HomeMy WebLinkAboutWPO201400030 Review Comments 2014-04-15Review Comments
Project Name: Briarwood Underground Detention Stormwater Management/BMP Plan
Date Completed: Wednesday, September 03, 2014
Reviewer: Ana Kilmer
Department /Division /Agency: CommDev- Central Ops
Reviews
8/25/2014 - swa submitted and forwarded to CAO
8/25/2014 - swa approved by CAO
8/28/2014 - swa signed by county executive
9/3/2014 - swa recorded in deed book 4531, page 253
Review Status: Approved
Review Comments
Project Name: Briarwood Underground Detention Stormwater Management/BMP Plan
Date Completed: IThursday, August 21, 2014
Reviewer: John Anderson
Department /Division /Agency: Engineering
Reviews
bond estimate complete 8/19/14
Review Status: See Recommendations
Review Comments
Project Name: Briarwood Underground Detention Stormwater Management/BMP Plan
Date Completed: Monday, August 18, 2014
Reviewer: John Anderson
Department /Division /Agency: Engineering
Reviews
Review Status: Approved
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44-11169
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road,Room 227
Charlottesville,Virginia 22902-4596
Phone(434)296-5832 Fax(434)972-4126
Project: Briarwood Underground Detention
Plan preparer: Scott Collins;Collins Engineering[200 Garrett St.,Suite K,Charlottesville,VA
22902,scott@collins-engineering.com]
Owner or rep.: Wendell Wood and Nena Harrell [ulcwww @embarqmail.com]
Woodbrier Associates L[P.0.Box 5548,Charlottesville VA 22905]
Plan received date: 11 April 2014
(Rev. 11 10 June 2014
(Rev.2) 24 July 2014
(Rev.3) 8 August 2014
Date of comments: 22 May 2014
(Rev. 1) 16 July 2014
(Rev.2) 4 August 2014
(Rev.3) 18 August 2014
Reviewer: John Anderson
Comments from previous revisions have been removed to help simplify this memo. They are still available for
viewing on the CountyView database system.
A.VSMP: SWPPP and Pollution Prevention Plan(WP0201400030)
(The Virginia stormwater management program, stormwater pollution prevention plan application and
documents)
1. (4 Aug-14 comment New#1,SWM Plan)
With respect to SWPPP dated 7/20/14 prepared hA Collins Engineering'for construction activities at
Briarwood Commercial Lots.received 7/24/14:
Registration Statemem(General VPDLS Permit)latitud ilongitude do not match SW PP project
coordinates;please reconcile, (Rev.3) Comment addressed.
Estimate start-finish installation-removal dates throughout the SWPPP. (Rev.3) Comment addressed.
Revise inspection schedule ip.26o Inspections are required at least once every 10 business days(plus
additional requirements), [Re:: OV_lC25-t40-70. Part 11. Stormwater Pol!utio,t Prevention ntion Prun, 1..
Inspections, 2.. Inspection Schedule] (Rev.3) Comment addressed.
SWPPP..p.26, identifies one individual responsible for inspection. Confirm that this individual accepts
sole responsibility,for scheduled inspection~- repo+rtinc, recordkeeping, notification,and for irectin g
corrective response relating to SWPPP proposed to cover all Briarwood Commercial projects. (Rev.3)
Comment addressed;also,email,FGM to JEA,Wed 8/6/2014 3:52 PM.
ltXHl}3rt"C<)SHo CoNcm E E \V'AsIiOCi' .POR A ruFnCS,AND 1'ti..t 1 NK>AREA(7r21/14):ShCor concrete wash
out area(trot shown), Concrete wash out area's may not drain to storm inlets. Propose treatment for concrete
wash waters. [§ 17-4.0411,1 (Rev.3) Comment addressed.
Show on-site dumpster. Provide treatment(or detention)of dumpster drain water. i)umpscer runoff may
contain contaminants that may not discharge freer downslope,to a storm inlet, or to any stream. Provide silt
fence or earthen berm at porta-johns as containment in event of spill. Furnish impermeable containment_a
harrier to infiltration designed to hold the entire volume of stored fuel in event of spill,with freeboard measure
of safety,for each fueling tank shown in the SWPP e;hihit. (Rev.3) Comment addressed.
•.ra.
Engineering Review Comments
Page 2 of 2
17-404.B.1.a. Wash waters tilininiire the discharge of pollutants from equipment and vehicle washing,
Wheel wash water,and other wash is'aters. Wash waters must he treated in a sediment nt haGss or alternative
control that provides equivalent or better treatment prior to discharge... Propose treatment for wash water.
(Rev.3) Comment addressed—Wash areas drain to trap or basin.
Construction entrance with wash rack to the north does not drain to a sediment basin:propose treatment.
(Rev.3) Comment addressed.
Label construction entrance on plan sheets as Paved CF,with wash rack irei. WPO20131110172.E&`.
Sequence of Construction Note 31. Provide detail found at p. 27 of ACDSM linl
httl_ :wvsvk.alhemurl ors>>/department.ash?department=cdd&ralpa<_>e-=4447 (Rev.3) Comment addressed.
-
'Transfer SWPPP best management practices to project plan sheets:practices or narrative nsted/shown it
SWPPP and on WPC)plans should mirror each other. (Rev.3) Comment withdrawn—not necessary in this
instance. See SWPPP dated 8/6/2014 for details re SWPPP fuel spill containment,concrete washout,porta-
John,and paved construction entrance details.
Revise SWPPP.SWPPP plan sheets,and corresponding\VPO plan sheets. (Rev.3) Comment addressed
—bullet above.
VSMP SWPPP and Pollution Prevention Plan approved. [REF.SWPPP 08/06/2014]
B.VSMP: SWPPP: Stormwater Management Plan(WPO201400030)
Comments from previous revisions have been removed to help simplify this memo. They are still available for
viewing on the CountyView database system.
(4 Aug-14 comment New#2,SWM Plan)
Furnish letter 01'coverage. VI)EQ General VPDFS Permit. (Rev.3) Comment addressed/Nena Harrell
to GEB/JEA email:Tue 8/12/2014 9:27 AM;Mark Graham to JEA email: Wed 8/13/2014 7:07 PM. Sara
Moore,DEQ EMAIL:Tuesday,August 12,2014 9:03 AM
VSMP SWM plan approved.
Permit coverage under the old 2009 permit remains in effect until you receive coverage under the new 2014
permit.Once you receive your 2014 coverage letter you will be operating under the new 2014 permit(see
9VAC25-880-30.H of the 2014 construction general permit regulation-coverage under the old 2009
construction general permit is administratively continued[i.e.,remains in effect]for operators that
submitted a complete reissuance registration statement).
Also:"The project for Briarwood is under number VAR107199—your coverage under 2009 permit remains
in effect until such time as we[DEQ] issue the 2014 permit.
-Sarah Moore„
[August 12,2014 9:03 AM;partial text;EMAIL:Sarah Moore,VDEQ,to Nena Harrell,Applicant/Owner]
C. VSMP: SWPPP: Erosion and Sediment Control Plan(WPO201400030)
Comments from previous revisions have been removed to help simplify this memo. They are still available for
viewing on the CountyView database system.
Text,J.Anderson email,6/2/2014 3:54 PM: "It would be fine to transfer ESC plan for the underground detention system into
the Road Plan WPO since Road Plan WPO already integrates UG storage construction into a 2-phase ESC plan. It would be
clearer if all aspects of ESC required to install the UG detention system are located on the Road Plan WPO.,,
VSMP ESC Plan approved.
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�'717G1L31P
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project:
Briarwood Underground Detention
Plan preparer:
Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA
22902, scott@collins- engineering com]
Owner or rep.:
Wendell Wood and Nena Harrell [ulcwww @embargmail.com]
Woodbrier Associates L [P. O. Box 5548, Charlottesville VA 22905]
Plan received date:
11 April 2014
Rev. 1
10 June 2014
(Rev. 2)
24 July 2014
Date of comments:
22 May 2014
Rev. 1
16 July 2014
(Rev. 2)
4 August 2014
Reviewer:
John Anderson
A. Stormwater Management Plan (WP0201400030)
Revise routing calculations to eliminate outlet structure 3. Change outlet structure 1 type to orifice, or
revise the design so that weir flow is more likely. Please revise SCS routing calculations. Storage pipe
length should be identical in plan section view (sheet 5) and as model input (pipe 2 given as 181'). (Rev. 1)
Comment addressed.
