UC Davis will pay a mandatory penalty of $27,000 to the California Water Quality Control Board for violations of effluent limits at the campus's wastewater treatment plant between April and December 2008.

The violations, technically described as "non-serious violations," were triggered automatically when effluent samples slightly exceeded the monthly limits for electrical conductivity set by the wastewater discharge permit then in force.

Campus officials said the problem was caused by salt in the water, and that investments in water and wastewater improvements should prevent the violations from recurring.

Most of the salt in the 2008 effluent originated as naturally occurring minerals dissolved in the groundwater that UC Davis uses as its water supply. A small amount came from the use of water softeners at the campus's central steam plant.

Since 2000, the campus has spent a total of $23 million to construct and then expand the wastewater treatment plant. About $300,000 has been invested in testing and reducing salt discharges from the central steam plant.

Since Jan. 1, 2009, the campus has operated under a new wastewater discharge permit.

"We expect to be in full compliance with the new permit," said David Phillips, director of utility services.

The university will ask the water board for approval to use the penalty monies for ongoing projects to improve Putah Creek, as allowed under state law.