HomeMy WebLinkAboutWPO200900050 Review Comments Stormwater Management Plan 2009-12-11ALg�,��
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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: South Plains Presbyterian Church; WPO- 2009 - 00050; SDP - 2009 -00080
Plan preparer: Mr. Bill Atwood; Atwood Architects
Ms. Ashley Cooper; Cooper Planning
Mr. Clark Gathwright; Daggett and Griggs Architects
Owner or rep.: South Plains Presbyterian Church
Date received: 23 September 2009
(Rev. 1) 25 November 2009
Date of Comment: 13 October 2009
(Rev. 1) 11 December 2009
Engineer: Phil Custer
The second submittal of the final site, ESC, and SWM plan for South Plains Presbyterian Church has been
reviewed. The following comments are provided.
A. SDP - 2009 -00080 Final Site Plan Comments
�. — &- ieering review recomme..u, L..a< «.,; parking lot along Black Cat Road be modified to provide
for one VDOT standard entrance. This is not a requirement due to a determination from the Chief
of Current Development.
(Rev. 1) Comment has been noted by the applicant.
2. Please modify the grading in the western portion of the courtyard /garden so that the topography
works with the raingarden/biofilter.
(Rev. 1) Comment has been addressed.
3. Please provide a detail for the sidewalk that meets or exceeds the county's requirement of 4" of
3000psi concrete @ 28days and 4" of stone base beneath. [DM]
(Rev. 1) Comment has been addressed.
B. WPO- 2009 -00050 Stormwater Management Plan Comments
1. A SWM facility maintenance agreement will need to be recorded before the site plan can be
approved. Please submit this document with $17 fee directly to Ana Kilmer after consulting the
guidelines available on the county website.
(Rev. 1) The agreement has been received and is currently being processed.
2. Please provide a modified simple removal rate spreadsheet for each drainage area/facility, not the
whole site, which corresponds to drainage area lines drawn on the plan. This is necessary to
confirm that each facility is sized appropriately for the watershed draining to it.
(Rev. 1) Using the information given in the existing plans, I have generated a modified simple
spreadsheet for each BMP (please see the documents accompanying this comment letter). Both
facilities require a 65% removal rate. To achieve a 65% removal rate, the infiltration trench
must store 512cf (]"over specified impervious area). The biofilter bed is sized appropriately to
achieve a 65% removal rate using the state's 5% of the impervious area guidelines. However,
this method assumes that the depth of the biofilter ponding is ]ft. Please provide ]ft of ponding
or double the size of the facility.
3. Please provide two permeability tests for the infiltration trench. The VMSH specifies that the in-
situ permeability tests must yield infiltration rates greater that 0.52" per hour in order to consider
infiltration facilities practical. The VSMH also states that the infiltration facility must drain in
48hours and the soil test must clearly show this. [VSMH 3.10]
(Rev. 1) Comment has not been addressed. The infiltration tests must be provided before plan
approval because the results will dictate the geometry of the facility. The maximum depth
equation that should be used for the infiltration facility should be 3.10 -5 from the VSMH,
where fd is half the measured infiltration rate (which must be greater than 0.52 in /hr). For
example, assuming an infiltration rate of 0.52 in/hr is found on site, the maximum depth of the
facility will be 31.2 inches which would require the footprint to be noticeably larger.
If soil tests are not performed at this time, please design this facility as a biofilter now. Then, if
during construction tests find the soil to be within the adequate range for infiltration practices,
you may submit a SWM amendment for the installation of an infiltration trench.
4. On the infiltration trench detail, please specify that the depth is 3ft minimum, the bottom of the
trench is flat, and the #57 gravel is clean- washed.
(Rev. 1) Comment has been addressed.
5. Engineering review recommends removing the filter fabric from the infiltration trench and
biofilter. Depending on the type used, the fabric could wind up being the limiting factor in both
facilities. If the filter fabric is removed from the biofilter, it should be replaced with a 4" layer of
pea gravel. If the filter fabric is to remain in the plan, I recommend specifying the product
number. This is not a requirement.