2. Update (or replace) critical slopes (sheet 2) with managed slopes (County GIS -web) so that review can
compare development with steep slope overlay district, and preservation or management requirements.
Steep slopes exist within project LOD. (Rev. 1) Comment addressed.
3. Drainage areas are confusing. For example, DA #lA is problematic, and does not define an actual drainage
area. This DA does not exist in prior submissions (see pre - development DA, WP0201300072, 11/25/13,
sheet 2; structure 24 DA, SUB201400066, sheet 8 of road plan). Please show drainage divides' upper
boundaries coincident with topographical high points. Topographic lines or labels require attention and
revision at several locations: Post - development DA (sheet 3) should bear close resemblance to post -
development DA, sheet 8, SUB201400066, which shows contours for the same development (portion of
new roadway); eliminate post - development contours associated with roadway from pre - development view
(Master Stormwater Development Plan —sheet 3); DA #lA is called out as 1.02 Ac. in plan view, 0.70 Ac.
in Watershed Summary table (sheet 4); and several other plan view -table mismatches (DA #1 C /post; totals)
(Rev. 1) Comment addressed.
Engineering comment (19 Dec 2013): "Please provide MS -19 with all WPO applications." With this
application, information pertaining to MS -19 and proposed development outlined in Briarwood Channel
Adequacy Report (Nov -4, 2013) has changed. The development areas and drainage areas have changed.
With loss of DA #4, required points of analysis for receiving channels now include outfalls from SWM
facilities to pipes on the west side of U.S. Rte. 29 (existing 24" CMP and 18" RCP associated with MS -19
cross - sections 1 and 3). With elimination of DA #4, 1% analysis continues beneath U.S. Rte. 29 to Herring
Engineering Review Comments
Page 2 of 5
Branch. Please include MS -19 for downstream 1% analysis points along Herring Branch. Analysis should
reflect routing calculations which will change given control structure and DA revisions noted in items #1, 3,
above (or elsewhere). Furnish topographic map that shows project site's (Minus DA #4) 1% relationship to
watershed. (Rev. 1) Comment partially addressed: See ESC comment #1, WPO201400059, 7- 14 -14,
and ESC comment #11, WPO201300072, 7- 15 -14: MS -19: photos indicate erosion down slope of pipe
outfalls beneath U.S. Rte. 29, an indication that receiving channels are inadequate. The computations
should reflect this, and appropriate measures should be specified to correct the problem. The computations
(roughness and velocities) appear to indicate conditions of adequacy that do not exist. (Rev. 2) Comment
addressed via discussion 7/31 with Mr. Graham Murray, Collins Engineering, and plan revisions dated
7/31/14.
5. When submitting revised MS -19 data or report, please ensure that channel cross - sections of ditches match
existing ditches, that photographs and captions correspond with analysis points. (Rev. 1) Comment
partially addressed. In response to letter request received with revised MS -19 report (rev: 9- Jun -14),
channel cross section locations, Channel Adequacy Exhibit (watershed areas; d. 6/4/14), and photographs
present suitable MS -19 analysis points. Only cross - section locations are provided. Channel geometry is
not included with MS -19 report, but would help when evaluating statement of adequacy for cross sections
#1 and #3 against existing conditions (slope ditches) at outfalls of 24" DIA and 18" DIA storm drain pipes
beneath U.S. 29. (Rev. 2) Comment addressed —see #4 above.
6. Given that post - development DA # 1 C is slightly smaller than pre - development DA #1 C, and with increased
impervious area, the post - development CN value should increase rather than decrease. (Rev. 1) Comment
addressed.
7. Final build -out (SCS routing, sheet 4) chart references inclusion of 28,OOOsf, post - development chart
references exclusion of 34,OOOsf. Correct discrepancy or clarify. (Rev. 1) Comment addressed; per
discussion/e -mail [June 26, 2014 10:47 AM], anticipate post- development chart will reference 29,500 SF.
8. Water quality: BMP Computations for Worksheets 2 -6 list %RR = 58 %. Provide required treatment for
improvements shown on this plan. The grass swale does not appear sufficient. Water quality treatment
requirements attach to proposed development; requirements that apply to proposed development may not be
met by referencing treatment elements associated with projects which may be delayed, or never built. (Rev.
1) Comment addressed ifproject eligible for technical review criteria found at 9VAC25- 870- 93/ -99
(technical criteria in effect before Jul- 1 -14). Design provides 4 Filterra units on Road `A' [ref. sheet 5, str.
#28, 30, 36, 38; letter, Filterra to Collins Engineering, June 9, 2014 affirms design adequate for contributing
drainage area]. VDOT restrictions on use of Filterra units within public RW set practical limits on extent of
water quality treatment. (Rev. 2) Comment acknowledged.
Elm Tree Court cul -de -sac is not included in any post- development drainage area. Please include Elm Tree
Court turnaround (increase in impervious area) in hydrologic models, DAs, etc. It appears runoff will reach
the cul -de -sac and release to slopes. Provide treatment for this area. (Rev. 1) Comment addressed;
structure 46, DI.
10. Show 24" CMP and 3' x 3' box culvert continuing beneath U.S. Rte. 29 SBL/NBL; sheet 2 is confusing in
this respect. (Rev. 1) Comment addressed.
11. Do not show the proposed three line SWM underground detention system as pre - development;
WPO201300018 approved a two -line system which was never constructed. Pre - development condition is a
Engineering Review Comments
Page 3 of 5
sediment basin that serves as SWM control for a portion of Briarwood Drive. (Rev. 1) Comment
addressed.
12. INV in/out for three -66" DIA pipes appear slightly off (0.03'); please check against 0.5 %slope and revise
if necessary. (Rev. 1) Comment withdrawn, per Collins' response, but revisions were actually made to
the underground detention system approved Aug -20, 2013 (WP0201300018; 2 -line system). Current
design proposes a 3 -line underground detention system.
13. Show STM 36A in detail inset (sheet 5); show 24" CMP between STM 36A and 36B as section of pipe to
be removed. Note ( "Contractor shall plug and remove the existing riser & barrel upstream of structure
3613") and arrow are confusing. (Rev. 1) Comment addressed.
14. It is unclear how the proposed 1' tall weir plates located inside each 66" DIA storage pipe will divert 1 X
WQV to the grass swale BMP given that top elev. of the lowest weir is 403.84'while INV IN of the 15"
bypass overflow is 408.5'. Unless water elevation at top of 1'weir plates is > 408.5', it would appear that
water in the storage system will not reach the grass swale via the 15" bypass overflow. Please clarify.
Provide a profile with these elements. (Rev. 1) Comment addressed.
15. ConTechTM manufacturer's approval of the underground detention system design is required. ConTech plan
details are not legible. (Rev. 1) Comment partially addressed; please confirm that Jul -8, 2013 ConTech
letter that affirms adequacy of design applies to 3 -line system under consideration, and not the 2 -line system
approved under WP0201300018. The debris cage detail is faint; please furnish legible detail. (Rev. 2)
Comment addressed.
16. Show pipe DIA and L for existing and proposed pipes beneath Briarwood Drive that carry ditch flow south
to north, across Briarwood Drive, near Int with U.S. Rte. 29. Existing pipe is approx 125 -ft, while
proposed pipe is approx 140 -ft in length. (Rev. 1) Comment addressed.
1. New -With respect to SWPPP dated 7/20/14 prepared by Collins Engineering for construction
activities at Briarwood Commercial Lots, received 7/24/14:
- Registration Statement (General VPDES Permit) latitude /longitude do not match SWPP project
coordinates; please reconcile.
Estimate start- finish / installation - removal dates throughout the SWPPP.
