General Motors identified stormwater as a priority issue, as the city of Detroit had implemented a US$2million annual fee for businesses discharging stormwater to the municipal combined sewer system. To address this, General Motors added a retention pond which brought the facility’s total capacity to 213 megaliters (enough to hold a 100-year storm event). The result of this has been to cut water-use by 20% through rainwater harvesting and save an additional US$140,000 annually, paying for itself outright within two years.
General Motor’s Hamtramck Assembly plant identified stormwater disposal as a priority issue after a US$2million annual fee was levied by the city of Detroit for treatment in its combined sewer system. This fee equated to 14% of the plant’s entire utility bill.
GM decided to add an additional retention pond (there were two already) at the Detroit-Hamtramck site, bringing the overall stormwater capacity of the site to 213 megaliters – the equivalent of a 100-year storm event. The DetroitHamtramck site covers almost 1.5km2, and stormwater is channeled into storm drains which lead to the pond. Floating pumps transfer this across the manufacturing facility where it is used as cooling water.
Given that the US$2million fine equated to 14% of General Motor’s Hamtramck plant’s annual utility bill, identifying the potential for rainwater conservation at an earlier juncture could have saved substantial funds. Furthermore, the use of water for cooling purposes could be further reduced by investing in more efficient systems, preserving more water for purification and use in more high-value processes (e.g. paint shop operations).
The remaining high purity water will be pumped to Detroit Renewable Power to produce steam to heat and cool the assembly plant, as well as 145 other Detroit businesses. Water reuse will continue to be an important commitment for GM.