HomeMy WebLinkAboutWPO201900060 Correspondence 2020-10-07TIMMONS GROUP
YOUR VISION ACHIEVED THROUGH OURS.
October 7. 2020
John Anderson
County of Albemarle
401 McIntire Rd Rm, 227
Charlottesville, VA 22902
608 Preston Avenue
Suite 200
Charlottesville, VA 22903
RE: UVA Foundation 1725 Discovery Drive — VSMP Permit Plan Review—
WP02019-00060- Comment Response Letter
Dear Mr. Anderson:
P 434.295.5624
F 434.295.8317
www.timmonr.com
We have reviewed your comments from Rev. 3 (dated September 29, 2020) and made the
necessary revisions.
Please find our responses to the comments below in bold lettering.
A. Stormwater Pollution Prevention Plan (SWPPP)
The SWPPP content requirements can be found in County Code Section 17-405. A
SWPPP must contain (1) a PPP, (2) an ESCP, (3) a SWMP, and (4) any TMDL measures
necessary.
Rev. 1: Comment persists. Engineering accepts this response and anticipates update
with the next submittal. (Ref. Applicant email: 01/13/2020 3:55PM)
Rev. 2: Comments persists. Defer revised SWPPP till future submittal (Applicant / county
email: April 1, 2020 10:36 AM; 11:00 AM).
An updated SWPPP will be provided with the next submittal.
Rev. 3: Comment persists.
A fully updated SWPPP is provided with this submittal. Sections 1, 6E, 8, and 9 to be provided
once obtained
a. Sec. 1 (Registration Statement): Complete 2019 VPDES (VAR10) Registration.:
b. Sec.4./5. — Update once ESC-SWM plan sheet revisions complete.
c. Sec.6.E. Name individual responsible for PPP practices.
d. Sec. 8 List named individual responsible for inspections.
e. Sec. 9 (Signed Certification) Please sign.
f. Sec. 11 (General Permit Copy) Please include 2019 VAR10.
g. Include 2019 Notice of VPDES Termination.
h. List WP02019-00060 on Cover of SWPPP.
CIVIL ENGINEERING I ENVIRONMENTAL I SURVEYING I CIS I LANDSCAPE ARCHITECTURE I CONSTRUCTION SERVICES
The PPP content requirements can be found in County Code section 17-404.
1. If Sec. 6 PPP Exhibit is revised, please provide an updated Exhibit.
2. Sec. 6.A Revise PPP Exhibits, p. 28-29 SWPPP, to show rain gauge location/s.
PPP Exhibits will be updated and provided with the next SWPPP.
Rev. 1: Comment Persists.
An updated SWPPP — with updated PPP - will be provided with the next submittal.
Rev. 3: Comments persist.
The PPP Exhibits have been updated and are included with this submittal.
C. Stormwater Management Plan (SWMP)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or
disapprove a SWMP. This plan is approved.
Rev. 1: Addressed.
Note: Rev. 2 submittal includes substantial change to project scope. New Rev. 2 SWM
Plan comments begin p. 5, with item 15.
1. Revise plan title to include ref. to VSMP / WPO20190060.
WPO number has been added to the Cover Sheet. See Sheet C0.0.
2. Revise vicinity map to more clearly identify site location.
Property line has been added to the vicinity map. See Sheet C0.0.
3. C2.0 — Provide existing contour labels; none are provided.
Existing contour labels have been added. See Sheet C2.0.
4. Include image, below (or similar), from Timmons Group UVA Foundation — 1725
Discovery Drive Design Calculations & Narrative, October 21, 2019, on C6.0 with
caption/label that identifies 1725 Discovery Drive (blue circle, image below) to cross-
reference and clearly identify project site, relative to Pond 1.
Image has been added to Sheet C6.0.
Rev. 2: Image removed w/ Rev. 2 comments.
5. Include image, below/similar: USGS 7.5' quadrangle, Earlysville, VA 2016, to show
approximate (county -estimate) watershed Pond 1 comprising -465 Ac., on Sheet C6.0.
Revise drainage area reference on C6.0 which may underreport actual size of Pond 1
watershed (revise 83.90 Ac. Reference to avoid confusion).
Image has been added and Narrative has been updated to include mention of the entire Pond
1 watershed. See Sheet C6.0.
