November Meeting and Breeze

11/2019 meeting at Lafayette from Tom Pfeffer at the City of Duluth

Hi Jim,

Apparently, out of ignorance, one of the TV news reporters suggested the pipe lining project would improve the standing water alone the curb lines…which is not the case.  During my “unplanned” presentation, one of the questions that came out was “…will this [sewer lining project] get rid of the standing water…” and my answer was “no, this project will reduce the amount of sewage that needs to be conveyed to WLSSD”.

We have multiple problems out there…1) the surface of the road is very flat and irregular which results in standing water (regardless of the source); 2) surrounded by lake superior, the high ground water surrounds and seeps into public sewers and private basements; 3) there is only one sanitary sewage pipe (currently on the lift bridge) that conveys sewage off the Point.

 

• Sanitary Sewer Flows are a composite of all that flows “down the drain”, plus ground water and rain water that seeps into pipes/manholes.  Based on CCTV video inspections of the underground pipes, we know that some water seeps into the pipe.   We know that when the lake level is higher and when it’s raining, we get more relatively clean water seeping into the sanitary sewer mixing with the sewage increasing the volume needed to be pumped to WLSSD.  Occasionally, the combined  volume is more than can be pumped off the point, and the sewage backs up in the pipes/manholes.   It eventually backs up out of the lowest elevation manholes, which (for the sanitary sewer) happen to be located near 17^th-19^th Streets.   The back-up of sewage comes out of the manhole and spreads out on the road and along the curb line or other low points.

 

• Surface/storm water flows to storm sewer catch basins and pipes which flow to the lake.  The sources of surface water are rain, melting snow, and sump pump discharges.   If the ground surface is flat and/or poorly graded, the surface water does not drain to the catch basins and thus does not go to storm sewer or the lake.  If the storm sewer pipes are plugged with sand, debris, or standing water, they do not drain.  In either case, the result is relatively clean water standing on roads and along gutter lines.

 

• Numerous homes have basements that are below ground water level.  They utilize sump pumps to capture the relatively clean water before it gets into their basements.  The water is pumped to discharge on the ground surface…thus, contributing to surface water flows.

This current project is phase 2 of the CIPP lining of the sewer main (public owned) pipes.   Once these mains are lined and made water tight, the next phase [3] we will resume inspecting and requiring private service lines be lined or replaced to stop any ground water from getting into the sanitary sewer.   THESE PROJECTS ARE REDUCING THE SANITARY SEWAGE FLOWS by reducing or eliminating ground water seeping into the system.  We are confident this will help lower flows enough to allow the current pump/pipe system to convey sewage off the Point without backup.  We are therefore reducing/eliminating the occasional ‘sewage backup’ on the road in the gutter.

This project does not fix ground surface drainage of yards and roadways.  This project does not add new storm sewer drainage systems.  This project does not eliminate or reduce surface water flows.

Back to your questions…”will this make any difference with all the standing water along the road”  yes and no.    YES, for that very small portion of standing water that is actually sewage that occasionally occurs due to sewage back up.  NO, the majority of the standing water is surface water that can’t get to the lake.

Your theory is sound in that by not entering the sanitary sewer system that water would remain in the ground/lake.   Again, in theory, perhaps you can say the lake level should rise after we effectively seal off the sanitary sewer and service pipes.   BUT, will that rise in the lake level be perceivable or measureable, I would say not.

Our first priority is to get the sanitary sewage safely off the Point and eliminate sewage backups.

Hope this helps,

Tom

Tom Pfeffer | Senior Engineer | MN Licensed PE | City of Duluth | 411 West First Street, Duluth, MN 55802 | 218-730-5104 | tpfeffer@duluthmn.gov