American Council of Engineering Companies

2003 Engineering Excellence Grand Award

CATEGORY D - WATER RESOURCES

WWTF UPGRADE & SEWER SYSTEM REHABILITATION

POULTNEY, VERMONT

After completing a combined sewer overflow improvement project only 2-1/2years earlier, Poultney still had quite a problem. They were still experiencing significantly higher flows into their wastewater treatment facility (WWTF) during any high groundwater and/or heavy rain event. These high flows would overwhelm their 28 year old facility, four to six times per year, resulting in untreated discharges to the Poultney River. The Vermont Department of Environmental Conservation (VTDEC) was prepared to issue a consent order to stop the overflows. VTDEC had already issued a sewer connection ban, effectively eliminating Poultney’s ability to connect any new users to the wastewater system. To compound their problems, Poultney’s discharge permit also required them to meet stringent phosphorous reduction limits no later than 2001, as part of the effort to clean up Lake Champlain. With an already heavy debt burden, Poultney trustees doubted they could get voter support for the necessary bond issue to support the project cost of improvements.

Based on past flow data, VTDEC was prepared to require Poultney to upgrade the WWTF to a 750,000 gpd capacity to handle the high seasonal flows.  This would have required extensive and costly improvements to the WWTF. Our work started with a comprehensive study of the wastewater collection system, to determine the sources of the high flows that were overwhelming the treatment facility. An innovative flow sensitivity study was conducted to determine how much flow could be eliminated by specific collection system improvements. This was critical to the overall success of the project. This study demonstrated that flows could be reduced through some specific collection system repairs and improvements, justifying a lesser capacity increase to 500,000 gpd at the WWTF. At this permitted capacity, the existing WWTF structures could be re-used for a majority of the upgrade, resulting in a substantial savings of construction costs.

One infiltration problem was along Grove Street where nearly one hundred year old sewer lines were buried nearly twenty feet deep. This section of line became flooded from the Poultney River during much of the spring. This line was so deteriorated that in-line repairs were not practical. The replacement of this line was coordinated with a pending VTrans road re-surfacing project to minimize the cost to the Village for the repairs. With a winter design and early spring bid, the Village was able to replace the sewer as well as a deteriorated water line in this roadway, provide storm drain improvements that eliminated a street flooding problem and have the road sub-base completely reconstructed without delaying the scheduled road resurfacing in mid August of the same year. Since VTrans saved the cost of co-planing this road prior to re-surfacing, they agreed to increase the thickness of the wearing surface of the completed road by 3/4" at no additional cost to the Village!

A backyard sewer serving residents along Bentley Avenue was another source of significant inflow and infiltration. This sewer also served as a storm drain inlet for an intersection of Maple St. and Main St. This sewer line was replaced and storm drain improvements were completed to separate the storm drain system from the sewer system and allow several roof drain leaders from commercial properties to be separated from the sewer system. Two undersized main waterlines were also replaced and each of their dead ends were closed to create a new loop. Bentley Avenue was re-constructed and re-graded to improve storm water collection.

The WWTF was converted from an extended air treatment process to a sequential batch reactor (SBR) treatment process. Several existing structures were re-used and we took advantage of biological phosphorus removal to reduce the use of chemicals and meet the phosphorus limits by 50%. Ultraviolet disinfection replaced chlorine for final treatment removing another chemical stream from the final effluent. Combining the treatment facility capacity increase with the phosphorus reduction improvements allowed the Village to maximize the benefit of the phosphorus grant funding. They were able to complete a $5.1M overall project with only 30% local share.

Poultney’s goals of reducing the amount of rainwater and groundwater flows to the WWTF and completing the improvements to the collection system and WWTF with a minimum of cost was achieved. This was possible because of the innovative flow sensitivity study that identified specific collection system improvements that assured substantial flow reductions. This allowed for a more reasonable permitted capacity for the WWTF. Since the completion of the project, it has been demonstrated through actual flow data that the sensitivity analysis was correct and the reductions in infiltration/inflow projected from our study were indeed achieved. With the ability of the SBR treatment system to handle high peak flows, the untreated bypass overflows to the Poultney River have been completely eliminated and Poultney is able to meet their new stringent phosphorus reduction limits in a new state-of-the-art and energy efficient WWTF. An additional benefit was the complete re-construction of two major roadways in the Village; Grove Street and Bentley Avenue, which demonstrates the practical benefit of multi-use design and construction.

HIGHLIGHTS

• Innovative flow sensitivity study reduced WWTF capacity requirements by 30%

• Collection system improvements have reduced flows to WWTF by 20%

• Phosphorus reduction has been achieved and untreated overflows were eliminated

• Maximized grants resulted in local share of only 30% of $5.1M total project cost

Photo and award plaque