HomeMy WebLinkAboutWPO201800068 Review Comments 2018-11-12 4! Dewberry Engineers Inc. 804.290.7957
S Dewberry. 4805 Lake Brook Drive, Suite 200 804.290.7928 fax
Glen Allen,VA 23060 www.dewberry.com
November 12, 2018
County of Albemarle, Department of Community Development
Attn: David James,VSMP Reviewer
401 McIntire Road,Room 227
Charlottesville,VA 22902-4596
RE: ACSA Operations Center Expansion Parking Lot Expansion
1st Re-submission
Project File Number: WPO201800068
Dear Mr. David James,
On behalf of the Albemarle County Service Authority,Dewberry Engineers Inc. is pleased to submit for
your review and approval the final plans for the ACSA Operations Center Expansion Parking Lot
Expansion revised per three(3) sets of county comments. Two (2)copies of the Final Design(100%)
plans signed November 12,2018 are being submitted for your review. Below are the comments along
with responses(shown in bold)that were received from your review dated October 4,2018.
A. General
1. Please submit only the VSMP plans (SWPPP, PPP, SWM, E&SC plans) for approval.
Response: A separate,stand-alone VSMP plan set has been created.
2. Remove sheets C3.0, C3.2,L1.0,L1.1, E1.0,E1.1 & E1.2.
Response: The specified sheets have been removed from the VSMP plan set. Per
comment numbers 1 and 20 from Site Plan Review comments,ESC has been
removed from sheet C2.0. C2.0 is now only the demolition plan and has also been
removed from this VSMP plan set.
3. Cover sheet-Remove '100% Submission' from title. Include the WPO#
WPO201800068' under title. Remove the approvals block.
Response: Specified revisions made.
B. Stormwater Pollution Prevention Plan(SWPPP)
1. Registration Statement—Section 7,Add the County of Albemarle as the MS4 operator. Section
8, The disturbed area reported(0.42ac) doesn't match the disturbed area of 0.56ac according to
the plan/calcs.
Response: County of Albemarle has been added as MS4 operator.The disturbed area
has been updated to 0.57 ac. This total land disturbance includes the parking lot(0.43 ac)
and the stairway access (0.14 ac). The total land disturbance(0.57 ac)is used for the
water quantity and quality calculations.
Page 1 of 5
Mr.James
ACSA Operations Center Expansion Parking Lot Expansion
WP0201800068
1st Submission Comment Responses
2. Section 6(B)—The print out copy did not show all the contents typed into the boxes,please
show all.
Response: Section 6(B) has been updated to show all contents.
3. Insert copy of General Permit coverage when obtained.
Response: Confirmed.
C. Pollution Prevention Plan(PPP)
1. Show any proposed clearing/grading activities,paving operations, landscaping operations, E&S
controls, staging, stockpile,borrow, fueling, waste disposal, vehicle/equipment washing,concrete
washout locations on the PPP.
Response: The PPP has been updated.
D. Stormwater Management Plan(SWMP)
1. Provide supporting calcs verifying discharge of orifice/weir design.
Response: Stage-Discharge and Stage-Storage tables and graphs are included on sheet
C6.3. The orifice and weir design is included the hyrdocad printout for the"Summary for
Pond 1P: Storage" for each storm.These hydrocad printouts are included for 1 year, 10
year and 100 year for the pond are on sheets C6.3-C6.4.
2. Provide HGL calcs for 10-yr design. Show HGL in profiles.
Response: HGL calculations have been included on sheet C4.1. The HGL is shown on the
profiles on sheets C4.0 and C4.1.
3. Show proposed easement over underground storage pipes. The easement width is calculated
according to equation in the Design Standards Manual, Section 6C. Label the easement as a
`SWM facility easement'. The easement should encompass the detention pipes and structures to
the outfall connection.
Response: The easement width was calulcated as 27' wide. The wider portion,from
centerline of pipe out,was placed to the outside of the underground SWM system. Due to
the geometry of the pipe system,the overall easement encompasses most of the parking lot.
The easement,with specified label, can be found on sheet C3.1.
4. Submit the VRRM spreadsheet,pdf is fine.
Response: VRRM spreadsheet will be submitted.
5. Sheet C6.0—Provide analysis/computations to verify the discharge values shown at the
outfall points.
Response: Computations and routings for outfall 1 and 2 have been provided on
sheets C6.3-C6.4.Water quantity narrative and summaries have been added to sheet
C6.2.
