20140333 Ver 1_IRT Comment Letter_20151006

WILDLANDS
ENGINEERING
May 8, 2015
Andrea Hughes
United States Army Corps of Engineers
Wilmington District
11405 Falls of Neuse Road
Wake Forest, NC 27587
RE: IRT Review Comments for Mitigation Plan
Holman Mill Mitigation Site (EEP #96316)
Cape Fear 03030002, Alamance County, NC
Dear Ms. Hughes,
We have reviewed the comments on the Mitigation Plan for the above referenced project dated April
24, 2014 and have revised the Mitigation Plan and plan set based on these comments. The revised
documents are submitted with this letter. Below are responses to each IRT member's comments. For
your convenience, the comments are reprinted with our response in italics.
Comments from Ginnv Baker. NCDWR (April 9. 2015)
1. Holman Mill Stream Mitigation is a well written and detailed mitigation plan.
Thank you!
2. The reference reach used for this study has a Rosgen E4 classification but a C4 is proposed.
Please explain the reasoning behind using the E4 stream as a reference for a channel to be built
as a C4.
Rosgen type C streams are designed and built in the Piedmont of North Carolina because of their
stability during and post construction. However, E channels are often the stable streamtype
found in reference situations at these locations in the landscape. Rosgen type E streams typically
have steep sideslopes due to the tight width to depth ratio. Steep banks are difficult to stabilize
post- construction both with temporary matting, seeding, and the establishment of permanent
vegetation. The small radius of curvature associated with E channels can also prove unstable
post - construction.
In order to build stable channels that represent reference conditions, Wildlands utilizes
dimensionless ratios from both type E and type C channels. Wildlands purposely designs type C
channels with low width to depth ratios to aid in the streams' self transition to E channels as
they reach a dynamic equilirbium with their landscapes. This transition may occur once a forest,
hearty bank vegetation, and a stabilized floodplain connection has been established.
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3. Please correct Figure 9 which indicates the lower section of UT2 -R1 is E1. The plan sheets indiate
this lower section is El and should be labeled as UT2 -132. UT2 -R2 and UT2 -113 on Figure 9 should
be labeled all UT2 -R3 as it is on the plan sheet. This correction also supports what is on the
Determination of Credits Table 9, p. 20, and written in the Project Implementation Section 9.6,
p. 30.
Figure 9 has been corrected.
4. NCDWR recommends removing red maple (Ater rebrum) from the plantin glist as this species
will establish on its own and replacing it with one of the other native trees that are known to
occur already on this project site such as American elm (Ulmus americana) or Sugar berry (Celtis
laevigata).
Red maple was added to this plan set at the request of the Division of Mitigation Services during
their review of the Mitigation Plan. Therefore, we have left that species in the planting plan.
Comments from Todd Bowers. USEPA (March 26, 2015)
1. Please explain the reasons behind the omission of the pond and stream at the head of UT213. It
appears that cattle will still have access to the pond and stream and there will continue to be a
stressor on water quality on the UT to Pine hill Branch (PHB). Cattle exclusion of the project
would logically include this area. If reasons include landowner unwillingness to include this area
I the conservation easement then it should be documented. Cattle could be provided an
alternate source of water and would not need access to the pond /stream. this would support
the opening paragraphs on Page 1.
The pond has not been included in this project to date per original negotiations with the
landowner and the DMS proposal. Although the landowner may choose to remove the pond and
plant it at some point in time, it will not be included in the conservation easement. Our
understanding is that the landowner does not plan to keep cattle on this site in the future.
Section 2.2: Wetlands present will be preserved and not proposed for credit at this time. Does
this imply that credit may be requested in the future?
Credits for wetlands are not anticipated at this site as they were not requested as part of the
Request for Proposals, and Wildlands has no plans to pursue wetland credits on this site.
3. Section 4.3 and Figure 4, Soils Map: HdC2 soil mapped color is not consistent with the Legend.
Please correct.
The HdC2 labels were for two small sections of soil that were along the conservation easement
boundary. We have edited the figure labels so that this is clear.
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4. Section 4.4 and Table 5. Stream valleys have slopes of 1.3 to 2.3 percent. Stream valley s;lopes
on Table 5 range from 0.7 o 3.0 percent. Please correct.
Section 4.4 has been corrected to say 0.7% - 3.0 %,
5. Section 4.5 and Figure 6: Hydrologic features outlined in Figure 6 should be shown as they are in
Figure 4 to denote perennial and intermittent streams. Reach Breaks for UT1 should be
displayed on Figure 6 also. Figure 6 (and 9 -11) also shows that the conservation easement for UT
to PHB is outside of the project boundaries. Is this a descrepancy?
Figure 6 has been updated to denote the hydrologic features as perennial and intermittent, to
include reach breaks on UT1, and to update the project limits to be outside of the conservation
easement.
6. Section 4.6, Table 5, Figure 6: A cross - section with data is included for UT to Pine Hill Branch.
Figure 6 does not show the location of this cross - section. Please correct.
The location of the cross - section along UT to Pine Hill Branch has been added to Figure 6.
7 Section 4.6.3: Celtis laevigata is noted for sugarberry however the Wetland Data Sheet for DP10
lists Celtis occidentalis for sugarberry. Please correct if this is an error.
