Central Wisconsin and communities along Lake Michigan’s shoreline experienced a building boom from the 1970s to 1990s. Steel septic and holding tanks, many from a now-defunct company, TMC Inc., were installed for new and replacement onsite systems. TMC offered several grades of tanks based on wall thickness. According to Chris Olson, assistant sanitarian for the Door County Sanitarian’s Department, most installers purchased the lighter, 1/8-inch-thick tanks, as they loaded easily for transport.Within 15 to 20 years, sometimes sooner, the tar-coated tanks became pitted on the bottom and sides, and especially above the liquid level and around the riser where gases
