HomeMy WebLinkAboutWPO202000039 Correspondence 2020-12-03608 Preston Avenue
P 434.295.5624
Suite 200 IF434.295.1800
T I M M O N S GROUP
Charlottesville, VA 22903 www.timmons.com
December 2, 2020
John Anderson
County of Albemarle
Dept. of Community Development
401 McIntire Rd, Rm 227
Charlottesville, VA 22902
RE: Crozet ES — VSMP Permit Plan Review — WP02020-00039 - Comment Response Letter
Dear Mr. Anderson:
We have reviewed your comments from September 23, 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.
1. Revise to include ref. to WPC202000039 in title.
Cover sheet has been updated to reference number in the title.
2. Sec. 1, Registration Statement, is blank. Complete with care. Additional comments
possible.
Registration Statement has been filled out with all known information at this time.
3. Sec. 3, Nature of Activity references construction dates as indicated on the Registration
Statement. No dates listed on Registration Statement.
Dates are now listed within the Registration Statement.
4. Sec. 4, 5: Update once all ESC/SWM-related review comments addressed.
ESC/SWM documents have been updated based on comments.
S. Sec. 6.A: SWPPP does not appear to include 11" x 17" SWPPP Exhibit. Provide exhibit
that shows:
a. Rain gauge
b. Non -hazardous solid waste dumpster, with cover
c. Portable sanitary facility (porta-john)
d. Solvent -chemical -paint storage
e. Concrete /stucco washout
ENGINEERING I DESIGN I TECHNOLOGY
f. Paved construction entrance, draining to trapping measure
g. On -site fuel storage containment, as required by site contractor [better to show
and not need, than to not show]; design secondary, impermeable lined
containment (10ml plastic lined) sized to hold [stored Vol. of fuel + 10-yr. storm
event (cf) x 1.1.
PPP exhibits have been provided with this submission.
6. Sec.6.E.: The SWPPP cannot be approved until named individual responsible for PPP is
identified. The VSMP cannot be approved unless SWPPP is approved. A VAR10 Permit
cannot be requested until the VSMP plan is approved. A grading permit cannot be
issued until the VAR10 permit is issued by DEQ.
Individual responsible for PPP is identified on the SWPPP.
7. Sec. 8, Qualified Personnel: Similar to item 6., SWPPP cannot be approved until named
individual is listed as qualified inspector.
All names are now listed on the SWPPP.
8. Sec. 9, Signed Certification: Please sign.
A signed certification has been included with this submission.
9. Sec.12, Inspection Logs, Inspection frequency: 2019 VAR 10 inspection frequency differs
from 2014 VAR 10, slightly. Please revise inspection frequency text consistent with 2019
VAR10, Part II.G.2.a.1./2.
Inspection frequency has been revised as requested.
B. Stormwater Management Plan (SWMP)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a
SWMP. This plan is disapproved for reasons listed, below. The stormwater management plan
content requirements can be found in County Code section 17-403.
1. Design Calculations and Narrative, Aug-10, 2020.
a. Revise cover to include ref. to WPO202000039.
The cover page of the calc book has been updated to reference the WPO number.
b. Pg. 3: Revise Water Quality Narrative to include ref. to proposed new
bioretention facilities.
The water quality narrative in the calc book has been updated with information
referencing the bioretention facilities and Stormtech Isolator Row.
c. Pg. 5-6: Include pipes 501 and 505 in VDOT LS-229 Storm Sewer Design
Computation Table.
Pipes 501 and 505 are culverts and have been checked for adequacy in HY-8.
Computations demonstrating their adequacy are provided on sheet C7.2.
d. Include Ex. Storm pipe at Ex. Central/main elementary school entrance. Assign ID
to this pipe.
Culvert computation for the existing 15" pipe to remain at the existing entrance is
provided on sheet C7.2.
e. Ensure Ex. Main entrance storm pipe conveys Q10-yr without flooding (Note: Ex.
Pipe is 15" DIA while proposed upstream pipe 505 is 18" DIA (both 501 and 505
are 18" DIA).
Culvert computations have been provided on sheet C7.2 for pipes 501 and 505. Both
have been decreased in size to a 15", which is more than adequate.
f. Include Exhibit or DA Map such that review can correlate VRRM.xIs with DA A, B,
C, D and with HydroCad routings.
Labels were provided in the calc book correlating the outfall numbers with the VRRM
drainage area letters. Additional labels have been added to sheets C5.4 and C5.5 to
help clarify the BMP drainage areas and where their credits are taken in the VRRM.
