HomeMy WebLinkAboutSUB201400106 Review Comments Final Plat 2014-08-06 (3)� OF AL
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: Cascadia, blocks 4 -7
Plan preparer: Dominion Engineering, Mike Myers [mmyers @dominioneng.com]
Owner or rep.: Redus VA Housing LLC., Charlie Armstrong [carmstrong@southem-
development.com]
Plan received date: 29 July 2014
Date of comments: 5 Aug 2014
Reviewer: Glenn Brooks, P.E.
The Cascadia plans have received Engineering Review. The Following items will need to be
adequately addressed prior to final approval:
A. Street plan (SUB2013000091)
(A separate road and drainage plan is required if the property is to be bonded for subdivision.)
1. VDOT approval is required. We are awaiting approval from VDOT.
B. Site plan (SDP2013000025)
(A site plan is a record of zoning compliance on the property. It should not include VSMP plans.)
1. All comments appear to be addressed. The stormwater management plan and road plans will need to
be approved before I can recommend approval to planning.
C. Plat (SUB2014000106)
(A plat is a record of property division or reservation. Code Chapter 14)
1. All streets and infrastructure must be approved and bonded prior to plat approval.
2. All easements must match approved stormwater and street plans. Please include all stormwater facility
easements, access, and easements for mitigation areas, per the VSMP plans.
D. VSMP: SWPPP and Pollution Prevention Plan (WP02013000032)
(The Virginia stormwater management program, stormwater pollution prevention plan application and
documents)
1. The swppp does not appear to give operator information.
2. Please provide the DEQ coverage letter.
Please provide a pollution prevention plan. A specific plan was not found in the SWPPP document.
Please consult the EPA guidance and templates in preparing your plan;
http: / /water.epa. goy /polwaste /npdes /stormwater / Stormwater- Pollution- Prevention - Plans -for-
Construction - Activities.cfm
Engineering Review Comments
Page 2 of 3
E. VSMP: SWPPP: Stormwater Management Plan (WPO20130000032)
Regarding the pond;
1. The footing for the gabion basket wall is inadequate. There is no way to key the baskets in a gravel
base of unknown dimensions as shown. A similar wall to this, constructed at Hollymead Town Center
has failed repeatedly. It was undermined by scour and sunk in a soft foundation. The foundation will
depend on the underlying bearing capacity of the soil, and on the scour action from the incoming flow.
It will need to be more substantial, and deep or keyed to rock.
2. A planting plan for the aquatic bench was not found.
3. The computation package contains only routings and drawdown. Please provide water quality checks
for volume according to standard spec. 3.06, and pool depth zones per 3.06 -2.
4. All details and sections must be drawn to scale, including the dam and structures.
5. Show vehicle access to all facilities with easements. Include easement to pond 1 from Delphi or an
internal road. Include access to the biofilters and water quality swale.
Regarding the biofilters;
6. The biofilters are too small. Provide sizing to 4% of impervious areas, allowing some small increase
for upstream 2:1 slopes and compacted soils. I get approximately 1000sf for biofilter 1, and 550sf for
biofilter 2.
7. Provide sections of the dams. Each needs an impervious core, minimum top embankment width of 8ft,
and the downstream slope needs to be 3:1 or flatter.
8. Computations need to be provided for the 10year and 100yr storm to ensure operation of spillways.
9. The dimension appear incorrect in the spillway. With a bottom width of 5' and sides slopes of 2:1, a
1' depth requires 9' total width. The dimension downstream beyond the dam would be different.
10. It is not possible to achieve a 1' facility ponding depth with a rip -rap channel spillway. The rip -rap is
going to be deeper than that, and irregular enough to negate any computation. Revise the spillway
liner, remove the bio- filter schematic, and provide an accurate depiction of the facility.
11. Continue the underdrains beyond the center of the facility, and provide actual planting plans. Remove
the generic schematic and provide an accurate depiction.
Regarding the water quality Swale:
12. Provide accurate details for the water quality swale. Show soil mixture, underdrain, minimum bottom
width, maximum slope, side slopes and top width.
13. Provide computations to show hydraulic adequacy per standard spec. 3.13.
14. Detail proper check dams per standard spec. 3.13, with spacing planned according to the planned
slope. Show proper dimensions of check dams to ensure flow over the center. The detail provided is
incorrect in every aspect.
15. Standard spec. 3.13 requires 3:1 or flatter side slopes.
16. Provide a better, to scale and dimensioned, detail of the channel transition, pipe under the access road,
stilling basin, and level spreader at the end of the water quality swale.
F. VSMP: SWPPP: Erosion and Sediment Control Plan (WPO2013000032)
1. The erosion and sediment control plan is approved. Comments have been addressed.
G. Mitigation Plan (WPO2013000032)
(A mitigation plan is a plan of buffer disturbances, and replanting or restorative measures)
1. The mitigation plan is approved. Buffers and easements for mitigation areas will need to be shown on
final plats.
H. Bond Estimate Request for VSMP plans (WPO2013000032)
Engineering Review Comments
Page 3 of 3
L The bond estimate request will be processed when all VSMP plans are approved.
File: E1_rp,fsp,fpt,vsmp_GEB _ template.doc