HomeMy WebLinkAboutSDP200500071 Review Comments Final Site Plan and Comps. 2005-12-06 y }
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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: Crossroads Waldorf School—Crozet(on Rio Road)
Plan preparer: McKee/Carson (fax 977-1194)
Owner or rep.: Betsy Ayyildiz, Crossroads Waldorf School, Inc. (fax 293-6470)
Date received: 06 December 2005
Date of Comment: 09 January 2005
Lead Engineer: Max Greene
Project Numbers: SDP200500071,WP0200500049
The site development plans for Crossroads Waldorf School—Crozet(on Rio Road)
received on 31 October 2005 have been reviewed. The engineering review for current
development recommends approval of the plans:
A. Site plan comments:
1. Previous site plan comments appear to have been adequately addressed.
B. Stormwater management plan comments:
2. Previous site plan comments appear to have been adequately addressed.
3. The Title pages has been corrected to state"Water Protection Plan."
4. Stormwater portion of the Water Protection bond is $21,000.00 and will become a part of
the whole Water Protection Bond amount.
5. A Stormwater Management Facilities Maintenance Agreement is required. Please submit
the latest version, dated August 1999, typed and signed in black ink by the owner, along
with the $16 recordation fee. Note: The plan cannot be approved until the Maintenance
Agreement has been received, approved and recorded.
C. Erosion and sediment control plan comments:
6. The Erosion and Sediment Control Plan was basically complete and has been approved
with the following minor changes made to the 4 copies submitted:
a. Title pages are now corrected to state"Erosion and Sediment Control Plan."
b. A modified mud trap has been added to the lower right corner of the plan sheet for
the stabilization of the reconstructed SCC.
c. Inlet protection was added to the pipe under the temporary construction entrance.
d. Storm Pipes have been labeled for size and length.
e. Proposed contours have been connected across the entry drive and parking area.
f. Diversion along entry road, lower area of plan sheet, has been properly labeled.
7. The Erosion and Sediment Control portion of the Water Protection Bond is $30,000.00
and will become a part of the whole Water Protection Bond amount. Please contact Pam
Shifflett for bondii .thformation. `d
A grading permit may be issued after items B & C above have been addressed.
Copy: file
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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
15
Project: Crossroads Waldorf School—Crozet(on Rio Road) I 0
Plan preparers McKee/Carson (fax 977-1194)
Owner or rep.: Betsy Ayyildiz, Crossroads Waldorf School, Inc. (fax 293-6470)
Date received: 31 October 2005
Date of Comment: 18 November 2005
Lead Engineer: Max Greene
Project Numbers: SDP200500071, WP0200500049
The site development plans for Crossroads Waldorf School—Crozet(on Rio Road)received on 31
October 2005 have been reviewed. The engineering review for current development cannot
recommend approval of the plans due to the following deficiencies:
A. Site plan comments:
1. Previous site plan comments appear to have been adequately addressed, with exception to
the mowed path through the SWM basin and across the drop inlet. Foot traffic is not
recommended through the SWM basin due to possible hazards to public and compaction
of the filter medium.
B. Stormwater management plan comments:
2. As mentioned previously, inlet structure#2 as submitted is a special order 15"riser with a DI-1
top grate into a 15"barrel pipe if constructible will be an expensive special order item. This office
recommends removing the 15"riser requirement and utilizing a standard DI-1 with a 15"barrel
outlet.
3. A Stormwater Management Facilities Maintenance Agreement is required. Please submit the latest
version, dated August 1999, typed and signed in black ink by the owner, along with the$16
recordation fee. Note: The plan cannot be approved until the Maintenance Agreement has been
received, approved and recorded.
C. Erosion and sediment control plan comments:
4. Sediment trap design does not meet the minimum requirements set forth in VESCH, Std. & Spec.
3.13, Sediment Trap. The wet storage(when excavated) is allowed a 1:1 slope, but the dry storage
will be a maximum 2:1 slope.