Rev. 2: Image removed w/Rev. 2 comments
6. C6.0 — Provide note that identifies project location in sub -basin shown on Design
Calculations & Narrative, p.9.
An image depicting the project site within Dewberry Page 9 and a note have been added to
the Stormwater Narrative on Sheet C6.0, and an exhibit and note have been added to the
VSMP Design Calculations & Narrative.
7. C6.0 — Provide additional qualifying descriptions to support how this 0.73 Ac. Impervious
gain fits within p. 9 projections for sub -basin ultimate development impervious land
cover without change to Exhibit CN value. Identify p. 9 sub -basin (Exhibit) CN value that
applies to project, a value that WPO plan and Design Narrative maintain is unchanged
with proposed development at 1725 Discovery Drive.
The "Drainage Subbasin Map — Developed Condition," otherwise known as "p. 9," by
Dewberry, provides the following information with respect to this project: The project site
falls in Subbasin C2 which is 85.84 acres with a CN value of 82. This plan is dated 7/23/1997.
Timmons Group created an Exhibit, dated 12/2018, entitled "Lewis and Clark Drive —
Stormwater Management Exhibit for Pond 1" which provides updated information based on
actual construction since 1997. The CN value for Area C2 (83.90 acres) in this Timmons Group
exhibit is 67. The 0.80 acre increase in impervious surface does not change the CN value.
Therefore, 67 is the CN value considered for stormwater quality and quantity. A similar note
has been added to Sheet C6.0.
8. C6.1: Pre/post CN value = 67 (reported with cross section 1-4 profiles) appears
unrelated to Exhibit p. 9 CN values. Please clarify. Ref. image, below.
The CN value of 67 reflects the updated build -out conditions as presented in the "Lewis and
Clark Drive—Stormwater Management Exhibit for Pond 1" by Timmons Group, dated
12/2018. However, the channel adequacy analysis presented on Sheet C6.1 has been updated
to consider future development. The CN values shown for each cross section are now for
estimated post "Ultimate Development Conditions".
Rev. 2: Image removed w/Rev. 2 comments.
9. Note: This and other development projects that rely on Pond 1 for quality and quantity
compliance are not strictly grandfathered unless requirement at 9VAC25-870-48.1.(iv) is
satisfied between individual project sites and Pond 1, yet, if (iv) is true at Pond I outfall,
and if Pond I was built per design, and if Applicant confirms that, to -date, watershed
development impervious area does not increase the CN value in any sub -basin of Pond I
(Ref. p. 9/Design Report), then review position is that Pond I provide SWM for projects
within Pond I watershed, per 9VAC5-870-48. Please confirm that this is the case: that CN
value in project sub -basin is unchanged with new building/additional parking. Albemarle
still considers channel and flood protection between proposed development and Pond 1.
While Pond I may provide SWM quality -quantity control at limits of analysis, channel
and flood protection between development sites and pond is a review and regulatory
concern, unless proven otherwise.
(9VAC25-870-48.1. fiv) has not been subsequently modified or amended in a manner resulting in
an increase in the amount of phosphorus leaving each point of discharge, and such that there is
no increase in the volume or rate of runoff.'] While there maybe increase in the amount of
phosphorus leaving a specific site compared with the pre -development condition,
provided proposed design of 1725 Discovery Drive is consistent with Dewberry & Davis,
October 1997 document CN value for its sub -basin, then review position is that there is
no increase in permitted volume or rate of runoff from Pond I outfall.
Acknowledged. See response to Comment 7 and 8, above. Please note that the post Phase 2
condition is being considered for stormwater quality and quantity, and the Ultimate
Development Conditions are being considered for channel adequacy analysis. Pond 1 as built
information is in the process of being obtained for confirmation that Pond 1 was built per
design.
10. C6.1: Channel Adequacy /capacity -velocity between 1725 Discovery Drive development,
and Pond I:
a. Ref. 9VAC25-870-97: Stream channel erosion, para. B., references 9VAC25-840-
40, Minimum Standards.
Reference numbers have been updated. See Sheet C6.1.
b. Min. Std. 19 (9VAC25-840-40.19.b(2)(a.) requires 'Natural channels shall be
analyzed by the use of a two-year storm to verify that stormwater will not
overtop channel banks nor cause erosion of channel bed or banks.'
