The Labyrinth

The Water Main tunnels run beneath the street grid of Downtown Saint Paul, carrying city water mains and providing the fire hydrants with water. They also carry fiber-optic trunk cables. These shallow-running tunnels seem to be the most heavy-traffic system in the Labyrinth, with new work in progress every time we explore them. They're all equipped with bright florescent lights, which are turned on in about 1/4 of the system at a given time, which is nice on the headlamp batteries.

The tunnels themselves are mostly through raw sandstone, although in some places there are brick or cinderblock walls. As in the Telephone Tunnels, all major intersections are marked with street signs. The main water main (heh heh), a pipe about 3 feet in diameter, runs along Wabasha Street.

There are short, dead end side tunnels throughout the system (not shown on our map): these are where water lines either go up (usually rungless) vertical shafts to hydrants or disappear up into the sandstone. At one point in the system there is a little office, complete with coffee maker, swivel chairs, and maps of the city's water mains (most of which do not run through tunnels, sadly).

The shallowest of the Labyrinth tunnels, the Water Main Tunnels often run into the foundation pits of construction sites in the downtown area. While exploring the Water Tunnels, we've come out in foundation pits three times, and once, when they were doing major road construction, we exited in the middle of Kellogg Boulevard.

The following excellent article is from a private newsletter distributed to city employees. While it is specifically about the Water Tunnels, much of the info applies to the other systems of the Labyrinth, as well.

PipelineExpress 2, no. 13 (July 13, 2001)

Most Saint Paul residents don't know it, but the sandstone under their downtown streets are riddled with hand dug tunnels. Over 2.6 miles of water tunnels, started by the private St. Paul Water Company in 1856, have been constructed in downtown Saint Paul. The arching walls, usually just bare sandstone, average four feet wide by six feet tall. However, in faulted areas brick arches of concrete walls supply additional support. Tunnel depths below ground elevation range from 25 feet in the west to less than 10 feet near Cedar Street.

The main entrance to the tunnels is through the courthouse, although emergency and service access can be gain through numerous man-holes scattered throughout the system. Security of the tunnel system is of primary importance, and all possible points of access are carefully secured to insure control and safety of the system.

In 1883, the City of Saint Paul was authorized to buy the water company by the Minnesota State Legislature, and during the years following this purchase, the tunnels were extended to a total length of over two miles.

The upper geology of the downtown Saint Paul area consists of a limestone layer covering a much softer layer of sandstone. This St. Peter sandstone contains many fine particles where were "cemented" together by the pressure of a great layer of overburden that has since been eroded away.

This sandstone, often referred to as sandrock, is still somewhat soft, and can be easily removed using simple hand tools. Since the overlying limestone is a much harder substance, tunnels were dug to carry water distribution pipes instead of the more typical "open trench" method.

Early tunneling was accomplished by hand laborers using shovels, picks, and wheelbarrows. The pickmarks of these laborers' tools can still be seen in the walls and ceiling of the tunnels today.

Present tunneling, though limited to very small service extensions called "drifts," is still constructed using the same basic methods of excavation, although air-powered tools have replaced the pick for breaking away the sandrock.

The tunnels contain pipes ranging in size from 4 to 20 inches in diameter, The pipes convey water to over 50 domestic and residential services in the downtown area. These customers consume nearly 10 million gallons of water per month. In addition, these pipes supply water for fire hydrants and auto-fire connections.

The tunnels provide ready access to the pipes and fittings, making maintenance and repair easy and fast. Continuous inspection and maintenance of the numerous valves and fittings lessens the possibility of interrupted service. Should a break or leak occur, any necessary repairs can be made without disrupting city traffic.