HomeMy WebLinkAboutSDP200900096 Assessment - Groundwater Final Site Plan and Comps. 2009-11-23VIAIVAT WHITMAN, REQUARDT ASSOCIATES, LLP
ENGINEERS • ARCHITECTS • PLANNERS EST. 1915
November 23, 2009
Mr. Gerald Gatobu
Albemarle County
Department of Community Development
401 McIntire Road
Charlottesville, VA 22902 -4596
Re: Albemarle County Service Authority - Camelot Pump Station - Final Site Plan Submittal
WR &A W.O. # 46466 -002
Dear Mr. Gatobu:
Transmitted with this letter are eight (8) copies of the final site plan for the Camelot Pump Station.
The Camelot Pump Station is part of the North Fork Regional Pump Station project for the Albemarle
County Service Authority (ACSA). As you know, Whitman Requardt & Associates (WR &A) is the
design engineer for this project.
In addition to the eight copies of the site plans, the following is included in this transmittal:
Review fees from the ACSA
Application for Site Development Plans
Final Site Development Plan Checklist
Erosion and Sediment Control Application Form
Rendering for Proposed Camelot Pump Station building (included as Attachment A)
WR &A has obtained a determination for Architectural Review Board (ARB) for the Camelot Pump
Station. The determination was made that the pump station would comply with the rendering
included in Attachment A. The site plan review and approval would be performed by Planning staff.
A formal review, presentation, and approval by the ARB is not required.
In addition to transmitting the final site submittal for the Camelot Pump Station, the intent of this
letter is to review storm -water quantity and quality management for the pump station site and
WWTP site.
CAMELOT PUMP STATION AND WWTP ABANDONMENT OVERVIEW
The Camelot Pump Station site will be situated south of and immediately adjacent to the existing
Camelot WWTP. The parcel to be subdivided for the pump station is currently owned by HMC
9030 Stony Point Parkway, Suite 220, Richmond, Virginia 23235 www.wrallp.com Phone: 804.272.8700 Fax: 804.272.8897
Baltimore, MD • Fairfax, VA • Georgetown, DE • Newport News, VA • Pittsburgh, PA • Richmond, VA • Wilmington, DE • York, PA
N: \ 46466 -002 \ Engineering\ Corresp \ Letters\ 112309 Camelot Site Plan Submittal ltr.doc
Mr. Gerald Gatobu Page 2
Albemarle County Department of Community Development November 23, 2009
Holdings, LLC (HMC). The proposed area of land acquisition from HMC by the ACSA is 0.60 acre.
Following the construction of the pump station and the improvements shown on the transmitted site
plan, the pump station site will have 0.04 acre of impervious cover while 0.49 acre of the property will
remain vegetated after construction. The vegetated and undisturbed portion of the property is the
floodplain of the North Fork of the Rivanna River. This portion of the property will remain
undisturbed and vegetated as the ACSA has no plans for future site improvements in the floodplain.
The Camelot Pump Station will replace the Camelot WWTP which currently resides on a 1.23 acre lot
immediately adjacent to the pump station site. The Camelot WWTP site currently has 0.07 acre of
impervious cover (5.7% of the total property area). The remaining 0.80 acre of the property is heavily
vegetated. The 0.07 acre of impervious area within the Camelot WWTP site does not include the
primary treatment basins and the existing storage tank within the site. The total area of the treatment
basin and tank equal an additional 0.07 acre. Upon construction and successful start -up of the
Camelot Pump Station, the Camelot WWTP will be decommissioned, demolished, backfilled, graded,
compacted, and seeded. The removal of the Camelot WWTP will result in a total of 0.14 acre of land
that will be restored to its original grassed or vegetated state. In addition, the existing discharge from
the Camelot WWTP will be eliminated, resulting in reduced pollutant (nitrogen and phosphorus)
loads and the elimination of a major point source discharge to the North Fork of the Rivanna River.
