The Russian and Petaluma rivers may be just 30 miles apart and in the same county, but they aren't treated equally.

Nor are the sewage treatment plants that discharge into them.

Petaluma is in the midst of spending $110 million to build a sewage treatment plant and disposal system that will process wastewater to two standards, secondary and tertiary.

The secondary level will be flushed down the Petaluma River between November and April or used to irrigate farmland. The tertiary, more highly treated water, will be used to irrigate parks and golf courses.

"The ranchers who use our wastewater don't need tertiary, so there is no need to go to that added expense. But for our parks, we will be going to tertiary," said Michael Ban, Petaluma's water resources and conservation director.

Ban said about 40 percent of the 2 billion gallons of wastewater Petaluma processes a year is now reused.

Cities and sewage districts north of Petaluma that discharge into the Russian River must treat their wastewater to the more expensive tertiary level in almost all cases.

Tertiary treatment means wastewater has had 99.99 percent of solids removed and can be used to irrigate edible crops, playgrounds and residential landscaping.

Catherine Kuhlman, executive officer for the North Coast Water Quality Control Board that oversees the 1,485-square mile Russian River watershed, said the extra level of protection is "because the community depends on the Russian River and its reputation as a place to drink clean water and recreate."

Petaluma, however, is in a different drainage basin and is under the authority of the San Francisco Bay Regional Water Quality Control Board.

Recreation on the Petaluma River is largely limited to boating while its drinking water suitability is tainted by the saltiness of San Pablo Bay's tidal basin.

You can reach Staff Writer Mike McCoy at 521-5276 or