Lyman Boulevard Phase 3 Permit Update 02-26-2014 Memorandum
SRF No. 0076098 3040
To: Terrance Jeffery, Water Resources Coordinator
City of Chanhassen
From: Matthew Meyer, Senior Environmental Scientist
Nathen Will, Senior Associate
Date: February 26, 2014
Subject: CSAH 18 (Lyman Boulevard) Phase 3
Wetland Permitting Update for Wetland 1A
Introduction
This memorandum transmits updated information and attachments to address the Technical
Evaluation Panel’s (TEP) comments related to the secondary impacts associated with Wetland 1A,
and to provide supportive evidence for the maintenance of hydrology, including the avoidance of
secondary impacts to the remaining project wetlands.
Wetland 1A Secondary Impacts
As part of this project, the existing CSAH 18 roadway profile is being lowered approximately 6 feet
to improve sightlines and safety at the intersection of Sunset Trail which includes the private
driveway adjacent to Wetlands W-1A and W-1B. This profile adjustment is reflected in the attached
cross sections, which show the proposed grading along entire CSAH 18 project. Refer to cross
sections from Station 216+50 to Station 217+50 (Plan Sheets 204 and 205 – Appendix B) for the
proposed grading impacts and driveway profile as compared to the existing ground line.
The proposed grade changes associated with the driveway approach at Station 216+70 RT
(eastbound CSAH 18) has the potential to reduce hydrology to the remaining 0.12 acres of Wetland
W-1A; creating a secondary impact. As a result of grade changes on the south-side of Wetland W-
1A, the basin is considered to be impacted in entirety due to hydrology alterations that will likely
drain the remaining portion of Wetland W-1A. Impacts have been revised in Table 1 (below).
The additional mitigation is not necessitated by safety, and will be purchased from wetland bank
number 1392 by Carver County.
Hydrologic Maintenance of Project Wetlands
Wetland 2 – The existing hydrology will be maintained to this wetland by perpetuating flow from
the existing drainage area north of CSAH 18 and west of Sunset Trail under CSAH 18 through a
cross culvert pipe at Station 209+60 constructed to match the existing culvert invert elevations.
Surface flow to this wetland will continue from the adjacent farm field south of CSAH 18.
Wetlands W-14, Bluff Creek and W-19 – The existing hydrology at these wetlands will be mostly
unaffected by the project other than the proposed fill needed to construct the roadway which is
impacting the wetlands. Refer to the attached construction plan sheets and cross sections for
grading impacts.
Table 1: Revised Wetland Impacts
Wetland ID,
Topographic
Setting
1/4
1/4 Sec.
(T116N,
R23W)
Type:
Eggers &
Reed/
Circ 39
Predominant
Vegetation
Total
wetland
area (ac)
Permanent
Roadway
Impacts
Temporary
Roadway
Impacts
W-1A NE SW
23
Shallow
marsh/3
Cattail 0.14 0.14 ac 0.00 ac
W-1B NE SW
23
Wet
meadow/2
Reed canary
grass
0.06 0.06 ac 0.00 ac
W-2 NE SE
22
NW SW
23
Wet
meadow/2
Reed canary
grass, willow,
common
buckthorn,
0.8 0.8 ac 0.06 ac
W-10,
tributary
SW NE 22 Wet
meadow/2
Reed canary
grass, cattail
>20 0.00 ac 0.00 ac
W-11, Flow-
through
SE NE 22 Shallow
marsh/3
Reed canary
grass, cattail
>5 0.00 ac 0.00 ac
W-12,
Isolated
SE NE 22 Wet
meadow/2
Diverse
sedges,
grasses, forbs
0.2 0.00 ac 0.00 ac
W-13,
Isolated
SE NE 22 Wet
meadow/2
Cattail,
sedges, forbs
<0.1 0.00 ac 0.00 ac
Bluff Creek SE NE, NE
SE 22
N/A Reed canary
grass
>20 0.13ac * 0.00 ac
W-14, Flow-
through
SE NE
22
Wet
meadow/2
Reed canary
grass, green
bulrush,
sedge
>5 0.86 ac 0.09 ac
W-18,
tributary
SW NW
23
Seasonally
flooded
basin/1L
Box elder,
maple,
buckthorn
0.2 0.00 ac 0.00 ac
W-19 NE SW
23
Seasonally
flooded
basin/1L
Green ash >0.3 0.01 0.00 ac
Total
Permanent
impacts
(2.00 ac)
Total
Temporary
impacts
(0.15 ac)
0.15 ac
Restored to
pre-
construction
conditions
* Proposed impacts at the edge of Bluff Creek consist of replacing culverts, grading, rock rip rap lining for outfall of culverts within
actual channel north and south of Lyman Boulevard. Channel cross-section characteristics will be modified to accommodate
the realigned culverts.
Note: Shading = revised numbers from previous submittal.
Wetland Mitigation Update
A total of 2.00 acres of permanent wetland impact and 0.15 acres of temporary impact are proposed
as a result of the roadway reconstruction. Of the 2.00 acres of impact, 0.33 acres are permanent and
safety-related and 1.67 acres are not eligible for safety credits.
Table 2 below summarizes the proposed mitigation strategies for each wetland identified along
this project.
Table 2: Summary of Proposed Wetland Mitigation for Each Wetland Impact within Project Area
Wetland ID Safety-related
Wetland Impacts
(acre)
Required Mitigation
(2:1) from BWSR
Road Replacement
Program
(acre)
Non Safety-Related
Wetland Impacts
Outside Safety
Improvements
(acre)
Required Mitigation
(2:1) from Private
Wetland Bank Credit
Purchase
(acre)
W-1A 0.00 0.00 0.14 0.28
W1-B 0.06 0.12 0.00 Self-mitigating ditch(1)
W-2 0.09 0.18 0.71 1.42
W-14 0.05 0.1 0.81 1.62
W-19 0.00 0.00 0.01 0.02
Bluff Creek 0.13 0.26 0.00 0.00
Total
Wetland
Impacts
(acre)
Safety-Related:
0.33 acres
0.66 acres
Non Safety-Related:
1.67 acres
3.34 acres
(1) This existing wetland ditch meets the three parameters of wetlands. The proposed roadway improvement
will re-establish a similar ditch that will be re-seeded with an appropriate wetland seed mix.
On behalf of the Carver County Public Works, we request the WCA LGU to notice the revised
wetland impacts, and associated information to the members of the TEP including the U.S. Army
Corps of Engineers.
Appendices List:
Appendix A – Revised Wetland Figures
Appendix B – Plan sheets and Cross Sections
Appendix A: Revised Wetland Figures
• Figure 3B Plan Sheet with Wetland Impacts
W-14 (SEE 3A)WETLAND 2(SEE 3A)
WE
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A
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1
A
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1
4
A
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.
(
N
O
N
-
S
A
F
E
T
Y
)
WE
T
L
A
N
D
1
B
0.
0
6
A
C
.
(
S
A
F
E
T
Y
)
W-
#
#
SP
-
#
#
H:\Projects\6098-P3\HI-MU\Graphics\WCA Permit\6098-P3_WCA01.dwg : WET-02Job # 6098-P32/11/2014 - 1:54PMREVISED 2/11/14 WETLAND
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MATCH LINE
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1
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CARVER COUN
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Appendix B: Plan Sheets and Cross Sections