Sewer District Master Plan
The Town, with the assistance of consultants Weston & Sampson, has engaged in a Sewer District Master Plan.
The Sewer Master Plan is for the Town Sewer District wastewater collection system, which is the collection system tributary to the Surfside Wastewater Treatment Facility. The sewer master planning for the Siasconset wastewater collection system will be completed as part of the Siasconset Comprehensive Wastewater Management Plan (CWMP).
Development of a Sewer Master Plan will help the Town of Nantucket to determine where and how to connect and route future wastewater flows into the Town Sewer District’s existing wastewater collection system. The potential future flows include the following:
- Needs areas identified in the 2014 CWMP Update,
- Development and redevelopment within the existing Town Sewer District,
- Areas of interest outside of the existing Town Sewer District that have expressed the need to connect to the collection system,
- Flow increases in the collection system, e.g. from multiple dwellings per property.
The additional wastewater flows should be accounted for in the master planning so that the capacity of the existing collection system and all needed downstream system upgrades can be analyzed together. This will allow the system upgrades to be properly planned and sequenced. Ongoing infrastructure planning, such as a new Sea Street Pump Station force main, would benefit from and be included in the master planning analysis.
The wastewater in the Town Sewer District collection system is pumped to the Surfside WWTF via the Sea Street Pump Station, the Surfside Road Pump Station, the South Valley Pump Station, and the new Monomoy South Pump Station recently completed as part of the Shimmo and Plus Parcels Sewer Extension Project. The Town Sewer District collection system consists of four (4) separate sub-systems which are tributary to the individual pump stations noted above, as shown on the image below.
The town is currently conducting a CMOM Program, which includes flow metering, partial sewer system capacity analysis and hydraulic model development. The flow inputs for that model are based on flow meters installed in eight (8) locations, mainly in the system that is tributary to the Sea Street Pump Station. Seven (7) of the flow meters were located in the Sea Street Pump Station tributary area. One (1) flow meter was located in a section of the Surfside Road Pump Station tributary area. Flow metering in the remainder of the Surfside Road Pump Station, South Valley Pump Station, and Monomoy South Pump Station tributary areas was not included in the CMOM Program. Therefore, the South Valley and Monomoy South areas were not modeled as part of the CMOM hydraulic modeling. As part of the Sewer Master Plan effort, Weston & Sampson will coordinate with Hazen & Sawyer, the Town’s CMOM consultant, to share data and information.
Scope of Work
Task 1 - Development of Future Wastewater Flows
Weston & Sampson will work with the town to identify the areas of future wastewater flow including the 2014 CWMP needs areas, planned development and redevelopment within the existing sewer district, areas of interest outside of the existing sewer district, and the anticipated allowance for the construction of multiple dwellings on properties. Once the future wastewater flow areas and the allowance for the construction of multiple dwellings per property are determined, the estimated future wastewater flows for each area will be determined.
Task 2 - Evaluate Routing Alternatives
Weston & Sampson will identify and evaluate routing alternatives for connecting the future wastewater needs areas to the existing collection system. A GIS map identifying the recommended routing alternatives for each of the needs areas will be provided. As part of the sewer routing evaluation, the downstream collection system capacity will need to be evaluated.
For future flows identified as tributary to the Surfside Road Pump Station collection system, Weston & Sampson will update the existing collection system hydraulic model developed as part of the Nantucket Harbor Shimmo and Plus Parcels Sewer Extension Project. The evaluation of the downstream pump stations will serve to provide additional details on the system operations and limitations for consideration in the capacity analysis. The pump stations anticipated to be included in this evaluation are Abrem Quarry, Aurora Way, Cato Lane, Pine Valley, Sachems Path, Sherburn Commons, and Surfside Road.
For future flows identified as tributary to the Sea Street Pump Station collection system, Weston & Sampson will provide the flow information and connection location to Hazen & Sawyer, the Town’s CMOM consultant, for evaluation of the downstream system capacity of the Sea Street Pump Station collection system.
