Ch. 18E.30 App. E Compensatory Mitigation Plan for Regulated Activities in Wetlands – Detailed Phase

18E.30.070 – Appendix E Compensatory Mitigation Plan for Regulated
Activities in Wetlands – Detailed Phase

A. The detailed mitigation plan shall contain the following:

1. Site specific, quantifiable criteria for evaluating whether or not the goals for the proposed compensation are being met. Such criteria shall include the establishment of viable plant communities, hydric soil formation, and establishment of wetland hydrology, and may include water quality standards, species abundance and diversity targets, habitat diversity indices, or other ecological, geological, or hydrological criteria (see subsection III. below for specific performance standards).

2. Pre-development analysis of the proposed compensation area including:

(a) Existing vegetation community analysis;

(b) Hydrological analysis that demonstrates the project will not adversely impact existing wetland and buffer areas and that ensures adequate hydrology for any created wetland areas (see subsection V. for specific requirements);

(d) Detailed description of flora and fauna existing on the site; and

(e) Description of existing site conditions in relation to historic conditions for those sites which have been recently altered or degraded.

3. Proposed post-development conditions within existing wetland and buffer areas and mitigation areas, including:

(a) Relationship of the project to the watershed and existing water bodies;

(b) Topography, using 1-foot contour intervals;

(d) Grading, filling, and excavation, including a description of imported soils;

(e) Irrigation requirements;

(f) Erosion control measures during construction; and

(g) Areal coverage of planted areas to open water areas (if any open water is to be present.

4. Detailed site diagrams, to-scale construction drawings with cross-section data, topographic maps showing slope percentage and final grade elevations, and any other drawings appropriate to show construction techniques or anticipated final outcome. The plan shall provide for elevations which are appropriate for the desired habitat type(s). The construction drawings must include a note that requires the contractor to refer to the approved mitigation plan.

5. Planting plan prepared by a wetland specialist that shall include the following:

(a) Soils and substrate characteristics;

(b) Specification of substrate stockpiling techniques;

(c) Planting instructions, including species, stock type and size, density or spacing of plants, and water and nutrient requirements; and

(d) Specification of where plant materials will be procured. Documentation shall be provided which guarantees plant materials are to be procured from licensed regional nurseries or from wetlands on site which are part of the mitigation plan.

6. Schedule showing dates for beginning and completing the mitigation project, including a sequence of construction activities.

7. Monitoring and maintenance plan which includes the following:

(a) Specification of procedures for monitoring and site maintenance; and

(b) Schedule for submitting monitoring reports.

8. Detailed contingency plan, consistent with subsection IV below.

9. Detailed budget for implementing the mitigation plan, including construction, monitoring, maintenance, and contingency phases.

10. Financial guarantee for the work to be performed as planned and approved. Separate guarantee estimates shall be prepared for the installation phase and monitoring and maintenance phase of the project.

11. Address and phone number of the person or organization responsible for monitoring requirements.

II. LOCATION CRITERIA. In cases in which it is determined that compensatory mitigation is appropriate, the following shall apply:

A. Compensatory mitigation shall be provided on-site, except where the applicant demonstrates that on-site mitigation is not scientifically feasible or practical due to physical features of the site.

B. When compensatory mitigation cannot be provided on-site, it shall be provided in the immediate vicinity of and within the same watershed as the regulated activity.

A. When regulated activities occur in wetlands, the applicant shall restore, create, or enhance equivalent areas of wetlands. Equivalent areas shall be determined according to acreage, functional value, type, location, time factors, and projected success. No overall net losses shall occur in wetland acreage, functions and/or values, and any restored, created, or enhanced wetland shall be as persistent as the wetland it replaces.

B. When an applicant proposes to alter or eliminate wetland, the applicant shall replace acreage at the following ratios:

Category I: 6:1 (acreage replacement: acreage lost)

Category II: 3:1

Category III: 2:1

Category IV: 1.5:1

C. Ratios provided are for proposed projects with on-site, in-kind replacement which occurs prior to regulated activities on the site. The Department may increase the ratios under the following circumstances:

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

2. Significant period of time between destruction and replication of wetland functions; or

3. Projected losses in wetland functions and value; or

4. Off-site and/or out-of-kind compensation.

D. The Department may allow enhancement of existing or created wetland area(s) as a means of reducing the standard acreage replacement ratio if the applicant demonstrates that no net loss of wetland function or value will result provided that:

1. Enhancement mitigation ratios shall be no less than twice the standard creation ratio of the impacted wetland.

2. The applicant may be required to complete an analysis of the impact and mitigation areas in support of the acreage replacement ratio reduction. An example of an acceptable analysis methodology is the Washington State Department of Ecology Wetland Function Assessment Methodology (Ecology Publication # 99-116); however, other methodologies may be proposed.

