HomeMy WebLinkAboutWPO201000073 Review Comments Erosion Control Plan 2010-12-09ALg�,��
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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- 2010 - 00073, Great Escapes Movie Theater at Hollymead Town Center
Plan preparer: Mr. Scott Collins, PE; Collins Engineering
Owner or rep.: Route 29 LLC
Date received: 25 October 2010
Date of Comment: 9 December 2010
Engineer: Phil Custer
The ESC plan for Great Escapes Movie Theater at Hollymead Town Center, 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 18 which the Program Authority can review for
compliance with the proffer.
2. The timing of the construction of the retaining walls is critical to the adequacy of this ESC plan.
The retaining wall must be built as the first step in Phase II. As the retaining wall is built, the
contractor must maintain a diversion directing water to sediment basin 1, and eventually 2. At the
end of step 6 of the construction sequence, state that the retaining walls must be constructed in a
matter that directs runoff to the south into sediment basin 1, and eventually 2. The diversion
shown on Phase I that is north of sediment basin 1 cannot be disrupted until the ESC inspector is
satisfied that the diversion (or pipe system) above the retaining wall is adequate to convey the
necessary runoff.
3. Please provide more information in the construction sequence regarding the modification and
removal of sediment basin 1. Phases I and 11 are snapshots of the construction process that
represent two days of the total timeline. I am concerned that during intermediate phases there will
not be adequate protection as the basin is filled and structure is modified.
4. Please include the regrading of sediment basin #2 (and 1 if necessary) in step 4 of the construction
sequence.
5. The purpose written in the ESC narrative appears to be referencing a mass grading plan rather than
a site specific ESC plan.
6. Please include the greenway and all associated grading within the limits of construction for the
project. Please provide ESC measures as necessary to achieve the grading as required by the trail
standard. Please update the total amount of disturbance stated in the ESC narrative accordingly.
7. Please state how the greenway trail west of Powell's Creek will be constructed and provide
appropriate ESC measures.
8. Please show the limits of the previously approved ESC plan for the adjacent Hollymead Al
development. The WPO plan referenced by the applicant (WPO- 2008 - 00086) does not include
the construction Meeting Streeet within its limits. Please remove any reference to this claim in the
plan. The Great Escapes ESC plan should expand its limits to include the Meeting Street
construction because this roadway is necessary for the Great Escapes site plan. The road plan
within the ESC plan must match the plan submitted for review under SUB - 2010 -00141 including
the location of all inlets and pipes. It is my understanding that the ESC basin south of the Kohls
building was sized to include a portion of this segment of Meeting Street, despite the fact that it
wasn't proposed for construction at that time.
9. In sheet 19, please show a diversion south of sediment basin #2 to the end of the limits of
construction for this plan.
10. When Sta. 17 +00 to Sta. 18 +75 of Meeting Street is constructed (either in sheet 20 or 21), show a
fill diversion along the slope and silt fence below it.
11. Please label the drainage areas on sheet 19 as it was done on sheets 20 and 21. The drainage area
to SB #2 will increase based on the above comments.
12. Please show the calculations table /detail for existing sediment basin 1 and make sure the facility is
adequate for the drainage area to it during Phase I.
13. The drainage area to sediment basin 2 should essentially be equal to the post - development
drainage area shown on sheet 24, including any additional runoff from Meeting Street. Please
update the calculations accordingly.
14. The time of concentration of 14 for sediment basin 2 appears to be too long, especially considering
that the pre - development rate was 11 minutes. Please update the calculations accordingly.
15. The diversions shown in Phase H in the middle of construction will be too difficult to maintain
during day to day operations as the site is regraded. Please remove the northwesternmost diversion
and update the sediment basin drainage areas.
16. Please identify the greenway trail, especially the stream crossing, as a critical area on the plan.
Please also identify the filling of the roadway close to Powell's Creek as being a critical erosion
area.
17. Please remove step 13 from the construction sequence and related notes on sheets 19, 20, and 21
since this is the final plan and all final stormwater measures will be bonded when this plan is
enacted.
18. Please show outlet protection (OP) at all drainage system outfalls.
19. Please provide dewatering orifice calculations for all sediment basins. My calculations show that
smaller orifices are required.
20. In sediment basin #2, please move the baffle 15ft to the south and extend to the 497 elevation
south of the diversion from Meeting Street.
21. In the phase II version of sediment basin #1, please rotate the baffle about 15 degrees counter-
clockwise so the baffle is between the end of the diversion and the sediment basin riser.
22. Please update the standard county ESC construction notes with the latest version found in the
design manual.
23. Please provide a detail for sediment basin 1's barrel through the proposed retaining wall. Is this
pipe to be removed after basin 1 is no longer necessary?
24. 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]
25. 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. 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.
c. The analysis studies just one channel downstream of the Great Escape Stormwater facility.
Please provide three more cross - sections between the Route 29 culvert and the outlet of
the Great Escapes Basin.
d. Please analyze a section at the greenway trail crossing. The bridge should be able to pass
the 10 -year storm without washout.
26. An ESC bond will be computed at the time of WPO plan approval.
File: El_esc_PBC _ wpo- 2010 -00073 Great Escapes Movie Theater.doc