Septic Tanks Targeted by GIS Maps in Topeka, Kansas

Topeka, Kan., is using GIS maps to identify homeowners who aren't hooked into the sewer system, which generates revenue.

by / February 25, 2009

Officials in Topeka, Kan. want septic tanks gone, so they use GIS maps to locate households capable of switching to the municipal sewer system. The project has been ongoing since the city passed an ordinance in 1997 mandating that homes close to the sewer system remove their septic tanks, said Kyle Tjelmeland, GIS system analyst for Topeka.

"It becomes a revenue stream for the city," said Tjelmeland. Citizens pay the city more than $1,000 to hook up to the municipal sewer system.

To locate prospects for conversion to the sewer, Topeka's GIS staff crafted a map with layers showing houses near the sewer system that receive water service but no sewer service.

"If they're paying a water bill, but they're not paying a sewer bill, there's a good chance they're using a septic system. Either that, or they're connected to the sewer system illegally," said Tjelmeland.

Septic Tanks Can Pollute

A septic tank receives all of a building's sewage, dissolves the solids, cleans the water and releases it into the ground. Built up solids are pumped out of a tank roughly every five years. One benefit of a septic tank is that it spares from the cost of paying for sewer service. The process is harmless to the environment until the tank starts malfunctioning -- sometimes when the tank has been in the ground 60 years or more, explained Tjelmeland.

"The bacteria and chemicals in wastewater can leach into the ground water. More often that water comes to the surface, getting you a bad smell and standing water, which can breed mosquitoes," Tjelmeland said.

The Environmental Protection Agency gave Topeka a grant years ago to pay for residential hookups, and many residents utilized it. That grant is done. Homeowners now must fund new sewer hookups themselves.

Andy Opsahl

Andy Opsahl is a former writer and features editor for Government Technology magazine.