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Case Study A comprehensive pilot test is critical for determining the most effective and cost-efficient treatment solution for a particular location. community's water district chose to explore ways of optimizing its use of existing groundwater supplies by pilot testing three water treatment technologies: coagulation/filtration, adsorptive filtration, and reverse osmosis (RO). While adding to the initial cost of install- ing a water treatment system, a comprehensive pilot test is critical for determining the most effective and cost-efficient treatment solution for a particular location. At the conclusion of its 2007 pilot study, the water district chose to implement a pressure media filtration system to reduce the amount of arsenic in its raw water to below the maximum contaminant level (MCL) of 10 ppb in accordance with California Department of Public Health standards. A pressure media filtration system would achieve the goal of blending filtered and other source water to achieve total arsenic levels below the MCL, while realizing lower installation, operations, and maintenance (O&M;) costs than the other two pilot-tested technologies. A high-level analysis of costs associated with the new water treatment installation proves instructive. The Solution: Two Automatic Filter Stations In 2010, the water district installed a new water filtration system at two separate treatment facilities. Designed for combined flow of 2,500 gallons/m inute, the two fully automated stations have six filter vessels (three each per site); two reaction vessels (one each per site); and standby capacity with automatic backwash and backwash recovery. At the time of installation, one complete load of application-specific permanent media was furnished for the system. An additional 5% of media was also provided for the first required media refresh in approximately five years, which will be necessary to replace media lost in backwashing. In addition to not requiring complete change-out, another key advantage of the new filtration system's media is that it is custom-designed for this water district's unique water treatment needs. The price for their new pressure media filtration 22 Water Online The Magazine, Cleanwater Edition ■ wateronline.com system was close to $14.5 million, a significant investment for the small municipality. However, this figure does not tell the whole story; a closer look at some key costs — including the lifecycle costs associated with operating the system — is critical. A Closer Look At Key Cost Drivers: Installation Versus Lifecycle Costs — Tanks And Waste Handling After considering all available options, the district chose a water filtration system with a highly efficient four-minute backwash cycle and a one-minute rinse, much shorter than many others in the market, which can run from 15 to 20 minutes with a 15-minute rinse. With an overall efficiency of 98.9%, its new 2,500 gallons/minute system produces approximately 1.3 billion gallons of water/year, and generates approximately 600 gallons of waste/year when reclaim solids are removed. The backwash volume from the system is 22,500 gallons per flush, versus 150,000 gallons from a system with a longer backwash cycle. A treatment system with a long backwash cycle will produce up to three million gallons more waste water per year than a comparable system with a short backwash cycle. Because their backwash volume is comparatively small, it can be stored in small reclaim tanks — unlike systems with longer backwash cycles and huge backwash volumes, which must discharge to a pond. The district's backwash water does not become surface water; rather, it is reintroduced into the system for further processing, and solids in the reclaim tank are settled and removed every six months. Waste disposal is limited to 600 gallons/year of nonhazardous materials, and there is no affiliated cost for drying beds. As result of this high system efficiency, the backwash and reclaim tanks are approximately 75% smaller than the competing systems' tanks, resulting in upfront capital costs savings for the water district and its community of at least $275,000. An additional benefit of these significantly smaller tanks is that they require a smaller installation footprint, which also can result in meaningful land