19970694 Ver 1_Stormwater Info_20020429

Since X97.9
THE JOHN R. McADAMS COMPANY, INC.
April 24, 2002
Mr. Todd St. John, PE
Environmental Engineer
North Carolina Division of Water Quality
2321 Crabtree Blvd.
Raleigh, North Carolina 27604
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I S I x
RE: Stormwater Sand Filter
The Gardens at Wakefield
Wake County, North Carolina
DWQ # 970694
FCC-01000
Dear Mr. St. John:
With regard to the review comments detailed in a letter from you, dated March 7, 2002,
the design of the proposed stormwater sand filter for The Gardens at Wakefield has been
revised. Enclosed you will find two (2) =nance of the revised sand filter detail sheet, along
with a copy of the signed operation and agreement.
The following is an item-by-item description of each of the comments and a brief
description on how each item has been addressed.
1. Side Slopes and Settling Basin
Per your request, a note has been added to the detail sheet specifying that the
side slopes of the sand filter and sediment basin be stabilized with vegetation.
2. Sand Specifications
Per your request, a section titled "Sand Specifications" has been added to the
detail sheet.
3. Operation and Maintenance Agreement
It is my understanding that a signed O & M agreement has been previously
forwarded to you. However, a copy of this agreement has been included in
this submittal for your convenience.
Hopefully the above letter helped to address all comments and aid in further review of the
proposed sand filter. Please contact me at telephone number (919)-361-5000 should you
have any questions or need any additional information.
Sincerely,
THE JOHN R. McADAMS COMPANY, INC.
-017
Brandon R. Finch, PE
Project Engineer - Stormwater Management Group
cc: D. Amos Clark, PE
Mike Munn, PE
John E. Schrum, El
CIVIL ENGINEERING • LAND PLANNING • SURVEYING
PO Box 14005 • Research Triangle Park, NC 27709 • [phone] . fax[phone]
www.johnrmcadams.com
Since X97.9
THE JOHN R. McADAMS COMPANY, INC.
April 24, 2002
Mr. Todd St. John, PE
Environmental Engineer
North Carolina Division of Water Quality
2321 Crabtree Blvd.
Raleigh, North Carolina 27604
•f
J j
I S I x
RE: Stormwater Sand Filter
The Gardens at Wakefield
Wake County, North Carolina
DWQ # 970694
FCC-01000
Dear Mr. St. John:
With regard to the review comments detailed in a letter from you, dated March 7, 2002,
the design of the proposed stormwater sand filter for The Gardens at Wakefield has been
revised. Enclosed you will find two (2) =nance of the revised sand filter detail sheet, along
with a copy of the signed operation and agreement.
The following is an item-by-item description of each of the comments and a brief
description on how each item has been addressed.
1. Side Slopes and Settling Basin
Per your request, a note has been added to the detail sheet specifying that the
side slopes of the sand filter and sediment basin be stabilized with vegetation.
2. Sand Specifications
Per your request, a section titled "Sand Specifications" has been added to the
detail sheet.
3. Operation and Maintenance Agreement
It is my understanding that a signed O & M agreement has been previously
forwarded to you. However, a copy of this agreement has been included in
this submittal for your convenience.
Hopefully the above letter helped to address all comments and aid in further review of the
proposed sand filter. Please contact me at telephone number (919)-361-5000 should you
have any questions or need any additional information.
Sincerely,
THE JOHN R. McADAMS COMPANY, INC.
-017
Brandon R. Finch, PE
Project Engineer - Stormwater Management Group
cc: D. Amos Clark, PE
Mike Munn, PE
John E. Schrum, El
CIVIL ENGINEERING • LAND PLANNING • SURVEYING
PO Box 14005 • Research Triangle Park, NC 27709 • [phone] . fax[phone]
www.johnrmcadams.com
TIE JOHN K McADAMS COMP
LETTER OF TRANSMITTAL
To: Mr. Todd St. John
North Carolina Division of Water Quality
Environmental Engineer
2321 Crabtree Boulevard
** FEDERAL EXPRESS **
Raleigh, North Carolina 27604
Re: The Gardens at Wakefield Job No.: FCC-01000
I am sending you the following item(s):
COPIES DATE NO. DESCRIPTION
2 Sand Filter Details
1 O and M Agreement
These are transmitted as checked below:
? As requested
® For approval
? For review and comment
Remarks:
Copy to: D. Amos Clark, J. Schrum
M. Munn
.`;. 9 2002
Date: April 25, 2002
? For your use
? --

Signed: ZZA:"?
Brandon R. Finch /-PE
Project Engineer
FOR INTERNAL USE ONLY
? Copy Letter of Transmittal Only to File
? Copy Entire Document to File
CIVIL ENGINEERING • LAND PLANNING • SURVEYING
PO Box 14005 • Research Triangle Paris, NC 27709 • [phone] • fax[phone]
www.johnrmcadams.com
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Since 1979
THE JOHN R. WADAMS COMPANY, INC.
nc??
,.?? GROUP
HANNOVER ASSISTED LIVLN ??? ?rnsFCrr N___
SAND FILTER DESIGN
DWQ Project # 970694
RALEIGH, NC
HHC-01000
J.E. SCHRUM, E.I.
May 10, 2002
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CIVIL ENGINEERING • LAND PLANNING • SURVEYING
PO Box 14005 • Research Tdangle Park, NC 27709 • [phone] • fax [phone]
www.johnrmcadams.com
HANNOVER ASSISTED LIVING
Storm Drainage and Sand Filter Design
General Description
Located on the corner of Wakefield Pines Drive and Spruce Tree Way at Wakefield
Plantation, Hannover Assisted Living is a proposed extended care facility with parking
areas and utilities. This property is located in the Wakefield Development and is
therefore subject to a 401 Water Quality Certification under DWQ Project # 970694. A
sand filter will be utilized to comply with the TSS removal.
The included Summary of Results demonstrates that the sand filter meets all design
requirements as set forth by the NCDENR Stormwater Best Management Practices
(BMP, April 1999). The required area of the sand filter is 972 sf in both the sand
chamber and the sediment chamber. The actual surface area is 1,099 sf in the sand
chamber and 1,142 sf in the sediment chamber. The required volume is 1,458 cf in both
the sand chamber and the sediment chamber. The actual volume in the sand chamber is
„ 2,819 cf while the actual volume in the sediment chamber is 3,026 c£ Required volume
of the 1" rainfall storage is 5,799 cf and the actual volume provided is 7,792 cf.
