HomeMy WebLinkAboutWPO202100043 Correspondence 2021-10-22 (2)SHIMP ENGINEERING, P.C.
Design Focused Engineering
October 22, 2021
John Anderson
County of Albemarle
Department of Community Development
401 McIntire Road, North Wing
Charlottesville, Virginia 22902
RE: Response Letter #1 for WPO2021-00043 Crozet Animal Wellness Center - VSMP
Dear John,
Thank you for your review of the VSMP request for Crozet Animal Wellness Center. This letter contains
responses to County comments dated 9/2/2021.Our responses are as follows:
A. Stormwater Pollution Prevention Plan (SWPPP)
1. Sec. II, G. —Complete Estimated Project dates.
RESPONSE: Estimated project dates have been added.
2. Review /revise Sec. II, C. if estimated area to be disturbed changes in response to comments,
elsewhere.
RESPONSE: Disturbed area has been updated.
3. Sec. III, Offsite Support Activity — Site is unbalanced. Cut north of existing east parking lot,
demolition, a stream relocation, and excavation (BMPs 1 and 2) will generate excess material.
Prior to receiving a Grading Permit, Construction Activity Operator must identify off -site
waste /spoil location, secure an off -site permit, if needed, and estimate volume and type of
material to be exported from this site. Proposed grading /demolition indicate export is
unavoidable. Revise Sec. III of Registration Statement as needed.
RESPONSE: Registration statement has been updated to include offsite disposal of excavated
material. The permit will be updated once the disposal location is determined.
4. Provide a complete SWPPP for project; use 12-section county template. Only Sec 1 of the
SWPPP. (Registration Statement) appears to have been submitted. Link to template: https://
www.albemarle.org/home/showpublisheddocument/166/637202310327530000 RESPONSE:
A SWPPP has now been provided using the 12-section template.
5. Include 2019 Notice of Termination form. Link:
http://www.albemarle.org/upload/images/forms_center/departments/Community_Developme
nt/form s/Engineering_and_W PO_Forms/CGP_Notice_of_Termination_2019_FINAL_20190
4.pdf
RESPONSE: Form has been included and will be completed upon termination of work.
6. Revise SWPPP title to include ref. to VSMP /WPO2021-00043
RESPONSE: SWPPP title includes assigned WPO #.
912 E. High Sr. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
C. Stormwater Management Plan (SWMP)
1. Please confirm routing output, p. 25, is consistent with p. 24 graphic which appears to group
and show sub -catchments IS, 3S routing to detention 1 (4P), sub -catchment 2S routing to
detention 2 (1P), and then 4S, 1P, and 4P evaluated as POAI. Pg. 25 output appears to group
modeled output differently. We can't follow it, but this may be due to general lack of
familiarity with how HydroCAD organizes data output. Please clarify, for our understanding.
RESPONSE: The routing output as shown on page 24 is correct. The information on page 25
provides basic information for each item and does not display them in the order that they are
routed. The model has been updated to remove BMP 2 and the developed area previously
shown for additional parking behind the building.
2. Pg. 11, PDF report: Provide RV pre-dev, RP post-dev calculations. Clarify source of these
energy balance equation values, which do not appear to derive from VRRM.xls provided in
calculation report.
RESPONSE: RV predev and postdev calculations are included in the respective hydrocad
reports. The energy balance equation is used for determining water quantity compliance and
is not necessarily the same area as the VRRM uses for water quality compliance. The energy
balance equation values are based on the drainage area of the site where as the VRRM is
based on the limits of disturbance.
3. Cl: Please revise to include ref. to WP02021-00043 (Applies to Cale. packet, SWPPP cover,
as well).
RESPONSE: The WPO # has been added to all submittals.
4. 3, C4
a. Show /label SWM Facility /Access easement. Ref easement diagram, ACDSM, p.
15, image below, ensure easement is adequate. [
https://www.albemarle.org/Home/ShowDocument?id=270 ]
b. Provide public drainage easement downstream of BMPs 1 and 2 to point of
confluence with relocated stream.
c. Respond to (any) County Water Resources review comments on design, generally, or
effect of design on downstream county BMP (constructed wetland), specifically.
RESPONSE: A 20' easement has been added for the SWM facility and storm pipe
downstream of BMP #L BMP #2 is no longer needed and has been removed.
