HomeMy WebLinkAboutWPO202000033 Correspondence 2020-08-19 (2)SHIMP ENGINEERING, P.C.
Design Focused Engineering
July 30, 2020
John Anderson
County of Albemarle
Department of Community Development
401 McIntire Road, North Wing
Charlottesville, Virginia 22902
RE: Response Letter #1 for WPO202000033 Malloy Ford
Dear John,
Thank you for your review of the VSMP plan for Malloy Ford. This letter contains responses to County
comments dated July 24, 2020.Our responses are as follows:
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.
1. A SWPPP was apparently not included with the Application. Provide SWPPP using county
template. Include reference to WPO202000033 in SWPPP title. Project is subject to
VESCPNSMP since LOD= 0.91 ac, but does not require a VAR10 state permit, since LOD <1
ac.
RESPONSE: Thank you, this was left out as there was a misunderstanding of the requirement for
a SWPPP with < 1 acre disturbance. A SWPPP is now included.
B. Stormwater Management Plan (SWMP)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP.
This plan is disapproved, and the reasons are provided in the comments below. The stormwater
management plan content requirements can be found in County Code section 17-403.
1. Revise plan to include reference to WPO202000033.
RESPONSE: This is now listed underneath the title on the cover sheet.
2. Label pre -development land use map, p.5 calc. packet, consistent with HydroCad node labels, p.6,
for clarity (2S, 3S).
RESPONSE: Drainage areas are shown on a separate map. The landuse information for each
drainage area is in a summary table on C9.
3. Note: Tables 1, 2, 3, included with 1-p. letter d. 6/5/20 addressed to `plan reviewer' are
confusing.
RESPONSE: Comment withdrawn per phone conversation (07/28/20).
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
4. Notwithstanding detail on C8, provide pre -developed land cover (turf/impervious area) tables for
areas within and outside LOD that drain to POA 1,2. Similarly, on C9 (post -development)
provide breakdown of buildings, pavement, walkways, etc. to provide context for 0.08 ac
decrease in impervious area and equal increase in managed turf in the post -developed condition,
to aid evaluation of Tables 1, 2, 3 (6/5/20 letter). Area values are particularly important. It is
unclear for the moment how calculations are derived, unclear how 0.08 ac. transitions from pre -
developed impervious to post -developed turf. It is unclear how energy balance values are derived.
RESPONSE: Landscape islands were added in the front of the site as well as within the site,
which account for this 0.08 ac transition from pre -developed impervious to post -developed turf.
5. Revise Calculation Packet for clarity:
a. Provide drainage maps/divides consistent with calculations / HydroCad routings, similar to
C8, C9, with clarity the objective. Ensure consistency of graphic / mapped pre -/post -
developed ground cover data with impervious/pervious values shown in HydroCad
input/output data values.
RESPONSE: Because of all the different drainage areas (inside LOD/outside LOD/POA
1/ POA 2) it is challenging to also show land use on the same sheet. Separate landuse maps are
included in the SWM calculations packet. Sheet C9 does include a table which summarizes the
drainage area acreage and cove number, which is consistent with the values used for HydroCAD.
Runoff volume data is an output from HydroCAD based on acreage, CN, TOC, and rainfall data.
The runoff volume information can be found in the HydroCAD output data in the SWM
calculations packet (bottom of page 8, for example).
b. Table 2 is perplexing. It is unclear how pre -/post -developed areas outside the LOD with
identical Ql values = 0.0 are subject to or influence compliance with 9VAC25-870-66.
RESPONSE: The zero "0" values have been changed to dashes ` -" to avoid confusion.