Drawdown of the runoff from the 1" rainfall will occur over a 22.1 hour period.
The sand filter pas-96s-the runoff from the 100-year storm event with a peak elevation of
3'07.3 ft.' The top of berm elevation is 308.0 ft in post-development. The freeboard in the
100-year storm event is therefore 0.7 ft.
Calculation Methodology for Storm Drainage and Sand Filter Design
• The Rational Method was used to generate flowrates in the design of the storm
drainage system.
• Routing of the sand filter was achieved using the Chainsaw Method developed by
H. Rooney Malcom, P.E., NCSU.
• Rainfall data used in the analysis is from USWB TP-40 and NOAA Hydro-35.
This data was used to generate an equation describing the IDF Curves for the
RDU region. The equation is in the form: Rainfall Intensity [in/hr] = g/(h + Time
of Concentration [minutes]), where g and h are constants dependent upon the
return period.
• The Time of Concentration was, in all cases, assumed 5 minutes because of the
small size of all the drainage areas.
• Using Wake County Soil Survey, the majority of on- -site soils were determined
to be from Hydrologic Soil Group `B'. Therefore, the SCS Curve Numbers used
in further hydrologic calculations are selected appropriately.
• On-site topography is from information collected by The John R. McAdams
Company, Inc.
SUMMARY OF RESULTS.xls
SAND FILTER
HHC-01000
SAND FILTER ROUTING -
TOP OF BERM = 308.00
RETURN
PERIOD OUTFLOW WSE FREEBOARD
(years) INFLOW (cfs) (cfs) (ft) (ft)
100 25.2 25.1 307.26 0.7
SAND FILTER BMP DESIGN ASPECTS =>
SAND CHAMBER
Required Area =
Actual Area =
Required Volume =
Actual Volume =
SEDIMENT CHAMBER
Required Area =
Actual Area =
Required Volume =
Actual Volume =
1" RAINFALL ASPECTS
Volume Required =
Volume Provided =
Drawdown Time =
972 sf
1099 sf
1458 cf
2819 cf
972 sf
1142 sf
1458 cf
3026 cf
J.E. SCHRUM, E.I.
5/9/02
5799 cf
7792 cf (Note - Riser crest elevation based upon detention control)
22.1 hours
DATA INPUTS
Since 1979
THE JOHN K McADAMS COMPANY, INC.
PIAR .4 2002
THE GARDENS AT WAKEFIELD PLANTATION ,
SAND FILTER DESIGN
NCDWQ PROJECT # 970694
RALEIGH, NC
FCC-01000
J.E. SCHRUM, E.I.
February 28, 2002
CIVIL ENGINEERING • LAND PLANNING • SURVEYING
PO Box 14005 • Research Triangle Park, INC 27709 • [phone] • fax [phone]
www.johnrmcadams.com
THE GARDENS AT WAKEFIELD PLANTATION
Sand Filter Design Calculations
General Description
Located off Spruce Tree Way, The Gardens at Wakefield Plantation is a proposed multi-
family housing site with parking areas and utilities. This property is located in the
Wakefield Development and is therefore subject to a 401 Water Quality Certification
under DWQ Project # 970694. This permit requires an approved stormwater
management program, which meets 85% TSS removal. A sand filter will be utilized to
comply with the TSS removal.
The site is composed of two drainage basins in the post-development condition. All
impervious portions of the sub-basin will be diverted to a sand-filter in post-development
in order to reduce post-development nitrogen loading and as the means of meeting the
85% TSS removal requirement.
The included Summary of Results demonstrates that the sand filter meets all design
requirements as set forth by the NCDENR Stormwater Best Management Practices
(BMP, April 1999). This includes meeting the requirements of surface area in both the
sediment and sand chamber and the volumetric requirements based upon storage of the V
rainfall. The sand filter also passes the flow resulting from the 100-year storm event with
1.2 ft of freeboard from the water surface elevation to the top of berm.
Calculation Methodology for Storm Drainage and Sand Filter Design
The Rational Method is used to generate post-development peak now rates in the
two-, ten- and 100-year storm events. A Rational C value of 0.85 is utilized for
post-development.
• Rainfall data used in the analysis is from USWB TP-40 and NOAA Hydro-35.
This data was used to generate an equation describing the IDF Curves for the
RDU region. The equation is in the form: Rainfall Intensity [in/hr] = g/(h + Time
of Concentration [minutes]), where g and h are constants dependent upon the
return period.
• The Time of Concentration was, in all cases, assumed 5 minutes because of the
small size of all the drainage areas.
• Using Wake County Soil Survey, the majority of on- -site soils were determined
to be from Hydrologic Soil Group `B'. Therefore, the SCS Curve Numbers used
in further hydrologic calculations are selected appropriately.
• On-site topography is from information collected by The John R. McAdams
Company, Inc.
• The sand filter was designed utilizing the guidelines as set forth in NCDWQ's
Best Management Practices (BMP, 4, 1999). All aspects of the sand filter design
conform to this manual.

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®McADAMS
DWQ SUMMARY OF RESULTS.xls
SAND FILTER
FCC-01000
SAND FILTER ROUTING =>
TOP OF BERM = 295.70
RETURN
PERIOD
(years)

INFLOW (cfs)
OUTFLOW
(cfs)
WSE
(ft)
FREEBOARD
(ft)
2 20.7 7.7 293.30 2.4
10 26.0 15.2 293.47 2.2
100 43.6 23.2 294.46 1.2
SAND FILTER BMPDESIGNASPECTS=>
SAND CHAMBER
Required Area =
TAclual Area =
Required Volume =
olume
SEDIMENT CHAMBER
RAq fired Area
Actual Area
Required Volume =
Actual Volume
1" RAINFALL ASPECTS
Volume Required
Volume Provided =
Drawdown Time =
1728 sf
1758 sf
2592 cf
";-4245 cf
J.E. SCHRUM, E.I.
2/28/02
1728 sf _
s 1742 k {sf
2592 cf
4334 cf
6173 - cf?
29710 cf (Note - Riser crest elevation based upon detention control)
13.9 hours
SAND FILTER DESIGN
J.E. SCHRUM, E.I.