Section 4.63 has been updated to match Wetland Data Sheet for DP10 with Common Hackberry,
Celtis occidentalis.
8. Section 4.6.4: UT2 in second paragraph should be UT2A. Please correct.
This has been corrected.
9. Section 4.6: Why is there no assessment of UT1A and UT213? I understand these are intermittent
reaches but some evaluation of their condition should be provided.
A short summary of conditions along UT1A and UT2B have been added to Section 4.6.
10. Section 7, Table 9: Proposed credit or UT2A should be 540. Error was not carried forward.
Table 9 has been updated.
11. Section 7, Table 9 and Figures 9 &11: Ut2 -R2 is listed as E1 approach and on maps it is shown as
restoration. The plan views of Ut2R2 also show E1 approach.
Maps 9 and 11 have been corrected to show UT2 -R2 as E1.
12. Section 9.6.1: The second paragraph discussion of UT2112 is confusing. It states E1 for the reach,
and then describes how the bed will be raised and a riffle pool sequence will be constructed (P1
restoration). The sentence that follows this statement should read "Ut2 (reach 3 and 4) to be
restored usin P1 restoration ". This is similar to comment in #11.
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For the purpose of mitigation crediting, UT2 -R2 is being called Enhancement 1. While the bed is
being raised and a riffle -pool sequence is being added, the channel dimension is not being
manipulated to create a true bankfull channel. The stream reach will still be somewhat incised.
The purpose of raising the bed along this reach is to allow for Priority 1 restoration on reaches
UT2 -R3 and UT2 -R4, while decreasing incision along UT2 -R2.
13. Section 9.6.2 and Sheet 3.1 on construction plans: recommend replacing the 10% of Acer
rubrum with another riparian hardwood species such as Ulmus americana, Carya ovata, or
Juglans nigra.
Acer rubrum was added to the plans at the request of the Division of Mitigation Services during
their review of the Mitigation Plan and has not been removed.
14. Section 9.6.2 ad Sheet 3.1: If Alnus serrulata is going to be planted can we depend on it reaching
an average height of 10 feet by the end of the monitoring period:?
After further review, we have decided to remove Tag Alder's from the planting plan, as their
mature height is between 8 -12 ft and it may take 10 years to reach that height.
15. Section 11.1.2: include what signs would indicate vertical or lateral instability.
Section 11.1.2 was updated to include bank scour, bank migration, and bed incision as
indications of vertical and lateral instability.
16. Section 11.1.6: Include a contingency plan on how to deal with volunteers. Will they or will they
not be counted towards meeting performance standards should planted stems fail to meet
stated density.
Section 11.1.6 states that success will be based on the number of "planted" stems per acre. This
does not include volunteers. However, volunteers are expected and encouraged to populate the
riparian buffer areas. No specific maintenance plan has been created to discourage the growth
of volunteer plants. This is based on past project experience where maintenance of volunteers
has not been necessary in order to meet success criteria.
17. Plan Sheets 2.1— 2.6: UT1 is divided into four reaches UT11 -4 with differing approaches. Figures
1 -11 do not illustrate UT1 -4 and the tables within the document do not diferentiate the reach
numbers.
Figures depicting restoration approaches have been updated to show reaches 1 -4 of UT1, as has
the credit determination table. However, existing data and design parameters have not been
separated by reach. There is no significant change in hydrology, stream and /or valley slope, bed
material, or dimension along the entirety of UT1 that would necessitate the separation.
18. Abandoned chanel plugs are not shown in Plan sheets where P1 restoration is being
implemented. I understand these are not the plans being used for construction.
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Chanel plugs will be included in the final plan set where necessary along P1 restoration reaches.
19. The cover and footer logs in pool bends are ilustrated in reverse of the Cover log diagram of
Sheet 6.3
What is shown on the plan and profile sheet is symbolic in nature, and the detail is what is used
for construction. Howerver, to avoid further confusion, the cover logs on the plan and profile
sheets have been reversed to match the detail.
20. Plan sheets 2.1 2.12: Recommend showing proposed cross - section locations on the planview
diagrams.
The proposed cross - section locations are shown in Figure 11 and will be shown on the As -Built
construction plans.
21. Wetland Data Forms contained within Pages 72 -171 in Appendix B have substituted DP2 for
DP5,8 „11- 1,19- 21,23 -2, and 31 -33. Please replace with appropriate DP data forms.
There was an error in the combination of PDF forms for the wetlands in the previous submittal.
This has been corrected in the Final Mitigation Plan.
Comments from Andrea Huehes, USACE (April 24, 2015)
1. Please ensure that a JD is obtained from the USACE Raleigh field ofice prior to submitting the
NW 27- permit Pre - Construction Notification (PCN).
A Jurisdictional Determination was approved by USACE on January 5, 2015. The approval letter
has been added to Appendix 3.
2. All temporary and permanent impacts to existing wetlands and streams must be accounted or in
the PCN and the loss or conversion of those waters must be replaced on -site. Please include a
map depicting the location of all impacts within the PCN.
The PCN is discussed in Section 5.1 of the Mitigation Plan and included in Appendix 10.
Sincerely,
r
Angela Allen, P.E., Assistant Project Manager
[e-mail]
wildlands Engineering, Inc. (P) 919.851.9986 • 312 West Millbrook Road, Suite 22S • Raleigh, NC 27609