HomeMy WebLinkAboutWPO201900015 Review Comments WPO VSMP 2019-09-26COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902-4596
Phone (434) 296-5832 Fax (434) 972-4126
VSMP Permit Plan Review
Project title:
Timberwood Square — VSMP
Project file number:
WP0201900015
Plan preparer:
Dustin Greene, EIT—Roudabush, Gale & Associates [dareene(abroudabush.com ]
172 S. Pantops Drive, Charlottesville, VA 22911
Owner or rep.:
Highlife Townhomes Inc., 307 West Rio Road [rhauser(a)stonehaus.net]
250 Pantops Mountain Road, Charlottesville, VA 22901
Plan received date:
3 Dec 2018 (submitted as WP0201500032)
(Rev. 1)
26 Feb 2019
(Rev. 2)
25 Apr 2019 (Digital)
(Rev. 3)
12 Aug 2019
(Rev. 4)
25 Sep 2019; 26 Sep 2019 (2 submittals)
Date of comments:
28 Dec 2018 (filed with WP0201500032, until App # assigned)
(Rev. 1)
27 Mar 2019
(Rev. 2)
10 May 2019
(Rev. 3)
23 Aug 2019 — Ref. New Items, p. 7
(Rev. 4)
26 Sep 2019 —Approve pending easement plat recordation
Reviewers:
John Anderson
WP02019-00015 (Also, WP0201500032-, SDP198800003 — Forest Lakes Townhouses Sec. "A")
County Code section 17-410 and Virginia Code §62.1-44.15:34 requires the VSMP authority to act on any
VSMP permit by issuing a project approval or denial. This project is approved pending easement plat
recordation. Engineering will format a Deed of Dedication of easement to accompany plat, and route for
internal review prior to requesting Applicant notarized signature.
General
1. Plan is virtually identical with WP0201500032. Please ref. WP0201500032 for background. (Rev. 1)
Addressed.
2. Albemarle County Code 17-411 indicates WP0201500032 is deemed withdrawn. Please see 17-411.B.
3. A permit fee is required with a new VSMP Application, half at time application is submitted ($1,350).
4. Please submit $1,350 VSMP permit application fee. (Rev. 1) Addressed. Fee was enclosed.
5. Review comments below are intended to expedite approval as Applicant submits fee and revises plan for
eventual VSMP/WPO plan approval.
6. Note: Thirty months have passed since last plan submission. Current review identifies limited areas of plan,
SWPPP, or calculations that require revision, update, or clarification. Albemarle is alert to issue of fairness
yet must ensure procedures important to DEQ and county are followed.
7. 15 Oct 2018 initial site plan Engineering review comments (SDP201800071 *) include this (item 2b.):
2b. Text, email, Engineering to Planning (6/18/2016 2:11 PM -also RMS docs, SDP201500023):
"(SDP201500023) —Engineering has No Objection to FSP design. Engineering comments addressed with
this or prior submittal. FSP Approval requires ROAD Plan Approval, and requires that roads (Lois Lane,
Landon Lane) be built or bonded. ROAD Plan is not approved. FSP Approval requires that WPO be
approved and bonded. Planning coordinator should confirm that SWM Maintenance Agreements have been
Engineering Review Comments
Page 2 of 9
signed, that project has received VPDES Permit coverage letter from DEQ. Please confirm WPO status
with Max Greene, Engineering Div."
* Note: As with WP0201500032, Initial and Final site plans for this project dating to 2015 presented similar design as
the current new initial site plan SDP201800071 (required once 2015 plans expired due to plan inactivity). Planning is
reviewing SDP201800071 as a new project. Engineering must consider the WPO plan with care. In fairness to
Applicant, Engineering limits comments to a minimum. In certain cases, comments request revision, update, or
clarification of items that were reviewed without comment in 2015 and 2016. This is a new VSMP /WPO Application.
Review requirements have not changed appreciably, and blue highlight items above persist as items required for final
site plan approval or WPO plan approval.
Once the $1,350 due with Application is received, a new application number will be assigned. Once a new
WPO# is assigned, please include WPO# in plan title. (Rev. 1) Plan is assigned file # WP0201900015.
Please revise plan title to include WP0201900015 (sheet 1).
Prepare SWPPP similar to SWPPP prepared for WP0201500032, which used Albemarle County template.
Experience with DEQ indicates certain items typical of a SWPPP are relatively more important to the state.
