In 2005, the New Mexico Department of Transportation (NMDOT), required by a Municipal Separate Storm Sewer (MS4) Permit requirement, created an NPDES Manual for use by both NMDOT and other New Mexico MS4 permittees. A 2012 update was completed; however, by 2020 the Manual required updates for current NPDES references and practices.
NMDOT took the initiative to not just update this Manual, but to transform it into a guidance document that includes green infrastructure (GI) and low impact development (LID) strategies for stormwater management in arid regions. The inclusion of GI/LID strategies was in support of Governor Michelle Lujan Grisham’s 2019 NM Climate Strategy with the goal of increasing the resilience of the built infrastructure and reducing the negative environmental impacts of road runoff. The 2020 Manual update benefited from engaging a diverse team of subconsultants and NMDOT professionals: civil engineers, landscape architects, NMDOT Environmental and Drainage Bureaus staff, and NMDOT district patrol construction and maintenance professionals.
The comprehensive team tackled this entire update during the COVID pandemic. In addition, NMDOT offered the Manual for review to over 30 agencies across the state, conducted a virtual presentation, and benefited from the valuable, diverse feedback received.
To start the update, the team researched GI and LID BMPs developed in arid regions of adjacent states (Arizona, Colorado, Texas, and Utah). The survey results, which included a combination of research, precedent identification, and phone interviews, assisted NMDOT in choosing additional BMPs to add to the revised Manual. The research findings also provided valuable information for BMP details and updates.
The Manual is organized into three regulatory sections, providing both general guidance as well as specific NMDOT practices (applicable to linear projects) for the Construction General Permit (CGP), Multi-Sector General Permit (MSGP), and an added section for MS4 Permits. The BMPs are the focus of the Manual’s Appendix A; BMP matrices as well as combined BMPs, or treatment train, examples for roadway projects were created for the updated Manual. Consistent portrayal of the BMPs, both with text sections and types of graphics, was an improvement focus area with this update. This project approach and structure, as well as the final NPDES Manual, can provide valuable resources to linear MS4s as well as other agencies looking to advance their NPDES guidance documents. The forward-thinking approach to transform an existing document into a more valuable, relevant resource can be applied to other areas and agencies.