Wetland Buffer Mitigation Plan.pdf17
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2182192nd Avenue West
Wetland Buffer Mitigation Plan
Edmonds, Washington
Prepared for
Rick Wichers
May 29, 2007
12655--02
Prepared by
Hart Crowser, Inc.-Pentec Environmental
120 Third Avenue South, Suite 110
Edmonds, Washington -98020-8471
Fax 425.778,9417
Tel 425.775.4582
www.hartcrowser.
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jUN 12007
PERMIT COUNiF-R
INTRODUCTION
General Site Conditions
Wetland Conditions 1
SITE DEVELOPMENT IMPACTS 2
PROPOSED MITIGATION 3
Enhancement Plantings, Log Placement, and Invasive Species Removal 3
Fencing and Signs 4
Post -Mitigation Wetland Buffer Functions and Values 5
GOALS AND PERFORMANCE STANDARDS 6
Goal 1, Enhance Wetland Buffer Areas through Installation of Native Vegetation 6
Goal 2: Remove Invasive Plant Species within the Existing Wetland Buffer 6
MAINTENANCE AND CONTINGENCY PROCEDURES 6.
CONSTRUCTION MANAGEMENT 6
MONITORING 7
Vegetation 7
Photopoints 8
Monitoring Schedule s
Performance Bond s
LIMITATIONS 9
REFERENCES 9
Hart Crowser, Inc.—Pentee Environmental Page 1
12655-02 May 29, 2007
CONTENTS (CONT.)
TABLES
1 Proposed Buffer Enhancement Plantings
2 Cost Estimate for Performance Bond
FIGURES
1 Vicinity Map
2 Wetland Delineation Plan
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12655-02 May 29, 2007
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21821 92ND AVENUE WEST
WETLAND BUFFER MITIGATION PLAN
EDMONDS, WASHINGTON
INTRODUCTION
This report discusses impacts and mitigation for a proposed subdivision located
at 21821 92nd Avenue West in Edmonds, Washington (Figure 1). The property
is recorded as parcel number 27043000200400 and is approximately 0.45 acres
in size. The property is located in S30, T27N, R4E.
The objective of this report is to discuss impacts to the on-site wetland buffer
j and provide mitigation measures to compensate for those impacts.
General Site Conditions
Dominant vegetation within the upland portion of the site consists of mowed
lawn with a fringe of forested vegetation located around the property boundary.
Douglas fir (Pseudotsuga menziesii), Pacific willow (Salixlasiandra), Scouler's
willow (S..scoulerana), Indian plum (Oemleria cerasiformis), and Himalayan
blackberry (Rubus armeniacus) dominate the forested portion of the site.
The topography of the property is generally flat. Near the eastern and southern
property boundaries, the property slopes to the south and east toward the
wetland system. The site is dominated by the Alderwood soil unit: a moderatefy
well -drained soil that forms on till plains.
Wetland Conditions
In May of 2007, we prepared a wetland delineation and categorization report to
document and describe the location and boundaries of the identified wetlands
within the subject property (Hart Crowser 2007). Our investigation identified.
one wetland (Wetland A) located near the southeastern property boundary.
Wetland A is a depressional wetland with a forested plant community class..
We rated Wetland A as a Category 111 wetland in accordance with the
Washington State Wetland Rating System for Western Washington - Revised
(Hruby 2004) based on the accumulation of 48 points. The wetland received
24 points for water quality function, 12 points for hydrologic function, and
12 points for habitat function.
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12655-02 May 29, 2007
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We prepared a functional assessment, which identified a moderate level of
overall function and values for Wetland A.
Our report docLimented a small patch of Himalayan (Rubus armeniacus) and
cut -leaf blackberry (Rubus lacinatus) near the southeastern property corner. The
wetland buffer contains low vegetative density and diversity, and is dominated
by lawn.
Our investigation did not document threatened or endangered species as
occurring on the subject property or within Wetland A.
Based on the City of Edmonds (City) critical area regulations, Wetland A requires
a 50 -foot buffer (Edmonds Municipal Code (EMC) 23.50.040(F)(1)). In addition,
a minimum building setback of 15 feet is required from the edge of the wetland
buffer (EMC 23.40.280).
