HomeMy WebLinkAboutWPO201800045 Review Comments WPO VSMP 2018-07-13COUNTY 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: Minor Hill Biretention Retrofit
Project file number: WP0201800045
Plan preparer: Kip Mumaw, Ecosystems Services [Kip@ecosystemservices.us]
Owner or rep.: Albemarle County / FES-Environmental Services Division
[scalos(&albemarle.org; wharris(a)albemarle.org]
Plan received date: 14 June 2018
Date of comments: 13 July 2018
Reviewers: John Anderson
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 denied. The rationale is given in the
comments below. The application may be resubmitted for approval if all of the items below are
satisfactorily addressed. The VSMP application content requirements can be found in County Code section
17-401.
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. Provide Project number [WP0201800045] on the SWPP document cover, and Title sheet of plans.
2. Use Albemarle County SWPPP template (see email sent July 11, 2018 2:40 PM; EcoSystem response:
7/12/2018 8:07 AM).
Link, county template:
httD://www.albemarle.ore/ui)load/imaees/forms center/departments/Community Development/forms/Enein
eerina and WPO Forms/Stormwater Pollution Prevention Plan SWPPP temDlate.Ddf
3. Provide Sec. 6 SWPPP Exhibit.
4. Include Ecosystem Name, Address, Telephone, principal contact on SWPPP cover. (Authorship)
SWM Plan
The Stormwater Management Plan requirements can be found in County Code section 17-403.
1. Water quality: This project proposes replacement of a nearly 40 year -old poor -performing SWM facility
(detention pond designed for detention, only) with clogged and broken outlet structure and pipe with a
Level 1 bioretention filter (VA DEQ Stormwater Design Specification No. 9) that provides 25%
phosphorus removal. By contrast, an extended detention pond (nearest VRRM.xIs equivalent to 40 year -old
facility) provides 15% phosphorus removal. Once design comments are addressed, the SWM Plan can be
approved.
2. Water quantity: Ref. B. Aubrey Huffman & Associates, Ltd., letter dated 10/2/79 that references initial
(pond) design maximum theoretical discharge of 11.3 cfs. EcoSystem Service in cover letter dated 6/11/18
presents (table value) proposed peak Qio-yeas outflow of 11.03cfs, which is slightly less than initial design.
No impervious area is added. No ground cover is converted. Runoff characteristics of upslope watersheds
are not altered. Energy balance calculation is waived by reviewer as this project provides channel and flood
protection benefits by retrofitting a decades -old facility with a newly constructed properly designed
stormwater management facility, and the Energy Balance equation is an inappropriate analytic measure for
evaluating the proposed bioretention filter. Once design comments are addressed, the SWM Plan can be
Engineering Review Comments
Page 2 of 4
approved.
3. General Note 13, plan sheet 9, states: "The construction of this project will not result in the development of
any new impervious surfaces. This project is a stormwater retrofit that treats a previously developed area,
and improves the water quality through construction of a bioretention area." This project would be exempt
from the VSMP if its only purpose were routine project maintenance (17-303.G). As it is, the project
delivers quality benefits that exceed original design.
4. Water Quantity:
a. Provide routings that support 6/11/18 letter proposed post -development peak outflow (Q2, Q10).
b. Ensure Q2 outlet velocity at Ex. 15" CPP outfall is <15fps. Calculate and report outfall velocity.
c. Provide B/M channel protection at Ex. 15" CPP, as needed, once Vel2-n calculated.
d. Provide riprap outfall protection at Ex. 15" CPP outfall. Dimension riprap (L x W x D).
5. Water quality: Explain and report methodology used to prepare the phosphorus reduction comparison table
included with 6/11/18 EcoSystem Services cover letter. Provide supporting calculations. Remove
reference to stream restoration; this does not appear to be a stream restoration project.
6. Sheet 2: Label all tax map parcels affected by project activity.
7. Sheet 3: Provide emergency spillway unless bioretention filter contains the 100-year event.
8. Sheet 3, 5:
a. Show /provide Access easement from Westfield Road to SWM Facility. Record with Deed of
Dedication prior to VSMP Approval.
b. Show /provide SWM /drainage easement that includes bioretention filter and that extends from
biofilter through outfall to natural channel. Record with Deed prior to VSMP Approval.
9. Sheet 4:
a. Sec. B-B proposed bioretention 10-year WSE (468') will cause slight backwater condition at Sec.
