Tables: Small-Scale Sand Filters
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1. Table 1
BMP 2021, Ch 9.9, p. 1
| N.J.A.C. 7:8 Stormwater Management Rules – Applicable Design and Performance Standards |
|
|
|
Green Infrastructure |
Yes |
|
Stormwater Runoff Quantity |
Yes, when designed as an on-line system |
| GR |
Groundwater Recharge |
Yes |
| % |
Stormwater Runoff Quality |
80% TSS |
| Stormwater Runoff Quality Mechanisms and Corresponding Criteria |
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|
| --- |
--- |
|
| Settling |
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| Storage Volume |
Entire Water Quality Design Storm Volume |
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| Filtration |
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| Maximum Contributory Drainage Area |
2.5 acres |
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| Maximum Design Storm Drain Time |
72 hours, using slowest design permeability rate |
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| Sand bed minimum thickness |
18 inches |
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| Maximum storage above sand bed |
24 inches |
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| Maximum design permeability rate of sand bed |
2 inches/hour |
|
| Minimum topsoil permeability rate, if using optional vegetative cover |
2x the permeability of the subsoil |
|
Source context and notes
Source revision: March 2021.
# 9.9 SMALL-SCALE SAND FILTERS (GI)
[Figure: img-0.jpeg (original PDF, p. 1)](SOURCE.pdf#page=1)
Small-scale sand filters are stormwater management systems designed to maximize the removal of pollutants from stormwater runoff. A small-scale sand filter consists of a pre-treatment zone and a treatment zone, which includes the sand bed as the filter media and its underlying materials. Pollutants are treated through settling, filtration and adsorption by the sand bed prior to discharging stormwater runoff by infiltration into the subsoil. The total suspended solids (TSS) removal rate is 80%.
| N.J.A.C. 7:8 Stormwater Management Rules – Applicable Design and Performance Standards | | |
| --- | --- | --- |
| | Green Infrastructure | Yes |
| | Stormwater Runoff Quantity | Yes, when designed as an on-line system |
| GR | Groundwater Recharge | Yes |
| % | Stormwater Runoff Quality | 80% TSS |
| Stormwater Runoff Quality Mechanisms and Corresponding Criteria | |
| --- | --- |
| Settling | |
| Storage Volume | Entire Water Quality Design Storm Volume |
| Filtration | |
| Maximum Contributory Drainage Area | 2.5 acres |
| Maximum Design Storm Drain Time | 72 hours, using slowest design permeability rate |
| Sand bed minimum thickness | 18 inches |
| Maximum storage above sand bed | 24 inches |
| Maximum design permeability rate of sand bed | 2 inches/hour |
| Minimum topsoil permeability rate, if using optional vegetative cover | 2x the permeability of the subsoil |
2. Table 2
BMP 2021, Ch 9.9, p. 13
| Area = |
1 acre |
| CN Value = |
98 (100% Impervious) |
| Calculated WQDS Runoff Volume = |
3,755 cf |
| Forebay Primary Outflow: |
Perforated Riser Pipe |
| Forebay Secondary Outflow: |
Broad-crested Weir |
| Sand Bed Permeability Rate = |
2 inches/hour |
| Subsoil Permeability Rate = |
8 inches/hour |
| Forebay Surface Elevation = |
1.10 ft |
| Sand Bed Surface Elevation = |
0.00 ft |
| Assumed Depth of Stormwater Runoff to be infiltrated = |
1 ft above the small-scale sand filter surface |
Source context and notes
# Small-Scale Sand Filters
Source revision: March 2021.
# Designing A Small-Scale Sand Filter
The example below illustrates how to design a small-scale sand filter to treat the stormwater runoff generated by the WQDS. The following parameters apply:
| Area = | 1 acre |
| --- | --- |
| CN Value = | 98 (100% Impervious) |
| Calculated WQDS Runoff Volume = | 3,755 cf |
| Forebay Primary Outflow: | Perforated Riser Pipe |
| Forebay Secondary Outflow: | Broad-crested Weir |
| Sand Bed Permeability Rate = | 2 inches/hour |
| Subsoil Permeability Rate = | 8 inches/hour |
| Forebay Surface Elevation = | 1.10 ft |
| Sand Bed Surface Elevation = | 0.00 ft |
| Assumed Depth of Stormwater Runoff to be infiltrated = | 1 ft above the small-scale sand filter surface |
## Step 1: Forebay Sizing
The forebay must be sized to hold 10% of the WQDS volume. Assuming the depth of stormwater runoff in the forebay is equal to the depth of the WQDS in the surface of the small-scale sand filter system, which is assumed to be 1 ft, a rectangular forebay with a width of 20 ft and a length of 20 ft will provide adequate storage volume. However, in order to facilitate drainage, the water surface elevation in the forebay must be greater than the water surface elevation in the small-scale sand filter; in addition, the perforations in the riser pipe must be designed to ensure that the forebay will drain within 9 hours.