The county template reflects this. Current submittal abandons template in favor of a proprietary format.
SWPPP dated 11/28/18 distributes information in atypical fashion, which may introduce issues for
inspectors, owner, county, and contractor. For quickest approval, revert to county template. If Applicant
opts not to use county template, please ensure SWPPP includes ESC plan sheets (Sec. 4 /template); I I" x
17" SWPPP Exhibit (Sec. 6); that Appendix H (equivalent to template Sec. 9, Certification), is signed; and
that the Pollution Prevention Certification is signed (no template equivalent). (Rev. 1) Partially
addressed. As follow-up: (Rev. 2) Addressed.
a. Revise Sequence ofMaior Activities to reflect ESC Plan review comment request for sequence
revisions —ref. ESC Plan comment, item 3.
b. Name of receiving: List Trib. to Powell Creek. Provide 8- or 12-digit HUC for Powell Crk.
c. Provide SWPPP Exhibit
Provide 11" x 17" Exhibit. Show solid/non-hazardous waste dumpster; sanitary facilities (port -a John);
solvent -paint storage; concrete wash -out; on -site fuel storage. DEQ, during periodic inspections of
active projects, instructs on importance of an Exhibit that shows location of these features. All should
drain to containment. For example, silt fence downstream of port -a John. Concrete wash -out,
dumpster draining to trapping device (lined, in case of concrete wash -out). On -site fuel storage berm
with 10ml liner sized to hold fuel volume + 2 yr. storm event. .PDF samples available. Exhibit is not
intended as a detailed design, but to show containment and locations which may change over time.
Exhibit is a construction aid and resource protection/inspection management tool.
d. Update Construction Plans, Appendix R, once all comments addressed.
10. Provide copy of recorded Stormwater Management Facility Maintenance Agreement that affirms owner of
property to be developed has pre-existing arrangement with Forest Lakes HOA to utilize Arbor Lake for
stormwater management purposes for Timberwood Square. Please furnish bk.-pg. reference to recorded
SWM Facility Maint. Agreement, or enter a Maintenance Agreement with Albemarle County. Ref. 17-415.
(Rev. 1) Not addressed. (Rev. 2) Not addressed. .PDF of document county provided applicant (for ref.)
is a recorded Maintenance Agreement between Forest Lakes and Albemarle, not an Agreement between
Forest Lakes and Applicant. An agreement between Forest Lakes and Applicant is required prior to VSMP
Plan approval. (Rev. 3) Addressed. Discussed 8/22/19. Also, see New items, below, p. 8, item 8.
(=o e:.PDF of Forest Lakes SWM Facility Maintenance Agreement, BK.-PG. 1940-258, 7/25/00, attached for
Applicant reference.)
A. Stormwater Pollution Prevention Plan (SWPPP)
The SWPPP content requirements can be found in County Code section 17-405.
Ref. General item #9, above. (Rev. 2) Partially Addressed. Asfollow-up: Provide signed Registration Statement.
Provide 2 print copies of SWPPP. SWPPP must include rev. 11" x 17" SWM /ESC Plan sheet (County template
Sec. 4, 5) inserts, and SWPPP Exhibit. (Rev. 3) Comment persists. Also, provide 2019 VPDES Permit
Registration Statement. Link:
Engineering Review Comments
Page 3 of 9
http://www.albemarle.org/upload/images/forms center/departments/Community Development/forms/Enizineering and W
PO_Forms/CGP Registration_ Statement _2019_FINAL _201904.pdf (Rev. 4) Addressed. Note: RGA to provide link to
plans. Engineering to update SWPPP with updated VSMP /WPO plan sheets. Ref. email sent 9/26/2019 4:15 PM.
SWM Plan — Also, see New Items, p. 7
The Stormwater Management Plan content requirements can be found in County Code section 17-403.
Provide reference to a County -approved Site or WPO plan # that includes Applied Technology and
Engineering designs shown on sheet 10 to confirm project eligible for 9VAC25-870-48 as a `grandfathered'
project, subject to water quality requirements at 9VAC25-870-96 (not 9VAC25-870-65). (Rev. 1)
Addressed. Ref. SDP198800003 and Albemarle County Water Resources SWF-056 Forest Lakes 4 Ponds
/Wetlands.
Provide SWM Plan narrative (on the plan) comparing county -approved Site or WPO plan full buildout or
anticipated full buildout of areas draining to Arbor Lake with existing buildout in areas draining to Arbor
Lake. Critical point of comparison is existing impervious area as a percentage of area draining to Arbor
Lake, compared with full buildout percentage of impervious area anticipated by Applied Technology and
Engineering design that would eventually drain to Arbor Lake. Provide narrative to support and clarify
Arbor Lake Drainage Area graphic, sheet 10, of plan. Clarify and compare % design imperviousness with
% current watershed imperviousness, pre -development, and % post -developed watershed impervious area.
(Rev. 1) Partially addressed. As follow-up: As supplement to Calculations booklet, please include
additional data (sent as .PDFs with review Memo). Please print /include relevant information; for example
2-14-89 J. W. Greene narrative discussion of dam and routing details. Revise calc. booklet cover index to
list information included in the booklet between pp. 141 and 142. Revise index to identify each document
that relates to SDP 198800003 or Albemarle County Water Resource FILE SWF-056, that supports current
application. (Rev. 2) Not addressed. Revised Calculations booklet not submitted. (Rev. 3) Comment
persists. See New items, below, p. 8, item 5. (Rev. 4) Addressed.
Note: Engineering cannot perform research that may be required by items 1 or 2. (Rev. 1) Engineering
requests Applicant use link to plans at CV/SDP198800003 to print and include all 4-sheets as -is without
revision other than to add labels that identify source as Approved SDP198800003. Also, item 2., above.
(Rev. 2) Not addressed. Contact Paul Bjornsen, Albemarle County, if link is inoperable, or visit with
flash -drive. 19 MB file size exceeds email limit. Please include these 4 sheets as sheets 15. - 18.
Link: http://www.albemarle.org/weblink/search.aspx?dbid=3&searchcommand=%7b%SbCDD-
Planninc%5d:%SbApplicationNumber%5d=%22SDP198800003%22%7d (Rev. 3) Addressed.
Coordinate purchase of a—.34- 2.82 lb. phosphorus nutrient credits with Ana Kilmer prior to purchase. Please
see 6/27/16 Engineering review comments: C. SWM Plan (pg.-2, review comment memo /Attached). (Rev.
2) Comment persists. Applicant may coordinate nutrient credit purchase. Note: Applicant must address
few remaining review comments for VSMP Plan approval. Addressing remaining comments and nutrient
credit purchase are both required for VSMP Plan approval. (Rev. 3) Addressed. _ nutrient credits
purchased 6/10/19 —see CV documents.
Hydraulic Calculations, pg. 2, table, lists SWF Original Design, Qto peak, post-dev —277.4 cfs, inconsistent with
(RGA) Hydraflow Autocad Qto peak, post-dev routing—376.88cfs (pg. 4, Hydrologic /Hydraulic calculations
report). Provide narrative that discusses/clarifies: (Rev. 1) Addressed.
a. Discrepancy in design then vs. design now values. (Applied Technology & Engineering vs. RGA)
b. How /where hydraflow hydrographs indicate stage/discharge elevation=475.73 (Qlo-,; p• 2 of
calculation report) when Stage/Discharge graph (p. 7 of report) shows discharge Elev. =480 @
180.00 cfs. Revise calculations, as needed.
c. Provide Qio hydraflow inputs/outputs that include Arbor Lake basin volume, as well as spillway
data, and that include discharge elevation for Qio-peak that corresponds with RGA reported value,
376.88cfs.
d. Calc. report /(cont.): (Rev. 1) Addressed.
Engineering Review Comments
Page 4 of 9
i. Revise worksheet 5D-5 consistent with sheet 2 proposed/existing impervious values. 5D-
5 lists 1.58 Ac. parking /roadway; sheet 2 lists 1.52 Ac.
ii. Revise worksheet 5D-6 consistent with sheet 2 existing impervious values. 5D-6 lists
0.61 Ac. parking, no roadway; sheet 2 lists 0.77 Ac.
C. Erosion and Sediment Control Plan (ESOP)
Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESOP. This plan
is approved. Please read itemc2�29 (reminder).
Sheet 2
1. Source of topography Note indicates survey by RGA, April 1989, field verified by Dominion Engineering
July, 2014. Engineering ESC Plan review checklist, p. 1, existing conditions plan view information states
`topography should be at least visually field verified by the designer within the last year.' Please field
verify topography and update sheet 2 topo note. (Rev. 1) Addressed.
Sheet 4
2. Along NE boundary of LOD, within LOD, provide and show contoured depressions similar to sediment
traps, if not sediment traps, to capture and redirect diversion dike channelized flow at two locations with
abrupt direction change. Channelized flow may either break through the dike, or invade the site, unless a
depression /stilling basin capture flow, prior to redirecting it. (Rev. 1) Addressed.
3. Revise construction sequence:
a. Item 6; list Ex. Str. 4, 4A, 5, 5A, 6. (Rev. 1) Addressed.
b. Switch items 5 and 6. (Rev. 1) Addressed.
c. Item 4: clarify. What existing 54" storm pipe inlets? (Rev. 1) Addressed.
d. Include phase 2 inlet /storm pipe installation in sequence. (Rev. 1) Partially addressed. As
follow-up:
i. Include Str. ID 6A with other listed phase 2 DI structures.
ii. Shift IP symbols so structure labels readable.
iii. Show IP for Str. 5A, sheet 5.
iv. Sheet 4: Revise plan view text label `Install 24" pipe run 1-1A-2-3-Ex. 4 and provide Min
3' cover during where possible construction' to read: `Install 24" pipe run 1-1A-2-3-Ex. 4
and provide Min 3' cover during construction, where possible.'
v. Include sequence for installation of pipe between Str. lA and 1B.
vi. Structure lA /Splitter requires separate detail, beyond plan/profile provided.
vii. Show 39.89' 12" RCP pipe between Str. IA and 1B in its entirety on sheet 6.
viii. Revise storm profile labels to clearly indicate H, V OUT to Str. 1B. (Sheet 9, X 2)
e. Revise to include installation of ST (shown on sheet 6). (Rev. 1) Addressed.
£ Revise item 9 to clarify county inspector approval is required prior to removal of SB-l. (Rev. 1)
Addressed.
g. If SB-1 installed after step/item 3, show SF downslope of storm pipe (step 3), until SB-1 is
installed. (Rev. 1) Partially addressed. As follow-up, see next item, 31.
h. New: Provide for silt fence to be installed between Lot 25-32 townhouses and temp. sediment trap.
i. New: Revise construction sequence item 13, to read: `Once site is stabilized, install IA to 1B and
with county approval, convert sediment trap to biofilter.'
4. Relocate lavatory, given construction at Ex4A. (Rev. 1) Addressed.
5. Show swale /proposed grading required to route parking lot runoff from Ex3A1 to SB-1 . (Rev. 1)
Addressed.
6. Label rectangular shape to left of soil/stockpile area. (Rev. 1) Addressed. (Shape removed.)
7. Provide caption for ** (symbols), SB-1. (Rev. 1) Addressed.
8. Label SB-1 floor dimensions. (Rev. 1) Addressed.
9. The 2 arrow flow lines north of SB-1 don't work; flow is perpendicular to contours. Revise. (Rev. 1)
Addressed.
10. Recommend remove `provide riprap distilling basin' label and leader line. (Rev. 1) Addressed.
11. Provide riprap outfall L X W X D dimensions /label at toe of 14' emergency spillway. (Rev. 1) Addressed.
Engineering Review Comments
Page 5 of 9
Applicant response: `All flow is going to go through the portion of the existing culvert to remain. There is
3' of freeboard between the design high water and the top of dam for the sediment basin. No emergency
spillway required.'
12. Show /label Arbor Lake waters edge. (Rev. 1) Addressed.
13. Add SFF to legend. (Rev. 1) Addressed.
14. Sheets 5, 6: Remove label reading: `Install 24" pipe run 1-2-3-Ex4 and...' since installed with ESC phase 1.
(Rev. 1) Addressed.
15. Sheet 6: Provide riprap L x W x D dimensions, ST outfall. (Rev. 1) Not addressed. Applicant response:
`Riprap outfall dimensions do not apply to the new design. Comment does not apply.' This is incorrect.
Sediment traps require a stone weir at release point. Ref. VESCH standard detail shown on sheet 6.
16. Sheet 7:
a. Provide buoyancy calculations: 6' x 1.5' SB-1 primary spillway riser base. (Rev. 1) Withdrawn.
Applicant response: `The spillway riser base has a design highwater of 477.1 with a riser structure
at 476.5. There is insufficient depth above this structure to worry about this structure floating.
You withdrew this comment at a meeting with Bob Hauser and Frank Pohl.'
b. Revise SB-1 Calculations:
i. Preliminary design, 11: provide Q25 routing to support design high water=479.55'. (Rev.
1) Partially addressed. Applicant response: `The design high water has been updated
with this design. No routing is required for this number. Plate 3.14-8 provides the head,
in feet above the riser structure of a 48" riser that a 25-yr storm will have. Since the basin
will have no emergency spillway the 48" riser must pass the 25-yr storm through the
principal spillway. 17.9 cfs gives a head of 0.6' resulting in the Design High Water to be
477. L' As follow-up: Provide Q25 calculation (Albemarle calculates 23.72 cfs (ciA: 0.6 x
6.84* x 5.78 Ac.). If Q25-peak increases, revise design as needed.
(* NOAA Atlas 14, Charlottesville /25-yr event)
ii. Revise distance from dewatering orifice to C/O level; should be 1.0. (Rev. 1) Addressed.
iii. Required principal spillway capacity appears to be 9.2 cfs (ref. Runoff), but is listed as
5.7 cfs at item 15 (principal spillway design). Revise design to ensure the principal
spillway passes the peak rate of runoff from the basin drainage area for a 2-yr storm event
(ref. VESCH). (Rev. 1) Partially addressed. As follow-up: comment ref. to 2-yr event
is irrelevant. Please see 16.b.i., above. Check Q25-peak, revise design as needed.
iv. Using Q peak2-yr =9.7cfs and VESCH, it appears (item 17) riser diameter should be 21".
Confirm 24" DIA is the smallest diameter required to pass Q peak2-,,. (Rev. 1) Partially
addressed. See item 16.b.i., and 16.b.iii., above. Revise as needed.
v. Item 23 /Anti -seep collar design:
1. Slope upstream face of dam is 2: 1; please revise. (Rev. 1) Addressed.
2. Slope of barrel-1.16%; please revise. (Rev. 1) Addressed.
3. Length barrel in Sat. zone (Ls) appears to be 18.9. Please verify Ls. (Rev. 1)
Addressed.
4. Provide anti -seep collars; provide ct. /dimensions (2 @ 2.5' x 2.5', for example).
(Rev. 1) Partially Addressed. As follow-up, please:
a. Revise sheet 7, SB-1 schematic to show 2.75' x 2.75' collars.
b. SB-1 detail: show anti -seep collars encircling pipe.
c. Include VESCH Plate 3.14-13 on plans.
d. Plate 3.14-2 shows minimum 1.0 vertical offset between riser crest and
design high water elevation; please revise to ensure 1.0' min. offset.
5. Show anti -seep collars in SB-1 profile schematic. (Rev. 1) Addressed.
c. Recommend show storm pipe, 1-2-3-Ex4 in SB-1 profile schematic. (Rev. 1) Withdrawn.
Applicant response: `The E&SC' elevation has been shown on the profile on sheet 8. The storm
pipe section is not connected in any way to the sediment basin...' Review of proposed SB-1
grades indicate at least 3' cover over storm pipes 1-2-3-Ex. 4.
17. Include VESCH Plate 3.14-10, Anti -vortex device design detail on plans. (Rev. 1) Addressed.
New:
18. As discussed 3/27, please make slight text changes, Sheet 8 /Stormwater Management Narrative:
Engineering Review Comments
Page 6 of 9
a. Revise 2" Table headings to include Asterix (*) .
b. Beneath table, include'* = SDP201100042 (Approved 11/4/11).'
c. Beneath table, revise Q2POST, Q10POST descriptors to read Q2 proposed /Q10 proposed.
d. Revise `Proposed plan with no biofilter' (33.25 /52.00cfs descriptor) to read: `Proposed post -
developed site + offsite, with no biofilter **'
e. Beneath this: I =Values include off -site runoff (beneath site) to Arbor Lake, via Ex. 54" pipe.'
f Revise `Proposed plan with biofilter' (27.74 /43.18cfs descriptor) to read: `Proposed post -
developed site + offsite, with biofilter.'
19. Include 4-sheets relating to SDP198800003 (Approved with conditions 2/23/88). Revise sheet 1 index to
ref. SDP198800003 plan or design information.
20. Provide turbidity curtain detail.
21. Provide L X W dimensions for eastern section of ST, sheet 6 (unconventional ST design). (Rev. 2)
Withdrawn.
22. Show SB-1 baffles, sheet 5. (phase 2, ESC plan)
23. Sheet 6: Label structures E7 and E2.
24. Sheet 6: Provide proposed ST profile since design does not match VESCH Std. (incl. contours 480'-475',
and riser, with note re. additional height added to SB-1 riser.). (Rev. 2) Withdrawn.
25. Sheet 8:
a. SB-1 Schematic:
i. Label elevation of bottom of biofilter media.
ii. Label Str. 15 (profile view)
b. Label Str. 15 (plan view)
c. Ditch 1 leads from Str. I to biofilter (upstream is splitter structure, A). Provide private drainage
easement for ditch 1 and 2.
d. Record SWM Facility /Access easement. (Engineering will format deed once SWM Facility
/Maintenance Agreement for biofilter is recorded.) (Rev. 2) Comment persists. (Rev. 3)
Recordation pending; Maintenance Agreement is or will soon be recorded by Albemarle County.
(Rev. 4) Addressed. Maintenance Agreement recorded at deed bk.-PR. 5215-175.
e. Remove portion of cantilever deck (Lot 32) super -adjacent to Ditch 1 drainage easement.
f. Label floor dimensions of biofilter.
Sheet 9:
26. Provide profile: Str. 15 Arbor Lake
27. Profile /Str. IA-1B: Add parenthetical (To 113) to `INV OUT — 480.75' label.
28. Profile /Str. 1 -Ex. 4: Add parenthetical (To 113) to `INV OUT = 480.75' label.
29. Specify watertight system design for Str. I to 1B; include sealed connections; include specifications,
material notes, labels, etc. (Rev. 2) Comment persists. Applicant response: `Watertight system design is
an industry standard and will be reviewed in the pipe video as -built design process.' County advises there is
risk with this approach. As -built information must include reports and materials of construction data that
substantiate that the system is watertight. (Rev. 3 /4) Comment persists.
Sheet 1:
30. Revise WP0201500032 Note to read: This VSMP Plan is virtually identical with the WP0201500032 plan
that was withdrawn due to inactivity. The WP0201500032 was near approval.
31. Add Nutrient Credit Purchase Note to read: `Plan proposes 2.82 lb. of nutrient /phosphorus credits.'
32. Add Prior Plan Reference Note to read: See also WP0201500032, SDP201800087, SDP201100042,
SDP198800003, and Albemarle County Water Resource File SWF-056 Forest Lakes.
33. Revise plan title to include WP0201900015.
Other:
34. Include Construction Record Drawing (As -built) for VSMP policy on the plans. Link:
httD://www.albemarle.ore/uDload/imaees/forms center/departments/Community Development/forms/Eneineerine and
_WPO Forms/WPO_VSMP_ Construction_ Record_ Drawings Policy 23MU2014.pdf
35. Include VA DEQ Stormwater Design Specification No. 9 Installation and Maintenance information on the
plans (http://www.swbLnp.vwrrc.vt.edu/wp-content/uploads/2017/11BMP-Spec-No-9_BIORETENTION_vl-
9 03012011.pdf)
Engineering Review Comments
Page 7 of 9
a. Ref. Sec. 8.2, Bioretention Installation, steps 1.42., verbatim.
b. Ref. Sec. 9: Review, then include notes that outline:
i. First year maintenance operation.
ii. Routine and non -routine maintenance.
36. Include periodic Maintenance Inspection checklist on the plans (.PDF Attached).
New items (8/23/19):
As follow-up to meeting 22-Aug, in response to county email sent 8/20/2019 4:37 PM, and in response to
Forest Lakes Community Association (FLCA) email sent 8/20/2019 6:36 AM, please:
Provide rational method routings based on As -built Arbor Lake structure conditions. Details and summary,
follow:
a. Using 1988 design values (190 Ac.; composite c-value =0.4) and 2019 RGA Timberwood Square
design values (164.8 ac.; composite c-value equivalent to TR-55 CN=71.9). During meeting 22-
Aug, RGA referenced 2019 design rational method c-value of 0.45. Please provide and support
2019 post -developed c-value via table with acreage -land cover breakdown (provide composite c-
value calculation). We appreciate RGA sensitivity to county concerns, including As -built
conditions, plan approval, and Arbor Lake water surface level (WSL). Again, please provide
(weighted) composite c-value for 164.8 Ac. watershed. (Rev. 4) Addressed.
Note: Timberwood Square site as it existed in 1988 (an undeveloped site) is assumed reflected in
Applied Technology and Engineering Inc. (APTE) calculations (hand-written calcs./grid sheet),
included with Calc. report; c-value =0.4.
a. 2019: (Rev. 4) i., Withdrawn; ii, Addressed.
i. Route pre -development existing land cover (current land cover; 164.8 Ac. watershed)
prior to Timberwood Square development. (1.16 Ac. impervious — Timberwood Square
site).
ii. Route post -development land cover (164.8 Ac.) after Timberwood Square is constructed.
(2.84 Ac. impervious — Timberwood Square site).
From Calc. Report, VSMH, Appendix 5D Worksheets:
• Post -developed impervious area (Ac.) proposed with WPO1201500032 (initial site plan
design approved, with conceptual and detailed SWM design, nearly approved in 2016):
2.4447 Acres.
• Post -developed impervious area (Ac.) proposed with WPO201900015, near point of
approval, with specific comments to be addressed prior to plan approval: 2.84 Acres.
[0.3953 Ac. increase ]
• Pre -developed existing impervious area (Ac.) proposed with both WPO1201500032 and
WPO201900015: 1.16 Acres.
Existing watershed land use /ground cover (prior to Timberwood Square) is presented in table in
Calc. report; 3rd pg. from end. 2019 post -developed values are assumed to increase impervious
area value by 1.68 Ac. Overall post -developed % impervious (Calc. report table) is anticipated to
increase from 50.46 pre -developed (2019 /pre) to 51.5% (2019 /post). This is anticipated to have
negligible effect on peak flows /routings. (Rev. 4) Withdrawn. The critical comparison is 1988
APTE approved design /design parameters (Qpea, WSE) with 2019 post -developed condition.
Rational method routings included in Hydrologic and Hydrologic report d. 9/25/19, table, p. 4
indicate 2019 post -developed WSE (10- 100-yr storm events) < 1988 APTE approved design
/design parameters. Reff, report, p. 4.
b. Summary of Requested Routings (Additional):
i. 1988 post -developed, using APTE rational method values (c-value =0.4, 190 Ac.) (Rev.
4) Addressed.
ii. 2019, pre -development, 164.8 Ac. C-value to be determined by RGA, equivalent to TR-
55 curve number CN =71.9. Anticipate c-value at or slightly less than 0.45. Provide
weighted c-value calculation. (Rev. 4) Withdrawn.
Engineering Review Comments
Page 8 of 9
iii. 2019, post -development, 164.8 Ac. C-value to be determined by RGA, equivalent to
curve number CN=71.9(f). Anticipate c-value at or near 0.45. Provide weighted c-value
calculation. An increase of either 0.3953 Ac. (WPO201500032 to WPO201900015
increased impervious area) or 1.68 Ac. impervious area (2019, pre- /post) should not
appreciably affect c-values, peak flows, or routings. Pre- /post- 2019 rational method
routings for 164.8 Ac. watershed are anticipated to be nearly indistinguishable. Separate
routings may make the point. Please include summary results on the WPO plan.
Routings may help illustrate negligible effect of 1.68 Ac. additional impervious area when
routed with 164.8 Ac. watershed (peak flows: 2-, 10-, 100-yr). (Rev. 4) Addressed.
c. Following discussion on 22- Aug, Albemarle anticipates As -built surveyed information for Arbor
Lake primary spillway, embankment, etc., including WSL and data that confirms 1988 pipe /riser
design type, length, slope, diameter, invert elev. etc. were installed, per design. Regardless,
rational method routings will be based on As -built conditions, including 1988 routings. All
routings will be evaluated against field surveyed WSL, such that plans will state unequivocally that
2019 post -developed design (Timberwood Square) will not increase 2-, 10- or 100-yr Arbor Lake
WSL. Albemarle anticipates no rise in Arbor Lake WSL given hydrologic characteristics,
including time of concentration, distance to far west reaches of watershed, and discussion on 22-
Aug. Runoff from proposed 1.68 Ac. new impervious area immediately adjacent to Arbor Lake
will likely concentrate in a brief period, with effects that precede delayed effect (longer transport
time) of runoff from more distant reaches of the 164.8 Ac. watershed. This hydrologic effect
should manifest in virtually identical design event peak runoff values, Q2, Q1o, and Qioo, both with
and without 1.68 Ac. Timberwood Square development impervious area. (Rev. 4) Addressed.
Note: Routings include 2.84 Ac. development impervious area (1.68 Ac. increase above existing
site pre -development impervious area.).