5. Sediment trapping measures will be designed for pre-, during, and post-development drainage
areas(which ever is the larger)in order to protect the site from the initial ground breaking to the
final site stabilization. Traps appear designed for the post development area and appear
undersized for the pre and during stages of development.
a. Pre-and during construction drainage area for sediment trap#1 appears to be @ 2 acres
instead of 1.5 acres.
b. Bio-filter#3 could be utilized for sediment control and the diversion removed for that
drainage area now leading into sediment trap#1.
c. Sediment trap 4 drainage area appears to be @ .6 acres du ng construction until the road
fill is completed.
6. All proposed grading will be shown within the disturbed area limits. For example: the grading
proposed above the clean water diversion adjacent to the existing parking area will be included
within the limits of disturbance.
7. Please be forewarned trees with proposed grading shown within or near the actual trip line are not
guaranteed protected from construction.
8. The proposed water and sanitary sewer lines are still shown within the proposed no disturb area.
9. Storm drain inlet#5 appears to be a semi permanent installation. During our last meeting,this
office recommended a much less expensive alternative-Temporary Slope Drain(Std. & Spec,
3.15). Either way, inlets will require contour shaping as described in Std. & Spec. 3.15, and
protected in accordance with Std. & Spec 3.08, Culvert Inlet Protection,and the diversions will be
designed as set forth in Std. & Spec. 3.12, Diversion.
10. The outlet elevation from storm drain#5 is stated in the narrative as 454. This elevation is 9 feet
above inlet#2 (Proposed elevation 445)and will require correction in either the plans or the
narrative.
11. A contour elevation 446 is missing around inlet#2 on sheet 4 of 15.
12. The previously approved Phase One Site Plan required a permanent Stormwater Conveyance
Channel(Std. & Spec. 3.17)as depicted on the existing topography to reduce the drainage area to
the basin. Any increase in drainage area requires the basin be reconstructed to handle the new
drainage area. With this in mind,this office recommends two options:
a. Reconstruct the basin for the new drainage area,utilize it for sediment control, and convert
to permanent SWM structure as in phase 1 eliminating the need for traps#2 and#3 and
their conversions resulting in a larger open space for the school.
b. Shorten pipe length from inlet#2, and outlet into the existing Stormwater Conveyance
Channel; leaving the existing basin to protect phase 1. Additional scour protection will be
required to reinforce the existing SCC in the area of the outlet and MS-19 will need to be
adequately addressed per VESCL.
13. The proposed diversion on the northern portion of the project does not appear to work until after
completion of grading in the area of the existing parking and construction entrance. Please address
the drainage problem created by the diversion across the SCC and existing pavement.
Due to required changes/corrections, additional comments and or conditions may be forthcoming.
Items B and C need to be completed before a grading permit can be issued for this project.
Copy: file
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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: Crossroads Waldorf School,phases 2a& lb
Plan preparer: McKee/Carson [fax 977-1194]
Owner or rep.: Betsy Ayyildiz, Crossroads Waldorf School, Inc. [fax 293-6470]
Plan received date: 15 Sep 2005
Date of comments: 18 Oct 2005
Reviewer: Mark Chambers
A. Final Site Plan (SDP200500071)
1. Proposed grading on the north side of the building does not provide adequate relief to
ensure complete drainage. Please re-consider proposed grading on the north side of the
building.
2. Please clearly label the limits of the access easement for future connection to parcel 61 —
172A.
3. Please route the pedestrian path around the periphery of bio-filter#3.
B. Stormwater Management Plan (WPO200500049)
1. Runoff from the parking areas where it concentrates between bumper blocks will cause
erosion that will foul the bio-filter soil media with sediment. Please show EC-2 matting
on the island between the parking areas and from the edge of the lower parking area to the
top of the bio-retention soil mix.
2. Pleases specify schedule 40 PVC for the under drain pipes on the bio-retention filter
details (DSM503.1.f.6).
