Unexpected Historic Discovery: Trolley Line is Unearthed during Sewer Project

This March, the construction crew of Green & Main started their day with the objective of laying pipe from the Pilot Project building to the existing sewer line on 19^th Street. However, renovation of the building’s basement made this project more than a simple connection into an existing sewer main.

This historic photo shows one of the many Des Moines streetcars that ran on the Sherman Hill trolley line until 1951.

The lower level of the Green & Mail Pilot Project will be used as a green education center for the public. So significant renovation is taking place in what was the basement of the building. Since the construction crew will have to underpin the entire building, there was a decision made to remove the basement floor and replace it. As part of this process, the entire floor will be lowered to increase the ceiling height, accommodating the comfort of future visitors. However, the elevation of the sewer in the street was already established, and the Green & Main crew needed to tie into the street sewer at a lower level.

Excavation Surprise

Sinkhole resulting from discovered trolley line.

Time to dig up the street!

Prior to digging, all possible existing utilities had been researched via Iowa One Call. (The Iowa One Call notification system is a free call and a free service to anyone planning an excavation in Iowa.) The street was marked to highlight various known lines and the location of the existing sewer. But, not surprisingly, this historic Sherman Hill street had some history to reveal under its layer of asphalt and then layer of brick.

The crew used a diamond saw to cut into the street from the exit of the building to the sewer main under 19^th Street. Suddenly, sparks started flying. Quickly discovered were two old trolley tracks that ran down 19^th Street, along with four wooden rail ties that had provided the frame for the tracks. While digging with an excavator to remove the tracks and rails from the street, the crew also discovered a four-inch cast iron pipe running parallel to the tracks, five feet under the street’s surface.

Des Moines Utilities and Public Works Lend a Hand

The sink hole discovered was the size of a Smart Car!

The construction crew stopped work immediately and made a few calls. Enter Des Moines Public Works, Water Works and Mid-American Energy. As the city crews cautiously investigated the situation, a small sinkhole was discovered under the old trolley line; then an even larger sinkhole emerged about the size of a Smart Car. However, the initial concern remained:  the proper identification of the pipe.

The pipes did not appear on any existing city utilities map. And so to identify the purpose and contents of the pipe, Public Works asked the Green & Main construction crew to drill into the pipe looking for either water or gas. Neither were found, but the pipe did contain some ground water and traces of a petroleum odor. (The electrical lines to run the trolley were typically coated with a tar-like substance to protect the wires). Once deemed safe to proceed, the crew cut and removed the abandoned pipe.

Excavation of street asphalt and brick layer to connect the new plumbing system to the city sewer.

As a precautionary step, Des Moines Public Works scoped the sewer line and discovered that about 25 feet of the existing main sewer line was cracked and had partially collapsed. The sewer line was cleaned and temporarily fixed and the main sewer line will be replaced sometime this year.

Still to be resolved, though, were the sinkholes. A self-leveling grout-type substance filler called K-Crete was pumped into the sinkhole to fill the void, preventing the street from becoming unstable. Public Works crews completed this and the resurfacing of the patched area.

Green & Main Pilot Project Benefits from New Sewer Main

Although this temporary fix resolved some surprise issues under the street’s surface, Green & Main crews won’t be able to connect to the main sewer line for some time as they await Public Works’ permanent repair of the main line. The good news? Since a new sewer main is necessary, when it is in place Public Works will run it directly up to the curb of the Pilot Project building which provides the depth we need to lower the sewer line.

Not only will this provide the needed elevation drop, accommodating the needs of the building, it allows the construction crew to proceed with the installation of the ground work and installation of a subsurface drain within the building. This installation will then allow the crew to reinstall the concrete floor. Much appreciation goes to Public Works’ Jay Bennett, Sewer Operations Manager, and Ron Silvers, Senior Construction Inspector, who worked extensively with the Green & Main crew to develop an ideal solution that would allow them to continue the groundwork inside the building.

The challenge will be that the building will lack the capacity to drain anything into the sewer until the city repairs the sewer and the street. But it’s worth the wait. Pending the completion of the new sewer line, we will continue to work on preparing the building for interior work and its future occupancy.

Street construction barricade around the sinkhole.

– Ann Wilde is a Des Moines marketing strategist and writer who also has a special interest in preserving and creating sustainable communities. She prefers it when plants bloom with minimal human attention.