- Revise inspection schedule (p. 26). Inspections are required at least once every 10 business days (plus
additional requirements). [Ref. 9VAC25- 880 -70, Part II, Stormwater Pollution Prevention Plan, F.,
Inspections, 2., Inspection Schedule]
SWPPP, p. 26, identifies one individual responsible for inspection. Confirm that this individual accepts
sole responsibility for scheduled inspections, reporting, recordkeeping, notification, and for directing
corrective response relating to SWPPP proposed to cover all Briarwood Commercial projects.
- ExHisrr TO SHOW CONCRETE WASH OUT, PORTA - JOHNS, AND FUELING AREA (7/21/14): Show concrete wash
out area (not shown). Concrete wash out area/s may not drain to storm inlets. Propose treatment for concrete
wash waters. [§ 17- 404.B.]
- Show on -site dumpster. Provide treatment (or detention) of dumpster drain water. Dumpster runoff may
contain contaminants that may not discharge freely downslope, to a storm inlet, or to any stream. Provide silt
fence or earthen berm at porta johns as containment in event of spill. Furnish impermeable containment, a
barrier to infiltration designed to hold the entire volume of stored fuel in event of spill, with freeboard measure
of safety, for each fueling tank shown in the SWPP exhibit.
17- 404.13. La. Wash waters — "Minimize the discharge of pollutants from equipment and vehicle washing,
wheel wash water, and other wash waters. Wash waters must be treated in a sediment basin or alternative
control that provides equivalent or better treatment prior to discharge." Propose treatment for wash water.
- Construction entrance with wash rack to the north does not drain to a sediment basin; propose treatment.
Engineering Review Comments
Page 4 of 5
Label construction entrance on plan sheets as Paved CE, with wash rack [ref. WP0201300072, E &S
Sequence of Construction Note 3]. Provide detail found at p. 27 of ACDSM –link:
http : / /www. alb emarle. org/dep artment. asp? d ep artment =c dd &relp age =4447
Transfer SWPPP best management practices to project plan sheets: practices or narrative listed/shown in
SWPPP and on WPO plans should mirror each other.
Revise SWPPP, SWPPP plan sheets, and corresponding WPO plan sheets.
New - Furnish letter of coverage, VDEQ General VPDES Permit.
B. Erosion Control Plan (WP0201400030)
Text, J. Anderson email, 6/2/2014 3:54 PM: "It would be fine to transfer ESC plan for the
underground detention system into the Road Plan WPO since Road Plan WPO already integrates
UG storage construction into a 2 -phase ESC plan. It would be clearer if all aspects of ESC required
to install the UG detention system are located on the Road Plan WPO."
1. Inlets on Briarwood Drive (STM -38, STM -37) outfall to the existing sediment basin that serves as stone
management via a 15" RCP (see sheet 2, 8/6/13/ WP0201300018 plan), but note on Sheet 7 does not
account for this runoff. It appears that the sediment trap should be designed to handle runoff from DA #113
( =2.30 Ac). (Rev. 1) Comment addressed.
2. The sediment trap outfall (stone weir) must continue to the roadside ditch (sheet 6, 8/6/13 plans). Furnish
scale plan/profile drawings of revised sediment trap, not just typical from VESCH, 1992 Edit. Show wet
storage side slopes of 2:1 or flatter. Provide 2:1 (min) length:width ratio for flow path. Proposed trap
dimensions (98'W X 14'L flow path) yield 0.14 ratio for overland flow, but ratio of 7.0 if overland flow is
diverted (dike) to the south end of the sediment trap to join 15" RCP runoff at that point. Diversion dikes,
not SF, must direct runoff to the sediment trap. Trap is centered on an existing drop inlet. Adapt trap
design to preserve inlet function and capacity— suggest plate 3.08 -2, VESCH. (Rev. 1) Comment may
apply if sediment trap restored as ESC measure for underground detention system installation. [see
WP0201300072, Road Plan WPO, ESC plan review comment #6, 7/15/14] (Rev. 2) Comment discussed
1- Aug -14, with Adam Long, Collins Engineering. Collins intends IP [plate 3.08 -2, VESCH] plus
secondary ESC measures as inlet protection at drop inlet. Diversion located within DA# 1B will divert
runoff to ST3. –Ref. WP0201300072, sheet 3. Anticipate revision to sheet 3.
3. The Road plan WPO (WP0201300072) indicates a 2 -phase ESC plan will be followed to make partial
roadway improvements ( Briarwood Drive /Elm Tree Court), and, in phase -I1, to construct Road `A' and
Road `B'. Between Phase I and 11, the underground SWM facility proposed with this application will be
built under its own ESC plan. Please ensure that ESC considerations tied to drainage areas contributing to
the existing sediment basin at the end of phase I road building are evaluated under this application. This
application bridges ESC Phase I and 1I of the road plan WPO. Phase I runoff, layout of piping, and
contributing drainage areas should match this application. Please revise ESC plan under this application Y
the 2 -phase ESC plan under the Road plan WPO will be followed. DAs in particular should match. (Rev.
1) Revised comment (since sediment trap for underground storage system installation has been removed):
There is no apparent provision for ESC during installation of the underground detention system north of
Briarwood Drive. Please provide ESC for this phase of work. [Ref. 7/15/14 WP0201300072 ESC plan
comment #6] (Rev. 2) Comment addressed –see #2, above.
4. With revision of DA contributing to the sediment trap, area and volume design requirements of the trap will
likely increase. (Rev. 1) Comment irrelevant, unless sediment trap restored to limit off -site sediment
transport during underground storage system installation. ( #2, above) (Rev. 2) Comment addressed.
Engineering Review Comments
Page 5 of 5
5. Furnish diversion dikes upslope of silt fence, adjacent to U.S. Rte. 29. (Rev. 1) Comment not addressed;
comment is relevant. ESC between underground storage system installation and U.S. 29 is required. (Rev.
2) Comment addressed —see #2, above.
6. Show SAF on plans. Briarwood Drive is in close proximity to residential properties. (Rev. 1) Comment
partially addressed; furnish SAF as necessary to discourage trespass from neighboring residential areas.
Excavation is required to install the underground detention system. Show ESC features required to install
underground detention system north of Briarwood on WPO201300072, ESC sheets. [Ref. 1. -5., above.]
(Rev. 2) Comment addressed.
7. Identify any off -site borrow or waste sites. (Rev. 1) Uncertain if addressed. Please identify any off -site
borrow or waste sites. (Rev. 2) Comment addressed.
8. (New) Sheet 5 — Typical Filterra Sidewalk Configuration: If geometry of typical detail is to be used, show
sidewalk width (plan view) at each location Filterra units will alter sidewalk width.. Also, please correspond
or speak with Chris Perez since he has explained he has not seen and is not familiar with design intent to
follow or adopt an alternative to uniform sidewalk width. Filterra /sidewalk configuration has planning
implications; it may not meet minimum sidewalk width requirements. (Rev. 2) Comment addressed.
9. (New) Per e -mail (June 26, 2014 10:47 AM), design will be revised to lower weir plate elevation to 407.55'
(sheet 4). SCS routing calculations will reflect increased segment area, modeled as an orifice. [SCS
routing, sheet 3, outlet structure 3: Equiv. DIA = 8.4 "] (Rev. 2) Comment addressed.
File: WPO201400030 -UG storage Briarwood - 080414Rev -2
Review Comments
Project Name: Briarwood Underground Detention Stormwater Management/BMP Plan
Date Completed: IThursday, July 24, 2014
Reviewer: Glenn Brooks
Department /Division /Agency: Engineering
Reviews
failed completeness check
Review Status: QC Denied
John Anderson
From: John Anderson
Sent: Wednesday, July 16, 2014 3:13 PM
To: 'Graham Murray'
Cc: Max Greene; Michelle Roberge; Glenn Brooks
Subject: WP0201400030, WPO201300072, WP0201400059 -Channel Adequacy - MS-19
Graham,
VESCH STD& SPEC 3.19 RIPRAP may be helpful when considering channel adequacy (MS-19) for areas below outfalls
of 18" and 24" pipes beneath U.S. 29. Parcel 32-5C1 is federal property, a high security area (NGIC). We do not seek
federal permission to access (or seek improvements on) this parcel as condition of WPO approval for listed projects.
