HomeMy WebLinkAboutWPO202100007 Correspondence 2021-06-24® COLLINS ENGINEERING
June 9, 2021
Emily Cox, PE
Department of Community Development
401 McIntire Road
Charlottesville, VA 22902
RE: Brookhill Blocks 16-17 VSMP Plan (WPO 20210007)
20o 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 March 10, 2021 on the above referenced project. Below are our detailed responses to your
comments. Should you have any questions during your review and approval of this project, feel free to contact Graham Murray at
¢raham(acollins-eneineerine.com or at (434) 566-3011.
A. Stormwater Pollution Prevention Plan (SWPPP)
1. Attached is the revised registration statement. It is just a continuation of the existing DEQ permit. We will send over the
updated coverage map as well.
2. An overall coverage map has been included with the revised SWPPP's submittal.
B. Pollution Prevention Plan (PPP)
1. The previous comments have been addressed and the PPP was updated with this plan's recent changes.
C. Stormwater Management Plan (SWMP)
1. This comment is acknowledged and the client is currently working on the agreement.
2. This comment is acknowledged. Please note, level spreader'A' has been relocated and no longer impacts the floodplain.
3. Brookhill is located within a Federal dam inundation zone with the Southfork reservoir. The Sunny day breach for the dam
on this section of the development is the 374 contour, as shown in the rezoning. The lot development is well above the
Sunny day dam breach inundation zone, as required. The county mapping shows an overlay of the state dam breach
inundation zone from the Sugar Hollow dam. The dam classification on this dam is already high hazard classification,
therefore, no additional study is required for properties within this dam inundation zone, per DCR when you have
development within an existing high hazard dam classification zone.
4. Sheets 11, 12 and 13 at the back of the VSMP set have been added. These sheets show the retaining walls, greenway,
steep slopes, buffers, SWM forest and open space easement, SWM conserved open space easement and other sensitive
areas.
5. The plans have been revised throughout to show and label the Polo Grounds Road buffer and the perimeter buffer.
6. A detail has been provided for the proposed segmental block retaining walls. Please see the upper -right corner of sheet 3.
7. Mr. Murray of Collins Engineering spoke with Ms. Cox of County Engineering on May 1311 concerning this comment letter.
In the conversation, it was Mr. Murray's understanding that the previous plans were not quite clear enough regarding the
VRRM limits of disturbance boundary. As a result, sheet 16A has been added to the plans to more clearly show the VRRM
limits of disturbance boundary, which encompasses all of the plan's proposed work.
8. Following the May 1311 conversation Mr. Murray updated sheet 15's stormwater management narrative. More specifically
as it pertains to this comment, the second to last paragraph was added to the narrative to address this comment and the
concerns over the potential increased sheet flow. The revised plans now mandate splash blocks be installed on the
detached single family homes' downspouts, upland of the steep slopes. Please also note, this project meets minimum
Stormwater quantity requirements. This is noted in the SWM narrative with specific references to how each subarea is
compliant with 9 VAC 25-870-66.
9. The plans have been updated and more clearly show where roof drains will be directed. Sheets 11, 12 and 13 at the back
of the set show the roof drains at a smaller scale, sheet 15 shows the roof drains within the overall drainage areas and the
SWM narrative on sheet 15 was revised to now include the last paragraph. Additionally, the second to last paragraph in
the narrative was revised to state the newly added splash blocks at the western detached homes downspouts outfall near
the homes upland of the steeper tie-in grades. These revisions were discussed in the May 13th phone conversation and
were considered to be an acceptable manner for addressing this comment.
10. The plans were revised and level spreader W is now located outside of the greenway. The applicant met with County
Engineering on June 2n1 to confirm the new level spreader's location was acceptable.
11. The Microsoft Excel files for the VRRM spreadsheets, and the overall Brookhill Water quality Tracking Table, have been
provided with this resubmission.
12. Underground detention system 'A' was revised to address this comment. The previous plans only provided one access
manhole. The plans now provide 4 access manholes. Also, underground detention system 'B' provides 7 access manholes.
13. In order to meet minimum channel protection requirements via the energy balance computations, a low -flow orifice less
than 3" in diameter is required. The SWM report submitted shows this. However to reduce the risk of clogging, the
applicant has revised the plans to provide low -flow orifices with a minimum diameter of 3". The minor increase in the low -
flow orifices' diameters increase the 1-year SCS outflows slightly, and is now above the energy balance's thresholds. As a
result, a request has been submitted to the County requesting this minor overage be accepted. In the May 13" phone
conversation this was deemed an acceptable resolution to addressing this comment.
14. The SWM facilities have been revised and now outfall directly to the stream's banks. In the May 13th phone conversation
this was deemed an acceptable resolution to addressing this comment.
15. The proposed level spreader'A' has been relocated and no longer impacts the floodplain.
16. The SWM report has been updated to provide pipe calculations for the SWM facilities' outfalls.
17. The set has been revised and no longer provides a mitigation sheet.
D. Erosion and Sediment Control Plan (ESCP)
1. Sheet 2 has been revised to show the deed book and page numbers for the existing easements.
2. The plans have been revised to address this comment. The approved building in block 3 is no longer shown in the plans.
Also, the plans have been revised to show the currently proposed phase II improvements to Polo Grounds Road, inclusive
of the pedestrian tunnel, culverts and storm sewer. In the May 13th phone conversation Collins Engineering informed
County Engineering that the Polo Grounds Road improvements would be needed to support Brookhill's blocks 16 & 17. As
result, these plans have been updated to include bold notes on sheet 2 (upper -right corner) and sheet 18 (bottom -center)
that states the construction of the phase 11 Polo Grounds Road improvements (provided under a separate plan) is required
prior to the issuance of certificates of occupancies for Blocks 16 & 17. The phase I and phase II erosion and sediment
control plans do not require the Polo Grounds Road improvements' construction and tie into the current Polo Grounds
Road. In these ESC phases the disturbances are treated through the measures shown. However for stormwater
management purposes, the improvements are required for the storm sewer's outfall and the blocks 16 & 17's entrance. As
a result, the aforementioned note has been added to the plans to ensure the Polo Grounds Road improvements are
constructed prior to the issuances of certificates of occupancies.
3. The plans do not propose slopes steeper than 2:1, and they have been revised on sheets 4 and 6-10 (in bold boxed text) to
specify landscaping that can withstand slopes steeper than 3:1.
4. The site is balanced, and a stockpile location is shown on sheets 5, 8 and 11.
5. Sheet 16B now'checks' the HDPE anti -vortex device option, and includes a note requiring its installation with dry basin 'A',
sediment basin 'A' and sediment basin '13'.
6. Sheet 13 was revised in the Sediment Basin Wand Sediment Basin 'B' details to specify the type of foundations required to
anchor the risers. Additionally, this sheet was revised in the lower -left corner to include a detail and construction
requirements for the anti -seep collars associated with the outfalls.
7. Sheet 3 was revised in the lower -left corner of the page to include a detail for the baffle. The detail specifies that the
baffles shall extend from the bottom to 6" above the overflow.
8. Sediment Basin 'A' has been revised and its bottom elevation is now 1' higher than the bottom elevation of dry detention
basin W.
9. The plans have been revised and the grading is now located a minimum of 5' from the preserved slopes and greenway.
Please note, the silt fence will be installed at the limits of the proposed grading hereby making the limits of disturbance,
silt fence and proposed treeline all located in one location in the field (a minimum of 5' off the preserved steep slopes and
greenway). However for clarity purposes the plans show these three lines staggered (with the proposed grading a
minimum of 5' off the preserved steep slopes and greenway).
Sincerely,
Graham Murray, PE