The town of Queensbury, New York?s existing water treatment plant, constructed in 1975, was approved to treat 3.25 mgd and served a customer base of just more than 1,500. Average water production was approximately 1.3 mgd. As the customer base climbed to 6,500 in the late 1980s, demand grew to average flows of 2.8 mgd to peak flows of 7.5-8 mgd. The plant was producing this volume with all equipment operating at full capacity. In addition, there was no standby capacity.
Preliminary discussions concerning expansion coincided with plans to become a regional water supplier, but the plant?s 1975 plans called for a total build-out capacity of 15 mgd, without avenues to accommodate further growth.
The town?s needs were as follows:
- Meet increased capacity demands
- Position the town to be a regional water supplier
- Expand the plant beyond its build-out capacity
- Provide cost-effective water rates to users
- Comply with federal and state environmental regulations
- Accomplish the objectives within defined budget constraints
Engineers from O?Brien & Gere began with a review of the water system and recommendations addressing a range of issues: system expansion/improvements to the supply, treatment, storage, transmission, distribution, and system administration. They delivered a report that contained a review of needs of surrounding communities, which could be served by an expanded system; flow projections and feasible water system expansion alternatives for each community; cost estimates for expansions to the existing treatment, transmission and distribution facilities; and detailed user costs for each community in the proposed regional service area.
Storage and Distribution
Hydraulic modeling developed information needed for storage and distribution system improvements for the town. The engineers simulated new water demands in the model to identify potential weak areas. Proposed improvements then were applied to the model to determine their effect on the water system.
To meet the increased flow requirement in the distribution system, a new 1-million gallon storage tank was proposed. To alleviate low-pressure problems, engineers recommended a new 16-inch diameter pipeline, to be installed under a divided highway in the area of the proposed tank.
Treatment Plant
Evaluation of the treatment plant included a review of process alternatives as well as facility expansion from 3.5 to 15 mgd. Design considerations included:
- plant capacity
- treatment process selection
- solids handling
Existing process components were evaluated to establish capacity increments and to optimize treatment processes. Low-head automatic backwash filters were compared with high-rate deep-bed, multi-media filtration. Existing sedimentation basins were compared with upflow solids contact clarifiers and tube settlers. A soda ash feed system also was evaluated for optimizing chemical coagulation.
Filters
The original treatment plant used a low-head automatic backwash filter. Upon review of the plant hydraulics and water quality produced by the filters, it was determined that existing filters could be maintained throughout the expanded plant. The addition of three filters provided a total capacity of 15 mgd, with one spare filter for standby. Each filter is rated at 3.75 mgd. During construction, however, the existing filters experienced difficulties and were replaced.
Clarifiers
Existing clarifiers at the plant were uncovered and encountered winter freezing problems. Final design and construction of the expansion included modifications to the existing two clarifiers and addition of two more. Tube settlers were included along with a new sludge collection system and pumping system. All four clarifiers were covered.
The rapid mix facility for this plant required modifications to feed the four flocculation clarifier basins. A new in-line rapid mix with bypass met this need.
Pumping Station
Design elements improved hydraulic performance without major capital expenses. The existing high-lift pumping station had difficulty meeting capacity demands due to wet well hydraulics. In lieu of drastic modifications to the wet well (located under the administration center), a new 15 mgd high-lift pumping station was included in the expansion design to operate in parallel with the existing station.
This provided improved utilization of clearwell storage capacity and emergency standby capabilities. The new pumping station is structurally designed to permit the addition of two additional pumps and future expansion to 30 mgd.
New variable speed motor controllers, installed for the existing raw water pumping station and the new high-lift pumping station, permit the town to achieve new peak flows in the summer and maintain operation during minimum flows in the winter.
The existing plant?s raw water pumping station consisted of vertical turbine pumps, constructed in cans embedded in concrete. The hydraulics study showed that the bottoms of the cans needed to drop 8 feet to provide hydraulics needed to increase flow. New pumps were then provided.
Chemical Feed System
The existing chemical feed system needed safety enhancements, design efficiencies, and operational necessities.
To address concerns regarding health hazards, the chlorine gas system was converted to a liquid hypochlorite system. This design feature eliminated the need for emergency notification and evaluation procedures as well as the need for a gas scrubber and structure to house the scrubber.
Water supplies are drawn from the Hudson River, which exhibits low alkalinity and low pH with a high natural organic material (NOM). Treatment processes included pH and alkalinity adjustment to enhance coagulation and NOM oxidation. Alum is used as the primary coagulant with caustic soda for finished water pH adjustment.
Sludge Management
Sludge disposal had been a recurring problem for Queensbury. Two new lagoons and three freeze/dry beds provided storage and long-term conditioning for waste removal. The natural freezing and thawing action released more water from the sludge and resulted in significant reductions of sludge volume and disposal cost savings. By recycling water to the head end of the plant, further economies were achieved.
The Hudson River raw water intake did not provide for control of zebra mussels. Chemical injection points were installed at each of the three existing screens to control zebra mussels and protect the water treatment process.
Instrumentation and Control
The instrumentation and control system was rehabilitated to improve reliability, maintainability, and monitoring of plant and remote sites. The distributed I/O topology minimized I&C wiring costs and provided improved system control, data monitoring, and data logging/storage.
Improvements to the electrical system include upgraded electrical service to 4,000 amps with new distribution to load centers throughout the facility. Low and high lift-pumps were retrofitted; new high-lift pumps are furnished with variable frequency drives for flow control and water demand monitoring. Harmonic distortion, typically a concern with large drives, was addressed in the equipment specifications to achieve compatibility between drives and the upgraded power distribution system.
The process layout and expansion exceeded the 1975 buildout capacity. The existing plant?s original design did not readily accommodate an expansion of this magnitude. Addressing this issue, the existing site layout was redeveloped to accommodate the new facilities for increased capacity and process changes. Existing facilities were totally incorporated into the final design to accomplish the final design requirements and to achieve cost savings.
Increased fresh air ventilation, in existing and new construction, is supplied through heating and ventilating system improvements. The boiler room was relocated to improve ventilation and to house upgraded equipment. A new dehumidification system improved conditions in the expanded gallery, and the new construction has multi-staged ventilation and perimeter heating for maximum flexibility in operation.
Conclusion
The plant went online in 1997. There was no loss of service during construction.
The expanded plant meets rigid standards, improves the plant?s indoor environment, and provides users with a reliable water source. The new facilities were designed to meet new federal regulations. These include D/DBP, enhanced coagulation, and enhanced surface water treatment.
The final cost of $12 million was more than $1 million under the estimated budget of $13.2 million. This included costs to replace the existing filters, an unexpected benefit.
The plant is capable of being expanded to a final capacity of 30 mgd, providing room for future growth and regional development. With the project more than $1 million under budget, the town passed its savings along to users in the form of reduced water rates. As regional communities purchase water, rates will continue to drop.
With the ability to serve as a regional supplier of water to surrounding communities, the area?s growth is promising. Rates are attractive, and resources are dependable and available.
