HomeMy WebLinkAboutWPO201200001 Review Comments Stormwater Management Plan 2012-04-12Philip Custer
From: Philip Custer
Sent: Thursday, April 12, 2012 5:48 PM
To: 'Tom Gallagher'; 'Tom Gallagher'; 'hwhite @wwassociates.net'
Cc: Glenn Brooks; Christopher Perez; Mark Graham
Subject: Engineering review of Stonefield Plans
Attachments: E2_mia esc swm_PBC_sdp- 2012 -00001 wpo- 2011 -00059 Town Center Amendment.doc
Good evening,
I have completed my review of the latest submittals for Stonefield.
The private street plans, SUB - 2012 - 00005, are hereby approved. A determination will need to be made by the county
engineer whether a bond adjustment will be necessary. Additional copies may be required to pass off to the inspections
division. If necessary, these will be requested by staff at a later date.
The stormwater management plan associated with the private street (WPO- 2012 - 00001) is hereby approved on the
condition that a stormwater facility maintenance agreement referring to this latest plan is recorded. A new SWM bond
also must be posted. Please provide a bond estimate request form to the county to receive an estimate. The site plan
amendment for the cinema cannot be approved until this bond is posted and the maintenance agreement recorded.
The ESC bond will remain unchanged under WPO- 2011 - 00036, but when the new SWM bond is posted, the old SWM
bond can be released. Additional copies may be required to pass off to the inspections division. If necessary, these will
be requested by staff at a later date.
All technical comments regarding the cinema site plan amendment (SDP- 2012 - 00001) have been addressed. However,
this plan cannot be approved until the SWM bond is posted and the maintenance agreement recorded for the swm
amendment to the road plan. Also, because the swm plan is no longer being completely thrown out, since 2 filterras
remain, a swm amendment will need to be processed. The plan itself is fine, but a $180 fee will be required. Please
direct this fee to original swm plan, WPO- 2011 - 00055. The $180 fee that was provided with the first submittal is now in
the process of being refunded to the applicant and cannot be recalled. After this fee is received, the new SWM bond for
the private road posted, and the maintenance agreement for the new road SWM is recorded, the applicant can request
a new bond computation for WPO- 2011 -00055 by submitting a bond estimate request. Additional copies will be
required to pass off to the inspections division. These will be requested by staff at a later date.
The Towncenter site and stormwater plan amendment cannot be approved at this time. Please refer to the attached
memo for further detail.
Please let me know if you have any questions.
Thanks,
Phil
(434) 296 -5832 x3072
ALg�,��
�'IRGINZ�
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: Stonefield Blvd. Plan Amendment; WPO- 2012 -00001 & SUB - 2012 -00002
Plan preparer: Mr. Herb White, PE; W & W Associates
Owner or rep.: Albemarle Place EAAP LLC
Date received: 28 December 2011
(Rev. 1) 31 January 2012
Date of Comment: 20 January 2012
(Rev. 1) 22 February 2012
Engineer: Phil Custer
The second submittal of the SWM and road plan amendments for Stonefield Blvd. (WPO- 2012 -00001 and
SUB - 2012 - 00002), received on 31 January 2012, have been reviewed. The plans can be approved after
the following comments have been addressed:
A. Stormwater Management Review Comments (WPO- 2012 - 00001)
1. The 7.5ft retaining wall so close to the roadway presents a considerable safety issue. If the wall
cannot be eliminated or reduced significantly, this design change may not be approved by county
staff or guardrails around half of the facility will be needed. It seems that there are two design
changes that led to the addition of the wall: the lowering of the invert of structure 46 and a
dramatic increase to the size of the BMP. In the original design of structure 46, the pipe seemed to
be at a sufficient depth below the pavement at the Sperry entrance. There also appears to be plenty
of fall in the system to allow the outlet to be raised and still meet minimum slope requirements.
The desire to have a larger footprint for the increased watershed is understandable, but please note
that the county accepts 4% of the impervious area as the biofilter bed, as opposed to 5% shown in
the calculation (the VSMH specifies both). Additionally, there seems to be room to stretch the
biofilter to the north and minimize the wall height on the west side.
(Rev. 1) A seven foot retaining wall is an unnecessary safety hazard this close to the roadway.
The necessary footprint of 4700sf can be achieved by locating the wall about I8ft from the back
of curb, grading from the back of curb down to the top of wall at a 3:1 slope, and extending the
wall 20ft to the north. I only needed a wall of 2ft on the west side of the biofilter to achieve this.
The guardrail would still be needed on the south side of the biofilter. Please specify end
sections for the guardrail that remains.
2. Please update all drainage area maps and calculations to include the proposed changes to the Regal
Cinema plan. The calculations for the system downstream of 46.4 seem to account for the parking
lot water, but the map does not match the calculations. The biofilter calculations and map do no
include this area; only a note references the reason for the increased size of the facility.
(Rev. 1) Comment has been addressed.
