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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