The 2-year storm velocity is listed above each channel cross section and shows the 2-
year storm will not cause erosion of the channel. Additionally, the water elevation
resulting from the 10-year storm is shown within each cross-section, illustrating that
the stormwater will not come close to overtopping the channel banks. (See next
comment response for additional detail on channel erosion.)
c. Ref. VESCH, 3rd , 1992, Table 5-22. Provide additional data on receiving stream
substrate. Compare with table values to ensure velocities at x-sections 1-4 are
non -erosive. Table 5-22 indicates velocities above 2.5 fps may be erosive in
certain unlined earthen (natural) channels. Report/list observed substrate
between development and Pond I at each x-section, on Sheet C6.1.
Per the NRCS Web Soil Survey, the soil type along the entire channel is 36C—
Hayesville loam, which, assuming the top layer of loam has washed away, is clay.
From the referenced Table 5-22, the permissible velocity for Stiff Clay is 5.0 ft/sec. This
information has been added to Sheet C6.1.
d. Ref. DEC. guidance/DCR Technical bulletin #1 (link:
www.deg.virginia.gov/portals/0/DEQ/Water/Publications/TechBulletinl.pdf)
Stream Channel Erosion Policy Guidance. Review especially guidance, DCR TBI, p.
11, Ultimate Development Conditions, and confirm analysis performed for
(WPO2019-00060) submittal includes Engineer's best estimate of ultimate
development along the receiving stream between 1725 Discovery Drive and
Pond I, which may in future contribute additional runoff, and increase volume or
velocity in this receiving stream (blue, circle, image, below).
The channel adequacy analysis has been updated to reflect this Ultimate Development
Condition. The estimated Ultimate Development Condition is shown as an exhibit in
the Design Calculation & Narrative. Sheet C6.1 has been updated with this information
as well.
Rev. 2: Image removed w/ Rev. 2 comments.
e. Once ultimate development conditions are analyzed, 'If existing natural receiving
channels or previously constructed man-made channels or pipes are not
adequate, the applicant shall 'consider measures listed at DCR TB1, p. 7. Also,
please review DCR TB1, pp. 8-11. Revise design, as needed.
The existing channel meets adequacy requirements. No redesign is needed with this
project, based on estimated future development.
f. Revise Water Quantity Analysis —Channel Adequacy text block, C6.1, as needed.
Velocity <5 fps is not always nonerosive. Also, base design on ultimate
development conditions. Please note multiple road stub -outs for future
development along Discovery Drive (GIS image, above).
This text has been updated to include information on soil type and Ultimate
Development conditions.
g. Channel cross sections panel:
i. Label Lewis and Clark Drive.
A road label has been added. See Sheet C6.1.
ii. Label Ex. Structure beneath L&C Drive.
Structure label has been added. See Sheet C6.1.
iii. Evaluate Ex. Structure beneath L&C Drive based on ultimate development
conditions. If inadequate to convey runoff from ultimate development,
proposed remedy.
The existing 72" RCP that carries stormwater under Lewis & Clark Drive has
been modeled in HydroCAD and PipeSoft. Using these models and considering
Ultimate Development conditions, the existing pipe clearly handles the 10-
year and 100-year storms. The pipe calculations are included in the Design
Calculations & Narrative.
iv. If design remedy requires modification to Ex. Structure beneath L&C
Drive, provide comprehensive profile and plan design information,
including LD-229.
Not Applicable. See above response.
11. Label drainage structures across plan sheets to correspond with Design Calculations &
Narrative, Pipe and Inlet Computations tables.
Structure numbers have been updated to be consistent across plan sheets and design
calculations.
12. Design Calculations & Narrative: Revise Project Narrative—Stormwater Management
Summary consistent with review comments above, and any plan or channel or pipe
revisions required by ultimate development conditions.
The Design Calculations & Narrative has been updated.
13. Note: Since Pond I Drainage Area > 460 Ac., analysis downstream of Pond 1 is
unnecessary. Project LOD <1% Pond 1 DA. Project total LOD = 1.29 Ac. Ref. DCR TB1 one -
percent rule, p. T61-7.
This point has been added to the Narrative on Sheet C6.0.
Rev. 1: As follow-up: Please see Sec. D., ESCP, below, minor item 1.
Xxxx
Rev. 2: Addressed.