There is no drainage area outside the LOD for POA2.
c.It is unclear how a site with relatively high impervious area (pre -/post -developed) complies
with 9VAC25-870-66 Energy Balance since C5 indicates connection to a manmade
storm conveyance system, uncles plan means to indicate compliance with 9VAC25-870-
66.3 to avoid analysis to Limits of Analysis (9VAC25-870-66.4). Note: This plan
proposes no detention. With precisely -drawn LOD, I.F. (energy balance) is 0.9 rather
than 0.8, as would be the case with LOD > 1 ac. Additional calculation and graphic
details are essential to aid review and understanding of compliance approach.
RESPONSE: Compliance is largely due to the decrease in impervious area from pre to
post development, which is shown on the landuse maps in the SWM calculations packet.
Additionally, a portion of the building pad draining to POA 1 is to remain undisturbed (gravel &
asphalt will be laid on top of it) which allows the disturbed area to remain under 1 acre, requiring
a less intensive improvement factor.
d. Show all calculations
i. Table 1, 2, Ql
ii. Table 3, Ql Allowable
iii. RV calculations
RESPONSE: Comment withdrawn per phone conversation (7/28/20).
6. C6: Include VDOT typ. Details for MH, inlets, MH steps, pipe bedding, inlet shaping, etc.
RESPONSE: These VDOT details are now included on C7.
7. CT LD-229 table caption reads Malloy Furniture Store. Plan title retains quality of an auto
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
dealership. Please clarify.
RESPONSE: The caption has been revised to Malloy Ford. Malloy Furniture Store is our internal
name for the project since it used to be a furniture store.
8. Show existing INV IN for ex. Storm pipe at Str. Al.
RESPONSE: The existing inverts into the Str. Al are now listed on the profile.
9. Provide ''/2" steel plate in floor of Str. Al. Label profile to indicate steel plate is provided.
RESPONSE: The profile is now labeled to show installation of steel plate.
10. C8, C9: Provide DA summary tables for C8 similar to DA summary tables shown on C9. Also,
items 4, 5, above.
RESPONSE: Comment withdrawn — see tables on C9.
11. Additional comments possible.
RESPONSE: Acknowledged.
C. Erosion and Sediment Control Plan (ESCP)
Virginia Code Sec. 62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This
plan is disapproved, and the reasons are provided in the comments below. The erosion plan content
requirements can be found in County Code section 17-402.
C3
1. Revise to indicate that portions of building shown as existing no longer exist. Ref satellite
imagery, 6/26/20. Note: Building demolition does not appear to have disturbed areas within
building envelope beneath slab. Note: Land disturbance requires a grading permit.
RESPONSE: The existing conditions show the building pad and building that currently remains,
though it was hard to distinguish the two in the previous submittal. The existing building pad is now
shown with a concrete hatch.
2. Show existing tree line, if C4 proposed tree line differs.
RESPONSE: The existing tree line is now shown. The portion of trees to be removed are called
out on the plans.
3. Provide TMP data for developed and adjacent properties (TMP #, owner name, deed bk — pg).
RESPONSE: TMP data for developed and adjacent properties are now included.
4. C4: C6 detail for straw wattle does not indicate how this measure can be installed in locations
shown, which include pavement. A filter cloth/stone filtering measure (VESCH) may be required
for paved locations. Please ensure whatever measure is proposed is resistant to proposed
construction activity and construction traffic. [Note: straw wattles do not appear to be a VESCH
measure; utilize VESCH measures.]
RESPONSE: Acknowledged. Realistically, any E&SC measure in that location would need to be
moved for a period of time for the asphalt to be cut up. Therefore, we are now specifying that silt fence be
installed. The construction sequence details that the asphalt in the location of the silt fence be removed
first and silt fence be immediately installed before more construction occurs.
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
5. C4: Show proposed tree line.
RESPONSE: Sheet C5 now shows the proposed tree line after the trees have been removed in
Phase 1.
6. C3, C4: Label all impervious surfaces: Ex. drive aisles, parking, building slab, etc. Identify
curbing, walks, etc. to help visualize proposed ESC measures. Ref. 6/26/20 satellite image.
RESPONSE: All impervious surfaces are now labeled.