Additionally, labels have been added on the individual VRRM pages of the calc book to
reference to the outfall numbering. Lastly the names of the hydrographs on the
Hydraflow routings correlate to the drainage area labels on sheet C6.0. Some of the
hydrograph print outs have been randomly selected and highlighted to show where to
look on the print outs for the names and other key information.
2. CO.1:
a. Revise plan title to include reference to WPO202000039.
Title has been revised to reference WPO number, see Sheet C0.0.
b. Note 4: Revise floodplain effective date to May 16, 2016, rather than Feb-4,
2005. [18-30.3.2,]
Note 4 has been revised as requested, see Sheet C0.1.
3. C2.2: Calc. packet explains existing bioretention [south edge of site?] is removed with
this project, but Ex. SWM does not appear to be removed on this demolition sheet.
Further, site outfall 2 is only accurate for a 13.77 Ac. Area if Str. 202 outfall combines
with bioretention facility 213 outfall, and it appears this does not occur with proposed
grading in proximity of bioretention 213 outfall, Str. 100. Please ensure facilities to be
removed are shown demolished, and that outfall 2 and corresponding calculations are
accurate. See C5.0 image, below.
Ex bioretention is on sheet C2.3 north of playground area and east of existing parking. Sheet
C2.3 has been updated to specifically call out the removal of the existing facility. The flow
from structure 202 does combine with the flow of structure 100 however it is a bit
complicated to see without understanding some of the existing site infrastructure. There are
two depressed areas labeled basin/retention on the east and west sides of the concrete
diversion structure just downstream of structure 100. When the school was built in 1990 this
diversion structure was installed to capture the water in the concrete ditch and redirect to the
two basin/retention areas which function as a large level spreader. There is also a bypass built
into the system for storm events that exceed the design. The discharge from structure 202
flows overland to the eastern basin/retention area and as such combines with the flow from
structure 100 and the concrete diversion structure. Below is the detail of the diversion
structure clipped out from the plans dated 8/22/1988 for reference.
•SO 2'oc. ex
F41
DIVERSION STRUCTURE
NTS
amsr
4. C4.0, C4.1: Label outfalls 1, 2, 3, consistent with Calc. packet.
Labels for each outfall with reference to the corresponding VRRM drainage area have been
added to sheets C4.0 and C4.1.
5. C5.1: Label rprap outfall protection, L x W x D.
Riprap outfall protection has been labeled on Sheets C5.0 — C5.1.
6. C5.4:
a. Label SWM1, and bioretention 2A, 213.
Both SWM facilities and bioretention facilities have been labeled on Sheets C5.4—
05.5.
b. Clarify pre-treatment (other than pretreatment cell) for bioretention facilities
2A, 213. Ref. VA DEQ Stormwater Design Specification No. 9, Table 9.3.
Underground or direct piped discharge to a Level 2 bioretention facility does not
qualify as bioretention pre-treatment.
Notes clarifying pretreatment have been added under the bioretention computations
on sheet C6.3.
c. Label Emergency Access. Also label this access SWM Access (bioretention 2A,
26). [No proposed easement linework or easement plat is required, since parcel
is county -owned.]
A label for SWM access has been added to the emergency access for bioretention 2A.
Bioretention 2b has been removed from the plans. Acknowledged that no easements
are needed because property is county owned.
d. Confirm that bioretention facility 26 obtains building setback requirement, 25'
downgradient from building.
Bioretention 2B has been removed from the plans.
e. Flow splitter (Str. 126) and direction of flow in several pipes (circled) is unclear.
Please add flow direction arrows, and small-scale plan / profile detail for splitter
structure 126.
Flow splitter structure has been removed from the plans as is no longer necessary
with the removal of bioretention 2B.
i. C7.0 Str. 108-Str 126 notes that Str. 126 is MH-1 with splitter weir. Unless
plan/profile detail overlooked, please provide.
Flow splitter has been removed from the plan.
ii. Ensure 6' MH has steps, that steps do not conflict with multiple pipe
connections, or weir.
Weir is no longer proposed as flow splitter is removed from plan. Steps will be
installed per typical VDOT MH-1 details.
iii. Revise C7.0 profile label (Str. 126) to read:
1. INV IN from Str. 128, else revise C5.4.
2. INV OUT to Str. 106, else revise C5.4.
3. INV OUT to Str. 110, else revise C5.4.
4. INV OUT to Str. 122, else revise C5.4.
Flow splitter has been removed from the plan. All storm profiles have been
updated to match the current stormwater design.
f. Additional comments possible.
Acknowledged.
7. C5.5:
a. Label SWM2, and bioretention 2C, 3A.
