The Josiah Chase Water Filtration Plant was put into service in 1990 and was designed to produce water that meets or exceeds all primary and secondary drinking water standards.  The treatment plant is designed to produce a maximum of four million gallons per day and is located off Chase’s Pond Rd across the street from Chase’s Pond Dam.  The treatment process at the plant is known as direct filtration.     Raw water enters the screen house next to the dam and flows by gravity through a 30” ductile iron main to the treatment plant.  Aluminum sulfate (the primary coagulant) and sodium hydroxide (used for pH adjustment) are added to the raw water to ensure proper coagulation and flocculation (chemical conditions) of the water before entering the clarifiers and finally the filters. Polymer(a coagulant aid) is occasionally added during the cold weather months to aid in the coagulation process.

The process water is then filtered using two up-flow adsorption clarifiers (roughing filters) and then sent to four conventional mixed media rapid sand filters (polishing filters). After the filtration process is complete, the finished water enters a 300,000 gallon clearwell where chlorine is added to promote proper disinfection by killing pathogenic organisms.  Finished water is then pumped up from the clearwell and two additional chemicals, Sodium Silicate and Ammonia, are added prior to entry into the distribution system.  Sodium Silicate is injected to help control or reduce corrosion in the distribution system and to also increase the finished water pH thereby reducing the corrosiveness of the treated water.  Ammonia is added to combine with free chlorine to form Chloramines, a weaker, yet longer lasting form of chlorine that prevents formation of Disinfection Byproducts (DBPs).

Disinfection Byproducts (DBPs) can form when chorine added to the water during the disinfection process reacts with natural organic compounds.  All surface and ground waters can be expected to contain some amount of natural organic compounds.  These compounds can react with the chlorine to form DBPs such as Trihalomethanes (Thms) and Haloacetic Acids (Haas).  Thms and Haas are regulated suspected carcinogens.  To reduce the risk of forming high levels of DBPs, the York Water District adds Ammonia to the finished water before it enters the distribution system.  Ammonia reacts with the chlorine to form Chloramines which prevent further formation of these DBPs while in the distribution system.

In 2004 and early 2005 significant changes were completed at the treatment plant as recommended by our engineers or required by new regulations.  These changes were approved by the Maine Drinking Water Program (DWP).  The first change relocated the aluminum sulfate storage and addition location from the screen house, at the head of Chase’s Pond Dam, to the treatment plant building. This change was mandatory to keep us in compliance with a new EPA rule called “the Filter Backwash Recycle Rule”.  The second change was to switch from use of chlorine gas to the less hazardous substance sodium hypochlorite or liquid chlorine.  The District has recently adopted a revision of our existing master plan that was prepared by our engineering consultants to guide the Districts capital improvement budget for the coming years.