Pintail Water Treatment Plant Arsenic Treatment Improvements

The Wild Wings County Service Area (CSA) is a rural residential golf community located in unincorporated Yolo County, just outside the City of Woodland. The water system, managed by the County of Yolo, supports 338 residences and includes two existing groundwater wells that serve as the community's primary water supply. Installed in 2005, the system consists of the Canvasback and Pintail Well sites, two 360,000-gallon water storage tanks, a potable water distribution network, and a raw water conveyance system. The Canvasback Well has been on emergency standby since 2009 due to arsenic concentrations exceeding the State Maximum Contaminant Level (MCL). Currently, this well is limited to providing irrigation water through the raw water system. As a result, the Pintail Well is the sole provider of potable water for the community. In recent years, the Canvasback and Pintail Wells have experienced significant declines in groundwater levels. Arsenic levels in both wells continue to fluctuate. The Pintail Water Treatment Plant (WTP) improvements were constructed to bring groundwater supplies into compliance with the State Water Resources Control Board—Division of Drinking Water (DWW) MCL for arsenic. The goal of the project is to enable the Canvasback Well to serve as an active production source by providing treatment at the Pintail WTP. The Pintail Well has historically remained below the MCL for arsenic, but the new facilities will also provide the capability to treat Pintail Well water if arsenic levels at that source rise above the standard in the future. As a result, the project ensures that either Canvasback or Pintail groundwater can be reliably used as a potable supply while meeting drinking water standards. The Pintail WTP consists of two-skid mounted filter vessels and associated piping, valving, and controls; a 225-gallon sulfuric acid tank and chemical feed equipment for pre-treatment pH adjustment; a 225-gallon sodium hydroxide tank and chemical feed equipment for post-treatment pH adjustment; and a 16,500-gallon backwash tank. The arsenic treatment system treats water from the Pintail Well directly. It also has capacity to treat water from the Canvasback Well via the raw water line between the Pintail and Canvasback Wells. All improvements are confined to the previously disturbed and developed footprint of the existing Pintail pump station, which is surrounded by a CMU block wall and two access gates. No grading or land expansion occurred beyond the existing facility boundary. No new wells were drilled, no increase in water supply capacity occurred, and there are no changes to the overall operation of the water system other than the treatment of existing groundwater to meet DDW drinking water standards. Pursuant to California Health and Safety Code Section 116275, a Public Water System (Community Water System) is required for the Wild Wings residential community. A Community Water System is defined in the Health and Safety Code as a “public water system that serves at least 15 service connections used by yearlong residents or regularly serves at least 25 yearlong residents of the area served by the system.”