Both SWM facilities and bioretention facilities have been labeled on Sheets C5.4—
05.5.
b. Clarify pre-treatment (other than pretreatment cell) for bioretention facilities 2C,
3A. Ref. VA DEQ Stormwater Design Specification No. 9, Table 9.3.
Notes clarifying pretreatment have been added under the bioretention computations
on sheet C6.3.
c. Label geothermal well field (linework around TMP 56-64E label).
Geothermal well field has been shown and labeled on Sheet C4.1.
d. Provide bioretention 2C, 3A close -approach vehicular access. Current design
force use of bus parking lot with no path for equipment or material to access
either facility. A possible access exists through curbing in bus circle, between
circle and basketball court (though this may be complicated by geothermal well
field). Provide roll -type curbing and a traversable, stable SWIM facility access
downslope to contour elevation 680'+.
Close vehicular access is provided by the bus loop for delivery of any materials and/or
equipment. Additional Access for maintenance activities is provided by the sidewalk
adjacent to both facilities. The typical maintenance for bioretention per VA DCR
specification No. 9 is maintaining the landscaping and mulch. Between the vehicular
access of the bus loop and the sidewalk path leading from the bus loop to these
facilities access for maintenance is provided.
e. Label proposed (gradually -falling) looping asphalt path.
Asphalt path has been labeled on Sheet C5.5.
f. Reinforce a 12' long section of this asphalt path with material sufficient to
support 6-ton vehicle or track equipment that may need to cross to the infield to
reach biofilter 2C.
It is not clear why a 6-ton vehicle is necessary to be able to access the specific location
identified. Per specification No 9 landscaping is the typical maintenance of
bioretention facilities. The only reason a 6-ton vehicle would need access to these
facilities is for the delivery of mulch which would be placed on site in a storage area to
be spread in the facilities by a landscaping crew. Vehicular access for offloading
equipment and materials is provided by the bus loop and additional access is provided
by the sidewalk pathways adjacent to the bioretention facilities. These pathways will
be strengthened to support any small maintenance vehicles that require access.
g. Propose pre-treatment for bioretention 2C; show in plan view (also, 7.b., above).
Pretreatment for bioretention 2C is provided in the upstream catch basin using an ACF
trash guard and gravel flow spreader. Detail provided on sheet C6.2
8. C6.0: Provide inset plan view, 1" = 10', for each of the six (6) SWM facilities. Label L x W
(x DIA) dimensions in each small-scale view of biofilter, or underground detention.
Please consider As -Built requirements when providing SWM facility design features,
dimensions, and details.
With the plans already at 1"=20' the requested dimensions have been added to sheets C5.4
and C5.5 without the need for 1"=10' inset views. Manufacturers details can and will be
provided on the plan for both detention systems for the final signature set submission.
Requests have been made for preliminary shop drawings from the manufacturers to help with
the future as -built requirements.
9. C6.1: Provide label for debris cage to be installed to prevent obstruction of 4.32" slot
weir (SWM1), and 4" x 11.5" slot orifice.' Note: Precision to a hundredth of an inch may
impose fabrication or post -construction expense to either manufacture to this
tolerance, or to perform routings, if As -built condition differs. Design rarely specifies
plate openings to this degree of precision, if tenth of a foot precision works nearly as
well.
Precision of the weir or orifice sizes has been revised to the closest half inch with routings
updated. A detail of a debris cage as been added with a note below the detail on sheet C6.2
for which orifices to protect with the cage.
10. C6.2: Revise bioretention profiles:
a. Label top or bottom of hardwood bark mulch layer.
Top and bottom of hardwood bark mulch layers have been labeled on sheet C6.2 for
all three bioretention filter details.
b. Label media invert elevation.
Soil medial invert/bottom elevation has been listed on the details for all three
bioretention filters on sheet C6.2.
c. Label #8 stone invert elevation.
Number 8 stone invert/bottom elevation has been listed on the details for all three
bioretention filters on sheet C6.2.
d. Provide small-scale, scale -accurate cross sections that include:
i. Pretreatment
ii. Labels
iii. Critical elevations
Small scale details are provided on sheet C6.2 with critical elevations and
labels. Notes have been added to the plan to describe the pretreatment
practices for each bioretention facility. Additionally, a detail for a gravel flow
spreader been added to sheet C1.2.
e. Show additional pretreatment.
Notes clarifying pretreatment have been added under the bioretention
computations on sheet C6.3.
f. Provide media mix specification (ref. DEQ Design Spec. No. 9, Table 9.3).
Soil media specifications from Spec. No. 9 have been added to sheet C6.2.
g. Ensure Max. ponding depth is 6 to 12 inches. Also, VA DEQ Design Spec. No. 9,
Table 9.3 footnote 2.