14. Furnish relevant Pond 1 As -Built data that corresponds with approved Pond I
dam/spillway elevation data. Although this data was requested in connection with
SUB201800171, unless mistaken, it was not furnished. As -Built data for pond 1
dam/spillway is requisite to approval of WPO201900060. Please see request sent
December 03, 2018 4:57 PM (J. Anderson to J. Showalter) in connection with
SUB20180017— Lewis and Clark Drive Extension, including text, reading (in part):
Rev. 1: Comment persists.
Rev. 2: Addressed. As follow-up: Revise title of Pond 1 Analysis report (a new submittal
with Rev. 2) to reference WPO201900060). This is only request relative to As -built
condition of Pond 1. Additional details request no revision. Pond 1 Analysis will be useful
for current/future land development projects at UVA Research Park, for areas draining
to Pond 1. Albemarle appreciates the effort and care taken to prepare this important
reference resource.
(Additional details):
UVA Research Park— Pond I Analysis, VSMP Design Calculations & Narrative, March 27,
2020
a. Pg. 13 is a HydroCAD (routing) diagram that correlates:
i. C6.0 Stormwater Narrative
ii. Dewberry & Davis Oct 1997 document
iii. C6.0 Image 2, Timmons Group Exhibit, Dec 2018
iv. 3/27/20 Discovery Drive Development Design Calculations and Narrative,
p. 12 Exhibit (*Drainage Divides and Area Names taken from Dewberry &
Davis, Oct 1997 report.)
v. Pond 1 As -built condition (schematic, below *; divides/area names, blue
circle, below).
b. Pg. 5-10 are Dewberry & Davis Pond 1 design documents.
c. Pg. 11-12 satisfy County request for 'As -built' information for Pond 1
embankment.
(As -built drawings d. March 20, 2020 by Timmons Group, checked by Joe
Medley)
(As -built drawings incl. w/94-p. Pond 1 Analysis under PE -seal, 3/27/20 /Craig
Kotarski)
d. Remainder of 94-p. report are routings (2, 10, 100-yr routings, with pond WSE)
e. Pg. 3-4, Pond outfall analysis:
(p•3)
Pond Outfall Analysis
The existing pond was originally designed to provide water quality and quantity
storage with the use of an earthen embankment, and a concrete spillway. The
asbuilt pond includes 2 9'x10' culverts, a concrete control structure, and an
earthen emergency spillway. The as -built pond with the ultimate offsite drainage
area and fully developed onsite drainage areas was analyzed using HydroCAD
software to determine that the as -built pond meets or exceeds the freeboard of
the original design. Below is a table comparing the design and asbuilt Water
Surface Elevation (WSE), the freeboard provided, and the flow in and out of the
facility.
(p.4) outfall analysis, cont.
Relevant pages from the approved design are provided in the appendix. The WSE
can be found on page 9 of 60 and 32 of 60. The HEC-1 routing of the designed
pond can be found in section 8 of the report. Also provided, is the survey dated
March 20, 2020 that was used to model the pond as it was constructed. Pond 1
was modeled utilizing the ultimate development offsite and post -developed
conditions onsite drainage areas from the approved design report. Sub basins
C1, C2, D1, D2, E1, E2, F1, F2, G1, and G2 drain to pond 1. The drainage area, CN
Values, and time of concentration values are listed in the table below.
f. Table 1:
g. Table 2:
Alb. County Dec. 03, 2018 4:57 PM email/text:
'Engineering needs to correlate Lewis & Clark Road Ext. to a prior -approved plan for
TMP #32-6R, under whatever guise (Approved Master Plan, Approved Cox Engineering
plans, Approved Dewberry Davis Study, etc.). Important documents are
contemporaneous with suspended site plans, but we cannot locate a clearly -approved
SWM plan for UVA Foundation Research Park, especially for ponds 1 and 2. Important
documents and applications are twenty years old. This is the task: identify a prior -
approved SWM plan (with SWIM facilities) meeting Part IIC design criteria for
improvements proposed under WPO201800073.
We need Timmons to make the connection —please consider:
1. Identification of prior -approved stormwater management plans for ponds 1 and 2. 1
have researched this without luck. 1 cannot make clear connection between a prior -
approval and this application. It is not enough that recently approved WPO plans may
have referenced Dewberry Davis Study, or Cox Engineering plans.
