An oil refinery in Roosevelt has agreed to pay more than $300,000 in penalties for dumping too much ammonia into the sewer system.

Pennzoil Products refinery was cited in August 1991 for violating its state permit for ammonia discharge.The permit allows Pennzoil to dump 100 parts of ammonia per million parts of water, but it has been dumping two to three times that rate.

Ammonia is toxic, but it also promotes algae growth in waterways, choking animal life and leading to the putrefaction of the waterway.

In a settlement reached this week with the state Division of Water Quality and the attorney general's office, Pennzoil has agreed to construct a wastewater treatment facility by May 1994 to bring the refinery into compliance with state water-quality regulations.

The company also agreed to pay a civil penalty of $303,000. Of that, $223,000 will be paid to the state in cash and $30,000 may be used to fund an environmental mitigation project somewhere in the state. A project in the Book Cliffs is under consideration.

The remaining $50,000 of the total penalty is suspended contingent upon Pennzoil's constructing the treatment facility on time. If the company fails to meet the deadline, it must also pay $9,000 per month for every month the facility is not in operation.

Coming to the refinery's rescue in February 1992, Roosevelt officials petitioned the state unsuccessfully to amend the refinery's permit so that it could discharge the high levels of ammonia.