3. Please replace the word"sand"with"soil mix" adjacent to the soil mix strata on bio-filter
detail G(DSM503.1.f.5).
4. The 15"riser to 15"barrel pipe connection in the bio-filter#3 will be difficult to
construct. Please use a VDOT standard DI-1 or DI-7 as the riser structure (DSM505).
5. A Stormwater Management Facilities Maintenance Agreement is required. Please submit
the latest version, dated August 1999, typed and signed in black ink by the owner, along
with the $16 recordation fee. Note: The plan cannot be approved until the Maintenance
Agreement has been received, approved and recorded.
C.Erosion Control Plan(WPO200500049)
1. The diversion dikes associated with sediment trap No. 1 do not provide positive drainage
toward the trap. (See dike north of trap that parallels 464 contour for 140' and dike south
of trap crossing 464 contour twice). Please reconfigure the diversion dikes and the
sediment trap as necessary to correct this condition (VESCH Std. & Spec 3.09).
2. The plan has the following deficiencies related to the clean water diversion(DD-1)that
must be addressed. We believe these deficiencies can be best addressed with a sediment
basin similar to the one shown on the previous submittal:
Siste '401.0
Engineering Review Comments
Page 2 of 2
a. Sediment trap #3 is undersized for the drainage area it is receiving (VESCH
3.13);
b. Disturbed area related to water and sanitary sewer installation inside the
boundaries of DD-1 does not drain to a sediment trapping device;
c. Disturbed area related to the installation of storm structure#3 and construction
of the entry road over storm structure#3 does not drain to a sediment trapping
device;
d. The area within the inner boundaries of DD-1 will likely be used as a staging
area and therefore will need to drain to a sediment trapping device;
e. The silt fence on the south side of the entry drive is running parallel with the
direction of runoff and therefore will not function as a sediment trapping
measure. Silt fence must run perpendicular to the direction of flow to provied
storage for sediment to accumulate.
Following are our comments regarding the sediment basin on the previous submittal:
3. Please provide the minimum bottom dimensions of the sediment basin (VESCH p.I11-
79);
4. Please provide a detail of the sediment basin outlet structure with the following
elevations and dimensions labeled (VESCH STD & SPEC 3.14);
a. Upstream and downstream invert of barrel pipe.
b. Diameter of barrel pipe.
c. Invert elevation and diameter of de-watering orifice.
d. Riser crest elevation and diameter.
e. Anti-vortex diameter.
f. Top of embankment elevation and width.
g. Emergency spillway cross section with dimensions, elevation and lining
provided.
5. Please provide a diversion dike north east of the sediment basin as necessary to direct
sediment laden runoff to the basin.
D.Requested waiver of Curb and Gutter requirement
The requested waiver of the requirement for curb and gutter along the entry drive is
granted.
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McKEE CARSON
CONSULTING ENGINEERS
LANDSCAPE ARCHITECTS
LAND PLANNERS
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13 September 2005 k�
Mr. Francis MacCall
SEP 1 2005
Senior Planner
Department of Planning and Community Development
County of Albemarle
Charlottesville, VA 22902
RE: SDP-2005-071 Crossroads Waldorf School Phase 1B&2A Final Site Plan.
Dear Mr. Francis MacCall:
Pursuant to your letter dated July 21, 2005, this memorandum addresses the comments pertaining to
the final approval for the subject property. Our responses are listed in order and concur with the
numbering system, which was employed in your comments.
Response to Comments from Francis MacCall, Planner:
1. Duly noted.
2. Special Use Permit Easement is denoted by a hatch. See Sheet 3-Existing Conditions.
Proposed pathway extended to Village square property. See Sheet 5-Layout Plan.
Greenway dedication is denoted by a hatch. See Sheet 2-Master Plan.
3. A signed conservation plan is submitted along with the site plan application. All items in the
checklist are listed on the sheet. See Sheet 7-Landscape Plan.
