HomeMy WebLinkAboutWPO201100071 Review Comments Stormwater Management Plan 2011-11-08ALg�,��
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: WPO- 2011 - 00071, RE- Store'n Station SWM Plan
Plan preparer: Mr. Nat Perkins, PE; NP Engineering
Owner: Jefferies IL LLC
Owner's Rep.: Mrs. Jo Higgins; Project Development Limited
Date received: 12 September 2011
Date of Comment: 8 November 2011
Engineer: Phil Custer
The SWM plan for the RE- Store'n Station (WPO- 2011 - 00071), received on 12 September 2011, has been
reviewed. The plan can be approved after the following comments have been addressed:
1. Please provide an approval letter from Filterra that the current layout and grading plan is
acceptable to them. I have concerns with the grading plan not allowing any water to some of the
structures. For instance, the contours are pitched away from the curb that F4 is placed on.
2. Please provide an approval letter from ACF Environmental that the current layout is acceptable for
the use of the modular Raintank system.
3. This application will require that a Stormwater Management Facility Maintenance Agreement be
recorded. Please complete this form and submit it to Ana Kilmer with a $17 recordation fee after
reading the instructions online. Please include all parcels contained in this site plan on this
agreement.
4. The modified simple spreadsheet must analyze the watersheds for each stormwater quality facility
proposed on site and should not analyze a watershed including offsite water. By doing so, you are
obligating yourself to treating that offsite water to that removal rate, which the current plan is not
doing and is also not desirable. Please update the modified simple spreadsheet for only the
drainage areas to the detention facility and to the cistern.
5. If removal credit is desired for the cistern, the four pages of the state's Cistern Design Spreadsheet
in Appendix C should be included in the Stormwater report in full so it can be evaluated. Page 4
is impossible to read and the first three pages are very difficult to read. Please indicate in the
stormwater report what the removal rate of the cistern is and provide justification in the
calculations. If the removal rate of the cistern does not meet the required rate after the modified
simple spreadsheet is amended per comment 4, the cistern must become larger, toilets in the gas
station must use water from the cistern, or another BMP facility (upstream or downstream) must be
provided.
6. Please provide pre- treatment and screening for the drainage system upstream of the cistern per VA
DCR Stormwater Design Specification No. 6.
7. The proximity of the Raintank 2 and one of the drainfields is a concern of the county. I'm not
certain that the two systems are far enough apart not to affect each other and I have contacted the
Virginia Health Department regarding this issue. An impervious liner may be required on this
system to make sure septic effluent does not find its way into the detention system and that the
detention system does not affect the efficiency of the drainfield.
8. Detention requirements have been met: the 2 and 10 year discharges for the 1.49 acre post -
development watershed has been reduced to the pre - development rates. For all other projects
submitted to this county, the updated IDF curves found in the Design Manual must be used. For
this project, you do not need to use the updated IDF curves because the routings are acceptable.
9. The control structures for the detention system must be accessible for inspection and maintenance.
The current design of the facility has the potential for clogging at the inlet end of the pipe inside
the facility where maintenance would be difficult. The control structure must have a trashrack
placed overtop of it that meets state minimum standards. I also recommend placing some sort of
screening or filter upstream of the detention system to prolong the life of the facility. This last
suggestion is not a requirement.
10. Please use a minimum of 15" diameter pipes in the stormwater facility to decrease the likelihood
of clogging.
11. An analysis of the downstream channel per Minimum Standard 19 was not provided with the
SWM or ESC plan. Please refer to page 7 (of 35) of the County's Design Manual and the Virginia
Erosion and Sediment Control Handbook for what the county expects for an analysis of
downstream channels. Per state law, this analysis must be performed using the 24 -hour storm.
According to DCR's Technical Bulletin #1, detention does not constitute compliance with MS -19
because total volume of runoff is increased and poses a potential threat to downstream properties.
12. To receive a bond estimate, please provide a completed Bond Estimate Request Form to the
County Engineer after all comments have been addressed.
File: E1 swm PBC WPO- 2011 -00071 RE- Store'n Station SWM Plan.doc