HomeMy WebLinkAboutWPO200800091 Review Comments Stormwater Management Plan 2009-03-17� OF AL
,. vIRGI1`IZP
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 - 00091, SDP - 2008 - 00134; The Meadows Expansion
Plan preparer: Brian Smith, PE
Owner or rep.: Jordan Development Corporation
Plan received date: (Rev. 1) 06 February 2009
09 September 2008
Date of comments: (Rev. 1) 17 March 2009
21 October 2008
Reviewer: Phil Custer
The major site plan amendment, SWM, and ESC plans for The Meadows Expansion, submitted on
06 February 2009, have been reviewed. The plans cannot be approved as submitted and will
require the following changes:
A. General Review (SDP- 2008 - 00134)
1. To engineering review, there appear to be several discrepancies between this plan and the
approved rezoning plan. The discrepancies are listed below:
A. The rezoning plan states that biofilters will be used on site. No biofilters were provided in this
site plan amendment.
(Rev. 1) Planning has determined that biofilters are not needed for this plan.
B. The location, orientation, and parking of building 8 do not match.
(Rev. 1) Review from the Director of Planning is pending. His determination will be
forwarded to you once it has been made.
C. In the application plan, a yard was proposed between buildings 10 and 11. SWM facility 2 is
currently proposed in that location.
(Rev. 1) Planning has determined that SWM facility's location between buildings 10 and 11
was consistent with the rezoning plan.
D. SWM facility 3 has been placed in an area reserved for a future interparcel connection. This
facility should be relocated.
(Rev. 1) Comment has been addressed.
The Planning Department will need to determine whether the plan is consistent with the approved
rezoning plan. If it is found to be not in general accord with the plan, a determination must be
made by the Zoning Department whether these deviations from the approved ZMA plan can
possibly be approved through a variation by the Director of Planning.
2. Please provide the date of the topographic survey.
(Rev. 1) Comment has been addressed.
3. Please show the stream buffer lines on all applicable sheets.
(Rev. 1) Comment has been addressed.
4. VDOT approval is required. VDOT approval has not been received at this time. As indicated in
the rezoning plan, a left turn lane on northbound Crozet Avenue may be required.
(Rev. 1) VDOT approval has not yet been received by the County.
Engineering Review Comments
Page 2 of 5
B. Major Site Plan Amendment (SDP- 2008 - 00134)
1. Slopes steeper than 3:1 require a low maintenance, non - grassed groundcover.
(Rev. 1) Comment has not been addressed. The groundcover must be non - grass. For a list of
suitable groundcovers, please see Table 3.37C of the VESCH. Engineering review is open to
similar groundcovers not on the list proposed by the applicant.
2. Please show all necessary signage.
(Rev. 1) Please provide a stop sign at the five entrances onto the VDOT road and at the
travelway south of building 13. Please show the existing "Do Not Enter" and "One Way"
directional signs on this plan.
3. Concentrated discharge appears to be running across several sections of the walking path /sidewalk.
Engineering review recommends that the walking path be placed uphill of the outfalls for Basins 2
and 3 and a drop inlet to be added at the northern corner of building 20 to prevent direct
stormwater discharge across these pedestrian areas.
(Rev. 1) Comment has been addressed.
4. Please provide a channel from the existing culvert west of building 8 around the fill for the parking
lot.
(Rev. 1) Comment has been withdrawn.
5. It appears private sanitary sewer easements are needed for several laterals as they cross property
lines.
(Rev. 1) Comment has been addressed.
6. The plan is missing a few drainage easements. Drainage easements are necessary for pipes
carrying water from public ROW or adjacent parcels.
(Rev. 1) Comment has not been addressed. An easement is needed for the culvert west of
building 8 and for the drainage pipes that cross the property boundary between TMP 56 -14C1
and 56 -14C.
7. Please show all easements on the Landscape plans. At least one of the new drainage easements
will require the relocation of a proposed tree.
(Rev. 1) Drainage easements do not appear to be shown on the site plan though all trees appear
to be out of the easement. Please show the easements on the landscape plan.
8. All necessary easements must be recorded before the site plan can be approved.
(Rev. 1) Comment remains the same.
9. Please show sight distance lines for all entrances onto the public ROW.
(Rev. 1) Comment has been addressed.