2. Design of ponds 1 and 2 relative to VSMH, 1999, Vol. 11, Appendix 5D worksheets (ponds
1 and 2).
3. As -Built condition of ponds 1 and 2 relative to approved plans. We cannot locate As -Built
drawings.
4. Location of ponds 1 and 2 relative to drainage divides, relative to improvements
(WPO201800073).
5. USACE approval of wetland impacts associated with WPO201800073 /SUB201800171.
6. Cumulative development (% impervious) relative to prior -approved SWM plan/s. That is,
with WPO201800073, % impervious cover from a cumulative standpoint.'
[Also, county email, James Howard -Smith to Jonathan Showalter, Timmons,
12/19/2018 7:07 AM. Re. SDP199800043 Approved Final Site Plan and Comps, Pond
I; Sheet 32: Spillway/Dam Profiles. Note: plan is metric.]
A survey of the requested as -built information is being obtained and will be provided to the
County under separate cover.
New (Rev. 2)
C6.0:
15. Narrative references Analysis Points 1 & 2. Cannot locate Point 2 in pre- / post -
development DA images.
Analysis Point 1 is the only AP now and has been clarified in the drainage area images.
REV. 3: Addressed.
16. "Air building" is shown in post -development drainage area. Please confirm that 2.32 Ac.
Impervious area includes Air building. If not, recommend revise impervious area to
include the Air building, and consider text edits, as needed, to Stormwater Narrative.
The Air Building has been removed from the proposed plan.
Rev. 3: NA. The air building has been removed from the propose plan.
17. 3/27/20 UVA Research Park— Pond 1 Analysis Design Calculations & Narrative: Provide
qualitative information on existing double 9 x 10 box culvert pond 1 outfall, relative to
stream bed / channel stability. Although this is beyond limits of analysis, request is
made in context of 'As -built' condition. Albemarle must ensure As -built condition of
pond 1 dam embankment / outfall is stable, on this date. Narrative, observational
statement that stream bed and channel banks are stable at pond 1 outfall is sufficient.
Please see below image of the outfall area. The bed and banks appear stable at outfall.
REV. 3: Addressed.
18. Note: 3/27/20 UVA Foundation - Discovery Drive Development Design Calcs & Narrative,
p.3, para. 3 states: "Drainage Area C2 consists of 83.90 ac. With a CN value of 67 (see
Table 1)". Table 1, p.5, reports CN=69. Revise for consistency.
The 67 references the "Lewis and Clark Drive — Stormwater Management Exhibit for Pond 1"
dated 12/2018 while the 69 is the updated CN value based on incorporating the numbers
within this WPO plan. To make this more clear, the "Lewis and Clark Drive — Stormwater
Management Exhibit for Pond 1" has been updated throughout the plans and Narrative. With
the new plan, the CN value updated to include the proposed development is 68.
REV. 3: Addressed.
19. C6.1: Confirm pipe capacity (LD-229) between Str. 300 and inlet, S side of Discovery
Drive, is adequate to convey runoff from (conservative estimate of) impervious areas
associated with potential air building. A goal discussed 3/6 with Applicant is an
approved plan that addresses SWIM quality / quantity requirements. (if not ESC)
associated with a potential air building; this plan comes quite close. Also, ESC Plan, item
13.
This pipe is now proposed to be removed the capacity of the new pipe crossing Discovery
Drive has been verified to be adequate.
REV. 3: Addressed.
20. C6.3: If WP0201900060 is to include potential air building, include inset for air building
on site drainage area Map 2 that shows DA parameters and location of air building,
relative to Phase 2 improvements.
The Air Building is no longer proposed.
REV. 3: NA. The Air Building is no longer proposed.
D. Erosion and Sediment Control Plan (ESCP)
Virginia Code 62.1-44.15:55 requires the VESCP authority to approve or disapprove an
ESCP. This plan is disapproved for limited reasons listed, below ( s). The
erosion control plan content requirements can be found in County Code Section 17-402.
A fteF F,.,,,,.,.,iRg F,.,,,sed «G W aR, t,.,e FRiAeF ;.,.ms iedit,. (Note: initial review comments
addressed;)
1. C3.0 total LOD Area (appears) = 1.31 Ac. Please revise (Check my math.)
Rev. 2: Partially addressed. As follow-up: see New item 8, below.