In this example, the WQDS water surface elevation (W.S.E.) in the forebay is 2.15 ft; this translates to a depth of 1.05 ft, with the additional 0.05 ft of depth resulting from head loss in the riser pipe. Based on the above elevations, the top of the riser pipe is set at an elevation of 2.20 ft. A grate or trash rack must be installed on the top of the riser to keep floatables from entering the riser pipe during large storm events.
3. Table 3
BMP 2021, Ch 9.9, p. 14
| Inflow Area = 43,560 sf,100.00% Impervious, Inflow Depth = 1.03" |
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| Inflow = 2.90 cfs @ 1.09 hrs, Volume= 3,755 cf |
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| Outflow = 0.14 cfs @ 1.89 hrs, Volume= 3,755 cf, Atten= 95%, Lag= 47.6 min |
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| Discarded = 0.14 cfs @ 0.70 hrs, Volume= 3,755 cf |
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| Primary = 0.00 cfs @ 1.89 hrs, Volume= 0 cf |
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| Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs |
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| Peak Elev= 1.98' @ 1.88 hrs Surf.Area= 1,520 sf Storage= 3,013 cf |
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| Plug-Flow detention time= 186.7 min calculated for 3,755 cf (100% of inflow) |
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| Center-of-Mass det. time= 186.6 min (256.9 - 70.3) |
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| Volume |
Invert |
Avail.Storage |
Storage Description |
|
| #1 |
0.00' |
6,080 cf |
Custom Stage Data (Prismatic) Listed below (Recalc) |
|
| Elevation (feet) |
Surf.Area (sq-ft) |
Inc.Store (cubic-feet) |
Cum.Store (cubic-feet) |
|
| 0.00 |
1,520 |
0 |
0 |
|
| 4.00 |
1,520 |
6,080 |
6,080 |
|
| Device |
Routing |
Invert |
Outlet Devices |
|
| #1 |
Discarded |
0.00' |
4.00 in/hr Exfiltration over Surface area |
|
| #2 |
Primary |
1.98' |
4.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads |
|
| Discarded OutFlow Max=0.14 cfs @ 0.70 hrs HW=0.04' (Free Discharge) |
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| T-1=Exfiltration (Exfiltration Controls 0.14 cfs) |
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| Primary OutFlow Max=0.00 cfs @ 1.89 hrs HW=1.98' (Free Discharge) |
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| T-2=Orifice/Grate (Weir Controls 0.00 cfs @ 0.13 fps) |
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|
Source context and notes
# Small-Scale Sand Filters
Source revision: March 2021.
# Summary Report:
| Inflow Area = 43,560 sf,100.00% Impervious, Inflow Depth = 1.03" | | | | |
| --- | --- | --- | --- | --- |
| Inflow = 2.90 cfs @ 1.09 hrs, Volume= 3,755 cf | | | | |
| Outflow = 0.14 cfs @ 1.89 hrs, Volume= 3,755 cf, Atten= 95%, Lag= 47.6 min | | | | |
| Discarded = 0.14 cfs @ 0.70 hrs, Volume= 3,755 cf | | | | |
| Primary = 0.00 cfs @ 1.89 hrs, Volume= 0 cf | | | | |
| Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs | | | | |
| Peak Elev= 1.98' @ 1.88 hrs Surf.Area= 1,520 sf Storage= 3,013 cf | | | | |
| Plug-Flow detention time= 186.7 min calculated for 3,755 cf (100% of inflow) | | | | |
| Center-of-Mass det. time= 186.6 min (256.9 - 70.3) | | | | |
| Volume | Invert | Avail.Storage | Storage Description | |
| #1 | 0.00' | 6,080 cf | Custom Stage Data (Prismatic) Listed below (Recalc) | |
| Elevation (feet) | Surf.Area (sq-ft) | Inc.Store (cubic-feet) | Cum.Store (cubic-feet) | |
| 0.00 | 1,520 | 0 | 0 | |
| 4.00 | 1,520 | 6,080 | 6,080 | |
| Device | Routing | Invert | Outlet Devices | |
| #1 | Discarded | 0.00' | 4.00 in/hr Exfiltration over Surface area | |
| #2 | Primary | 1.98' | 4.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads | |
| Discarded OutFlow Max=0.14 cfs @ 0.70 hrs HW=0.04' (Free Discharge) | | | | |
| T-1=Exfiltration (Exfiltration Controls 0.14 cfs) | | | | |
| Primary OutFlow Max=0.00 cfs @ 1.89 hrs HW=1.98' (Free Discharge) | | | | |
| T-2=Orifice/Grate (Weir Controls 0.00 cfs @ 0.13 fps) | | | | |
Source: HydroCAD® Summary Report; HydroCAD is a register trademark of HydroCAD Software Solutions LLC. Used with permission.
