Rocky Mountain Section - 64th Annual Meeting (9–11 May 2012)

Paper No. 11
Presentation Time: 11:45 AM


AGRAWAL, Ashish and NARASIMHAN, Ramesh, NCS Engineers, Phoenix, AZ 85012,

The Coyote Creek Water System (CCWS) is located at the border of New Mexico and Arizona and serves approximately 200 people. In 2008, the CCWS constructed a new 1,600 foot deep well that can produce about 100 gpm. The well’s water quality data show that the water exceeds primary maximum contaminant levels (MCLs) for gross alpha particles and combined radium, and exceeds secondary MCLs for TDS, chloride, zinc, iron and manganese. The gross alpha particles and combined radium concentrations are 75.6 pCi/L and 53.24 pCi/L, respectively. The secondary contaminant exceedances are elevated to the point that the water is not suitable for domestic use. TDS levels are very high (3,500 mg/L), and iron, zinc, and manganese concentrations are 22.2 mg/L, 33.1 mg/L, and 0.21 mg/L, respectively. Water of this complex quality must be treated via high pressure reverse osmosis (RO); however, this approach typically yields only 60-65% recovery. Several pretreatment and primary treatment techniques were evaluated for their ability to help meet regulatory requirements. Costs and non-cost factors (e.g., energy requirements and amount of sludge produced) were considered in the evaluation. The selected multi-step approach includes preoxidation using chlorination to flocculate the iron, manganese, and zinc; plate-settler pretreatment to remove the flocs; lime softening to remove hardness; and high pressure RO treatment to remove TDS, gross alpha particles, and combined radium. Sludge drying beds will be constructed for iron, manganese, and zinc sludge. An evaporation pond will be constructed to handle brine generated from the RO system. The result is a zero liquid discharge process, which is important because the brine cannot be discharged to a wash and there are no nearby sewers. This multi-step approach will increase the overall water recovery up to 75%. Pilot testing of the treatment approach will be performed in the pre-design phase. This presentation will discuss the treatment and costs evaluations performed, the economic impacts related to the quality of the groundwater and the process used to obtain funding for this rural community project.