Maximum ponding depth of bioretention filter 2A, 2C, and 3A is 6 inches. Please see
computations on sheet C6.3 and details on sheet C6.2 illustrating the maximum design
ponding depth of 6 inches.
h. Show cleanout graphically accurately, with 45-deg bends, not 90-deg T
connection.
A note has been added to the details referencing the specific detail for cleanouts on
sheet C1.1 for greater clarity to the contractor on how to construct the cleanouts
within the bioretention facilities.
i. Include plant details (Recommend L-series landscape plan sheet for bioretention
SWM facilities):
i. Level 2 design requires plantings in addition to turf.
Bioretention filter plantings are shown and listed on sheets 1.1.1 and L1.2.
ii. If turf proposed, label/specify turf type.
Turf is not a proposed planting in the bioretention filter areas.
iii. Provide plant schedule, to be drawn from list of Albemarle County native
plants: provide common or scientific name, qty. to aid review, inspection,
and As -built review.
Proposed bioretention filter plan species are listed in the legend for the hatch
area on sheets L1.1 and L1.2.
j. Consider plan and profile elements and dimensions to be reported as As -Built
condition, deemed necessary for proper detention or bioretention performance.
Label, show, and provide items needed to report As -built conditions.
Additional information has been added to the details of the bioretention filters for
greater specificity in the construction of the facilities. In addition, a note has been
added to sheet C6.2 to bring attention to the as -built requirements that need to be
documented.
11. C6.2 or C1.2:
a. Provide Nyloplast dome grate detail.
A detail has been provided on Sheet C3.3.
b. Provide Nyloplast Mfr-recommended installation notes, as needed.
Notes have been provided on Sheet C1.3.
c. Provide Typ. Details:
i. VDOT PB-1
ii. Nyloplast pipe bedding
iii. VDOT IS-1 (inlet shaping)
Details have been provided on Sheet C1.3.
d. 5.96 Ac. Total disturbed area is inconsistent with SWPPP, Sec. 3, and C3.0 Project
Description (6.51 Ac). Please reconcile.
Total disturbed area is 5.41 acres and has been reconciled throughout.
12. C6.4: Include attached file as text, on C6.4 (bioretention periodic inspection).
The attached file has been included as text on Sheet C6.4.
C7.0:
13. Label SWM1, SWM2.
Stormtech chambers and SWM 2 have been labeled on Sheets C7.0 — C7.1.
14. Label underground detention system slope, if any.
SWM 2 slope has been indicated on Sheet C7.1.
C. 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 reasons listed below. The erosion control plan content
requirements can be found in County Code Section 17-402.
1. C3.0:
a. ST1: Check bottom of stone weir elevation (possible error, since higher than
crest of stone weir).
Sediment trap 1 has been renamed to ST2 for the updated phasing. The elevations of
the trap have been updated and checked with the new design of the trap.
b. ST2: List bottom of trap elevation, likely 678.0'.
The first submission ST2 has been removed from the plan and ST1 has been
renumbered to ST2. Trap bottom elevations have been listed.
2. C3.1: Include paved wash rack detail (PCE); ref. ACDSM, p.8.
This detail has been provided on Sheet C3.1.
3. C3.2, C3.3: Although design tables include ST floor dimensions, label trap (L x W)
dimensions in plan view.
Trap dimensions have been provided for all sediment traps in plan view.
4. C3.3: ST3 bottom of trap elevation (680.5') is lower than bioretention 2C No. 57 stone
invert elevation (681.00') Please ref. VA DEQ Design Stormwater Specification No. 9,
Sec. 6, 8.1, Construction Sequence, Construction Stage E&S Controls which requires
notes and graphic details on the E&S plan specifying that (1) the maximum excavation
depth at the construction stage must be at least 1 foot above the post -construction
installation, and (2) the facility [sediment trap] must contain an underdrain.
ST3 has been renamed ST1 to better align with the sequence of construction. The bottom of
trap elevation has been raised as requested, and the underdrain has been shown.
5. C3.3, C3.4: Show and label ST1, ST2, ST3 underdrains in plan view, each sediment trap.
Show ST underdrains running through embankments to daylight.
Underdrains have been shown and labeled in respective E&S phases.
6. C3.3: Revise ST3 bottom of trap elevation, per VA DEQ Design Spec. No. 9 guidance.
ST3 has been revised as described in #4 above.
7. C3.5:
a. Label ST3
ST3 has been renamed ST1 to better align with construction sequencing. In this phase,
ST3 (ST1) is to be replaced with bioretention facility 2C. A note has been added to this
effect on Sheet C3.5.
b. 2 sets of proposed contours at future SWM bioretention 3A; resolve contour
conflicts.
