Plant Spotlight Fall 2017: City of Asheville North Fork Water Treatment Plant

Originally published in the Fall 2017 issue of NC Currents magazine.

General

The City of Asheville is located in
Buncombe County and has a current
population of approximately 124,300. The
City of Asheville, known for its tourism,
is home to the Biltmore Estate and is
nationally known for its craft brewery
industry. Access to the Blue Ridge
Parkway and many scenic parks are just a
short drive from the city.

The City of Asheville currently
operates three publicly owned water
treatment plants. The North Fork and
William DeBruhl Water Treatment Plants
use direct filtration to treat water from
pristine reservoirs, which are surrounded
by 20,000 acres of limited access
watershed. The William DeBruhl Water
Treatment Plant (WTP) draws water from
the 500-million-gallon capacity Bee Tree
Reservoir, while the North Fork WTP
draws water from the 5.75-billion-gallon
capacity Burnett Reservoir.

Asheville Water Resource has 58,198
service connections within the City of
Asheville and Buncombe County. The
water system is designated a “Class
A” system that is permitted to serve a
population of 124,300.

The water system serves an area of
183 square miles, and has 1,681 miles of
water line, 32 water storage tanks,
37 pumping stations, and three water
treatment facilities, with a capacity to
produce and deliver 43.5 million gallons of
water per day.

The North Fork WTP has a design flow
of 31 million gallons per day (mgd) and
operates with an average daily flow of 15
mgd. The maximum daily flow is 16.9 mgd.

History

Water System Improvements: 1948-1967
The original water supply dates back to
1903. In 1951, construction began on the
Burnett Dam and Reservoir. In 1955, the dam
was completed and the reservoir filled. The
resulting reservoir was completed at the cost
of $2.5 million, with 5.7 billion gallons of water
storage capacity and increased water security
for the Asheville/Buncombe County area.

This provided water to the distribution system
through two 16-inch lines, and a 24-inch line.
The Bee Tree and North Fork WTPs treated
their respective waters without filtration.
In 1960, the City began to plan for
increased capacity from the North Fork
WTP by adding a 36-inch water line. In
1963, construction of the 36-inch pipeline
was completed. In 1967, the City began
fluoridation of the water system.

Water System Improvements: 1978-1992
In 1976, construction began on the new
North Fork WTP, which included the
addition of filtration. Four filters were added
giving the North Fork WTP a production
capacity of 25 mgd.

In 1992, plant upgrades at the North Fork
WTP added two additional filters and brought
the production capacity to 31 mgd.

Process Flow Description

Key Treatment Information

1 – Intake tower – three intakes
@ 20’, 50’, 80’
1 – Flocculation basin
6 – 722 sq. ft. filters
1 – Sodium bicarbonate feed system
1 – Sodium hypochlorite feed system
1 – 5 MG clearwell
5 – Chemical injection points

Raw Water Reservoir & Intake Structure

Filter Operation

The Filter Basins include six dual-media filters that are made up of anthracite, sand, gravel and an air scour backwash system. Each filter has an area of 722 square feet and a flow rate of 5 gpm/SF and is equipped with an airscour system  and washwater troughs. The pipe gallery instrumentation includes filter effluent turbidimeters and flow meters. Six filter consoles are located directly above the pipe gallery on the main floor of the filter building. From each console, a manual or automatic backwash control can be initiated via a touch screen graphic display. Automatic backwash can also be initiated from the SCADA system in the operations building, but standard operating procedure is to perform this function at the filter console so that the operator can see the backwash in progress.

Chemical Feed and Disinfection System

Coagulation is achieved using aluminum sulfate prior to the filters. Pre- and postchlorination is achieved using 12% sodium hypochlorite. Post-chlorination occurs after filtration and before the clearwell to allow for the correct CT ratios. The 5 MG clearwell allows time for contact and plant response if high demand occurs (fire, line break, etc.).

Sodium Bicarbonate is added to the treated water to raise the alkalinity to approximately 25 mg/l. caustic soda is added to adjust pH, and zinc orthophosphate is added to provide a protective coating along the interior of the distribution system piping. Finally, fluoride (hydrofluosilicic acid) is added to protect dental enamel.

Solids Treatment

All solids are processed through three tiered lagoons. Backwash water enters Lagoon #1 and flows through to an effluent structure, then enters Lagoon #2. Water enters Lagoon #2 and flows through to an effluent structure then enters Lagoon #3. Lagoon #3 is the largest lagoon and slows the water considerably before it exits through a parshall flume to record and track effluent flow from this system. As backwash waters flow through this tiered system and lose velocity, solids settle out and form a sludge blanket. Primary settling occurs in Lagoons #1 and #2. Typically, sludge is removed from Lagoons #1 and #2 on an annual basis. In 2017, 675,000 gallons were removed from the lagoons. This sludge is taken to the Metropolitan Sewage District and discharged into their ash basin for later treatment. Removal takes approximately five days. Currently, the plant does not have a biosolids program.

SCADA System and Controls

The original WTP built in 1978 was equipped with a control panel with analog instrumentation and a graphic display panel. The expansion in 1992 replaced the panel with a SCADA system. This system consists of multiple computer monitors, Human Machine Interface (HMI) software and a communication network that incorporates programmable logic controllers. This allows the staff to monitor and control plant processes with transducers and actuated valves that will maintain levels within the flocculation basin and filters. Backwash cycles are automated and can be performed in either automatic mode or manual mode.  

The emergency generator and switching gear are designed to start the generator and transfer the WTP to the emergency power source in the event of a power failure. When power returns to the grid, the switching gear senses the availability and begins a time-closed transition switch over. If the grid remains stable for 30 minutes without interruption, the WTP will transfer back to the grid. This transfer is seamless because of paralleling and the closed transition.

The North Fork WTP has two raw water pumps that are run by variable frequency drives. Each, when activated, will operate off a transducer signal to maintain the level in either the flocculation basin or the filters. 

Personnel Development Programs and Certification Programs

Asheville Water offers continuing education classes to their employees. In addition to this, they provide access to professional organizations such as AWWA and NCWOA. A more formalized career ladder for the City of Asheville Culture of Leadership is expected in the future. 

The following certifications are offered for the plant staff

• Surface operator certification
• Distribution certification
• Backflow certification
• Numerous lab certification
• Physical Chemical 1 certification 

Plant Safety and Health Program

Currently, Asheville Water provides basic safety training at the plant level with opportunities for more in-depth training from the City’s Risk Department and Water Administration. They have an individual who is working to provide more training opportunity for all Water Resources Department divisions. 

Awards

• Area Wide Optimization Program
• Clean Air Compliance Award 

Unique Features

• History of the water system – Providing water to Asheville as early as 1903
• Size and quality of the watershed and water (20,000-acre controlled watershed)

Wildlife

The plant sits on the lower portion of a 20,000 acre watershed. It has abundant wildlife living on acreage surrounding the facility. Wildlife such as deer, turkey, bear and eagles nesting can often be seen.

Future Expansion

 The last expansion occurred in 1993 with the addition of two new filters, which increased the WTP capacity from 25 mgd to 31 mgd. The plant currently has excess capacity, and there are no plans to expand it in the near future. The focus is on maintaining, renewing and modernizing existing facilities. Since a biosolids plan does not exist at present, lime stabilization or some other method to deal with the sludge that the facility generates will need to be considered in the future.

Contact Information

Bill Hart, Water Plant Supervisor

3374 North Fork-Left Fork Rd.

Black Mountain, NC 28711

Phone: 828-271-6101

bhart@asheville.gov