5. Submit separate plat application for SWM Facility /access and public drainage easements. A
deed is required to be recorded with this easement plat. Link to easement plat application:
hMs://www.albemarle.ore/home/shomTublisheddocument/1052/637624089314100000
RESPONSE: A plat application will be submitted. Drainage easements are shown for the
SWM facility and storm pipe.
6. Drainage easements are to be labeled on plans and plats, "Drainage Easement" and
"dedicated to public use"
RESPONSE: All drainage easement labels have been added.
7. Drainage easement plats must be accompanied by a deed. Standard deeds are provided by the
Count Attorney, along with administrative guidelines. These are also available in the
documents forms center of the county website.
RESPONSE: The drainage easement has been indicated on the plans. A plat and deed will be
submitted at a later date.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
8. C4 proposes BMP #2, Sir. B1, nearly coincident with the relocated stream. Provide
additional plan detail to show how design will effect intersection between B 1 riprap outfall
and the relocated stream, resistant to erosion. Provide labels, notes, elevations, etc., to ensure
outfall riprap is resistant to 2-yr event velocity of the relocated stream, not just BMP #2
discharge velocity. This outfall will experience erosive forces of the relocated stream.
RESPONSE: Structure B 1 and BMP #2 have been removed as the additional parking area
behind the property is no longer being constructed. Additionally, the stream relocation is no
longer required.
9. C4: Label L x W x D riprap dimensions, at Str. B1.
RESPONSE: Structure B 1 is no longer needed and has been removed.
10. C5: Provide a storm profile for the entire length of BMP #2. Provide prominent existing
grade linework, since this BMP occupies a former streambed. On this profile, please include
notes, labels, etc. that specify suitable fill in area (former streambed) undercut to provide
adequate material and compaction for BMP #2.
RESPONSE: BMP #2 has been removed as the additional parking area behind the property is
no longer being constructed. Additionally, the stream relocation is no longer required.
11. C5: Provide adequate cover above crown of pipe at ES-1, Sir. A5. Crown of pipe may not be
exposed. Engineering recommends MH with grate inlet at this location for performance,
safety, and maintenance reasons. Proposed grade Str. A5 may concentrate debris, occlude
inlet, or partially block 15" HDPE pipe, if no grate, or if poorly maintained. Proposed design
may inadvertently admit substantial debris directly into BMP # 1.
RESPONSE: Acknowledged, the ES-1 has been replaced with a DI-7 grate inlet and manhole
to reduce chance of blockages.
12. C9
a. Revise so that —70-deg proposed bend in stream is less severe. Revise to maximum
extent, using as much space as is available on site to create a less severe bend around
the new parking area. Area 1, image below.
b. Design and label structural bank stabilization (riprap /grouted rip rap) for
streambank, Area 2, image below.
c. Provide details for natural design concept (channel re-routing), including: in -stream
structures, bank stabilization, riffle -run, etc. Reference Albemarle County Chapel
Hill Stream Restoration project plans for example of detail provided with a natural
design concept. [WPO201800038]
RESPONSE: Modifying the stream is no longer required as the additional parking area has
been removed.
13. C10: Provide (small diameter orifice) debris cage detail.
RESPONSE: A debris cage detail has been provided on sheet C 12.
14. C11
a. Please confirm that BMP #2 4" SCH. 40 perf. PVC underdrain INV=653.00 beneath
the BMP, is intended to transition to INV IN=653.83 at Manhole B3.
b. It appears from CI I (and C13 Stormtech details) that both BMPs 1 and 2 are
effectively submerged during the 10-yr event to a stone -void saturated depth higher
than the top of each system. Please:
i. Confirm whether this is the case.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
ii. Calculate buoyant force on Std. MH and provide buoyancy calculations for
Stormtech system, and MIT Albemarle Engineering cannot assume or
interpret Mfr. literature for ADS SC -740 Stormtech chambers with isolator
row, in this regard. Provide conventional buoyancy calculations, assuming
0.4 stone void ratio.
iii. List C13 Table 1 Acceptable Fill Material A, B, C, D specs on CI II i.e., label
foundation stone, embedment stone, initial fill, final fill (unless NA) on C 11
profiles for BMP 1, 2.
c. Stability of MHs is a particular concern with this design given WSL, 10-yr. Provide
narrative, notes, labels, specifications as needed to ensure MH-to-Stormtech
connection is rigid and inflexible, if consistent with manufacturer's recommendations
and design/performance intent. Long-term performance and system integrity pose
concern, given 10-yr WSL.
d. List SC-740 top of pipe elevation on C 11 profile, BMP 1 and 2.
