ORS § 371.515
The district shall pay the county for all the actual expenses and salary of the county engineer while the county engineer is engaged in work for and at the request of the board of directors, and for the cost of all work done by the county in the district at the request of the board of directors, which shall be the amount agreed upon between the county court and board of directors prior to the time such work is commenced or, if no agreement is made, the actual cost of the work done by the county, including a reasonable charge for depreciation of county equipment used. If, after written demand by the county court, the district fails to provide sufficient funds by taxation for the payment of all sums owing to the county, the county court may, by its order entered in its records, extend a special assessment against all the taxable property within the district in an amount sufficient to pay the amounts due the county. This assessment shall be extended upon the county tax roll and shall be assessed and collected in the same manner as the assessments levied by the district, but shall be credited by the county treasurer, when received, to a special fund, to be held for the payment of the indebtedness of the district to the county until such indebtedness is paid from this fund or other funds of the district.
ORS 371.515