HomeMy WebLinkAboutWPO200800079 Review Comments Erosion Control Plan 2009-01-12ALg�,��
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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- 2008 - 00079, Moore's Creek WWTP ESC and SWM Plan
Plan preparer: Mr. Matthew Buswell, PE; Hazen and Sawyer fax 919.833.1828
Owner or rep.: Rivanna Water and Sewer Authority info @rivanna.org
Date received: 4 August 2008
(Rev. 1) 8 December 2008
Date of Comment: 8 August 2008
(Rev. 1) 12 January 2009
Engineer: Phil Custer
(Rev. 1) Phil Custer
The SWM and ESC plans for the expansion to the Moore's Creek WWTP, received on 8 December 2008,
have been reviewed. The plans can be approved after the following changes have been made:
A. General Review Comments
1. It appears that all proposed stream buffer disturbances are exempt under Sections 17 -319.13 and
17- 320.13. Though, the disturbance of the buffer for ESC measures will be exempt only if the area
is replanted. This replanting would simply need to appear on the site plan and would not require a
mitigation plan. Eliminating the mitigation plan review will also reduce the final WPO bond
amount RWSA will have to pay before construction begins. On sheet C13, please note that the
stream buffer area disturbed by ESC measures will be replanted to existing vegetation or
equivalent. Please contact Ana Kilmer (296 -5832 x3277) to receive a refund of the mitigation
plan fee.
2. (Rev.]) The last note for the County's General Construction notes for ESC and SWM plans
appears to be missing from the ESC and SWM lists on Sheet C30.
B. ESC Plan Review Comments
1. Construction entrances need to be 12ft wide by 70ft long.
(Rev. 1) Comment has been addressed.
2. Please give minimum dimensions for the sediment trap on sheet EC2 (bottom dimensions, depth of
wet storage, etc.).
(Rev. 1) Comment has been addressed.
3. Please provide dust control, permanent seeding, and temporary seeding symbols where necessary.
(Rev. 1) Comment has been addressed.
4. Please show existing soil boundaries on the ESC plan. Soil boundary information is available on
the county's GISWeb application.
(Rev. 1) Comment has been addressed.
5. Please show a staging /parking area on the plan.
(Rev. 1) Please provide a staging /parking area for the work on the northside of the stream.
6. Please show the entire temporary gravel access roaa in the plan and the necessary LoC measures.
Please contact Summer Frederick (296 -5832 x3565) regarding the tree disturbance for the access
road and site plan implications.
(Rev. I) Comment has been addressed.
Please provide protection measures for all disturbed areas. This plan does not seem to show the
protection measures required for the underground utility work. Please label these disturbed areas
as "underground utility work to be coordinated with on -site inspector."
(Rev. 1) Please show silt fence on the downstream side of all underground utility work that is to
be installed /repaired in grassed areas. After further consideration of the above note, it is
necessary to show the protection measures on the plan so that they can be bonded. Disturbance
draining to the holding ponds in sheet C20 will not require silt fencing.
The sediment trap north of the chemical filling station should be constructed so that it can remain
in place during the filling operation needed to prepare building pads. The trap also has an
embankment that is too tall (5ft maximum). It appears that setting the embankment of the trap
closer to the fence at an elevation of 536 could solve both issues. Then, the diversion dike could
be run at a lower elevation and capture more of the disturbed area (from the sludge pumping
station to the scum incinerator) and the need for silt fence could be reduced, if not eliminated.
Please show sediment trap grading on Sheet C13 with note stating that after stabilization has
occurred, the trap should be removed and the entire buffer should be replanted to existing
vegetation or equivalent.
(Rev. 1) Sediment calculations seem to be in order. However, the drainage area to the trap
appears to be larger than shown in the drawing and used in the calculations. The drainage
area should extend to aeration basin 1 and the western wall of the sludge pumping station. The
increase to the drainage area may necessitate redesigning the sediment trap.
9. Please show the maximum drainage area for the trap on EC3 so that the calculations can be
confirmed.
(Rev. 1) The drainage area to the trap appears to be larger than shown in the drawing and used
in the calculations. The drainage area should extend to aeration basin 1 and the western wall
of the sludge pumping station.
10. Please show inlet protection on the storm inlet in the southwest corner of sheet C 13.
(Rev. 1) Comment has been addressed.
11. The ESC portion of the WPO bond will be computed once all comments have been addressed.
(Rev. 1) Comment remains unchanged.
12. Please note that a grading permit will be withheld until a copy of the state VSMP permit is given
to the county. Please contact Mr. Matthew Grant, DCR, at 804.225.3068 for more information.
(Rev. 1) This is no longer required.
C. SWM Plan Review Comments
Please note that the VSMH does not recommend the use of sand filters for watersheds that do not
have high impervious areas ( <65 %). The handbook states that grass clippings and eroded soil
often clogs sand filters. County engineering review has no objection to the use of the sand - filter as
the BMP for this site.
2. The inlet and outlet pipes for the sand filter must be at least 15" and sized to pass a 10 -year storm.
The current design may prevent the water quality volume from being treated for quick, high -
intensity storms. [DM]
(Rev. 1) Comment has not been addressed. The pipes have been increased to 15 ". but it does
not appear that the 10 year peak storm can be treated with the current design. With the 8" weir
wall in JB -12, a flow rate of just 1.5cfs is routed through the system, compared to the 4.03cfs
found in the calculation to line 1.
The applicant has stated that directing the peak flow discharge through the filter will damage
the system but we have not been presented with any concrete justification for this claim. If the
10 year peak storm was routed through the filter, my calculations indicate that the average
velocity through each weir would be approximately 0.5fps. The velocity through each weir with
the current setup would be close to 0.25fps. I do not see enough of a difference in these
numbers to justify bypassing some of the higher discharges through JB -12 away from the
treatment facility.
3. All changes in direction in a stormsewer system must be accessible.
(Rev. 1) Comment has been addressed.
4. The detail for the bypass structure is not correct. The structure is listed in the drainage profiles as
being 7.65ft tall, but the detail shows that it will be at least 9ft. Please clarify.
(Rev. 1) Comment has been addressed.
5. Access to the bottom of structure CB -16 is difficult as designed. Please provide VDOT standard
steps within the structure and line up the cut into the lower vault so that it is below the access point
from the ground elevation. Also, the opening should be increased to 20" so that no point in the
opening is narrower than the VDOT Standard MH -1 frame and cover.
(Rev. 1) Access to the bottom of the facility is still an issue. The height of the 4'x4' box will
likely be around 2ft. Please either line up the 20" access cut with the grate or provide a taller
vault (perhaps 6ft would work).
6. A signed Stormwater Management Facility maintenance agreement and recordation fee will need
to be submitted. Please contact Pam Shifflett (x 3246) for questions regarding this procedure.
(Rev. 1) This agreement has not yet been received.
7. The SWM portion of the WPO bond will be computed once all comments have been addressed.
Please provide a cost estimate from the supplier of sand - filter facility to assist in the bond
computation.
(Rev. 1) The SWM bond will be computed at a later date.
8. (Rev. 1) It appears that JB -12 should be a DI -I since it is away from the curb by several feet.
9. (Rev. 1) Please provide a modified simple spreadsheet for the engineering trailer watershed
where new impervious areas are being added to determine whether water quality treatment is a
concern. By my calculations, it appears that a BMP is needed.
File: E2 esc swm PBC 08 -079 Moore's Creek WWTP.doc