The future flows from the Shawkemo area have already been identified as tributary to the new Monomoy South Pump Station. The evaluation was included in the downstream capacity analysis completed as part of the Nantucket Harbor Shimmo and Plus Areas Sewer Extension Project. A dedicated low-pressure main has been installed as part of the Nantucket Harbor Shimmo and Plus Parcels Sewer Extension Project to convey the future wastewater from the Shawkemo area to the Monomoy South Pump Station. If additional future wastewater flows beyond the Shawkemo area are added or if it is determined that the allowance for multiple dwellings on the properties in the Shimmo and Shawkemo areas need to be increased, the downstream capacity analysis completed as part of the Nantucket Harbor Shimmo and Plus Parcels Sewer Extension Project will be revised.
For future flows identified as tributary to the South Valley Pump Station collection system, Weston & Sampson will evaluate the capacity of the collection system tributary to the Airport Pump Station and the South Valley Pump Station. The evaluation of the downstream pump stations will serve to provide additional details on the system operations and limitations for consideration in the capacity analysis. Recognizing that other evaluations have been completed recently at the South Valley Pump Station and the Airport Pump Station, our work will be limited to evaluation of the potential hydraulic impacts.
For future flows from the Miacomet Needs Area and from properties along South Shore Road, Weston & Sampson will evaluate the feasibility of installing a gravity sewer along South Shore Road from the intersection with Surfside Road and Fairgrounds Road to the Surfside WWTF. This option would allow for the diversion of flow from several of the existing pump stations along South Shore Road (Abrem Quarry, Sachems Path and Sherburn Commons), which currently pump flow to the Surfside Road Pump Station. This would allow for additional capacity at the Surfside Road Pump Station. This option would require a new pump station at the WWTF to pump the flow into the headworks. However, based on the depth of the proposed sewer, several of the existing and proposed pump stations along South Shore Road could potentially be eliminated.
Task 3 – Develop an Overall Force Main System Model
The wastewater in the Town Sewer District collection system is pumped to the Surfside WWTF via three (3) force mains that manifold together just prior to the WWTF headworks. The force mains include the 20-inch DI force main from the Sea Street Pump Station, the 16-inch HDPE force main from the Sea Street Pump Station and the 12-inch PVC force main from the South Valley Pump Station. The Surfside Road Pump Station force main is configured so that it can discharge into either the 20-inch DI Sea Street Pump Station force main or the 16-inch HDPE Sea Street Pump Station force main. The Monomoy South Pump Station force main is manifolded into the 12-inch PVC South Valley Pump Station force main.
Weston & Sampson will develop an existing force main system hydraulic model to identify the overall system hydraulics with multiple pump stations operating with multiple force mains. Once the existing force main model is calibrated, a future force main system hydraulic model will be developed. This model will provide the town with a mechanism to identify the force main system hydraulics with planned future pump stations/force main systems operating, including a new Sea Street Pump Station force main and a new Madaket Pump Station and force main. The hydraulic model will provide a mechanism for the town to evaluate future pump station/force main connections for areas that may not have been envisioned as part of the current sewer master planning.
Task 4- Review Ongoing Infrastructure Planning
Ongoing infrastructure planning including a new Sea Street Pump Station force main, NGRID upgrades, water system upgrades, stormwater system upgrades and roadway improvements will be reviewed. Weston & Sampson will evaluate potential impacts and logistics coordination of the ongoing infrastructure planning with the recommended wastewater collection system upgrades.
Task 5- Review Surfside WWTF Capacity
Weston & Sampson will review the flow and loading capacity of the Surfside WWTF as determined in the 2014 Updated CWMP. The flow and loading analysis will be updated based on the projected future flows identified in Task 1.
Task 6 – Prepare the Sewer Master Plan Report
The Sewer Master Plan Report will be prepared, summarizing the findings of Tasks 1 through 5. As part of the report, Weston & Sampson will prepare preliminary cost estimates for the recommended downstream collection system upgrades; will advise on changes needed to sewer regulations for consistency with the Sewer Master Plan; and will prepare written protocols for the Town on how to handle potential future developments that may arise in areas outside of the Sewer Master Planning.
Task 7 – Project Administration and Meetings
Monthly progress meetings will be held with the town staff to review project status and address the technical aspects of the work. In addition to the monthly progress meetings, this task includes presenting the Sewer Master Plan at public hearings/meetings, as well as providing Town Meeting support for the addition of properties to the Town Sewer District.
This page was created and last updated on November 12, 2019.