Comparing Stormwater Control Measure Effluent Quality with Road Runoff Management in Mind

Road runoff has been identified as a source of urban stormwater pollution. Bridges represent a special case, as they often directly discharge through deck drains near or into open water. As such, the runoff is usually not treated with a swale and filter strip, as it would be in the typical highway cross-section; recently, departments of transportation have begun using closed pipe drainage systems to deliver stormwater to a stormwater control measure (SCM) for treatment. This is a costly retrofit both in terms of up-front and long-term maintenance capital. Bridge runoff quality (in terms of nutrients, sediment, and heavy metals) was contrasted against effluent concentrations from six commonly used SCMs. Runoff quality samples from 41 different SCMs were collected and compared with those from 15 different bridges across the three ecoregions of North Carolina (mountains, piedmont, and coastal plain). SCMs examined in this study were permeable friction course (PFC) overlays, wet retention ponds (WP), bioretention cells (BRC), vegetated filter strips (VFS), constructed stormwater wetlands (CSW), and grassed swales (GS). Bridge runoff concentrations were statistically compared with SCM effluent concentrations; all SCMs were unable to produce statistically lower total nitrogen effluent concentrations than those from bridge runoff. For total phosphorus, all SCMs were shown to reduce bridge runoff concentrations, though only PFC, BRC, and WP did so significantly. For total suspended solids (TSS), median effluent concentrations from the SCMs were significantly and substantially lower than those draining from bridges (>15 mg/L in all cases). Similar results were observed for copper, lead, and zinc; BRC, GS, and CSW were able to lower total metals concentrations significantly when compared with bridge runoff. Dissolved metal concentrations appeared difficult to reduce with current SCM technology. These results suggest that for certain pollutants, treatment of bridge runoff may yield improvement. However, the appropriateness of installing SCMs to treat bridge deck runoff must account for increased cost of closed pipe drainage systems beneath bridges and limited space in the right of way and weighed against the relative ease of retrofitting stormwater treatment infrastructure into other transportation corridors.

Language

  • English

Media Info

  • Media Type: Web
  • Features: References;
  • Pagination: pp 115-124
  • Monograph Title: World Environmental and Water Resources Congress 2014: Water without Borders

Subject/Index Terms

Filing Info

  • Accession Number: 01528598
  • Record Type: Publication
  • ISBN: 9780784413548
  • Files: TRIS, ASCE
  • Created Date: May 30 2014 3:01PM