Please provide adequate channel between outfall of 18" pipe east of U.S. 29 (inlet located south of Briarwood Drive),
listed as cross-section#3 in Channel Adequacy Report (Nov-4, 13, rev.Jun-9-14), and federal property.
The area of analysis between pipe and federal property does not reach all the way to Herring Branch. Herring Branch at
this point is within federal property. Avoid federal property.
Please consider the entire area between outfall of 24" pipe beneath U.S. 29 and Herring Branch. This may require
coordination with Next Generation LLC, an entity with Charlottesville address, listed as owner of parcel 32-5C in County
GIS. This area is listed as cross-section#1 in the Channel Adequacy Report. I appreciate your speaking with me about
this earlier today—please let me know if you have any questions. Thank you, Graham
1
John Anderson
From: John Anderson
Sent: Wednesday, July 16, 2014 3:42 PM
To: 'Graham Murray'
Cc: Glenn Brooks; Michelle Roberge
Subject: RE: Briarwood SWM Comments- Summary of phone conversation
blue text, below—thank you, Graham
From: Graham Murray [mailto:graham(acollins-engineering.com]
Sent: Wednesday, July 16, 2014 3:18 PM
To: John Anderson
Subject: Briarwood SWM Comments- Summary of phone conversation
Good afternoon John,
I wanted to follow up our phone conversation this afternoon with an e-mail summarizing our determinations. If I'm errant in this
account, please let me know.
Thanks again for your assistance with this project and fielding my phone call.
Graham
SWM comments for Road Plan (WPO 201300072)
2. It was determined inlets would be needed along Briarwood Drive near the intersection of route 29. It was also determined these
inlets would need to be connected to the currently proposed pipe/culvert#23 and would outfall into the existing roadside ditch,
presumably because the currently proposed storm sewer and underground detention system in this vicinity is upland of the
intersection and it's not practical to direct the runoff uphill via a gravity storm sewer. DESIGN:STR 24, INV-OUT=404.25';STR 37A,
INV OUT(TO UNDERGROUND DETENTION)=404.90'. It is acceptable to outfall this discharge into the existing roadside ditch
provided existing contours(which, 7-7-14,did not match existing contours on plans)are graded to allow runoff reaching this point
(INV-OUT of new 134.23'-24" DIA pipe beneath Briarwood Dr)to pass west-to-east beneath U.S. 29 via existing 24" pipe(cross-
section 1,Channel Adequacy report).
14. It was determined that adding a note describing this area as a schematic future development not associated with this set of plans
would resolve this comment. It was also determined a future credit of impervious area could be achieved with the approval of this
plan for this area,though separate submissions would be required for construction.Please note, on the phone I stated the future
impervious area accounted for in the SWM design was 29,500sf, however I recalled this incorrectly and the previously submitted
plans under review(WPO 201400030)account for 30,000sf of future development. I believe the UG system will be sized to accept
runoff from an additional 29,500 sf(future development).
SWM comments for Gas Station (WP0201400059)
1&7: It was determined the applicant needs to provide an approved VPDES general permit from DEQ dated prior to July 15`, 2014 to
utilize the pre-July 2014 regulations and that new VSMP applications and fees would not trigger the need to utilize post July f
regulations. With copy of permit,we'll know more—it's my hope to continue to apply technical review criteria that governed prior
to Jul-1.
SWM comments for Underground Detention System(WP0201400030)
4&5: It was determined these comments could be resolved by mandating the contractor install substantial channel armoring via
riprap on the plans. Such proposed riprap armoring would extend from the upstream outlet of the existing 24"CMP and 18"
concrete culverts to the limits of the eastern VDOT right-of-way near the stream. Calculations showing the new riprap lined
channels,which will likely be trapezoidal,will need to be updated for cross sections#1 and#3 and cross sections of the proposed
channels will need to be provided. please ref email, 7/16/2014 3:13 PM,JA to GM—please let me know if you have any questions.
Graham Murray,P.E.
COLLINS ENGINEERING
www.collins-engineering.com
1
200 Garrett Street, Suite K MI/
Charlottesville, VA 22902
Cell: (434) 566-3011
graham @collins-engineering.com
2
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Owner Information
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John E.Anderson,PE I Civil Engineer II
Department of Community Development I County of Albemarle,Virginia
401 McIntire Road I Charlottesville,VA 22902
434.296.5832 ext.3069
3
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�'717G1L31P
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project:
Briarwood Underground Detention
Plan preparer:
Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA
22902, scott@collins- engineering com]
Owner or rep.:
Wendell Wood and Nena Harrell [ulcwww @embargmail.com]
Woodbrier Associates L [P. O. Box 5548, Charlottesville VA 22905]
Plan received date:
11 April 2014
Rev. 1
10 June 2014
Date of comments:
22 May 2014
Rev. 1
16 July 2014
Reviewer:
John Anderson
A. Stormwater Management Plan (WP0201400030)
Revise routing calculations to eliminate outlet structure 3. Change outlet structure 1 type to orifice, or
revise the design so that weir flow is more likely. Please revise SCS routing calculations. Storage pipe
length should be identical in plan section view (sheet 5) and as model input (pipe 2 given as 181'). (Rev. 1)
Comment addressed.
2. Update (or replace) critical slopes (sheet 2) with managed slopes (County GIS -web) so that review can
compare development with steep slope overlay district, and preservation or management requirements.
Steep slopes exist within project LOD. (Rev. 1) Comment addressed.
Drainage areas are confusing. For example, DA #1A is problematic, and does not define an actual drainage
area. This DA does not exist in prior submissions (see pre- development DA, WP0201300072, 11/25/13,
sheet 2; structure 24 DA, SUB201400066, sheet 8 of road plan). Please show drainage divides' upper
boundaries coincident with topographical high points. Topographic lines or labels require attention and
revision at several locations: Post - development DA (sheet 3) should bear close resemblance to post -
development DA, sheet 8, SUB201400066, which shows contours for the same development (portion of
new roadway); eliminate post - development contours associated with roadway from pre - development view
(Master Stormwater Development Plan —sheet 3); DA #lA is called out as 1.02 Ac. in plan view, 0.70 Ac.
in Watershed Summary table (sheet 4); and several other plan view -table mismatches (DA #1 C /post; totals)
(Rev. 1) Comment addressed.
Engineering comment (19 Dec 2013): "Please provide MS -19 with all WPO applications." With this
application, information pertaining to MS -19 and proposed development outlined in Briarwood Channel
Adequacy Report (Nov -4, 2013) has changed. The development areas and drainage areas have changed.
With loss of DA #4, required points of analysis for receiving channels now include outfalls from SWM
facilities to pipes on the west side of U.S. Rte. 29 (existing 24" CMP and 18" RCP associated with MS -19
cross - sections 1 and 3). With elimination of DA #4, 1% analysis continues beneath U.S. Rte. 29 to Herring
Branch. Please include MS -19 for downstream 1% analysis points along Herring Branch. Analysis should
reflect routing calculations which will change given control structure and DA revisions noted in items #1, 3,
Engineering Review Comments
Page 2 of 4
above (or elsewhere). Furnish topographic map that shows project site's (Minus DA #4) 1% relationship to
watershed. (Rev. 1) Comment partially addressed: See ESC comment #1, WPO201400059, 7- 14 -14,
and ESC comment #11, WPO201300072, 7- 15 -14: MS -19: photos indicate erosion down slope of pipe
outfalls beneath U.S. Rte. 29, an indication that receiving channels are inadequate. The computations
should reflect this, and appropriate measures should be specified to correct the problem. The computations
(roughness and velocities) appear to indicate conditions of adequacy that do not exist.
5. When submitting revised MS -19 data or report, please ensure that channel cross - sections of ditches match
existing ditches, that photographs and captions correspond with analysis points. (Rev. 1) Comment
partially addressed. In response to letter request received with revised MS -19 report (rev: 9- Jun -14),
channel cross section locations, Channel Adequacy Exhibit (watershed areas; d. 6/4/14), and photographs
present suitable MS -19 analysis points. Only cross - section locations are provided. Channel geometry is
not included with MS -19 report, but would help when evaluating statement of adequacy for cross sections
#1 and #3 against existing conditions (slope ditches) at outfalls of 24" DIA and 18" DIA storm drain pipes
beneath U.S. 29.