3. Biorention facilities, as well as most BMPs in the Virginia Stormwater Management Handbook,
are volume -based facilities and achieve their specific removal rates by capturing the first flush
(1/2" or 1 ", depending on RR) of storm events. The full first flush volumes cannot be caught with
current configurations of structures 39.1 and 46.1. For the Sperry facility, if you wish to provide a
bypass pipe for larger storms, please size all pipes to the biofilter (no restrictor plates) for the full
discharge, add a structure just south of the biofilter wall, move the bypass pipe to the newly added
structure, and set the elevation of the bypass pipe at lft above the bed elevation. A similar
arrangement will need to be made for the northern biofilter.
(Rev. 1) The current configuration is acceptable if IS -1 is proposed on this manhole and the
bypass pipe is raised 6" so it is the same elevation of the top of the pipe going to the biofilter, as
it had been proposed in the first submittal.
4. Sediment forebays are required on all SWM quality facilities. Biofilter forebays should be
between 10% and 20% of the biofilter floor area.
(Rev. 1) Comment has been addressed.
5. Please specify the rim elevation of Structure 42.1 in the biofilter details.
(Rev. 1) Comment has been addressed.
6. Please provide details of the retaining wall in this set. The set of details should include a typical
cross - section and specific details for the pipes through the wall. The pipe from the facility is likely
designed through the wall's footer or base.
(Rev. 1) Comment has not been addressed.
7. What material are the walls made out of? Will the walls be permeable? Is it possible for the drain
behind the wall to be a point that ponded water from the biofilter can bypass the treatment media?
The wall will need to be watertight up to the rim of the grate.
(Rev. 1) Watertight specifications should be extended to the bottom of the facility as well
especially since a permanent water pool will existing in the stone layer.
8. The invert out of the drop inlet is only 2.5ft below the bed elevation. A typical biofilter design sets
this elevation at 3.5ft to 4ft below the bed elevation because of the underdrain. Please address this
oversight. The underdrain cannot be placed in the biofilter media mix. The bed must be raised at
least lft, the outlet pipe and structure must be dropped at least lft, the underdrain must be
eliminated with soil tests supporting an acceptable infiltration rate, or the applicant must design
elbow fittings on the underdrain so that a permanent pool of water exists inside the facility as long
as the water elevation is at least 18" below the top of the bed elevation (Internal Water Storage).
(Rev. 1) Comment has been addressed.
9. This application will require that a new Stormwater Management Facility Maintenance Agreement
be recorded. Please complete this form and submit it to Ana Kilmer with a $17 recordation fee
after reading the instructions online. The applicant should wait until they are sure they are going
forward with this application to record this agreement.
(Rev. 1) Comment has been noted.
10. The SWM bond will increase with this revision. Before any road plan amendment is authorized
for construction, a SWM bond will need to be posted under this application, WPO- 2012 - 00001.
The SWM bond with WPO- 2011 -00036 can then be released. Please provide a completed Bond
Estimate Request Form to the county engineer to receive a new SWM bond.
(Rev. 1) Comment has been noted.
11. (Rev. 1) Another $180 fee is needed for the review of this SWM plan amendment.
12. (Rev. 1) Please refer to the separate SWM memo provided at the same time as this comment
letter.
B. Road Plan Review Comments (SUB- 2012 - 00002)
I. ...-- of $400 is required for this private street review. [14 -203]
(Rev. 1) Comment has been addressed.
2. Please see comments A.1, A.2, and A.3.
3. Major deviations from the public street plans such as the reduction of clear zones, restriction of
entrance widths, removal of gutter pans, and addition of the 4 -way stop have been reviewed by the
county engineer in conjunction with ZMA- 20 1 1 - 00007. The plan cannot be approved until it is
consistent with the plan/proffers approved by the Board of Supervisors.
(Rev. l) Comment has been noted.
4. One of the items not identified in the staff report is the southern median at the intersection of
District Avenue and Bond Street. County engineering staff does not approve of the extension of
the median to the curb line tangent of Bond Street. The plan does not have to meet the median
design approved by VDOT, but County engineering staff will require the median to be moved at
least IOft from the tangent line. [14 -412B]
(Rev. I) Comment has been addressed.
5. Street furniture must be shown on District Avenue as designated by Appendix B of the Code of
Development.
(Rev. I) As recommended by the applicant, this will be reviewed with the Towncenter site plan
amendment.
