When a resource is inexpensive, safe, and convenient, it’s easy to take it for granted. For most Americans, access to clean, plentiful drinking water is as easy as turning on the faucet. Greenwood area residents have an extra advantage—our municipal water supply is among the best in the world.
In general, South Carolina water treatment facilities have an exemplary record, but Greenwood stands out among them. Our Commission of Public Works (CPW) has received prestigious awards in the industry and maintains the highest standard of excellence. Meeting these standards requires unwavering commitment and unsurpassed technological expertise.
Deep Well Pump House
It all begins at Lake Greenwood, where deep well pumps, forty feet deep and forty feet long, extract an average of 10-11 million gallons per day. The facility, developed with growth in mind, has a much greater potential of up to 48 million gallons. Jeff Chapman, Water Department Director, pointed out that “the potential for greater capacity is appealing to industries that may be looking at our area as a place to bring their businesses.”
Incoming Water Pipes
The pipes from the individual pumps converge into one line on their way to the plant. At the first treatment step, carbon is added to absorb objectionable taste and odor, caused primarily by compounds in algae. The concentration of these compounds fluctuates with the seasons, and must be monitored to ensure that the right amount of carbon is used. Our Greenwood facility submits samples to a specialized lab in Indiana each week for this analysis. Incomplete removal of these compounds can result in an earthy taste, but this is mainly an aesthetic quality and has no effect on the safety of the drinking water. All health and safety indicators are tested daily in on-site labs.
The second step is the addition of chlorine dioxide, the primary disinfectant. This kills bacteria and viruses and also oxidizes metals, like iron and manganese, that may discolor the water. The water is mixed with the disinfectant in a contact chamber before flowing to the next step, the rapid mixer.
At this stage, alum (aluminum sulfate) is added to adjust the pH balance and aid in the removal of sediment. (Alum is also used in canning pickles and is placed around azaleas to lower the pH of soil.) The rapid mixer induces coagulation. Metallic particles lose their charge and precipitate from the water, forming a substance called floc. From here the water flow is split to travel to several floculation chambers, where giant paddles slowly stir the floc through the water. The floc attracts sediment, which sticks to it, preparing the water for the sedimentation stage.
In sedimentation pools, dirt and mineral particles fall to the bottom, where they drain through a sludge collector. These pools are drained and washed out, on an alternating schedule, every six months. The sludge resulting from the water purification process is treated and taken to a landfill, where it serves as inert material to cover landfill cells.
As the sediment drops to the bottom of the pool, the clear water at the surface drains into collection flumes through small V-shaped notches.
Collection flume with v-notches.
At this point 95% of all particles have been removed from the water. From here it moves to filtration chambers, made primarily of anthracite coal developed for this purpose. The model below shows a cross section of the filtration bed.
After the water is filtered, a secondary disinfectant, sodium hypochlorite (bleach), is added. Our facility makes its own, using solar salt, which is mixed with ammonia to make chloramine. This is a longer lasting disinfectant to protect the water through the distribution process. Lime is added to optimize the pH and minimize pipe corrosion. Finally, fluoride is added, carefully regulated to no more than 0.7 milligrams per liter, well below the maximum recommended exposure level.
The water is finally ready for distribution, and flows into clear wells, one below ground and one above, holding four million gallons and three million gallons, respectively. (These tanks must be periodically inspected by scuba divers who have been completely disinfected.) From here, water is pumped to elevated storage tanks around the county.
Four million gallons of water are stored underground here.
At various stages during the process, the turbidity (particle content) of the water is measured. Typical readings might start at around 200 NTU (nephelometric turbidity units) at the lake, dropping to 1-2 NTU at sedimentation, and then to less than 0.1 after filtration.
Jay Daniels and Jimmy Nix test water quality.
The EPA standard for water leaving a treatment facility is 0.3 NTU. “We have less than 0.1, 100% of the time”, stated David Tuck, water plant supervisor.This places Greenwood’s water quality among the very best in the nation. The American Water Works Association’s Partnership for Safe Water recognized this achievement with their Excellence in Water Treatment award. Mr. Tuck added, “We were the fourth utility company in the country to ever receive this award. There have been only ten of these awards so far. This says a lot for our plant, our staff, and the board that supports us. It takes a lot of maintenance to keep up a facility like this and we have dedicated employees who take pride in the plant and strive to make it look and operate the best it can 24/7."
David Tuck and Jeff Chapman
The next time you fill a glass with water, take a moment to appreciate both the importance of this critical resource, and the extraordinary accomplishment of members of our community dedicated to doing a job the best that it can be done.