Bridge Stormwater Runoff Analysis and Treatment Options (2014) / Chapter Skim
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Pages 9-18
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From page 9... ...
9 State of the Practice This chapter describes the state of the practice for bridge deck runoff based on a literature review and DOT survey. It gives a general overview on how and when DOTs are conveying and treating runoff from bridge decks, and discusses the mechanisms for pollution discharge from bridge decks.
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From page 10... ...
10 • Pipe joints must have sufficient flexibility to move consistent with the allowable expansion of the bridge joint; • Pipe systems may not be compatible with the aesthetics of the bridge; • The additional weight of the pipe system may require a larger bridge cross section; • Deck drain or scupper maintenance is hazardous and may interrupt traffic flow due to limited shoulder area to work; and • Pipe materials can corrode and leak. By contrast, conventional roadway cross sections generally have a relatively wide shoulder for safety and conveyance of flow.
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From page 11... ...
11 highway. In one case, MDSHA raised the lip height of scuppers to avoid direct discharge of the first flush.
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12 Reduced salt usage is one of the best source control actions a DOT can take in areas where receiving water hardness is problematic and salt is applied for deicing. For example, Caltrans implemented a reduced salt-use policy that requires their districts to develop specific route-by-route plans (NCHRP 2004)
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From page 13... ...
13 Other DOTs are contemplating how vehicle sources could be better controlled, outside of reducing vehicle spray through greater use of PFC. For example, NCDOT is interested in determining if rumble strips prior to the bridge deck could shake off pollutants from the undercarriage of vehicles, to minimize the pollutants that are being carried onto bridges and being sprayed off splash, during precipitation events or are deposited during dry weather.
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14 • Phase I permit coverage as a co-permittee with other Phase I entities, only in Phase I coverage areas. • Phase II individual permit coverage for all DOT facilities.
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15 is protected from irresponsible and unregulated discharges of dredged or fill material that could permanently alter or destroy these valuable resources. The USACE Regulatory Program administers and enforces Section 10 of the Rivers and Harbors Act of 1899 and Section 404 of the CWA.
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From page 16... ...
16 compelling evidence that bridge deck runoff in North Carolina is higher in pollutants typically associated with stormwater runoff as compared to runoff from other roadways." Of all the characteristics investigated by URS, the urban versus rural designation appears to have the most influence on pollutant loading. All solids parameters studied were higher in urban areas, as well as most total recoverable metals and dissolved copper and lead.
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From page 17... ...
17 affected the biota or other receiving water uses. In addition, the study did not consider whether observed increases could be attributed at least partially to dry deposition.
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From page 18... ...
18 2.3.3 Stormwater Quantity Impacts Bridge deck runoff quantity can be characterized by runoff volume and peak flow rate, both of which are considerations when evaluating the potential hydrologic effect of bridge deck runoff on receiving streams. Hydromodification should not be an issue from bridge decks alone, since the runoff coefficient is identical to rainfall on the receiving water.
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