HomeMy WebLinkAboutWPO201000072 Review Comments Erosion Control Plan 2010-12-09ALg�,��
�'IRGINZ�
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project:
Plan preparer:
Owner or rep.:
Date received:
Date of Comment:
Engineer:
WPO- 2010 - 00072, Lockwood Townhomes
Mr. Scott Collins, PE; Collins Engineering
Route 29 LLC
25 October 2010
9 December 2010
Phil Custer
The ESC plan for Lockwood Townhomes, received on 25 October 2010, has been reviewed. Comments
from the review of the site plan submittal have been provided in a separate comment letter. The comment
letter for the SWM plan will be transmitted at a later date. The ESC plan can be approved after the
following corrections are made:
1. Proffer 913 states that the owner shall provide additional erosion and sediment controls to achieve a
sediment removal rate of 80%. I cannot find anywhere in the plan where measures above and
beyond the minimum requirements have been provided. On the next submittal, please add these
additional measures and provide a list on sheet ESC -1 which the Program Authority can review for
compliance with the proffer.
2. Please state within the construction sequence that the existing diversion cannot be removed until
the alley and eastern ditch have been rough graded.
3. The drainage area limits for the sediment basin seems to be larger than the 13.92 acres shown on
the plan. At the very least, the drainage area line should be relocated to the center of the roofs of
the existing townhomes on Lockwood Drive. Also, the survey file shows that at Abington Dr. the
drainage system is being diverted into this basin. It appears that a significant portion of the
Abington development is being routed to this facility.
4. Please note on the ESC plan that work to the sediment basin embankment is required to raise the
embankment to the specified elevation. Please include this in one of the initial steps of the
construction sequence.
5. The sediment basin calculations detail states that baffles are required, but I see none proposed on
the plan.
6. The sediment basin is located on a separate parcel. A permanent easement will be required for the
stormwater facility. For ESC purposes, the owner of 32 -45 will also need to be party to the ESC
bond.
7. Please note on the plan that VDOT pipes are proposed as conveying water sediment -laden water to
the sediment basin. When VDOT accepts the road and the drainage system, an ESC additional
bond may be required for the washing of the drainage system after stabilization.
8. Please clarify the meaning of the last sentence in the note northeast of the sediment basin. The
earthen embankment should not be constructed until the site is fully stabilized and the facility is
being converted into the stormwater facility. The sediment basin will not have enough wet storage
capacity if the embankment is built while construction is ongoing.
9. Please update the standard county ESC construction notes with the latest version found in the
design manual.
10. Please reduce the limits of construction east of the grading shown on the site plan to only the
minimum area needed for a stockpile, if a stockpile will be necessary. Existing stabilized areas
shall not be denuded unnecessarily.
11. In both the construction sequence and the project description of the ESC narrative, please state that
permanent seeding will be applied to all disturbed areas, except for areas the Program Authority
determines are otherwise permanently stabilized or are under construction with an approved
building permit. [Proffer 9C]
12. Engineering review has the following comments regarding the MS -19 analysis:
a. The project area used to compute the total drainage area for the 1% rule is the total
development, not subphase. In the case of the Great Escapes and Lockwood Townhome
ESC plans, the project area includes all other areas of the A2 rezoning plan. The analysis
provided does not appear to have reached the I% rule.
b. Please provide the shoulder elevation for the culvert calculation. If the headwater
encroaches too close to the shoulder elevation, a relief culvert may be required at this
crossing.
c. The slopes used in most of the computations appear to be underestimating the average
slope of the segment of the stream. When I measured the distances between the county's
4ft contours I found slopes greater than 2% for most of Powell's Creek.
d. Please analyze a section at the greenway trail crossing. The bridge should be able to pass
the 10 -year storm without overtopping.
13. An ESC bond will be computed at the time of WPO plan approval.
Pitc: El_csc_PBC _ wpo- 2010 -00073 Great Escapcs Mo% is Thcatcr.doc