- There’s no denying our natural environment is paying the price for the roads that are replacing wide open spaces. The impervious surfaces covering our cities and neighborhoods are increasing pollutant runoff to nearby streams and lakes.
But what if transportation networks harbor hidden stormwater-management opportunities? Specifically, can interchanges be used to address post-construction permit requirements? Could infield open space be used for something other than wasting existing pavement during reconstruction? Can this otherwise fallow land be repurposed to implement best management practices (BMPs)?
Keeping with the mantra of public works departments nationwide — fix what we have first — my team at Gresham, Smith and Partners presented the Ohio DOT (ODOT) with considerations for adapting state interchanges for stormwater management purposes.
Combined with successful interchange BMP projects in California, Florida, and North Carolina, our research can help engineers elsewhere rethink the use of similar public lands.
Next Page: Ohio DOT’s two-permit puzzle
Ohio DOT’s two-permit puzzle
Federal law requires storm sewer system owners and operators to develop and implement stormwater management plans. These plans must outline development, implementation, operation, and maintenance of BMPs that will, to an extent, practically address water quality and, in some cases, water quantity issues. They must also address five minimum control measures, one of which is post-construction runoff.
Ohio has its own environmental protection agency that acts as an extension of EPA at the state level. Ohio EPA is responsible for ensuring that entities regulated under the National Pollutant Discharge Elimination System (NDPES) Municipal Separate Storm Sewer Systems (MS4s) permit and Construction General Permit (CGP) comply with permit requirements.
In addition to addressing erosion and sediment control and post-construction water quality on projects that disturb more than 1 acre, the latter also encourages BMP implementation to address total maximum daily load recommendations for water quality problems associated with MS4 discharges.
ODOT owns and operates storm sewer systems and manages projects that disturb more than an acre. Thus, the agency has permit compliance liability associated with both permits, a common dilemma for DOTs nationwide.
Next Page: Research supports interchange BMP feasibility
Research supports interchange BMP feasibility
Engineers, planners, landscape architects, and scientists working on the Big Creek Watershed Plan determined that highways contain open and underused land within their right-of-way where storage can be implemented by diverting runoff into these areas. Most common treatment options for retrofits are constructed wetlands or linear bioretention and swales along wider medians and rights-of-way. The team learned that:
These options would increase the urban watershed’s stormwater capacity. Highway retrofits are ideal because their runoff pollutant concentration is high.
- Land costs are relatively low since the retrofit is located in a public right of way.
Retrofitting interchange infields to meet stormwater requirements
Retrofitting interchange infields to meet stormwater permit requirements.
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Almost 13,000 of the 21,000 acres of interchange area in Ohio can be repurposed to manage stormwater. This is a significant amount, especially considering increasing land prices. These numbers also emphasize the importance of taking advantage of what the Ohio Department of Transportation already owns.