6. Given that post - development DA # 1 C is slightly smaller than pre - development DA #1 C, and with increased
impervious area, the post - development CN value should increase rather than decrease. (Rev. 1) Comment
addressed.
Final build -out (SCS routing, sheet 4) chart references inclusion of 28,OOOsf, post - development chart
references exclusion of 34,OOOsf. Correct discrepancy or clarify. (Rev. 1) Comment addressed; per
discussion/e -mail [June 26, 2014 10:47 AM], anticipate post - development chart will reference 29,500 SF.
8. Water quality: BMP Computations for Worksheets 2 -6 list %RR = 58 %. Provide required treatment for
improvements shown on this plan. The grass swale does not appear sufficient. Water quality treatment
requirements attach to proposed development; requirements that apply to proposed development may not be
met by referencing treatment elements associated with projects which may be delayed, or never built. (Rev.
1) Comment addressed if project eligible for technical review criteria found at 9VAC25- 870- 93/ -99
(technical criteria in effect before Jul- 1 -14). Design provides 4 Filterra units on Road `A' [ref. sheet 5, str.
#28, 30, 36, 38; letter, Filterra to Collins Engineering, June 9, 2014 affirms design adequate for contributing
drainage area]. VDOT restrictions on use of Filterra units within public RW set practical limits on extent of
water quality treatment.
9. Elm Tree Court cul -de -sac is not included in any post - development drainage area. Please include Elm Tree
Court turnaround (increase in impervious area) in hydrologic models, DAs, etc. It appears runoff will reach
the cul -de -sac and release to slopes. Provide treatment for this area. (Rev. 1) Comment addressed;
structure 46, DI.
10. Show 24" CMP and 3' x 3' box culvert continuing beneath U.S. Rte. 29 SBL/NBL; sheet 2 is confusing in
this respect. (Rev. 1) Comment addressed.
11. Do not show the proposed three line SWM underground detention system as pre - development;
W0201300018 approved a two -line system which was never constructed. Pre - development condition is a
sediment basin that serves as SWM control for a portion of Briarwood Drive. (Rev. 1) Comment
addressed.
12. INV in/out for three -66" DIA pipes appear slightly off (0.03'); please check against 0.5% slope and revise
if necessary. (Rev. 1) Comment withdrawn, per Collins' response, but revisions were actually made to
Engineering Review Comments
Page 3 of 4
the underground detention system approved Aug -20, 2013 (WP0201300018; 2 -line system). Current
design proposes a 3 -line underground detention system.
13. Show STM 36A in detail inset (sheet 5); show 24" CMP between STM 36A and 36B as section of pipe to
be removed. Note ( "Contractor shall plug and remove the existing riser & barrel upstream of structure
3613") and arrow are confusing. (Rev. 1) Comment addressed.
14. It is unclear how the proposed 1' tall weir plates located inside each 66" DIA storage pipe will divert 1 x
WQV to the grass swale BMP given that top elev. of the lowest weir is 403.84'while INV IN of the 15"
bypass overflow is 408.5'. Unless water elevation at top of 1'weir plates is > 408.5', it would appear that
water in the storage system will not reach the grass swale via the 15" bypass overflow. Please clarify.
Provide a profile with these elements. (Rev. 1) Comment addressed.
15. ConTechTM manufacturer's approval of the underground detention system design is required. ConTech plan
details are not legible. (Rev. 1) Comment partially addressed; please confirm that Jul -8, 2013 ConTech
letter that affirms adequacy of design applies to 3 -line system under consideration, and not the 2 -line system
approved under WP0201300018. The debris cage detail is faint; please furnish legible detail.
16. Show pipe DIA and L for existing and proposed pipes beneath Briarwood Drive that carry ditch flow south
to north, across Briarwood Drive, near Int with U.S Pt,- 'Q rusting pipe is approx 125 -ft, while
proposed pipe is approx 140 -ft in length. (Rev. 1) Comment addressed.
B. Erosion Control Plan (WP0201400030)
Text, J. Anderson email, 6/2/2014 3:54 PM: "It would be fine to transfer ESC plan for the
underground detention system into the Road Plan WPO since Road Plan WPO already integrates
UG storage construction into a 2 -phase ESC plan. It would be clearer if all aspects of ESC required
to install the UG detention system are located on the Road Plan WPO."
1. Inlets on Briarwood Drive (STM -38, STM -37) outfall to the existing sediment basin that serves as storm
management via a 15" RCP (see sheet 2, 8/6/13/ WP0201300018 plan), but note on Sheet 7 does not
account for this runoff. It annears that the sediment trap should be designed to handle runoff from DA #113
( =2.30 Ac). (Rev. 1) Comment addressed.
2. The sediment trap outfall (stone weir) must continue to the roadside ditch (sheet 6, 8/6/13 plans). Furnish
scale plan/profile drawings of revised sediment trap, not just typical from VESCH, 1992 Edit. Show wet
storage side slopes of 2:1 or flatter. Provide 2:1 (min) length:width ratio for flow path. Proposed trap
dimensions (98'W x 14'L flow path) yield 0.14 ratio for overland flow, but ratio of 7.0 if overland flow is
diverted (dike) to the south end of the sediment trap to join 15" RCP runoff at that point. Diversion dikes.
not SF, must direct runoff to the sediment trap. Trap is centered on an existing drop inlet. Adapt trap
design to preserve inlet function and capacity— suggest plate 3.08 -2, VESCH. (Rev. 1) Comment may
apply if sediment trap restored as ESC measure for underground detention system installation. [see
WP0201300072, Road Plan WPO, ESC plan review comment #6, 7/15/14]
3. The Road plan WPO (WP0201300072) indicates a 2 -phase ESC plan will be followed to make partial
roadway improvements ( Briarwood Drive /Elm Tree Court), and, in phase -II, to construct Road `A' and
Road `B'. Between Phase I and II, the underground SWM facility proposed with this application will be
built under its own ESC plan. Please ensure that ESC considerations tied to drainage areas contributing to
the existing sediment basin at the end of phase I road building are evaluated under this application. This
application bridges ESC Phase I and II of the road plan WPO. Phase I runoff, layout of piping, and
contributing drainage areas should match this application. Please revise ESC plan under this application Y
Engineering Review Comments
Page 4 of 4
the 2 -phase ESC plan under the Road plan WPO will be followed. DAs in particular should match. (Rev.
1) Revised comment (since sediment trap for underground storage system installation has been removed):
There is no apparent provision for ESC during installation of the underground detention system north of
Briarwood Drive. Please provide ESC for this phase of work. [Ref. 7/15/14 WP0201300072 ESC plan
comment #6]
4. With revision of DA contributing to the sediment trap, area and volume design requirements of the trap will
likely increase. (Rev. 1) Comment irrelevant, unless sediment trap restored to limit off -site sediment
transport during underground storage system installation. ( #2, above)
5. Furnish diversion dikes upslope of silt fence, adjacent to U.S. Rte. 29. (Rev. 1) Comment not addressed;
comment is relevant. ESC between underground storage system installation and U.S. 29 is required.
6. Show SAF on plans. Briarwood Drive is in close proximity to residential properties. (Rev. 1) Comment
partially addressed; furnish SAF as necessary to discourage trespass from neighboring residential areas.
Excavation is required to install the underground detention system. Show ESC features required to install
underground detention system north of Briarwood on WP0201300072, ESC sheets. [Ref. 1. -5., above.]
7. Identify any off -site borrow or waste sites. (Rev. 1) Uncertain if addressed. Please identify any off -site
borrow or waste sites.
8. (New) Sheet 5 — Typical Filterra Sidewalk Configuration: If geometry of typical detail is to be used, show
sidewalk width (plan view) at each location Filterra units will alter sidewalk width. Also, please correspond
or speak with Chris Perez since he has explained he has not seen and is not familiar with design intent to
follow or adopt an alternative to uniform sidewalk width. Filterra /sidewalk configuration has planning
implications; it may not meet minimum sidewalk width requirements.