1/29/02
f ` REQUIRED AREAs AND: VOLUMES
SAND CHAMBER:
is
Required Area = 1728 sf /
vctual2;Area,;., 1758 sfV
Required Volume = 2592 cf
:Actual Volume = 4245 cf
SEDIMENT CHAMBER
Required Area = 1728 sf
Actual Area = 1742 sf
Required Volume = 2592 cf
.-Actual Volume = 4334 cf

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POST-DEV TO SAND FILTER
i, Small Watershed Method Hydmaranh Generation
(Rf.• "Elements of Urban Storrnwater Design, H. R. Malcom, PE)
Drainage Area Description =_>
Total DA = 4.24 AC c= 0.85 and CN = 96
Design Storm Description / Watershed Sensitivity =_>
Time of Concentration = 5.0 minutes
Enter known IDF factors to compute the intensity, or enter a known intensity in the area
marked "known intensity". If known, clear all IDF factors from the chart.
IDF Factors:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
g 132 169 195 232 261 290
h 18 21 22 23 24 25
Calculated Intensities (do not enter known values here):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Intensity 5.74 6.50 7.22 8.29 9.00 9.67
(in/hr)
Known Intensities (enter known values here if not calculating above, else enter zero):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
intensity 0.00 0.00 0.00 0.00 0.00 0.00
(in/hr)
Design storm flowrates =_>
Foowrates are calculated using the rational method, and incorporating frequency
POST-DEV TO SAND FILTER
coefficients for the 25, 50, and 100 year storms. These frequency coefficients are
1.1, 1.2, and 1.25 respectively.
Calculated design flowrates:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Flowrates 20.68 23.43 26.03 32.85 38.92 43.55
(CFS)
Formulate hydrograph using step-function estimated SCS dimensionless UH ==>
Ultimate Soil Storage:
S = 0.38 inches
Precipitation Depths for 6 hr design storm:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
P-depth 2.65 3.38 3.90 4.62 5.19 5.75
(inches)
SCS runoff depth using default initial loss characteristics (0.2S and 0.8S):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Q* 2.24 2.96 3.48 4.19 4.76 5.32
(inches)
Time to peak for design hydrograph (for step-function hydrograph):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Tp 20.01 23.34 24.66 23.55 22.56 22.53
(minutes)
Resultant SWM design hydrographs ==>
2 year = 20.68 CFS @ 20.01 minutes
5 year = 23.43 CFS @ 23.34 minutes
10 year = 26.03 CFS @ 24.66 minutes
25 year = 32.85 CFS @ 23.55 minutes
50 year = 38.92 CFS @ 22.56 minutes
100 year = 43.55 CFS @ 22.53 minutes
SAND .FILTER DESIGN CALCULATIONS
SAND FILTER BASIC DESIGN CHARACTERISTICS.As
SAND FILTER
HSS-01000
REOUIRED AREAs AND VOLUMEs
SAND CHAMBER:
Required Area = 972 sf
Actual Area = 1099 sf
Required Volume = 1458 cf
Actual Volume = 2819 cf
SEDIMENT CHAMBER
Required Area = 972 sf
Actual Area = 1142 sf
J.E. SCHRUM, E.I.
5/9/02
Required Volume = 1458 cf
Actual Volume = 3026 cf
HANNOVER ASSISTED LIVING RAT HYD GEN.xIs
SAND FILTER
HHC-01000
Small Watershed Method Hydroaragh Generation
(Rf. Elements of Urban Stormwater Design, H. R. Malcom, PE)
Drainage Area Description =_>
Total Drainage Area =
J. E. SCHRUM, E.I.
5/9/02
Impervious area = 2.02 AC @ c= 0.95 and CN = 98.0
Open / Grassy / Landscaped Area = 0.68 AC @ c= 0.25 and CN = 61.0
Wooded Area = 0.00 AC @ c= 0.00 and CN = .0.0
Other undescribed area = 0.00 AC @ c= 0.00 and CN = 0.0
Total DA = 2.70 AC c= 0.77 and CN = 89
Design Storm Description / Watershed Sensitivity =_>
Time of Concentration = 5.0 minutes
Enter known IDF factors to compute the intensity, or enter a known intensity in the area
marked "known intensity". If known, clear all IDF factors from the chart.
IDF Factors:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
g 132 169 195 232 261 290
h 18 21 22 23 24 25
Calculated Intensities (do not enter known values here):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Intensity 5.74 6.50 7.22 8.29 9.00 9.67
(in/hr)
Known Intensities (enter known values here if not calculating above, else enter zero):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Intensity 0.00 0.00 0.00 0.00 0.00 0.00
(in/hr)
HANNOVER ASSISTED LIVING RAT HYD GEN.xIs
SAND FILTER
HHC-01000
Design storm flowrates =_>
Flowrates are calculated using the rational method, and incorporating frequency
coefficients for the 25, 50, and 100 year storms. These frequency coefficients are
1.1, 1.2, and 1.25 respectively.
Calculated design flowrates:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Flowrates 11.99 13.58 15.09 19.04 22.56 25.24
(CFS)
Formulate hydrograph using step-function estimated SCS dimensionless UH =_>
Ultimate Soil Storage:
S = 1.28 inches
Precipitation Depths for 6 hr design storm:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
P-depth 2.65 3.38 3.90 4.62 5.19 5.75
(inches)
SCS runoff depth using default initial loss characteristics (0.2S and 0.8S):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Q* 1.56 2.22 2.70 3.38 3.92 4.46
(inches)
Time to peak for design hydrograph (for step-function hydrograph):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
TP 15.30 19.19 21.01 20.83 20.41 20.75
(minutes)
Resultant SWIM design hydrographs =_>
2 year = 11.99 CFS @ 15.30 minutes
5 year = 13.58 CFS @ 19.19 minutes
10 year = 15.09 CFS @ 21.01 minutes
25 year = 19.04 CFS @ 20.83 minutes
50 year = 22.56 CFS @ 20.41 minutes
100 year = 25.24 CFS @ 20.75 minutes
J. E. SCHRUM, E.I.
5/9/02
STAGE-STORAGE.XLS
SAND FILTER TOTAL
HHC-01000
Stage-Storage Function
Average Incremental Accumulated Estimated
Contour Contour Contour Contour Stage
Contour Stage Area Area Volume Volume w/ S-S Fxn
(feet) (feet) (SF) (SF) (CF) (CF) (feet)
304.0 0.0 2241
306.0 2.0 3605 2923 5846 5846 2.00
308.0 4.0 4818 4212 8423 14269 4.00
Storage vs. Stage,
16000
14000
y = 2395.1x12874
12000 R2 = 1
V 10000
m 8000
6000
N
4000
2000
0
0.0 1.0 2.0 3.0 4.0 5.0
Stage (feet)
KS = 2395.1
b = 1.2874
J.E. SCHRUM, E.I.
