HomeMy WebLinkAboutWPO200900014 Review Comments Erosion Control Plan 2009-08-06 (3)*-&A
County of Albemarle
Department of Community Development
Memorandum
To: Phil Custer, Engineer
From: Glenn Brooks, County Engineer
Date: 5 Aug 2009
Subject: Biscuit Run, Erosion and Sediment Control Plan (WPO2000900014)
The erosion control plan has been reviewed with regard to meeting proffer 5B, which calls for erosion
control measures to the maximum extent practicable as determined by the Program Authority. The extra
measures that could be found on the plans were; (1) some wire reinforced silt fence, (2) chain link fence
for tree protection, and (3) sediment basins that provide 1.5 times the required volume
Each of these measures has merit, but the nature of the plan limits their usefulness. (1) Wire reinforced silt
fence is used below basins and traps, which are the primary perimeter controls. As a secondary measure it
is useful, but it is only a backup for most of the plan. (2) Chain link fence for tree protection is also useful,
but the only areas where this really matters are the tree preservation areas, and only if it can be placed
before land clearing, which seems problematic. There are not really any areas internal to the site, and the
site is not a tight urban setting, or highly visible, where this kind of measure can make a significant
difference. (3) The extra sediment basin volumes can have a significant impact, but the erosion and
sediment control plan undermines this by over - complicated diversions and bypasses to place basins in
unnatural locations, increasing maintenance, the likelihood of failures and significant field alterations.
The plan must be simplified by removing the too - complicated system of dual basins and diversions.
Basins should be placed in the natural low points of the topography at the perimeter of the work, allowing
work to proceed without hindrance. A sketch of the changes that might accomplish this has been provided
below, along with a few other necessary changes.
It appears necessary to revise the preservation areas. There does not appear to be room to provide
adequate perimeter control between the preservation areas and the road.
In addition to the changes above, it is recommended that a monitoring program be developed to document
and report the effectiveness of erosion control measures and downstream conditions. This would address
extra erosion control, and MS -19 in part. I did not find any demonstration of adequacy for the surveyed
channels shown on the plan and in the narrative. Only routings for the various biofilters were provided,
and these did not use the 24hr storm as required. It would also appear to require some analysis of the
various outfalls to find flows, and then composite channel computations to evaluate maximum velocities.
However, I would emphasize the monitoring and documentation rather than too much design analysis.
An aggressive permanent seeding program should also be provided on the plan and in the narrative. Soil
tests, fertilizers, seed mixes, matting on slopes, mulches, and topsoiling should be specified in detail.
The stormwater management plan should be separated from the erosion and sediment control plan. The
erosion and sediment control plan will be temporary, and will be discarded. The stormwater plan will be
permanent. There is not enough information at this time to determine where the project might be in regard
to proffer 5D (extra water quality). It is suggested that any stormwater management approvals be
conditional, with final approval to occur with final development plans.
Albemarle County Community Development
Engineering Review comments
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filc: EI_ csc _GEB_BiscuiLRun_80 %proffcr.doc