Squamscott River Siphon Improvement Project regularly updated

Updates from Public Works regarding the ongoing Squamscott River Siphon Improvement Project.

Project Updates

7/26/24 - The sewers are all constructed and active as required by the project.  The previous siphon has been discontinued.  For next week, there is another sewer manhole cover in the parkway that needs to be lowered and landscaping activities will continue.  

7/19/24 - Sewer lines were installed at the Mill side of the river connecting the sewer collection system to the new inlet structure and siphons.  The new siphon is now active.  Next week's activities include pipe testing of new sewer lines, finishing the inverts and covers for the structures and starting the restoration efforts.

7/12/24 - Sewer and drain lines are being constructed near the Mill buildings.  Progress is slow because of rubble and buried structures from previous building foundations and disinfectant contact chambers. Swasey Parkway was patched and the work area consolidated for the weekend events.  Work will continue next week installing sewers at the Mills to connect to the new siphon inlet chambers.

7/10/24 - The contractor continues to lay sewer and drain line on the Mill side of the project. On Thursday and Friday an additional crew will begin cleaning up Swasey Parkway in preparation for public events. 

6/28/24 - The siphon inlet and outlet structures have been set and the siphon pipes have been connected to them.  The sewer manhole that connects to the existing pumpstation piping required modification and will be set next week.  On Saturday, crews will form up the concrete chambers within the inlet and outlet structures.  Next week gravity sewer main work will commence on the Mill side of the river.  The contractor will not work next Thursday, Friday and Saturday for the holiday.

6/21/2024 - The contractor installed the siphon outlet structure and connected the siphon pipes to it on the Swasey Parkway side of the river.  On Saturday, 6/21 crews will set the inlet structure on the Mills side of the river.  Next week, siphon pipes will be connected to the inlet structure.  The crews will then return to the Swasey side and connect the outlet structure to the pumpstation piping.

6/14/2024 - The drilling contractor demobilized from the site. Concrete structures and PVC piping were delivered to the project. Excavation for the outlet structure began on the Swasey Parkway side.  Crews will work on Saturday to set the outlet structure.  Work will continue on the Swasey side of the river next week. Towards the end of the week, work will start on the MIll side of the river to install the inlet structure. The following week, work will continue installing sewer on the Mill side of the river.

6/7/2024 - The 12-inch HDPE siphon pipe was delivered to the Mill side of the river and was fused together. The 12 inch bore hole was reamed to 18 inches in diameter on Wednesday, June 5th. The siphon pipe was successfully installed on Friday, June 7th. A small crew will be filling the newly installed pipe with water over the weekend in preparation for testing on Monday, June 10th. The drilling subcontractor will be demobilizing from the project. Work will begin next week on the Swasey side of the project installing sewer pipe and structures to accommodate the new siphons. Exeter TV produced a short video update on the successful pipe pull which can be viewed on their YouTube channel.

5/31/2024 -  Drilling efforts with a paddle bit were successful in making it across the river on Friday from the Mills to Swasey Parkway. Next week, the second drill rig will be utilized with an 18-inch reamer to enlarge the hole from Swasey Parkway toward the Mills. Twelve-inch HDPE pipe will be delivered to the Mill side of the project on Monday where it will be fused together. Once the reaming operation is completed, the pipe will be pulled across the river.

5/24/24 - The 6-inch rock drill was successful in drilling through the ledge knob.  A 12-inch reamer has enlarged the hole in the ledge.  Next week a paddle bit will be inserted through the 12 inch ledge hole in an effort to make it to the Swasey Park side of the river.

5/17/24 - The contractor removed rubble from the clarifier remains at the mills prior to drilling operations. A 6-inch rock drill is currently underway.

5/10/24 - On Wednesday, May 2^nd, the Sewer Siphons Project drilling subcontractor began drilling an exploratory probe using a paddle bit. This probe, which occurred at the original plan elevation, was performed to ascertain if any other ledge outcroppings exist between Swasey Parkway and the known outcropping on the Mill side of the river. On Tuesday May 7^th, the probe reached the known Mill side ledge, confirming that no additional ledge outcroppings exist between that location and Swasey Parkway. On Wednesday, May 8^th, the paddle bit was adjusted both horizontally and vertically in an attempt to find a path over the ledge outcropping. This effort proved unsuccessful after several attempts. The exploratory probe was then removed from the river.
Based on the findings, the general plan for the next phase of the work is to bore from the Mill side of the river with a 6-inch rock bit to establish a pilot hole through the ledge outcropping. This hole will then be reamed to a diameter of 12 inches. Once enlarged, the paddle bit will be inserted through the bored hole and drilling will proceed until it reaches Swasey Parkway.  It is anticipated that the hole bored through the ledge will need to be enlarged to 18 inches prior to siphon pipe installation.

Updates 2020 - April 2024

PLEASE TAKE NOTE:

· Appropriate traffic control measures will be in place.  
· All driveways will remain accessible.
· Soil borings will cause some noise and disruption.
· Fieldwork will occur between 7:00 AM and 5:00 PM

If you have any questions regarding any of this work, please do not hesitate to contact Paul Vlasich, P.E. at pvlasich@exeternh.gov or by phone at (603) 773-6160.  

Project Background

There are two parallel 8 inch inverted sewer siphon pipes under the Squamscott River that transport sewage from approximately half of Portsmouth Avenue and surrounding neighborhoods via the Webster Pump Station. These siphons were installed in 1965. Engineering analysis has determined the siphons are at capacity during normal dry weather flows and undersized for any further additional new connections or during extreme wet weather events. Sanitary sewer overflows (SSOs) have occurred immediately upstream of the two siphons at Duck Point at the bottom of Jady Hill Avenue.

The original scope of this project was to continue use of the existing siphons and to add another siphon pipe to increase the current capacity. This increased capacity would in turn allow improvements to the Webster Avenue sewage lift station, thereby increasing its pumping capacity as well. This project would provide capacity for future sewer uses such as sewer extension to Holland Way, Hospital expansion, or development along Portsmouth Avenue. This project will also reduce the probability of sanitary sewer overflows (SSOs)

This project is eligible for financing through the Clean Water State Revolving Loan Fund (SRF) including 10% loan principal forgiveness.

Note that this project description was updated 4/15/2021 to reflect the findings of the siphon inspections and the resulting change in project scope.

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