## WQDS Routing Table Excerpt:
| Time (hours) | Inflow (cfs) | Storage (cubic-feet) | Elevation (feet) | Outflow (cfs) | Discarded (cfs) | Primary (cfs) |
| --- | --- | --- | --- | --- | --- | --- |
| 0.00 | 0.00 | 0 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.10 | 0.00 | 0 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.20 | 0.00 | 0 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.30 | 0.00 | 0 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.40 | 0.02 | 1 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.50 | 0.07 | 12 | 0.01 | 0.03 | 0.03 | 0.00 |
| 0.60 | 0.15 | 33 | 0.02 | 0.08 | 0.08 | 0.00 |
| 0.70 | 0.22 | 62 | 0.04 | 0.14 | 0.14 | 0.00 |
| 0.80 | 0.30 | 102 | 0.07 | 0.14 | 0.14 | 0.00 |
| 0.90 | 0.63 | 211 | 0.14 | 0.14 | 0.14 | 0.00 |
| 1.00 | 1.84 | 558 | 0.37 | 0.14 | 0.14 | 0.00 |
| 1.10 | 2.89 | 1,403 | 0.92 | 0.14 | 0.14 | 0.00 |
| 1.20 | 1.60 | 2,197 | 1.45 | 0.14 | 0.14 | 0.00 |
| 1.30 | 0.76 | 2,552 | 1.68 | 0.14 | 0.14 | 0.00 |
| 1.40 | 0.44 | 2,705 | 1.78 | 0.14 | 0.14 | 0.00 |
| 1.50 | 0.39 | 2,801 | 1.84 | 0.14 | 0.14 | 0.00 |
| 1.60 | 0.33 | 2,883 | 1.90 | 0.14 | 0.14 | 0.00 |
| 1.70 | 0.30 | 2,944 | 1.94 | 0.14 | 0.14 | 0.00 |
| 1.80 | 0.26 | 2,997 | 1.97 | 0.14 | 0.14 | 0.00 |
| 1.90 | 0.12 | 3,012 | 1.98 | 0.14 | 0.14 | 0.00 |
| 2.00 | 0.10 | 3,000 | 1.97 | 0.14 | 0.14 | 0.00 |
| 2.10 | 0.04 | 2,977 | 1.96 | 0.14 | 0.14 | 0.00 |
| 2.20 | 0.00 | 2,931 | 1.93 | 0.14 | 0.14 | 0.00 |
| 2.30 | 0.00 | 2,881 | 1.90 | 0.14 | 0.14 | 0.00 |
| 2.40 | 0.00 | 2,830 | 1.86 | 0.14 | 0.14 | 0.00 |
4. Table 4
BMP 2021, Ch 9.9, p. 14
| Time (hours) |
Inflow (cfs) |
Storage (cubic-feet) |
Elevation (feet) |
Outflow (cfs) |
Discarded (cfs) |
Primary (cfs) |
| 0.00 |
0.00 |
0 |
0.00 |
0.00 |
0.00 |
0.00 |
| 0.10 |
0.00 |
0 |
0.00 |
0.00 |
0.00 |
0.00 |
| 0.20 |
0.00 |
0 |
0.00 |
0.00 |
0.00 |
0.00 |
| 0.30 |
0.00 |
0 |
0.00 |
0.00 |
0.00 |
0.00 |
| 0.40 |
0.02 |
1 |
0.00 |
0.00 |
0.00 |
0.00 |
| 0.50 |
0.07 |
12 |
0.01 |
0.03 |
0.03 |
0.00 |
| 0.60 |
0.15 |
33 |
0.02 |
0.08 |
0.08 |
0.00 |
| 0.70 |
0.22 |
62 |
0.04 |
0.14 |
0.14 |
0.00 |
| 0.80 |
0.30 |
102 |
0.07 |
0.14 |
0.14 |
0.00 |
| 0.90 |
0.63 |
211 |
0.14 |
0.14 |
0.14 |
0.00 |
| 1.00 |
1.84 |
558 |
0.37 |
0.14 |
0.14 |
0.00 |
| 1.10 |
2.89 |
1,403 |
0.92 |
0.14 |
0.14 |
0.00 |
| 1.20 |
1.60 |
2,197 |
1.45 |
0.14 |
0.14 |
0.00 |
| 1.30 |
0.76 |
2,552 |
1.68 |
0.14 |
0.14 |
0.00 |
| 1.40 |
0.44 |
2,705 |
1.78 |
0.14 |
0.14 |
0.00 |
| 1.50 |
0.39 |
2,801 |
1.84 |
0.14 |
0.14 |
0.00 |
| 1.60 |
