MGM National Harbor Resort
Client: W.G. Tomko Engineers
The 23-acre resort in southern Prince George’s County includes a 24-story hotel with 308 rooms, 125,000 square foot casino, restaurants from celebrity chefs, and a luxury spa and salon. Wahaso engaged with the design team of Smith Group JJR and engineers at W.G. Tomko, Inc. The owner and teams were seeking LEED Gold certification and wanted to include rainwater harvesting in their sustainable initiatives for the project.
System Type: Rainwater for Irrigation, Toilets and Cooling Towers
Commissioning Date: January, 2017
Challenge: LEED requirements called for the system to meet all the irrigation and toilet flushing requirements for the property, but it was the cooling tower make-up component that would easily consume most rain events. The team needed a design that could ensure meeting LEED while still maximizing water savings. Local codes required residual chlorine and blue dye for any water sent to toilets, but those additives were not necessary or desirable for the cooling tower supply.
Solution: Wahaso designed a system that could treat the rainwater at 60 GPM into a 1,000-gallon processed water holding tank or “day tank.” That buffer tank helped keep the treatment system cost down while ensuring adequate supply for the 150 GPM pressurization pumps. Pressurized output was split so that a separate non-potable stream was destined for the toilets. Wahaso designed injection systems for residual chlorine and blue dye for the toilet stream to meet local codes. Special control logic was implemented that monitored average irrigation and toilet demand as well as the cistern levels so that a 21-day supply was reserved for those uses. When the cistern level dropped to the 21-day level, no additional water was sent to be sent the towers until another rain event raised cistern levels.
Results: The project earned LEED Gold certification for a number of environmentally-friendly initiatives including rainwater harvesting, water conservation, energy efficiency, waster and recycling and more. In addition to contributing to meeting the LEED certification requirements, the project ranks as one of Wahaso’s most successful projects in terms of water savings, with projected annual reduction of 10.7 million gallons of municipal demand, saving the owners over $120,000 per year in water and sewer costs at current rates. ROI breakeven should occur in year three.