19950153 Ver 5_Email 3:50pm_20170104

Burdette, Jennifer a
From: Burdette, Jennifer a
Sent: Wednesday, January 04, 2017 3:50 PM
To: 'Nuwan Wijesuriya'; '[e-mail]'
Cc: Wehner, Judy
Subject: Benson Quarry Diversion Channel
Nuwan,
Part of the Section 404/401 Permit/Certification for the proposed pit expansion at the Benson quarry includes
construction of a diversion channel to relocate the flow from Stony Fork around the permitted pit
expansion. This expansion will impact 17 acres of riparian wetland. The diversion channel is not required for
mitigation. Payment to a private mitigation bank has been permitted to mitigate the wetland impact.
Because the diversion channel involves the relocation of and connects to a classified surface water, it is
important to make sure that it does not cause a violation of water quality standards. Throughout the
permitting/certification process, Brian North made assurances that Martin Marietta (MM) would construct a
thalweg within the trapezoidal channel using natural channel design and plant the area outside the thalweg
with native woody plant species. Because the diversion channel was not utilized to provide mitigation, a
specific planting plan was not provided. This Office previously indicated that matting along the thalweg and
stabilization with ground cover would be necessary prior to routing water through the channel, but that
planting of woody species could be completed later.
Runoff from Hurricane Matthew created a breach in the berm around the existing pit. The berm was only
temporarily repaired due to site conditions at the breach. To avoid failure of the berm repair, MM has
requested approval to proceed with routing the flow through the newly constructed diversion channel.
On December 21St, Mac Haupt and I conducted an inspection of the recently constructed channel with you and
the plant manager. The trapezoidal channel is complete with a thalweg that has been matted. Upstream of the
culvert crossing, the channel and thalweg appear stable with matting and ground cover. Downstream of the
culvert has little vegetative ground cover and water is standing behind the rock dam across the channel flooding
the thalweg up to the culvert. We observed erosion on the north side of the channel downstream of the culvert
where a low area drains to the channel.
This Office recommends breaching the rock dam across the channel to allow the standing water to drain to see
if this dries the section downstream of the culvert out sufficiently to allow vegetative cover to establish. We
recommend planting woody species within the channel outside the thalweg and live stakes at the outside bends
of the thalweg as soon as possible to help with the long term stability of the channel as it takes about two years
for this vegetation to establish. The area of drainage on the north side of the channel should also be stabilized
with rock where the low area discharges into the channel.
Sincerely,
Jennifer
Jennifer Burdette
401/Buffer Coordinator

Division of Water Resources - 401 & Buffer Permitting Branch
Department of Environmental Quality
919 807 6364 office
jennifer.burdetteQncdenr.gov
1617 Mail Service Center
Raleigh, NC 27699-1617
(Physical Address: 512 N. Salisbury St, Raleigh, NC 27604 - 9th FIr Archdale Bldg — Room 942F)
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