SITE DEVELOPMENT IMPACTS
in order to accommodate the proposed subdivision, buffer reduction with buffer
enhancement is proposed. Development activities will result in permanent
wetland buffer impacts of approximately 2,423 square feet.
The proposed subdivision has been designed to avoid impacts to critical areas to
the maximum extent practical, while still accomplishing the goals of the
development activities. No direct or indirect impacts will occur to Wetland A.
The proposed development has been placed as far away from Wetland A and its
buffer as possible.
EMC 23.50.040(F)(3) allows for a reduction of a standard buffer width of up to
50 percent for Category III and IV wetlands providing:
■ The plan provides evidence that wetland functions and values will be
increased or retained through plan implementation;
■ The plan documents existing native plant densities and provides for increases
in buffer native plant densities to no less than three feet on center for shrubs
and eight feet on center for trees;
■ The plan requires monitoring and maintenance; and
Mart Cromer, Ino—PoMeo Environmental Page 2
12655-02 May 29, 2007
■ The plan documents methodology and provides performance standards for
assessing increase in wetland buffer functioning as related to:
• Water quality protection;
• ProvFsion of wildlife habitat;
• Maintenance of wetland hydrology; and
• Restricting wetland intrusion and disturbance.
The project applicant proposes a 40 percent buffer reduction accompanied by
buffer enhancement to improve the functions and. values of the existing buffer
area. The proposed 40 percent reduction would reduce the existing 50 -foot
buffer to 30 feet. The remaining buffer area will be enhanced with native
vegetation to improve wildlife habitat, restrict intrusion and disturbance in the
wetland, and increase the functions and values provided by the current buffer
area.
The project proposes 2,423 square feet of permanent buffer impacts, and
1,295 square feet of buffer enhancement.
PROPOSED MITIGATION
The project applicant proposes improvement of the functions and values
provided by the buffer of Wetland A through buffer enhancement. The
proposed enhancement will include removal of invasive vegetation, specifically
Himalayan and cut -leaf blackberry, followed by the installation of native trees,
shrubs, groundcovers, and a habitat log. The proposed mitigation will maintain
and improve the wetland buffer functions and values over time.
Enhancement Plantings, Log Placement, and Invasive Species Removal
Buffer Enhancement Plantings
A variety of native trees, shrubs and groundcover species have been selected to
improve water quality, provide wildlife habitat, maintain wetland hydrology, and
restrict access to the wetland.
We identified one planting area for the project site (Figure 2). The planting area
is located within the southeastern portion of the property adjacent to Wetland A.
This area is currently dominated by lawn. The existing forested fringe on the
subject property will remain undisturbed.
The overall transplant densities for the planting area has been selected to
eventually provide a moderately dense, structurally diverse plant community in
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12655-02 May 29, 2007
the buffer area. Natural volunteer vegetation of the species listed for planting
shall be counted towards the desired densities of enhancement plants.
Volunteer vegetation not listed below may substitute for the specified plants.
with approval ofCity staff, provided the plants are not invasive species.
Buffer enhancement planting densities are as follows:
■ Trees - S feet on center
■ Shrubs - 5 feet on center
■ Groundcover - 3 to 5 feet on center
Native plant species, sizes and quantities for the proposed planting areas are
listed in Table T. Native groundcover enhancement is not required; however,
we provide groundcover plant species for optional planting.
We recommend that plant installation occur during the early spring or late fall,
and plant material be obtained from a reputable nursery. Plant species can be
placed randomly throughout the identified buffer enhancement area at the
densities previously discussed.
Log Placement
We recommend placement of a minimum of one log within the wetland buffer
to provide additional habitat for birds and small mammals. No logs will be
placed directly in Wetland A. logs should be a minimum of 12 inches in
diameter and a minimum of 6 feet in length. We recommend interspersing
native vegetation with the log to further improve habitat.
Invasive Species Removal
Prior to plant installation, we recommend removal of a small patch of Himalayan
and evergreen blackberry within the existing buffer area. Manual removal is
recommended to reduce impacts to adjacent existing native and desirable
vegetation. Care shall be taken not to impact existing vegetation adjacent to the
blackberry.
Fencing and Signs
if determined necessary by the director, a split -rail fence will be constructed
along the edge of the wetland buffer and permanent signs will be installed along
the fence per EMC 23.50.040(G) (see Figure 2).
