HomeMy WebLinkAboutWPO201000074 Review Comments Erosion Control Plan 2010-12-17� OF AL
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: North Pointe Phase 3 Road Improvements [WPO- 2010 - 00074]
Plan preparer: David Jensen, PE; WW Associates
Owner or rep.: Richard Spurzem; Neighborhood Investments — NP LLC
Plan received date: 2 November 2010
Date of comments: 17 December 2010
Reviewer: Phil Custer
The Erosion and Sediment Control Plan for the North Pointe Phase 3 Road Improvements project,
submitted on 2 November 2010, has been reviewed. The letter from the county review of the road and
SWM plan will be provided at a later date. County engineering can approve this plan after the following
comments have been addressed.
A. General Review
1. This ESC plan cannot be approved until the road and SWM plans are approved.
2. The ESC bond (and all other bonds) must be posted prior to the approval of the site plan for the
northwest residential area.
3. To be in general accord with the application plan, the applicant must include a "pedestrian tunnel"
underneath North Pointe Blvd. in approximately the same location.
4. To be in general accord with the application plan, the applicant must include a "picnic area" at the
outlet of the culvert at Sta. 23 +30 in approximately the same location with the same square
footage.
5. To be in general accord with the application plan, the applicant must include a flat 1Oft (or wider if
a path greater than 5ft is desired by the property owner) wide shelf in the roadway embankment,
above the culvert endsections, between Sta. 22 +30 and 24 +50 so that a Class A pedestrian path
and appropriate drainage swales and culverts can be established when future site plans are
submitted for the park and clubhouse.
6. The plan shows a stream at Sta. 23 +30. Please provide the county with approval from the Army
Corps of Engineers or the Virginia DEQ. Please also provide the county with a copy of the
application submitted to the Army Corps of Engineers. Any required Army Corps mitigation must
occur on site. If on -site ACE mitigation cannot be provided, the applicant must contact the county
for a list of off -site opportunities. [Proffer 4.4] This ESC plan cannot be approved until consent
from one of these agencies is received.
B. ESC Plan Review Comments
1. Please provide a note in the construction sequence that this project is contingent upon WPO -2010-
00017 for access to the limits of disturbance as well as use of the sediment basin that will be
converted to SWM facility 10. Please include in the note that a grading permit cannot be given
until a bond Northwest Passage has been constructed to the property line to the satisfaction of the
County ESC inspector.
2. Please provide a list of all ESC methods above and beyond state standards in list form on sheet 21
and the County Engineer will review these proposals upon the next submittal. (Proffer 4.3.a)
Albemarle County Community Development
Engineering Review Comments
Page 2 of 2
3. The silt fence on the east and west side of the embankment between Sta. 22 +00 and Sta. 24 +50 of
North Pointe Blvd. is not adequate. The applicant must provide a sediment basin below this
culvert per county policy. It appears that the construction of SWM facility 3 on Sheet C of the
application plan will provide more than enough volume to meet the state sediment basin
requirements. For more information, please refer to the County Engineer's Commentary #4 that
discusses ESC measures required at roadway culvert crossings.
4. From its intersection with North Pointe Blvd., please provide a diversion dike on the west side of
Lewis and Clark Drive to the sediment basin which would later be converted to SWM facility #10.
A temporary construction easement from TMP 32 -22P will be necessary. Alternatively, it looks
as though a sediment trap can be designed west of the entrance at Sta. 28 +70 that can outlet into
the existing valley without the need for an easement. Because of the existing topography in this
area, silt fence would not be adequate.
5. The plan proposes silt fence at the toe of the cut slopes on North Pointe Blvd. from its intersection
with Lewis and Clark Drive to Sta. 19 +00. However, there is no protection in the plan during the
first few weeks of construction when sediment -laden runoff will flow according to existing or
intermediate contours. Please provide diversions, traps, and silt fence as necessary to protect the
site for existing topography and intermediate grading. Please be cognizant of the drainage area
size, drainage area width, and slope (must be placed parallel to contours) limitations of silt fence.
6. Please provide the TSC symbol and specify the size of the temporary pipe on Sheet C -20.
7. The construction sequence in the ESC narrative implies that the culvert at Sta. 23 +40 will be
constructed offset in the dry and, when installation is complete, the stream will be diverted into it.
However, the culvert has been located in or around the stream bed for most of its length. Please
clarify or modify the construction sequence as necessary.
8. Please supplement the site survey with the county aerial topography on Sheet C -20.
9. Please show the tree line and trees on all appropriate sheets. The drainage area maps and
calculations assume full forests but it appears there are noticeable patches of meadow.
10. The applicant has provided an analysis of three downstream cross - sections using a trapezoidal
channel manning's equation one would normally see for constructed roadside ditches. Please
provide an analysis of these cross - sections as irregular channels. For each segment of the surveyed
cross - section, please provide a computed n -value (Tables 5 -16, 5 -17, 5 -18, 5 -19, 5 -20, and 5 -21),
permissible velocity (Table 5 -22), and calculated velocity. Please provide photographs for each
existing cross - section as well.
11. State law requires that downstream analysis be provided until the project area is 1% of the
watershed of the stream. However, the 1% rule is not computed with each incremental ESC plan,
but the whole area approved in the rezoning plan. For this reason, Flat Branch to its confluence
with the Rivanna River is technically subject to review with each NP application. The North
Pointe rezoning application constitutes more than 20% of the Flat Branch watershed at the outlet
to the Rivanna River (269acres /1150acres) and becomes more influential upstream.
With this ESC application, the basic elements and backbone of a project -long MS -19 analysis,
which will be updated with each subsequent phase of the North Pointe development plan, should
be agreed upon by County Engineering and all North Pointe owners.
12. After all technical comments have been addressed, the applicant must request that an ESC bond be
computed. To request a bond, please complete the bond estimate request form. If this form is not
available online, please contact me when all comments have been addressed.
E1_esc_PBC_North Pointe Phase 3 Road Improvements_wpo201000074.doc