HomeMy WebLinkAboutWPO200800044 Review Comments Erosion Control Plan 2008-06-09ALg�,��
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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: WPO- 2008 - 00044, Warthen Estates
Plan preparer: Mr. Kirk Hughes, LS; Kirk Hughes and Associates fax 434.295.7540
Owner or rep.: Mr. Benjamin Warthen fax 804.359.0405
Date received: 25 April 2008
Date of Comment: 9 June 2008
Engineer: Phil Custer
The SWM, ESC, and road plans for Warthen Estates, received on 25 April 2008, have been reviewed. The
plans cannot be approved as submitted and will require the following corrections before approval can be
granted:
A. General Review Comments
1. Please accurately show stream buffers on all plan sheets. Please note that the stream buffer layer is
not 100% accurate and a field visit to check the limits of the stream's intermittency should be
performed by the applicant. The county may visit the parcel to verify the buffer placement by the
applicant.
2. All slopes steeper than 2:1 will require a low maintenance, non - grassed groundcover. This
requirement includes ditches and around biofilters. Please specify the planting spec on the road
section, road plan, and ESC sheets. [DM]
3. Please provide on the plan Albemarle County's latest set of notes titled "General Construction
Notes," "General Construction Notes for Streets," "General Construction Notes for Erosion and
Sediment Control Plans," and "General Construction Notes for Stormwater Management Plans."
The latest set of plans can be found in the design manual on the county website.
4. Please label contours on the road and ESC plans.
5. Why is there a detail for a "Paved Outlet Channel" on Sheet 2 -00? I cannot find a paved channel
on the plan.
6. Please show the benchmark on the plan.
B. ESC Plan Review Comments
1. Please provide adequate channels for all temporary and permanent discharge points.
2. The proposed ESC measures do not appear to be sufficient to protect the site. Engineering review
will require basins on the downhill side of all culverts. Please see the attached commentary from
County Engineer Glenn Brooks.
3. The construction of the road between Sta. 10 +00 and Sta. 14 +00 appears to be lacking protection
measures.
4. Please show a construction entrance on the plans. Please note that a construction entrance must
drain to a sediment trap or basin. [DM, VESCH]
5. Please provide a staging and parking area on the plans [DM]
6. Please provide a temporary soil stockpile area. [DM]
7. Please provide dust control (DC) on the plan. [DM]
8. Silt fence cannot run across contours. The silt fence at the end of the cul -de -sac is not an
appropriate measure at this location.
9. Culvert inlet protection with silt fence has a maximum drainage area of 1 acre. Culvert inlet
protection with a sediment trap has a maximum drainage area of 3 acres. Please specify what type
of CIP is to be used at each culvert inlet. Culverts with drainage areas greater than 3 acres cannot
have a CIP symbol next to it. CIP will not likely be necessary based on ESC comment #2.
10. Please provide an adjacent areas description in the ESC narrative.
11. The ESC portion of the WPO bond will be computed once all comments have been addressed.
12. Please note that a grading permit will be withheld until a copy of the state VSMP permit is given
to the county. Please contact Mr. Matthew Grant, DCR, at 804.225.3068 for more information.
13. Additional comments may be required based on the necessary changes to address the above
comments.
C. SWM Plan Review Comments
1. Please replace the biofilter detail with the latest from current edition of the design manual
available online. The sand /soil media layer must be 2.5ft. The rock layer must be 1.5ft. The
biofilter media must meet "state standards." The underdrain pipe must be 6 ".
2. Please provide an overall drainage area map showing the areas captured by each biofilter. [DM]
3. There is no calculation on the plan confirming that each biofilter is appropriately sized.
Engineering review maintains a policy that in order to obtain a 50% removal rate for a biofilter, the
bed area should be sized to equal 2.5% of the impervious area draining to it. To achieve a 65%
removal rate, the bed should be sized to equal 4% of the impervious area draining to it.
