection-molded plastic and contains 36 thin-walled cylindrical columns connected by T-shaped beams. A single panel measures 40 by 40 by 4 in. (1 square meter) and weighs 14 lb.
To conform to project requirements, one unit can be used alone, or the units can be stacked for a variety of depths up to 8 ft, 4 in. (25 units). Compression fittings between layers create a rigid structure when the units are stacked, while openings in the bottom of each cylinder allow water to move throughout the assembled columns. The structure can be assembled to any length and width in 40-in. increments to fit almost any site.
“Sometimes, RS3 is the only option to store storm water underground because of its unique ability to be configured at different heights and footprints,” Glist said.
In addition to the product’s design flexibility, it offers one of the highest efficiencies on the market. Brian Francis, vice president of Geoproducts, Inc., a distributor of RS3, said, “The ideal applications for RS3 are small sites that need a lot of detention/retention. The product stores more water per square foot than any competitor.”
With plastic making up only 6% of the system’s volume, one RS3 unit can hold up to 25 gal of water. According to Glist, “The product itself is 94% void space, so RS3 works like a skeletal system, holding up everything around it and creating this open chamber for water to run into.”
Grand Rapids project
In early 2003, the city of Grand Rapids, Mich., was planning to relocate its Water Systems Department staff to a new facility to accommodate the expansion of a local company at the previous location. The new Grand Rapids Water/Environmental Services Facility was to be a 79,600-sq-ft building with a related parking area, loading dock and material storage area located on a 5-acre lot.
Elaine Westhouse, who at the time of the project was president/owner of WB Engineering, was the design engineer responsible for the site civil engineering design, drawings and specification. According to Westhouse, now senior project manager for Driesenga & Associates, Inc., “One acre of the parcel is part of a surface water drainage easement; therefore, it cannot be covered with a building or used for a storm water detention facility. The proposed building and pavement area equaled approximately 3 acres, which left 1 acre for green space and storm water detention.”
Although these constraints allowed only a small area to be used for storm water management, the city of Grand Rapids storm water management ordinance required detention to store at least a 25-year storm event with a controlled discharge of 0.15 cfs/acre.
“The irregular shape of the parcel and size of building did not provide available space for a typical detention pond,” Westhouse said. “Therefore, alternative solutions were needed.”
Westhouse examined various options, including porous pavers, rain gardens, leaching basins, roof-top storm water storage, underground storm water storage in pipe, arched chambers and RS3.
The final design incorporated porous pavers, leaching basins and trenches, a rain garden and underground storm water storage. RS3 would be used under the area that would become the main parking lot for the facility.
“The RS3 product was chosen because the required storage volume could be contained in a smaller footprint than other products utilizing a higher vertical dimension,” Westhouse said. “RS3 provides greater volume capacity per square foot than pipe or arched chambers due to its geometry, and it does not require the drainage aggregate bedding that other systems require.”
One challenge the design team encountered was that the RS3 system needed water entering the structure to be filtered. Excessive sediment could clog the geotextile filter fabric surrounding the structure, limiting the infiltration into the surrounding soil. Westhouse solved this problem by using two methods: incorporating a sediment/debris/oil filtration structure and allowing the storm water to drain across a grass swale to filter out sediments and oils.
According to the U.S. Green Building Council (USGBC), West Michigan Chapter, when the Water/Environmental Services Facility project was taken to the Grand Rapids Planning Commission for site plan review, members of the commission suggested the project staff pursue Leadership in Energy and Environmental Design (LEED) certification. The LEED Green Building Rating System is a voluntary, consensus-based national standard for developing high-performance, sustainable buildings.
“The site and storm water management design was completed before the owner decided to get LEED certification,” Westhouse said. “However, no major changes were required in the site design in order to get the certification.”
Geoproducts’ Francis worked with Westhouse through the conceptual, design and construction phases, co-coordinated product delivery schedules and supervised construction. Before installation could begin, the product needed to be delivered to the site. That, however, didn’t go exactly as planned.
“We sent the first few truckloads of product out for delivery by rail, as this shipping method usually takes one week to deliver,” Francis said. “The plan was to ship the remaining product over the road so all 11 trucks would arrive within a three-day period. The rail shipping method also is about two-thirds the cost of road shipping. A few of the rail trucks, however, got hung up in the Chicago terminal and delayed our schedule slightly.”
Despite the delay, 5,634 RS3 units, stacked nine units high, were installed over a four-day period in June 2004.
“We had planned on unloading three or four trucks per day; however, the installation was so simple we could have installed five or six trucks per day,” Francis said.
According to Invisible Structures’ Glist, the RS3 units can be moved by hand or powered lift, depending on the structure height.
Essentially, system installation includes:
- Excavating the site;
- Placing a layer of geogrid (a plastic matrix that stabilizes and adds support) on the excavation floor;
- Placing a layer of geotextile filter fabric (fabric that keeps out sediment and other debris);
- Positioning the RS3 units;
- Placing another layer of geogrid on top of the RS3 units;
- Encasing the entire structure in geotextile filter fabric;
- Placing another layer of geogrid on top;
- Backfilling; and
- Leveling and surfacing the site with gravel, asphalt, concrete, landscaping, etc.
Maintenance ports can be added by removing a column from a RS3 unit during installation. When complete, the site will meet H-20 loading requirements and support any street-legal vehicle.
When the Grand Rapids Water/Environmental Services Facility project was completed, its environmentally friendly design and construction earned the facility the LEED certification and allowed Grand Rapids to become Michigan’s first city to receive this certification for one of its municipal buildings. Today, the Grand Rapids area is home to 11% of the LEED-certified buildings in the country.
According to Fishbeck, Thompson, Carr & Huber, Inc. (FTC&H), the company responsible for assisting the city and its design team in pursuing LEED certification, the new facility features:
- Energy savings through efficient building design;
- Employee access to public transportation;
- Employee bike storage and shower facilities;
- Efficient storm water management systems;
- Reduced light pollution;
- Heating, ventilation and air-conditioning systems;
- Recycling systems for office waste;
- Use of building materials composed of recycled content including carpet, steel, ceiling tiles and insulation;
- Sustainable design educational materials for visitors; and
- Use of locally and regionally obtained materials.
USGBC President, CEO and Founding Chairman Rick Fedrizzi presented the LEED certification to the city on Jan. 27, 2005. The presentation took place during a meeting of the Michigan Local Government Management Association, a gathering of city managers from across the state.
“This is an important milestone for Grand Rapids and for Michigan,” said Keith Winn of FTC&H. “Grand Rapids has established a benchmark for other Michigan cities committed to environmentally responsible building. We now join an exclusive but growing group of progressive communities nationwide that are adopting successful green building programs.”
Grand Rapids continued its implementation of sustainable building when in January 2006, the Grand Rapids City Commission passed a resolution establishing the Sustainability Policy for City Buildings, which sets standards for constructing, renovating and managing city-owned buildings. The new policy requires that all city building construction projects examine the LEED principles during the project design phase and conduct a thorough cost-benefit analysis to determine what principles should be used in the final project design. In addition, the policy stipulates that all new building construction and renovation projects over 10,000 sq ft and $1 million in costs are required to obtain LEED certification.
A growing industry
As in Grand Rapids, cities across the U.S. are incorporating more efficient storm water management systems, as well as other environmentally friendly building techniques. There are currently nine RS3 systems installed in Michigan, and use of the product is increasing in other areas.
“Sales are building,” Glist said. “That really is due to all factors, such as our representatives recommending the product and storm water regulations increasing. It’s a must-do. The whole industry is growing. We’re pushing to grow, and we’re being pulled to grow at the same time.”