11 Dewberry
Page 2 of 5
Mr.James
ACSA Operations Center Expansion Parking Lot Expansion
W PO201800068
15t Submission Comment Responses
6. Sheet C6.0/C6.1 —Show the land cover areas of site. (%)Impervious cover. Show/indicate
structure#6 mentioned. Is this STRM 6 shown on sheet C1.0?
Response: Existing and proposed land cover have been added to sheets C6.0 and C6.1.
STRM 6 has been added to sheet C6.0/C6.1. This is the same STRM 6 shown on sheet
C1.0 and is the existing manhole that the detention pipes outfall into. STRM 6 is also
Outfall 1.
7. Additional impervious area is being proposed with sidewalk/stairway. This area must be
accounted for water quantity/quality analysis. Show that it meets reg. requirements under Part
II B.
Response: The land disturbance and additional impervious from the sidewalk/
strairway has been accounted for in the water quantity and quality calculations included
in this plan set. The parking lot expansion has a disturbance of 0.43 ac and the stairway
access has a disturbance of 0.14 ac. The total disturbance analyzed for the VRRM is 0.57
ac. The total removal required for both the parking lot and the stairway access is 0.35
lb/yr.This is met through the purchase of nutrient credits,proof of which is provided on
sheet C6.3.
The stairway access project is included in water quantity computations for outfall 1
because all the flow from that project flows into a stormsewer system that flows to
STRM 6,which is outfall 1. The total site area from the stairway flowing to outfall 1 is
0.14 ac.
8. Sheet C6.3 —Energy Balance worksheet shown is confusing! You're showing `Channel type' as
Natural—wrong! You can't use Energy Balance because the runoff from site does not discharge
into a natural conveyance system.You must demonstrate that water quantity {9VAC25-870-66}
requirements are satisfied by showing the 2-/10-yr design post-dev discharge is confined within
the SWM system onsite and satisfies limits ofanalysis.
Response: Channel type has been updated to say"Stormsewer."
The energy balance spreadsheet calculates the allowable 1-year discharge from the
site area and takes into account the"offsite" area from the existing parking lot that
flows into the detention pipes and is contained in the system.This area is
considered the"offsite area peak discharge" and is added to allowable site
discharge that is calculated from the energy balance equation. This calculates the
maximum allowable peak discharge of 0.77 cfs.
Manmade outfalls are allowed to use Energy Balance to meet channel protection
criteria. 9VAC25-870-66.B.1.b. states that for water quantity analysis of a
manmade stormwater conveyance system "the peak discharge requirements for
concentrated stormwater flow to natural stormwater conveyance systems in
subdivision 3 of this subsection shall be met." Subdivision 3 is the energy balance
Dewberry®
Page 3 of 5
Mr.James
ACSA Operations Center Expansion Parking Lot Expansion
W PO201800068
151 Submission Comment Responses
method which is not required to be analyzed to the limits of analysis listed in
Subdivision 4.
9. ACSA to contact Ana Kilmer (Management Analyst) regarding nutrient credit agreement and
necessary documentation. Provide verification of nutrient credit purchase. — 0.35 lb/yr cr.
needed per VRRM
Response: The Affidavit of Phosphorus Credit Sale from Eastview Farm is included on
sheet C6.2. The amount of credits purchased was 0.35 pounds.
E. Erosion and Sediment Control Plan(ESCP)
1. Show date and source of topography information:All topography should be at least visually
field verified by the designer within the last year. Provide date when site was last inspected.
{9VAC25-870-66}
Response: Date and source of topography described in EXISTING CONDITIONS note 1
under GENERAL NOTES. Site was last visually inspected in September 2018.
2. Show areas of managed slopes on sheet C 1.0&C3.1. This may impact the currently proposed
wall and grading in or adjacent to those areas. (18-30.7.5}
Response: Managed slope areas were originally shown only on sheet CO.3 to preserve
clarity on grading plan. These areas have now been added to requested sheets. Per note 7
from Site Plan Review comments,the retaining wall design with 1' bench at base is
permissible. Please refer to Site Plan Review comments for further detail regarding wall
and associated grading.
3. Adjust your limits of disturbance(LOD)to include the grading behind proposed wall.
Response: LOD has been adjusted to include grading behind wall.
4. Show area of the new sidewalk/stairway improvements on the E&SC phase sheet(s) with
control practices in place.
Response: Per phone conversation with reviewer,showing ESC for the stairwell is
unnecessary. Disregard comment.