4. All water quality facilities must have an appropriately sized sediment forebay.
5. Please encompass all biofilter facilities in a SWM easement.
6. Please provide vehicular access to all critical features (sediment forebay and outlet structure) of
each facility. The access must be 1Oft wide, encompassed in an easement, with a maximum slope
of 20 %, and graveled if the slope exceeds 10 %. [DM]
7. Please provide a planting schedule for each biofilter. The planting plan for each biofilter should
be designed to the standards listed in VSMH 3.11 (pages 3.11 -16 to 3.11 -12). A variety of 3
species of trees and 3 species of shrubs should be provided for in each biofilter.
8. The rock weirs for the biofilters are incorrect. The weirs from the sediment trap cannot remain as
the outlet for the biofilter. Each weir should be replaced and sized to pass the 100 -year storm will
maintaining a freeboard of 1 ft.
9. The steepest downstream slope allowed on an embankment is 3:1.
10. A signed Stormwater Management Facility maintenance agreement and recordation fee will need
to be submitted. Please contact Pam Shifflett (x 3246) for questions regarding this procedure.
11. The SWM portion of the WPO bond will be computed once all comments have been addressed.
12. Additional comments may be necessary based on the required changes to the ESC and SWM
plans.
D. Road Plan Review Comments
1. The -2% cross -slope of Ambrose Commons Drive should be extended 20ft onto Warthen Estates
Drive so that the low point is provided off of the intersection between existing and new pavement.
[DM]
2. Please show in the culvert computations that the 25 -year storm does not overtop the road and
prevent access to the subdivision.
3. Please provide drainage easements over all channels (including roadside ditches) and culverts. A
deed of easement will be needed when the final plat is reviewed. [DM]
4. In many cases where the road comes from a cut to a fill section, the grading for the ditch
disappears. Please show the grading for all roadside ditches. [DM]
5. At fill slopes, as the ditch continues at the base of the fill, the slope of the channel may produce
velocities in excess of 10fps and may require riprap. Please show calculations for these instances.
6. The channel being filled over by the grading for the cul -de -sac needs to be designed.
7. Please provide a table with the starting and end stations for ditch matting. This table will be used
for bonding purposes.
8. Vertical curve data is missing from two curves on sheet 5 -10. [DM]
9. Please provide stationing for culverts in the road profile with invert elevations.
10. Please show the existing culvert in the road profile.
11. Please show all VDOT cross drains.
12. Please show and label all traffic control signs on the plan. The posted speed limit for this road
should be 10 mph; the design speed is not 25mph. The design does not meet the state's 20 mph
design standards (K- sag =17, K- crest =7).
13. Please label all curb radii at the entrance onto Ambrose Commons Dr. and at the cul -de -sac. [DM]
14. Please show the street name sign on the plan.
15. The fill grades at the end of the cul -de -sac must be 3:1 or a guardrail will be required.
16. A culvert computation and profile for the existing culvert at Sta. 10 +10 must be provided even if it
is not to be replaced.
17. Please show the dimensions of the riprap outlet protection on the plans. Outlet protection should
be designed using the standard in the VESCH, not the VDOT standard since this is not a public
road.
18. Outlet velocities cannot be greater than 15fps. It appears this maximum velocity was exceeded for
structures 5 -6, 7 -8, and 11 -12. [DM]
19. Please provide a VDOT Standard for anchors if a slope of 16% is used for a culvert.
20. Please show adequate sight distance at the intersection of Ambrose Commons Drive.
21. Please provide a VDOT standard PE -1 entrance at the existing driveway.
22. A road bond has not been computed at this time. Engineering review will compute a road bond
once the plan is approved, the applicant has completed and submitted a Subdivision Road Bond
Estimate Request, and the applicant has completed and submitted a Schedule of Completion for
Bonded Improvements.
File: E1_esc swm rp_PBC_08 -044 Warthen Estates