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The Appomattox River Water Authority was created by the General Assembly in 1962 under the Water & Sewer Authorities Act to provide an adequate water supply to its members. Membership is made up of the City of Petersburg, the City or Colonial Heights, Chesterfield County, Dinwiddie County and Prince George County.
The Brasfield Dam impounds the Appomattox River to form the Chesdin Reservoir. The reservoir stores approximately 9.3 billion gallons of water. The dam is 55 feet at the highest point, 1250 feet long and has an 800 foot long spillway.
Raw water from the Chesdin Reservoir is pumped up to the treatment plant using raw water pump stations #1 & 2 through a 42 and 54 inch water main to the treatment plant.
Water enters the rapid mix building and pre-feed chemicals are mixed. Lime (pH adjustment & alkalinity addition) and alum (coagulant) can be added here. The water passes through a combination of mixing chamber and is mixed by one or both of the turbine mixers.
Raw water with chemicals added is sent to the flocculators. All ten flocculators are horizontal paddles and over/under baffles. Stirring is done at progressively slower speeds, called step flocculation, as the mixture proceeds through the three chambers of the flocculator.
Water is distributed from the flocculators into one of twelve settling basins. The majority of the floc created by chemical addition drops to the bottom of these basins because of the density and weight of the floc.
Sludge is removed daily by siphon from the basins using a Clar-A-Vac system.
The settled water is taken off the top at the ends of the basins by v-notch weirs and deposited into a pre-filter flume from one end of the plant to the other.
Water is distributed from the pre filter flume into the filters located inside the main or filter building. There are 32 filters that work in pairs. The maximum filter rate is 4 gallons per square foot of filter area per minute. Normally filters are used at less than the maximum rate of flow.
Filters #1-16 are comprised of 24″ of granular activated carbon, 12″ of sand and 12″ of gravel in the filters. Filters #17-32 have 24 inches of granular activated carbon and 24 inches of sand. Granular activated carbon helps in the removal of contaminants including taste and odor compounds, organic color, total organic carbon (TOC), and industrial organic compounds.
When the filter’s pores become clogged, they need to be cleaned. One of the best ways to clean a drinking water system’s filter is to backwash it, meaning reversing the flow and increasing the velocity at which water passes back through the filter. All filters are equipped with air scour to aid in backwash cleaning. The air scour allows for better filter cleaning in a shorter period of time.
The pipe gallery collects filtered water from the effluent of filters 1 thru 32 and proceeds to post mixer #1. The pipe gallery also contains piping for filter backwash.
Filtered water enters mixer #1 where post chemicals are added and mixed. Post chemicals chemical addition includes: sodium hypochlorite (disinfection), caustic soda (pH adjustment), phosphate (pipe corrosion protection) and fluoride (dental decay protection).
After leaving CW#3 the water is metered, sampled, additional sodium hypochlorite is added, ammonia is added and caustic (ph adjustment) may be added. The sodium hypochlorite & ammonia mix is called chloramines, a weaker but longer lasting disinfectant than chlorine that retards DBP (Disinfection-By- Products).
There are three clearwells, underground water storage reservoirs, on site. Clearwell #3 has approximately 5.5 MG of storage and usually accepts filtered water that has been chlorinated. Clearwell #2 has approximately 5.5 MG of storage and usually accepts finished water from CW#3 and after sodium hypochlorite and ammonia has been added. Clearwell #1 has approximately 1.0 MG of storage and usually accepts finished water from CW#2.
Finished water can be fed to the transmission system or pumped out if necessary. Gravity feed is preferred to keep costs down and prevent excess pressure in the system. Pumping can be done from either finished water pump station #1 or finished water pump station #2.