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Bridge Deck Run Off Assessment. Problem Background. Existing and pending state and federal regulations require significant reductions in pollution from stormwater runoff from bridge decks. Problem.

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Presentation Transcript
problem background
Problem Background
  • Existing and pending state and federal regulations require significant reductions in pollution from stormwater runoff from bridge decks.
  • In Alaska, are bridge deck runoff discharges are regulated – are there state or federal criteria govern the discharge?
  • Do these discharges add significant contamination to the water body, such that the water quality is degraded?
  • what storm water management practices should the AKDOT&PF incorporate into designs for new bridges or bridge replacement and retrofit projects?
The overall objective of this study is to help AKDOT&PF bridge designers select the best method of stormwater mitigation.
  • Outline legal and regulatory framework
  • Outline BMP for Highways
  • Outline BMP for Bridges
  • BMP for Cold Weather
  • BMP for Cold Weather Bridges?
why bmp
  • Contamination from roadways to waterbodies.
discuss law and regulations
[discuss law and regulations]
  • Why DOT needs to do
  • What?
highway bmp general
  • National Menu of Stormwater Best Management Practices
    • Public Education
    • Public Involvement
    • Illicit Discharge Detection & Elimination
    • Construction
    • Post-construction
    • Pollution Prevention/Good Housekeeping
highway runoff bmp
Highway Runoff BMP
  • Non-Structural BMPs
  • Institution
  • Structural
non structural bmps highways
Non-Structural BMPs (Highways)
  • Pollution Prevention
    • Housekeeping
    • Streetsweeping
    • Litter Control
    • Chemical Management
      • Deicing
    • Spill Prevention and Clean up.
Runoff volume Minimization
    • Grass drainage channel
    • Soadaway pit/drywell
    • Stormwater Planter
institutional bmps
Institutional BMPs
  • Pollutant Trading
  • Mitigation Banking
structural bmp
Structural BMP
  • Treatment
    • Bioretention
    • Ponds
    • Extended Detentino Basin
    • Constructed Wetland
    • Stormwater wetland
structural bmp1
Structural BMP
  • Infiltation Practices
    • Infilatraion Basin
    • Infiltration Trench
  • Filtration Pracitces
    • Media Filter
    • Sand and organic filters
  • Vegitative Practices
    • Grass Swales
    • Vegitated Buffer Strip
structural bmp2
Structural BMP
  • Runoff Pretreatment Practices
    • Drain Insert
    • Catch Basins insert
    • Catch Basin Cleaning
    • Wet vault
    • Floatable Skimmer
    • Water Quality Inlets
    • Vortex Separator
    • Buffer Boxes
bridge design and retrofit constraints
Bridge Design and Retrofit Constraints
  • There is no lateral right-of-way on which to build mitigation measures.
  • Mitigation measures can be located only at substantial cost, or storm water must be gravity- drained back to land.
  • The topography slope may preclude design or retrofit for gravity drainage back to land.
  • The additional load of storm water piping must be considered for retrofit and in new bridge design.
  • The length and slope of some bridges preclude gravity drainage to land.
  • Maintenance may be difficult, and additional safety measures may need to be considered.
basic epa recommendations
Basic EPA Recommendations
  • Direct pollutant loadings away from bridge decks by diverting runoff waters to land for treatment.
  • Restrict use of scupper drains on bridges less than 400 feet in length and on bridges crossing very sensitive ecosystems.
  • Site and design new bridges to avoid sensitive ecosystems.
  • On bridges with scupper drains, provide equivalent urban runoff treatment in terms of pollutant load reduction elsewhere on the project to compensate for the loading discharged off the bridge.
basic bridge bmp
Basic Bridge BMP
  • nonstructural BMPs that are potentially applicable to bridges include:
  • – Street sweeping,
  • – Inlet box/catch basin maintenance,
  • – Maintenance management,
  • – Deicing controls, and
  • – Traffic management (e.g., high occupancy vehicle lanes, and mass transit).
A large number of structural BMPs are available to effectively reduce storm water runoff volume and/or pollutant, loading. Several techniques are used for storm water runoff
  • disposal from bridge decks:
  • • Discharging runoff through multiple open scuppers directly into the receiving water.
  • • Discharging runoff through piping down from the bridge deck directly into the receiving water.