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12655-02 May 29, 2007
The split -rail fence shall be constructed of cedar or a similar type of wood. The
fence will allow for wildlife movement between the wetland, buffer and
surrounding upland areas, but will discourage human access within the
enhanced buffer.
A sign designating the presence of an environmentally sensitive area shall be
posted along the edge of the wetland buffer. A minimum of one sign will be
posted for the subject property_ The sign shall be worded as follows:
PROTECTED WETLAND AREA
DO NOT DISTURB
CONTACT THE CITY OF EDMONDS
REGARDING USES AND RESTRICTIONS
Post -Mitigation Wetland Buffer Functions and Values
Post -construction functions and values will be increased and improved through
proposed wetland buffer enhancement. The addition of native trees, shrubs and.
groundcovers will improve water quality, flood/stormwater control, habitat
j functions, and cultural/socioeconomic functions. Enhancement plantings within
( lawn areas will slow surface water flows during storm events and filter the
.surface water before it enters Wetland A. These plantings will also increase
plant and wildlife species diversity and habitat. Specifically, amphibian, mammal
and bird habitat will increase from a low level of function to a moderate level of
function. Finally, the plantings will provide an increased aesthetic and
educational value.
We used the Semi -Quantitative Assessment Method (SAM) 2000 (Cooke, 2000)
to evaluate the pre -and post -construction functions and values for the wetland
buffer within the project area.
51,41
00 -on" W"�'
Flood/Storm Water Control
Low
Low — Moderate
Base Flow/Ground Water Support
NA
NA
Erosion/Shoreline Protection
NA
NA
Water Quality Improvement
Moderate
Moderate — High
Natural Biological Support
Low — Moderate
Moderate
Overall Habitat Functions
Low — Moderate
Moderate
Specific Habitat Functions
Low
Moderate
Cultural/Socioeconomic
Low— Moderate
Moderate
Overall Functions and Values:
Low — Moderate
Moderate
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12655-02 May 29, 2007
GOALS AND PERFORMANCE STANDARDS
EMC 23.50.040(3)(c) requires wetland monitoring be performed for a period of 3 or
more years. We identify goals and performance standards for the proposed
mitigation and monitoring of the site below.
Goal is Enhance Wetland Buffer Areas through Installation of Native Vegetation
Performance Standards:
a) Survival of planted native trees, shrubs, and groundcover.will be a minimum
of 80 percent after 3 years.
• Year 1: 100 percent survival of installed plants
• Year 2: 80 percent survival of installed plants
• Year 3: 80 percent survival of installed plants
b) Areal coverage of native trees, shrubs, and groundcover will be a minimum of
80 percent after 3 years.
• Year 1: 20 percent cover
• Year 2: 60 percent cover
• Year 3: 80 percent cover
Goal 2: Remove Invasive Plant Species within the Existing Wetland Buffer
a) Invasive plant areal coverage will be less than 10 percent after 3 years.
• Years l through 3: 10 percent or less coverage of invasive plants
MAINTENANCE AND CONTINGENCY PROCEDURES
Maintenance and contingency actions shall consist of irrigation, pruning,
replacement of dead/dying or undesirable transplants with the appropriate
vegetation, substitution of plant species, and weeding and removal of noxious
and invasive weeds. No post -planting applications of fertilizer are anticipated.
We recommend occasional deep irrigation of.the mitigation plantings during the
summer months of the first year.
CONSTRUCTION MANAGEMENT
The contractor shall be responsible for protection of the required wetland buffer
area, maintaining appropriate protective barriers, and field staking the
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12655-02 May 29, 2007
3.
MONITORING
Vegetation
construction areas. A contractor who is familiar with landscape and plant
installation shall perform buffer enhancement installation and invasive species
removal. A qualified biologist may be present on site to oversee buffer
enhancement activities.
The City of Edmonds requires a minimum 3 -year monitoring period for
mitigation activities (EMC 23.40.130). Buffer enhancement monitoring will
include quantitative and qualitative data collection to measure the success of the
proposed mitigation. A project biologist or mitigation specialist will implement
all monitoring methods. '
The project biologist or mitigation specialist conducting monitoring activities will
make a number of qualitative observations on vegetation and wildlife during
quantitative data collection. Qualitative data on plant cover, density, survival
and naturally colonizing plants will be collected. in addition, observations of
wildlife use, including birds, amphibians, reptiles, and small.mammals, will be
recorded during each monitoring visit.
