HomeMy WebLinkAboutSDP200500133 Review Comments 2006-02-21pg ALp
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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: Peter Jefferson Place 6 & 7
Plan preparer: Jordan Consulting Engineers [fax 272 -7088]
Owner or rep.: Worrell Land & Development Company [fax 977 -6578]
Plan received date: 29 Nov 2005
Date of comments: 6 Jan 2006
Reviewer: Glenn Brooks
A. Final site plan (SDP200500133)
1. VDOT approval is required. [DM905]
2. Phase 2, shown in dashed lines on the plan, has not been reviewed in full with these phase 1 plans.
3. The plan topography must be updated to meet the accuracy standards of 18- 32.6.6h. The existing
condition appears to be different than shown.
4. If a subdivision is to occur in the future, the subdivision ordinance will require that the road serving the
two or more parcels be a private road [14 -233]. If this is the case, separate road plans will be required.
The standard will be according to 14 -412B.
5. The travelway and parking in front of the building does not appear to meet the minimum required
dimensions. A 24' wide aisle is required, and the plan measures 20' to 23'.
6. Please provide end sections (ES -1) and scour protection (EC -1) on all pipe outlets. [DSM909.1B,
505C6, 505D13]
7. Please use inlet shaping (IS -1) rather than rip -rap in the manholes. [DSM505E9]
8. Please provide more complete information in the drainage computations, and correct errors.
[DSM909.IA, 505G]
a. Please enlarge or clarify the drainage area map. It is too small to be clearly legible.
b. The spread computations appear to use incorrect hydrology taken from the pipe computations. Please
use the VDOT standard intensities of 4 and 6.5, and reference any carryover.
c. The spread computations appear to use incorrect slopes, and arrive at incorrect results, and do not
contain the information for gutter (compound sections). The Visual Urban program is recommended,
available for free from FHWA.
d. The stationing in the spread computation table is meant for stationing along the road or travel lane.
Providing stationing along the pipe profiles does not appear to serve any purpose.
d. In the pipe computations, the flow values do not appear to be correct.
e. Please reference additive areas in the pipe computations. Not all of the computations could be
followed.
f. The hydraulic grade -line computations are unnecessary. All design should be within open channel
flow capacities.
B. Stormwater Management Plan (WP0200500100)
1. Please provide copies of any state and federal permits. [17- 303B &C, DSM WRA, MS -14]
2. The removal rate computations appear to be preliminary computations for the entire site, rather than final
computations for each facility. The removal rates for these facilities are around 65 %. A sample
computation is included below for basin 1:
Engineering Review Comments
Page 2 of 3
Albemarle County Water Protection Ordinance BMP computation
Design Manual pages 5 -33, section 503.2C
project drainage area; A = 6 acres
impervious area fraction before; Ipre = 0.20 (min. 20% in develpment area)
impervious area fraction after; Ipost = 0.65
water quality volume; A *Ipost *(0.5/12) *(43560/27) _ _262.17 cy
pollutant concentration; C = 0.7 (0.35 resevoir wshed, 0.4 rural, 0.7 dev area)
pollutant export before; Lpre = 8.77 *(0.05 +0.9 *Ipre) *C *A
pollutant export after; Lpost = 8.77 *(0.05 +0.9 *Ipost) *C *A
f = 1.0 (see DM p. 5 -39; for dev area where Ipre > 20% use 0.9)
REMOVAL REQUIREMENT; (Lpost- f *Lpre) *100 / Lpost = 63.8
2. Enhanced extended detention basins (VSMH Min. Stnd. 3.07) to provide 50% removal rates must have
forebays, shelves, and plantings.
3. The filteras are not evident on the plan. Please provide labels, drainage areas, sizes, details, etc.
4. Please provide vehicle access to facilities per DSM909.2A and DSM503.ID.
5. Please provide easements over facilities and access per DSM909.2A, 503.1C and 1101.
6. A facilities maintenance agreement must be recorded prior to approval. [ 17 -323, DSM909.2B]
7. Designs details must be dimensioned, with structure sizes, inverts, grades, slopes, etc.
8. Designs must meet Virginia Stormwater Management Handbook minimum standards. This will depend
on the standards selected per comment 2. Please include planting plans and details for the facilities.
