Sunday, January 20, 2019

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24/7 Emergency Number 363-2265

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Raw pond water travels from Chases Pond through a thirty inch intake pipe near the bottom of the pond into the Screen House next to the dam. Here large flow through screens remove weeds, leaves, sticks, with other large debris and prevent aquatic animals from entering the filtration plant. The water then flows downhill by gravity through a thirty inch main to the filtration plant. The entire treatment process utilizes only those chemicals which are approved for use in drinking water by the National Sanitation Foundation (NSF) International. Under tough treatment conditions, such as with unusually high metals concentrations during pond turnover or during taste and/or odor problems associated with Algae Blooms, pre-treatment is needed to aid in their removal or destruction. The amount of pre-treatment required varies based on the conditions at the given time and can require multiple techniques and continual adjustment. Under the most challenging situations multiple pre-treatment techniques may be necessary to produce high quality water.

The two pre-treatment techniques which have been used periodically are; chemical oxidation and adsorption. Potassium Permanganate chemical is added to chemically modify or break down objectionable compounds to less objectionable by-products or products that can be removed by filtration. Powdered Activated Carbon or PAC may be added to remove objectionable taste and odor compounds through the process of adsorption directly to the particles and then both are removed during the filtration process. PAC is the most common technique used specifically for taste and odor control because it adsorbs a broad range of taste and odor compounds.
 
The treatment process in the plant starts with the addition of Aluminum Sulfate (the primary Coagulant used) and Sodium Hydroxide (used for pH adjustment) to the raw pond water to create the conditions and reactions required to cause Coagulation; the settling out of previously stable particles and impurities in the water. Turbulence is created through what is known as a static mixer which forces the water into a cork screw like mixing motion. Particles and substances present, those from natural sources and from the chemicals added, grow larger as they collide under the influence of this agitation eventually building to form larger size visible flakes known as “floc”. This process is known as Flocculation. A chemical Polymer is sometimes added during the cold weather months to aid in the coagulation and filtration processes since cold water negatively impacts the process.

  The water now enters the clarification stage which will remove most of the floc particles formed. The plant has two up-flow Clarifiers filled with what are essentially pea sized pieces of plastic material. As the water moves through this material, up to 95 percent of the floc solids are removed. The clarified water then travels to one of four multi-media filters (filters containing three types of filter materials) which will remove or filter particles down to approximately five microns, or fifteen times smaller than the diameter of a human hair at seventy-five microns. At this point, the water has been pre-treated where necessary, then coagulated, flocculated, clarified, and filtered. These processes act as multiple barriers to disease causing organisms. Bleach or liquid chlorine is then added to “disinfect” the water or to kill disease causing organisms that might be present. The chlorinated water now travels in a twisting path through a 300,000 gallon chambered holding tank below the facility known as a Clearwell. The clearwell is designed to provide more than enough time for the chlorine to properly disinfect the water before it reaches the final holding chamber where, when needed, it can be pumped into the distribution system.  

 Disinfection Byproduct (DBPs) can form when chorine added during the disinfection process reacts with natural organic materials.All surface and ground waters can be expected to contain some amount of natural organic materials. These natural compounds can react with chlorine to form DBPs such as Trihalomethanes (THMs) and Haloacetic Acids (HAAs). High levels of THMs and HAAs are regulated as suspected carcinogens. To control formation of DBPs, the York Water District adds Ammonia to finished water as it is withdrawn from the clearwell but before it enters the distribution system. Ammonia combines with the free chlorine to form Chloramines, a less reactive and longer lasting form of combined chlorine. Chloramines form very few DBPs while the water is traveling through the miles of distribution system piping to your home. In addition to the Ammonia, Sodium Silicate, a corrosion inhibitor, is added to the finished water before it enters the distribution system. Sodium Silicate reduces the corrosiveness of the water by raising pH and while in the distribution system it forms a thin protective film on pipes to reduce natural corrosion. Sodium Silicate also helps to stabilize iron and manganese in the system by keeping them soluble in water thereby preventing staining of plumbing fixtures and some water discoloration.


Many plant functions operate through a computer Supervisory Control And DataSCADA Process SCreen Acquisition systemor SCADA.  Where treatment conditions are stable, the filtration plant SCADA system is capable ofmaking drinking water without assistance from operators for short periods of time. The SCADA system also receives and monitors data and information from pump stations and numerous remote sites such as water system storage tanks. The filtration plant is operated based on the amount of water stored in system storage tanks. When a tank drops below a specific level (starting level) the plant starts producing and pumping water from the plant into the water distribution system and when the tanks are full; the plant shuts down. This produces a daily water level fluctuation of more than ten feet in the storage tanks. The District maintains and operates a two million gallon tank at York Heights and a three million gallon storage tank at Simpson Hill. The two system storage tanks are strategically located in the distribution system to improve water pressure and store water for periods of high consumption and fire protection.

Water travels to customers through a large network of water pipes known as mains. These mains vary in size from one-quarter of an inch in diameter to thirty inches depending on the water needs of the area and the individual consumer. The York Water District operates and maintains a water transmission and distribution system that includes more than 90 miles of both year round and seasonal water mains serving over 5000 customers. Approximately fifteen percent of the water produced during the year goes to seasonal customers with the majority being used by year round customers. There are also more than 400 fire hydrants in the system maintained by the District for town fire protection.

Table 1 contains some of the most recent production and system information.

Table 1
 Recent Production And System Information
 YEAR: 2006  2007  2008  2009  2010 
 Total Water Produced (in Millions of Gallons):  342.5  360.1  343.5  314.6  369.7
 Average Daily Production (in Millions of Gals):  0.94  0.98  0.94  0.86  1.01
 Maximum Daily Production/Date:  2.41 (7/25)  2.47 (7/26)  2.29 (7/16)  1.97 (9/7)  2.47 (8/20)
 Minimum Daily Demand:  0.39  0.32  0.36  0.42  0.31
 Active Metered Customers*:  5040  5066  5105  5118  
 Total Miles of Piping(Transmission+Distribution)  91.1  91.3  91.2  91.5  
 *Annual, Seasonal, and Summer Lines
York Water District 86 Woodbridge Road PO Box 447 York Maine 03909 207-363-2265