HomeMy WebLinkAboutWPO201500057 Review Comments WPO VSMP 2015-09-28�pF A
COUNTY 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:
Avinity Estates
Project Number:
WP0201500057
Plat preparer:
Scott Collins; Collins Engineering [200 Garrett St., Suite K,
Charlottesville, VA 22902, scott&collins -en ing eerin'g com]
Owner or rep.:
Avon Properties LLC, P. O. Box 1467, Charlottesville, VA 22902
Plan received date:
19 Aug 20145
Date of comments:
28 Sept 2015
Reviewer:
John Anderson
A. Stormwater Pollution Prevention Plan (SWPPP)
The SWPPP content requirements can be found in County Code section 17 -405. A SWPPP must contain (1)
a PPP, (2) an ESCP, (3) a SWMP, and (4) any TMDL measures necessary.
1. Sec. 6 Name an individual responsible for pollution prevention practices.
2. Sec. 6 — Revise Exhibit LOD: 12.20 and 13.60 Ac. both listed. 12.20 Ac. listed on VPDES registration.
3. Sec. 6 —Given discussion at unrelated project meeting (24 -Sep; CCS /pre -con), please include /propose list of
chemical contaminants /products to include with Sec. 6. DEQ places emphasis on a comprehensive list of
on -site pollutants with potential to enter or impact waterways.
4. Sec. 9 —Sign certification.
5. Sec. 12 —Use increased inspection frequency. Delete (inspection log) standard inspection frequency,
consistent with Sec. 7 TMDL, Moore's Creek/impaired waterway.
B. VSMP: SWPPP: Stormwater Management Plan (WP0201500057)
VSMP Regulation 9VAC25- 870 -108 requires the VSMP authority to approve or disapprove a SWMP. This plan is
disapproved for reasons provided in comments below. The stormwater management plan content requirements can be
found in County Code section 17 -403.
1. Accept/respond to any VDOT plan review comments.
2. Title p. — Delete SWM general note reference to upland rain gardens. Reference dry swales.
3. Calculations packet
a. In numerous tables, yellow text is unreadable. Reserve right to comment once text readable.
b. "Dry Treatment Swale" `A' — Please consider totality of VA DEQ Stormwater Design No. 10.
Proposed facility `A' is neither a (linear) dry swale, nor a bioretention basin. It is most nearly an
extended detention facility —item briefly discussed with S. Collins, 24- Sept. Revise
design/calculations. Also —see SWM items # 6/7, below.
c. Revise Energy balance calculation to reflect revised Facility `A' design.
d. Please email VaRRM .xls to reviewer.
4. Sheet 3 — Delete Note 6, a design note. Provide design. Also —see SWM item # 8, below.
Engineering Review Comments
Page 2 of 4
5. Sheet 5 — Revise proposed dry treatment swale `A'. It does not meet VDEQ BMP Clearinghouse design
specification. See related comments, items #3.b, above; 6, 7, below.
Sheet 6
6. Swale `A' does not match BMP design specification: shape (linear; parabolic or trapezoidal cross - section);
ponding time /depth = 6 -hr /12 "/1\4ax. Revise design. 55' wide, non - linear design most nearly resembles an
extended detention basin. Attached VaRRM (.xls) illustrates hypothetical design that nearly matches
phosphorus load reduction of proposed swale `A'. It appears feasible using one possible combination
(bioretention with separate extended detention) to nearly replicate proposed design P -load reduction.
Sizing forStrmwater Quantity
In order to accommodate a greater stormwater quantity credit for channel protection or flood
control, designers may be able to create additional surface storage by expanding the surface
ponding behind the check dams by either increasing the number of check dams, or by expanding
the swale width at selected areas. However, the expanded surface storage footprint is limited to
the pending area directly behind the check dams and is also limited to twice the channel bottom
width. Care must be taken to ensure that (1) the check dams are properly entrenched into the side
slopes of the Swale, and (2) adequate overflow capacity is provided over the weir.
Shape. A parabolic shape is preferred for dry swales for aesthetic, maintenance and hydraulic
reasons. However, the design may be simplified with a trapezoidal crass - section as long as the
soil filter bed boundaries lay in the flat bottom areas.
Side Slopes: The side slopes of dry swales should be no steeper than 3H:1 V for maintenance
considerations (i.e., mowing). Flatter slopes are encouraged where adequate space is available, to
enhance pre - treatment of sheet flows entering the Swale. Swales should have a bottom width of
from 4 to 8 feet to ensure that an adequate surface area exists along the bottom of the swale for
Filtering- If a swale will be wider than 8 feet, the designer should incorporate berms, check dams,
level spreaders or multi -level cross - sections to prevent braiding and erosion of the swale bottom.