Contour conflicts have been resolved on all sheets.
c. Evaluate swale / ditch velocity (Q2-yr) to ST3 to ensure velocity in swale is non -
erosive.
A normal depth computation has been provided in the calc book after the 2yr inflow
hydrograph in the routings section for Bioretention 3A.
8. C3.5, C3.7: Proposed grading shows —10' vertical interval across outdoor activity / loop
trail area. While ST3 is provided at N end of this area of disturbance, SF, or even SSF is
inadequate ESC at S end of this relatively large disturbed area. Moreover, the 100'
stream buffer in several locations lies inside and upslope of proposed super silt fence
(SSF / wire -backed silt fence). This ESC design and level of stream buffer protection is
inadequate. Maximum length of graded slope draining to silt fence is 100'. Provide
additional measures, including diversion to additional trap/s. Additional review
comments possible.
Super silt fence is provided upstream of the 100' stream buffer to the greatest extent
practical. Additional SSF has been provided to act as additional layers of protection upstream
of the 100' stream buffer and to meet the requirements of VESCH STD & SPEC 3.05. It should
also be noted the vast majority of this area is the existing playground which is a very flat area
at an existing grade of less than 2%. There are also large areas of the existing playground that
will not be disturbed as they are existing play areas to remain. Additionally, super silt fence
has been added in two stages along the existing swale between the playground and recreation
field (outside of the limits now). One stage of super silt fence would be sufficient per 3.05 as
the maximum area to the swale is less than 1 acre and 1 CFS. The area draining to the swale
with ST1 in place is 0.49 acres at a C value of 0.36 which in a 30yr storm would still only yield
0.88 CFS. These additional areas of super silt fence should provide more than adequate
protection for the WPO area.
9. C3.7, C3.9: Sheets indicate looping asphalt trail is constructed prior to completion of
bioretention facility 2C. This trail is likely to incur significant damage during transition of
ST3 to bioretention facility 2C. Please ensure design allows construction of ST3/SWM
facility 2C without damaging other improvements.
Phasing has been revised throughout E&S sheets. Bioretention 2C and 3A are installed at the
same time as the looping trail and playground work in Phase II. A note was added to ensure
stabilization of upstream drainage areas prior to installation of bioretention facilities. See
Sheets C3.4 — C3.5.
10. C.3.5, C3.7, C3.9: These sheets show grading and construction of SWM bioretention
facility 3A. This future SWM facility receives swale runoff from contractor staging and
storage area. That area, in turn, will transition to temporary classrooms, first, then a
basketball court. These transitions involve land disturbance, meaning the swale shown
in ESC Plan, Phase II, III, IV appears to need to drain to a sediment trap, that may
transition to bioretention facility 3A once all contributing upslope drainage areas are
stabilized. Please consider sequencing and likely need for a fourth sediment trap to
receive sediment -laden runoff until contributing drainage areas are stabilized. SWM
facilities may not be constructed until then.
The E&S phasing has been updated to more accurately reflect the overall phasing plans
prepared by the architect. The contractor staging area will remain until almost the end of the
project with the basketball court as the final work to be done in the rear of the site after the
staging area is no longer necessary. Phase II and III have been updated to show the contractor
staging area to remain in phase II and be transitioned to the basketball court in phase III
where the small amount of work can be controlled by silt fence.
11. C3.8:
a. Label Emergency Access.
Emergency Access has been labeled on Sheet C3.8.
b. Provide note that Emergency Access will be utilized once upslope areas stabilized
to construct bioretention facilities 2A, 2B.
Note has been provided as requested on Sheet C3.8.
12. C3.9: If ST3 in ESC Plan Phase IV is actually, by this point, SWM bioretention facility 2C,
include note similar to note on C3.8 for permeable pavers; i.e.: 'Install bioretention 2C
once all uphill drainage area has been stabilized.'
This note has been added to phase II on sheet C3.5 as bioretention 2C and 3A will be installed
during phases I and II once the surrounding areas have been stabilized.
13. General: Coordinate SDP202000058 Major Site Plan Amendment Engineering Review
comments with VSMP Plan revisions.
Comments will be coordinated between submissions.
D. Pollution Prevention Plan (PPP) Ref. SWPPP.
The PPP content requirements can be found in County Code section 17-404. This plan requires
an Exhibit.
1. Include WPO202000039 on 11" x 17" Exhibit.
References have been made to the WPO plan on all PPP exhibits.
We have included PDF copies of the plans and calculations for your review. If you have any
questions or comments, please feel free to give me a call at 434.295.5624.
Sincere
Bryan Cichocki, PE
Project Manager