Hunter Industries was the general contractor for the recently completed I-35 improvements to the Texas Department of Transportation (TXDOT) on-system interstate reconstruction through New Braunfels, Texas.
Noteworthy to the project were the environmental controls, particularly with respect to storm drainage and water quality.
Construction sites of all sizes are legally required to take steps to prevent stormwater pollution. This has given rise to the field of stormwater management, which has evolved rapidly in recent years.
Construction sites can be major polluters of stormwater. Vehicle leaks from construction equipment can run off into storm drains, as can various solvents, emulsifiers, and concrete residue. However, the single largest pollutant of storm drains from construction sites is dirt.
In the case of the I-35 project, the contractor installed structural stormwater controls, as paid for in the contract documents. Installation along environmentally-sensitive areas, such as “No-Name Creek,” the mundane moniker for a roadway crossing of the project that is habitat to aquatic flora and fauna associated with wetlands.
The contractor used backhoes with buckets suitable for the topography of the creek crossings, featuring buckets that are of less-than-standard width for typical heavy-highway construction projects. One such bucket is the 24 in. (60.9 cm) heavy-duty bucket for the John Deere 310 backhoe, equipped with teeth that can scarify a carefully-isolated creek section, without disrupting more of the native vegetation than necessary.
Such “Best Management Practices” (BMPs), are structural. These are on-the-ground devices that are designed to keep silt away from storm drains and natural streams. Some examples of structural BMPs include silt fence, rock construction entrances, hydromulch, and rock check dams. Such dams are composed of individual pieces of rock, placed perpendicular to the flow of surface water along a stream or roadside bar ditch.
Another commonly used BMP is a rock construction entrance. Similar to check dams, these construction entrances also use rock to filter out dirt from construction activities. Construction traffic drives over the rocks when departing from the site. The rock scrapes dirt from the tires of the vehicle, thus catching dirt before it is tracked onto the street.
Steve Rothwell, of Manhattan Construction, stressed that construction entrances require periodic maintenance. “A front end loader needs to turn the rocks and the dirt will fall to the bottom. The contractor will have to apply some clean rock to the entrance from time to time as well.”
A third measure of protection against stormwater pollution is instant vegetation via a hydromulch machine. Hydromulch is an organic applicant that covers non-vegetated areas, thus preventing dirt from washing out to a storm drain or nearby stream.
Hydromulch can be applied by the Finn Corporation T-90/120 Series II Hydroseeder. This machine has a discharge distance of up to 180 ft. (55 m), and a liquid capacity of 940 gal. (3558L). Its diesel engine produces 33.5 hp (25 kW), has four cylinders, and is water-cooled.
As the emerging field of stormwater management continues to evolve, both contractors and municipalities alike will be working together in the day-to-day precautions that prevent stormwater pollution, using as examples successful projects such as I-35 in New Braunfels.
(David H. Recht owns an Irving-based civil engineering and construction firm.) CEG