Wetland buffer enhancement plant communities will be sampled along a
permanent vegetation transect using a circular quadrant (]-meter radius). A
minimum of two transects will be established in the enhanced buffer. Transect
lengths will range between 25 and 50 feet. A minimum of 3 permanent
quadrants will be established along each transect. In order to ensure the same
locations are monitored each year, permanent markers will be established at the
ends of each transect and at each quadrant sampling point (either PVC, wood
lathe, or a combination of PVC and rebar). A map of the vegetation zones,
sample plots, and property boundaries will be created for use during monitoring
events.
Buffer enhancement plantings will be visually evaluated along.each transect to
determine the rate of survival, health, and vigor. Plants will be recorded as live,
_ stressed, or dead/dying. Plant survival will be calculated by dividing the number
of installed living plants by the number of initially installed plants.
The percent cover of individual plant species present within each quadrant will
be visually estimated. Data collection will consist of species composition and
percent cover, total percent plant cover, percent cover of volunteer plants, and
percent cover of invasive species such as Himalayan blackberry, reed
Mari Crowser, Inc.—Pentec Environmental Page 7
( 92655-02 May 29, 2007
Photopoints
canarygrass, Scot's broom; English ivy, etc. Species coverage values will be
summed to determine the total areal coverage in each quadrant.
To supplement the qualitative data, permanent photopoints will be established
within the buffer enhancement area. Photopoints will be established at
topographic vantage points that provide complete views of the enhancement
area, if possible. Photos will document relative changes in plant cover, density,
and height. Permanent markers will be established at each photo point (either
PVC, wood lathe, or a combination of PVC and rebar).
Monitoring Schedule
The following project monitoring reports will be provided to the City:
■ At time of construction;
■ Year 1;
■ Year 2; and
■ Year 3 (Final).
The project applicant shall submit an "At time of construction" or "As -built
report" to the City within 30 days after completion of plant installation. The
report will document mitigation site conditions at completion of plant installation
and invasive species removal, and will be used as a baseline for future
monitoring events.
We recommend that monitoring occur during the fall and prior to leaf drop of
Years 1 through 3. Years 1, 2, and 3 (Final) detailed monitoring reports will be
submitted to the City by December 1 of each year.
Performance Bond
The City requires a maintenance, monitoring, and performance bond equal to
120 percent of the cost of the mitigation for a period of 3 years to ensure
applicant compliance with approved mitigation (EMC 23.40.290). The bond
shall be released after a 3 -year period providing that the mitigation performance
standards have been met. If the performance standards have not been met after
the 3 -year monitoring period outlined above, a contingency plan shall be
implemented. A cost estimate for the performance bond is provided in Table 2.
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12655-02 May 29, 2007
a LIMITATIONS
REFERENCES
Work for this project was performed, and this report prepared, in accordance
with generally accepted professional practices for the nature and conditions of
the work completed in the same or similar localities, at the time the work was
performed. It is intended for the exclusive use of Rick Wichers for specific
application to the referenced site. This report is not meant to represent a legal
opinion. No other warranty, express or implied, is made.
Subsurface conditions interpreted from observations of soil materials and
seepage encountered in our explorations and/or investigations, in conjunction
with soil properties inferred from field tests, formed the basis for developing our
recommendations in this report. The nature and extent of conditions between
the explorations and/or investigations may change over time and may not
become evident until site work begins. if significant variations then appear
evident, we should be consulted to re-evaluate the conclusions and
recommendations in this report. It should be noted that fluctuations in the level
of the groundwater may occur and are dependent on variations in rainfall,
temperature, and other climatic factors.
Cooke, Sarah S. ed., 1997. A Field Guide to the Common Wetland Plants of
Western Washington and Northern Oregon. Seattle Audubon Society, Seattle,
Washington.
Cooke, Sarah S., 2000. Wetland and Suffer Functions, a Semi -quantitative
Assessment Methodology. Cooke Scientific Services, Inc., Seattle, Washington.
Debose, A. and M.W. Klungland, 1983. Soil Survey of Snohomish County Area,
Washington. U.S. Department of Agriculture; Soil Conservation Service. July
1983.
