Manufactured Treatment Device (MTD)¶
Source: NJ Stormwater BMP Manual, Chapter 11, Section 11.7 (2026) | NJDEP MTD Certification Program
Manufactured Treatment Devices (MTDs) are proprietary stormwater treatment units designed and factory-manufactured as pre-engineered stormwater quality systems. They include a wide variety of technologies: media filtration cartridges, vortex separators, multi-stage settling and filtration systems, and hybrid units combining settling, filtration, and adsorption in a single vault or manhole-insert structure. MTDs are installed below grade and are typically used where a compact footprint is required and surface-level engineered BMPs cannot be accommodated.
MTDs are evaluated and certified by NJDEP based on independent third-party laboratory or field testing data. Only certified MTDs receive regulatory water quality credit in NJ SWM Reports. The NJDEP MTD certification list specifies each unit’s approved removal efficiency (TSS% at design flow rate) and applicable design conditions.
2026 Classification: MTDs are classified as Non-GI. They do not generate VRC credit toward the GI Requirement. Some certified MTDs meet the 80% TSS standard and can serve as a primary water quality BMP; others meet only a pretreatment-level removal efficiency. Check current NJDEP certification data for the specific unit proposed.
Primary stormwater functions:
- Water quality — TSS removal per certified performance (range: 50–80%+ depending on MTD type)
- Compact urban deployment — installed in below-grade utility structure; minimal surface footprint impact
- Pretreatment or primary WQ compliance — depends on certification level
- Non-GI: no VRC; no groundwater recharge
Source: NJ Stormwater BMP Manual, Ch. 11, Section 11.7; NJDEP MTD Certification Program (2026)
| Parameter | 2026 Requirement | 2023 Requirement | Notes |
|---|---|---|---|
| NJDEP certification | Required; unit must appear on current NJDEP approved MTD list at time of permit submission | Same | Verify current certification status at design; not at concept |
| Design flow rate | Sized per manufacturer’s certification table for WQV design storm peak flow rate | Same | Exact flow rate match to certification data required |
| TSS removal efficiency | Per NJDEP certification data: some units ≥80% (primary WQ); some units < 80% (pretreatment) | Same | Confirm certification level before claiming WQV compliance |
| Bypass | High-flow bypass required for flows above design capacity; bypass path designed for 10-year flow | Same | Do not route large storm flows through MTD |
| Access | 24-inch minimum access port for maintenance; confined space protocol if personnel entry needed | Same | Vacuum truck access within 25 ft required |
| Pre-treatment | If MTD is primary WQ BMP, OGS pretreatment recommended for drainage areas with petroleum loading | Same | Protects MTD media from premature clogging |
Source: NJ Stormwater BMP Manual, Ch. 11, Section 11.7 (2026)
NJDEP MTD Certification Status
- MTD manufacturers receive time-limited certifications; verify that the specific model and configuration are currently certified before specifying in construction documents
- Product lines change over time; model numbers or configurations from older projects may not match current certification data
Flow Rate Matching
- MTD performance is certified at a specific design flow rate; installation where actual drainage area flow rate exceeds the certified rate results in below-specification TSS removal
- Multiple units in parallel may be required for large drainage areas
Petroleum-Impacted Areas
- MTDs with filtration media are susceptible to petroleum clogging from fueling station, vehicle service, or high-impervious parking drainage; OGS or HDS pretreatment recommended
Not a GI BMP
- MTDs are fully confined, below-grade structures with no connection to native soil; GI Requirement must be met through separate GI measures
Source: NJ Stormwater BMP Manual, Ch. 11, Section 11.7 (2026)
Follow Manufacturer’s Maintenance Protocol Strictly
- MTD certification is often conditioned on adherence to manufacturer’s maintenance schedule; failure to follow protocol may void NJDEP certification status for that installation
- Maintenance frequency specified in O&M Agreement must match manufacturer’s requirement
Annual Inspection and Media Replacement
- Inspect filtration cartridges or media (where applicable) for loading and saturation; replace per manufacturer’s replacement schedule or condition-based assessment
- Inspect sediment sump for accumulation; vacuum clean per manufacturer’s trigger criteria
Performance Documentation
- Maintain maintenance records per O&M Agreement; NJDEP or local authority may request maintenance logs for permit compliance verification
Source: NJ Stormwater BMP Manual, Ch. 8; Ch. 11, Section 11.7 (2026)
Design Errors
- Non-certified unit specified — manufacturer’s product not on current NJDEP list; water quality credit denied at permit review; redesign required
- Unit selected based on outdated certification — model discontinued or certification lapsed since previous project; current NJDEP website not checked at time of design
- Undersizing — drainage area flow rate exceeds design flow rate of selected unit; TSS removal below certified level at design storm events
Construction Issues
- Incorrect orientation or inlet/outlet invert — MTD installed with incorrect inlet orientation; flow does not traverse treatment chamber; performance significantly reduced
Long-Term Performance Risks
- Maintenance neglect — filtration media saturates and becomes ineffective; sediment sump overflows into treatment chamber; no removal; downstream water quality degrades
- Petroleum media saturation — hydrocarbon loading without pretreatment saturates sorption media; media replacement required at accelerated frequency
Source: NJ Stormwater BMP Manual, Ch. 11, Section 11.7 (2026)
Governing Regulations
| Rule Section | Topic | Engineering Relevance |
|---|---|---|
| N.J.A.C. 7:8-5.3(d) | Water Quality Treatment | TSS removal per NJDEP-certified removal rate; some units satisfy 80% standard |
| N.J.A.C. 7:8-5.3 | Green Infrastructure Requirement | Non-GI — VRC not generated; GI must be provided separately |
| NJDEP MTD Program | Manufactured Treatment Device Certification | Required certification for water quality credit |
BMP Manual Sources
- NJ Stormwater BMP Manual, Chapter 11, Section 11.7 (2026) — Manufactured Treatment Devices
- NJ Stormwater BMP Manual, Chapter 8 (2026) — Operation and Maintenance
- NJDEP Stormwater Website — Current list of certified MTDs and performance data
Related OPAL Pages