7. Provide site layout sheet consistent with SDP202000039. Note: C5 may suffice if title is revised
to: E&SC Plan Ph 2 — Site Layout.
RESPONSE: The title of Sheet C5 has been revised to E&SC Plan Ph 2 — Site Layout.
8. Site Layout sheet:
a. Include linework, notes, labels, etc. that indicate limits of disturbance begin / end as shown
on C4, C5 (`saw cut' `No soil disturbance' etc.)
RESPONSE: C5 is to be used as the `site layout' sheet.
b.Include spot elevations that indicate direction of sheet or concentrated runoff, west to east,
in the vicinity of Rt. 29. No additional storm runoff as surface runoff into U.S. Rt. 29 is
permissible.
RESPONSE: Most of the existing travelway between Route 29 and the site is sloped towards a DI
that exists in the median before Route 29. A small portion of the travelway between the medians is sloped
towards Route 29 (note that VDOT built the road this way). However, because of the new landscape
island in front of the site (in lieu of existing impervious surface for parking spaces) and the overall
reduced drainage area to POA2, the volume of runoff to Route 29 is actually decreased. This is
demonstrated by the energy balance equation calculations for POA2. Please let me know if a separate
exhibit would be useful to demonstrate this point, I am happy to email / discuss.
C5
9. Ensure no site runoff enters U.S. Rt. 29. Provide RWD.
RESPONSE: A diversion dike is now provided on the entrance closest to Route 29 (the other two
entrances are pitched to drain almost completely into the site). A DD was specified instead of RWD since
this entrance is not supposed to be used as a construction entrance.
10. Label existing storm pipe (material/DIA) that enters MH Str. Al.
RESPONSE: Existing storm pipe materials and diameter are now labeled on the plans on C5 as
well as on the profile.
11. Evaluate conditions of existing storm pipe from Str. Al to next downstream MH structure, or
property line, whichever is more distant. Condition of existing pipe must be rated by a qualified
engineering professional to be satisfactory, requiring no repair (or repair or replacement must be
complete), if it is to be relied upon for stormwater conveyance. Note date of visual inspection and
identifying name of individual performing pipe evaluation must be included on the plan.
RESPONSE: Justin and I visited the site on July 29, 2020 to inspect the conditions of the existing
storm system from Str. Al to the next manhole downstream. It had just rained the night before, so we
were able to witness water flowing through both manholes and saw no need for repair. A note has been
added to the plans on C5 regarding the date of / individual performing this inspection.
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
D. Pollution Prevention Plan (PPP)
The PPP content requirements can be found in County Code section 17-404.
With PPP (Sec. 6 SWPPP), provide I I"xI7" exhibit that shows the following elements (at a minimum as
needed):
1. On -site lined containment for fuel, if on -site fuel storage is proposed.
RESPONSE: On -site fuel storage is now shown by the building.
2. Chemical/solvent storage, including concrete curing compounds.
RESPONSE: Chemical storage is shown with the fuel storage by the building.
3. Portable sanitary facility (porta John).
RESPONSE: Porta John location is now shown.
4. Rain gauge.
RESPONSE: Rain gauge location is shown with the SWPPP mailbox.
5. Concrete washout, draining to trapping measure.
RESPONSE: A concrete washout location is shown with a silt fence below.
6. CE/PCE with wash rack, draining to containment.
RESPONSE: Construction entrance location is shown. CE will drain into the site.
7. Non -hazardous solid waste dumpster (with cover).
RESPONSE: No dumpster will be located on site since the building has already been removed.
Any concrete waste will be loaded into trucks and hauled offsite.
8. Include WPO202000033 on Exhibit.
RESPONSE: The WPO number is included on the exhibit.
If you have any questions or concerns about these revisions, please feel free to contact me at
kendra(c)shimp-engineering.com or by phone at 434-227-5140.
Regards,
Kendra Patrick
Shimp Engineering, P.C.
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com