Draft Mit Plan Comment Memo_NCDMS SITE Devils Alley_SAW-2022-02399

DEPARTMENT OF THE ARMY
WILMINGTON DISTRICT, CORPS OF ENGINEERS
69 DARLINGTON AVENUE
WILMINGTON, NORTH CAROLINA 28403-1343

June 5, 2024

CESAW-RG/Haywood

MEMORANDUM FOR RECORD

SUBJECT: Action ID. NCDMS Devils Alley Mitigation Site- NCIRT Comments from 30-
day Mitigation Plan Review, Chatham County, NC

PURPOSE: The comments listed below were received from the NCIRT during the 30-
day comment period in accordance with Section 332.8(d)(7) of the 2008 Mitigation Rule.

USACE AID#: SAW-2022-02399 30-Day Comment Deadline: April 07, 2024
DWR# 2022-1569

Maria Polizzi, NCDWR:
1. Page 1, DMS Comments: The first sentence refers to the project as the Longhorn
Buffer Mitigation Plan. Please update accordingly.
2. If the stream origin for UT5 is just off-site, is the ford crossing necessary? Or
could the property be accessed upslope of this feature?
3. DWR questions whether Headwater Forest is an appropriate wetland type for
WAM forms 2 and 3. Typically headwater forests are located at the upper extents
of small ephemeral to intermittent streams. Please provide justification for why
these wetlands are headwater forest or consider running the WAM tool again
with a more appropriate wetland type. The scores are highly dependent on the
wetland type selected.
4. DWR appreciates the inclusion and layout of Figure 4, this is very helpful.
5. In Table 13b on page 31, WAM form 2 (I believe this should actually be WAM 3,
please confirm) has an overall score of medium, but on Figure 4 it is shown as
low. Please update accordingly.
6. DWR is unsure of whether wetland PR (as referenced in the JD) should be
considered rehabilitation. The gauge data from 2023 shows that hydrology was
achieved 10.6% of the growing season, which is very close to meeting
performance now. Since only a partial year of data has been provided it is difficult
to know if this is a representative average for this location, but with relatively
successful hydrology in this area, an enhancement ratio may be more
appropriate.
7. Was a soil investigation performed on all wetland reestablishment areas? Most
soil borings shown are from enhancement areas, and only one from a
reestablishment area. If more borings were performed, please show all locations
on the map and include them in the appendix. Otherwise, how were these
drained hydric locations determined? No discussion or data was provided about
these locations.
8. Based on Figure 4 it appears that the reference reach is a section of UT1 Reach
3 that is proposed for restoration. Does this location need restoration if it is in
reference condition? Typically reference reaches are on preservation quality
streams. If restoration is needed, this may not be an appropriate reference reach.
9. Page 19, Table 7:
a. Are proposed conditions for UT 1 the same throughout the length of the
stream? It seems that with significantly different drainage areas and
conditions throughout the length of the stream, it may be worth subdividing
the reach into multiple sections. This is especially noticeable because the
Devils Alley Reference Reach is part of UT 1 and has different values than
UT 1 shown on this table and Table 11 (this comment applies to Table 11
as well). It appears that UT 1 on these tables is for the most downstream
portion of the project, as the drainage area is listed as the max drainage
area of the stream. If all of UT1 is designed based on this input DWR is
concerned that it may oversize upstream portions of the feature.
b. It appears that the natural substrate for most project streams is silt (as
described in reach descriptions but not described in Table 7), sand and
gravel. However, proposed conditions are shown as gravel and cobble. Is
there a reason why substrate particle size is being increase across the
board? DWR understands that preventing degradation is important and
increasing particle size is a way to minimize transport of material, but it is
also preferable to keep bed substrate as similar to natural conditions as
possible.
10. Figure 12, Monitoring Plan: DWR recommends moving the stream flow gauges
on UT1 and UT4 more upstream and closer to the stream origins.
11. Thank you for including photos with the reach descriptions. This helps to
minimize flipping back and forth while reading through the report.
12. DWR would also like to request that flow performance criteria be increased to 90
days of consecutive flow for this project. There is concern, specifically for UT3
that raising the channel may severe the groundwater connection. DWR would
also support benthic monitoring with a 30-day consecutive day minimum as an
alternative to the 90 day standard.
13. DWR appreciates that power lines will be relocated outside of the easement.
14. Please provide more details about the understory plantings. It appears that the
species will be the same as the Dry-Mesic Oak Hickory Forest, is that correct?
What density is proposed in these areas? Have containerized plantings been
considered?
15. Page 44, Section 8.8 Fencing: Regarding the fence offsets from the conservation
easement boundary, there is a sentence that states “Clearwater will request the
fence to be offset approximately 2-ft…”. Does this mean that this is still open to
negotiation? Please clarify.
16. Page 45, Table 19: For vegetation performance, volunteer stems can only be
counted towards success if they have been observed for 2 years. Please update
text to reflect this.
17. Page 48, Section 9.2.1 Beaver and Invasive Species: Please note that
management of invasive species is expected throughout the entire duration of
the monitoring period. The statement “when invasive species controls are
required by the IRT….” indicates that invasive treatment will only occur as a
result of a direct request by the IRT. Please revise this wording, as this is a
standard expectation during the monitoring timeframe.
18. Please include discussion about contingency for landowner encroachments.
19. Why are two crossing types proposed at the same crossing? Two separate
crossings on UT1 show both a ford and a bridged crossing or a ford and a piped
crossing. What is the benefit of two crossing types? Is there one crossing type
that would be able to satisfy the needs of the crossing? DWR highly recommends
minimizing each crossing location to one crossing structure.