5/9/02
IOF 1
QUALPOND.XLS
Sand Filter
HHC-01000
Water Quality Pond Design Sheet
Project Name: HANNOVER ASSISTED LIVING
Designer: J. E. Schrum, E.I.
Job Number: HHC-01000
Date: 5/9/02
Ks = 2395.1
b = 1.2874
Calculation of Runoff Volume required for storage
J.E. SCHRUM, E.I.
The runoff to the pond for the 1" storm detention requirement is calculated using the SCS curve
number method. Impervious areas that directly enter the pond are counted as Directly Connected
Impervious Areas (DCIAs). No infiltration calculation will be provided for these areas. Areas
not directly connected will be accounted for in a composite curve number.
From SCS Soils Survey map, predominant hydrologic soil type = B
Using basic SCS runoff methodology, with no adjustments made
to initial abstractions (0.2*S and 0.8*S).
Impervious Area, directly connected (DCIA) = 2.02 acres
@CN= . 98
Other areas draining to pond (not DCIA) = 0.68 acres
@CN= 61
Runoff from DCIAs =_>
Precipitation amount = 1.0 inches
S = 0.204 inches (calculated)
Q* = 0.791 inches (calculated)
Runoff volume = 5799 CF
Runoff from non-connected areas =_>
Precipitation amount = 1.0 inches
S = 6.393 inches (calculated)
Q* = 0.000 inches (calculated)
Runoff volume 0 CF
Therefore, total runoff from precipitation in question = 5799 CF
Page 1
QUALPONDALS
Sand Filter
HHC-01000
This amount of runoff must be stored in the pond above normal pool elevation,
and be released in a period of two (2) to five (5) days, by an inverted PVC
siphon, the invert end of which is set at permanent pool elevation.
J.E. SCHRUM, E.I.
Calculation of depth required for runoff storage pool (above normal pool)
Normal pool depth (above invert) = 0.00 feet
Storage provided at permanent pool depth = 0 CF (calculated)
Total storage required for normal + storage pool = 5799 CF
Stage (above invert) associated with this storage = 1.99 feet
Therefore, depth required above normal pool for storm storage = 1.99 feet
23.85 inches
Therefore set crest of principal spillway at stage = 2.50 feet
and EL = 306.50 feet
At principal spillway crest, storm pool storage provided = 7792 CF
Page 2
sand filter drawdown.xis
Sand Filter
HHC-01000
Sand Filter Drain Pipe Desian Sheet
D siphon =
No. siphons =
Ks =
b=
Cd siphon =
Siphon Invert
=
Volume @ Normal Pool =
Basin Invert
=
6 inches
1
2395.1
1.2874
0.60
302.50 feet
0 CF
304.00 feet
WSEL
feet Vol. Remaining
c Siphon Flow
cfs Avg. Flow
cfs Incr. Vol.
c Incr. Time
sec
306.500 7792 1.828
306.292 6967 1.776 1.802 825.2 457.9
306.084 6163 1.723 1.750 803.9 459.4
305.875 5382 1.669 1.696 781.1 460.5
305.667 4625 1.612 1.640 756.5 461.2
305.459 3895 1.554 1.583 729.8 461.0
305.251 3195 1.493 1.523 700.4 459.8
305.043 2527 1.429 1.461 667.5 456.9
304.834 1897 1.363 1.396 630.1 451.4
304.626 1311 1.293 1.328 586.1 441.4
304.418 779 1.219 1.256 531.9 423.5
Drawdown Time = 0.05 days
By comparison, if calculated by the average head over the orifice (assuming
average head is half the total depth), the result would be:
Average driving head on orifice = 1.875 feet
Orifice composite loss coefficient = 0.600
X-Sectional area of 1 - 6" inverted siphon = 0.196 fe
Q = 1.2946 cfs
Drawdown Time = Volume / Flowrate / 86400 (sec/day)
Drawdown Time = 0.07 days
Conclusion : Use 1 - 6" Diameter PVC drain pipe to drawdown the accumulated
volume from the 1.0 " storm runoff, with a required time of about 0.06 days
Therefore, the pipe will not constrain the drainage of the sand media.
J.E. SCHRUM, E.I.
5/9/02
SIPHONS.XLS
sand filter drawdown.xls
Sand Filter
HHC-01000
Drainage through the Sand Media:
J.E. SCHRUM, E.I.
5/9/02
Per NC DENR DWQ, the sand to be used in the filter is to be less than 2 mm in average diameter.
DWQ assumes-this.sand to have a permeability of 0.04 gal/min/SF (with 1 foot of head over the sand surface).
Average depth of water over sand surface (1/2 maximum depth) = 1.25 feet
The DWQ assumption for sand permeability will be used.
Calculation of drawdown time through the sand =_>
Surface area of horizontal sand surface = 1099 SF
Assumed permeability of sand = 0.04 gal/min/SF
Volume stored during storm of interest = 7792 CF
Time required to drawdown through the sand media= 0.92 days
In this case, the sand media is the restricting factor, resulting in a drawdown time
of 0.92 days (22.1 hours). This is within the DWQ requirement that requires the sand filter
drained within a 24 hour time period.
SIPHONS.XLS
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conc riser antiflotation.xis
SAND FILTER
HHC-01000
Manhole Riser/Barrel Anti-
Input Data =_>
Inside diameter of manhole =
Wall thickness of manhole =
Base thickness of manhole =
Base diameter of manhole =
Inside height of Manhole =
Concrete unit weight =
OD of barrel exiting manhole =
Size of drain pipe (if present) _
Trash Rack water displacement =
Concrete Present =_>
Total amount of concrete:
J.E. SCHRUM, E.I.
5/9/02
Flotation Calculation Sheet
4.0 feet
5.0 inches
6.0 inches
4.8 feet
10.1 feet
142.0 PCF Note: NC Products lists unit wt. of
24.5 inches manhole concrete at 142 PC F.
