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19.07.190 Wetlands.
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A. Designation and Typing. Wetlands shall be identified and their boundaries delineated in accordance with the approved federal delineation manual and applicable regional supplements described in WAC 173-22-035. Wetlands shall be rated according to the Washington State Rating System for Western Washington: 2014 Update (Hruby, 2014), or most current update.

B. General Review Requirements.

1. In addition to the critical area study requirements listed in MICC 19.07.110, Critical area study, critical area studies on wetlands shall also include:

a. Wetland rating forms and datasheets;

b. Discussion of landscape setting;

c. A functional analysis of the project demonstrating that there will be no loss of ecological function; and

d. A mitigation plan.

2. Wetland delineations are valid for five years.

3. Wetlands must be delineated and rated by a qualified professional.

C. Development Standards – Buffers.

1. The following minimum buffers shall be established from the wetland boundary:

Wetland Category

Standard Buffer

With 3 – 5 habitat points

With 6 – 7 habitat points

Category I

75 ft

110 ft

Category II

75 ft

110 ft

Category III

60 ft

110 ft

Category IV

40 ft

2. Where a legally established and constructed street transects a wetland buffer, the department may approve a modification of the standard buffer width to the edge of the street if the isolated part of the buffer does not provide additional protection of the wetland and provides insignificant biological, geological or hydrological buffer functions relating to the wetland.

3. Prohibited Activities. The following uses are prohibited within any wetland or associated buffer: removal, excavation, grading, or dredging of material; draining flooding or disturbing the wetland, water level or water table; construction, reconstruction, demolition, or expansion of any structure.

4. Neither lot coverage nor hardscape shall be permitted within a wetland or wetland buffer except as specifically provided in this chapter.

5. Buffer Averaging. Buffer width averaging shall be allowed provided the following requirements are met:

a. The applicant has demonstrated how impacts have been avoided consistent with MICC 19.07.100, Mitigation sequencing;

b. The applicant has demonstrated how all proposed impacts have been mitigated consistent with subsection E of this section and will not result in a loss of ecological function;

c. The proposed buffer width is not less than 75 percent of the standard buffer width at any point; and

d. The total area of the buffer is equal to the area required without averaging.

6. Buffer Reduction. Buffer width reduction shall be allowed provided the following requirements are met:

a. The applicant has demonstrated that buffer averaging would not feasibly allow development;

b. The applicant has demonstrated how impacts will be minimized and that avoidance has been addressed consistent with MICC 19.07.100, Mitigation sequencing;

c. The applicant has demonstrated how all proposed impacts have been mitigated consistent with subsection E of this section and will not result in a loss of ecological function;

d. The proposed buffer width is not less than 75 percent of the standard buffer width at any point; and

e. The proposed buffer reduction is not proposed in conjunction with buffer averaging.

7. Buildings and other structures shall be set back a minimum of 10 feet from the edges of a wetland buffer. The distance may be reduced to five feet if:

a. The wetland is:

i. Hydrologically isolated;

ii. Category III or IV;

iii. Less than 1,000 square feet;

iv. In an area that is not associated with riparian areas or buffers;

v. Not part of a wetland mosaic; and

vi. Does not contain habitat for WDFW priority species;

b. A split-rail fence is installed along the perimeter of the buffer; and

c. Survey markers are installed along the perimeter of the buffer to establish its field location.

8. The following may be allowed in the critical area setback, provided no structures nor building overhangs may be closer than five feet from the edge of a wetland buffer:

a. Landscaping;

b. Uncovered decks less than 30 inches above existing or finished grade, whichever is lower;

c. Building overhangs if such overhangs do not extend more than 18 inches into the setback area;

d. Hardscape and driveways; provided, that such improvements may be subject to requirements in Chapter 15.09 MICC, Storm Water Management Program;

e. Split-rail fences;

f. Trails, consistent with the requirements of this chapter; and

g. Subgrade components of foundations; provided, that any temporary impacts to building setbacks shall be restored to their previous condition or better.

