Thurston County, WA Environmental Rules: Stormwater Management (2026)

010 doesn't write drainage standards into the code text itself; instead it adopts the Drainage Design and Erosion Control Manual on file in the water resources program manager's office as amended, currently the 2022 Edition, by reference as though set forth herein in full. That manual, not the code section, carries the technical requirements for how a project designs and builds its stormwater and erosion control systems. 040 backs the manual up with money: a project proponent must post a financial guarantee equal to twenty-five percent of the construction cost of the drainage facilities, covering at least a two-year maintenance period from final plat approval, in the form of a cash escrow, a bank account assignment, an irrevocable letter of credit, or a bond.

050 makes clear that getting a permit approved doesn't excuse noncompliance: failure to comply is grounds for denying or withdrawing a permit, forfeiting the guarantee, and the county refusing to accept the finished work. 030 lets the county perform emergency erosion or drainage repairs itself and bill the property owner or proponent, who is jointly and severally liable for costs plus attorney's fees and interest at the delinquent-property-tax rate. 80 RCW and Title 26 TCC, heard in court under state civil infraction procedure. 120 sets the monetary penalty by infraction class.