10. Please provide a VDOT designation on the plan for each new entrance.
(Rev. 1) Please call out a specific VDOT standard for each entrance onto the VDOT road. (PE-
I looks appropriate to me, though please verify with VDOT.)
11. The minimum radius on an entrance to VDOT ROW is 12.5ft (VDOT's requirement may be
larger).
(Rev. 1) Please see the entrance to building 8.
12. Please provide a traffic generation summary for the site onto the existing public road.
(Rev. 1) Comment has been addressed.
13. Curbing is required in more areas than where it is currently shown on the plan. In all locations
where improvements are made, curbing is required. Curbing requirements can only be waived by
Current Development Engineering when pavement drains to Stormwater Management Facilities.
(Rev. 1) Comment has been addressed.
14. Please provide a VDOT designation for the endsections in the profiles.
(Rev. 1) Comment has been addressed.
15. Please specify the grate type for each DI -1.
(Rev. 1) Comment has been withdrawn
16. Concrete inlet shaping IS -1 is required on all structures with a 4ft or greater drop, including drops
Engineering Review Comments
Page 3 of 5
from surface level.
(Rev. 1) Comment has been addressed.
17. In the profiles, please label and dimension the outlet protection from each pipe system.
(Rev. 1) Comment has been addressed.
18. The profiles for 3 culverts are missing from the plan. Spot elevations for culvert inverts should
also be provided in plan view.
(Rev. 1) Comment has not been addressed.
19. Calculations for the culverts are required. Culverts must not have a head greater than 1.5 x
Diameter and the water level must be 18" below the shoulder elevation.
(Rev. 1) Comment has not been addressed.
20. The inlet drainage area map is missing watersheds for several existing and proposed structures and
channels. The text on the plan is also difficult to read.
(Rev. 1) The text has been made clearer however there are still a few structures without the
drainage areas delineated. The watershed for three new culverts and the existing culvert south
of build 8 should be shown.
21. For each watershed in the inlet drainage area map, please provide the average C -value and time of
concentration. [DM]
(Rev. 1) The average C -value for each watershed is not specified on DP -1.
C. Stormwater Management Plan Review (WPO- 2008 - 00091)
1. SWM facility 3 should be moved outside of the area reserved for interparcel connection.
(Rev. I) Comment has been addressed.
2. A copy of the Lickinghole Basin pro -rata share for the site will be calculated by County
Engineering once the plans are ready for approval.
(Rev. 1) Comment remains the same.
3. For each watershed in the SWM facility drainage area maps (both pre and post), please provide the
average hydrologic coefficient.
(Rev. 1) The watershed to facility 4 does not appear to be accurate. The culvert entering D -6
seems to have a watershed that is not considered.
4. During the review of the plan I've found the following discrepancies that should be corrected on
the next submittal:
A. The embankment details for Basin 1 and 2 specify widths of 8ft, but both embankments
are shown wider on the plan. All embankments are satisfactory as drawn in plan view.
(Rev. 1) The embankment for Basin 1 still does not match between the plan and detail.
B. The invert of the culvert in Basin 3 is mislabeled in the section detail.
(Rev. 1) Comment has been addressed.
C. The grading for Basin 2 does not appear to show an emergency spillway at elevation 633
as suggested in the embankment detail. It does not appear that a spillway is necessary for
this facility and the grading can remain as shown
(Rev. 1) Facility has been reconfigured and the comment does not apply.
D. A 664 contour line is labeled as 666 in Basin 3.
(Rev. 1) Comment has been addressed.
5. Please provide an overall detention compliance table for each facility.
(Rev. 1) Comment has been addressed.
6. The latest (July 2005) 24 hour rainfall totals for the 2, 10, and 100 years storms are 3.7in., 5.6in,
and 9.lin., respectively. Please update calculations.
(Rev. 1) Comment has been addressed.
7. Please raise the elevation of the incoming 15" pipes in storm lines E and D to the highest invert as
possible to limit the backing water into the smaller pipe.
(Rev. 1) Comment has been addressed.
Engineering Review Comments
Page 4 of 5
8. The SWM portion of the bond will be computed when the plans are ready for approval.
(Rev. 1) Comment remains the same.
9. Additional requirements may be necessary depending on the determinations of the Planning and
Zoning Departments regarding the biofilters shown on the approved rezoning plan. Please see
comment A. 1.A.
(Rev. 1) The planning department has determined that biofilters are not required.
