Extracted images: Sand Filters With Underdrain (Non-GI)

Printed revision: January 2026.

Back to source | Original PDF | Image metadata

Original Mistral crops are preserved byte for byte. A crop can be a figure, table, equation, or other visual; no visual content is inferred as a numerical rule. Record and table associations use the same PDF page unless a direct image placeholder is identified. Nearby OCR excerpts are context, not verified captions.

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Mistral ID: img-0.jpeg. Extraction bundle(s): 2026_BMP_11.4_Sand_Filters_With_Underdrain. Original page | Image file

Tables on the same PDF page: Table 1

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# 11.4 SAND FILTERS WITH UNDERDRAINS (NON-GI)

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A sand filter with underdrain is a stormwater management system designed to maximize the removal of pollutants from stormwater. It consists of a pre-treatment zone and a treatment zone, which includes the sand bed and the underlying components. Pollutants are treated through settling, filtration, and adsorption by the sand bed. The total suspended solids (TSS) removal rate is 80%. However, sand filters

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Mistral ID: img-1.jpeg. Extraction bundle(s): 2026_BMP_11.4_Sand_Filters_With_Underdrain. Original page | Image file

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een infrastructure.

Sand filters with underdrains must have a maintenance plan and must be reflected in a deed notice recorded in the county clerk's office to prevent alteration or removal.

# Applications

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Only if a waiver or variance form the green infrastructure requirements of N.J.A.C. 7:8-5.3 is obtained may sand filters with underdrains that are designed to convey storm events larger than the Water Quality Design Storm (WQDS) be used to meet the stormwater runoff quantity requirements. Additionally, regardless of the design storm chosen, all sand filters with underdrains must be designed for stabili

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face of the WQDS. The following illustrations depict the basic components of sand filters with underdrains and include an outlet structure designed to attenuate flow produced by storms larger than the WQDS.

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Plan View – Sand Filter with Underdrain

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Mistral ID: img-3.jpeg. Extraction bundle(s): 2026_BMP_11.4_Sand_Filters_With_Underdrain. Original page | Image file

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# Profile View – Sand Filter with Underdrain

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# Cross-section View – Sand Filter with Underdrain

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All of the following design criteria must all be met in order to receive the 80% TSS removal rate for this BMP. It is critical that all sand filters with underdrains are designed in accordance with these criteria in order to ensure proper operation, to maximize the functional life of the system and to ensure public safety.

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Mistral ID: img-4.jpeg. Extraction bundle(s): 2026_BMP_11.4_Sand_Filters_With_Underdrain. Original page | Image file

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# Profile View – Sand Filter with Underdrain

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# Cross-section View – Sand Filter with Underdrain

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All of the following design criteria must all be met in order to receive the 80% TSS removal rate for this BMP. It is critical that all sand filters with underdrains are designed in accordance with these criteria in order to ensure proper operation, to maximize the functional life of the system and to ensure public safety.

## Pretreatment

As with all other best management practices, pretreatment can

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scharge, computed on the basis of the net area of opening through rack;
Constructed of rigid, durable and corrosion-resistant material; and
Designed to withstand a perpendicular live loading of 300 lbs./sf.

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- An overflow grate is designed to prevent obstruction of the overflow structure. If an outlet structure has an overflow grate, the grate must comply with the following requirements:

The overflow grate must be secured to the outlet structure but removable for emergencies and maintenance;
The overflow grate spacing must be no greater than 2 inches across the smallest dimension; and
The overflow grate m

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- Any flow control device, such as an orifice, weir, grate or perforated pipe, at the outlet of the stormwater management measures shall be designed to prevent the clogging of the flow control device while achieving the design and performance standards at N.J.A.C. 7:8-5.4, 5.5 and 5.6.
- Blind connections to down-gradient facilities are prohibited. Any connection to down-gradient stormwater management

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Mistral ID: img-7.jpeg. Extraction bundle(s): 2026_BMP_11.4_Sand_Filters_With_Underdrain. Original page | Image file

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Example - Sand Filter System with Underdrain

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Mistral ID: img-8.jpeg. Extraction bundle(s): 2026_BMP_11.4_Sand_Filters_With_Underdrain. Original page | Image file

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Example - Sand Filter System with Underdrain

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Mistral ID: img-9.jpeg. Extraction bundle(s): 2026_BMP_11.4_Sand_Filters_With_Underdrain. Original page | Image file

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Example - Sand Filter System with Underdrain

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