(1) Except as provided in subsection (4) of this section, vendors shall pay interest on overpayments at the rate of one percent per month or portion thereof. Where partial repayment of an overpayment is made, interest accrues on the remaining balance. Interest must not accrue when the overpayment occurred due to authority error.

(2) If the overpayment is discovered by the vendor prior to discovery and notice by the authority, the interest begins accruing ninety days after the vendor notifies the authority of such overpayment.

(3) If the overpayment is discovered by the authority prior to discovery and notice by the vendor, the interest begins accruing thirty days after the date of notice by the authority to the vendor.

(4) This section does not apply to:

(a) Interagency or intergovernmental transactions; and

(b) Contracts for public works, goods and services procured for the exclusive use of the authority, equipment, or travel.

Effective date—Findings—Intent—Report—Agency transfer—References to head of health care authority—Draft legislation—2011 1st sp.s. c 15: See notes following RCW 74.09.010.