2. Provide As -built information for Arbor Lake, as discussed, needed to perform routings and to confirm that
As -built condition reflects 1988 design parameters in relevant respects. (Rev. 4) Addressed. Applicant
response (9/23/19): `Sealed as -built information has been provided on sheet 14 of the VSMP plan.'
3. After meeting, I visited Water Resources, hoping to recover 1988 post -developed JWG rational method
routing (input, output), but the entire file repository of Water Resource is off -site in NOVA to be scanned.
Anticipate files will be returned in early September. No Water Resource print files (including 1988 Arbor
Lake design /routings) are available. Once available, files will be available in digital format.
4. Try to simplify routings to eliminate including secondary riser between Timberwood Parkway, and
embankment near edge of lake (ref. sheet 14). Meaning and intent of narrative, pg. 3, 3rd paragraph, Calc.
Report, is unclear. Statement `our routing program does not allow us to use more than one riser per pond so
we used...' should be avoided, if possible. (Rev. 4) Addressed. Applicant response: `The secondary riser
was not taken into account with this review since the water never reaches the secondary riser structure.'
5. Revise Hydrologic /Hydraulic Calculations Report, as discussed (revised routings, revised tables, etc.).
Please ensure final copies of Calc. Report are identical. (Rev. 4) Addressed.
6. Engineering considered but is unable to undertake review of Forest Lakes files within a reasonable period of
time, soon enough to help with current review (WPO201900015). Please find list of CV projects with SDP
—'Forest Lakes' descriptors. image, .
7. Since Albemarle is reasonably certain RGA will not resubmit without current surveyed As -built elevations,
any as -built file information may recede in importance as new 2019 As -built data will confirm design
parameters. A thorough file review may in the end yield no As -built information for Arbor Lake.
Engineering is unaware of any As -built information for Arbor Lake.
8. County position relative to Forest Lakes Community Association duty to maintain Arbor Lake as a SWM
facility is outlined in email sent 8/15/2019 4:17 PM (J. Anderson to Derek Duval, President, FLCA), and in
Stormwater Management Facilities BMP Maintenance Agreement recorded at bk.-pg. 1940-258 (plat of
parcel /Arbor Lake recorded at bk.-pg. 1304-346).
9. Please review comments and notify Engineering of any mistake or misunderstanding, or if you have any
questions.
Engineering Review Comments
Page 9 of 9
Engineering is grateful for RGA design effort, developer patience. Four print copies of VSMP /WP0201900015
delivered 9/26/19 for stamped approval.
Process
After approval, plans will need to be bonded. The bonding process is begun by submitting a bond estimate request
form and fee to the Department of Community Development. One of the plan reviewers will prepare estimates and
check parcel and easement information based on the approved plans. The County's Management Analyst will
prepare bond agreement forms, which will need to be completed by the owner and submitted along with cash,
certificates or sureties for the amounts specified. The agreements will need to be approved and signed by the County
Attorney and County Engineer. This may take 2-4 weeks to obtain all the correct signatures and forms.
Stormwater Management Facilities Maintenance agreements will also need to be completed and recorded. The
County's Management Analyst or other staff will prepare the forms and check for ownership and signature
information. The completed forms will need to be submitted along with court recording fees.
After bonding and agreements are complete, county staff will need to enter project information in a DEQ database
for state application processing. DEQ will review the application information based on local VSMP authority
approval. At this time, the DEQ portion of the application fees will need to be paid directly to the state. For fastest
processing, this is done electronically with the emails provided on the application. DEQ should notify applicants
with instructions on how to pay fees. When DEQ approves the application, they will issue a permit coverage letter.
This should be copied to the county.
After DEQ coverage is issued, via the coverage letter, the County can hold a pre -construction conference. Applicants
will need to complete the request for a pre -construction conference form, and pay the remainder of the application
fee. The form identifies the contractor and responsible land disturber, and the fee remaining to be paid. This will be
checked by county staff, and upon approval, a pre -construction conference will be scheduled with the County
inspector. At the pre -construction conference, should everything proceed satisfactorily, a joint VSMP and grading
permit will be issued by the County so that work may begin.
County forms can be found on the county website forms center under engineering;
htt D : //www. albemarle. ore/dei)tforms. asp? department=cdenavmo
Thank you
J. Anderson 434.296-5832 —x3069
WP0201900015 Timberwood Square 092619rev4 -see also WP0201500032.doc