Conduit crossing projects shall incorporate mitigation measures as necessary to achieve no-net-loss of productive capacity of fish and shellfish habitat. An HPA is not required for conduit crossings attached to bridge structures. The following technical provisions shall apply to conduit crossing projects:
(1) Conduit alignment shall be as nearly perpendicular to the watercourse as possible.
(2) The conduit shall be installed at sufficient depth so that subsequent disturbance of the bed of the watercourse is avoided.
(3) If the method used is boring or jacking:
(a) Pits shall be isolated from surface water flow;
(b) Wastewater, from project activities and dewatering, shall be routed to an area outside the ordinary high water line to allow removal of fine sediment and other contaminants prior to being discharged to state waters.
(4) If the method used is trench excavation:
(a) Trenches shall be excavated in the dry or shall be isolated from the flowing watercourse by the installation of a cofferdam, culvert, flume, or other approved method;
(b) Plowing, placement, and covering shall occur in a single pass of the equipment;
(c) Disturbance of the bed as a result of the plowing operation shall be limited to the amount necessary to complete the project.
(5) Trenches shall be backfilled with approved materials and the bed shall be returned to preproject condition.
(6) Excess spoils shall be disposed of so as not to reenter the watercourse.
(7) The conduit approach trench shall be isolated from the watercourse until laying of the conduit across the watercourse takes place.
(8) Alteration or disturbance of the banks and bank vegetation shall be limited to that necessary to construct the project. All disturbed areas shall be protected from erosion within seven days of completion of the project, using vegetation or other means. The banks shall be revegetated within one year with native or other approved woody species. Vegetative cuttings shall be planted at a maximum interval of three feet (on center), and maintained as necessary for three years to ensure eighty percent survival. Where proposed, planting densities and maintenance requirements for rooted stock will be determined on a site-specific basis. The requirement to plant woody vegetation may be waived for areas where the potential for natural revegetation is adequate, or where other engineering or safety factors preclude them.
[Statutory Authority: RCW 75.08.080
. WSR 94-23-058 (Order 94-160), § 220-110-100, filed 11/14/94, effective 12/15/94; WSR 87-15-086 (Order 87-48), § 220-110-100, filed 7/20/87. Statutory Authority: RCW 75.20.100
and 75.08.080. WSR 83-09-019 (Order 83-25), § 220-110-100, filed 4/13/83.]