4. Duly noted. See Sheet 7-Landscape Plan.
5. Old TMP numbers have been removed. See Sheet 2-Master Plan.
6. A letter requesting the proposed number of parking spaces has been submitted to the zoning
administrator along with a Parking study. The letter is attached.
7. Overflow parking spaces are not required based on the parking study. They are replaced by a
basket ball court. See Sheet 5-Layout Plan.
8. A new sheet cannot be produced showing that the luminaires are full-cut off, since the general
description shown on the cut sheet is a standard description provided by the company, but does
not apply to all projects. Hence, notes have been added to the photometric plan that all fixtures
will be full-cutoff. See Sheet 8 Lighting and Photometric plan.
Affiliated with Field Sport Concepts,Ltd.
301 East High Street• Charlottesville,Virginia 22902•434-979-7522 • Fax:434-977-1194•me@mckeecarson.com•www.mckeecarson.com
*140.1
Mr. Francis H. MacCall
13 September 2005
Page 2 of 3
Response to Comments from Mark Chamber & Glenn Brooks, Engineers:
A. Final Site Plan (SDP200500071)
1. Provided.
2. The dumpster pad and location have been redesigned based on the County Code recommended.
See Sheet 5-Layout Plan.
3. Grading has been revised to respond to this comment. Spot elevations have been provided to
supplement the design. See Sheet 6-Grading& Utilities Plan.
4. TMP 61-174 is now a part of the Waldorf School. A parking lot is provided infront of the
parcel which provides access to the building on that parcel from the road. See Sheet 3-Existing
Conditions.
5. Special Use Permit Easement is denoted by a hatch. See Sheet 3-Existing Conditions
6. All Slopes have been graded to 4:1 slopes. See Sheet 6-Grading& Utilities Plan.
7. Overflow parking spaces are not required based on the parking study. They are replaced by a
basket ball court. See Sheet 5-Layout Plan.
8. All computations requested are provided. See Storm Water Management Narrative.
9. 10-Yr Storm runoff from the porch area is approx. 0.3 cfs. A 6" storm drain is adequate to
divert this runoff from porch to the proposed Biofilter in order to get treated. See storm drain
analysis in Storm Water Narrative.
10. Cistern system has been reoriented to outfall into a bio-retention system. See Sheet 6-Grading
& Utilities Plan and Sheet 10 for Cistern Outfall Profile.
B. Storm Water Management Plan (WP0200500049)
1. Updated BMP computation sheet has been attached to the narrative. See Storm Water
Management Narrative.
2. The detention pond is no longer a part of the new storm water management plan. It will be
unaffected. See Sheet 6-Grading& Utilities Plan.
3. Not Applicable based on the new design.
4. Embankment is provided as recommended. See Sheet 6-Grading & Utilities Plan.
5. Duly noted. See Sheet 6-Grading& Utilities Plan.
6. See Storm Water Management Narrative.
7. Shown as recommended. See Sheet 14-Site Details.
8. Shown as recommended. See Sheet 6-Grading & Utilities Plan.
9. See Storm Water Management Narrative.
10. Notes included. See Sheet 14-Site Details.
11. Duly noted. Changes made accordingly. See Sheet 7-Landscape Plan.
12. Duly noted. Changes made accordingly. See Sheet 7-Landscape Plan.
13. Shown as recommended. See Sheet 5-Layout and Dimension Plan.
14. a. Duly noted. See Storm Water Management Narrative.
b. Cistern will be used specifically for toilets and outside irrigation. Cistern is reoriented and
bio-retention has been proposed to capture the overflow.
C. Erosion and Sediment Control Plan (WP0200500049)
I. Narrative
1. Added. See Erosion and Sediment Control Narrative.
2. Description of the site soils is provided in the geo-technical report. See attached report.
Mr.Francis H. MacCall
13 September 2005
Page 3 of 3
3. Reference removed. See Erosion and Sediment Control Narrative.
4. Suggested and applicable control measures have been added. See Erosion and Sediment
Control Narrative.
