DWR Comments for Newton Grove, Timber Drive, Ritter Park final

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Water kesour�es
ENVIR4NMENT:tL �UfILITY
February 8, 2016
Leilani Paugh
NC Department of Transporation
1548 MSC
Raleigh NC, 27699
Todd Tudwell
US Army Corps of Engineers
Wilmington District,
11405 Falls of the Neuse Rd
Wake Forest, NC 27587
PAT MCCRORY
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Subject: Requested Comments to NCDOT and the ACOE on the Preliminary Prospectus for the
Newton Grove Spoil Pile Alternative Mitigation Site, Timber Drive Alternative
Mitigation Site, and Ritter Park Alternative Mitigation Site
DWR Comments for Alternative Mitigation Site, Newton Grove
1. DWR would like to know more about the origin of the spoil pile, was it a byproduct of the
construction of I-40? DWR questions if it would be appropriate for mitigation credits to be
generated for restorative measures that will stabilize / remove the spoil pile if the spoil pile was
a by-product of the construction of I-40.
2. DWR would like to learn more about the need for stream and wetland credits in the Beaverdam
Swamp Watershed area, will this project be proposed as DOT off-site Permittee Responsible
since DMS is not interested in using it for In Lieu Fee mitigation.
3. P5, first listed goal. Regenerative Stormwater Conveyances are not in the NC BMP manual so
what design criteria would be used for the proposed RSCs? Would operation and maintenance
of the RSC be continued after site closeout?
4. P6, Monitoring of Spoil Pile. DWR would suggest adding an overall cover of native plant species
to the success criteria in addition to the standard 260 stems/acre at 5yrs OR 220 stems/acre at 7
5
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years.
Will the approximate 3000' linear feet of stream located downstream of the spoil pile that was
observed to be receiving excessive sediment load from the spoil pile be put into conservation
easement? If that 3000' of stream will be put into conservation easement have other restorative
measure such as buffer plantings, stream bank stabilization, and addition of channel structures
been considered?
Although Enhancement is a sliding scale, it should be noted that Enhancement II typically
generates 2.5:1 credit not 2:1, albeit this project is not a typical EII project.
State ofNorth Carolina � Environmental Quality � Water Resouroes
161 l Mail service Center I Ralcigh, North Carolina 27699-161 I
919 707 9000

7. P8, Option 2. DWR believes that finding a"typical" stream restoration site for accurate
comparison of erosion rates with the Newton Grove site would be difficult since streams vary
considerably in terms of geology, soil type, channel size, hydraulics etc which in turn effects
erosion and sedimentation rates.
8. P9, Option 3. The USDA Revised Universal Soil Loss Equation, described in Option 2, does use
some site specific data and therefore seems to be a more accurate method for determining
sediment input.
9. Option 1 indicates there have been 3000 feet of stream impacts due to the spoil pile effects on
stream sediment load. Are the effects along the bed and banks consistent along the entire 3000
feet? It would seem the upstream areas closer to the spoil pile and sediment load inputs would
have been affected more.
DWR Comments for Alternative Mitigation Site, Timber Drive
1. RSCs are not in the NC BMP manual, please explain what design criteria would be used for the
RSC?
2. How were TSS, TP, and TN removal rates calculated for the RSC and BMP?
3. RSCs and BMPs are a form of alternative mitigation that the IRT has reviewed and accepted on
other projects on a case by case basis more typically at a 1:1.5 ratio. Currently the IRT is looking
into ways to be consistent with crediting for BMPs and other alternative forms of mitigation but
nothing has been formally accepted at the programmatic level. One of the reasons alternative
mitigation generally does not qualify for a 1:1 ratio is that this form of mitigation does not
replace all of the functions (e.g. habitat) that traditional mitigation does.
4. Would operation and maintenance of the RSC and stormwater wetland BMP be maintained
after closeout ensure they continue to function properly?
DWR Comments for Alternative Mitigation Site, Ritter Park
1. See the above BMP related comments (comments 2-4) for Timber Drive.
CC: Amy Chapman, NCDWR
Mac Haupt, NCDWR