STORM -WATER MANAGEMENT REVIEW AND DETERMINATION
Storm -Water Quality Review
WR &A recently met with the Department of Community Development to review storm -water quality
control for the Camelot Pump Station and the decommissioning of the Camelot WWTP. Following an
overview of the sites' drainage patterns, it was determined that the Camelot Pump Station site will be
considered as a redevelopment area with regard to storm -water quality control as shown on the
County's Water Protection Ordinance computation spreadsheet.
Following a review of the area types outlined in the spreadsheet, the Camelot Pump Station and the
decommissioning of the Camelot WWTP do not fall under the area type of "Rural Land ". In addition,
a review of the County GIS layers revealed that the project sites are not in the area type of "Drinking
Water Watersheds ". As a result, it is WR &A's opinion that the Camelot Pump Station and Camelot
WWTP fall in the area type of "Development Area ".
Two methods were used to confirm the need for storm -water quality control for the Camelot Pump
Station and the decommissioning of the Camelot WWTP. These methods are summarized as follows:
Offsite and Onsite Drainage to a Point of Analysis - Under this method, the offsite and onsite
drainage that is not conveyed in a separate storm drain system is analyzed at a single point of
analysis on the Camelot WWTP site. The drainage area is 0.77 acre. The pollutant loads and
N: \ 46466 -002 \ Engineering\ Corresp \ Letters \ 112309 Camelot Site Plan Submittal ltr.doc
Mr. Gerald Gatobu Page 3
Albemarle County Department of Community Development November 23, 2009
required pollutant removal for this method are shown on Worksheet 1 of the Water Protection
Ordinance computation spreadsheet and are illustrated on Figure 1. Worksheet 1 and Figure 1
are included in Attachment B.
Parcel Area Drainage to River - Under this method, the total of the Camelot Pump Station and
Camelot WWTP parcel areas are evaluated for pollutant loads and removal requirements. The
drainage area is 1.83 acres (0.60 acre for the Camelot Pump Station site + 1.23 acres for the
Camelot WWTP site). The pollutant loads and required pollutant removal for this method are
shown on Worksheet 2 of the Water Protection Ordinance computation spreadsheet and are
illustrated on Figure 2. Worksheet 2 and Figure 2 are included in Attachment C.
The results of each of these methods are described in the following subsections.
Offsite and Onsite Drainage to a Point of Analysis
A drainage area of 0.77 acre is shown in Worksheet 1 and on Figure 1. This drainage area is a
combination of existing offsite and onsite areas as shown on Figure 1. The existing offsite impervious
area is 12,000 square feet. This existing offsite impervious area is shown under both the pre- and
post - construction tabulations. Worksheet 1 shows the pre - development and post - development
impervious cover equaling 45 %. Even with the same impervious area (as a function of percentage) in
the pre -and post - construction conditions, the worksheet shows that the required pollutant removal is
9% for the "Development Area" area type.
As summarized above, the area within the existing floodplain of the North Fork of the Rivanna River
will remain undisturbed, vegetated, and will function as a vegetative filter. This existing vegetative
filter is approximately 1.3 acres in area. Based on the 9% required pollutant removal, a vegetative
filter strip is an appropriate selection as an adequate Best Management Practice (BMP) as outlined in
Table 1 in Chapter 1 of the Virginia Storm -water Management Handbook (VSM Handbook).
Based on this analysis and the understanding that the existing floodplain will remain and act as a
vegetative filter, an additional BMP for storm -water quality management is not warranted under this
method of analysis.
Parcel Area Drainage to River
A drainage area of 1.83 acres is shown in Worksheet 2 and on Figure 2. This drainage area is a total of
the parcel areas of the Camelot Pump Station and the Camelot WWTP sites. Using the sum of the
parcel areas as the drainage area and the pre- and post - construction impervious areas for both
parcels, Worksheet 2 shows that both the pre- and post - construction impervious areas equal 3
percent. Similar to the method outlined above, the development of the Camelot Pump Station and
the decommissioning of the Camelot WWTP results in no net increase in impervious area for the
combination of these two parcels.