(Rev. 1) Please show all downspout roofdrain pipes on the site plan sheets for buildings 10, 11,
and 12. The SWM plan assumes that the rear of these buildings drain to detention facilities
and this should be shown.
11. (Rev. 1) Please specify trash racks on the orifices in the underground detention facility.
(However, please see comment D1. This comment may not be necessary.)
12. (Rev. 1) Please provide a low flow channel in Basin 2 from the west end.
D. Erosion and Sediment Control Plan Review (WPO- 2008 - 00091)
1. Engineering review is concerned about the lack of adequate channels for all of the concentrated
discharge from pipes and channels. Please provide channel adequacy calculations or provide level
spreaders at each outfall. Each level spreader should be included inside either a SWM or drainage
easement depending on where the water is coming from.
(Rev. 1) Please move the level spreader of basin 2 farther east so it does not direct water onto
the trunks of existing trees. The level spreader for Basin 3 should be adjusted so the outfall is
perpendicular to the contour lines.
After further consideration of the existing conditions on a site visit, I do not think the use of
level spreaders at the outfall of basin 1 and the underground facility are appropriate. The use
of level spreaders assumes a well stabilized outfall and a low chance of reconcentration. In
both of these cases, the water would be directed into a treeline where tree trunks and root mats
would not allow uniform sheet flow. The water would also recollect immediately after outfall in
downstream gulleys /channels. Please provide a new graded channel from the outfall from the
site at Basins I and 4 to the perennial stream at the northern edge of the property. The channel
should be sized and armored accordingly. Engineering review will grant a detention waiver for
these drainage areas (Basins 1 and 4) due to the large watershed of Slabtown Branch. A public
drainage easement should be provided for the channel along Crozet Avenue because it will
carry VDOT water.
In addition, the swale at trap 1 should remain a graded trapezoidal channel until it intersects
the constructed channel from Basin 1.
2. A sediment trap appears to be necessary at the end of the reconstructed channel (west of the two
15" cedar trees) between buildings 8 and 9. A fill diversion should be extended to the west to
direct all runoff for the area around building 8 to this trap.
(Rev. 1) Sediment traps must have I foot from the top of dam to the crest of the stone weir.
Please also show the stone weir in plan view.
3. The elevation of the dam in sediment trap 1 should be lft above the crest elevation of the weir.
Engineering review recommends that a culvert inlet sediment trap be used in this location so
minimal earthwork is required when converting from ESC to SWM in the final stage of
construction. Please see VESCH standard 3.08 for CIP -ST requirements.
(Rev. 1) In the first phase of construction, facility I should be built and the culvert should be
protected as a CIP- sediment trap ( VESCH Plate 3.08 -2). There is no need to construct
sediment trap 2 and then construct the culvert inlet protection sediment trap. (However, please
see comment DI. This comment may not be necessary.)
Engineering Review Comments
Page 5 of 5
4. Not all land disturbances have been included in the limits of construction. For instance, the
waterline across Meadows Drive is not shown within the limits of construction.
(Rev. 1) Comment has not been addressed.
5. Please place a construction entrance near building 20. The gravel base of the parking lot can be
used as a construction entrance during the earthwork operations as long as it meets the minimum
dimensions for a CE.
(Rev. 1) Comment has been addressed.
6. The existing soil boundaries on the plan are confusing. Please clarify or provide a smaller map
detail on another sheet.
(Rev. 1) Comment has been addressed.
7. Please provide a staging and parking area on the plan. The parking spaces and areas adjacent to
each building could be used as parking and staging areas.
(Rev. 1) Comment has been addressed.
8. Four hundred feet of additional silt fence is needed on sheet SS -1 for the construction of the
sanitary sewer line.
(Rev. I) Comment has been addressed.
9. Silt fence is needed downhill of the private sanitary sewer line on sheet ESC -3.
(Rev. 1) Comment has not been addressed. The sanitary line North of the community center
needs ESC measures.
10. The ESC portion of the bond will be computed when the plans are ready for approval.
(Rev. 1) Comment remains the same.
11. (Rev. 1) On sheet ESC -4, please provide a note adjacent to Basin 2 stating that Basin 2 must be
fully constructed and the CIP installed before any other construction south of Meadows Dr. can
begin.
File: E2_fmj esc swm _PBC_WP0200800091_SDP200800134 Meadows Expansion.doc