5. Show any offsite improvements including grading operations in a permanent easement.
Provide evidence that neighboring property owner is in agreement with this offsite work in the
easement. This can be a letter of agreement signed by neighboring property owner. {DSM,
Sect. 8C, 3F}
Response: An easement has been added to sheet C3.1 and labeled"Proposed temporary
construction and permanent maintenance easement". An agreement is being pursued
with adjacent property owner. Evidence letter in progress.
6. Sheet C2.0—Show paved construction entrance at 70'. Extend to proposed access gate.
111 Dewberry. Page 4 of 5
Mr.James
ACSA Operations Center Expansion Parking Lot Expansion
WPO201800068
151 Submission Comment Responses
Response: 70' paved construction entrance per Albemarle County DSM has been added
and extended to access gate.
7. Sheet C5.0—The County requires paved construction entrances. The current CE detail with the
one in the County's Design Standards Manual. {DSM, Sect.3F}
Response: The construction entrance detail has been exchanged with Albemarle County
DSM detail.
8. Please show the steep slopes or managed/preserved slopes.
Response: Steep/Managed slope area have been shown on the following three (3) sheets:
CO.3, C1.0, and C3.1.
9. Show location of all existing and proposed utilities and easements with deed book
references.
Response: Existing utilities, easements, and deed book references are shown on
sheet C1.0. Proposed SWM Facility Easement is shown on sheet C3.1.
10. Provide low maintenance(not grass)ground cover specified on the plans where
grades are steeper than 3:1. (DSM, Sect 8A}
Response: Low maintenance ground cover has been provided on 2:1 slopes at
base of wall and can be found on sheet L1.0. The updated plant schedule is
on sheet L1.1
11. Indicate slopes 3:1 and over.
Response: 3:1 and steeper slopes have been labeled on new sheets C2.1 (Phase 1 ESC Plan)
and C2.2 (Phase 2 ESC Plan).
12. Provide some permanent stabilization measure for the ditches in front of wall to
prevent erosive action.
Response: Permanent stabilization has been provided for ditches. See sheet
C2.2. Detail has been added to sheet C5.1.
This letter is provided as part of the resubmittal process and addresses all of the comments above. If you
have any questions or require clarification please let us know.
Sincerely,
Kevin A. Pennock
•
it Dewberry® Page 5 of 5
•
m Name: ACSA5tna -
ParkingExpansion
CLEAR ALL I d
Date: 10/11/201R (nrlashrfr.6) constant values
Linear Development Project?- No • akolation cells 1
Site Information fi„re,a,,
Post-Development Project(Treatment Volume and Loads)
•
Enter Total Disturbed Area(acres) 4=MOM Check:
RMP Design Specifications List:2013 Draft 5tds&Specs
Maximum reduction required: r® linear project? No
The site's net increase In impervious cover(acres)Is:Ilirnill Land cover areas entered correctly? s/
Post-Development TP Load Reduction for Site/lb/yr):IIIIMIIM Total disturbed area entered? ,/
Pre-ReDevelopment Land Cover(acres)
A Soils B rolls C Soils D Soils Total,
Forest/Open Span(acres)-undisturbed
forest/open space 0.10 0.10 •
Mastered Turf(anal-disturbed.graded for
yards or other turf to bemawed/managed 0.35 035
Impervious Cover(oat) 0.12 0.12
057
Post-Development Land Cover(acres
A Solis B Soils C Solis 0 Soils Totals
Forest/Open Span(acres)-undisturbed,
•
protected forest/open space or reforested land 0.01 0.01
Managed Turf(acres)-disturbed,graded for
yards or other turf to be mowed/managed 026 0.26
Impervious Cover(acres) 0.30 030
Area Check OK OK OK OK. 057
•Form/Open Space areas must be protected In accedence with the V4pMo Runoff Reduction Method
Constants Runoff Coefficients(Re)
Annual Rainfall(inches) 43 A Soils B Solis C Soils °Soils
Target Rainfall Event(inches) 1.00 Forest/Open Space 0.02 0.03 0.04 0.05
Total Phosphorus)TP)EMC(m6/1) 0.26 Managed Turf 0.15 0.20 0.22 0.25
Total Nitrogen(TN)EMC(mg/1.) 1.36 mpervious Cover 0.95 0.95 0.95 0.95
Target TP toad(lb/acre/yr) 0.41
PI(unideu correction factor) 0.90
LAND COVER SUMMARY-PRE-REDEVELOPMENT LAND COVER SUMMARY--POST DEVELOPMENT
Land Coverwmma -_.
