A bigger dig: How GM saved millions by reusing stormwater in Detroit-Hamtramck

In 2014, the engineering team at General Motors' Detroit-Hamtramck Assembly plant realized that stormwater discharge fees were eating up a whopping 14 percent of the plant's utility bill. Two years and 20,000 dump-truck loads later, the plant is recycling its own stormwater at an annual savings of over $2 million.The plant, which produces the Chevrolet Volt, achieved that turnaround by digging a massive stormwater retention pond, adding to two retention ponds that were already on site to increase the site's retention capacity to 47 million gallons of water. Todd Clippard, the plant's paint shop manager and former manufacturing engineering manager, spearheaded the stormwater retention project. "We really looked at the trend of stormwater discharge fees being charged by the city of Detroit, and it was an almost exponential growth," Clippard says. "There were year-over-year increases for several years, and it ended up equating to $193,000 a month. Whether it rained or not, it was such a significant part of our overall utility cost."GM hammered out a deal with the Detroit Water and Sewerage Department (DWSD) to obtain drainage credits for either redirecting water that it would normally send to DWSD, or for retaining stormwater until DWSD's system has the chance to revert to dry-weather mode after a storm. DWSD deputy director and chief engineer Palencia Mobley says those kinds of credits were developed recently as part of a much larger overhaul at DWSD. The department has also retooled its billing system and is working on a city ordinance encouraging property owners to manage their own stormwater."Each thing is a tool in the toolbox to ensure that we are better managing rain where it actually falls," Mobley says. "It's a lot of cost to convey the stormwater to the Detroit wastewater treatment plant."Mobley says the department's conversations with GM became a "very collaborative partnership" that allowed DWSD to develop the comprehensive set of drainage charge credits that it rolled out for all customers in October."It was a win-win situation," Clippard says. "We're basically paying for everything for them, and they can use us as a model to possibly encourage other Detroit water and sewer customers that want an alternative to paying the discharge fees."Retain and reuse

Clippard and his team originally planned to use the new retention pond solely to accumulate water, holding onto it until DWSD was no longer in high-volume mode after a storm to achieve a credit on GM's bill. But during lengthy negotiations with DWSD, Clippard and his team began looking into ways they could reuse the water themselves without sending it to DWSD at all. The result was a broad variety of reuse applications that are now in place at the plant."We knew that if we could get the water to the powerhouse, which is about three-quarters of a mile away from the ponds, that would open up a whole series of potentials for us to use it for other processes," Clippard says. "That's really what we got moving towards quickly."Clippard and his team installed floating pumps in the retention ponds, similar to those used in mining operations, and laid 3,600 feet of pipe from the ponds to the plant's powerhouse. Water is pumped from the ponds through a series of filters and into a 50,000-gallon storage tank inside the plant. That water is then initially used to feed the plant's cooling towers as "make-up water," replacing water that turns to steam in the towers. "We were able to reuse 400,000 gallons of water the very first day, which nearly doubled our projections of what we thought we would consume on a high-temperature day," Clippard says. "That was a real good stroke of business there."Stormwater reuse in the plant's cooling towers saves the plant $140,000 annually.

But that's only the first stop for stormwater once it hits the plant. After further purification, the water is used in the plant's sludge system, which breaks down sludge from painting cars, and the phosphate system used to prepare and treat metal used in vehicles. Soon, the remaining water will likely be used to power other Detroit businesses. GM is currently working out a deal to provide purified water to Detroit Renewable Power (DRP), a steam energy producer that resides just across I-94 from the plant.Going greener and greener

The entire project results in significant savings on multiple levels. Between DWSD credits, reduced water usage, and the pending agreement with DRP, the new system will save the plant $2.3 million per year, making back its $3.1 million cost in little over a year. The project also reduces the plant's water usage by a whopping 20 percent."That was a corporate goal to achieve that by 2020," Clippard says. "Essentially, in one fell swoop, we are going to achieve that goal significantly on our city water consumption."GM sustainability director David Tulauskas says Detroit-Hamtramck's stormwater reuse project is a first for the company, and its scope is unprecedented at a national level in general. But Tulauskas says the company values the project and other sustainable initiatives like it for the example they end up setting for GM's other plants."On the manufacturing side this stuff isn't sexy, doesn't get the headlines like the Chevrolet Volt," Tulauskas says. "But it's critical to us operating efficiently and ultimately improving our bottom line so we can invest the money we save in vehicles like the Chevrolet Volt."

The stormwater retention and reuse project is only the latest example of sustainability-oriented practices at the Detroit-Hamtramck plant. In 2011 the plant partnered with DTE Energy to install a six-acre solar power array, and it also currently uses waste-derived steam energy from DRP. Some of the plant's sustainability initiatives are simpler, like shutting lights off on the floor during lunch hours.Clippard says he could list 37 "significant" sustainability initiatives the plant has implemented over the past three years, and many smaller ones. He says there's a basic profit motivation for GM or any other company to reduce energy usage, but his own commitment to improving his plant's sustainability arises from a much bigger-picture mentality."Anything you don't need to consume from an energy standpoint immediately benefits the bottom line, and as a shareholder and employee that's important to me to improve our financial position," Clippard says. "But also, as I've grown in my career, I've become much more in tune with the impact it has on the environment and the community. It's really a far greater impact if you look at it through that lens."

This story is part of a series on measuring on the role of green infrastructure projects in Detroit's redevelopment. Support for this series is provided by the Erb Family Foundation to Greening of Detroit, Model  D, and The Nature Conservancy. Read more articles from the series here.

All photos by Doug Coombe.