HomeMy WebLinkAboutWPO202100063 Review Comments WPO VSMP 2021-11-18John Anderson
From: John Anderson
Sent: Thursday, November 18, 2021 4:25 PM
To: Chris Mulligan
Cc: Frank Pohl
Subject: Planning Application Review for WP0202100063 DUNLORA FARM - VSMP . [
Engineering review comments ]
The Review for the following application has been completed:
Application Number = WP0202100063
Reviewer = John Anderson
Review Status = QC Denied
Completed Date = 11/18/2021
This email was sent from County View Production.
Chris,
Per 17-409.D. Application for Dunlora Farm is deemed incomplete. We comment on plan submittals whenever possible, but
there are enough gaps relating to stormwater compliance that Engineering deems the Application incomplete; specifically:
• While plan information submitted is helpful, gaps make it impossible to confirm compliance; specifically:
o Sheet 17 indicates:
• Drainage Area A (VRRM.xls): 9.33 Ac. of managed turf to VRRM.xls practice 9a., sheetflow to
conservation area; plan does not indicate conservation area, or portions routing to it. Plan does not
provide detail sufficient to evaluate compliance with this BMP option.
• Note: Specific downslope Max. gradient /pre-treatment /typical details attend Virginia DEQ
Stormwater Design Specification No. 2 /Sheet flow to a vegetated filter strip or conserved open
space. Plan does not provide detail sufficient to evaluate compliance with BMW option.
• Drainage Area C (VRRM.xls) indicates no BMP practice, yet Total TP load reduction achieved in DA
C =2.87 lb. Plan does not provide sufficient detail to evaluate 2.87 TP load reduction in DA C.
o Plan submittal does not include a conventional calculation packet, with:
• Complete 1-,2-,10-,25-,100-year routings. Note: 25-yr routings may not be required; remainder
are. Plan includes 1-yr and 1,000-yr routings, sheet 16 for SWM4, SWM3, SWM2, SWMI.
• Routings sufficient to evaluate compliance with detention system design (10-yr, 100-yr), at a
minimum. Please provide 10-yr and 100-yr hydrologic routings.
• Stormwater narrative. Please provide text narrative that identifies requirements, and method of
compliance with 9VAC25-870-65, -66.
• Complete (hydrocad) model results ; partial results are included. Provide complete modeling (with
calculation packet).
• Pre -developed Q Pe.k for each point of analysis.
• Energy balance (EB) equation. Provide EB, reporting all variables for each point of release to a
natural conveyance.
• Note: entire 80.77 Ac. development appears to release to a natural conveyance, at each discharge
point. If this is the case, every point of analysis is evaluated against energy balance.
• Definite points of analysis (POA). Clarify Q p�k post -developed as occurring coincident with SWM
facility outfall/s. SWM facility outfalls provide Q peak for energy balance equation. Clarify each
POA, with leader lines.
• Note: If all development discharge points are subject to energy balance compliance demonstration,
which appears to be the case, there is no need for points of analysis at any distance removed from the
development; simply demonstrate discharge meets energy balance requirements at 9VAC25-870-
66.B.3.
o Water quality (sheet 17):
• 16.50 lb./yr. TP load reduction required.
• 7.71 lb. achieved on -site.
• 8.79 lb. load reduction remains.
• Plan does not indicate how additional TP load reduction occurs.
• 9VAC25-870-69 requires developments with over 5 Ac. of land disturbance and > 10 lb. load
reduction to achieve at least 75% of phosphorus reduction on -site. Plan does not provide detail
sufficient to evaluate compliance with 9VAC25-870-69.
o Forest /open space (sheet 17
• Site information VRRM.xls tab indicates 35.77 Ac. in Forest -Open space. Plan does not provide
sufficient detail or narrative required to evaluate proposed 35.77 Ac. FOS easement.
Please submit a complete SWM Plan (including items listed above, and at 17-403) that shows compliance with 9VAC25-870-
65, water quality compliance, and 9VAC25-870-66, water quantity.
Thanks for your help with this.
best,
John E. Anderson, PE I Civil Engineer 11
Department of Community Development I County of Albemarle, Virginia
401 McIntire Road I Charlottesville, VA 22902
434.296.5832 ext. 3069