II. Site Plan
5. Cover sheet is attached to the plan set.
6. Limits of construction shown on the plan. See sheet 4-Erosion and Sediment Control Plan.
7. Soils map is provided. See sheet 12-Erosion and Sediment Control Details.
8. Dust control symbols have been added. See sheet 4-Erosion and Sediment Control Plan.
9. Notes added. See sheet 4-Erosion and Sediment Control Plan.
10. Corrected. See sheet 4-Erosion and Sediment Control Plan.
11. Diversion dike and tree protection fence have been redesigned to avoid the conflict. Notes have
been added to the sheet to avoid conflict during construction. See sheet 4-Erosion and Sediment
Control Plan.
12. No longer applicable.
13. Corrected. See sheet 4-Erosion and Sediment Control Plan.
14. Not applicable based on the new design.
15. Not applicable based on the new design.
16. Not applicable based on the new design.
Requested waiver of curb and gutter requirement
We continue with our request for a waiver of the curb and gutter requirement. All
recommendations by Albemarle Co. Water Resources/Engineering Departments have been met. In
addition, we have incorporated the necessary IMP (Integrated Management Practices) outlined in the
Prince Georges County LID Handbook to achieve what we believe are close to 100% LID measures
(Low Impact Development). Please review our resubmitted drawings and SWM narratives for details.
Response to Comments from James Barber:
There is an existing public fire hydrant at 420' from the site which has a fireflow of 2681 gpm+/- at
20psi residual. We are also proposing a new fire hydrant closer to the building and the building will be
equipped with sprinkler system.
Response to Comments from Gary Whelan:
Plumbing fixture has been submitted to size meter. Existing water and sewer will be dedicated.
We trust that attached plans and narratives will adequately address your comments. Please call should
you have any questions or comments.
Sincerely yours,
Eugene Ryang
Enclosures: See Transmittal
• ''
•
THE CAMPAIGN FOR THE
greenest school in America
CHARLOTTESVILLE WALDORF FOUNDATION
August 3, 2005
Jan Sprinkle
Albemarle County Zoning Administrator
401 McIntire Rd.
Charlottesville, VA 22902
RE: Charlottesville Waldorf School Parking
Dear Ms. Sprinkle,
With due consideration to the traffic study done by Mr. J. R. Wade(attached) and the
estimated population of our grade school (max: 230 students and staff, current population
110 students+ staff), we are requesting approval of a 30 stall parking lot in conjunction
with the construction of the grade school building.
Please note that Mr. Wade's study is based on the assumption of a school with 350
students, K-12. Although we ultimately hope and expect to reach this capacity at the end
of all 5 phases, this building houses grades 1-8.
Please contact me is you have any questions or need additional information.
Sincerely,
<air.___.__Th
Kevin O'Brien
for the Charlottesville Waldorf Foundation.
'P.O. Box 4474• Charlottesville, Virginia 22905 1434 293 3900 I campaign@greenestschool.org I www.greenestschool.org
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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: Crossroads Waldorf School,phases 2a& lb
Plan preparer: McKee/Carson [fax 977-1194]
Owner or rep.: Betsy Ayyildiz, Crossroads Waldorf School, Inc. [fax 293-6470]
Plan received date: 28 June 2005
Date of comments: 20 July 2005
Reviewer: Mark Chambers, Glenn Brooks
A. Final Site Plan (SDP200500071)
Engineering reviewed the subject site plan. We do not recommend approval, but request the
following changes to bring the plan into compliance with County Code; The following comments
cannot be nsidered comprehensive as the site design may change dramatically with the next
subm. al.
