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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
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.
Today
Outline legal and regulatory frameworkOutline BMP for HighwaysOutline BMP for BridgesBMP for Cold WeatherBMP for Cold Weather Bridges?
WHY BMP
Contamination from roadways to waterbodies.
Highway runoff constituents and their primary sources (NCHRP 2002)
Constituent Primary Source
Particulates Pavement wear, vehicles, atmosphere, maintenance
Nitrogen, phosphorus Atmosphere, roadside fertilizer application
Lead Leaded gasoline (automobile exhaust), tire wear (lead oxide filler material), lubricating oil and grease, bearing wear
Zinc Tire wear (filler material), motor oil (stabilizing additive), grease
Iron Automobile body rust, steel highway structures (guard rails, etc.), moving engine parts
Copper Metal plating, bearing and bushing wear, moving engine parts, brake lining wear, fungicides and insecticides applied by maintenance
operations
Cadmium Tire wear (filler material), insecticide application
Chromium Metal plating, moving engine parts, brake lining wear
Nickel Diesel fuel and gasoline (exhaust), lubricating oil, metal plating, bushing wear, brake lining wear, asphalt paving
Highway runoff constituents and their primary
sources (NCHRP 2002) Cont’edConstituent Primary Source
Manganese Moving engine parts
Bromide Exhaust
Cyanide Anti-cake compound (ferric ferrocyanide, Prussian blue or sodiumferrocyanide, yellow prussiate of soda) used to keep deicing salt
granular
Sodium, calcium Deicing salts, grease
Chloride Deicing salts
Sulfate Roadway beds, fuel, deicing salts
Petroleum Spills, leaks or blow-by of motor lubricants, antifreeze and hydraulic fluids, asphalt surface leachate
PCBsc, pesticides Spraying of highway rights-of-way, background atmospheric deposition, PCB catalyst in synthetic tires
Rubber Tire wear
Pathogenic bacteria (indicators)
Soil, litter, bird droppings, trucks hauling livestock and stockyard waste
[discuss law and regulations]
Why DOT needs to doWhat?
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
Non-Structural BMPs InstitutionStructural
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
Pollutant TradingMitigation Banking
Structural BMP
Treatment Bioretention Ponds Extended Detentino Basin Constructed Wetland Stormwater wetland
Structural BMP
Infiltation Practices Infilatraion Basin Infiltration Trench
Filtration Pracitces Media Filter Sand and organic filters
Vegitative Practices Grass Swales Vegitated Buffer Strip
Structural BMP
Runoff Pretreatment Practices Drain Insert Catch Basins insert Catch Basin Cleaning Wet vault Floatable Skimmer Water Quality Inlets Vortex Separator Buffer Boxes
Bridges
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
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
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.
Cold
Practices in cold states
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
Washington
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
Wisconsin 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
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
Don’t reject street sweeping High Efficiency can reduce contamination to
water Maintenance is straight forward Contrast with frozen pipes
Cost
Insert Cost
Deicing
Use clean deicersClean sandCMA, KA
High cost alternatives to NaCl
Smart applicators
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 NumberStructure NameHighwayMilepoint/LocationADTBorough or LocationDOT region
Sub-region
Main material Steel, prestress
Type Orthotropic Box Tee
Service Under Water, rail, other highway
Prioritization
(On ADT tab)PrioritizationTrucksUrbanizedBridge LengthLand use
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)
Climatic Condition BMP Design Challenge
Cold Temperatures Pipe freezingPermanent pool ice CoveredReduced biological activityReduced oxygen levels during ice coverReduced settling velocities
Deep Frost Line Frost heaving Reduced soil infiltration Pipe freezing
Short Growing Season
Short time period to establish vegetationDifferent plant species appropriate to cold climates than moderate climates
Significant Snowfall High runoff volumes during snowmelt and rain-on-snowHigh pollutant loads during spring meltOther impacts of road salt/deicersSnow management may affect BMP Storage
Nationwide the chemical characteristics of bridge deck runoff have not been extensively documented and only a few studies have focused on them [NCHRP 2002].
Methodology
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 parametersgrouped 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.
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