Design Plans
1. Consider using multiple riffle specifications, to provide more varied habitat,
preferably incorporating some with woody material. In general, more structure
variability is preferable.
2. Are the spot bank stabilization and bank treatment areas on UT5 Reach 1
proposed to be completed by hand? The LOD does not include this reach.
3. Fencing Plan L2.03: Why are gates not proposed for the culvert crossing on UT 1
~STA 18+25? Typically the IRT prefers all crossings to be gated.
4. Details C8.01: The Log Cross Vane detail mentions “native channel material”, but
this is not defined. What is composition of this material?

Emily Dunnigan, USACE:
1. Section 8.7.1 and sheet L5.01 do not include a discussion of live stake planting;
please update. Are the stream-side assemblage species intended to be live
stakes? Please clarify in the table and include a separate table for live stakes if
applicable. If the stream-side assemblage list is live stakes, I question the
success/survival of tag alder, river birch, ironwood, sycamore, water oak, and
willow oak planted as live stakes. Consider adding buttonbush to the live
stake/stream-side list.
2. A flow gauge on UT5 was requested by the IRT on the upper 1/3 of the reach;
please add one.
3. The construction drawings are missing the existing powerline on UT1 (~STA
7+00), upstream of UT2.
4. Based on the Fencing Plan, some of the crossings appear to be quite narrow with
fence on both sides (UT1 piped road at STA 18+00 & UT6). Are these areas wide
enough for whatever equipment/vehicles need to use them? The ford crossing on
UT1 @ STA 18+00, UT1 @ STA 40+00, and the bridge crossing on UT6 can only
be accessed by single gates. Are those appropriate for what the landowner will
need to traverse? I concur with DWR’s comment regarding the need for two
crossing types at a single crossing.

Casey Haywood, USACE:

