20072022 Ver 2_Staff Comments_20080425

Project Name: Sierra
County: Durham
DWQ Project #: 07-2022v2
Date: 4/25/08
Ian & Annette:
These comments are for phases I & II, assuming they are asking for the 401 for both
phases since they have provided the documents for Phases I and II. Otherwise, they will
have to come again in future for 401 and/or Buffer Authorization for phase II, which I
doubt they will. You may want to point it out to them that if they are only asking for the
impacts associated with phase 1, then they should respond with information applicable to
phase I, BUT stress that they MUST reapply for phase II impacts, whether for only
Buffer Authorization and/or another 401 if there will be stream impacts.
1. Please resubmit site plans NS-1 and NS-Ion a larger scale, preferably 1"= 50'.
Each BMP and its outlet structures, and topographic contours through adjacent
buffers all the way to the receiving stream must be shown.
2. For the proposed on-line bypass channels through the buffers that receive flows
from the BMPs, please include
a. Their impacts in your PCN, clearly identifying each one, and with larger
impact maps (impacts are allowable),
b. Channels shall not intersect streams perpendicularly, but be angled at
approximately 75° to avoid bank erosion at opposite side of stream.
c. Channel (sizing and lining) design information, with cross sections,
discharge velocity calculations for the 10-year storm (flows the BMPs).
3. Please clearly identify all impacts (stream, wetland, buffer) on the site plans, and
provide detailed plan view of each impact. Individual impacts must be
enumerated on the impact maps by zone (e.g. zone 1 = 0.2 acres, etc).
4. Please provide detailed impervious area calculations for each drainage area shown
on drainage map NS-7. In particular, please include average lot size, number of
lots, street and driveway dimensions, etc used in estimating the impervious
amount in each drainage area.
5. Please include culvert design and its attendant plunge pool velocity dissipater
sizing calculations, and provide cross sections of streams showing culverts and
dissipater pads.
6. If Atlas Drive is a thoroughfare that will be taken over in the future by the
Department of Transportation (DOT), please provide a written approval that the
locations of the proposed wetlands DB #9 and DB # 8A & 8B are acceptable - i.e.
they meet their safety, vehicle recovery area and maintenance/right of way
setbacks.