N: \46466- 002 \Engineering \Corresp \Letters \112309 Camelot Site Plan Submittal ltr.doc
Mr. Gerald Gatobu Page 4
Albemarle County Department of Community Development November 23, 2009
In addition, Worksheet 2 tabulates the required pollutant removal to be a negative number for the
Development Area" area type, under the Redevelopment area of the worksheet. This result clearly
indicates that a BMP is not needed based on this analysis method.
Storm -Water Quantity Review
Figures 1 and 2 as included in Attachments B and C, respectively, show that most of the offsite
drainage will be conveyed through a new storm drainage system. The conveyance of this offsite
drainage through a new system is meant to maintain the existing drainage pattern at the Camelot
Pump Station site. The new storm drainage system is also detailed on the transmitted site plans. The
system is sized for the 10 -year storm event.
As part of storm -water quantity review, Minimum Standard (MS) 19 must also be reviewed for this
new point source discharge to confirm that an adequate receiving channel exists. Sheet C1 -03 in the
submitted site plan shows the cross - sections of the receiving channel. The cross - sections and
tabulation shown on Sheet C1 -03 indicates that the existing channel at the discharge location of the
new storm drainage system has the necessary depth to convey the design flows. To control velocity
under the design storm, a permanent rip rap outfall has been designed and shown on the submitted
site plan. As indicated on Sheet C1 -03, the discharge velocity is 1.54 fps at the rip rap outfall, resulted
in a non - erosive discharge condition. The discharge velocity at cross - section 0 +00 (which is below the
outfall, at existing grade) is 2.58 fps. This discharge velocity is also considered non - erosive for a
heavily vegetated floodplain and overland area. Based on the results of this analysis, MS -19 has been
satisfied.
The storm sewer design computations and hydraulic grade line computations are included in
Attachment D. The open channel flow computations for the cross - sections used for the MS-19
analysis are included in Attachment E.
Based on no -net increase in impervious area as summarized above and compliance with MS -19,
storm -water quantity control is not warranted for the Camelot Pump Station and for the
decommissioning of the Camelot WWTP.
Storm -Water Management Review Conclusion
Based on the storm -water quality and quantity review outlined in this letter, the supporting
attachments, the information contained on the site plans, and the removal of the existing point source
and process discharge of the Camelot WWTP, storm -water quality and quantity control for the
Camelot Pump Station and for the decommissioning of the Camelot WWTP are not warranted.
N: \46466- 002\ Engineering \Corresp \Letters \112309 Camelot Site Plan Submittal ltr.doc
Mr. Gerald Gatobu Page 5
Albemarle County Department of Community Development November 23, 2009
We trust that this letter adequately summarizes our analysis and transmits the required information
for final site plan review. Should you have any questions, please do not hesitate to call. Thank you
for your cooperation in this matter.
Very truly yours,
Whitman, Requardt & Associates, LLP
Charles Luck, P.E.
