Tables: Wet Ponds (Non-GI)
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1. Table 1
BMP 2021, Ch 11.6, p. 1
| N.J.A.C. 7:8 Stormwater Management Rules – Applicable Design and Performance Standards |
|
|
|
Green Infrastructure |
Not Allowed |
|
Stormwater Runoff Quantity |
Only with a waiver or variance from N.J.A.C. 7:8-5.3 and when designed as an on-line system |
| GR |
Groundwater Recharge |
Not Allowed |
| % |
Stormwater Runoff Quality |
Only with a waiver or variance from N.J.A.C. 7:8-5.3, 50% TSS removal with 1:1 pool volume ratio; up to 90% TSS removal if extended detention is also provided |
| Stormwater Runoff Quality Mechanisms and Corresponding Criteria |
|
|
| --- |
--- |
|
| Settling |
|
|
| Minimum Ratio of Permanent Pool Volume to WQ Design Storm Runoff Volume |
1:1 |
|
| 12 to 24-Hour Extended Detention |
Optional |
|
| Recommended Minimum Pool Length to Width Ratio |
3:1 |
|
| Presence of a Permanent Pool |
Required |
|
| Surface Area of Permanent Pool |
Minimum of 0.25 acre |
|
Source context and notes
# 11.6 WET PONDS (NON-GI)
[Figure: img-0.jpeg (original PDF, p. 1)](SOURCE.pdf#page=1)
Wet ponds, also known as retention basins, have an elevated outlet structure that creates a permanent pool where stormwater runoff is detained and attenuated. Wet ponds can be designed as multi-stage, multi-function systems; extended detention in the permanent pool provides pollutant treatment for runoff from the Water Quality Design Storm through sedimentation and biological processing; detention and attenuation are also provided for larger storm event through the
higher elevation outlets. When designed in accordance with this chapter, the total suspended solids (TSS) removal rate is $50 - 90\%$ , depending upon the storage volume in the permanent pool and the duration of detention time, if extended detention is provided. However, wet ponds can only be used to address stormwater runoff water quality and the quantity impacts of development when a waiver or variance from N.J.A.C. 7:8-5.3 is granted as they are not considered to be green infrastructure.
| N.J.A.C. 7:8 Stormwater Management Rules – Applicable Design and Performance Standards | | |
| --- | --- | --- |
| | Green Infrastructure | Not Allowed |
| | Stormwater Runoff Quantity | Only with a waiver or variance from N.J.A.C. 7:8-5.3 and when designed as an on-line system |
| GR | Groundwater Recharge | Not Allowed |
| % | Stormwater Runoff Quality | Only with a waiver or variance from N.J.A.C. 7:8-5.3, 50% TSS removal with 1:1 pool volume ratio; up to 90% TSS removal if extended detention is also provided |
| Stormwater Runoff Quality Mechanisms and Corresponding Criteria | |
| --- | --- |
| Settling | |
| Minimum Ratio of Permanent Pool Volume to WQ Design Storm Runoff Volume | 1:1 |
| 12 to 24-Hour Extended Detention | Optional |
| Recommended Minimum Pool Length to Width Ratio | 3:1 |
| Presence of a Permanent Pool | Required |
| Surface Area of Permanent Pool | Minimum of 0.25 acre |
2. Table 2
BMP 2021, Ch 11.6, p. 9
| Design Number |
Permanent Pool Volume (ac-ft) |
WQ Runoff Volume |
Extended Detention Period |
|
|
Ratio of Permanent Pool to WQ Runoff |
% TSS Removal |
|
|
|
12 Hr |
18 Hr |
24 Hr |
|
|
| 1 |
1.246 |
1.246 |
- |
- |
- |
|
|
| 2 |
2.764 |
1.481 |
X |
- |
- |
|
|
| 3 |
0.704 |
0.058 |
- |
- |
X |
|
|
Source context and notes
[Figure: img-6.jpeg (original PDF, p. 9)](SOURCE.pdf#page=9)
TSS Removal Rates for Wet Ponds
The following example illustrates how to use the chart to determine the TSS removal rate provided.