1). (New) Per e -mail (June 26, 2014 10:47 AM), design will be revised to lower weir plate elevation to 407.55'
(sheet 4). SCS routing calculations will reflect increased segment area, modeled as an orifice. [SCS
routing, sheet 3, outlet structure 3: Equiv. DIA = 8.4 "]
File: WP0201400030 -UG storage— Briarwood - 071614Rev -1
John Anderson
From: Graham Murray[graham @collins-engineering.com]
Sent: Wednesday, June 25, 2014 4:47 PM
To: John Anderson
Subject: Briarwood SWM Plans
Attachments: 503857 Contech Review Letter 6-9-2014.pdf; Filterra Plan Review Letter 06-09-14.pdf;
481237 Contech Review Letter 7-8-2013.pdf; Plan Review Letter.pdf
Good afternoon John,
I want to follow up our phone conversation this afternoon with an e-mail correspondence. Please let this document supplement the
previously provided plans currently under review for the County's project files.
1. Attached is Filterra's signed approval letter for the gas station SWM plan
2. Attached is Contech's signed approval letter for the gas station SWM plan
3. Attached is Filterra's signed approval letter showing treatment for the access road in the amendment to the underground
detention system SWM plan
4. Attached is Contech's signed approval letter for the underground detention system SWM plan.This approval is from the
originally approved plans,which is still valid since the system itself has not changed since the originally approved plans in
2013.
5. The applicant would like to point out several items concerning the previously approved bypassed areas of Briarwood Drive
at its connection with Route 29,which is shown currently in the underground detention system SWM plans.
A. Under the originally approved plans created by The Engineering Groupe,the portion of Briarwood Drive between route
29 and Elm Tree Court was approved to be bypassed without permanent water quality treatment and detention.As
such,any approved permanent SWM facility with a SWM maintenance agreement for Briarwood Drive south of Elm
Tree Court would be an enhancement above and beyond minimum requirements already satisfied.
B. When the underground detention system amendment plans were approved in 2013 the plans proposed two
permanent SWM facilities in the form of a water quality swale and an underground detention system to provide
treatment and detention for this section of Briarwood Drive and future development. As such,this plan provided
treatment above and beyond what was originally approved for Briarwood Drive,further making the development at
large compliant with County and State regulations. Please note that the water quality treatment provided in the form
of the water quality swale,which is 15%per VSMH regulations,is roughly equivalent(determined by County
Engineering)to the alleged water quality treatment provided by a temporary sediment basin approved to be removed
that exists onsite currently. Thus these plans continue to provide treatment for what exists currently,and above what
was previously approved.
C. With the amended underground detention system plans currently under review,the same approach was taken and it
continues to provide water quality treatment and detention via permanent SWM facilities under a SWM maintenance
agreement.Similarly,these measures are above and beyond what was originally approved under the plans created by
The Engineering Groupe.These plans capture runoff(for water quality treatment at 15%and detention)within
Briarwood Drive at approximately the same location as the previously approved amendment plans by Collins
Engineering in 2013. In general,the same concept approved in 2013 is proposed in the current plans.
D. Lastly,the applicant would like to express their belief that significant efforts have been made to a reasonable and
feasible point to capture the Briarwood Drive runoff at its intersection with route 29 and feel the minor impervious
areas being released to route 29's roadside ditch are negligible. Furthermore,the applicant wishes to reiterate the
proposed plans capture and treat this area to the fullest extent reasonable.
Thanks,
Graham Murray.P.E.
COLLINS ENGINEERING
www.collins-eng ineering.com
200 Garrett Street, Suite K
Charlottesville,VA 22902
Cell: (434) 566-3011
gra ha mecollins-engineerina.com
1
C v1 _ a Contech Engineered Solutions LLC
� 605 Global Way.Suite 113
�T� Linthicum.MD 21090
ENGINEERED SOLUTIONS Phone 866-740-3318
www ContechES.com
Graham Murray, PE July 8th, 2013
Collins Engineering
200 Garrett Street,Suite K
Charlottesville, VA 22902
RE: Review of CMP Detention Design for Briarwood in Albemarle County,VA.
The purpose of this letter is to document for Albemarle County our review of the plans and the proposed application of
the CMP Detention system at this site as you have requested.
Contech has reviewed underground detention system design for new construction Briarwood. The layout of the tees,
elbows, manhole risers and outlet control weir plate are located in the proper places and can easily be fabricated at a
Contech plant. The configuration of the system inlet and outlet pipes is acceptable. The system appears to be
constructible and is located in order to facilitate maintenance activities. It should be noted that the soil influence zones
of the CMP system and 4'tall retaining wall should not touch.
In summary,the system is expected to operate in accordance with Contech Engineered Solutions'design intent.
Please feel free to contact me if you have any questions or concerns.
Sincerely,
a...-
Aaron M. Lowe I
Design Engineer—Stormwater Products
Contech Engineered Solutions LLC
alowell@conteches.com
Graham Murray filterra
Collins Engineering
200 Garrett St., Suite K
Charlottesville, VA 22902 A Growing Idea in Stonnwater Filtration
June 9, 2014
Plan Review of Filterra®
Briarwood Underground Detention, Charlottesville, VA
Dear Sirs
Thank you for submitting the revised plans on 9 June 2014 for our review of the
Briarwood Underground Detention project.
Filterra® structures F-28 (6x4), F-30 (6x4), F-36 (8x4), and F-38 (8x4) were studied for;
• Planned Filterra® box size
• Filterra® contributing drainage area meeting project's regional sizing specification
• Filterra® invert elevations are higher than effluent invert elevations
• The bypass is lower than the Filterra® elevation(spot elevations)
• The grading pattern encourages cross linear flow and not head-on flow
• The Filterra® outlet drain pipe is sized correctly and exits perpendicular to the wall
• For any conflicting structures such as storm drain pipes below Filterra®
• For most efficient placement of Filterra® units
The plan review concluded that the Filterra® structures listed above is sited and sized
appropriately to treat stormwater to our published specifications.
Operational consistency with these specifications is contingent upon the stormwater unit
being installed correctly and according to the plans, as well as regular maintenance being
performed. Installation Help documents will be forwarded to the Buyer at time of order.
The Filterra® Installation, Operation and Maintenance Manual will be made available
upon request.
Yours sincerely
IL-
Drew Quinn
Engineer Support
Filterra® Bioretention Systems
Manufactured by Americast T: (804)798-6068 ttM E R I CAST
11352 Virginia Precast Road F: (804)798-8400 not just concrete.concrete solutions.
Ashland, VA 23005 E: design @filterra.com www.filterra.com
Contech Engineered Solutions LLC
. 605 Global way.Suite 113
Linthicum.MD 21090
ENGINEERED SOLUTIONS Phone:866.740-3318
www.ContechES.corn
Graham Murray, PE June 9th, 2014
Collins Engineering
200 Garrett Street,Suite K
Charlottesville,VA 22902
RE: Review of CMP Detention Design for Briarwood-Gas Station in Albemarle County,VA.
The purpose of this letter is to document for Albemarle County our review of the plans and the proposed application of
the CMP Detention system at this site as you have requested.
Contech has reviewed underground detention system design for new construction at the Briarwood Gas Station. The
layout of the bulkheads, manhole risers and outlet control weir plate are located in the proper places and can easily be
fabricated at a Contech plant. The configuration of the system inlet and outlet pipes is acceptable. The system appears
to be constructible and is located in order to facilitate maintenance activities.
In summary,the system is expected to operate in accordance with Contech Engineered Solutions'design intent.
Please feel free to contact me if you have any questions or concerns.
iftvg i
Sincerely,
Aaron M. Lowell
Design Engineer—Stormwater Products
Contech Engineered Solutions LLC
alowe(I_ contecheS.com
John Anderson
From: John Anderson
Sent: Thursday, June 26, 2014 11:33 AM
To: 'Graham Murray'
Cc: Glenn Brooks
Subject: RE: Briarwood SWM Plans
This appears reasonable—please ensure that effects of weir ELEV change, CN revision, and 500-sf impervious area
decrease transfer to plans- update SCS routing (ELEV/peak cfs), labels, narrative, and details as necessary(sheets 3,4).