RESPONSE: a. BMP #2 and manhole B3 have been removed as the additional parking area
behind the property is no longer being constructed. Additionally, the stream relocation is no
longer required. b. The 10-yr WSE is above the top of the Stormtech system but below the top of
stone. The manholes are concrete and have a weight greater than potential buoyant force of water.
A buoyancy calculation was performed on the Stormtech system itself. The weight of the stone
and asphalt above the system far exceeds the buoyant force of water assuming a completely frill
chamber. The calculation has been provided with this submittal. Acceptable fill material from
C 13 Table 1 is now indicated on the BMP profile on sheet C 11. c. All connections are rigid and
in accordance with manufacturers recommendations. The manholes are precast concrete and are
resistant to the buoyant force of water in the system. d. A note indicating top of pipe has been
added.
15. Show /label debris cage for 3" orifices, weir A2. vm°eir B2 details, C I I .
RESPONSE: A note has been added to the weir details indicated a debris cage over the 3" orifice.
D. Erosion and Sediment Control Plan (ESCP)
1. C6
a. Management Strategy and Sequence of Construction
i. Phase 1 lists clean water diversion of existing engineered channel, but provides
no narrative detail relative to this aspect of construction. C7 shows a line with
arrows which corresponds to Phase 1 clean water diversion of existing
engineered channel, but no other details. C9 includes label that reads: `re-route
channel using natural design concepts.' Please provide general detail, a detailed
sequence, labels, natural design concept details, VESCH diversion channel
(crossing) plates (may modify), VESCH dewatering details, channel lining, etc.
ii. Specifically, include VESCH Std. & Spec. plates, details, notes, guidance,
installation sequence for:
1. 3.25
a. Include plate 3.25-1 (may modify, as appropriate)
b. Include plate 3.25
c. Notes concerning undercutting material unsuitable to serve as
subgrade to BMP 42
2. 3.26
RESPONSE: The channel diversion is no longer required as the parking area behind the building
and BMP #2 has been removed. VESCH 3.25 and 3.26 are no longer needed.
912 E. High St. Charlottesville, VA 22902 1434.227,5140 1 shimp-engineering.com
2. C7
a. Revise stone CE to paved CE.
b. Where CWD crosses paved CE, label diversion paved RWD. In effect, construct paved
berm across paved construction entrance, or provide suitable alternative diversion across
site entrance.
c. N-S CWD traps water just south of existing entrance to site against N face of E-W CWD.
Revise to avoid ponding, or diversion break-thru at this location.
d. C7 or C8: Indicate pavement TBR. Revise SWPPP, Sec. 1 (Registration Sec. III) to
indicate off -site demolition debris export.
RESPONSE: a. A paved construction entrance has been added. b. The diversion has been labeled
paved RWD. c. The CWD has been updated to avoid any ponding. d. Pavement to be removed is
now indicated on sheet C2 and C7.
3. C8
a. Label ST floor dimensions (L x W) to aid review, bond estimate, inspection.
b. Label Area of Limits of Disturbance (x.xx Ac.).
c. Provide ST design table, and data. If overlooked, please notify reviewer.
d. Note: Limits of Disturbance are anticipated to increase and appear somewhat arbitrary to
limit LOD <1.0 Ac. Revising grade to introduce a gradual stream bend N of new parking
west of building will increase LOD.
e. Label proposed grade N of building (3:1, 2:1, etc.).
f Any grade steeper than 3:1 requires permanent vegetative stabilization hardier than grass.
Specify permanent stabilization for grade steeper than 3:1,
RESPONSE: a. ST dimensions have been added. b. Limits of disturbance area has been labeled.
c. ST design table is provided on sheet C10. See detail 6. d. Revised limits of disturbance is 0.64
ac with removal of channel diversion and additional parking behind building. LOD is not
anticipated to exceed the area shown on the plans. e. All proposed grade has been labeled with
elevation. Proposed grade for pavement also indicates slope. Slope north of building is 2:1. f.
Permanent stabilization is specified on sheet C6 for slopes steeper than 3:1.
If you have any questions or concerns about these revisions, please feel free to contact me at
chriskshimp-engineerine.com or by phone at 434-227-5140.
Regards,
Chris Marshall, EIT
Staff Engineer
Shimp Engineering, P.C.
912 E. High St. Charlottesville, VA 22902 1434.227,5140 1 shimp-engineering.com
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom