HomeMy WebLinkAboutWPO200900025 Review Comments Erosion Control Plan 2009-06-09� 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 County Vehicle Maintenance Facility - Major Amendment.
Plan preparer: Timmons Group [fax 295 -8317]
Owner or rep.: County of Albemarle [fax 975 -9341]
Plan received date: 26 May 2009
Date of comments: 5 June 2009
Reviewer: Max Greene
The plans for Albemarle County Vehicle Maintenance Facility - Major Amendment submitted on
26 May 2009 have received Engineering review. The plans may be approved after the following
items from the Albemarle County Design Manual Check list have been adequately addressed:
A. Site and drainage plans (SDP200900044)
1. Existing site conditions requires the following information added:
a. Date and source of the topographic information: All topography should be at least
visually field verified by the designer within the last year [18- 32.6.6, 14 -302,
Policy for date]
b. Benchmark location, elevation and datum for topography. An existing utility or
other known position will suffice. [Policy]
2. Please have all edges of existing and proposed pavement labeled (where there is no
curbing)
3. Labels on all drainage structures provided (and should match the drainage computations
and profiles)
4. Please include typical sections for proposed channels with locations referenced from the
plan view sheets.
5. Drainage profiles: (applicable to site plans, road and drainage plans) [14 -311, 18 -32]
drainage profiles for each pipe, structure or channel must contain:
a. existing ground
b. proposed ground
c. any channel linings
d. a label on each structure to correspond with the computations
e. material and strength class or gage of each pipe
f. pipe slopes at 0.5% min. to 16% max. (per VDOT stnds for anchors over 16 %)
g. all invert elevations for each structure (with positive flow drop between inverts).
h. scour outlet protection at all outlets, corresponding to computations
i. There are no excessive outlet velocities (> 15fps)
j. All proposed systems are designed within open channel full flow capacities.
k. ditch linings specified per plans meet velocity requirements
1. headwaters < 1.5 x culvert height, and 18" below shoulder elevation of streets.
m. dimensions and stone sizes for all outfalls
n. limits of all areas and sub -areas draining to proposed structures, and existing
structures or channels which will be impacted
Engineering Review Comments
Page 2 of 3
o. acreage of each drainage area as used in computations
p. hydrologic coefficient for each drainage area as used in the computations
q. time of concentration for each drainage area as used in the computations
r. destination structure labeled for each drainage area
B. Stormwater Management and Mitigation Plan (WPO200900025)
1. Cross - section details of each facility including;
a. embankments (between 3 and 25 ft in height)
b. top width 8ft min., 10' for heights 15' to 20', 12' for dams over 20', heights
measured from the outside toe
c. upstream face slope 2:1 or flatter, labeled
d. downstream slope 3:1 or flatter, labeled
e. 10yr and 100yr high water elevations labeled with 1 ft freeboard for 100yr storm
with emergency spillway or 2 ft freeboard without emergency spillway
f. an impervious core
g. a cutoff trench of minimum 4' wide, 4' deep and 1:1 sloped sides
h. principle spillway
i. riser crest l' below emergency spillway if present
j. riser crest stays within weir flow control during the 10yr storm
k. trash racks over all inlets and controls to prevent clogging
1. trash rack over riser crest is not flat (no DI-Ts)
m. riser size and materials labeled
n. barrel size, strength, material, inverts and slope labeled
o. all orifices, weirs or other control devices labeled with dimensions and inverts
p. control orifices not more than 25% of riser perimeter at any point (does not affect
riser structural integrity, 25% is a target)
q. riser base size and dimensions labeled
r. access to riser is provided (riser should be in dam, not free - standing)
s. emergency spillway dimensioned and labeled
t. invert labeled
u. dimensions in control section
v. dimensions in channel section provided if different than control section
w. linings labeled and shown where applicable
x. spillway over native soils, and/or sufficient armoring provided
y. sediment forebays provided for all retention basins, constructed wetlands, and
basin biofilters at all inlets
z. sized to 0.25" of runoff per impervious acre (can be included in WQV)
aa. direct vehicle access provided
i. access graded to 10' width and less than 20% grade
ii. minimum 10' wide permanent easement over access
iii. Albemarle County
iv. gravel surface or better for grades over 10%
2. Please provide as -built data for existing pond and drainage structure and facilities
3. Existing ponds and drainage structures and facilities will be brought up to current
standards.
C. Erosion Control Plan (WPO200900025)
Narrative:
1. Please state the acres to be disturbed in the narrative. Even though no fee is being charged
the County is required to keep a total acreage of annual disturbed area.
Engineering Review Comments
Page 3 of 3
2. Existing site conditions will follow the State Erosion and Sediment Control Handbook
requirements for descriptions. [VESCH page VI -2 and VI -24] The existing basin has
major erosion that will need to be repaired with this plan.
3. Please provide a soils description in the narrative and show the soil boundaries on the plan
sheet.
4. Stormwater runoff consideration appears to be missing from the narrative.
5. Sediment basin "design computations" are missing from the narrative.
6. The existing basin is in bad repair and has significant erosion from the existing outlet
structure. MS -19 analysis is required.
Plan sheet:
1. Show dust control symbol (DC).
2. Show Temporary Seeding (TC).
3. Show Permanent Seeding (PS).
4. Show existing soils boundaries.
5. Basin construction details are required.
Once these comments have been addressed, please submit 2 copies of the revised plans, calculations, and
narratives to Current Development Engineering. Due to the required additions and information required,
additional comments and/or corrections may be required.
Current Development Engineering is available from 2:30 -4 PM on Thursdays to discuss these review
comments. Please contact Max Greene at 434 - 296 -5832 ext. 3283 or email mareene @albemarle.oriz to
schedule an appointment.
File: CDE1_esc,swm,fsp_MRG_Albemarle County Vehicle Maintenance Facility - Major Amendment.doc.doc