Comment will remain but will note that design alternative to requested change has been submitted (e-mail, below).
All that's left at that point is a check (first sentence,above).
Thank you,Graham
From: Graham Murray [mailto:graham @collins-engineering.com]
Sent:Thursday, June 26, 2014 10:47 AM
To: John Anderson
Subject: RE: Briarwood SWM Plans
John,
I think what you proposed would be a problematic installation and would be more costly. Lowering the weir plate elevation less than
1.5 inches seems like a better solution.
If we do this,it will not alter the peak outflows during the post-development scenario,as witnessed in the attached calculations.
Please note,these calculations are the exact same as the ones previously submitted aside from lowering the weir plate elevation to
407.55'and increasing its equivalent diameter to 8.4".
In the final buildout state it will have a negative impact on the peak post-development outflows though making it exceed the pre-
development rates. However since we're designing the plans for a future development that has yet to be designed we can remedy
this concern by arbitrarily limiting the future impervious area credit to 29,500sf(instead of 30,000sf).This difference of 500sf offsets
the lowering of the weir plate less than 1.5"and causes the final build out composite CN value to change from 801.5 to 81.4. When I
then apply this new CN value of 81.4 to the previously submitted routing calculations,which have now been updated to show the
8.4"equivalent diameter orifice at elevation 407.55' noted above,the final buildout peak flows are again compliant.
So in summary,lowering the weir plate to an elevation of 407.55'and reducing the future credit to 29,500sf will resolve your
comment noted below.
WATERSHED SUMMARY(updated per toweling of weir plate LS".and CN vale tts 81.4
2 year Storm Event
Pre-Development Area Flow Post-Development Area HOW Final Build Out
0,A ill Gt(Pre-Deu) 2,26 ac 1.56 cis 0.A3r1B(Post-D ;) 3:29 at. 1.1', cis t2.A at1B(Final Build
D A #1C(Pre-Dev.) 3..83 at 2.87 cis tD.Adi((Post-Dew) 1.814 at. 2.29 cis t,A#1C fP*st«Dea.)
Total 5.09 4.22 Total= 5.093 3.4a
10 year Storm Event
Pre-Development Area Flow Post-Development Area Flow Final Build Out
D.A#]B(Pre-Des,) 2.2E at 5.21 cis 0,A#1Ei(Post-Der, 3.29 az. a.; CIS 'D A,,al(Final Budd
D.A.#1C(Pre Dev.) 2.83 at 7.44 cis D.A#1C(Post-Dev.) 1.80 ac. 5.78 cfs .D:A#€1C(Post,Dev.)
Total= 5,09 12.65 Totat:- 5.09 10.03
I'm available to discuss this with you if you would like as well.
1
Thanks,
Graham
From: John Anderson [mailto:janderson2 @albemarle.org]
Sent:Thursday, June 26, 2014 10:16 AM
To: Graham Murray
Subject: RE: Briarwood SWM Plans
Graham,
That would alter modeled peak flow,wouldn't it?—I do not want to increase peak flow,or decrease detention time. I
was thinking limited change,without lowering 407.65' (current)elevation—an increase in pipe DIA at the lower end of
the system, a larger pipe DIA just prior to the weir plate (with corresponding increase in weir plate DIA), for example.
Please call if you like-
Thank you-
434.296-5832-x3069
From: Graham Murray [mailto:graham(acollins-engineering.com]
Sent: Thursday, June 26, 2014 10:02 AM
To: John Anderson
Subject: RE: Briarwood SWM Plans
John,
Thank you for your e-mail.So to summarize your e-mail below,you want me revising the weir plate elevation to 407.55'(3" below
top of pipe). Is this correct?
If so, perhaps your comment could read that instead?
Thanks,
Graham
From: John Anderson [mailto:janderson2Ca>albemarle.orq]
Sent: Thursday, June 26, 2014 9:34 AM
To: Graham Murray
Cc: Glenn Brooks
Subject: RE: Briarwood SWM Plans
Graham,
This is very helpful. I appreciate your speaking with me yesterday. I have a better understanding of design
considerations on this project.
There is an item that we did not discuss that you will see as a new comment(WP0201400030).
After reviewing routing for the 3-line UG detention system north of Briarwood,I realize the height above the weir plate
inside the UG system(outlet structure 3, orifice, EMER spillway simulation, 0.183 sf, equiv DIA=5.800") is only 0.15',
or 1.8" The modeled 10-yr storm ELEV=408.563'. This exceeds top of pipe at the weir plate(407.8'),though not the
higher end of the system(408.73').
For openings<3"DIA,there is immediate concern. 10-yr flow control depends on this opening remaining unobstructed.
The parallel 66"DIA lines are sufficient,but given corrugated(not smooth)pipe walls with corrugated pleats that may
further restrict an already narrow opening,please consider design revision in the immediate vicinity of the weir plate. No
dimension should be<3"(0.25'). This is not a request to increase DIA of either 175' line, or the 181' line.
2
Storm debris could obstruct the 1.8"high opening, or cause flooding.
Please ensure that all underground detention system openings are>0.25'.
The modeled hydraulic capacity of system should not decrease.
I would have let you know yesterday had I thought of it.
Thank you, Graham.
From: Graham Murray [mailto:graham@collins-engineering.com]
Sent:Thursday, June 26, 2014 7:13 AM
To: John Anderson
Subject: RE: Briarwood SWM Plans
Good morning John,
Please also letter this e-mail serve as confirmation that everything has been completed to the applicant's best ability to provide
water quality treatment for this portion of Briarwood Drive.
The applicant would also like to point out Filterra inlets cannot be installed along Briarwood Drive because this is a public,State-
maintained road and VDOT does not allow Filterra inlets within their right-of-way.
Thanks,
Graham
From: Graham Murray
Sent: Wednesday, June 25, 2014 4:47 PM
To: John Anderson <janderson2@albemarle.orq> (janderson2 @albemarle.org)
Subject: Briarwood SWM Plans
Good afternoon John,
I want to follow up our phone conversation this afternoon with an e-mail correspondence. Please let this document supplement the
previously provided plans currently under review for the County's project files.
1. Attached is Filterra's signed approval letter for the gas station SWM plan
2. Attached is Contech's signed approval letter for the gas station SWM plan
3. Attached is Filterra's signed approval letter showing treatment for the access road in the amendment to the underground
detention system SWM plan
4. Attached is Contech's signed approval letter for the underground detention system SWM plan.This approval is from the
originally approved plans,which is still valid since the system itself has not changed since the originally approved plans in
2013.
5. The applicant would like to point out several items concerning the previously approved bypassed areas of Briarwood Drive
at its connection with Route 29,which is shown currently in the underground detention system SWM plans.
A. Under the originally approved plans created by The Engineering Groupe,the portion of Briarwood Drive between route
29 and Elm Tree Court was approved to be bypassed without permanent water quality treatment and detention.As
such,any approved permanent SWM facility with a SWM maintenance agreement for Briarwood Drive south of Elm
Tree Court would be an enhancement above and beyond minimum requirements already satisfied.
B. When the underground detention system amendment plans were approved in 2013 the plans proposed two
permanent SWM facilities in the form of a water quality swale and an underground detention system to provide
treatment and detention for this section of Briarwood Drive and future development. As such,this plan provided
treatment above and beyond what was originally approved for Briarwood Drive,further making the development at
large compliant with County and State regulations. Please note that the water quality treatment provided in the form
of the water quality swale,which is 15%per VSMH regulations,is roughly equivalent(determined by County
Engineering)to the alleged water quality treatment provided by a temporary sediment basin approved to be removed
3
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that exists onsite currently. Thus these plans continue to provide treatment for what exists currently,and above what
was previously approved.
C. With the amended underground detention system plans currently under review,the same approach was taken and it
continues to provide water quality treatment and detention via permanent SWM facilities under a SWM maintenance
agreement.Similarly,these measures are above and beyond what was originally approved under the plans created by
The Engineering Groupe.These plans capture runoff(for water quality treatment at 15%and detention)within
Briarwood Drive at approximately the same location as the previously approved amendment plans by Collins
Engineering in 2013. In general,the same concept approved in 2013 is proposed in the current plans.
