Trucks rumbling across Sonoma County?s roadways ? moving rock for construction projects and trash to the dumps ? may be forced to pay a tonnage tax because the weight of their cargo is damaging to pavement.

County transportation officials are considering using provisions of their Aggregate Resources Management plan to levy a tonnage fee on rock-bearing trucks in order to defray repair costs on the county?s 1,387 miles of roads.

They calculate that one double container truck, fully loaded with 25 tons of quarry rock, does road damage equivalent to that of 10,000 cars.

?These roads are being worn out in a year or less,? said Walt Keiser, a planning consultant hired by the county to study the issue.

Perhaps surprisingly, some aggregate industry leaders don?t reject the notion of a tonnage fee. But they want the tax applied to other companies that run dump trucks, water trucks, food trucks and grape trucks that also use county roads.

?It bothers me that the aggregate operators are willing to pay a small fee but you have all kinds of trucks out there bring things into the county,? said Marv Soiland, whose family owns the Stony Point quarry. ?There are other people utilizing these roads and we would like to see everyone treated fairly.?

Wendel Trappe, owner of Canyon Rock in Forestville, called the tonnage fee ?like another nail in the coffin to local industry.? He and the BoDean Company, owner of Blue Rock Quarry in Forestville, are already paying $3.5 million for road and intersection improvements in the west county.

?Garbage trucks run year-round and the rock trucks are sitting around for most of the year,? Trappe said.

Environmental activists say payment into the roadway mitigation fund is long past due.

?We support the recommendation and do not support any alternative because that would delay repairs to the roads,? said Kate Wilson, representing the Russian Riverkeeper group.

Dispute over tonnage fee assessment has its roots in the Aggregate Resources Management plan, which supervisors adopted in 1981. It contained a provision for rock extraction companies to pay mitigation fees for road damage, but the practice was suspended in 1994 when aggregate industry interests objected, saying the county lacked a scientific methodology for determining mitigation fees.

In 1996, the county transportation department proposed a 25-cent per ton fee, which was whittled back to 18 cents and still prompted outrage from rock haulers.

Finally, in an attempt to settle continuing disagreement over tonnage fee calculations, the county hired Keiser?s firm to come up with a figure. Keiser calculated that aggregate companies should be charged 57 cents a ton, which would generate from $1.5 to $1.8 million annually.

Armed with statistical back-up, county officials told supervisors last Tuesday that they are prepared to press forward with plans to take up the issue again. The topic was given new emphasis under the supervisors' Strategic Plan, which identified road repair as one of Sonoma County?s most neglected issues.

?The question of the day is not whether to set the fee, but whether or not there should be a phase-in (period),? said Permit and Resources Management Department Director Pete Parkinson.

A report by the planning and the transportation department concluded that supervisors should set the fee on rock trips and then move to set similar ones for waste haulers, logging trucks, water tankers and even buses.

?The most significant factor that causes damage to the supporting structure of the roadway is the number of trucks with maximum legal loads the roadway experiences over time,? the report concluded.

Board chairman Paul Kelley said he was frustrated that the issue had been festering for more than a decade while the county?s road system has deteriorated. A ?pavement condition index? from the Metropolitan Transportation Commission now rates the county?s roads in the ?poor? category, meaning most show signs of road base failure such as potholes and surface deformation.

?I have seen this last a lot longer than it should,? Kelley said. ?I am frustrated that we have not solved this.?

Nonetheless, Kelley acknowledged significant differences of opinion on the level of tonnage fees, so he appointed an ad hoc committee to report back with a recommendation to supervisors in two months.

The group includes Supervisor Efren Carrillo and himself, Parkinson and county transportation director Phil Demery, BoDean general manager Bill Williams and Homer Canelis, whose family operates Austin Creek Ready Mix Inc. in Cazadero.