CARLISLE, Pa. (WHTM) – The Pennsylvania Department of Environmental Protection says a contractor working for the borough of Carlisle is responsible for pollution that caused the deaths of more than 200 fish in North Middleton Township last month.

In a notice of violation sent to the borough this week, the DEP says the contractor was performing a “cure in place” pipe installation about 50 feet upstream of the fish kill in Letort Spring Run, on the grounds of the Army War College.

The work was part of the borough’s ongoing Letort Interceptor rehabilitation project.

The installation process used by the contractor used heated water in contact with a Styrene-based resin. Styrene was found in water samples from five stream locations, according to the notice.

In addition, an unpermitted release of raw sewage was observed from a portable pump hose flowing onto the ground and into Letort Spring Run. The pump station was used by the same contractor, the notice states.

DEP requested that the borough submit a written report of its own findings within 15 days. The department’s investigation is ongoing.

It’s estimated that approximately 250 brown trout died, along with about 60 smaller fish.