1. DMS comment 13 (Section 7.4). Please be sure to include any correspondence
with the county floodplain administrator in the appendix when it is received.
2. Section 3.4- The plan needs to have a reach-by-reach description of existing
conditions to not only help describe on site conditions but to demonstrate functional
uplift. This is especially important since several of the reaches changed from EI or
EII to restoration from the post-contract site visit (especially UT1 reach 3 that was
identified as a reference reach). The plan was somewhat difficult to navigate since
several of the reaches were lumped together in both the existing and proposed
sections of the plan. For example, the existing conditions for UT1 reaches 2-9 are
lumped together but appear to have different approaches when they are discussed
again in 8.1.1 in the Restoration Approach for UT1 Reaches 3-7 section. I
appreciate the inclusion of Table 16, but it would help with the review if the
discussion was consistent throughout the document. In general, it is not
appropriate to lump reaches together especially if the existing conditions and
approaches are different because ultimately those factors correlate to the
functional uplift that’s anticipated.
3. The plant community is described in Section 3.5.3 as dominated by fescue. Please
note that we strongly recommend treating fescue during site construction/prep to
ensure planted vegetation is not outcompeted. As a lesson learned, we have seen
greater success treating fescue at construction as opposed to during monitoring.
Also, do you anticipate preserving any mature trees in riparian areas along
channels with existing forest? If so, please be sure to note visual observations of
tree survival; the IRT is interested in tree survival on mitigation sites following
construction.
4. Section 4.1.1.4- It is unclear why UT1 Reach 3 is a reference reach when it is being
proposed as restoration (originally EII) when in Section 8.1.1 described that a
detailed assessment of the existing conditions indicated the existing pattern
parameters were well outside design parameters. Given the results of the
assessment it is not appropriate to use this reach to inform design. Will a new
reference reach be identified?
5. In general, Section 4.1.1.4 notes that UT1 Reach 3 does not exhibit extensive
destabilization, but in 8.1.1 states the assessment indicated there was significantly
more erosion and tight meander bends. Please clarify. Was an NCSAM form
completed in this location for the assessment?
6. Section 8.1.1 Marsh treatment areas- To confirm, will shallow pools be designed
off the channel (Sheet C8.08)? Please clarify and add additional detail to this
discussion. It may be helpful to show the shallow pools on the overall design sheets
as well.
7. Table 16 (UT1) notes that a dam and small pond used for cow watering will be
removed, but it was not mentioned in Section 3.4. How large is the pond? The plan
needs to specifically address how the dam will be dewatered and removed, and
identify the approach used for stream restoration within the pond bed. Please call
out the pond location on Figure 4.
8. Wetlands-
a. Section 8.4 Wetland rehabilitation- 2023 Hydrology data shows this area at
10.6% for only a small portion of the growing season. I agree with DWR that
it is difficult to know if this is representative given the limited amount of data.
Is it possible to provide the remaining 2023 data to determine if the
hydrology is already meeting the 12% success criteria? I question whether
enhancement would be more appropriate if the uplift would only come from
planting. Lastly, is the placement of the gauge representative for the entire
rehab area?
9. Table 17/Figure 11- It would be helpful to identify the species proposed for the
understory supplemental planting in the table. Are all species proposed for the Dry-
mesic oak hickory forest appropriate for understory planting? It would be
interesting to know the survivability rate of the planted species at the end of
monitoring.
10. Section 9.0 Please add a statement indicating that the success criteria for the
Project will follow the 2016 USACE Wilmington District Stream and Wetland
Compensatory Mitigation Update and subsequent agency guidance (which should
also be listed in references).
11. Please include a figure of the landowner parcels.
12. Concur with DWR’s comment. It appears UT5 originates just offsite. Is it possible
to capture the origin so that the crossing could be eliminated or moved to avoid
impacts to the reach? Also, the crossing on UT5, Figure 5 is labeled as a ford
crossing but the description on the Figure calls it out as a bridge, please update.
Additionally, are there any stability concerns with having the crossing close to the
origin point such as head-cutting? What are the current conditions of the top this
reach, and will any work need to be done to ensure it is stable? If you are able to
capture the origin, it may be beneficial to install a BMP above the feature.
13. Section 7.8/Figure 8:
a. I appreciate the approaches/work being called out on the figure. Two
locations on UT1 R1 call out a forded crossing paired with either a piped
crossing or a bridge crossing. I appreciate the number of crossings being
reduced from 7 to 3 however, it is unclear why two different crossing types
are needed at a single location (in particular for the crossing below the
UT1/2 confluence. In general, a single crossing type/design should
accommodate, and be determined by considering all aspects of the project
(landowner use, future development, aquatic passage, size/hydrology of the
watershed, etc). Therefore, it doesn’t seem appropriate to have 2 different
crossing types at a single crossing as this would not only be more for the
landowner to maintain but would also pose a greater risk to the Site and
potentially impact the overall stability of the reach.
b. This section should be expanded to describe the current condition of any
existing crossings and explain how it will be improved (ie the driveway).
Also, an explanation as to why the crossings are not internal to the
easement, if gates are proposed, and the intended use of the crossings
should be included.
c. Section 7.5 mentions existing powerlines were being relocated outside the
easement. Please show the relocation location on this figure.

14. Table 20- The schedule/frequency section should indicate when monitoring will
occur (baseline, years, annually). It is understood that there will be continuous
recording of gauges through the monitoring period, but will it occur annually, semi-
annually, quarterly? The IRT strongly encourages quarterly inspections of
monitoring equipment to avoid data loss. The table should also include a project
boundary parameter to identify any encroachments or fence damage and should
also include visual observations of invasive and/or nuisance vegetation.
15. Section 9.2- I appreciate the level of detail and consideration of this section. To
confirm, are ephemeral pools being proposed as part of the project or is this just
canned language in the wetland and vegetation contingency sections? Please be
sure to include the locations of these features on the project drawings. This section
should also note that observation of BMPs will also occur during monitoring visits.
16. Figure 12-
a. Please add photo points to the BMPs on UT1, 2, 3, and 4.
b. Please add a flow gauge to the upper third of UT5 (as noted in Appendix L).
c. Will there be an on-site rain gauge? If so, please update the Figure to
include the rain gauge or include the rainfall data source location in the
narrative.
17. Appreciate the detailed AMP found in Appendix J and welcome this in future
reports.
18. Design sheet C8.05- Please note that the IRT does not support the use of smooth
wall HDPE because of the difficulty that certain aquatic species have in moving
through the culvert.

Casey Haywood
Mitigation Project Manager
USACE Regulatory Division

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