3. The County will not allow the acreage replacement ratio to be reduced to less than 1:1 except as described in III-E below.

E. In the case of Category II, III, and IV wetlands, the replacement ratio may be decreased to a ratio of less than 1:1 if, following a public hearing, the Hearing Examiner determines the following:

1. A replacement ratio of greater than 1:1 is either not feasible on-site or would be likely to result in substantial degradation of other natural features; and

2. The mitigation plan shows that a net increase in wetland functional values will result from the mitigation; and

3. The mitigation is completed, and then monitored by the Department for one year prior to the issuance of permits. If after one year of monitoring, the Department is not satisfied that the anticipated final outcome of the mitigation plan will be met, modifications to the mitigation plan and further monitoring may be required. When the Department is satisfied that the mitigation will be successful, permits pending will be issued.

F. In-kind compensation shall be provided except where the applicant demonstrates that:

1. Greater functional and habitat values can be achieved through out-of-kind mitigation; and

2. The wetland system is already significantly degraded; or

3. Problems such as the presence of exotic vegetation and changes in watershed hydrology make implementation of in-kind compensation infeasible; or

4. Out-of-kind replacement will best meet identified regional goals (e.g., replacement of historically diminished wetland types).

G. Design requirements for the mitigation plan shall, at a minimum, include the following:

1. Use only native plants indigenous to Pierce County (not introduced or exotic species);

2. Use plants appropriate to the depth of water at which they will be planted;

3. Use plants that originate and are available from local sources;

4. Use plant species high in food and cover value for fish and wildlife;

5. Plant mostly perennial species;

6. Avoid committing significant areas of site to species that have questionable potential for successful establishment;

7. Water depth is not to exceed 6.5 feet (2 meters);

8. The grade or slope that water flows through the wetland is not to exceed 6 percent;

9. Slopes within the wetland and buffer should not be steeper than 3:1 (horizontal to vertical);

10. Planting densities and placement of plants shall be shown on the design plans;

11. The wetland should not contain more than 60 percent open water as measured at the seasonal high water mark;

12. Stockpiling shall be confined to upland areas and contract specifications should limit stockpile durations to less than four weeks. Erosion control measures shall be in effect at the stockpiling location;

13. Planting instructions shall describe proper placement, diversity, and spacing of seeds, tubers, bulbs, rhizomes, sprigs, plugs, cuttings, and transplanted stock;

14. Apply controlled release fertilizer at the time of planting and afterward only as plant conditions warrant (determined during the monitoring process), and only to the extent that the release would be conducted in an environmentally sound manner;

15. Install an irrigation system, as necessary, until plants are established.

H. Mitigation projects are unique and performance standards will differ based upon the goals and objectives of the project. However, performance standards pertaining to water regime, vegetative structure and establishment, and hydric soil formation are to be established for all mitigation projects, as defined below:

1. The mitigation wetland must meet the technical criteria for wetland hydrology, seasonal inundation, and/or saturation to the surface for a consecutive number of days greater than or equal to 12.5 percent of the growing season. Areas that are seasonally inundated and/or saturated to the surface for a consecutive number of days between 5 percent and 12.5 percent of the growing season may also be wetlands. Hydrology may be monitored through the use of one or a combination of the following: groundwater wells, piezometers, crest gauges, hand-dug soil pits, staff gauges, and continuous recording flow meters.

2. At a minimum, vegetative success equals the establishment of a multi-species, mixed canopy community comprised of emergent, scrub-shrub, and tree species. Yearly standards pertaining to survival and aerial coverage shall also be established for each vegetative stratum.

3. Hydric soil characteristics shall be monitored through the use of one or a combination of the following: Munsell soil color, pH, particle size, redox potential, organic content, microbial activity, time and duration of saturation or ponding, and alkalinity.

A. A contingency plan shall be established for compensation in the event the mitigation project is inadequate or fails. The contingency plan is to provide specific corrective measures for such common mitigation plan failings as plant mortality, vandalism, damage due to wildlife grazing, grading errors, and hydro-regime problems. A financial guarantee on a form acceptable to the County is required for the duration of the monitoring period, and the guarantee plus any accrued interest will be released by the County when the required mitigation and monitoring are completed. To determine the amount of the financial guarantee, an estimate shall be submitted to the County detailing the work to be accomplished and the cost thereof. The estimate shall be based on current costs. The County will review the estimate and, if acceptable, will establish the financial guarantee at 125 percent of the estimate to allow for inflation and administration expenses should the County have to complete the project.