D. Development Standards – Additional Criteria for Specific Activities.

1. Alterations to wetlands are allowed when the applicant has demonstrated how mitigation sequencing has been applied pursuant to MICC 19.07.100, Mitigation sequencing, and when the applicant has demonstrated that the wetland is:

a. All isolated Category IV wetlands less than 4,000 square feet that:

i. Are not associated with riparian areas or their buffers;

ii. Are not associated with shorelines of the state or their associated buffers;

iii. Are not part of a wetland mosaic;

iv. Do not score five or more points for habitat function based on the 2014 update to the Washington State Wetland Rating System for Western Washington: 2014 Update (Ecology Publication No. 14-06-029, or as revised and approved by Ecology);

v. Do not contain a priority habitat or a priority area for a priority species identified by the Washington Department of Fish and Wildlife, do not contain federally listed species or their critical habitat, or species of local importance identified in MICC 19.07.170.

b. Wetlands less than 1,000 square feet that meet the above criteria and do not contain federally listed species or their critical habitat are exempt from the buffer provisions contained in this chapter.

2. The construction of trails within wetland buffers is allowed subject to the following requirements:

a. Trail surfaces shall be constructed of pervious materials and may not be wider than five feet;

b. Trails shall be located to minimize the need for tree removal; and

c. Trails shall be located only in the outer 25 percent of the buffer area.

d. The trail width shall be added to the buffer width applied to the wetland (e.g., if a trail is three feet wide, the wetland buffer for the portion of the wetland where the trail is located shall be expanded by three feet); except that the trail width shall not be added to the buffer width when trails are being created for public access and contained within a public access easement or right-of-way.

3. Development proposals shall incorporate the following measures unless the applicant can demonstrate that they would result in no net environmental benefit or that they are not applicable:

Disturbance

Required Measures to Minimize Impacts

Lights

Direct lights away from wetland

Noise

Locate activity that generates noise away from wetland

If warranted, enhance existing buffer with native vegetation plantings adjacent to noise source

For activities that generate relatively continuous, potentially disruptive noise, such as certain heavy industry or mining, establish an additional 10-foot heavily vegetated buffer strip immediately adjacent to the outer wetland buffer

Toxic runoff

Route all new, untreated runoff away from wetland while ensuring wetland is not dewatered

Establish covenants requiring the use of integrated pest management techniques to limit the use of pesticides within 150 feet of wetland

Storm water runoff

Retrofit storm water detention and treatment for roads and existing adjacent development

Prevent channelized flow from lawns that directly enters the buffer

Use low impact development techniques

Changes in water regime

Infiltrate or treat, detain, and disperse into buffer new runoff from impervious surfaces and new lawns

Pets and human disturbance

Protect wetlands and associated buffers with conservation or native growth protection easements

Dust

Use best management practices to control dust

Disruption of corridors or connections

Maintain connections to off-site areas that are undisturbed

Restore corridors or connections to off-site habitats by replanting

E. Mitigation Requirements. When mitigation for wetland and/or wetland buffer impacts is required, mitigation shall meet the requirements listed below:

1. Compensatory mitigation for alterations to wetlands shall be used only for impacts that cannot be avoided or minimized and shall achieve equivalent or greater biologic functions compared to predevelopment conditions. Compensatory mitigation plans shall be consistent with Wetland Mitigation in Washington State – Part 2: Developing Mitigation Plans – Version 1, (Ecology Publication No. 06-06-011b, Olympia, WA, March 2006, as revised), and Selecting Wetland Mitigation Sites Using a Watershed Approach (Western Washington) (Publication No. 09-06-32, Olympia, WA, December 2009, as revised).

2. Mitigation for alterations to wetland(s) and/or wetland buffer(s) shall achieve equivalent or greater ecological function.

3. No Net Loss. Wetland mitigation actions shall not result in a net loss of wetland area.

4. Mitigation actions shall be in-kind and conducted within the same sub-basin and on the same site as the alteration except when the following apply:

a. There are no reasonable on-site opportunities for mitigation or on-site opportunities do not have a high likelihood of success due to adjacent land uses;

b. On-site buffers or connectivity is inadequate;

c. Off-site mitigation has a greater likelihood of providing equal or improved wetland functions than the impacted wetland; and

d. Off-site locations have been identified and evaluated in the following order of preference:

i. Within the same drainage sub-basin;

ii. Within the city limits;

iii. Within the Mercer Island service area for an approved mitigation bank program site within the WRIA 8 in accordance with the requirements in subsection (E)(6) of this section.

e. Where feasible, off-site mitigation projects shall be completed prior to activities that will disturb wetlands. In all other cases, mitigation shall be completed immediately following site disturbance and prior to use or occupancy of the activity or development. Construction of mitigation projects shall be timed to reduce impacts to existing wildlife and flora.

