Monitoring Roadway Runoff and Development of a Design Guide for Roadway BMPs John Stansbury, Ph.D., P.E.Massoum Moussavi, Ph.D., P.E., and Tian Zhang, Ph.D., P.E.
Outline• Introduction• Field Study• BMP Design Guide• Summary
Regulatory Background• Clean Water Act (CWA, 1972): requires NPDES permit (National Pollutant Discharge Elimination System). – Municipal Separate Storm Sewer System (MS4)– discharges/regulation: MS4 defined as: A system of conveyances owned/operated by a public body. – Designed or used for collecting or conveying stormwater. – Not a combined sewer & not part of a POTW.• MS4s discharges are regulated nonpoint source pollution. – MS4s regulation is part of the CWA (1987 amended): Phase I (passed in 1990): requires MS4s to submit Storm Water Pollution Prevention Plans (SWPPP) to the US EPA. – Phase II (passed in 1999): requires 6 minimum BMPs. – The objective of MS4s is to reduce pollutant effluents to the Maximum Extent Practicable (MEP) (so not linked with numeric limits).
Regulatory Background• NDOR is a non-traditional MS4 and is required to manage roadway runoff pollution within MS4 boundaries.• NDOR is required (by NDEQ): To capture/treat the first 0.5″ Water Quality Volume (WQV) that runs off of any new/redeveloped impervious area.• Currently treatment levels are only required to be the Maximum Extent Practicable (MEP).
Project Objectives• Determine water quality of runoff.• Evaluate performance of the existing BMPs.• Improve design guidelines of treatment BMPs.
Field Study• Location and six sub-basins• Methods: – Flow Measurement – Sampling Sites – Sample Analysis• Results
Location• Intersection between I-80 and I-680 in Omaha, Nebraska
Results• Metals (Cu, Cd, and Zn), COD, TSS, & TDS are the major contaminants found in the highway runoff.• SVOCs and VOCs were below the detection limits.• A weak correlation between concentrations, TSS, antecedent dry period (ADP), total rainfall, and volume of runoff.• Roadside vegetation (site B) is very efficient to reduce runoff/pollution via infiltration.• The existing BMP (detention pond) seems to be somewhat effective in reducing heavy metals, chloride, COD and TSS loads.
Introduction to BMPsBMPs defined as: – schedules of activities – prohibitions of practices – maintenance procedures – structural and/or managerial practices that, when used singly or in combination, prevent or reduce the release of pollutants to waters of the US.Six minimum BMPs (control measures) identified by CWA: – Public participation and involvement – Public education and outreach – Illicit discharge – Construction site storm water runoff control – Post-construction storm water runoff control – Municipal operations pollution prevention and good housekeeping
Chapter 3: Post ConstructionStormwater Control• Treatment BMPs include: – Permanent structural BMPs, such as: • Settling of particulate matter • Filtration • Biological uptake • Soil adsorption• Non-structural BMPs for source control such as policies/ordinances that: – Provide requirements and standards – Protect sensitive areas (wetlands and riparian areas) – Maintain/increase open space – Provide buffers along sensitive water bodies – Minimize impervious surfaces – Minimize disturbance of soils and vegetation
Bioretention Design Criteria• Media: compositions depending on needs• Can be designed as infiltration• Flexible layout
Horizontal Filter DesignCriteria• Media filled trench in ditch bottom• Temporarily store WQV in media• Cobble armoring (1ft above flow depth)
Project Overview• Three-year project (July 2008–March 2011)• Six events sampled each year. – Two samples in spring, summer, and fall seasons – Total: • 12 storms for sampling sites A, C, D, and E • 10 for site B• Data analysis• Development of design manual
Summary• Metals (Cu, Cd, and Zn), COD, TSS, & TDS were the major contaminants found in the highway runoff.• SVOCs and VOCs were below the detection limits.• There was a weak correlation between concentrations, TSS, antecedent dry period (ADP), total rainfall, and volume of runoff.• Roadside vegetation (site B) was very efficient in reducing runoff/pollution via infiltration.• The existing BMP (detention pond) seems to be somewhat effective in reducing heavy metals, chloride, COD, and TSS loads.• Effectiveness of different BMPs needs to be evaluated.• BMP design is case sensitive, but development of general design procedures is possible.
Summary• NDOR defines priority stormwater outfalls as: Concentrated stormwater flow locations directly discharging from state ROW to the following:• Streams (Perennial and Intermittent)/Lakes/Wetlands/MS4s• Ephemeral drainage that directly discharges to one of the above within 500 feet beyond the ROW line
Chapter 3: Post constructionStormwater Control• Responsibility: Treatment of first ½” of runoff (first flush). – Runon – New Development• BMPs selection criteria (NDOR): – Primary treatment: 80% removal TSS – Metals are secondary treatment concern – Low maintenance – Cost Effective – No open water – Implement BMP within existing right of way as much as possible – Infiltration should not be a primary removal mechanism near roadway – Aesthetics
Cr Concentration versus TSS Concentrationfor the West Pipe Outlet
Cr Concentration versus TSS Concentrationfor the East Pipe Outlet
Cr Concentration versus TSS Concentrationfor the Basin Outlet Pipe
Conclusions of Field Study• Roadside vegetation showed strong potential to reduce runoff via infiltration.• Metals (Cu, Cd, and Zn), COD, TSS, and TDS are the primary contaminants found in the highway runoff.• SVOCs and VOCs were below the detection limits.• A weak correlation between concentrations, TSS, antecedent dry period (ADP), total rainfall, and volume of runoff.• The existing BMP seems to be somewhat effective in reducing the heavy metals, chloride, COD, and TSS loads. Effectiveness is limited to low intensity rainfall events.