Where applicable, content Copyright 2007,
City of Martinsville
55 W. Church St.,
Martinsville, VA 24114

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WATER TREATMENT PLANT

The City of Martinsville maintains a Water Treatment Plant near Clearview Drive. The purpose of the plant is to provide clean, safe and dependable drinking and process water to the public.

Raw water enters the plant from the Beaver Creek Reservoir, which is the usual, primary source. Water from other sources, at Leatherwood and Little Beaver Creeks, may be employed during droughts and emergencies. These are all usually very clean sources, but treatment and testing are required for any surface water source.

Once raw water enters the head of the plant, chemicals such as alum, fluoride, lime and chlorine are added and then mixed in flash mixer. The chemical-water mix enters a series of compartments called flocculators that stir the mixture at decreasing rates of speed. Any dirt or organic matter in the water reacts with aluminum sulfate and lime to create snowflake-size particles of a size and mass to settle out of water.

This settling process takes place in long sedimentation basins. These basins are cleaned of the accumulated sludge, with its entrapped matter. This is evacuated to a special sludge dewatering lagoon and sent to the wastewater plant for further processing.

The disinfected water is then given a finishing process through filtration. Deep filter beds of anthracite, sand and gravel are used to filter away any trace of particulate matter. There are five filters, each capable of filtering 2 million gallons per day. Filters are back-flushed regularly to keep clean water flowing into the clearwell, a special containment area where final adjustments are made to the water prior to pumping it into storage tanks supplying business and residents.

At the clearwell, sodium hexametaphosphate is added to reduce water corrosivity. The pH, or acid-alkaline balance of the water, is adjusted to 7.6 with trace amounts of caustic soda, and chlorine is added for disinfection. The water is then ready for drinking, and is pumped into storage.

BACKGROUND

The current Water Purification Plant was built in 1948 (on the site of prior plants dating back to 1893), with a then maximum capacity of 5.0 million gallons per day. In 1981, the plant was expanded to treat a maximum of 10.0 million gallons per day. Approximately three million gallons are currently pumped each day to eight storage tanks with a combined capacity of 5.7 million gallons located at different points within and outside the City.

The plant is in operation 24 hours per day, seven days per week. It is staffed by state certified operators and management personnel. The laboratory technician operates the bacteriology lab, located on premises and manages laboratory equipment. Maintenance personnel may be employed as needed.

Operators attend short schools and complete various training courses that enable them to sit for state certified examinations. Operators holding a Class I certificate are at the most advanced level.  The operators are responsible for maintaining chemical dosages, performing required laboratory testing, and reporting the results to state regulatory agencies. The Virginia Department of Health (VHD) is the primary supervising agency for water operations in Virginia.

The laboratory is certified for bacteriological examinations. No less than 15 samples are taken from various locations throughout the city. Results are reported monthly, and public notice may be given if any condition exists that would be hazardous to the public. This is generally required of all types of samples.  Copper and lead samples may also be taken within the city, at specified times, with the results being reported to the appropriate agency.

WATER CHEMISTRY

Following is a list of chemicals used to treat water. Usual chemical addition is in parts per million, equivalent to mg./L., the weight of chemical material used to treat water often being no more than a trace amount per gallon.

Aluminum Sulfate- Aluminum Sulfate, or "Alum" is used in water treatment as a coagulant. Dirt and organic particles suspended in natural, untreated water normally carry a negative electrical charge. These particles are attracted to the positive charges created by aluminum sulfate. Combined alum-contaminant particles grow in size, eventually settling out of suspension and being removed from the water. The measurement of matter in water, turbidity, determines the dosage, which is generally around 40 mg./L.

Lime- Lime is used for pH adjustment and corrosion control. The city has very soft water, but with the addition of lime (Calcium Hydroxide) to water, a pipe-protecting coating is created within the distribution system. The average dosage of lime is about 3 mg./L.

Hydrofluosilicic Acid- This is fluoride, added to drinking water to prevent tooth decay. Fluoride at the optimum levels, of 0.9 to 1.2 mg./L. added by the city to treated water, can reduce the incidence of tooth decay among children by 65%.

Sodium Hydroxide- Sodium hydroxide, or "caustic soda" is used for pH control. The influent or "raw" water from the city reservoir has an average pH of 7. This is neutral on the pH scale measuring acidity and alkalinity. After addition of other treatment chemicals, the pH drops to 6.0, which is weakly acidic. Sodium Hydroxide is added to adjust the final pH of treated water to 7.6. This is considered an ideal pH goal and is weakly alkaline. The average dosage is about 15 mg./L.

Sodium Hypochlorite-Sodium Hypochlorite is a solution containing chlorine used for water disinfection. It is the most important water treatment chemical. Toxic bacteria and viral material are killed or rendered harmless by chlorine. Water is safeguarded from the presence of typhoid and other pathogens that killed many people before water treatment became widespread. The chlorine level remaining in treated water is about 1.3 mg./L.

Sodium Hexametaphosphate-Phosphates are added to treated water to prevent pipe corrosion. Although phosphates soften water, the city uses phosphates in conjunction with lime to form over time, a cement-like pipe coating. The usual dosage is about 1.0 mg./l.

Carbon-Activated carbon is used when necessary for taste and odor control. During spring and fall months seasonal changes occur in water sources causing the lake to "turn-over." This natural change may bring an increase in the raw water of minerals such as iron and manganese combined with sulfur. This may cause discolored water, and create taste and odor problems. Certain algae may also cause problems. Activated carbon added at these times at a dosage of about 1.0 mg./L. can remove odorous constituents. Problems generally last for about one week, and may not occur at all.

Polymer- Polymers are organic coagulants that act much like alum. Used only experimentally at the City’s plant, they may be used seriously for improving water quality, once necessary testing has been completed.

FUTURE

The Water Purification Plant has created a radio SCADA (Supervisory Control and Data Acquisition) system to monitor storage and flow and control chemical levels. Using the talents of operators proficient in computer skills, the treatment plant continues to develop technologically sophisticated applications for the water field. Many manual operations have been harnessed to the power of the computer and made more reliable and cost efficient.