6.0 inches
52.0 CF
Base of Manhole = 9.174 CF
Manhole Walls = 58.392 CF
Adjust for openings:
Opening for barrel = 1.364 CF
Opening for drain pipe = 0.082 CF
Total Concrete present, adjusted for openings = 66.120 CF
Weight of concrete present = 9389 Ibs
Amount of water displaced =_>
Displacement by concrete = 66.120 CF
Displacement by open air in riser = 126.921 CF
Displacement by trash rack = 51.954 CF
Total water displaced by riser/barrel structure = 244.995 CF
Weight of water displaced = 15288 Ibs
Page 1
conc riser antiflotation.xls J.E. SCHRUM, E.I.
SAND FILTER 5/9/02
HHC-01000
Calculate amount of concrete to be added to riser =_>
Safety factor to use = 1.15 (recommend 1.15 or higher)
Must add = 8192 Ibs concrete for buoyancy
Concrete unit weight for use = 142 PCF (note above observation for NCP concrete)
Buoyant weight of this concrete = 79.60 PCF -
Buoyant, with safety factor applied = 69.22 PCF
Therefore, must add = 118.348 CF of concrete
Standard based described above = 9.174 CF of concrete
Therefore, base design must have = 127.522 CF of concrete
Calculate size of base for riser assembly =>
Diameter = 7.400 feet
Thickness = 36.0 inches
Concrete Present = 129.026 CF OK
Check validity of base as designed =_>
Total Water Displaced = 364.847 CF
Total Concrete Present = 185.972 CF
Total Water Displaced = 22766 Ibs
Total Concrete Present = 26408 Ibs
Actual safety factor = 1.16 OK
Results of design =_>

Base diameter= 7.40 feet
Base Thickness = 36.00 inches
CY of concrete total in base = 4.72 CY
Concrete unit weight in added base >= 142 PCF
Page 2
TIE JOHN K McADAMS COMP
LETTER OF TRANSMITTAL
To: Mr. Todd St. John
North Carolina Division of Water Quality
Environmental Engineer
2321 Crabtree Boulevard
** FEDERAL EXPRESS **
Raleigh, North Carolina 27604
Re: The Gardens at Wakefield Job No.: FCC-01000
I am sending you the following item(s):
COPIES DATE NO. DESCRIPTION
2 Sand Filter Details
1 O and M Agreement
These are transmitted as checked below:
? As requested
® For approval
? For review and comment
Remarks:
Copy to: D. Amos Clark, J. Schrum
M. Munn
.`;. 9 2002
Date: April 25, 2002
? For your use
? --

Signed: ZZA:"?
Brandon R. Finch /-PE
Project Engineer
FOR INTERNAL USE ONLY
? Copy Letter of Transmittal Only to File
? Copy Entire Document to File
CIVIL ENGINEERING • LAND PLANNING • SURVEYING
PO Box 14005 • Research Triangle Paris, NC 27709 • [phone] • fax[phone]
www.johnrmcadams.com
x
PIS n?
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Since 1979
THE JOHN R. WADAMS COMPANY, INC.
nc??
,.?? GROUP
HANNOVER ASSISTED LIVLN ??? ?rnsFCrr N___
SAND FILTER DESIGN
DWQ Project # 970694
RALEIGH, NC
HHC-01000
J.E. SCHRUM, E.I.
May 10, 2002
??`•?O??H EAR p
EAL
-
2 495
??iO FNQ, d?.il$
m
5.6 ,oZ
CIVIL ENGINEERING • LAND PLANNING • SURVEYING
PO Box 14005 • Research Tdangle Park, NC 27709 • [phone] • fax [phone]
www.johnrmcadams.com
HANNOVER ASSISTED LIVING
Storm Drainage and Sand Filter Design
General Description
Located on the corner of Wakefield Pines Drive and Spruce Tree Way at Wakefield
Plantation, Hannover Assisted Living is a proposed extended care facility with parking
areas and utilities. This property is located in the Wakefield Development and is
therefore subject to a 401 Water Quality Certification under DWQ Project # 970694. A
sand filter will be utilized to comply with the TSS removal.
The included Summary of Results demonstrates that the sand filter meets all design
requirements as set forth by the NCDENR Stormwater Best Management Practices
(BMP, April 1999). The required area of the sand filter is 972 sf in both the sand
chamber and the sediment chamber. The actual surface area is 1,099 sf in the sand
chamber and 1,142 sf in the sediment chamber. The required volume is 1,458 cf in both
the sand chamber and the sediment chamber. The actual volume in the sand chamber is
„ 2,819 cf while the actual volume in the sediment chamber is 3,026 c£ Required volume
of the 1" rainfall storage is 5,799 cf and the actual volume provided is 7,792 cf.
Drawdown of the runoff from the 1" rainfall will occur over a 22.1 hour period.
The sand filter pas-96s-the runoff from the 100-year storm event with a peak elevation of
3'07.3 ft.' The top of berm elevation is 308.0 ft in post-development. The freeboard in the
100-year storm event is therefore 0.7 ft.
Calculation Methodology for Storm Drainage and Sand Filter Design
• The Rational Method was used to generate flowrates in the design of the storm
drainage system.
• Routing of the sand filter was achieved using the Chainsaw Method developed by
H. Rooney Malcom, P.E., NCSU.
• Rainfall data used in the analysis is from USWB TP-40 and NOAA Hydro-35.
This data was used to generate an equation describing the IDF Curves for the
RDU region. The equation is in the form: Rainfall Intensity [in/hr] = g/(h + Time
of Concentration [minutes]), where g and h are constants dependent upon the
return period.
• The Time of Concentration was, in all cases, assumed 5 minutes because of the
small size of all the drainage areas.
• Using Wake County Soil Survey, the majority of on- -site soils were determined
to be from Hydrologic Soil Group `B'. Therefore, the SCS Curve Numbers used
in further hydrologic calculations are selected appropriately.
• On-site topography is from information collected by The John R. McAdams
Company, Inc.
SUMMARY OF RESULTS.xls
SAND FILTER
HHC-01000
SAND FILTER ROUTING -
TOP OF BERM = 308.00
RETURN
PERIOD OUTFLOW WSE FREEBOARD
(years) INFLOW (cfs) (cfs) (ft) (ft)
100 25.2 25.1 307.26 0.7
SAND FILTER BMP DESIGN ASPECTS =>
SAND CHAMBER
Required Area =
Actual Area =
Required Volume =
Actual Volume =
SEDIMENT CHAMBER
Required Area =
Actual Area =
Required Volume =
Actual Volume =
1" RAINFALL ASPECTS
Volume Required =
Volume Provided =
Drawdown Time =
972 sf
1099 sf
1458 cf
2819 cf
972 sf
1142 sf
1458 cf
3026 cf
J.E. SCHRUM, E.I.
