In three separate sewage-line ruptures in 2012 and 2014, millions of gallons of untreated waste spilled into Valley Forge National Historical Park and a federally protected tributary of the Schuylkill.

In an agreement between Tredyffrin Township and Pennsylvania's Department of Environmental Protection late last year, Tredyffrin officials had until early 2016 to decide on a long-term plan to prevent more sewage spills.

Township officials decided this summer to install a new pipe that will fit into the existing Wilson Road Force Main sewage pipeline, which is nearly 40 years old.

This week, Tredyffrin's board of supervisors approved an agreement to share the costs of fixing the pipeline with the four other municipalities the pipeline serves.

East Whiteland Township officials said they would sign the agreement if several revisions were adopted, including capping the township's share of the project at a little more than $5 million.

On Tuesday, Tredyffrin urged those in Malvern, Easttown Township and Willistown Township to quickly sign agreements.

The agreement Tredyffrin officials approved this week creates a cost-sharing formula based on each municipality's average sewage flows for the last three years and projected future flows.

The Valley Creek Trunk Sewer System transports untreated sewage from the municipalities to the Valley Forge Sewer Authority wastewater-treatment plant in Phoenixville. The Tredyffrin Municipal Authority owns the system, which the township operates on behalf of the other member townships.

Tredyffrin officials called the agreement "a cooperative solution in ensuring the safe operation of the line and the protection of human health and the environment well into the future."

The Department of Environmental Protection found that Tredyffrin and its municipal authority violated the Clean Streams Law when more than 18.3 million gallons of sewage spilled into Valley Creek in 2012 and 2014.

Under Tredyffrin's agreement with the Department of Environmental Protection, the township had to submit an emergency response plan in case of future ruptures to the state agency by last January.

Tredyffrin officials plan for construction to begin in January 2016. Their goal is to finish by early summer to prevent construction from thwarting activities at the national park.

mbond@philly.com 610-313-8207 @MichaelleBond