Example: A number of wet pond designs are to be evaluated for TSS removal rates.
| Design Number | Permanent Pool Volume (ac-ft) | WQ Runoff Volume | Extended Detention Period | | | Ratio of Permanent Pool to WQ Runoff | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- | --- |
| | | | 12 Hr | 18 Hr | 24 Hr | | |
| 1 | 1.246 | 1.246 | - | - | - | | |
| 2 | 2.764 | 1.481 | X | - | - | | |
| 3 | 0.704 | 0.058 | - | - | X | | |
Step 1: For each row of the designs, determine the ratio of the Permanent Pool Volume to the volume of stormwater generated by the WQDS. The result is located in the column below the red arrow symbol.
| Design Number | Permanent Pool Volume (ac-ft) | WQ Runoff Volume | Extended Detention Period | | | Ratio of Permanent Pool to WQ Runoff | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- | --- |
| | | | 12 Hr | 18 Hr | 24 Hr | | |
| 1 | 1.246 | 1.246 | - | - | - | 1.0 | |
| 2 | 2.764 | 1.481 | X | - | - | 1.9 | |
| 3 | 0.704 | 0.058 | - | - | X | 12.1 | |
3. Table 3
BMP 2021, Ch 11.6, p. 9
| Design Number |
Permanent Pool Volume (ac-ft) |
WQ Runoff Volume |
Extended Detention Period |
|
|
Ratio of Permanent Pool to WQ Runoff |
% TSS Removal |
|
|
|
12 Hr |
18 Hr |
24 Hr |
|
|
| 1 |
1.246 |
1.246 |
- |
- |
- |
1.0 |
|
| 2 |
2.764 |
1.481 |
X |
- |
- |
1.9 |
|
| 3 |
0.704 |
0.058 |
- |
- |
X |
12.1 |
|
Source context and notes
| --- | --- | --- | --- | --- | --- | --- | --- |
| | | | 12 Hr | 18 Hr | 24 Hr | | |
| 1 | 1.246 | 1.246 | - | - | - | | |
| 2 | 2.764 | 1.481 | X | - | - | | |
| 3 | 0.704 | 0.058 | - | - | X | | |
Step 1: For each row of the designs, determine the ratio of the Permanent Pool Volume to the volume of stormwater generated by the WQDS. The result is located in the column below the red arrow symbol.
| Design Number | Permanent Pool Volume (ac-ft) | WQ Runoff Volume | Extended Detention Period | | | Ratio of Permanent Pool to WQ Runoff | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- | --- |
| | | | 12 Hr | 18 Hr | 24 Hr | | |
| 1 | 1.246 | 1.246 | - | - | - | 1.0 | |
| 2 | 2.764 | 1.481 | X | - | - | 1.9 | |
| 3 | 0.704 | 0.058 | - | - | X | 12.1 | |
4. Table 4
BMP 2021, Ch 11.6, p. 11
| Design Number |
Permanent Pool Volume (ac-ft) |
WQ Runoff Volume |
Extended Detention Period |
|
|
Ratio of Permanent Pool to WQ Runoff |
% TSS Removal |
|
|
|
12 Hr |
18 Hr |
24 Hr |
|
|
| 1 |
1.246 |
1.246 |
- |
- |
- |
1.0 |
50% |
| 2 |
2.764 |
1.481 |
X |
- |
- |
1.9 |
79% |
| 3 |
0.704 |
0.058 |
- |
- |
X |
12.1 |
90% |
Source context and notes
# Wet Ponds (Non-GI)
Source revision: March 2021.
The resulting percent TSS Removal Rates appear in the last column of the table below.
| Design Number | Permanent Pool Volume (ac-ft) | WQ Runoff Volume | Extended Detention Period | | | Ratio of Permanent Pool to WQ Runoff | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- | --- |
| | | | 12 Hr | 18 Hr | 24 Hr | | |
| 1 | 1.246 | 1.246 | - | - | - | 1.0 | 50% |
| 2 | 2.764 | 1.481 | X | - | - | 1.9 | 79% |
| 3 | 0.704 | 0.058 | - | - | X | 12.1 | 90% |
## Considerations
A number of factors should be considered when utilizing a wet pond to treat stormwater runoff.
## Pretreatment
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