HomeMy WebLinkAboutWPO201900027 Correspondence 2020-10-08® COLLINS ENGINEERING
October 2, 2020
Emily Cox, PE
Department of Community Development
401 McIntire Road
Charlottesville, VA 22902
RE: Pleasant Green Connector Road VSMP Plan (WPO 201900027)
200 GARRETT ST, SUITE K CHARLOTTESVILLE VA 22902
��434.293.3719 PH 434.293.2813 FX
www.coll ns-eng ineeri ng.com
Thank you for your comments dated May 14, 2019 on the above referenced project. Below are detailed responses to your comments.
A. Stormwater Pollution Prevention Plan (SWPPP)
1. A SWPPP has been provided with this resubmittal.
B. Pollution Prevention Plan (PPP)
1. A PPP has been provided with this resubmittal.
C. Stormwater Management Plan (SWMP)
1. A'Stormwater Management � le' has been added to this plan, as shown on sheet 6 in the bottom -middle portion of the page,
depicting how water quality and quantity requirements are met. Water quality requirements are met for this project via the
installation of a level II bioretention basin. The biofilter treats the proposed improvements, as well as mitigates the water quality
losses from the proposed disturbances in an existing SWM Forest and Open Space easement. In regards to stormwater quantity
requirements, compliance with minimum channel protection requirements is met via 9 VAC 25-870-66 sections B.1.a and section
B.4.a. Flood protection compliance is met via 9 VAC 25-870-66 sections C.2.a and C.3.c.
2. This comment is acknowledged. The vacation of this portion of the SWM Forest and Open Space easement shall be recorded prior
to this plan's approval.
3. The attached WPO plan addresses the water quality requirements for this project, and accounts for the water quality losses
associated with the proposed impacts to the existing SWM Forest and Open Space easement. Because of this, and the requirement
to vacate this portion of the existing SWM Forest and Open Space easement prior to approval, the applicant believes an
amendment to WPO 201600069 can be avoided with this plan's approval.
4. The plans have been revised and continue to reference other County project numbers, however the notes no longer reference
'currently under review. Also, the WPO numbers have been added to this plan per this comment.
5. The VSMP plan has been updated to include mitigation plans and details. Please see sheet 9.
6. This comment is acknowledged. All applicable permits for work in Powells Creek will be provided prior to approval.
7. This comment is acknowledged. The triple box culvert and wing walls are proposed under SUB 201900058 and the approval of this
plan is required prior to the approval of this plan.
D. Erosion & Sediment Control Plan (ESCP)
1. Sheet 4, in the upper -right corner in the 'Triple Culvert Installation Notes', was revised to now include note #5. This note addresses
how the area used for a temporary stream diversion will be stabilized.
2. The note referenced in this comment has been corrected.
3. The proposed grades have been revised to have a maximum slope of 3:1, and the note referenced in this comment has been
removed.
4. The proposed plan contains two outlet protections. The first outlet protection is shown, labeled and dimensioned on sheet 4 and is
for the temporary culvert located at the construction entrance in ESC phase I. The second outlet protection is for the triple box
culvert and its riprap is shown, labeled and dimensioned on sheets 4 and 5 in ESC phases I and II. Also, calculations have been
provided for this outlet protection in accordance with the VDOT drainage manual. Please note, the VDOT drainage manual was
used to design the triple box culvert's outlet protection instead of the VESCH since the drainage area exceeds 1 square mile (next
ESCP comment). Please see the attached calculations packet for this outlet protection design.
5. The drainage area to the proposed triple box culvert is 2,037 acres, or 3.18 square miles. This is per the FEMA flood insurance study
#51003CVODOC. Because this drainage area exceeds 1 square mile, the outlet protection for the triple culvert was design per the
VDOT Drainage manual instead of the VESCH.
6. Sheet 4 has been revised to specify a Type C channel lining for the temporary stream diversion. Please see the riprap depiction in
plan view, as well as the'Stream Diversion During Culvert Installation b- .' and the 'Triple Culvert Installation Notes' in the
upper -right corner of the page. The attached calculations packet also provides a Manning's calculation for the temporary stream
crossing depicting the peak velocity and depth.
Please contact Scott Collins at scott0collins-enaineering.com or Graham Murray at graharn0collins-engineerinH.com with any questions.
Sincerely,
Graham Murray, PE