Acknowledged
REV. 3: Addressed. LOD is now 3.41 Ac.
2. C3.1 Check for CE-SF conflict; it appears SF may partially obstruct CE. Limit SF to avoid
conflict.
Rev. 2: Addressed.
1. C3.0 Since LOD areas of this two-phase project (building; parking) do not overlap, revise
project description to clarify that total limits of disturbance = 1.29 Ac.
Total Disturbance has been added to the Project Description. See Sheet C3.0.
2. C3.1— Provide RWD at end paved construction entrance.
The construction entrance has been moved slightly and since little stormwater is anticipated
to travel across this area, a right of way diversion is not being added.
3. C3.3 — Label existing contours.
Existing contour labels have been added. See Sheet C3.3.
4. C3.4 (Also, site plan -related).
a. Eliminate nuisance ponding in right-angle corners of lower elevations of
proposed upper parking lot.
Inlets have been provided at the corners of the lower elevations of the proposed
upper parking lot. Metal plates are being proposed to bridge gutter pan to allow water
to reach the proposed inlets. See Layout & Utilities sheets, C4.0 and C4.1.
b. Label CG-2 / CG-6.
The Layout & Utilities sheets, C4.0 and C4.1, have been added to the VSMP/WPO
Plans.
c. Label drive aisle width.
The Layout & Utilities sheets, C4.0 and C4.1, have been added to the VSMP/WPO
Plans.
d. Provide typ. Dimensions, parking spaces.
The Layout & Utilities sheets, C4.0 and C4.1, have been added to the VSMP/WPO
Plans.
e. Label concrete ribbon curb at each entrance to upper parking lot. Provide detail.
These are two small sections of mill & overlay. Sheet C4.1 clarifies this and this sheet
has been added to the VSMP/WPO Plans. Additionally, this comment was withdrawn
per John Anderson email dated 12/27/2019.
f. Recommend profile for north and south side entrances to proposed upper
parking lot that show smooth transitions, and spot elevations.
This comment was withdrawn per John Anderson email dated 12/27/2019.
g. Recommend receiving walks on east side of existing lower parking lot that align
with proposed sidewalks (2 locations) on west side of lower parking lot.
Acknowledged. Receiving walks are not being added at this time.
h. Label retaining wall.
The Layout & Utilities sheets, C4.0 and C4.1, have been added to the VSMP/WPO
Plans.
i. Please ref. 18-30.7.5.a.1./2. Construction standards, re. wall ht.; stepped walls
required if wall ht. >6' (proposed design wall ht. = 10.3' on managed steep slopes
cannot be approved.)
Proposed retaining walls have been revised to be stepped within managed steep slope
areas. See Sheet C4.1.
Image removed with Rev. 2 comments.
j. Apply for building permit for retaining wall.
Acknowledged.
k. WPO plan approval does not approve retaining walls.
Acknowledged.
I. Provide CG-12 wherever walks encounter curbing (label ramps).
CG-12 ramps are not being proposed at the new sidewalks from upper to existing
lower parking areas because there are step, so these are not intended to be accessible
paths.
5. Provide safety fence to protect building occupants and visitors during all phases of
project.
Safety fencing is proposed in the E&S Plan Sheets C3.1-0.4.
New: (Rev. 2: Scope of work revised / discussed with Timmons, Albemarle Planning /
Engineering, and UVAF at meeting at county office building, 03/06/20.)
6. C3.5: Recommend label sediment traps as ST1, ST2 (excavated drop inlet ST) in plan
view.
Labels have been added to the sediment traps accordingly.
REV. 3: Addressed.
7. It appears excavated drop inlet sediment trap does not provide 100.5 cy wet storage
volume. If top of inlet elev.=540.5' and volume provided at elevation 541'=94.2cy, it
appears wet storage volume is insufficient.
The excavated drop inlet has been revised and calculations have been updated accordingly.
REV. 3: Addressed. As follow-up: Also see item 26, below.
See response to item 26 below.
8. Please confirm total LOD = 4.10 Ac (C3.0, Project Description). Phase 2 (2.54 Ac.), Phase
1 (0.47 Ac.). If "Air building" comprises— 1.09 Ac. Disturbance, then on C3.0, please
reference possible location of "Air building" shown on C6.0, C6.1.