File: E2_swm rp_PBC _ wpo- 2012 -00001 sub - 2012 -00002 Stonefield Blvd. Plan Amendment.doc
ALg�,��
�'IRGINZ�
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: Stoneiield Blvd. Plan Amendment; WPO- 2012 -00001 & SUB - 2012 -00002
Plan preparer: Mr. Herb White, PE; W & W Associates
Owner or rep.: Albemarle Place EAAP LLC
Date received: 28 December 2011
Date of Comment: 20 January 2012
Engineer: Phil Custer
The SWM and road plan amendments for Stoneiield Blvd. (WPO- 2012 -00001 and SUB - 2012 - 00002),
received on 28 December 2011, have been reviewed. The plans can be approved after the following
comments have been addressed:
A. Stormwater Management Review Comments (WPO- 2012 - 00001)
1. The 7.5ft retaining wall so close to the roadway presents a considerable safety issue. If the wall
cannot be eliminated or reduced significantly, this design change may not be approved by county
staff or guardrails around half of the facility will be needed. It seems that there are two design
changes that led to the addition of the wall: the lowering of the invert of structure 46 and a
dramatic increase to the size of the BMP. In the original design of structure 46, the pipe seemed to
be at a sufficient depth below the pavement at the Sperry entrance. There also appears to be plenty
of fall in the system to allow the outlet to be raised and still meet minimum slope requirements.
The desire to have a larger footprint for the increased watershed is understandable, but please note
that the county accepts 4% of the impervious area as the biofilter bed, as opposed to 5% shown in
the calculation (the VSMH specifies both). Additionally, there seems to be room to stretch the
biofilter to the north and minimize the wall height on the west side.
2. Please update all drainage area maps and calculations to include the proposed changes to the Regal
Cinema plan. The calculations for the system downstream of 46.4 seem to account for the parking
lot water, but the map does not match the calculations. The biofilter calculations and map do no
include this area; only a note references the reason for the increased size of the facility.
3. Biorention facilities, as well as most BMPs in the Virginia Stormwater Management Handbook,
are volume -based facilities and achieve their specific removal rates by capturing the first flush
(1/2" or 1 ", depending on RR) of storm events. The full first flush volumes cannot be caught with
current configurations of structures 39.1 and 46.1. For the Sperry facility, if you wish to provide a
bypass pipe for larger storms, please size all pipes to the biofilter (no restrictor plates) for the full
discharge, add a structure just south of the biofilter wall, move the bypass pipe to the newly added
structure, and set the elevation of the bypass pipe at Ift above the bed elevation. A similar
arrangement will need to be made for the northern biofilter.
4. Sediment forebays are required on all SWM quality facilities. Biofilter forebays should be
between 10% and 20% of the biofilter floor area.
5. Please specify the rim elevation of Structure 42.1 in the biofilter details.
6. Please provide details of the retaining wall in this set. The set of details should include a typical
cross - section and specific details for the pipes through the wall. The pipe from the facility is likely
designed through the wall's footer or base.
7. What material are the walls made out of? Will the walls be permeable? Is it possible for the drain
behind the wall to be a point that ponded water from the biofilter can bypass the treatment media?
The wall will need to be watertight up to the rim of the grate.
8. The invert out of the drop inlet is only 2.5ft below the bed elevation. A typical biofilter design sets
this elevation at 3.5ft to 4ft below the bed elevation because of the underdrain. Please address this
oversight. The underdrain cannot be placed in the biofilter media mix. The bed must be raised at
least lft, the outlet pipe and structure must be dropped at least lft, the underdrain must be
eliminated with soil tests supporting an acceptable infiltration rate, or the applicant must design
elbow fittings on the underdrain so that a permanent pool of water exists inside the facility as long
as the water elevation is at least 18" below the top of the bed elevation (Internal Water Storage).
9. This application will require that a new Stormwater Management Facility Maintenance Agreement
be recorded. Please complete this form and submit it to Ana Kilmer with a $17 recordation fee
after reading the instructions online. The applicant should wait until they are sure they are going
forward with this application to record this agreement.
10. The SWM bond will increase with this revision. Before any road plan amendment is authorized
for construction, a SWM bond will need to be posted under this application, WPO- 2012 - 00001.
The SWM bond with WPO- 2011 -00036 can then be released. Please provide a completed Bond
Estimate Request Form to the county engineer to receive a new SWM bond.
B. Road Plan Review Comments (SUB- 2012 - 00002)
1. A fee of $400 is required for this private street review. [14 -203]
2. Please see comments A.1, A.2, and A.3.
3. Major deviations from the public street plans such as the reduction of clear zones, restriction of
entrance widths, removal of gutter pans, and addition of the 4 -way stop have been reviewed by the
county engineer in conjunction with ZMA- 20 1 1 - 00007. The plan cannot be approved until it is
consistent with the plan/proffers approved by the Board of Supervisors.
4. One of the items not identified in the staff report is the southern median at the intersection of
District Avenue and Bond Street. County engineering staff does not approve of the extension of
the median to the curb line tangent of Bond Street. The plan does not have to meet the median
design approved by VDOT, but County engineering staff will require the median to be moved at
least 1Oft from the tangent line. [14 -412B]
5. Street furniture must be shown on District Avenue as designated by Appendix B of the Code of
Development.
File: E1_swm rp_PBC _ wpo- 2012 -00001 sub - 2012 -00002 Stonefield Blvd. Plan Amendment.doc