5/9/02
5799 cf
7792 cf (Note - Riser crest elevation based upon detention control)
22.1 hours
DATA INPUTS
Since 1979
THE JOHN K McADAMS COMPANY, INC.
PIAR .4 2002
THE GARDENS AT WAKEFIELD PLANTATION ,
SAND FILTER DESIGN
NCDWQ PROJECT # 970694
RALEIGH, NC
FCC-01000
J.E. SCHRUM, E.I.
February 28, 2002
CIVIL ENGINEERING • LAND PLANNING • SURVEYING
PO Box 14005 • Research Triangle Park, INC 27709 • [phone] • fax [phone]
www.johnrmcadams.com
THE GARDENS AT WAKEFIELD PLANTATION
Sand Filter Design Calculations
General Description
Located off Spruce Tree Way, The Gardens at Wakefield Plantation is a proposed multi-
family housing site with parking areas and utilities. This property is located in the
Wakefield Development and is therefore subject to a 401 Water Quality Certification
under DWQ Project # 970694. This permit requires an approved stormwater
management program, which meets 85% TSS removal. A sand filter will be utilized to
comply with the TSS removal.
The site is composed of two drainage basins in the post-development condition. All
impervious portions of the sub-basin will be diverted to a sand-filter in post-development
in order to reduce post-development nitrogen loading and as the means of meeting the
85% TSS removal requirement.
The included Summary of Results demonstrates that the sand filter meets all design
requirements as set forth by the NCDENR Stormwater Best Management Practices
(BMP, April 1999). This includes meeting the requirements of surface area in both the
sediment and sand chamber and the volumetric requirements based upon storage of the V
rainfall. The sand filter also passes the flow resulting from the 100-year storm event with
1.2 ft of freeboard from the water surface elevation to the top of berm.
Calculation Methodology for Storm Drainage and Sand Filter Design
The Rational Method is used to generate post-development peak now rates in the
two-, ten- and 100-year storm events. A Rational C value of 0.85 is utilized for
post-development.
• Rainfall data used in the analysis is from USWB TP-40 and NOAA Hydro-35.
This data was used to generate an equation describing the IDF Curves for the
RDU region. The equation is in the form: Rainfall Intensity [in/hr] = g/(h + Time
of Concentration [minutes]), where g and h are constants dependent upon the
return period.
• The Time of Concentration was, in all cases, assumed 5 minutes because of the
small size of all the drainage areas.
• Using Wake County Soil Survey, the majority of on- -site soils were determined
to be from Hydrologic Soil Group `B'. Therefore, the SCS Curve Numbers used
in further hydrologic calculations are selected appropriately.
• On-site topography is from information collected by The John R. McAdams
Company, Inc.
• The sand filter was designed utilizing the guidelines as set forth in NCDWQ's
Best Management Practices (BMP, 4, 1999). All aspects of the sand filter design
conform to this manual.

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®McADAMS
DWQ SUMMARY OF RESULTS.xls
SAND FILTER
FCC-01000
SAND FILTER ROUTING =>
TOP OF BERM = 295.70
RETURN
PERIOD
(years)

INFLOW (cfs)
OUTFLOW
(cfs)
WSE
(ft)
FREEBOARD
(ft)
2 20.7 7.7 293.30 2.4
10 26.0 15.2 293.47 2.2
100 43.6 23.2 294.46 1.2
SAND FILTER BMPDESIGNASPECTS=>
SAND CHAMBER
Required Area =
TAclual Area =
Required Volume =
olume
SEDIMENT CHAMBER
RAq fired Area
Actual Area
Required Volume =
Actual Volume
1" RAINFALL ASPECTS
Volume Required
Volume Provided =
Drawdown Time =
1728 sf
1758 sf
2592 cf
";-4245 cf
J.E. SCHRUM, E.I.
2/28/02
1728 sf _
s 1742 k {sf
2592 cf
4334 cf
6173 - cf?
29710 cf (Note - Riser crest elevation based upon detention control)
13.9 hours
SAND FILTER DESIGN
J.E. SCHRUM, E.I.
1/29/02
f ` REQUIRED AREAs AND: VOLUMES
SAND CHAMBER:
is
Required Area = 1728 sf /
vctual2;Area,;., 1758 sfV
Required Volume = 2592 cf
:Actual Volume = 4245 cf
SEDIMENT CHAMBER
Required Area = 1728 sf
Actual Area = 1742 sf
Required Volume = 2592 cf
.-Actual Volume = 4334 cf

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POST-DEV TO SAND FILTER
i, Small Watershed Method Hydmaranh Generation
(Rf.• "Elements of Urban Storrnwater Design, H. R. Malcom, PE)
Drainage Area Description =_>
Total DA = 4.24 AC c= 0.85 and CN = 96
Design Storm Description / Watershed Sensitivity =_>
Time of Concentration = 5.0 minutes
Enter known IDF factors to compute the intensity, or enter a known intensity in the area
marked "known intensity". If known, clear all IDF factors from the chart.
IDF Factors:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
g 132 169 195 232 261 290
h 18 21 22 23 24 25
Calculated Intensities (do not enter known values here):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Intensity 5.74 6.50 7.22 8.29 9.00 9.67
(in/hr)
Known Intensities (enter known values here if not calculating above, else enter zero):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
intensity 0.00 0.00 0.00 0.00 0.00 0.00
(in/hr)
Design storm flowrates =_>
Foowrates are calculated using the rational method, and incorporating frequency
POST-DEV TO SAND FILTER
coefficients for the 25, 50, and 100 year storms. These frequency coefficients are
1.1, 1.2, and 1.25 respectively.
