HomeMy WebLinkAboutWPO202000048 Correspondence 2020-12-07I® COLLINS ENGINEERING 200 GARRETT ST, SUITE K CHARLOTTESVILLE VA 22902
434.293.3719 PH 434.293.2813 FX
www. co l l i ns-engi nee ri ng xom
December 4, 2020
David James
County of Albemarle
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, VA 22902
RE, Mill Creek Industrial Lot 11 VSMP Plan, WPO 202000048
Dear Mr. James:
Thank you for the comments dated November 20, 2020 on the above referenced project. Below are responses to
these comments.
A. General
1. The Owner's correspondence information will be e-mailed to the County Engineer.
2. The WPO number has been added to sheet 1, in the upper -center portion of the page, and the previously
shown approval block has been removed from the lower -right portion of sheet 1.
3. A note has been added to sheet 1, in the lower -left portion of the page, mandating the contractor obtain the
required VDOT entrance permits prior to construction, hereby addressing this comment.
4. This plan does not require any offsite easements. All disturbances and improvements are located onsite, or
within public right-of-way, hereby addressing this comment.
B. Stormwater Pollution Prevent Plan (SWPPP)
1. The applicant has updated the registration statement and will be providing it to the County Engineer.
2. The SWPPP packet completed by CE follows the County's template.
C. Pollution Prevent Plan (PPP)
1. A PPP has been completed.
D. Stormwater Management Plan (SWMP)
1. The sizes of the curb cuts have been modified to have lengths of 2', in accordance with County
Engineering's October 22nd SDP 202000049 comment #23, herby addressing this comment. Also, concrete
bumper blocks are now proposed with the SDP to provide additional safety measures.
2. The plans have been revised to capture additional impervious areas near the entrance. The revised plans
also route the trench drain's runoff to basin A, which will capture the bulk of the impervious areas
highlighted in this comment. The other impervious areas added at the entrance are required by VDOT with
their standard taper requirements. The entrance ramps up from the existing edge of pavement, as is
typical for commercial entrances, and getting the runoff back to basins A or B is not possible. This runoff
however safely sheet flows to the existing ditch and inlet and is not concentrated with the proposed
improvements. The revised plans also confirm the existing inlet can handle this additional impervious
runoff. This information is shown on sheet 7 in the lower -left corner, and in the attached calculations
packet. Per an e-mail correspondence from Mr. James on November 241", this methodology was deemed
appropriate for addressing this comment.
3. It was agreed upon in a November 23'd phone conversation between Mr. James and Mr. Murray, and later
confirmed in a November 20 e-mail, that the routing of the entire drainage area through the
interconnected basins is acceptable. Both basins A & B share a single outfall system/barrel, and water
simultaneously backs up in both of the basins that discharge into the one barrel (structure 3). Additionally,
basins A and B have the same general range in depths/elevations. Also, it was determined in this call that
the revised plans would need to show the 10-year HGL in the outfall pipes. And if the HGL exceeds the top
of the pipe then the 24" pipe(s) will be required to be watertight. After an evaluation of the storm sewer's
drainage computations, only structure 1's HGL (narrowly) crests the crown of the proposed 24" piping. The
HGL can be seen in sheet 8's profile in the lower -right corner of the page and in the SDP's calculations. As a
result of this analysis, the plans have been updated to specify structure 1 as being a watertight pipe. With
respect to comment 7b, the 448.48' elevation is correctly listed on the plans for structure 7. However the
routing calculations lower 449.00' elevation was previously listed incorrectly for structure 3. Consequently,
the routing calculations were corrected to now list a 446.67' invert for str. 3's upper end at Basin A's riser,
matching what is shown on the plans/sheet 7.
4. Please see the response above to comment D.2. And as it relates to this comment, the existing inlet (str.
EX-1) was analyzed/confirmed to be able to intercept its surface runoff without causing flooding in the
proposed entrance. This was determined to be acceptable in the aforementioned November 20 e-mail.
Please see sheet 7 in the lower -left corner, and the attached calculations packet, for details showing the
inlet's adequacy.
5. Please see the response above to comment D.3. In the November 241h e-mail it was determined that a
singular routing of the interconnected basins was acceptable given this project's unique hydraulics/layout.
6. The peak design backwater elevations are now also shown in basin A, within sheet 8's profile entitled'Str
8- EXV.
7. The nutrient credit availability letter will be provided separately from this submittal. The applicant has
attempted to address all plan -related comments with this submission, and the nutrient credit availability
letter and SWM maintenance agreement will be executed upon confirmation that all other plan -related
comments have been addressed.
8. It is acknowledged that the nutrient credit purchase is required prior to the issuance of a grading permit.
9. This comment is acknowledged. Please see the response above to comment D.7.
E. Erosion and Sediment Control Plan (ESCP)
1. Sheet 4 previously showed the County defined managed steep slopes. With this resubmittal, a
label has been added to more clearly notate this. Sheets 5 and 6 have also been revised to now
show and label the County defined managed steep slopes.
2. Sheet 3's VESCH stone construction entrance detail, previously shown in the top -right corner, has
been removed. Sheets 4, 5 and 6 now depict the construction entrance as being paved, and have
a note referencing Albemarle County's standard paved wash rack detail shown on sheet 3.
3. Sheets 5 and 6 have been revised to call out the areas where proposed grades are steeper than
3:1. The notes read, ?he proposed embankment at the eastern & southern sides of the site is in
cut, with a maximum 2:1 slope. Slopes greater than 3:1 shall be planted with a native steep slope
mix with annual ryegrass by Ernst conservation seeds at a rate of 60 lbs. per acre, or 1 lb per
1,000 sf, unless otherwise specified. This is typical for areas of proposed slopes steeper than 3:1,
and these areas shall not be mowed: This same note has been added to the bottom -left corner
of sheet 3, directly below the permanent seeding schedule, hereby addressing this comment.
This seed mix was recommended to Collins Engineering by Albemarle County Inspections.
Should you have any questions during your final review and approval of this project, feel free to contact
the applicant at scott@collins-engineering.com or at graham@collins-engineering.com.
Sincerely,
Graham Murray, PE