5. Mitigation Ratios.

a. The following ratios shall apply to required wetland mitigation. The first number specifies the acreage of replacement wetlands and the second specifies the acreage of wetlands altered.

b. Permanent Wetland Mitigation. The following ratios of area of mitigation to area of alteration apply to mitigation measures for permanent alterations:

Wetland Category

Creation

1:1 Wetland reestablishment or wetland creation (R/C) and wetland enhancement (E)

Category I

4:1

1:1 R/C and 12:1 E

Category II

3:1

1:1 R/C and 8:1 E

Category III

2:1

1:1 R/C and 4:1 E

Category IV

1.5:1

1:1 R/C and 2:1 E

c. Temporary Wetland Mitigation. The following ratios of area of mitigation to area of alteration apply to mitigation measures for temporary alterations where wetlands will not be impacted by permanent fill material:

Wetland Category

Creation

Enhancement

Category I

1.5:1

3:1

Category II

0.75:1

1.5:1

Category III

0.5:1

1:1

Category IV

Not applicable

Not applicable

d. Wetland Buffer Replacement Ratio. Altered wetland buffer area shall be replaced at a minimum ratio of one-to-one; provided, that the replacement ratio may be increased if needed to replace lost functions and values.

e. Increased Mitigation Ratio. The code official may increase the ratios under the following circumstances:

i. Uncertainty exists as to the probable success of the proposed restoration or creation; or

ii. A significant period of time will elapse between impact and replication of wetland functions; or

iii. Proposed mitigation will result in a lower category wetland or reduced functions relative to the wetland being impacted; or

iv. The impact was an unauthorized impact.

f. Decreased Mitigation Ratio. The code official may decrease these ratios under the following circumstances:

i. Documentation by a qualified professional demonstrates that the proposed mitigation actions have a very high likelihood of success. This documentation should specifically identify how the proposed mitigation actions are similar to other known mitigation projects with similar site-specific conditions and circumstances that have been shown to be successful; or

ii. Documentation by a qualified professional demonstrates that the proposed mitigation actions will provide functions and values that are significantly greater than the wetland being impacted; or

iii. The proposed mitigation actions are conducted in advance of the impact and have been shown to be successful over the course of at least one full year.

6. Wetland Banking.

a. Credits from a wetland mitigation bank may be approved for use as compensation for unavoidable impacts to wetlands when:

i. The criteria in subsection (E)(4) of this section are demonstrated to have been met;

ii. The bank is certified under Chapter 173-700 WAC;

iii. A qualified professional has demonstrated that the wetland mitigation bank provides appropriate compensation for the authorized impacts;

iv. The proposed use of credits is consistent with the terms and conditions of the bank’s certification; and

v. The compensatory mitigation agreement occurs in advance of authorized impacts.

b. Replacement ratios for projects using bank credits shall be consistent with replacement ratios specified in the bank’s certification.

c. Credits from a certified wetland mitigation bank may be used to compensate for impacts located within the service area specified in the bank’s certification. In some cases, bank service areas may include portions of more than one adjacent drainage basin for specific wetland functions.

7. Preference of Mitigation Actions. Compensatory wetland mitigation shall occur in the following order of preference:

a. Restoration;

b. Creation;

c. Enhancement;

d. Preservation.

8. Site Protection. As a condition of any permit or land use approval, the code official may require permanent fencing and signage to be installed around the wetland or buffer. Fencing installed as part of a proposed activity or as required in this subsection shall be designed to not interfere with species migration, including fish runs, and shall be constructed in a manner that minimizes impacts to the wetland and associated habitat. (Ord. 19C-05 § 1 (Exh. A)). (Ord. 19C-05 § 1 (Exh. A), 2019.)

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