Associate
Enclosures
cc: Tom Garrison — ACSA
File 46466 -002
N:\ 46466 - 002 \Engineering \Corresp \Letters \112309 Camelot Site Plan Submittal ltr.doc
Attachment B
Worksheet 1 and Figure 1
Short Version BMP Computations For Worksheets 2 - 6
Albemarle County Water Protection Ordinance: Modified Simple Method
CAMELOT PUMP STATION
Plan: WORKSHEET NO. 1 Water Resources Area:Development Area
Preparer:YLM Date: 18- Nov -09
Project Drainage Area Designation DA# 2
L storm pollutant export in pounds, L = [P(Pj)Rv /12 ] [ C(A)2.72 ]
Rv mean runoff coefficient, Rv = 0.05 + 0.009(1)
Pj small storm correction factor, 0.9
1 percent imperviousness
P annual precipitation, 43" in Albemarle
A project area in acres in subject drainage area,A =0.77
C pollutant concentration, mg /I or ppm target phosphorus
f factor applied to RR
required treatment volume in cy, 0.5" over imperv. area = A(I)43560(0.5/12)/27
RR required removal , L(post) - f x L(pre)
RR removal efficiency , RR100 /L(post)
Impervious Cover Computation (values in feet & square feet)
Item
pre - development Area post - development Area
Roads Length Width subtotal Length Width subtotal
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0
0 0 0 0
Driveways Length Width no.subtotal Length Width no.subtotal
and walks 0 0 0 12000 0 0 0 12000
0 0 0 0 0 0 0 2175
0 12000 0 0 0 0 14175
Parking Lots 1 2 3 4 1 2 3 4
0 0 0 0 0
Gravel areas Area 3778 Area 734
x 0.70 =2644.6 x 0.70 =513.8
Structures Area no.subtotal Area no.subtotal
0 0 608 0 0 300
O 0 0 0 0 0
O 0 0 608 0 300
Actively - grazed pasture &Area Area
yards and cultivated turf x 0.08 =0 0 x 0.08 =0
Active crop land Area Area
x0.25=0 x0.25=0
Other Impervious Areas
0 0
Impervious Cover 45%45%
l(pre)post)
Rv(post) V
0.45 23.1
New Development (For Development Areas, existing impervious cover <= 20 %)
C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type
0.70 1.00 20% 0.46 2.17 2.14 0.03 2% Development Area
0.35 1.00 0% 0.46 1.09 1.07 0.02 2% Drinking Water Watersheds
0.40 1.00 1% 0.46 1.24 1.22 0.02 2% Other Rural Land
min. values
Redevelopment (For Development Areas, existing impervious cover > 20 %)
C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type
0.70 0.90 20% 0.46 2.17 2.14 0.18 9% Development Area
0.35 0.85 0% 0.46 1.09 1.07 0.15 14% Drinking Water Watersheds
0.40 0.85 1% 0.46 1.24 1.22 0.17 14% Other Rural Land
Interim Manual, Page 70 rev. 16 Feb 1998 GEB
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ALBEMARLE COUNTY SERVICE AUTHORITY
CAMELOT PUMP STATION SCALE
FIGURE 1 0 40'80'
Attachment C
Worksheet 2 and Figure 2
Short Version BMP Computations For Worksheets 2 - 6
Albemarle County Water Protection Ordinance: Modified Simple Method
CAMELOT PUMP STATION
Plan: WORKSHEET NO. 2 Water Resources Area:Development Area
Preparer:YLM Date: 18- Nov -09
Project Drainage Area Designation DA# 2
1.storm pollutant export in pounds, L = [P(Pj)Rv /12 ] [ C(A)2.72 ]
Rv mean runoff coefficient, Rv = 0.05 + 0.009(1)
Pj small storm correction factor, 0.9
percent imperviousness
P annual precipitation, 43" in Albemarle
A project area in acres in subject drainage area,A =1.83
C pollutant concentration, mg /I or ppm target phosphorus
f factor applied to RR
V required treatment volume in cy, 0.5" over imperv. area = A(I)43560(0.5/12)/27
RR required removal , L(post) - f x L(pre)
RR removal efficiency , RR100 /L(post)
Impervious Cover Computation (values in feet & square feet)
Item
pre - development Area post - development Area
Roads Length Width subtotal Length Width subtotal
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0
0 0 0 0
