20201177 Ver 1_More Info Received_20200925 (2)

Strickland, Bev
From: lagnocco, Michael <[e-mail]>
Sent: Friday, September 25, 2020 12:15 PM
To: Johnson, Alan
Cc: Kotheimer, Joshua L.
Subject: [External] RE: Unity charter 20-1177
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Hey Alan — hope you're well; thanks for reaching out; just hung up with Bryan Roden -Reynolds to review the Corps
review comments; I think that by describing our stream relocation plan in the project description of the PCN (Section 4i)
some of our details may have been missed in Bryan's initial review; in any event, you are correct — A is the discharge
from the BMP which treats the impervious runoff; B is the discharge from the pervious open field area; C discharges
from the main SW BMP to the undisturbed Wetland A; as described in our excerpt below from PCN Section 4i, for
instream structures, we currently have 4 boulder cross -vanes with a %' drop at each structure with a 2.5' drop in
elevation in the stream reach between each boulder cross -vane; there is a minor elevation drop at the tie-in to the
existing channel accomplished with the rock drop structure; after talking with Bryan, we'll be proposing a woody
planting plan along the relocated stream along with the riparian seed mix, a post -construction monitoring plan,
extending the grading plan and sinuosity further up the relocated channel, and also paying a fee into DMS for 1.75:1 for
compensatory mitigation; I'll check with the civil engineer re: use of a French drain in the portion of the existing
intermittent stream to be filled; we appreciate your attention to this.
Excerpt from PCN Section 4i:
The project will result in the initial loss of 170 linear feet of intermittent Stream A. The project proposes to mitigate for
this initial impact to 170 linear feet of intermittent Stream A by
relocating the 170 linear feet of stream and creating an additional 245 linear feet of headwater stream channel for a
total of 415 linear feet of functionally improved channel, see exhibits
prepared by LITTLE entitled Unity Classical Charter School Stream Relocation, Bulletin Drawings 1 through 10. As
indicated in the exhibits, the stream relocation grading plan has been
designed to extend above the current upper elevation of the existing stream allowing any existing groundwater to enter
the new channel. The grading and drainage within this Sub -Basin
have been carefully considered to help maintain as much of the original drainage area as possible that contributed flow
to the intermittent stream. The sand filter in Sub -Basin 2 will be
utilized to treat the impervious run-off that will be directed toward the upper reaches of the relocated intermittent
stream — the sand filter will be situated immediately north of the Arrival
Drive as shown on Bulletin Drawing 1 of 10. The drawdown time will help extend the time stormwater will flow into the
relocated portion of the stream as well as the remainder of the
existing stream. Stormwater will also be directed to the relocated channel from the open field that has been incorporated
into the campus immediately north of the Arrival Drive.
Other key elements of the stream relocation plan include the incorporation of grade control structures including four
boulder cross -vanes and a rock drop structure. The rock drop
structure will be incorporated immediately upstream of the relocated channel's confluence with the existing channel. The
locations of these in -stream structures are shown on Bulletin
Drawing 1 of 10 (plan view) as well as in the profile views presented in Bulletin Drawings 2 thru 5. There is a 1/2 foot
drop at each boulder cross -vane structure and then a 2.5 foot drop
in the stream run until the next structure. The confluence point has been specifically targeted to occur at a non -
jurisdictional swale that currently intersects the existing channel. Coir

fiber matting will be utilized for initial bank stabilization, in order to reduce erosion and establish seeding faster (see
Bulletin Drawings 1 and 8). In addition, a native riparian seed mix will
be utilized from the normal water level to one foot beyond the top of bank on either side of the stream. Riparian seed mix
is typically applied in the fall which should coincide with the
anticipated construction schedule. The relocated stream corridor will be replanted with native woody species following
construction. The combined elements of the grading plan and
profile, along with the interception of existing groundwater and post -construction drainage plan will promote stream
stability, mitigate channel incising, and offer improved function. The
intermittent stream is being located within the City's required vegetated zoning buffer.
Michael A. lagnocco, PWS
STV Engineers, Inc.
michael.iagnoccoa-stvinc.com
Office: [phone] Mobile: [phone]
Direct: [phone]
Please consider the environment before printing this e-mail
From: Johnson, Alan <[e-mail]>
Sent: Friday, September 25, 2020 11:01 AM
To: lagnocco, Michael <[e-mail]>
Subject: Unity charter 20-1177
Clarification. The impact is 170 of impact? And the plan is to self mitigate from the SW
discharge? IS A the discharge from the BMP? If so, what is B? And C discharges to the
wetland.
At minimum, a "french drain" type fill/system should be utilized for the 170 ft of fill.
It may be a better idea to create the step down throughout the length of the new channel,
rather than waiting to the very end. Typically you end up with a staircase type step down. See
sheet 4 of 10, rather than a single drops over 30 ft, have more variable number of drops
through out the reach which should reduce a major stepped down at the end. .

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Alan D Johnson — Senior Environmental Specialist
NC Dept. of Environment & Natural Resources (NCDENR)
Division of Water Resources - Water Quality Regional Operations
610 East Center Ave., Suite 301, Mooresville, NC 28115
Phone: [phone] Fax: [phone]
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