Hart Crowser, Inc., 2007. Critical Areas Report Wetlands, Wichers Property at
21821 952nd Avenue West, Edmonds, Washington. May 3, 2007. Project
number 12655-01.
Hruby, T., 2004. Washington State Wetland Rating System for Western
Washington - Revised. Washington State Department of Ecology Publication
#04-06-025.
Hart Crowser, Inc.—Pentec Environmental Page 9
12655-02 May 29, 2007
Pojar, Jim and Andy MacKinnon et al., 1994. Plants of the Pacific Northwest
Coast: Washington, Oregon, British Columbia, and Alaska. B.C. Forest Service,
Research Program. Lone Pine Publishing. Vancouver, British Columbia.
Reed, P.B. Jr., 1988. National List of Plant Species that Occur in Wetlands; 1988
Northwest (Region 9). U.S. Fish and Wildlife Service, Inland Freshwater Ecology
{ Section, Biological Report 88 (26.9), St. Petersburg, Florida.
E
Reed, P.B. et al., 1993. Supplement to List of Plant Species that Occur in
Wetlands; Northwest (Region 9). U.S. Fish and Wildlife Service, Inland
Freshwater Ecology Section, Supplement to Biological Report 88 (26.9),
St. Petersburg, Florida.
7opoZone. U.S.G.S. Edmonds East quadrangle, Snohomish County, Washington.
http-//www.topozone.com. Accessed on September 8, 2006. Scale 1:50,000.
Washington State Department of Ecology, U.S. Army Corps of Engineers Seattle
District, and U.S. Environmental Protection Agency Region 10, March 2006.
Wetland Mitigation in Washington State - Part 1: Agency Policies and Guidance
(Version 1). Washington State Department of Ecology Publication #06-06-011a.
Olympia, Washington.
Washington State Department of Ecology, U.S. Army Corps of Engineers Seattle
District, and U.S. Environmental Protection Agency Region 10, March 2006.
Wetland Mitigation in Washington State - Part 11: Developing Mitigation Plans
(Version 1). Washington State Department of Ecology Publication #06-06-071 a.
Olympia, Washington.
00655\002\Wichers Wetland Delineation 05-29 2007\Wichers Wetland Buffer Mitigation Report.doc
Hart Crowser, Inc.—Pentec Environmental Page 10
12655-02 May 29, 2007
Table 'I - Proposed Buffer Enhancement Plantings
00655\002\Withers Wetland Delineation 05-232007\Tables T and 2.dac
Tree
Western redcedar
Thuja plicata
1 -gallon
7
Tree
Douglas fir
Pseudotsuga menzuesii
1 -gallon
7
Tree
Big -leaf maple
Acer macrophyllum
1 -gallon
6
Shrub
Red elderberry
Sambucus racemosa
1 -gallon
6
Shrub
Indian plum
Oemleria cernsiformis
1 -gallon
5
Shrub
Salal
Gaulthena shallon
4 -inch or 1 -gallon
7
Shrub
Vine maple
Acer circinatum
1 -gallon
6
Shrub
Snowberry
Symphoricarpus albus
1 -gallon
7
Shrub
Beaked hazelnut
Corylus cornuta
1 -gallon
6
Shrub
Pacific rhododendron
Rhododendron
macrophyllum
1 -gallon
5
Shrub
Sword fern
Polystichum munitum
1 -gallon
ZQ
Groundcover
Wild ginger
Asarum caudatum
4 -inch
---
Groundcover
Bleeding heart
Dicentra formosa
4 -inch
---
Groundcover
Woodland or wild
strawberry
Fragaria vesca or
virginiana
4 -inch
=--
00655\002\Withers Wetland Delineation 05-232007\Tables T and 2.dac
Table 2 - Cost Estimate for Performance Bond
rl
Trees
$4.50
20
$ 90.00
Shrubs
$4.00
52
$ 208.00
Installation
--
----
$ 300-00
Monitoring
$100/hour
25
$ 2,500.00
Maintenance
$150/year
3
$ 450.00
Subtotal
----
--
$ 3,548-00
120 percent of estimated costs
$ 709.60
ESTIMATED PERFORMANCE
$ 4,257,60
00655\002\Wichem Wetland Delineafiwi 05-212007\Tables 7 and 2.doc
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