HomeMy WebLinkAboutWPO200600043 Review Comments Erosion Control Plan 2008-06-16� 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:
Birdhouse Farm Subdivision (WP0200600043) (SUB200600381)
Plan preparer:
Gloeckner Engineering /Surveying Inc. [fax 293 -7612]
Plan received date:
7 Jun 2006 (Road Plans, SWM Plans, ESC Plans)
4 Dec 2006 (Revl, Road Plans)
2 Jan 2008 (Rev2, Road Plans)
14 Mar 2008 (Rev3, Road Plans/Revl, SWM Plans, ESC Plans)
22 Apr 2008 (Rev2, SWM Plans, ESC Plans)
09 June 2008 (Rev3, ESC Plans)
Date of comments:
4 Aug 2006 (Road Plans, SWM Plans, E &S Plans)
18 Dec 2006 (Rev I, Road Plans)
30 Jan 2008 (Rev2, Road Plans)
10 Apr 2008 (Rev3, Road Plans/Revl, ESC and SWM Plans)
03 Jun 2008 (Rev2, SWM Plans, ESC Plans)
16 June 2008 (Rev3, ESC Plans)
Reviewer:
Jonathan Sharp
A. Road and drainage plans
We received the approval letter from VDOT and have received your schedule of completion and
bond estimate request. The bond will be computed along with the bonds for SWM and ESC once they
have been approved.
B. Stormwater Management Plan
1. The following comments pertain to the BMP Plan:
a. Post development drainage areas III, IV, & V do not have any water quality measures in
place. All of area V and portions of area III and IV can be diverted to the detention basin
so they can then be treated by the biofilter. Lowering the bottom elevation basin and outlet
6 a foot will allow for more area to be drained to the basin. Please divert as much runoff as
possible to the biofilter.
b. The BMP calculations should use a project area when calculating for removal rates, not
the entire parcel area. Separate calculations should be made for each drainage area or areas
which have different (or no) BMPs. Impervious areas not included in the drainage area
going to a BMP do not need to be included. Removal rates should also be provided for
areas which have no water quality measures in place with an explanation for why they
should not or cannot be treated for water quality.[VSMH 5.10]
c. For the removal rates you provided, a biofilter area of 2.5% of the entire impervious area
must be provided. The current biofilter design includes only the proposed road for
impervious areas. Proposed or future driveways, structures, etc. located within your
drainage area need to also be included. Impervious areas not included in the drainage area
going to the biofilter do not need to be included. [VSMH 3.11]
Revl: comments addressed.
2. Please provide final contour elevation labels.
Revl: comments addressed.
Engineering Review Comments
Page 2 of 3
3. Please provide details for the detention basin. [DSM 909.2A]
Rev]: comments not addressed. Please provide a cross section of the facility including the
embankment and outlet structures. The outlet to the detention facility requires a trash rack.
Rev2: comments addressed.
4. Please provide pipe profiles for all pipes. [18- 32.6.6dl,2, DSM909.113,D]
Rev]: comments addressed.
5. Please show all stormwater management facility easements. [DSM 909.2B(2), 503.1C, 1101]
Rev]: comments addressed.
6. Please provide an inspection and maintenance easement to the stormwater management facility.
[DSM 909.2A, 503.1D]
Rev]: Please show that adequate access is provided to each facility embankment, forebay, and
outlet structure: 10 foot wide easement, no steeper than 20 01c, if steeper than 10 0/0, gravel is
required. The existing driveway may be able to serve as access to the biofilter.
Rev2: comments addressed.
7. A minimum of three species of shrubs and three species of trees are needed in the biofilter. Please
include a planting plan and schedule showing the location, species, type, size of stock, and
planting notes. [DSM 503179]
Revl: comments not addressed. Three species of trees and three species of shrubs should be
specified for the biofilter.
Rev2: comments addressed.
8. Due to the lack of computations and details with this submittal, additional comments may be
necessary upon revision.
9. (Reel) Please show the grading required to install the biofilter on the plans.
Rev2: comments addressed.
10. (Reel) The biofilter outlet should specify a trashrack.
