Tables: Extended Detention Basins (Non-GI)
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1. Table 1
BMP 2021, Ch 11.2, 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 |
| GR |
Groundwater Recharge |
Not Allowed |
| % |
Stormwater Runoff Quality |
Only with a waiver or variance from N.J.A.C. 7:8-5.3, 40 - 60% TSS Removal, depending on duration of detention |
| Stormwater Runoff Quality Mechanisms and Corresponding Criteria |
|
|
| --- |
--- |
|
| Settling |
|
|
| Minimum Detention Time for Calculation of TSS Removal Rate |
12 hours |
|
| Maximum Detention Time for Calculation of TSS Removal Rate |
24 hours |
|
Source context and notes
# 11.2 EXTENDED DETENTION BASINS (NON-GI)
[Figure: img-0.jpeg (original PDF, p. 1)](SOURCE.pdf#page=1)
An extended detention basin is a stormwater management system that temporarily stores and attenuates stormwater runoff. In addition, extended detention basins provide pollutant treatment for runoff from the Water Quality Design Storm through settling. When designed in accordance with this chapter, the total suspended solids (TSS) removal rate is 40 - 60%, depending on the duration of runoff detention. However, extended detention basins can only be used to address the
stormwater runoff quantity control aspects of development and stormwater runoff water quality 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 |
| GR | Groundwater Recharge | Not Allowed |
| % | Stormwater Runoff Quality | Only with a waiver or variance from N.J.A.C. 7:8-5.3, 40 - 60% TSS Removal, depending on duration of detention |
| Stormwater Runoff Quality Mechanisms and Corresponding Criteria | |
| --- | --- |
| Settling | |
| Minimum Detention Time for Calculation of TSS Removal Rate | 12 hours |
| Maximum Detention Time for Calculation of TSS Removal Rate | 24 hours |
2. Table 2
BMP 2021, Ch 11.2, p. 10
| Design Number |
Time to Peak Elevation (hr) |
Peak Storage Volume for WQ Design Storm (cf) |
10% Peak Storage Volume (cf) |
Time to 10% WQ Volume (hr) |
Detention Time Used (12<=Td<=24) (hr) |
% TSS Removal |
| 1 |
3.5 |
1536.0 |
|
|
|
|
| 2 |
2.4 |
584.5 |
|
|
|
|
| 3 |
1 |
182.0 |
|
|
|
|
Source context and notes
# Extended Detention Basins (Non-GI)
Source revision: March 2021.
Example: A number of extended detention basins are to be evaluated for TSS removal rates
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | | | | |
| 2 | 2.4 | 584.5 | | | | |
| 3 | 1 | 182.0 | | | | |
Step 1: For each of the designs, multiply the peak storage volume by 0.10 (10%). The result is located in the column below the red arrow symbol.
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | 153.6 | | | |
| 2 | 2.4 | 584.5 | 58.5 | | | |
| 3 | 1 | 182.0 | 18.2 | | | |
Step 2: For each of the designs, determine the time at which the outflow volume is reduced to 10%. For this example, they are as shown in the following table below the red arrow.
3. Table 3
BMP 2021, Ch 11.2, p. 10
| Design Number |
Time to Peak Elevation (hr) |
Peak Storage Volume for WQ Design Storm (cf) |
10% Peak Storage Volume (cf) |
Time to 10% WQ Volume (hr) |
Detention Time Used (12<=Td<=24) (hr) |
% TSS Removal |
| 1 |
3.5 |
1536.0 |
153.6 |
|
|
|
| 2 |
2.4 |
584.5 |
58.5 |
|
|
|
| 3 |
1 |
182.0 |
18.2 |
|
|
|
Source context and notes
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | | | | |
| 2 | 2.4 | 584.5 | | | | |
| 3 | 1 | 182.0 | | | | |
Step 1: For each of the designs, multiply the peak storage volume by 0.10 (10%). The result is located in the column below the red arrow symbol.
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | 153.6 | | | |
| 2 | 2.4 | 584.5 | 58.5 | | | |
| 3 | 1 | 182.0 | 18.2 | | | |
Step 2: For each of the designs, determine the time at which the outflow volume is reduced to 10%. For this example, they are as shown in the following table below the red arrow.
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | 153.6 | >27.5 | | |
| 2 | 2.4 | 584.5 | 58.5 | 21 | | |
| 3 | 1 | 182.0 | 18.2 | 14 | | |
Step 3: For each of the designs, the detention time is calculated by subtracting the value in the Time to Peak Elevation (hr) column from the value in the Time to 10% WQ Volume (hr) column. A detention time less than 12 hours will result in a 0% TSS removal rating; the maximum allowable TSS rating of 60% is applied to all detention times of 24 or more hours.
