The $700 million Interstate 99 (I-99) construction project has unearthed a water pollutant that could affect its completion.

While excavating a section of Skytop Mountain last fall, construction crews found acid rock in a sandstone layer. This environmental hazard could negatively affect the high quality of Buffalo Run, a tributary of Spring Creek.

"The levels of acidity and certain metals could be potentially damaging to the plants and aquatic life there," said Dan Spadoni, north-central region spokesman for the Department of Environmental Protection (DEP).

Spadoni said these acid rock discharges from five locations were unexpected. Although preliminary tests are always conducted and assembled before construction in an official Environmental Impact Statement (EIS), events like this still occur.

"The potential for these kinds of accidents always exists, but is very rare," said Marla Fannin, spokeswoman for Pennsylvania Department of Transportation (PennDOT). "In this case, the formation of rock was vertical. But the core boring is used primarily for showing horizontal rock formations."

The environmental threats are not man-made. Instead, the harmful substance comes from a fill area where water comes into contact with pyretic materials, a combination of acidic and metallic substances, Spadoni said.

In the five years working on the highway project to connect Grays Woods to Port Matilda, PennDOT has encountered no setbacks, aside from this current pollution problem.

Locally, this roadway will cut the commute for thousands of people driving from Philipsburg and Altoona. Deb Sipe, who works in the Earth and Mineral Sciences' dean's office, is a Philipsburg resident who carpools to Penn State. She is looking forward to I-99's benefits. "On an average day, it takes 35 minutes, assuming we don't hit a lot of congestion or an accident of some sort," Sipe said. "But if the weather is bad, it can take several hours. I-99 will sure help congestion around Port Matilda, because we won't have that traffic light to be concerned with."

PennDOT is chemically treating the environmental hazards on I-99. Spadoni said PennDOT has submitted a monitoring and remedial plan to DEP, the Pennsylvania Fish and Boat Commission and Patton Township. "PennDOT should respond sometime next month," Spadoni said. "Our goal is to see this issue solved in the most environmentally responsible manner."

Although this pyritic material presents an added difficulty to I-99's projected completion this year, Fannin said she does not believe it will have a large impact on the construction process. "Since we are in the middle of the winter season, this hasn't had that significant of an impact so far," Fannin said. "There is the potential at Skytop to set us back a couple months at most. As we look at this, we are still on schedule."

The Associated Press contributed to this report.