1. 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.
2. Outline
• Introduction
• Field Study
• BMP Design Guide
• Summary
3. 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).
4. 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).
5. Project Objectives
• Determine water quality of runoff.
• Evaluate performance of the existing BMPs.
• Improve design guidelines of treatment BMPs.
6. Field Study
• Location and six sub-basins
• Methods:
– Flow Measurement
– Sampling Sites
– Sample Analysis
• Results
24. 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.
26. Introduction to BMPs
BMPs 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
28. Chapter 3: Post Construction
Stormwater 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
30. Guidance Manual Format
• Fact Sheets
– Pollutant removal potential
– Construction and maintenance costs
– Siting constraints
– Maintenance operation
• Design Guides
– Design criteria
– Design process
– Example
31. Vegetated Filter Strip Design Criteria
• WQV flow depth < 1 inch
• WQV velocity below < 1 ft/s
• Slopes in flow direction from 2–15%
• Minimum 15 foot flow path
• 80% Vegetated Cover
32. Bioretention Design Criteria
• Media: compositions depending on needs
• Can be designed as infiltration
• Flexible layout
33. Horizontal Filter Design
Criteria
• Media filled trench in ditch bottom
• Temporarily store WQV in media
• Cobble armoring (1ft above flow depth)
34. 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
35. 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.
36. 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
37. Chapter 3: Post construction
Stormwater 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
52. 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.