  • • Conveying the storm water runoff over the surface of the bridge to one or both ends for BMP treatment or discharge.
  • • Conveying the storm water runoff via piping or open troughs over to one or both ends of the bridge for BMP treatment or discharge.
  • • Detaining and treating the storm water under the bridge deck.
  • Practices in cold states
states with programs
States with programs
  • Maine
    • Trying to eliminate scuppers
    • Flow to catch basins
    • New project to connect scuppers with pipes, but worry that it will be a maintenance headache
  • Minnesota
    • Convey to end, if possible, if not
    • Use drainage system
      • Scuppers, closed or open, depends on project
      • Maintenance problems with trough systems
      • MgCl2 spray
  • State storm water manual
    • Section on bridges
    • (see later on priority)
  • Belive high-efficiency street sweepers are useful
      • New technolgoy, old were not that helpful
  • Research program on treatment system to fit on pile caps combinded with sweeping
    • In progress
    • Do high-efficiency street sweeping
    • Drain to end
      • Filter with grass swale
      • Settling device – catchbasin
    • Don’t use proprititary filter systems because of maintencance requirements.
    • Plan to address BDRO in manual soon
    • Tested two decivices but decided HESS is more cost-effective
other states per nchrp
Other States per NCHRP
  • It is typical for storm water to be conveyed over the surface to the end of the bridge deck and routed to a drain inlet that leads to a discharge via grassy ditch or some sort of BMP, such as a pond.
  • States that explicitly noted that they follow this policy were Florida, Minnesota, Oregon, Washington, Massachusetts, Delaware, Nevada, Maine, New Jersey, Utah, New
  • Mexico, and Idaho. Other states potentially follow this policy but did not explicitly mention it. Regardless, state DOTs have identified this practice as effective and economical (NCHRP2002).
cold climate bridges bmp
Cold Climate Bridges BMP
  • Don’t reject street sweeping
    • High Efficiency can reduce contamination to water
    • Maintenance is straight forward
    • Contrast with frozen pipes
  • Insert Cost
  • Use clean deicers
  • Clean sand
  • CMA, KA
    • High cost alternatives to NaCl
  • Smart applicators
pous pavement
Pous Pavement
  • Porous pavement is another BMP can be used for highways in cold climatese if the base course excavated below the frost line. However, this techniques is not applicable to bridges in very cold climates because the whole bridge freezes so there is no frost line.
data base
  • Bridge Number
  • Structure Name
  • Highway
  • Milepoint/Location
  • ADT
  • Borough or Location
  • DOT region
    • Sub-region
Main material
    • Steel, prestress
  • Type
    • Orthotropic
    • Box
    • Tee
  • Service Under
    • Water, rail, other highway
  • (On ADT tab)
  • Prioritization
  • Trucks
  • Urbanized
  • Bridge Length
  • Land use
priority scheme
Priority Scheme
  • Score = (A + B) + (C1 ´ D) + C2 + [(E1 + E2 + E3 + E4) ´ E5] + E6 + F.
  • Where: • A = Type and size of receiving water body.
  • • B = Beneficial uses of receiving water body.
  • • C = Pollutant loading.
  • • D = Percentage contribution of highway runoff to watershed.
  • • E = Cost/pollution benefit.
  • • F = Values trade-off.
  • These factors are described more fully below.
challenges to the design of runoff management practices in cold climates caraco and claytor 1997
Challenges to the Design of Runoff Management Practices in Cold Climates (Caraco and Claytor, 1997)
Nationwide the chemical characteristics of bridge deck runoff have not been extensively documented and only a few studies have focused on them [NCHRP 2002].

In examining Alaska’s hundreds of bridges, what are the factors that would indicate that pollution is indeed unlikely or likely?

Washington DOT has developed a system that involves parameters

grouped into the following general categories (based on NCHRP 2002 data and worked these into a priority rating for BMP:

  • Traffic characteristics—speed, volume, vehicular mix (cars/trucks), congestion
  • factors, and state regulations controlling exhaust emissions;
  • • Highway design—pavement material, percentage impervious surface, area, and
  • drainage design;
  • • Maintenance activities—road cleaning, roadside mowing, herbicide spraying,
  • road sanding/salting, and road repair;
  • • Accidental spills—sand, gravel, oils, and chemicals. [NCHRP 2002]

To which we would add:

  • • Climate, rainfall and snow and ice practices – plowing frequency.