0.33 |
2,883 |
1.90 |
0.14 |
0.14 |
0.00 |
| 1.70 |
0.30 |
2,944 |
1.94 |
0.14 |
0.14 |
0.00 |
| 1.80 |
0.26 |
2,997 |
1.97 |
0.14 |
0.14 |
0.00 |
| 1.90 |
0.12 |
3,012 |
1.98 |
0.14 |
0.14 |
0.00 |
| 2.00 |
0.10 |
3,000 |
1.97 |
0.14 |
0.14 |
0.00 |
| 2.10 |
0.04 |
2,977 |
1.96 |
0.14 |
0.14 |
0.00 |
| 2.20 |
0.00 |
2,931 |
1.93 |
0.14 |
0.14 |
0.00 |
| 2.30 |
0.00 |
2,881 |
1.90 |
0.14 |
0.14 |
0.00 |
| 2.40 |
0.00 |
2,830 |
1.86 |
0.14 |
0.14 |
0.00 |
Source context and notes
| T-1=Exfiltration (Exfiltration Controls 0.14 cfs) | | | | |
| Primary OutFlow Max=0.00 cfs @ 1.89 hrs HW=1.98' (Free Discharge) | | | | |
| T-2=Orifice/Grate (Weir Controls 0.00 cfs @ 0.13 fps) | | | | |
Source: HydroCAD® Summary Report; HydroCAD is a register trademark of HydroCAD Software Solutions LLC. Used with permission.
## WQDS Routing Table Excerpt:
| Time (hours) | Inflow (cfs) | Storage (cubic-feet) | Elevation (feet) | Outflow (cfs) | Discarded (cfs) | Primary (cfs) |
| --- | --- | --- | --- | --- | --- | --- |
| 0.00 | 0.00 | 0 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.10 | 0.00 | 0 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.20 | 0.00 | 0 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.30 | 0.00 | 0 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.40 | 0.02 | 1 | 0.00 | 0.00 | 0.00 | 0.00 |
| 0.50 | 0.07 | 12 | 0.01 | 0.03 | 0.03 | 0.00 |
| 0.60 | 0.15 | 33 | 0.02 | 0.08 | 0.08 | 0.00 |
| 0.70 | 0.22 | 62 | 0.04 | 0.14 | 0.14 | 0.00 |
| 0.80 | 0.30 | 102 | 0.07 | 0.14 | 0.14 | 0.00 |
| 0.90 | 0.63 | 211 | 0.14 | 0.14 | 0.14 | 0.00 |
| 1.00 | 1.84 | 558 | 0.37 | 0.14 | 0.14 | 0.00 |
| 1.10 | 2.89 | 1,403 | 0.92 | 0.14 | 0.14 | 0.00 |
| 1.20 | 1.60 | 2,197 | 1.45 | 0.14 | 0.14 | 0.00 |
| 1.30 | 0.76 | 2,552 | 1.68 | 0.14 | 0.14 | 0.00 |
| 1.40 | 0.44 | 2,705 | 1.78 | 0.14 | 0.14 | 0.00 |
| 1.50 | 0.39 | 2,801 | 1.84 | 0.14 | 0.14 | 0.00 |
| 1.60 | 0.33 | 2,883 | 1.90 | 0.14 | 0.14 | 0.00 |
| 1.70 | 0.30 | 2,944 | 1.94 | 0.14 | 0.14 | 0.00 |
| 1.80 | 0.26 | 2,997 | 1.97 | 0.14 | 0.14 | 0.00 |
| 1.90 | 0.12 | 3,012 | 1.98 | 0.14 | 0.14 | 0.00 |
| 2.00 | 0.10 | 3,000 | 1.97 | 0.14 | 0.14 | 0.00 |
| 2.10 | 0.04 | 2,977 | 1.96 | 0.14 | 0.14 | 0.00 |
| 2.20 | 0.00 | 2,931 | 1.93 | 0.14 | 0.14 | 0.00 |
| 2.30 | 0.00 | 2,881 | 1.90 | 0.14 | 0.14 | 0.00 |
| 2.40 | 0.00 | 2,830 | 1.86 | 0.14 | 0.14 | 0.00 |
Source: HydroCAD® Output; HydroCAD is a registered trademark of HydroCAD Soft-ware Solutions LLC. Used with permission.
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