Tables: Wet Ponds Non-GI
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1. Table 1
BMP 2026, 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 2026, Ch 11.6, p. 10
| 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
# Wet Ponds Non-GI
Source revision: January 2026.
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 | |
Step 2: For each of the designs, find the ratio along the x-axis and project a vertical line up towards the curves. If the ratio is greater than 3.0, use 3.0. Stop at the curve that matches the period of extended detention the wet pond provides. Design #1 provides no extended detention; therefore, the lowest curve is used to determine the TSS removal rate. Designs #2 and 3 provide extended detention and therefore, use the upper set of curves.
3. Table 3
BMP 2026, Ch 11.6, p. 10
| 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 | |
Step 2: For each of the designs, find the ratio along the x-axis and project a vertical line up towards the curves. If the ratio is greater than 3.0, use 3.0. Stop at the curve that matches the period of extended detention the wet pond provides. Design #1 provides no extended detention; therefore, the lowest curve is used to determine the TSS removal rate. Designs #2 and 3 provide extended detention and therefore, use the upper set of curves.
[Figure: img-7.jpeg (original PDF, p. 10)](SOURCE.pdf#page=10)
4. Table 4
BMP 2026, 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
Source revision: January 2026.
Step 3: For each of the designs, at the intersection of the vertical line from Step 2 with the respective curve, draw a horizontal line from right to left over to the y-axis to get the TSS removal rate.
[Figure: img-8.jpeg (original PDF, p. 11)](SOURCE.pdf#page=11)
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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