4. Table 4
BMP 2021, Ch 11.2, p. 10
| Design Number |
Time to Peak Elevation (hr) |
Peak Storage Volume for WQ Design Storm (cf) |
10% Peak Storage Volume (cf) |
Time to 10% WQ Volume (hr) |
Detention Time Used (12<=Td<=24) (hr) |
% TSS Removal |
| 1 |
3.5 |
1536.0 |
153.6 |
>27.5 |
|
|
| 2 |
2.4 |
584.5 |
58.5 |
21 |
|
|
| 3 |
1 |
182.0 |
18.2 |
14 |
|
|
Source context and notes
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | 153.6 | | | |
| 2 | 2.4 | 584.5 | 58.5 | | | |
| 3 | 1 | 182.0 | 18.2 | | | |
Step 2: For each of the designs, determine the time at which the outflow volume is reduced to 10%. For this example, they are as shown in the following table below the red arrow.
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | 153.6 | >27.5 | | |
| 2 | 2.4 | 584.5 | 58.5 | 21 | | |
| 3 | 1 | 182.0 | 18.2 | 14 | | |
Step 3: For each of the designs, the detention time is calculated by subtracting the value in the Time to Peak Elevation (hr) column from the value in the Time to 10% WQ Volume (hr) column. A detention time less than 12 hours will result in a 0% TSS removal rating; the maximum allowable TSS rating of 60% is applied to all detention times of 24 or more hours.
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | 153.6 | >27.5 | 24 | |
| 2 | 2.4 | 584.5 | 58.5 | 21 | 18.6 | |
| 3 | 1 | 182.0 | 18.2 | 14 | 13 | |
5. Table 5
BMP 2021, Ch 11.2, p. 10
| Design Number |
Time to Peak Elevation (hr) |
Peak Storage Volume for WQ Design Storm (cf) |
10% Peak Storage Volume (cf) |
Time to 10% WQ Volume (hr) |
Detention Time Used (12<=Td<=24) (hr) |
% TSS Removal |
| 1 |
3.5 |
1536.0 |
153.6 |
>27.5 |
24 |
|
| 2 |
2.4 |
584.5 |
58.5 |
21 |
18.6 |
|
| 3 |
1 |
182.0 |
18.2 |
14 |
13 |
|
Source context and notes
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | 153.6 | >27.5 | | |
| 2 | 2.4 | 584.5 | 58.5 | 21 | | |
| 3 | 1 | 182.0 | 18.2 | 14 | | |
Step 3: For each of the designs, the detention time is calculated by subtracting the value in the Time to Peak Elevation (hr) column from the value in the Time to 10% WQ Volume (hr) column. A detention time less than 12 hours will result in a 0% TSS removal rating; the maximum allowable TSS rating of 60% is applied to all detention times of 24 or more hours.
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | 153.6 | >27.5 | 24 | |
| 2 | 2.4 | 584.5 | 58.5 | 21 | 18.6 | |
| 3 | 1 | 182.0 | 18.2 | 14 | 13 | |
6. Table 6
BMP 2021, Ch 11.2, p. 12
| Design Number |
Time to Peak Elevation (hr) |
Peak Storage Volume for WQ Design Storm (cf) |
10% Peak Storage Volume (cf) |
Time to 10% WQ Volume (hr) |
Detention Time Used (12<=Td<=24) (hr) |
% TSS Removal |
| 1 |
3.5 |
1536.0 |
153.6 |
>27.5 |
24 |
60% |
| 2 |
2.4 |
584.5 |
58.5 |
21 |
18.6 |
51% |
| 3 |
1 |
182.0 |
18.2 |
14 |
13 |
42% |
Source context and notes
# Extended Detention Basins (Non-GI)
Source revision: March 2021.
| Design Number | Time to Peak Elevation (hr) | Peak Storage Volume for WQ Design Storm (cf) | 10% Peak Storage Volume (cf) | Time to 10% WQ Volume (hr) | Detention Time Used (12<=Td<=24) (hr) | % TSS Removal |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 3.5 | 1536.0 | 153.6 | >27.5 | 24 | 60% |
| 2 | 2.4 | 584.5 | 58.5 | 21 | 18.6 | 51% |
| 3 | 1 | 182.0 | 18.2 | 14 | 13 | 42% |
# Considerations
A number of factors should be considered when utilizing an extended detention basin to treat stormwater runoff.
# Pretreatment
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