Fourteen years later, the city of Des Moines is still paying the cost for leaky gasoline tanks.

Gasoline contamination was discovered in the soil and groundwater near the two city gas tanks at the Des Moines City Public Works Building in 1992.

The tanks, which were found to have been leaking, were removed and cleanup work was started on the site.

In 1994, contaminated soil that hadn't already been removed was cleaned using a soil vapor extraction system. The soil contamination was found to be at or below cleanup levels in 2006.

A pump and treat system for cleaning the groundwater was started, which has continued until recently. The clean water was then discharged to the Midway Sewer District system.

Thirteen monitoring wells were installed, two of which were used for groundwater extraction.

Only seven of the wells initially indicated contamination above cleanup levels. Today only the two extraction wells are showing contamination above the cleanup levels.

The level of gasoline contamination has dropped from 200,000 parts per billion (ppb) in 1994 to 91,000 ppb in 2008.

In April of this year, Midway Sewer District sent city officials a letter indicating a permit from the state Department of Energy (DOE) was required before discharging the cleaned water into the sewer system.

The DOE ordered the operation be shut down until a permit was obtained. There is a one-time application fee of $4,151 and an annual permit fee of $1,038.

Des Moines contracted AMEC Earth Environmental for $151,559 to help with the permit process, expanding the water cleanup efforts and making the project compliant with the requests of the DOE.

The city will also pay the sewer district $.05 per gallon, including back charges for the last year as of the notice date.

Des Moines' projected cost to Midway for discharge from April 2007 into 2009 is $15,625.

The pump and treat system is old not treating the water as well as a new system could, said Paul Stull, a senior engineer for AMEC.

"It's undersized, it's been out there for quite some time and the equipment is starting to fail," Stull said at a presentation to the city council on Sept. 11.

"I'm surprised it's lasted this long, these systems typically last six to 10 years."

The city must install an activated carbon treatment device to reduce the effluent levels of the treated water to acceptable levels before being discharged.

Des Moines must also resume quarterly inspections of the wells. Sampling was cut back to twice a year as a cost saving measure.

The DOE also states that the monitoring wells should be properly shut down before operation. One of the monitoring wells was accidentally paved over when Water District 54 put in a new water tank.

The well must be found and uncovered so it can be abandoned properly.

Expansion of the cleanup process will include three air diffusers placed into the wells that will pump air into the groundwater, promoting natural biodegradation of the gasoline.