HomeMy WebLinkAboutWPO200600038 Review Comments Erosion Control Plan 2008-09-26� OF AL
,. vIRGI1`IZP
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: Albemarle Place Town Center
[aka Albemarle Place- WP0200600038]
Plan preparer: Herb White, III, P.E., W.W. Associates [fax (434) 978 -1444]
Owner or rep.: Albemarle Place E.A.A.P., L.L.C. [fax (301) 652 -35881
Plan received date: 13 August 2008
Date of comments: 19 September 2008
Reviewer: Max Greene
The Mass - grading plan amendment for Albemarle Place, now referred to as Albemarle Place
Town Center, submitted 13 August 2008 has received engineering review. This submittal appears
to be a new submittal for the replacement of the previously approved Mass — grading plan.
Mass grading (also called rough or early grading plans that contain only approximate finished grades and
culverts necessary to grade.) can only be permitted within planned developments where a concept - grading
plan was approved with the rezoning. The agent (Director of Planning) needs to formally determine that
the grading plan is in general conformity with the approved rezoning plan. Otherwise, all final plans need
to be approved prior to issuance of grading permits. After approval by the Agent, the following items will
be adequately addressed prior to final Mass - grading plan approval:
1. The approved plan must be included in the plan set, with the specific areas of amendment clearly
outlined by bubbling or circling. The approved plan must not otherwise be altered. Alternatively,
a new plan can be submitted for review. A detail on a subsequent new sheet must provide the
amended features as referenced in the bubbled or circled area of the approved plan.
2. Please show benchmark location, elevation and datum for topography. An existing utility or other
known position will suffice. [Policy]
3. Please remove the notes from the plan that do not apply to this submittal such as the "Water and
Sewer Notes" and the "Site Plan Notes"
4. Northern temporary lay -down area requires a sediment trap due to the size and slope of the area
shown.
5. All entrances except approved construction entrances will be shown blocked to prevent the ingress
or egress from the site. VDOT barricades are recommended.
6. Off -site grading easements are required from all adjacent property owners with proposed grading
or property disturbance.
7. The proposed wall appears to be in the way of the overland relief from the basin area above the
site. This office suggests expanding the proposed grading into the backyards instead of a wall to
allow for overland relief. Otherwise, please provide an access route to the inlet structure located at
the base of the proposed retaining wall for inspection and maintenance of the inlet.
8. VDOT approval required.
Engineering Review Comments
Page 2 of 5
9. Existing drainage areas do not appear correct and do not match the approved plan. Please revise
the drainage areas accordingly.
10. The jack/bore operation will require at least one staging area for equipment and a platform area
excavated and constructed prior to installation of the 72" pipe under Route 29 North and South
lanes. Please show the grading and E &SC measures required to install the pipe under Route 29.
11. Please provide an adequate channel study for the outflow of the 72" pipe.
12. Please show how the roof drains for the 7/11 food stop /gas station will be addressed.
13. Please show the anti - vortex design for the riser structures. [Std. & Spec. 3.14]
14. Basin calculations do not appear correct. Some of the spreadsheet appears to have been filled in
incorrectly. The basins appear too small for the drainage areas.
15. Baffles are required in the basins to acquire the 2:1 inlet to outlet ratio. Please show the baffles
per VESCH 3.14.
16. Safety fence is required to encompass both Temporary Sediment Basins with at least two signs
stating "Danger Quicksand" or "Hazardous Area — Keep Out ". The signs will be placed so that
anyone approaching the protected area can see them.
City of Charlottesville comments are provided as a courtesy.
In conclusion, Off -site areas will be approved sites for borrow and fill. Transportation of soils to and from
this site will be pre- approved prior to any transportation.
Additional comments may be generated due to the level of changes /corrections required by this review.
Half hour meetings to discuss the comments are available on Thursday afternoons. Please contact Mrs.
Amy Pflaum [ext. 3069] to arrange a meeting.
File: E1 ESC MRG Albemarle Place Town Center.doc
Engineering Review Comments
Page 3 of 5
Memorandum
Neighborhood Development Services
Office of the City Engineer
City Hall Annex, 610 East Market St., Charlottesville
To: Khadija Abdur - Rahman
From: Sujit Ekka
Date: September 8, 2008
Subject: Albemarle Place- Review of Amended Erosion and Sediment Control Plan
Please find the review comments on amended erosion and sediment control plan submitted by WW
Associates on August 14, 2008.
General Stormwater Comments:
Both Meadow Creek and a segment of Rivanna River downstream are listed as "impaired waters" by
Virginia DEQ. A stream restoration project for Meadow Creek by the City of Charlottesville is
slated to start soon.
