Savannah River Diversion
The Savannah River supplies North Augusta’s drinking water. Water taken directly out of the river is NOT SAFE TO DRINK due to bacterial and parasitic conditions. It would probably make a person sick from ingesting pathogenic bacteria and parasites such as Cryptosporidium and Giardia. The water to be treated is pumped out of the river and is piped underground into our raw water settling basin.
Pre-Sedimentation
The Pre-Sedimentation basin is where the treatment process really begins. The raw water is delivered to the headwork’s of the water treatment plant where the first of 5 major unit water treatment processes start the treatment to make the water safe to drink. The major processes include chemical coagulation, flocculation, sedimentation, filtration, and disinfection. There are chemicals added to the water as it enters the various treatment processes.
Chemical Coagulation
The first chemical added is chlorine dioxide and it is an oxidant used to break down naturally occurring organic matter such as decaying leaves and other plant material. A chemical coagulant known as aluminum sulfate is used as the primary coagulant. The coagulants are added at the rapid mix unit; this is a unit that creates turbulent mixing energies to help thoroughly disperse the chemical coagulants into the raw water and to begin the coagulation process. The coagulants cause very fine particles to clump together into larger particles that can then be removed later in the treatment process filtration.
Flocculation
The coagulated water then flows to the next major unit process, the flocculation process. Flocculation is a slow stirring process that causes the small coagulated particles to form floc. The flocculation process promotes contact between the floc particles and the particulates in the water. Generally, these contacts or collisions between particles result from gentle stirring created by a mechanical mixing. There are four sets of flocculation basins that contain mechanical mixers that the water passes through to gently stir the coagulated water. The floc formed creates a surface in which the particulates in the water adhere to the surface of the floc thus forming larger particles for ease of removal by sedimentation and filtration.
Sedimentation
The flocculated water then flows to the next major unit process, the sedimentation process. The purpose of the sedimentation process is to remove suspended solids that are heavier than water and to reduce the particulate load on the filters. Sedimentation is accomplished by decreasing the velocity of the water being treated below the point where it can transport settleable suspended material, thus allowing gravitational forces to remove particles held in suspension. When water is almost still in sedimentation basins, settleable solids will move toward the bottom of the basin. This process of sedimentation removes almost ninety percent of the solids in the water. The clearer water on the surface is collected in the launder tubes that direct the water to the filter to remove the remaining ten percent of solids.
Disinfection
The settled water then flows from the Sedimentation basin to the filter influent troughs. Before arriving at the filters, sodium hypochlorite is added to the water at the pre-chlorination point to begin the disinfection process. The disinfection process is designed to kill or inactivate most microorganisms in water, including essentially all pathogenic organisms whether they are from bacteria, viruses or intestinal parasites. Pathogenic organisms are the microscopic “bugs” in the water that can cause waterborne diseases such as gastroenteritis, typhoid, dysentery, cholera, and giardiasis.
Filtration
The chlorinated settled water then flows into the filters for the last of the major unit processes used to treat the drinking water. Filtration is the process of passing water through material such as a bed of coal, sand, or other granular substance to remove particulate impurities that were not removed during the sedimentation process. The water treatment plant uses rapid rate dual media gravity filter beds. The filters are comprised of a top layer of anthracite, a middle layer of filter sand and then a bottom layer of garnet sand and one an underdrain system that collects the filtered water. The water enters on top of the filter media and passes down through the filter beds by gravity. The different materials work like a giant strainer and trap remaining particulates. When the filters start to get packed full with particles, the operators clean them using a procedure called “backwashing”. Potable water is run backwards through the filters releasing the entrapped particulates that are collected in drain troughs. The backwash water is sent to the waste holding tank and then on to the Aiken County Public Service Authority Wastewater Treatment Plant.
The water that is collected from the bottom of the filters is then considered potable. Before the water leaves the clearwells chlorine is added a second time for post-disinfection. The additional chlorine ensures that the water remains safe to drink even at the furthest reaches of the distribution system. In addition to the chlorine, fluoride is added to our drinking water at the plant. When fluoridated water is drank during the years of tooth development, the fluoride strengthens teeth and prevents tooth decay. The United States Public Health Service has determined the optimum concentration for fluoride in United States water to be in the range of 0.7 to 1.2 parts per million. Dissolved fluoride-containing minerals are measured year round in the water of the Arkansas River. The natural fluoride content of the river water averages .4 part per million. The water treatment plants enough fluoride to raise that level to .9 parts per million. The fluoride level is measured daily at the water treatment plant and monthly at the tap to make sure it is sufficient to meet the concentration recommended by USPHS.
Finished Water Storage
After the water leaves the Filtration Facility all of it then flows into the two finished water storage tanks. Water sampling lines from the tanks are piped to the Water Treatment Plant Laboratory so that testing can be performed to ensure the finished water is safe to drink.