B. Requirements of the monitoring program are as follows:

1. Scientific procedures are to be used for establishing the success or failure of the project.

2. Monitoring reports prepared by a wetland specialist are to be submitted for Department review. Monitoring reports shall include discussions of wildlife utilization of the site, vegetation establishment, water quality, water flow, stormwater storage and conveyance, and existing or potential degradation, according to the following schedule:

(a) At completion of construction of mitigation project (as-built report);

(b) Thirty days after completion;

(d) End of the first growing season after construction;

(e) Twice the second year; and

(f) Annually after the second year.

3. Monitor for a period of time appropriate to the nature of the project (single-family versus commercial) and the complexity of the mitigation project. The majority of monitoring programs will last a minimum of five years.

4. The County will require a Right of Entry Form, as set forth in PCC 18E.10.140 – Appendix C, be recorded that allows County staff access to the mitigation area through completion of the monitoring program.

5. Correct for failures in the mitigation project.

6. Replace dead or undesirable vegetation with appropriate plantings.

7. Repair damages caused by erosion, settling, or other geomorphological processes.

8. If necessary, redesign mitigation project and implement the new design.

9. Correction procedures shall be approved by a wetland specialist and the Department Director or designee.

A. Applicants are required to ensure that the proposed development does not result in adverse impacts to regulated wetland and/or buffers. To achieve this, an applicant must demonstrate the project will not adversely affect the wetland hydroperiod. To determine existing hydroperiod, use one of the following methods, listed in order of preference:

1. For Category I, II, III, and forested Category IV wetlands:

(a) Estimation by a continuous simulation computer model. The model should be calibrated with at least one year of data taken using a continuously recording level gage under existing conditions and should be run for the historical rainfall period. Acceptable computer models include HSPF, KCRTS, or Department of Ecology WWHM. The resulting data can be used to express the magnitudes of depth fluctuation, as well as the frequencies and durations of surpassing given depths.

(b) Measurement during a series of time intervals (no longer than one month in length) over a period of at least one year of the maximum water stage, using a crest stage gage, and instantaneous water stage, using a staff gage.

(1) The resulting data can be used to express water level fluctuation (WLF) during the interval as follows:

Average base stage = (instantaneous stage at beginning of interval + instantaneous stage at end of interval)/2

WLF = Crest stage – Average base stage

(2) Compute mean annual and mean monthly WLF as the arithmetic averages for each year and month for which data are available.

2. For scrub-shrub and emergent Category IV wetlands a single-event model may be used to ensure that there is no change in the volume of water delivered to the wetland under post-development conditions.

B. To forecast future hydroperiod, complete an estimation by the continuous simulation computer model calibrated during pre-development analysis and run for the historical rainfall period. The resulting data can be used to express the magnitudes of depth fluctuation, as well as the frequencies and durations of surpassing given depths. [Note: Post-development modeling results should generally be compared with pre-development modeling results, rather than directly with field measurements, because different sets of assumptions underlie modeling and monitoring. Making pre- and post-development comparisons on the basis of common assumptions allows cancellation of errors inherent in the assumptions.]

C. A hydroperiod analysis is to be used to ensure that the following hydroperiod limits are met:

1. Mean annual WLF (and mean monthly WLF for every month of the year) does not exceed 20 cm. Vegetation species richness decrease is likely with: (1) a mean annual (and mean monthly) WLF increase of more than 5 cm (2 inches or 0.16 feet) if pre-development mean annual (and mean monthly) WLF is greater than 15 cm, or (2) a mean annual (and mean monthly) WLF increase to 20 cm or more if pre-development mean annual (and mean monthly) WLF is 15 cm or less.

2. The frequency of stage excursions of 15 cm above or below pre-development stage does not exceed an annual average of six.

3. The duration of stage excursions of 15 cm above or below pre-development stage does not exceed 72 hours per excursion.

4. The total dry period (when pools dry down to the soil surface everywhere in the wetland) does not increase or decrease by more than two weeks in any year.

5. The following hydroperiod limits characterize wetlands inhabited by native amphibians listed as regulated wildlife species in PCC 18E.40.020 and apply to breeding zones during the time period of February 1 through May 31. (Note: If these limits are exceeded, then amphibian breeding success is likely to decline.)

(a) The magnitude of stage excursions above or below the pre-development stage does not exceed 8 cm, and the total duration of these excursions does not exceed 24 hours in any 30-day period.

(b) To apply this guideline a continuous simulation computer model needs to be employed. The model should be calibrated with data taken under existing conditions at the wetland being analyzed and then used to forecast post-development magnitude and duration of excursions.