One of the project's final stormwater discharge point (hereafter referred as "North Study Point ") is
across Route 29 into an existing Creek that is a tributary to Meadow Creek, which ultimately drains
into Rivanna River. A storm sewer system consisting of 60" pipes with a final section of 72 "pipe at
the outfall is proposed to carry the offsite stormwater through the site to the tributary. In addition, a
sediment basin is proposed onsite for grading and construction operations, which will discharge
through an existing 42 "City storm pipe into this tributary as well. The potential impact on this
tributary as well as Meadows Creek downstream can be huge if the post - development rate, volume,
and velocity are higher than the pre - development hydrologic conditions either during or after
construction.
Another point of discharge is across Route 29 through a City storm system (hereafter referred as
"South Study Point "). The storm sewer finally drains into Meadow Creek as well but the stormwater
goes through a city - maintained detention basin. This detention basin currently receives urban
stormwater runoff from highly urban areas in the Seminole sub - basin. The potential impact on this
detention basin as well as Meadows Creek downstream can be huge if the post - development rate,
volume, and velocity are higher than the pre - development hydrologic conditions either during or
after construction.
The stormwater management plan and ultimate development plans for the site are not included with
this submittal. In order to fully evaluate the impact of this development on City's waterways, it will
be critical to have the information on ultimate site conditions, pre - development hydrology, post -
development hydrology, and plans to mitigate any increase in stormwater runoff quantity and
quality. Please submit the information along with the plans.
Engineering Review Comments
Page 4 of 5
1. Please note that the demolition of existing weir and other hydraulic structures should be
accounted for in the pre -and post - development hydrologic routing calculations i.e. they
should be used when computing pre - developed runoff and not in post - developed
conditions.
2. Rational method will be okay for storm sewer computations only. However, if there is more
than 20 acres draining to an inlet then use TR -55 methodology to compute runoff. For
example, Ex. Str #90 draining to Str #10 has a drainage area of 20.17ac.
3. TR -55 method should be used for runoff calculations and routings when evaluating the
whole watershed scenario for both E &S and final stormwater management calculations and
plans.
4. Various channel cross - sections will be required to prove channel adequacy at the North and
South study points and further downstream for both during and after construction phases to
comply with the MS -19 requirements and protect City's waterways.
5. Water quality BMWs will be required onsite to prevent the impact of development on water
quality of the City's waterways.
Other comments are as follows:
6. Please indicate the timeline (start and end dates for the project) on the E &S narrative sheet.
7. How will the roof runoff from the building (7/11 store) on the corner of Route 29 and
Hydraulic Road get to the storm drain if the 15 "RCP and is demolished.
8. All construction entrances should have mandatory wash -rack to prevent any sediment from
getting onto nearby roads.
9. Please delineate the lay -down area on existing pavement for the contractor on the south side
clearly.
10. For both the north and south side of the site, it appears that a significant amount of
sediment will be generated due to grading and installation of North and South diversion
pipes. This sediment can potentially make its way through the existing channel and the
42 "pipes under Route 29 and create damage downstream. Please provide appropriate
perimeter control measures to avoid this situation.
11. The plans do not show the future development for which the site is being graded.
12. We could not locate the outlet structure for the "Commonwealth Pond" under
Commonwealth Dr. It appeared to be draining into a hole in the ground. Please advise how
you obtained the information on the size of the pipe.
13. Both North and South sediment basin calculations need to be revised using TR -55
methodology.
14. For embankment heights proposed for the sediment basins, a core - trench will be needed to
prevent wash -off of the embankment.
15. An anti -seep collar or filter diaphragm is highly recommended for the embankment.
16. Please show the elevations on the sediment basin details. In addition, provide a profile
through the sediment basin and the embankment.
17. It is not clear if it is proposed to replace the pipe after Ex. Structure# 89 or #90? The plans
and storm sewer computations do not agree. In addition, we could not locate the Ex.
Structure #86 on the plans that is shown on the storm sewer computations.
Engineering Review Comments
Page 5 of 5
18. The storm sewer calculations are incorrect for North diversion pipe. The flow from 15 -14 -8
(18cfs) is not accounted for in the final discharge.
19. The velocity for the runoff being discharged from the proposed 72 "pipe is too high to be
acceptable.
20. The runoff from different methods (rational and TR -55) cannot be added to obtain the 100 -
year design flow for sizing the North diversion pipe. They are two very different methods
based on totally different assumptions. We recommend using TR -55 for all sub -areas to add
the hydrograph.
21. Please provide hydraulic grade line computations and show them graphically in the storm
sewer profiles.
Please be advised that these comments are based on the current submission and future submissions
may generate additional comments. Let me know if you wish to discuss these or have any questions.
Thank you,
Sujit Ekka, EIT
Civil Engineer