. Please provide a signed and dated professional seal on the cover sheet;
'' (,�' e t. 2 The dumpster pad does not meet the standards set forth in Section 18-4.12.19.b of the�� Q� County Code. The concrete pad must extend no less than 8' beyond the front of the
(1)i‘ gel- Bio- dumpster and runoff must not drain through the dumpster pad area. Curbing and a
P° T. 1".""a% concrete flume will be necessary to ensure runoff from the travel way and adjacent
eN� r k-°4. parking will be directed around the dumpster pad and into the bio-retention filter;
`� ho As shown stormwater runoff drains toward the north side of the proposed building
k,S I6r-S. ,foundation with no means for relief to prevent ponding against the structure and
associated problems. Please provide adequate information to ensure runoff is directed
1'046 F away from the proposed building foundation on all sides i.e. spot elevations, 1' contours,
5 . .,, � flow arrows, location of swales;
°) P"‘'' qD An access road and easement must be provided to the adjacent Daniel property TMP 61-
`7 174 as required in preliminary site plan review correspondence by Francis MacCall dated
%`� \n7 January 15, 2003. Please clearly label the limits of the access easement, and any necessary
A improvements for the driveway such as road grading, driveway surface material, curb,
aprons etc.;
5. lease clearly label the limits of the access easement for future inner parcel connection
.ckQ)T
between the entrance road and parcel 61 — 172A;
. A guardrail must be provided along the south side of the entrance road adjacent to the
areas of 2:1 slope. An alternative to installing the guardrail would be to grade the adjacent
. 0,'-or slope at 4H:1 V;
'-..),,o- . The 12 overflow parking spaces must be revised to meet the standards set forth in
-rSections 18-14.12.14, 16 & 17 of the County Code.
�x to 8. Ple provide hydrology and hydraulic computations for all proposed culverts, pipes and
W , -S wales (See DSM909.1.A&C, 505.C.2, D2 and E);
v3`.r. . The 8"diameter HDPE pipes used to convey stormwater in drainage area 1 must be
`4•11.0' Engineering Review Comments
Page 2 of 5
increased to a minimum 15"diameter(DSM505.C.5, 505.D.5). In addition, please
include profiles for this drainage system (18-32.6.6d1,2 &DSM909.1.B,D);
"10:Please include the cistern system in the storm profiles.
B. Stormwater Management Plan (WPO200500049)
The following list of Stormwater management plan comments cannot be considered
comprehensive and may not all apply as the SWM plan design may change substantially with the
next submittal.
1. The provided BMP computation worksheet is incorrect, therefore, a comprehensive
review of the SWM plan cannot be completed at this time. The required size of the
proposed bio-retention filter and the design aspects of the extended detention basin are
based on the required pollutant removal efficiency(%RR) on the BMP computation
worksheet. The site will require two worksheets, one for each BMP and associated
drainage area(see Design Standards Manual Chapter 5 Sec. 503.2.C).
2. Due to problems with clogging, the minimum diameter for an extended detention draw
down orifice is 3". If the required drawdown time cannot be achieved through a 3"or
larger orifice an extended detention basin is not an appropriate BMP for this site. In
addition, where the %RR is greater than 35% extended detention ponds must include a
forebay, and areas of shallow, and deep marsh (see the Virginia Stormwater Management
Handbook Minimum Standard 3.07).
3. Please provide a cross section of the extended detention pond outlet structure including
elevations and dimensions (DSM909.2A and VSMH3.01).
4. The minimum top width of 8' is required for the bio-retention filter embankment
(VSMH-3.01). This requirement may be waived if bio-retention filter is not used for
detention and provides a maximum of 1' pond depth above the filter.
5. The down stream gradient of the bio-retention filter embankment must be 3:1 or flatter
(VSMH-3.01). This requirement may be waived if bio-retention filter is not used for
detention and provides a maximum of 1' pond depth above the filter.
6. The bio-retention filter must have an outlet structure to pass larger storm events
(DSMWR-11, 12, 13 & 15).