Driveways Length Width no.subtotal Length Width no.subtotal
and walks 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 2175
0 0 0 0 0 0 2175
Parking Lots 1 2 3 4 1 2 3 4
0 0 0 0 0
Gravel areas Area 2635 Area 0
x0.70=1844.5 x0.70=0
Structures Area no.subtotal Area no.subtotal
0 0 608 0 0 300
0 0 0 0 0 0
0 0 0 608 0 300
Actively - grazed pasture &Area Area
yards and cultivated turf x 0.08 =0 0 x 0.08 =0
Active crop land Area Area
x0.25=0 x0.25=0
Other Impervious Areas
0 0
Impervious Cover 3%3%
l(pre)post)
Rv(post) V
0.08 3.8
New Development (For Development Areas, existing impervious cover <= 20 %)
C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type
0.70 1.00 20% 0.23 2.58 0.88 1.71 195% Development Area
0.35 1.00 0% 0.08 0.44 0.44 0.00 0% Drinking Water Watersheds
0.40 1.00 1% 0.08 0.50 0.50 0.00 0% Other Rural Land
min. values
Redevelopment (For Development Areas, existing impervious cover > 20 %)
C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type
0.70 0.90 20% 0.23 2.58 0.88 1.45 166% Development Area
0.35 0.85 0% 0.08 0.44 0.44 0.07 15% Drinking Water Watersheds
0.40 0.85 1% 0.08 0.50 0.50 0.08 15% Other Rural Land
Interim Manual, Page 70 rev. 16 Feb 1998 GEB
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CAMELOT WWTP SITE =1.23 ACRES)
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ALBEMARLE COUNTY SERVICE AUTHORITY
CAMELOT PUMP STATION SCALE
FIGURE 2 0 40'80'
Attachment D
Storm Sewer Design and Hydraulic Grade Line Computations
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Attachment E
Open Channel Flow Computations for MS -19 Analysis
Worksheet for Trapezoidal Channel - STA 0 +00
Project Description
Friction Method Manning Formula
Solve For Normal Depth
Input Data
Roughness Coefficient 0.033
Channel Slope 0.00500 ft/ft
Left Side Slope 0.04 ft/ft
Right Side Slope 0.23 ft/ft
Bottom Width 4.50 ft
Discharge 10.72 ft /s
Results
Normal Depth 0.55 ft
Flow Area 6.97 ft
Wetted Perimeter 20.80 ft
Hydraulic Radius 0.34 ft
Top Width 20.72 ft
Critical Depth 0.38 ft
Critical Slope 0.02549 ft/ft
Velocity 1.54 ft/s
Velocity Head 0.04 ft
Specific Energy 0.59 ft
Froude Number 0.47
Flow Type Subcntical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 0.55 ft
Critical Depth 0.38 ft
Channel Slope 0.00500 ft/ft
Bentley Systems, Inc. Haestad Methods Solution Center Bentley FlowMaster [08.11.00.03]
11/23/2009 10:22:46 AM 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1- 203 - 755 -1666 Page 1 of 2
Worksheet for Trapezoidal Channel - STA 0 +00
GVF Output Data
Critical Slope 0.02549 ft/ft
Bentley Systems, Inc. Haestad Methods Solution Center Bentley FlowMaster [08.11.00.03]
11/23/2009 10:22:46 AM 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1- 203 - 755 -1666 Page 2 of 2
Worksheet for Triangular Channel - STA 0 +16
Project Description
Friction Method Manning Formula
Solve For Normal Depth
Input Data
Roughness Coefficient 0.045
Channel Slope 0.04650 fUft
Left Side Slope 0.06 ft/ft
Right Side Slope 0.04 ft/ft
Discharge 10.72 ft /s
Results
Normal Depth 0.44 ft
Flow Area 4.15 ft
Wetted Perimeter 19.01 ft
Hydraulic Radius 0.22 ft
Top Width 18.99 ft
Critical Depth 0.43 ft
Critical Slope 0.04923 ft/ft
Velocity 2.58 fUs
Velocity Head 0.10 ft
Specific Energy 0.54 ft
Froude Number 0.97
Flow Type Subcritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 0.44 ft
Critical Depth 0.43 ft
Channel Slope 0.04650 ft/ft
Critical Slope 0.04923 ft/ft
Bentley Systems, Inc. Haestad Methods Solution Center Bentley FlowMaster [08.11.00.03]
11/23/2009 10:22:03 AM 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1- 203 - 755 -1666 Page 1 of 1