Summary-Pre Land Cover Summary-PPM Mho° Land cover Summary-Part Land Cover summary-Pose
Pre-Re:mbpmem listed Adjusted' Post ReDev.&New Impervious Post-RaDanbpmem Post-Development New Impervious
Forest/Open SCover Forest/Open Space Forest/Open Space
(acres) 0.10 0.01 0.01 0.01
Cover(acres) ._ .r:!T._cl?F'n)_..
Weighted Rv(forest) 0.03 0.03 Weighted Rv(forest) 0.03 ._,Weighted Ru)forea_l. 0.03
Sparest 18% 3% %Forest 2% %Forest 3%
Managed Turf Coverlacresl 0.35 0.26 Managed Turf Cover 0.16 Managed Turf Cover 0.26
(acres) (acres(
Weighted Marl) 0.20 0.20 Weighted Re(turf) 0.10 Weighted Rv(turf) 0.20
%Managed Tun' 61% 67% %Managed Turf 46% %Managed Turf 67%
RenaImpervious Cover(acres) 0.12 0.12 Impervious Cover(acres) .es) 030 Covef(�M;us 0.12 New Im;eMo;iCow 0.16
Rv)impervious) 0.95 0.95 Rv(impervious) 0.95 Rvlimpeenaal 0.95 Ar[aervlpta) i 0.95
%Impervious 21% 31% %Impervious 53% %Impervious 31%
Taal Site Area'acres) 057 039 Final Site Area(acres) 0.57 Tool ReOa.She Area 039
she Re 033 043 Final Port Des Site Rv 059 ReDe05Re Rv 0.43
T
Treatment Volume and Nutrient Load Treatment Volume and Nutrient Load
•
Pre-0.e0evelPpment treatment Volume Final Post.0evebpment Pat-ReDevelopment Postoevelopeant
lane N) 0.0156 0.0139 Treatment Volume 0.02E11 Treatment Volume 0.0139 Treatment Volume 0.0143 i
•
(acre-ft) (acre-N) (acre%)
- 1
Yre Nerhvela Final Past-Development Post-Reoevebp Post.Development PDevelo I
pment Treasmem Volume p (cable j 621
i
(cubic fart( 679 604 Treatment Volume 1,224 Treatment Volume 604 Treatment Volume
(oak feet) (oak feet) feet)
-
Pre-ReDevelopment TP Load Final Post Post-Reoevebpment Pat-Development TP
pb/yrl 0.03 036 Development TP load 0.77 Load(TM 0.38 oestoa l lb/n) 0.39
0b/yr) la/yrl•
Pre Re col Post-Development rP ae0oelopmentre - - -
DevNjnPv<r�;oa per,<,< pre ace) T load per acre US OBI
pa/weir) LOb/acre/art
Rauline TP load(Ib/yr) as.Reduction Required
IDAI lbs/acre/w applied to preredessiopment area including Pervious 0.16 (Below ere- ins
land proposed for new lmpannon cover( De•Nopment ball
'AdjustedtendCover Summary TP load Reduction
T Load Reduction
Pre MOevelopment land cover minus pervious land cover fforen/open space or Required for 0,04 Required for New 0.32
monoped turf)ocreage proposed for new impervious cover Redeveloped Area Impervious Area(lb/al
Ills/yr)
Adjusted total acreage is consistent with PostnNhve(opment acreage(minus wear
of new impervious awe)).
Column)shows load reduce an regraiemene for new impervious cover(fined on new
development bad limit,Odd tW e/Yeach
Post-Development Requirement for Site Area
TP Load Reduction Required(lb/yr) 035
Nitrogen Loads(Informational Purposes Only)
Final Post-Development TN Load
Pre-ReDevelopment TN load OWN 3.05 (post'ReOeveiopment&New Impervious) 5.50
(Ib/yr)
DEQ Virginia Runoff Reduction Method Re-Development Compliance Spreadsheet -Version 3.0
BMP Design Specifications List: 2013 Draft Stds&Specs .
