The Nicholasville Water Treatment Plant was originally constructed as a .75 MGD facility in 1954. The original plant consisted of a river intake pumping station, chemical mix facilities, flocculation/settling basin, filtration, finished water storage and pumping.
In 1967, the plant was expanded to 1.5 MGD with the addition of a second intake pumping station and raw water main along with an additional flocculation/settling basin, two additional filters, and a second finished water storage tank.
In 1975 the plant underwent a "high rate" expansion, which increased treatment capacity to 3.6 MGD. This project included intake pumping improvements, the addition of "tube settlers" to existing settling basins, high rate expansion of existing filters with the addition of dual (anthracite and sand) media, and construction of a third finished water storage tank.
Continued growth of Nicholasville and Jessamine County has resulted in the most recent 1990-1992 expansion of the plant to its current capacity of 6.0 MGD. The recent expansion also addressed concerns about the adequacy of the existing intake pumping stations during low river pool levels, which were experienced during the 1988 drought. The plant expansion included a new river intake pumping station (with deeper intakes), a new 24-inch raw water transmission main, new chemical feed facilities and chemical mix basin, additional flocculation basins, additional settling basins, two additional filters, a new treated water storage tank, new high service and backwash pumping station, new sludge lagoons, and an upgrade of the computer plant instrumentation system for the monitoring and control of treatment plant operations.
In 1993, at the annual convention of the Kentucky/Tennessee chapter of the American Water Works Association, the Nicholasville Water Treatment Plant was presented the "Award for Excellence in Operations" for treatment plants in the capacity range of 5-10 million gallons per day. This award was given, in part, in recognition of the superior quality water produced at the Nicholasville Water Treatment Plant.
Nicholasville's water treatment plant draws surface water from Pool 8 of the Kentucky River for treatment. The existing plant is a conventional turbidity removal plant that utilizes chemical coagulation, flocculation, settling and filtration to remove suspended particles from the raw water.
The following is a brief and simplified description of the various treatment processes, which are utilized within the Nicholasville Water Treatment Plant.
Raw Water Pumping—Untreated water is pumped from the Kentucky River (approximately 330 feet vertically) to the plant for treatment. Raw water pumping facilities consist of three intake/pumping towers, each of which supports two vertical turbine pumps. The newest tower, constructed in the 1990-1992 expansion, has the capability to withdraw water at a depth of 10 feet below river pool stage (allowing maximum utilization of pool storage during a drought).
Chemical Mix Basin—The raw water enters a high energy-mixing chamber where it is treated with several chemicals for a variety of purposes.
The primary coagulant, which is added to aid in the removal of fine suspended solids, is polyaluminum chloride or PAC, which has a specific gravity of 1.29. Since these solids by themselves, are too small to be removed from the water by gravitational settling within a practical period of time, a coagulant is added to increase particle size and weight, thus improving solids removal during the sedimentation and filtration processes.
A liquid polymer is also added as a coagulant aid to increase the efficiency of the coagulation process, and to help remove Total Organic Carbons, or TOC's.
Potassium permanganate can also be added as an oxidant to reduce taste and odor form several naturally occurring organic formations found in the Kentucky River such as algae growth during the summer months.
Powdered activated carbon is also available to be fed for occasional taste and odor problems or possible chemical spills in the Kentucky River.
The plant has the capability to feed either chlorine or chloramines for disinfection. These chemicals are used to destroy or inactivate potentially harmful bacteria and other microorganisms in the water, and also to provide residual disinfection within the distribution system.
Flocculation Basins—The PAC reacts with the natural alkalinity of the water to form a gelatinous precipitate. As the water passes through the flocculation mixing chambers, this gelatinous precipitate entraps the fine suspended solids and forms larger and denser masses called "floc".
Water is gently mixed in the flocculation basins with "stirring paddles" which facilitate the creation of larger "floc" particles as the suspended solids come into contact with each other.
Settling Basins—From the flocculation basins, the water flows to settling basins where quiescent settling conditions permit the "floc" to settle out of the water. To facilitate more efficient settling, each basin is equipped with "tube settling" modules. The clarified water is collected in weir troughs and is conveyed to the filters.
Filtration—After the treatment process of coagulation and sedimentation, the clarified water flows into dual media filter beds to remove any remaining solids.
The filter beds are constructed of layers of anthracite, filter sand, and supportive gravel. Twenty inches of anthracite having an approximate diameter of 1.0 mm rest over ten inches of fine sand with an average diameter of 0.5 mm.
As the water passes down and through the filters, the remaining suspended solids become entrapped in the interstices of the filter media. At routine intervals, the filters are cleaned of the entrapped solids by forcing clear, finished water in the reverse direction at high velocities. This reverse flow is called backwashing, and is required to remove the build-up of captured solids within the upper levels of the filter media.
The Nicholasville Water Treatment Plant has six filters. The four older filters each have a rated capacity of .75 MGD and the two newest filters have a rated capacity of 1.5 MGD each.
After filtration, fluoride is added to the treated water to improve dental hygiene. Chlorine (or chloramines) is added after filtration for disinfection.
Corrosion Control—After filtration, zinc orthophosphate, a corrosion inhibitor is added to inhibit the leaching of lead and copper from the pipes in your homes, by creating a thin film on your pipes.
Finished Water Storage and Pumping—Following filtration, the treated water is temporarily stored in concrete reservoirs called "clearwells". The Nicholasville Water Treatment Plant has four clearwells with a combined storage capacity of over 900,000 gallons. From the clearwells, the treated water is pumped directly to the Nicholasville water distribution system.
Instrumentation—Plant operations are monitored and controlled by a computer based Supervisory Control and Data Acquisition (S.C.A.D.A.) system. The S.C.A.D.A. system monitors and controls pumps, chemical feeds, treatment equipment, flow rates, water levels, etc.
Water Quality Monitoring—Continuous water quality testing is performed at the Nicholasville Water Treatment Plant. Water is tested for turbidity, alkalinity, hardness, iron, manganese, fluoride, pH, corrosiveness, and disinfectant residual.