The removal of the proposed Air Building eliminates this confusion. LOD is now 3.41 acres.
REV. 3: Addressed.
9. Include Ex. Pipe/structure demolition in sequence of construction notes. Ensure storm
runoff conveyance via existing or new storm lines (structures) is continuous during all
phases of construction (C2.4 / C3.0).
The sequence of construction has been updated.
REV. 3: Addressed. Also, as follow-up: See item 26.e., below.
See response to item 26.e below.
10. C3.5: Provide proposed grading and/or label to ensure ST1 discharge is to the new inlet
structure located just SW of ST1 weir.
E&SC Plans have been updated.
REV. 3: Addressed.
The following comments also relate to site improvements. Please ensure final site plan
(SDP2020-00009) and WPO plan are consistent.
11. C2.1, C5.0: Provide CG-12 at each end of the short sheltering short walk between new
access to metal building and existing parking, 1725 Discovery Drive (blue circles, below).
Also, provide CG-12 ramp within 1725 site to receive middle ramp pedestrian traffic
(image rt., below).
There are two existing curb ramps in these locations that had not been picked up by the
surveyor.
[Images removed with Rev. 3 comments.].
REV. 3: Addressed.
12. C5.0: Check LD-229, Narrative & Design Calc, p. 7 (pipe 315), against plan sheet labels,
pipe 315, to / from.
LD229 design computations have been updated.
REV. 3: Addressed.
13. C5.0, C5.1: Label all existing structures (listed on the LD-229) in plan view drawings;
image, below.
Existing structures and pipes have been labeled in the plan sheets as reflected on the LD-229
calculations.
[Images removed with Rev. 3 comments.]
REV. 3: Addressed.
14. LD-229 lists Ex 7 — Ex 1 at 99.46% pipe capacity. Recommend more conservative design.
Pipe calcs and areas have been checked and updated. Pipe is now at 75% capacity.
REV. 3: Addressed.
15. C5.2: Provide swale/similar and label/s at top of retaining wall to ensure storm runoff is
not channelized at the top of the wall but is separated by swale or grading from the top
of the wall.
Grading has been designed to ensure stormwater runs away from proposed walls.
REV.3: Withdrawn.
16. C5.1: Assign storm line label to 10" HDPE line N of Str. 310. Provide a structure at bend
in this line. Assign Str. ID.
This line has been removed.
REV.3: NA. This line has been removed.
17. C5.1, C7.0: Revise storm 309 grade to <_ 16%.
All storm pipe are proposed to be no more than 5%.
REV. 3: Addressed. Note it appears two lines are <0.50%. Engineering does not request revision
but will request As -built calculations should either line be installed at <proposed 0.489 and
0.497% slope. ACDSM and Drainage Plan Checklist for plan reviewers require Min. slope >0.5%.
Acknowledged.
18. Increase pipe 309 diameter >_ 10" (upstream pip: 10" DIA HDPE; Str. 309: 11.11' of 8"
HDPE @19.80%).
Storm pipe network has changed, and this comment no longer applies.
REV.3: NA
19. C5.1: "10" HDPE (1% slope min.)" label is ambiguous. Provide profile. Defines
pipe/slope. Also, item 17, above.
Storm pipe network has changed, and this comment no longer applies.
REV. 3: NA
20. C5.1: Provide grading at Str. 316 to accommodate 13.464" ponding depth at inlet to
ensure capture (ref. LD-204).
Storm pipe network has changed, and this comment no longer applies.
REV. 3: NA
21. C5.1: Revise throat length, inlet 400. 6.114" depth appears to exceed DI-3C 5.5" high
inlet opening.
Inlet 400 throat length has been increased to 10 feet to ensure depth does not exceed top of
inlet. This change has been verified with the updated Inlet Drainage Area.
REV. 3: Addressed. [Image removed with Rev. 3 comments.]
22. Provide details / notes, etc. for T-connections in storm lines (similar to inlet shaping) to
ensure flow at Inserta tees is not susceptible to debris accumulation, or obstruction.
Inlet shaping is required within structures to re -direct flow to minimize chance of
accumulation, or obstruction.
An InsertaTee detail has been added to sheet C1.1. The incoming pipe at the InsertaTee
location is proposed to connect above the bottom of the pipe. This will aid in preventing
obstruction at the invert of the connection.
REV. 3: Withdrawn.
