§ 24.30.080. Wetland mitigation—Ratios.

A.

Mitigation Ratios. The ratio of impacted wetland acreage to mitigation acreage shall be determined using the ratios specified in Table 24.30-3. Buffer mitigation shall occur at a 1:1 ratio of buffer impact to mitigation impact. The approval authority, in consultation with Ecology, shall establish the ratio of impacted wetland acreage to mitigation acreage on a case by case basis, based on the factors listed in subsection (B) below. The ratio of impacted wetland and buffer acreage to mitigation acreage shall not be less than 1:1, provided that buffers for created wetlands are sized consistent with TCC 24.30.035—24.30.065.

B.

The approval authority shall consider, at a minimum, the following when establishing the mitigation ratio:

1.

The category and quality of the impacted wetland(s) and buffer(s) and, if the mitigation is proposed to occur at existing wetlands off-site, the quality of any wetlands at the mitigation site;

2.

The direct and indirect impacts to the affected wetlands and buffers.

3.

The degree to which the proposed alteration would destroy or reduce wetland and/or buffer functions at the impacted site, including consideration of impacts to hydric soil and disruption of groundwater or surface water flows. Hydric soils are shown in Table 24.30-5 at the end of this chapter.

4.

The probable success of the proposed mitigation in fully replacing all lost and diminished wetland and buffer functions based on:

a.

The project team's demonstrated success in designing, constructing, and monitoring the proposed type of mitigation in wetlands of the same hydrogeomorphic classification (e.g., slope, riverine, or depressional);

b.

Documentation indicating that the hydrologic and soil conditions at the mitigation site are supportive of the proposed mitigation and that the site is free of invasive plants and noxious weeds or will be made free of such plants;

c.

If the mitigation was conducted in advance of the impact, whether it is successful in achieving the performance standards specified in the mitigation plan;

d.

The long-term functions and values of the proposed mitigation;

e.

The timing of the proposed mitigation relative to the proposed wetland and buffer impacts and the time frame within which the wetland and buffer functions will be fully replaced;

f.

The quality and completeness of the applicant's proposed mitigation plan (see TCC 24.35.380); and

g.

Other relevant factors.

C.

Category III and IV Wetlands. The maximum mitigation ratio for impacts to Category III and IV wetlands shall be 1:1 under the following circumstances:

1.

The wetland is not located in a riparian habitat area (see TCC 24.25.015—24.25.040);

2.

The wetland is not a functional part of a mosaic wetland (as described in the Wetland Rating System for Western Washington);

3.

The wetland has a score for habitat of four or fewer points under the Wetland Rating System for Western Washington;

4.

The applicant's qualified professional has evaluated the wetland and determined that it does not provide essential habitat for priority wildlife species (see TCC 24.25.065);

5.

A hydrologic analysis performed by a qualified professional demonstrates that the wetland does not provide important hydrological functions that cannot be replaced at another location (such as cleansing contaminated stormwater that would otherwise flow to a water body or preventing flooding of structures). The analysis shall be at the applicant's expense; and

6.

The impacted wetland is under four thousand square feet in size.

D.

Credit/Debit Method. To aid in the implementation of off-site mitigation, the county may develop a program which allows mitigation based on the "credit/debit" method developed by the department of ecology ("Calculating Credits and Debits for Compensatory Mitigation in Wetlands of Western Washington: Final Report (March 2012), Publication #10-06-011, or as revised).

Table 24.30-3

Category and Type of Wetland	MAXIMUM MITIGATION RATIOS
	Re-establishment or Creation	Rehabilitation	Re-establishment or Creation (R/C) and Rehabilitation (RH)	Re-establishment or Creation (R/C) and Enhancement of Water Quality or Storage Functions (E)	Enhancement of Water Quality or Storage Functions Only
	The acreage of compensating wetlands and buffers (calculated separately): The acreage of impacted wetlands and buffers (calculated separately) The ratio for buffer mitigation is 1:1.
All Category IV	1.5:1	3:1	1:1 R/C and 1:1 RH	1:1 R/C and 2:1 E	6:1
All Category III	2:1	4:1	1:1 R/C and 2:1 RH	1:1 R/C and 4:1 E	8:1
Category II - Estuarine	12:1 or case-by-case basis, whichever is greater	4:1 Rehabilitation of an estuarine wetland only	12:1 or case-by-case basis, whichever is greater	12:1 or case-by-case basis, whichever is greater	Not allowed
All other Category II	3:1	8:1	1:1 R/C and 4:1 RH	1:1 R/C and 8:1 E	12:1
Category I - Mature/old growth forested wetlands	Not allowed	12:1	1:1 R/C and 10:1 RH	1:1 R/C and 20:1 E	Not allowed
Category I - Scoring 23 points or more for functions	4:1	8:1	1:1 R/C and 6:1 RH	1:1 R/C and 12:1 E	16:1
Category I - Wetlands of High Conservation Value	Not allowed	6:1 Rehabilitation of a Natural Heritage site only	Not allowed	Not allowed	Not allowed
Category I - Coastal Lagoon	Not allowed	6:1 Rehabilitation of a coastal lagoon only	Not allowed	Not allowed	Not allowed
Category I - Bog	Not allowed	6:1 Rehabilitation of a bog only	Not allowed	Not allowed	Not allowed
Category I - Estuarine	12:1 or case-by-case basis, whichever is greater	6:1 Rehabilitation of an estuarine wetland only	12:1 or case-by-case basis, whichever is greater	12:1 or case-by-case basis, whichever is greater	Not allowed

 

(Ord. No. 14773, § 3(Att. B), 7-24-2012; Ord. No. 15291, § 1(Att. A), 5-10-2016)