HomeMy WebLinkAboutWPO201000072 Review Comments Erosion Control Plan 2011-02-11ALg�,��
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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:
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
(Rev. 1) 5 January 2011
9 December 2010
(Rev. 1) 11 February 2011
Phil Custer
The first resubmittal of the ESC plan for Lockwood Townhomes, received on 5 January 2011, has been
reviewed. Comments from the review of the site and SWM plan submittals have been provided in a
separate comment letter. 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.
(Rev. 1) The proposed extra ESC measures are acceptable to the program authority except the
limits of disturbance /safety fence should be located much closer to the edge of the grading and
a greater distinction between the limits of disturbance and the property line should be made.
Also, the dewatering orifice should be sized for the required, not provided, volume. Please
revise this calculation and specification accordingly.
2. Please state within the construction sequence that the existing diversion cannot be removed until
the alley and eastern ditch have been rough graded.
(Rev. 1) Comment has been addressed.
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.
(Rev. 1) The survey file has been modified and the drainage area has been confirmed.
Comment has been addressed.
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.
(Rev. 1) Comment has been addressed.
5. The sediment basin calculations detail states that baffles are required, but I see none proposed on
the plan.
(Rev. 1) Comment has been addressed.
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.
(Rev. 1) Comment has been acknowledged.
7. Please note on Luc Flan 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.
(Rev. 1) Comment has been addressed.
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.
(Rev. 1) Comment has been addressed.
9. Please update the standard county ESC construction notes with the latest version found in the
design manual.
(Rev. 1) Comment has been addressed.
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.
(Rev. 1) See comment 1.
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]
(Rev. 1) Comment has been addressed.
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.
(Rev. 1) Remove all references to the I% of the total drainage area from the adequate
channel narrative.
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.
(Rev. 1) I will note at this time that I'm not sure I agree with the 25% reduction to the
hydrologic information of this watershed. But VDOT has now accepted this roadway
and culvert, so future deliberation is pointless. No further analysis or modification is
necessary to address this comment.
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.
(Rev. 1) Comment has been addressed.
d. Please analyze a section at the greenway trail crossing. The bridge should be able to pass
the 10 -year storm without overtopping.
(Rev. 1) Comment has been acknowledged.
13. An ESC bond will be computed at the time of WPO plan approval.
(Rev. 1) After all plans have been approved, please provide a Bond Estimate Request to the
County Engineer to receive a bond computation.
File: E2_esc_PBC _ wpo- 2010 -00072 Lockwood Townhomes.doc