[DSM503.1 ]
9. Please provide complete plan views for each facility. Basin 2 is not shown in its entirety on the grading
plans.
10. Regarding the detention computations:
a. Please provide drainage area maps for pre- and post - hydrology.
b. Please provide enough information in the routings to verify detention times and peaks, basin
geometry, structure information, and hydrology. Please provide a summary of compliance with
Water Protection Ordinance section 17 -314.
c. The detention volume computations were not understood. It appears the modified rational method
manual approach to preliminary basin sizing was used, but the routings refer to a 12hr (not 24hr)
SCS dimensionless hydrograph input. For a final design, the routing demonstration should be used.
d. The water quality volume computations were not understood. Water quality volume should be 0.5"
over impervious areas, or a sizing method referenced in the VSMH.
11. More comments may be necessary when designs are more final and complete information is provided.
The stormwater management computations and details provide with this submittal appear to be only
preliminary. A complete review of stormwater management was not possible, and further review will be
necessary when complete final plans and computations are provided.
C. Erosion Control Plan (WP0200500100)
1. Please update topography per comment A3. Please indicate what erosion control features are already in
place and will remain, or be removed or modified.
2. Erosion control measures cannot be in the way of construction activities.
a. The diversion dykes shown on sheet 4 are in the way of access and filling. It appears these must be
removed, and the basins sized accordingly. The silt trap should be converted to a basin.
b. The diversion dyke on top of the fill slope is in the way of filling activities. This diversion can only
be placed when construction is complete. When the silt trap is redesigned to a basin this dyke should
not be necessary.
3. Please complete all items from the state checklist. Please organize the elements on sheet 3 into an erosion
control narrative according to the state checklist. Missing items are;
a. Existing site conditions per comment 1.
Engineering Review Comments
Page 3 of 3
b. Adjacent areas.
c. Off -site areas.
4. Missing items from the state checklist with regard to the plan are;
a. Existing contours and vegetation per comment 1.
b. Soil boundaries.
c. Drainage patterns. The plan refers to different areas that are not all shown.
d. Off -site areas. The plan and narrative should indicate off -site borrow areas, or stock pile or staging
areas.
5. Concentrated runoff from the finished parking lot must be addressed with an adequate channel. The
current concept of discharging over the newly created fill will create a gulley. [MS -8]
6. Please provide outlet protection at all pipe outlets. [MS -11]
7. Please provide dust control (DC), temporary seeding (TS) and permanent seeding (PS) on the plan sheets.
8. The geometry of basin 1 does not appear to be workable from a practical standpoint. It will operate as
two basins, one discharging into the other, and the channel connecting the two will likely fill with
sediment.
9. Please provide scaled details where dimensions are close. The riser bottom is above the basin floor in the
current detail for basin 1.
10. Please provide dimensions on the plan views for basin length and width so the inspectors can reasonably
check sizes in the field.
11. Please ensure the structures are the same as will be used in the permanent BMP facilities, to avoid
rebuilding the dams and basins.
12. Trapping and diversion measures must be installed as a first step. [MS -4] Basin 1 cannot be installed as
shown until the storm drainage system in place. An alternative outlet and emergency spillway would be
necessary until the storm drainage system is in place.
13. Regarding the basin computations;
a. Basin 2 appears to be larger than required for erosion control.
b. Computations for basin 1 and the other trap /basin could not be reviewed at this time due to
anticipated changes.
The engineering group in Current Development is available for meetings regarding comments for plans under
review every Thursday from 2 -4 in Room 214 of the County office building. Please call 296- 5832x3273 if
you would like to reserve a time.
File: E1_fsp,esc,swm GEB PJP6 &7.doc