Calculated design flowrates:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Flowrates 20.68 23.43 26.03 32.85 38.92 43.55
(CFS)
Formulate hydrograph using step-function estimated SCS dimensionless UH ==>
Ultimate Soil Storage:
S = 0.38 inches
Precipitation Depths for 6 hr design storm:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
P-depth 2.65 3.38 3.90 4.62 5.19 5.75
(inches)
SCS runoff depth using default initial loss characteristics (0.2S and 0.8S):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Q* 2.24 2.96 3.48 4.19 4.76 5.32
(inches)
Time to peak for design hydrograph (for step-function hydrograph):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Tp 20.01 23.34 24.66 23.55 22.56 22.53
(minutes)
Resultant SWM design hydrographs ==>
2 year = 20.68 CFS @ 20.01 minutes
5 year = 23.43 CFS @ 23.34 minutes
10 year = 26.03 CFS @ 24.66 minutes
25 year = 32.85 CFS @ 23.55 minutes
50 year = 38.92 CFS @ 22.56 minutes
100 year = 43.55 CFS @ 22.53 minutes
SAND .FILTER DESIGN CALCULATIONS
SAND FILTER BASIC DESIGN CHARACTERISTICS.As
SAND FILTER
HSS-01000
REOUIRED AREAs AND VOLUMEs
SAND CHAMBER:
Required Area = 972 sf
Actual Area = 1099 sf
Required Volume = 1458 cf
Actual Volume = 2819 cf
SEDIMENT CHAMBER
Required Area = 972 sf
Actual Area = 1142 sf
J.E. SCHRUM, E.I.
5/9/02
Required Volume = 1458 cf
Actual Volume = 3026 cf
HANNOVER ASSISTED LIVING RAT HYD GEN.xIs
SAND FILTER
HHC-01000
Small Watershed Method Hydroaragh Generation
(Rf. Elements of Urban Stormwater Design, H. R. Malcom, PE)
Drainage Area Description =_>
Total Drainage Area =
J. E. SCHRUM, E.I.
5/9/02
Impervious area = 2.02 AC @ c= 0.95 and CN = 98.0
Open / Grassy / Landscaped Area = 0.68 AC @ c= 0.25 and CN = 61.0
Wooded Area = 0.00 AC @ c= 0.00 and CN = .0.0
Other undescribed area = 0.00 AC @ c= 0.00 and CN = 0.0
Total DA = 2.70 AC c= 0.77 and CN = 89
Design Storm Description / Watershed Sensitivity =_>
Time of Concentration = 5.0 minutes
Enter known IDF factors to compute the intensity, or enter a known intensity in the area
marked "known intensity". If known, clear all IDF factors from the chart.
IDF Factors:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
g 132 169 195 232 261 290
h 18 21 22 23 24 25
Calculated Intensities (do not enter known values here):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Intensity 5.74 6.50 7.22 8.29 9.00 9.67
(in/hr)
Known Intensities (enter known values here if not calculating above, else enter zero):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Intensity 0.00 0.00 0.00 0.00 0.00 0.00
(in/hr)
HANNOVER ASSISTED LIVING RAT HYD GEN.xIs
SAND FILTER
HHC-01000
Design storm flowrates =_>
Flowrates are calculated using the rational method, and incorporating frequency
coefficients for the 25, 50, and 100 year storms. These frequency coefficients are
1.1, 1.2, and 1.25 respectively.
Calculated design flowrates:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Flowrates 11.99 13.58 15.09 19.04 22.56 25.24
(CFS)
Formulate hydrograph using step-function estimated SCS dimensionless UH =_>
Ultimate Soil Storage:
S = 1.28 inches
Precipitation Depths for 6 hr design storm:
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
P-depth 2.65 3.38 3.90 4.62 5.19 5.75
(inches)
SCS runoff depth using default initial loss characteristics (0.2S and 0.8S):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
Q* 1.56 2.22 2.70 3.38 3.92 4.46
(inches)
Time to peak for design hydrograph (for step-function hydrograph):
2 year 5 year 10 year 25 year 50 year 100 year
storm storm storm storm storm storm
TP 15.30 19.19 21.01 20.83 20.41 20.75
(minutes)
Resultant SWIM design hydrographs =_>
2 year = 11.99 CFS @ 15.30 minutes
5 year = 13.58 CFS @ 19.19 minutes
10 year = 15.09 CFS @ 21.01 minutes
25 year = 19.04 CFS @ 20.83 minutes
50 year = 22.56 CFS @ 20.41 minutes
100 year = 25.24 CFS @ 20.75 minutes
J. E. SCHRUM, E.I.
5/9/02
STAGE-STORAGE.XLS
SAND FILTER TOTAL
HHC-01000
Stage-Storage Function
Average Incremental Accumulated Estimated
Contour Contour Contour Contour Stage
Contour Stage Area Area Volume Volume w/ S-S Fxn
(feet) (feet) (SF) (SF) (CF) (CF) (feet)
304.0 0.0 2241
306.0 2.0 3605 2923 5846 5846 2.00
308.0 4.0 4818 4212 8423 14269 4.00
Storage vs. Stage,
16000
14000
y = 2395.1x12874
12000 R2 = 1
V 10000
m 8000
6000
N
4000
2000
0
0.0 1.0 2.0 3.0 4.0 5.0
Stage (feet)
KS = 2395.1
b = 1.2874
J.E. SCHRUM, E.I.
5/9/02
IOF 1
QUALPOND.XLS
Sand Filter
HHC-01000
Water Quality Pond Design Sheet
Project Name: HANNOVER ASSISTED LIVING
Designer: J. E. Schrum, E.I.
Job Number: HHC-01000
Date: 5/9/02
Ks = 2395.1
b = 1.2874
Calculation of Runoff Volume required for storage
J.E. SCHRUM, E.I.
The runoff to the pond for the 1" storm detention requirement is calculated using the SCS curve
number method. Impervious areas that directly enter the pond are counted as Directly Connected
Impervious Areas (DCIAs). No infiltration calculation will be provided for these areas. Areas
not directly connected will be accounted for in a composite curve number.
From SCS Soils Survey map, predominant hydrologic soil type = B
Using basic SCS runoff methodology, with no adjustments made
to initial abstractions (0.2*S and 0.8*S).
Impervious Area, directly connected (DCIA) = 2.02 acres
@CN= . 98
Other areas draining to pond (not DCIA) = 0.68 acres
@CN= 61
Runoff from DCIAs =_>
Precipitation amount = 1.0 inches
S = 0.204 inches (calculated)
Q* = 0.791 inches (calculated)
Runoff volume = 5799 CF
Runoff from non-connected areas =_>
Precipitation amount = 1.0 inches
S = 6.393 inches (calculated)
Q* = 0.000 inches (calculated)
Runoff volume 0 CF
Therefore, total runoff from precipitation in question = 5799 CF
Page 1
QUALPONDALS
Sand Filter
HHC-01000
This amount of runoff must be stored in the pond above normal pool elevation,
and be released in a period of two (2) to five (5) days, by an inverted PVC
siphon, the invert end of which is set at permanent pool elevation.