(Rev. 1) Comment has been noted by the applicant.
6. The following modifications are required to the biofilter /rain garden detail:
a. The depth of the biofilter mix must be 2.5ft.
b. The thickness of the gravel layer must be between 12" and 18 ".
c. The soil media must be called out as state approved mix.
(Rev. 1) Comment has not been addressed. Remove the specification of Luckstone Mix.
7. Please provide a planting plan for the biofilter. There must be at least three species of shrub
proposed.
(Rev. 1) Comment has been addressed.
8. Please provide the following note on sheets C1.1 and C3.1:
When the stormwater management plan for Phase H is submitted, detention and stormwater
quality computations will need to consider the pre- development condition as the property before
the construction of the fellowship hall.
(Rev. 1) Comment has been addressed.
9. A SWM bond will be computed once the WPO plan is ready for approval.
(Rev. 1) Comment remains unchanged.
C. WPO- 2009 -00050 Erosion and Sediment Control Plan Comments
1. Please add to the set the County's standard ESC notes. These notes can be found in the design
manual, available online.
(Rev. 1) Comment has been addressed.
2. The limits of construction areas should be connected.
(Rev. 1) The plan no longer shows two isolated areas of disturbance.
3. Please add Dust Control (DC) to the plan.
(Rev. 1) Comment has been addressed.
4. Please provide silt fence on the north side from the treeline of the 9" spruce to the midpoint
between the 9" Holly and the 9" Dogwood.
(Rev. 1) Comment has been addressed.
5. Tree protection is being shown throughout the site but the tree layer has been turned off. Please
show the dripline of all trees on the ESC plan. Construction cannot be shown within the dripline
of trees required to be protected. This rule appears to have been violated in the garden /courtyard
and adjacent to the fill area. To rectify this, the grading of the courtyard can be modified to keep
fill out of the dripline of the cherry and dogwood trees or tree wells can be provided. Regarding
the fill area, I recommend moving it to the northern border because fill will likely be necessary to
construct the parking lot in Phase II at the minimum parking lot grade of 5%. (The area of fill was
also shown outside the limits of work on the approved SP plan and may require a determination
from the Zoning Administrator if the applicant wishes to continue to propose fill in this location.)
Please remove grading from within the dripline of 12" Holly. Also, please move the infiltration
trench to the south as much as possible out of the roots of the 27" Gum.
For all other areas showing the limits of construction within the dripline of tree, please provide a
letter from a certified arborist attesting that the latest revision of the site/ESC plan would not
compromise the health of any tree shown with construction within its dripline.
(Rev. 1) Please show all driplines on the Erosion and Sediment control plan. The letter from
the certified arborist is acceptable. If damage to any tree shown as being protected in the
approved SP plan is suffered, a zoning violation will be pursued.
6. Please demonstrate that this development meets VESCH Minimum Standard 19 regarding
adequate channels.
(Rev. 1) MS -19 requirements apply to the outfall from the culvert to the stream. MS -19
regulates downstream channels, which doesn't necessarily mean offsite drainways. However,
after the drainage area to this culvert has been graphically demonstrated by the applicant, the
county with withdraw this comment because of the low peak discharges if outlet protection is
specified on the plan. The length, width, and stone size of the outlet protection should be called
out on the plan. MS -19 will be a larger concern in Phase H of this project.
7. An ESC bond will be computed once the WPO plan is ready for approval.
(Rev. 1) Comment remains unchanged.
8. (Rev. ])The construction sequence on the cover sheet refers to an area on the plan where waste
from the foundation excavation will be placed. However, I could not find its location in either
the site plan or ESC sets. It appears that this notation should be removed because it conflicts
with the direction given to the contractor in the narrative.
File: E1_fsp swra esc_PBC_wpo0900050- sdp0900080 South Plains Presbyterian. doc