A 47,000-foot pipeline buried beneath the Casper area quietly carries the wastewater of thousands of residents — and it’s starting to show its age.

The North Platte Sanitary Sewer Interceptor, or NPSSI, begins on the west side of Paradise Valley and snakes its way underground, collecting flow from Casper, Mills, Bar Nunn, and several Natrona County water and sewer districts. It all ends up at the Sam H. Hobbs Regional Wastewater Treatment Plant on the city’s east side.

It’s a piece of infrastructure most people never think about — until it fails.

City engineers say the massive concrete pipe has been slowly eaten away by hydrogen sulfide gas, a corrosive byproduct that forms in wastewater systems. A 2012 assessment flagged the problem and recommended lining the interceptor and replacing

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