C7.0:
23. Note that concrete inlet shaping (IS-1) is to be provided on all structures may not be
possible with Nyloplast line of dome grate/risers. Clarify IS-1 is possible for Str. 310.
Also, item 22, above.
The note on sheet C7.0 has been updated to reflect inlet shaping for all concrete structures.
REV. 3: Addressed.
24. Provide Ex. 24" (CPP) storm profile from Str. 300 (beneath Discovery Drive) to inlet
structure on S side of Discovery Drive.
This comment no longer applies.
REV. 3: NA
25. Plan note stating that MH Str. Over 8-ft in height shall require a stepdown structure with
%2 steel plate to serve as a safety slab appears more stringent than VDOT standard.
Please confirm design intent to equip all MH Str. Over 8-ft. in height with SL-1. Ref.
VDOT SL-1 Std., below.
After further review of the height of the structures, the referenced note has been removed
from Sheet C7.0.
REV. 3: Addressed. [Image removed with Rev. 3 comments].
New:
26. Engineering recommends (C3.5):
a. Consider infrequent event (less frequent than design event), since any failure of
ST2 will likely have immediate impact on Discovery Drive that may disrupt facility
access, construction, or both. This caution applies since proposed trap is located
immediately adjacent to Discovery Drive.
While we understand the need for caution directly adjacent to Discovery Drive, ST2
has been designed to meet all required standards. We do not anticipate failure of this
trap, as the inlet has served the existing development and will continue to serve the
proposed development in the future.
b. Label weep holes for dewatering in plan view (See ST2 Detail, Excavated Drop
Inlet Sediment Trap, C3.1).
A label indicating weep holes have been added to Sheets C3.4 and C3.5.
c. Confirm Ex. 15" plastic line beneath Discovery Drive utilized as outfall for ST2 is
in good condition without visible defects between DI-7 and flared end section S
of Discovery Drive. Applicant may address via Note to contractor, but lack of
information now risks less than ideal required response during construction if
contractor discovers defect or deficiency with Ex. Line beneath Discovery Dr.
Engineering recommends Timmons examine integrity of this of this pipe now,
rather than shift burden to site contractor, later. Ref. C2.4, C3.5.
A note to the contractor has been added to Sheets C3.4 — C3.6.
d. Recommend a label reference to Note on C2.4 (to contractor to replace DI-7 top
with DI-3C set per final grading plan) on both sheets C3.4, C3.5.
A label has been added to Sheets C3.4 and C3.5 as requested.
e. Consider interim phase between ESC Phase 2B and 2C when ST2 is removed.
Anticipation may define success as site transition from unbuilt to final condition
(parking/building), once ST2 is removed. ST2 must remain until all upslope areas
are stabilized and while proposed conveyance is constructed. Phase 2B shows
pipes and protected inlets; what is less clear is how site runoff transitions from
sediment trap to storm inlet catchment, all while limiting potential for sediment -
laden runoff to leave the site.
We do not believe an additional phase is needed; however, we have added additional
notes to Sheets C3.4 — C3.6 to clarify construction sequence and ensure that sediment -
laden runoff does not leave the site.
27. C1.2: Include VDOT ST-1, IS-1, PB-1 details (MH steps, inlet shaping, pipe bedding),
unless overlooked.
Details have been provided on Sheets C1.0 and C1.1.
28. C2.0: Label Discovery Drive.
Discovery Drive has been labeled on Sheet C2.0 as requested.
29. C3.1: Include VESCH Plate 3.01-1; also, please include label/s for safety fence post
embedment in asphalt, since SAF is proposed to be installed in asphalt.
VESCH Plate 3.01-1 has been added to Sheet C3.1 as requested. Fence post installation means
and methods will be determined by the contractor; however, we anticipate that a fence
similar to the below example will be utilized so that the asphalt does not have to be patched
where the posts are located.
30. C3.2, C3.3: It is unclear how building occupants that may park south of the building will
enter the building along a safe path that does not conflict with construction activities,
CE, or SAF. Please clarify.
Safety fencing has been extended (with a gate) to act as a barrier, separating pedestrians from
construction activity to the extent that is possible.
We have included PDF copies of the plans for your review. If you have any questions or
comments, please feel free to give me a call at 434.295.5624.
Sincerely,
Craig Kotarski, PE