Site Summary
Project Title:ACSA Spotnap Parking Expansion
Date:43384 Total Rainfall(in): 43
Total Disturbed Acreage: 0.57
Site Land Cover Summary
Pre-ReDevelopment Land Cover (acres)
A soils B Soils C Soils D Soils Totals %of Total
Forest/Open(acres) 0.00 0.10 0.00 0.00 0.10 18
Managed Turf(acres) 0.00 0.35 0.00 0.00 0.35 61
Impervious Cover(acres) 0.00 0.12 0.00 0.00 0.12 21
0.57 100
Post-ReDevelopment Land Cover (acres)
A soils B Soils C Soils D Soils Totals %of Total
Forest/Open(acres) 0.00 0.01 0.00 0.00 0.01 2 «
Managed Turf(acres) 0.00 0.26 0.00 0.00 0.26 46
Impervious Cover(acres) 0.00 0.30 0.00 0.00 0.30 53
*Forest/Open Space areas must be protected in accordance with the Virginia Runoff Reduction Method 0.57 100
Site Tv and Land Cover Nutrient Loads
Pre-
Final Post-Development Post- Post- Adjusted Pre- ReDevelopment Final Post-Development Post-ReDevelopment TP
(Post-ReDevelopment ReDevelopment Development ReDevelopment TP Load per acre TP Load per acre Load per acre
&New Impervious) (New Impervious) (Ib/acre/yr) (Ib/acre/yr) (Ib/acre/yr)
Site Rv 0.59 0.43 0.95 0.43 0.97 1.35 0.97
Treatment Volume(ft3) 1,224 604 621 604
TP Load(lb/yr) 0.77 0.38 0.39 0.38
Total TP Load Reduction Required(Ib/yr) 0.35 0.04 0.32
Final Post-Development Load Pre-
(Post-ReDevelopment&New Impervious) ReDevelopment
TN Load(Ib/yr) 5.50 3.05
Site Compliance Summary
Maximum%Reduction Required Below 10%
Pre-ReDevelopment Load
Total Runoff Volume Reduction(ft3) 0
Total TP Load Reduction Achieved(Ib/yr) 0.00
Total TN Load Reduction Achieved(Ib/yr) 0.00
Remaining Post Development TP Load
(lb/yr) 0.77
Remaining TP Load Reduction(Ib/yr) 0.35
Required
Drainage Area Summary
D.A.A D.A.B D.A.C D.A.D D.A.E Total
Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0.00 -
Managed Turf(acres) 0.01 0.00 0.00 0.00 0.00 0.01
Impervious Cover(acres) 0.22 0.00 0.00 0.00 0.00 0.22
Total Area(acres) 0.23 0.00 0.00 0.00 0.00 0.23
Drainage Area Compliance Summary
D.A.A D.A.B D.A.C D.A.D D.A.E Total
TP Load Reduced(Ib/yr) 0.00 0.00 0.00 0.00 0.00 0.00
TN Load Reduced(Ib/yr) 0.00 0.00 0.00 0.00 0.00 0.00
Drainage Area A Summary
Land Cover Summary
A Soils B Soils C Soils D Soils Total %of Total
Forest/Open(acres) 0.00 0.00 0.00 0.00 0.00 0
Managed Turf(acres) 0.00 0.01 0.00 0.00 0.01 4
Impervious Cover(acres) 0.00 0.22 0.00 0.00 0.22 96
0.23
BMP Selections
Managed Turf Impervious Cover TP Load from
BMP Treatment Untreated TP Load TP Removed TP Remaining Downstream Treatment
Practice Credit Area Credit Area Upstream
(acres) (acres) Volume(fts) Practices(Ibs) to Practice(Ibs) (Ib/yr) (Ib/yr) to be Employed
14.b.Manufactured Treatment Device-
Filtering 0.22 758.67 0.00 0.48 0.35 0.12
Total Impervious Cover Treated(acres) 0.00
Total Turf Area Treated(acres) 0.00
Total TP Load Reduction Achieved in D.A.
(Ib/yr) 0.00
Total TN Load Reduction Achieved in D.A.
(Ib/yr) 0.00
Runoff Volume and CN Calculations
L
1-year storm 2-year storm 10-year'storm_
Target Rainfall Event(in) 0.35 0.42 0.55
Drainage Areas RV&CN Drainage Area A Drainage Area B Drainage Area C Drainage Area D Drainage Area E .
CN 96 0 0 0 0
RR(ft3) 0 0 0 0 0
RV wo RR(ws-in) 0.11 0.00 0.00 0.00 0.00
1-year return period RV w RR(ws-in) 0.11 0.00 0.00 0.00 0.00
CN adjusted 96 0 0 0 0
RV wo RR(ws-in) 0.15 0.00 0.00 0.00 0.00
2-year return period RV w RR(ws-in) 0.15 0.00 0.00 0.00 0.00
CN adjusted 96 0 0 0 0
RV wo RR(wsdn) 0.25 0.00 0.00 0.00 0.00
10-year return period RVw RR(ws-in) 0.25 0.00 0.00 0.00 0.00
CN adjusted 96 0 0 0 0