Eliminating Expenses

July 10, 2017
Minneapolis warehouse achieves 100% in storm water credits through sustainable improvements

About the author: Rebecca Carlson, P.E., is principal for Wenck. Carlson can be reached at [email protected] or 763.252.6824.

Murphy Warehouse Co. in Minneapolis was facing costly capital improvements and potential disruption of its business. Escalating storm water fees were impacting the bottom line, and a deadline from the city to disconnect 7 acres of drainage from the municipal sanitary system was looming.

The company’s 22-acre site was 98% impervious, and its location in a highly urbanized area of Minneapolis, as well as limited adjacent storm water utilities, made the problem complex and potentially expensive to solve. However, facing $68,000 in annual utility fees and an additional $24,000 in fines made the cost of waiting to take action too high to ignore.

Richard Murphy, FASLA, president and CEO of Murphy Warehouse Co., contacted consulting firm Wenck because he was concerned about the potential environmental impact of ongoing operations and was looking for ways to make the operations more sustainable.

“Murphy [Warehouse Co.] has a long-standing interest in sustainability, which allows us to minimize waste and environmental impact in a way that makes good business sense,” Murphy said. “We saw the opportunity to work with Wenck to not only eliminate the storm water issue and resulting fees, but also to create a beautiful retention system with native prairie landscape that was good for us and for our neighbors—both the people and the pollinating insects and birds. And, like all of [the company’s] green initiatives, this would deliver a solid [return on investment] within a few short years.”

Wenck conducted an initial evaluation and concept design for the project. However, instead of taking a typical “engineering” approach to developing a solution, Wenck took a more comprehensive business approach and considered not only storm water issues, but also other site issues, such as traffic flow, how the facility was used, safety, regulatory impacts and permitting.

It was critical that the client receive a written commitment from the city of Minneapolis for the credit before proceeding with the proposed capital improvement project. Wenck worked with key city staff—including regulatory staff, inspection staff and elected officials—for months during the permitting for the development.

With the credit secured, Wenck next guided the client through the city’s permitting process, prepared construction documents, bid the project and observed construction. Wenck considered the client’s other business needs and recommended that the client combine the project with another planned project to replace a loading dock. By doing so, Murphy Warehouse Co. could permit the projects together and avoid going through the city’s lengthy permitting process twice, saving time and money.

The process took more than a year from initial permitting to securing written commitment of credits and then completing construction.

Construction and implementation were completed with a compressed timeline and minimal interruptions to business operations.


Because Murphy Warehouse Co. is a logistics firm, the campus was busy with a high volume of truck traffic. Wenck planned the construction and implementation phase of the project with a compressed timeline and coordinated closely with necessary contractors to minimize potential interruptions to the business.

Storm water runoff from warehouse rooftops and paved lots previously entered an 8-in.-diameter vitrified clay pipe sanitary sewer. The project redirected runoff via the installation of storm water management features, including a large vegetated infiltration/rate-control pond (slope stability provided through native vegetation), and three bioretention cells, as well as pipes, catch basins and sumps. Open-grate sanitary sewer castings were reconstructed with solid cover castings, eliminating storm water inflow. A staged pond outlet was designed to maximize pond storage and infiltration in the summer, while preventing exposure to road salt in the winter for native plantings and groundwater. The outlet also assures compatibility with a capacity-restricted city storm sewer system.

Wenck also assisted the client in securing bids and the services of a Minnesota licensed plumber to complete building roof drain disconnections and reconnections to the new storm system. The bidding and construction schedule was coordinated with site improvements, bringing the entire system online as quickly as possible.

Visual aesthetic also was a major concern. In addition to being president and CEO of Murphy Warehouse Co., Murphy is a registered landscape architect, so maintaining the existing, highly visible green spaces on site was a high priority. The existing green spaces were improved with plantings and used for infiltration and rate control. The storm water management features enhance the beauty of the site while effectively managing runoff from the rest of the mostly impervious site. Incorporating green space and the use of infiltration and evapotranspiration, the project represents a sustainable design. It couples an existing highly impervious area with responsible storm water management at a reasonable return on investment.

Credit Negotiation

The city’s rules governing credits were ambiguously written, so Wenck spent a significant amount of time working with the city to navigate what was needed to document and confirm the credit. Without a storm water expert by its side to pore over the city codes, meet with city officials and explain the project’s benefits, it is unlikely Murphy Warehouse Co. would have secured the credits needed to make the project feasible.

Wenck staff used their understanding of the applicable regulations to demonstrate the redesigned site’s ability to handle a 10-year storm event, earning the site a fee credit. Additional credit was negotiated for the resulting improved water quality. As a combined result, Wenck negotiated the first major 100% storm water credit of this type in the city of Minneapolis, saving Murphy Warehouse Co. $92,000 annually in fees and fines.

Murphy pointed out that Wenck’s “as-built” drawings and calculations earned a 102% credit—and he is fond of reminding the city how it owes the company that 2%.

Murphy Warehouse Co. invested the time and money to have Wenck design storm water solutions to mitigate or eliminate both the pending expense to meet regulatory requirements, as well as ongoing annual fees. This investment has a longer return on investment than is typical for most capital investments. However, compared to treating the project as a loss or a cost of doing business, the project was a success because securing the credit turned a significant liability into an opportunity to secure ongoing financial returns for years into the future.

By approaching a problem at a higher level and thinking holistically from the business’s perspective, Wenck was able to help Murphy Warehouse Co. turn a liability into a business opportunity. 

By taking a business approach to the project, the team was able to consider all site issues, saving time and money.

About the Author

Rebecca Carlson