HomeMy WebLinkAboutWPO201100008 Review Comments Erosion Control Plan 2011-03-25ALg�,��
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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 - 00008; NGIC ESC Amendment (Sediment Basin 2)
Plan preparer: Mr. Scott Collins, PE; Collins Engineering
Owner or rep.: Next Generation, LLC.
Date received: 10 February 2011
Date of Comment: 25 March 2011
Engineer: Phil Custer
The latest ESC amendment for the NGIC site has been reviewed. The original ESC plan for this project
was approved on February 14th 2008. On July 7t'' of that year, an amendment to the plan was approved
which moved sediment basin 2 to a more natural position within the existing gully immediately uphill of
the headcut of the intermittent stream. At the same time, an amendment to the Stormwater Management
Plan was submitted, and later approved, that proposed a biofilter in the general footprint of sediment basin
2.
After discussions with the County and DCR inspectors for this site, it is my understanding that the current
situation in the field does not match the latest approved plan (July 2008). The county inspector believed
the intention of this ESC plan amendment was to provide an analysis of the as -built condition in the field
to assure compliance with state regulations. After a visit to the site this morning, I noticed that the latest
submittal does not match condition in the field. I also observed the July 2008 plan also didn't match the
as -built situation in at least two areas: the footprint of the constructed facility appeared to be 80 -85% of the
footprint of the approved plan and there is a berm in the middle of the facility further reducing the volume
of the pond. I did not carry any surveying equipment on my site visit so I was not able to confirm the
elevation of the dewatering orifice and crest of the spillway. If the intention of this plan is to prove that the
existing condition is adequate, please provide an as -built survey showing all contours of the pond and of
the riser structure with calculations showing all standards of VESCH 3.14 have been met.
The revised design of this sediment basin appears to match the footprint of the permanent stormwater
facility (approved as an amendment to the original plan) almost exactly (please see comment 3). Since this
work has to ultimately be done, I support the concept to revise the ESC plan and reconstruct this sediment
basin to the newest proposed contours (though, please see the comments to follow). If this is the
applicant's intention, please address the following comments:
1. The set that was submitted to the county includes an amendment to just phase 1, not phase 2,
despite the fact that the site is halfway built. Instead of revising sheet ESC -2, please revise sheet
ESC -3 and show all as -built characteristics of the site accurately. If the ESC plan does match the
approved site plan, a site plan amendment may be needed (see the following comment).
2. The ultimate drainage area for this basin will be 13.92 acres according to sheet SWM -2 of the
approved site (SDP- 2008 - 00112) and stormwater plan amendment. The sediment basin must be
sized for this drainage area, not 10.36 acres.
3. For the most part, the grading of the facility appears to match the approved SWM plan amendment
showing the biofilter behind building 2 except that the embankment of the ESC pond is 2ft higher.
Please clarify. The applicant should attempt to use the same embankment dimensions for the ESC
and SWM plans if possible.
4. Please provide the calculations for the dewatering orifice. It appears that the orifice is oversized.
5. If the embankment and the riser structure are to remain unmodified, please provide an as -built
survey of these structures. If either of these aspects need to be changed, please note the required
changes on the plan. (The anti - vortex specified on the plan does not appear to have been used in
the field.)
6. A baffle will likely be needed for the outlet of the drainage system that comes from behind
building 1.
File: El_esc_PBC_wpo201100008 NGIC SB2 amendment.doc