Rev2: comments addressed.
11. (Rev]) The biofilter requires an adequate forebay to capture the concentrated discharge from the
detention facility. Typically, a ring of rip rap is placed in the biofilter around the end section of
the pipe outletting into the facility. The forebay should be sized at 10% to 25% of the biofilter
floor, and no plants should be specified in the forebay.
Rev2: comments addressed.
12. (Revl) The sand/soil mix must be 2.5 ft deep.
Rev2: comments addressed.
13. (Revl) The underdrain gravel must be 1.5 ft deep.
Rev2: comments addressed.
14. (Revl) Please provide a SWM maintenance agreement signed by the landowner, along with a $17
fee.
Rev2: comments not addressed.
Rev3: comments not addressed.
15. (Rev]) A SWM bond will be computed by the County once the plans have been approved.
C. Erosion Control Plan
1. The location of the sediment trap does not allow for all runoff to be captured. See comment 1 in
the stormwater management plan. Divert as much area as possible to run to the sediment trap. The
drainage area will exceed three acres with the increased runoff. Please make the sediment trap a
sediment basin. In addition, placing a sediment trap on the other side of the road would allow the
entire development area to be captured.
Rev]: Please address the following comments in regards to ESC protection:
a. Please clarify how sediment trap #1 will function during the ESC phase of the project.
Will Pipe 7 -8 be closed or plugged so that sediment can be trapped? Currently, the trap is
Engineering Review Comments
Page 3 of 3
shown with no wet or dry storage. Please indicate the weir location on the plans.
Rev2: comments addressed.
b. It appears that sediment trap #2 is located uphill and that associated diversion dikes are
running uphill.
Rev]: comments addressed.
c. The diversion dikes to sediment trap #2 are capturing all drainage from sediment trap #1.
Rev2: comments not addressed.
Rev3: comments not addressed.
d. Please show the grading necessary to install sediment trap #2 on the plans.
Rev2: The sediment trap is located within the road and on top of culvert 11 -12. The entire
project will be draining through the trap. Engineering recommends moving the trap out of
the road and culvert and placing directly uphill of the culvert in order to capture laden
sediment from the road and ditch construction. Additional cut would be necessary to
install the trap.
Rev3: The sediment trap is located directly below the culvert. All of the drainage from
the entire site will be draining through the sediment trap, which is not sized for all the
drainage shown flowing through it. The ESC plans must be in accord with all the
minimum standards in the Virginia Erosion and Sediment Control Handbook. It
appears there are several options:
i. Move trap #2 above the culvert so that drainage from the culvert does not drain
through trap.
ii. Size trap #2 as a basin to handle all of the ESC control for the site.
iii. Phase the ESC plans.
e. Moving sediment trap #2 directly downhill of the proposed construction entrance at the
end of the proposed roadside ditch may adequately capture the disturbed area in
drainage area III as well as capturing sediment from the construction entrance, while
avoiding capturing the drainage from sediment trap #1.
Rev2: See above, 1d.
Rev3: See above, Id.
f. Please show that the proposed waste area has adequate ESC measures. Without the
topography in this area, it is difficult to tell. Protection of the nearby stream and
neighboring parcel is very important.
Rev2: comments addressed.
2. Please show existing vegetation on the plans. [VESCH VI - 13 -14]
Rev]: Please show the existing vegetation (treeline) on the plans.
Rev2: comments addressed.
3. Please provide existing drainage areas on the plans. [VESCH VI - 13 -14]
Rev]: comments addressed.
4. Please provide a maintenance schedule on the plans. [VESCH VI - 13 -14]
Rev]: comments addressed.
5. Narrative indicates that Culvert Inlet Protection and Outlet Protection are used; but abbreviations
and symbols are not shown on the plans. Please indicate on plans where Culvert Inlet Protection
and Outlet Protection are located. [VESCH VI - 13 -14]
Rev]: comments addressed.
6. (Rev]) An ESC bond will be computed by the County once the plans have been approved.
If you have any questions, you can reach me, Jonathan Sharp, at (434) 296 -5832 ext. 3025 or my email:
jsharp@albemarle.org.