D-D inlet channel, and more pronounced backwater condition at Sec. E-E forebay weir. Revise
such that 10-year storm event is contained within features shown in profile Sec. A -A, and plan
view.
b. Sec. B-B:
i. Label riser bottom of base elev.
ii. Label riser base depth /thickness.
iii. Provide base bedding detail.
iv. Provide pipe (6" Sch 40; 12" HDPE) INV elev. in riser.
v. Provide floor of riser (MH) elevation (< 1NV/out, 12" HDPE elev.).
c. Label Sec. C-C 6" ponding elevation=465.1'.
d. Label stone surface elevation at bottom of channel, and top of sideslope, similar to labels provided
with Sec. E-E. Label sideslope slope; 1:1 for example.
e. Recommend Sec. E-E provide > 1" proposed freeboard between top of weir and 10-yr WSE.
B. Pollution Prevention Plan (PPP)
The PPP content requirements can be found in County Code section 17-404.
1. Provide with Sec. 6 of Albemarle County SWPPP template.
C. Erosion and Sediment Control Plan (ESCP)
Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This plan
is disapproved, for reasons provided in comments below. The erosion control plan content requirements can
be found in County Code section 17-402.
Sheets 5, 6, 7: Provide reference to sheet 10 details, as required.
Sheet 5
a. Revise sheet title to match index.
b. Label residential buildings.
c. Provide contour labels
d. Label street at PCE.
C. Show Ex. trees. (Google image, below)
f. Note trees TBR.
Engineering Review Comments
Page 3 of 4
g. Provide TP, especially since working within stream buffer*
* Mitigation offset plantings not required; this is not a stream crossing.
3. Sheet 6:
a. Show existing trees.
b. Provide SF and berm containment downslope of SWPPP elements /staging area.
c. Provide grading for containment (recommend depression).
4. Sheet 7: Provide terrain contour labels.
5. Sheet 9:
a. Construction Sequence (Note 2): Revise to read, "Install paved construction entrance and mulch
access road where indicated on plans."
b. Include VA DEQ Desijzn Specification No. 9, Sec. 8.2, Bioretention Installation, p. 34 and 35.
Include these two pages (Narrative Steps) of the DEQ specification in their entirety. Link:
hLtps://www.vwrrc.vt.edu/swc/documents/2013/DEQ%20BMP%20Spec%20No%209 BIORETENTION Fi
nalDraft vl-9 03012011.pdf
c. Install Periodic Inspection checklist attached to these comments, in its entirety.
6. Sheet 10:
a. Provide paved construction entrance with wash rack detail located at pg. 8 /Albemarle County
Design Standards Manual (ACDSM) —Link:
http://www.albemarle.org/upload/images/forms center/departments/community development/forms/design s
tandards manual/Albemarle County Design Standards Manual 2015-04-25 draft.pdf
b. Provide drainage pipe bedding detail.
c. Provide Filter Log Detail.
Google image
The VSMP permit application and all plans may be resubmitted for approval when all comments have been
satisfactorily addressed. For re -submittals please provide 2 copies of the complete permit package with a completed
application form.
Engineering Review Comments
Page 4 of 4
Engineering plan review staff are available from 2-4 PM on Thursdays, should you require a meeting to discuss this
review.
Process
After approval, it is my understanding a SWM Facilities Maintenance Agreement will need to be completed and
recorded, but Engineering will confirm. It likely depends on whether Minor Hill Townhouses HOA is relieved of
future Maintenance responsibility with this retrofit project, or not. If an Agreement is required, 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.
A Deed of Dedication is required whether Albemarle County assumes maintenance responsibility for
bioretention filter and outfall pipe, or whether future SWM facility maintenance is an HOA responsibility. The
deed will dedicate easement/s to the county across HOA and individual private parcels. Engineering will look
into this further. Easement plats are required.
Deed of Dedication of Easement must be recorded prior to VSMP plan approval.
After agreement is complete and deed recorded, Applicant (Albemarle County /FES) will need to complete
request for a pre -construction conference form. The form identifies the contractor and responsible land disturber.
Since this is a county project with less than 1.0 Ac. land disturbance, no state -portion of a VPDES permit fee is
required. The form 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 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.orv/dei)tforms.asi)?der)artment--cdena"o
Thank you.
J. Anderson — 434.296-5832 —0069
Minor Hill BMP Retrofit WP0201800045 071318.doc