7. Please label the following elevations on the bio-retention filter detail (DSM 503.f.1):
a. Top of embankment;
b. Inverts of outlet structure;
c. Top of soil mix;
d. Top of under-drain layer.
8. Please show location of under-drains and cleanouts on plan view drawing of bio-retention
filter.
9. Please size the bio-retention filter as follows (VSMH Table 3.11-4):
a. If the%RR< 50% the area of the top of the bio-filter soil mix must be>2.5% of
the contributing impervious drainage area;
b. If the%RR> 50% the area of the top of the bio-filter soil mix must be> 5.0% of
the contributing impervious drainage area.
10. Please include the following notes with the bio-retention filter detail
(DSM503.1.F.10&11):
t ngineering Review Comments
Page 3 of 5
a. The bio-retention filter is not to be installed until the site is considered adequately
stabilized by the Albemarle County Engineering Inspector(434) 296-5832;
b. The bio-retention filter soil mix must be Luck Bio-filter Mix or tested and
approved equivalent. For more information please call Water Resources personnel
at (434)296-5832;
c. The bio-retention filter soil mix must be stabilized with EC-2 matting and seed
mixture of native grasses or 3" of shredded hardwood mulch, along with the trees
and/or shrubs listed on the plan.
11. Please remove the trees and shrubs planted in the bio-retention filter embankment. There
can be no woody plants shown on the embankment because the roots adversely affect the
long term stability of the structure (VSMH3.01). This requirement may be waived if bio-
retention filter is not used for detention and provides a maximum of 1' pond depth above
the filter.
12. Please provide trees and shrubs in the bio-retention filter soil mix (bio-retention area on
plan). The bio-retention area is dependent on the trees and shrubs for part of the pollutant
removal function of the filter. A minimum of 10 plants per 1,000 s.f. of filter area is
required. Please choose plants from the Recommended Species For Use in Bio-retention
Table 3.11-7B in The VSMH (see VSMH-3.11 and DSM 503.1.F.8&9);
13. Runoff from the parking areas where it concentrates between bumber blocks will cause
erosion that will foul the Bio-filter soil media with sediment. Please show EC-2 matting
on the island between the parking areas and from the edge of the lower parking area to the
top of the bio-retention soil mix;
14. Regarding the proposed LID design for the drainage areas on the site:
a. Drainage area 1 is not accounted for in the hydrology or hydraulic computations. As
designed, the 8" storm system, the overflow parking area and portions of the access
road and travel way are bypassing the bio-retention filter. It is unlikely the pre-
development hydrology has been maintained through the site design in drainage area
1. In addition the 8" storm system and the bio-retention filter overflow will produce
concentrated flows that do not outlet to an adequate channel as required by Virginia
Erosion and Sediment Control Regulations, Minimum Standard 19;
b. Drainage area 2 incorporates a single detention pond as the primary BMP. There is a
proposed cistern on the plan but no information is given on what the cistern will be
used for, (landscape maintenance, non-potable water supply) and there is no
provision for a secondary infiltration system to draw water out of the cistern between
storm events. Consequently, it is assumed the cistern will not have available storage
volume and is not considered in the post development hydrology computations. If the
cistern cannot be accounted for, or counted on, it's useless in achieving the overall
LID goal. The grass swale does not meet the maximum slope standard of 6%
required by the LID handbook and alone is not capable of mitigating the large
amount of impervious runoff in this drainage area. The only remaining BMP in
drainage area 2 is the detention pond at the bottom of the drainage area, which is not
considered an LID integrated management practice;
C. Erosion Control Plan (WPO200500049)
' Ilvin
gineering Review Comments
Page 4 of 5
I. Narrative
1. Please include the acres of disturbance in the project description (VESCH, E&SC Plan
Checklist).
2. Please include a description of on site soils (VESCH, E&SC plan checklist). Soils
information is an important factor in LID design and should be incorporated in to the
SWM plan.