D. Lastly,the applicant would like to express their belief that significant efforts have been made to a reasonable and
feasible point to capture the Briarwood Drive runoff at its intersection with route 29 and feel the minor impervious
areas being released to route 29's roadside ditch are negligible. Furthermore,the applicant wishes to reiterate the
proposed plans capture and treat this area to the fullest extent reasonable.
Thanks,
Graham Murray,P.E.
COLLINS ENGINEERING
www.collins-engineering.com
200 Garrett Street, Suite K
Charlottesville,VA 22902
Cell: (434) 566-3011
gra ha m(c�collins-enqineerinq.com
4
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: Briarwood Underground Detention
Plan preparer: Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA
22902, scottAcollins- engineering com]
Owner or rep.: Wendell Wood and Nena Harrell [ulcwww @embarqmail.com]
Woodbrier Associates L [P. O. Box 5548, Charlottesville VA 22905]
Plan received date: 11 April 2014
Date of comments: 22 May 2014
Reviewer: John Anderson
A. Stormwater Management Plan (WP0201400030)
1. Revise routing calculations to eliminate outlet structure 3. Change outlet structure 1 type to orifice, or
revise the design so that weir flow is more likely. Please revise SCS routing calculations. Storage pipe
length should be identical in plan section view (sheet 5) and as model input (pipe 2 given as 181').
2. Update (or replace) critical slopes (sheet 2) with managed slopes (County GIS -web) so that review can
compare development with steep slope overlay district, and preservation or management requirements.
Steep slopes exist within project LOD.
Drainage areas are confusing. For example, DA #lA is problematic, and does not define an actual drainage
area. This DA does not exist in prior submissions (see pre - development DA, WP0201300072, 11/25/13,
sheet 2; structure 24 DA, SUB201400066, sheet 8 of road plan). Please show drainage divides' upper
boundaries coincident with topographical high points. Topographic lines or labels require attention and
revision at several locations: Post- development DA (sheet 3) should bear close resemblance to post -
development DA, sheet 8, SUB201400066, which shows contours for the same development (portion of
new roadway); eliminate post - development contours associated with roadway from pre - development view
(Master Stormwater Development Plan —sheet 3); DA #lA is called out as 1.02 Ac. in plan view, 0.70 Ac.
in Watershed Summary table (sheet 4); and several other plan view -table mismatches (DA #1C /post; totals)
Engineering comment (19 Dec 2013): "Please provide MS -19 with all WPO applications." With this
application, information pertaining to MS -19 and proposed development outlined in Briarwood Channel
Adequacy Report (Nov -4, 2013) has changed. The development areas and drainage areas have changed.
With loss of DA 44, required points of analysis for receiving channels now include outfalls from SWM
facilities to pipes on the west side of U.S. Rte. 29 (existing 24" CMP and 18" RCP associated with MS -19
cross - sections 1 and 3). With elimination of DA #4, 1% analysis continues beneath U.S. Rte. 29 to Herring
Branch. Please include MS -19 for downstream 1% analysis points along Herring Branch. Analysis should
reflect routing calculations which will change given control structure and DA revisions noted in items #1, 3,
above (or elsewhere). Furnish topographic map that shows project site's (Minus DA #4) 1% relationship to
watershed.
5. When submitting revised MS -19 data or report, please ensure that channel cross - sections of ditches match
existing ditches, that photographs and captions correspond with analysis points.
Engineering Review Comments
Page 2 of 3
6. Given that post - development DA #1C is slightly smaller than pre - development DA #1C, and with increased
impervious area, the post - development CN value should increase rather than decrease.
7. Final build -out (SCS routing, sheet 4) chart references inclusion of 28,OOOsf; post- development chart
references exclusion of 34,OOOsf. Correct discrepancy or clarify.
8. Water quality: BMP Computations for Worksheets 2 -6 list %RR = 58 %. Provide required treatment for
improvements shown on this plan. The grass swale does not appear sufficient. Water quality treatment
requirements attach to proposed development; requirements that apply to proposed development may not be
met by referencing treatment elements associated with projects which may be delayed, or never built.
9. Elm Tree Court cul -de -sac is not included in any post - development drainage area. Please include Elm Tree
Court turnaround (increase in impervious area) in hydrologic models, DAs, etc. It appears runoff will reach
the cul -de -sac and release to slopes. Provide treatment for this area.
10. Show 24" CMP and 3' x 3' box culvert continuing beneath U.S. Rte. 29 SBL/NBL sheet 2 is confusing in
this respect.
11. Do not show the proposed three line SWM underground detention system as pre - development;
WPO201300018 approved a two -line system which was never constructed. Pre - development condition is a
sediment basin that serves as SWM control for a portion of Briarwood Drive.
12. INV in/out for three -66" DIA pipes appear slightly off (0.03'); please check against 0.5% slope and revise
if necessary.
13. Show STM 36A in detail inset (sheet 5); show 24" CMP between STM 36A and 36B as section of pipe to
be removed. Note ( "Contractor shall plug and remove the existing riser & barrel upstream of structure
3613") and arrow are confusing.
14. It is unclear how the proposed 1' tall weir plates located inside each 66" DIA storage pipe will divert 1 x
WQV to the grass swale BMP given that top elev. of the lowest weir is 403.84'while INV IN of the 15"
bypass overflow is 408.5'. Unless water elevation at top of 1'weir plates is > 408.5', it would appear that
water in the storage system will not reach the grass swale via the 15" bypass overflow. Please clarify.
Provide a profile with these elements.
15. ConTechTM manufacturer's approval of the underground detention system design is required. ConTech plan
details are not legible.
16. Show pipe DIA and L for existing and proposed pipes beneath Briarwood Drive that carry ditch flow south
to north, across Briarwood Drive, near Int with U.S. Rte. 29. Existing pipe is approx 125 -ft, while
proposed pipe is approx 140 -ft in length.
B. Erosion Control Plan (WPO201400030)
1. Inlets on Briarwood Drive (STM -38, STM -37) outfall to the existing sediment basin that serves as storm
management via a 15" RCP (see sheet 2, 8/6/13/ WPO201300018 plan), but note on Sheet 7 does not
account for this runoff. It appears that the sediment trap should be designed to handle runoff from DA #113
( =2.30 Ac).
The sediment trap outfall (stone weir) must continue to the roadside ditch (sheet 6, 8/6/13 plans). Furnish
scale plan/profile drawings of revised sediment trap, not just typical from VESCH, 1992 Edit. Show wet
Engineering Review Comments
Page 3 of 3
storage side slopes of 2:1 or flatter. Provide 2:1 (min) length:width ratio for flow path. Proposed trap
dimensions (98'W X 14'L flow path) yield 0.14 ratio for overland flow, but ratio of 7.0 if overland flow is
diverted (dike) to the south end of the sediment trap to join 15" RCP runoff at that point. Diversion dikes.
not SF, must direct runoff to the sediment trap. Trap is centered on an existing drop inlet. Adapt trap
design to preserve inlet function and capacity— suggest plate 3.08 -2, VESCH.
The Road plan WPO (WPO201300072) indicates a 2 -phase ESC plan will be followed to make partial
roadway improvements ( Briarwood Drive/Elm Tree Court), and, in phase -II, to construct Road `A' and
Road `B'. Between Phase I and 11, the underground SWM facility proposed with this application will be
built under its own ESC plan. Please ensure that ESC considerations tied to drainage areas contributing to
the existing sediment basin at the end of phase I road building are evaluated under this application. This
application bridges ESC Phase I and II of the road plan WPO. Phase I runoff, layout of piping, and
contributing drainage areas should match this application. Please revise ESC plan under this application if
the 2 -phase ESC plan under the Road plan WPO will be followed. DAs in particular should match.
4. With revision of DA contributing to the sediment trap, area and volume design requirements of the trap will
likely increase.
5. Furnish diversion dikes upslope of silt fence, adjacent to U.S. Rte. 29.
6. Show SAF on plans. Briarwood Drive is in close proximity to residential properties.
7. Identify any off -site borrow or waste sites.
File: WPO201400030 -UG storage – Briarwood - 052114