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Highway Runoff Manual - Frequently Asked Questions

Highway Runoff Manual cover

Who maintains the Highway Runoff Manual (HRM)?
The Headquarters Environmental Services Office Stormwater and Watersheds Program and Headquarters Hydraulics Section are jointly responsible for revision and implementation oversight of the manual. The manual's upkeep uses a technical team made up of water quality, stormwater, and erosion control specialists; designers; hydrologists; geotechnical and hydraulic engineers; landscape architects; and maintenance staff. The technical team also includes several county representatives, and benefits from a close working relationship with Washington State Department of Ecology staff and contributions by consultants and outside reviewers.

How can I get a printed copy of the HRM?
While there are no plans to distribute printed copies, the manual is available on the Internet at the WSDOT Engineering Publications On-Line Technical Manual Library. Upon request, printed copies and CD ROM versions may be purchased from WSDOT Printing Services by submitting requests using their on-line order form.

However, users referencing printed copies and CD ROM versions should continually consult the online version and the Highway Runoff Manual web page for postpublication updates to ensure they are using the most current design guidance.  To receive e-mails announcements of postpublication updates, send a blank e-mail to: subscribe-stormwater_list@lists.wsdot.wa.gov.

Who should I contact with comments or suggestions about the HRM?
The HRM will be periodically updated to clarify its content and reflect changes in the regulatory landscape, advancements in stormwater management, and improvements in design tools. Comments and suggestions for improving the HRM should be e-mailed to MaurerM@wsdot.wa.gov or mailed to:

Highway Runoff Manual
Attention: HRM Program Manager
WSDOT
PO Box 47329
Olympia, WA 98504-7329 

What happens when compliance with the HRM is not economically feasible, physically possible, or environmentally responsible?
While WSDOT cannot grant itself variances, it can document site constraints via the Engineering and Economic Feasibility checklist (see HRM Appendix 2A ) as part of the process for seeking approval from the Department of Ecology using the demonstrative approach.

The 2010 HRM contains BMPs that WSDOT finds acceptable for widespread highway application. However, in recognition that site and project constraints may compel a designer to consider alternatives, the 2010 HRM outlines the process for seeking authorization for alternative BMP options. BMPs approved by the Department of Ecology, but not recommended for highway application are referred to as "Category 1 BMPs" (pdf 1.98 mb). Additional information on emerging technology BMPs is also available on the Department of Ecology's website.

What if I want to use a BMP not listed in the HRM?
The HRM only contains Department of Ecology-approved BMPs that WSDOT finds acceptable for highway applications. Section 5-3.5 of the 2010 HRM describes the process for seeking authorization to use BMPs not contained in the HRM.

Where can I find guidance for the design of stormwater management facilities? Is training on the manual available?
WSDOT's stormwater management-related guidance, procedures, and tools can be found on the Water Quality-Stormwater page. Information on HRM training is available online.

How do I determine the qualifying areas of elevated roads and parking structures for Minimum Requirement 5 (Runoff Treatment)? 
When a brand new fly-over ramp is constructed over the existing highway, in plan view, the flyover ramp area directly over the existing highway would be considered a replaced pollution generation impervious surface (PGIS). This is also true in situations where an existing roadway is proposed to be significantly raised (new pavement greater than 1 foot thick directly on top of old pavement) or elevated without widening. PGIS that undergoes planing or mill and fill operations are not considered replaced PGIS. A parking lot structure that is proposed to be built over an existing parking lot without expansion of the parking area is considered replaced PGIS.

When a roadway or bridge is proposed to be widened over an existing non-pollution-generating impervious surface, that area should be considered new PGIS. An example of this is when an existing bridge spanning a lake is proposed to be widened by one lane; that new lane would be considered new PGIS.

Note that these area determinations of replaced PGIS do not require excavation of existing roadway. 

How do I determine the qualifying areas of elevated roads and parking structures for Minimum Requirement 6 (Flow Control)?

When a brand new flyover ramp is constructed over the existing highway, in plan view, the fly-over ramp area directly over the existing highway would be considered a replaced impervious surface. This is also true in situations where an existing roadway is proposed to be significantly raised (new pavement greater than 1 foot thick directly on top of old pavement) or elevated without widening. Impervious surfaces that undergo planing or mill and fill operations are not considered a replaced impervious surface. A parking lot structure that is proposed to be built over an existing parking lot without expansion of the parking area is considered a replaced impervious surface. When an existing bridge that spans a lake is proposed to be widened by one lane, that new one lane would be considered a replaced impervious surface.

Note that these area determinations of replaced impervious surface do not require excavation of the existing roadway.

Who should I contact with questions about the HRM?
As a general rule, direct questions about the content of the HRM to region environmental, hydraulic, water quality, and/or maintenance staff before contacting the Headquarters Hydraulics Section, Headquarters Highway Runoff Program, Environmental Services Office Stormwater and Watersheds Program, and/or Headquarters Highway Maintenance environmental staff.

Questions about stormwater facilities inventory, stormwater retrofit priorities, NPDES Municipal Stormwater Permit, water quality monitoring/sampling, (use of experimental best management practices (BMPs), and BMP research and development) should be directed to Headquarters Design Office Highway Runoff Program staff.