3. Please remove the EPA reference under critical areas in the narrative. All E & S
measures will conform to the Virginia Erosion& Sediment Control Handbook 3rd
addition.
4. Under erosion and sediment control measures please add the following items and
describe how all of the measures will be used on this site(VESCH, E&SC plan
checklist):
a. Inlet Protection;
b. Temporary Sediment Basin;
c. Tree Protection;
d. Stormwater Conveyance Channel;
e. Safety Fence.
II Site Plan
5. Please provide a vicinity map for the Erosion and Sediment Control plan or attach the
cover sheet from the site plan(VESCH, E&SC Plan Checklist).
6. Please show the limits of clearing and grading(VESCH, E&SC Plan Checklist).
7. Please provide a soils map (VESCH, E&SC Plan Checklist).
8. Please add the Dust Control Symbol to areas of disturbance on the plan sheet(VESCH,
3.39).
9. Please add the standard Virginia Erosion and Sediment Control Notes to the plan(see
VESCH Table VI-15).
10. The sediment trap embankment does not meet the minimum top width requirement.
Please correct this condition(VESCH, 3.13).
11. The diversion dike is in conflict with the tree protection around several trees and will
result in root damage and probable loss of the tree. Please remove the tree protection
fence and symbols from these areas or redesign the diversion dike to avoid the conflicts.
12. The diversion dike is blocking the sediment basin emergency spillway please correct this
condition.
13. The diversion dike conflicts with the HDPE storm drain outlet in drainage area 1. Please
relocate the diversion dike below the outfall of the storm drain system to divert water to
the sediment trap. If necessary to provide adequate slope on the diversion dike a section
could be left off the end of the storm drain until the site is stabilized and the diversion
dike is no longer needed but this must be outlined on the plan.
14. We are not sure what the rectangular wall like boundary around the perimeter of the
sediment basin denotes. If this is meant to be safety fence please use the standard safety
fence symbol. Safety fence and danger signs are required around the sediment basin and
must be shown on the plan(VESCH 3.01);
15. please provide the minimum bottom dimensions of the sediment basin (VESCH p.III-79)
16. Please provide a detail of the sediment basin outlet structure with the following
elevations and dimensions labeled(VESCH STD & SPEC 3.14):
Engineering Review Comments
Page 5 of 5
a. Upstream and downstream invert of barrel pipe;
b. Diameter of barrel pipe;
c. Invert elevation and diameter of de-watering orifice;
d. Riser crest elevation and diameter;
e. Antivortex diameter;
f. Top of embankment elevation and width;
g. Emergency spillway cross section with dimensions, elevation and lining
provided.
D. Requested waiver of Curb and Gutter requirement
The requested waiver of the requirement for curb and gutter on the site travelway has
been reviewed. This waiver request was based on a desire to design the site according to LID
principles. The County does not have an LID standard, but recognizes the validity of the LID
goals and practices as set forth in the Prince Georges County Handbook referenced in the waiver
request. However, the proposed"Hybrid LID"stormwater plan does not appear to meet the
standards and goals set forth in this reference.
The goal of LID is to mimic predevelopment hydrology through the use of intergrated
management practices (IMPs) and innovative site design. Currently, the plan appears to be a
typically institutional site with stomwater collection BMP's. (Please see the stormwater
management plan comments for more information concerning the proposed BMP's.) Other
opportunities to use IMPs to accomplish the LID goal are not used. For example, we would like
to see the use of green roof technology on the building, pervious pavers or a similar technology
in the parking stalls, grass pave or a similar technology in the overflow parking area, and soil
amendments in graded areas to restore permeability, etc.
We support your goal of developing an LID SWM plan for this site and will gladly work
with you in developing a plan that meets the goals and requirements of LID Design. However, we
feel this design doesn't warrant waiver of the County requirement for curb and gutter. If more
effort is made to meet LID goals through the use of IMPs in the site design we will reconsider
waiving the curb and gutter requirement to facilitate the overall LID aspect of the plan.