J.E. SCHRUM, E.I.
Calculation of depth required for runoff storage pool (above normal pool)
Normal pool depth (above invert) = 0.00 feet
Storage provided at permanent pool depth = 0 CF (calculated)
Total storage required for normal + storage pool = 5799 CF
Stage (above invert) associated with this storage = 1.99 feet
Therefore, depth required above normal pool for storm storage = 1.99 feet
23.85 inches
Therefore set crest of principal spillway at stage = 2.50 feet
and EL = 306.50 feet
At principal spillway crest, storm pool storage provided = 7792 CF
Page 2
sand filter drawdown.xis
Sand Filter
HHC-01000
Sand Filter Drain Pipe Desian Sheet
D siphon =
No. siphons =
Ks =
b=
Cd siphon =
Siphon Invert
=
Volume @ Normal Pool =
Basin Invert
=
6 inches
1
2395.1
1.2874
0.60
302.50 feet
0 CF
304.00 feet
WSEL
feet Vol. Remaining
c Siphon Flow
cfs Avg. Flow
cfs Incr. Vol.
c Incr. Time
sec
306.500 7792 1.828
306.292 6967 1.776 1.802 825.2 457.9
306.084 6163 1.723 1.750 803.9 459.4
305.875 5382 1.669 1.696 781.1 460.5
305.667 4625 1.612 1.640 756.5 461.2
305.459 3895 1.554 1.583 729.8 461.0
305.251 3195 1.493 1.523 700.4 459.8
305.043 2527 1.429 1.461 667.5 456.9
304.834 1897 1.363 1.396 630.1 451.4
304.626 1311 1.293 1.328 586.1 441.4
304.418 779 1.219 1.256 531.9 423.5
Drawdown Time = 0.05 days
By comparison, if calculated by the average head over the orifice (assuming
average head is half the total depth), the result would be:
Average driving head on orifice = 1.875 feet
Orifice composite loss coefficient = 0.600
X-Sectional area of 1 - 6" inverted siphon = 0.196 fe
Q = 1.2946 cfs
Drawdown Time = Volume / Flowrate / 86400 (sec/day)
Drawdown Time = 0.07 days
Conclusion : Use 1 - 6" Diameter PVC drain pipe to drawdown the accumulated
volume from the 1.0 " storm runoff, with a required time of about 0.06 days
Therefore, the pipe will not constrain the drainage of the sand media.
J.E. SCHRUM, E.I.
5/9/02
SIPHONS.XLS
sand filter drawdown.xls
Sand Filter
HHC-01000
Drainage through the Sand Media:
J.E. SCHRUM, E.I.
5/9/02
Per NC DENR DWQ, the sand to be used in the filter is to be less than 2 mm in average diameter.
DWQ assumes-this.sand to have a permeability of 0.04 gal/min/SF (with 1 foot of head over the sand surface).
Average depth of water over sand surface (1/2 maximum depth) = 1.25 feet
The DWQ assumption for sand permeability will be used.
Calculation of drawdown time through the sand =_>
Surface area of horizontal sand surface = 1099 SF
Assumed permeability of sand = 0.04 gal/min/SF
Volume stored during storm of interest = 7792 CF
Time required to drawdown through the sand media= 0.92 days
In this case, the sand media is the restricting factor, resulting in a drawdown time
of 0.92 days (22.1 hours). This is within the DWQ requirement that requires the sand filter
drained within a 24 hour time period.
SIPHONS.XLS
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conc riser antiflotation.xis
SAND FILTER
HHC-01000
Manhole Riser/Barrel Anti-
Input Data =_>
Inside diameter of manhole =
Wall thickness of manhole =
Base thickness of manhole =
Base diameter of manhole =
Inside height of Manhole =
Concrete unit weight =
OD of barrel exiting manhole =
Size of drain pipe (if present) _
Trash Rack water displacement =
Concrete Present =_>
Total amount of concrete:
J.E. SCHRUM, E.I.
5/9/02
Flotation Calculation Sheet
4.0 feet
5.0 inches
6.0 inches
4.8 feet
10.1 feet
142.0 PCF Note: NC Products lists unit wt. of
24.5 inches manhole concrete at 142 PC F.
6.0 inches
52.0 CF
Base of Manhole = 9.174 CF
Manhole Walls = 58.392 CF
Adjust for openings:
Opening for barrel = 1.364 CF
Opening for drain pipe = 0.082 CF
Total Concrete present, adjusted for openings = 66.120 CF
Weight of concrete present = 9389 Ibs
Amount of water displaced =_>
Displacement by concrete = 66.120 CF
Displacement by open air in riser = 126.921 CF
Displacement by trash rack = 51.954 CF
Total water displaced by riser/barrel structure = 244.995 CF
Weight of water displaced = 15288 Ibs
Page 1
conc riser antiflotation.xls J.E. SCHRUM, E.I.
SAND FILTER 5/9/02
HHC-01000
Calculate amount of concrete to be added to riser =_>
Safety factor to use = 1.15 (recommend 1.15 or higher)
Must add = 8192 Ibs concrete for buoyancy
Concrete unit weight for use = 142 PCF (note above observation for NCP concrete)
Buoyant weight of this concrete = 79.60 PCF -
Buoyant, with safety factor applied = 69.22 PCF
Therefore, must add = 118.348 CF of concrete
Standard based described above = 9.174 CF of concrete
Therefore, base design must have = 127.522 CF of concrete
Calculate size of base for riser assembly =>
Diameter = 7.400 feet
Thickness = 36.0 inches
Concrete Present = 129.026 CF OK
Check validity of base as designed =_>
Total Water Displaced = 364.847 CF
Total Concrete Present = 185.972 CF
Total Water Displaced = 22766 Ibs
Total Concrete Present = 26408 Ibs
Actual safety factor = 1.16 OK
Results of design =_>

Base diameter= 7.40 feet
Base Thickness = 36.00 inches
CY of concrete total in base = 4.72 CY
Concrete unit weight in added base >= 142 PCF
Page 2