Ponding Depth. Drop structures or check dams can be used to create ponding cells along the
length of the swale. The maximum ponding depth in a swale should not exceed 12 inches at the
most downstream point.
Version 1.9, Mardi 1, 2011 Page 13 of 21
7. Review of Facility `A' suspended when reached p. 13 of Clearinghouse Spec. No. 10: Max. ponded depth.
Proposed Qio depth = 4.697'.
8. Show Facility `A' retaining walls in profile. Show geogrid length if geogrid provided. Provide design for
inundated conditions to the 100 -year storm elevation. If the lowest retaining wall is compromised, entire
south slope of facility is jeopardized. 2 -, 10 -, 100 -yr events inundate lower portion of lowest retaining wall,
Elev. =492'. Furnish design capable of withstanding inundation. Provide specifications, details, notes, etc.
9. Swales 2, 3 — provide parabolic or trapezoidal cross - sections /label dimensions. Show media. Label depth
of media. Show underdrains. Provide infiltration rate testing (6.2, p. 12 /Spec. 10). Label L x W /plan
view.
Sheet 7
10. Swale 1 — Provide items listed in item #9 above.
11. Provide dimensions sufficient to construct the atypical geometry of SWM Facility #B. Provide more than
L, W. Dimension max length, insets, pinch points, etc.
12. Revise bioretention basin `B'. Max. ponded depth =12 in. Ref. recent CE bioretention facility designs.
(CMA, Glenmore K2C, CCS).
13. Level 2 bioretention basin `B' & Level 1 Filter Strip design detail: provide cross - section of ELS.
Engineering Review Comments
Page 3 of 4
14. Level 1 Filter Strip detail: Spec. No. 2 Table 2.2 provides options. Select and apply one of the options.
Labeling is confusing: it appears as if all three slope /length options apply, appears that total L =150'. At
most, 6% to 8% slope requires L =65'. State that first 10' @ 2% slope (or <) is a minimum requirement,
not an option.
15. Level 1 Filter Strip detail: Provide cross - section of filter strip.
16. Level 1 Filter Strip detail: Provide retaining wall (RW) length. Provide geotechnical RW details.
17. Dimension wall length.
18. Floor elevation of SWM bioretention basin `B' must be at least 1' below floor elevation of SB -2.
19. Provide SWM Notes: Clearinghouse construction/inspection /maintenance specifications, all BMPs.
C. VSMP: SWPPP: Erosion Control Plan (WPO201500057)
Virginia Code §62.1- 44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This plan is disapproved
for reasons provided in comments below. The erosion control plan content requirements can be found in County Code
section 17 -402.
1. Sheet 8 - Provide paved CE detail.
2. Sheet 9 - Reconcile LOD =12.2 and 13.6 Ac.
3. Sheet 9 - Remove Filter strip /ELS: do not show with ESC Plans
4. Sheet 10 - Provide additional existing off -site contour elevation labels west and south of development.
5. Sheet 10 - Provide additional proposed contour labels.
6. Sheet 9/10 - Filter strip: Add note "Prevent soil compaction by heavy equipment." [Spec. No. 2, Table 2.2.]
Sheet 11
7. SB -1 /plan: Label floor dimensions (58' X 120').
8. SB -1 /plan: Adequate space does not exist for 52 L exit channel. Revise design.
9. SB -2 /plan: Adequate space does not exist for 70 L exit channel. Revise design.
10. SB -2 /plan: Label floor dimensions (43' X 115') - provide full complement of dimensions required to
construct. Also, SWM item # 11.
11. SB -2 /plan: Remove Filter strip/ELS: do not show with ESC Plans. Add note: "Prevent soil compaction by
heavy equipment." [Spec. No. 2, Table 2.2.]
12. SB -1/2 Design Tables, or profiles: Address riser anchoring per VESCH spec. 3.14, p. III -107.
13. SB -1/2 Design Tables, or profiles: Specify riser embedment in concrete base.
14. SB -1 Design table: Revise depth of water at spillway crest. (= 3.70')
15. SB -1 Design table v. plan view emergency spillway bottom widths are inconsistent (41'v. 35'). Revise.
16. SB -2 Design table: Revise emergency spillway slope of existing channel. 3% should likely read 33 %.
17. SB -2 /profile: Bottom of basin must be at least 1' higher than floor of proposed SWM bioretention facility.
18. SB -2 /profile: Delete extraneous rock weir label.
Engineering plan review staff are available from 2 -4 PM on Thursdays, should you require a meeting to discuss this
review. Plan review staff are also available at 434 - 296 -5832 (- x3069) should you have questions.
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
Engineering Review Comments
Page 4 of 4
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 request a pre - construction conference by completing a 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;
htW : / /www.albemarle.org/deptforms .asp ?department--cdengnoo
Thank you - 434.296 -5832 —0069
File: WPO201500057 Avinity Estates VSMP- 092815