BMP Criteria Comparison¶
Compare the actual practice and configuration before comparing numbers. The 2023 and 2026 headings identify collections; a chapter may retain an earlier publication date. Both Chapter 12 copies are dated March 2024, so they do not establish the exact July 2023 historical text.
The January 2026 volumetric-reduction framework adds an objective. Existing reuse, infiltration and evapotranspiration processes already occur in the earlier practice chapters. See Chapter 14.
Chapter eligibility tables describe the ordinary pathway. See GI requirements for conditional exceptions, including qualifying public transportation projects.
Bioretention¶
| Criterion | Earlier chapter collection | 2026 chapter collection |
|---|---|---|
| Contributing drainage area | Maximum 2.5 acres contributory drainage area PDF | Maximum 2.5 acres contributory drainage area PDF |
| Maximum ponding depth | WQDS maximum 12 in flat-bottom; 18 in at down-gradient end of sloped-bottom system (maximum longitudinal slope 10%) PDF | WQDS maximum 12 in flat-bottom; 18 in at down-gradient end of sloped-bottom system (maximum longitudinal slope 10%) PDF |
| Typical ponding depth | No separately specified typical depth; use the configuration-specific maxima PDF | No separately specified typical depth; use the configuration-specific maxima PDF |
| Engineered media depth | 80% TSS: minimum 18 in with terrestrial forested vegetation or 24 in with site-tolerant grasses; 90% TSS: minimum 24 in with terrestrial forested vegetation PDF | 80% TSS: minimum 18 in with terrestrial forested vegetation or 24 in with site-tolerant grasses; 90% TSS: minimum 24 in with terrestrial forested vegetation PDF |
| Filter media composition | 85–95% sand by volume (no more than 25% of sand fine/very fine); no more than 15% silt/clay including 2–5% clay; amend with 3–7% organics by weight PDF | 85–95% sand by volume (no more than 25% of sand fine/very fine); no more than 15% silt/clay including 2–5% clay; amend with 3–7% organics by weight PDF |
| Drawdown time | Maximum 72 hours; 24 hours recommended where pedestrians can access standing water PDF | Maximum 72 hours; 24 hours recommended where pedestrians can access standing water PDF |
| Underdrain required when | Select the configuration for site conditions and objectives; underdrained systems cannot meet recharge requirements or include exfiltration in quantity routing PDF | Select the configuration for site conditions and objectives; underdrained systems cannot meet recharge requirements or include exfiltration in quantity routing PDF |
| SHWT separation | Underdrained: at least 1 ft below gravel bottom, with specified impervious-structure exception. Infiltrating: Example 3 applies 2 ft minimum below lowest soil-bed bottom PDF | Underdrained: at least 1 ft below gravel bottom, with specified impervious-structure exception. Infiltrating: Example 3 applies 2 ft minimum below lowest soil-bed bottom PDF |
| K_design calculation | min(slowest eligible tested rate / 2, 10 in/hr), subject to practice criteria and hydraulic-impact assessment PDF | min(slowest eligible tested rate / 2, 10 in/hr), subject to practice criteria and hydraulic-impact assessment PDF |
| Pretreatment required | Required when exfiltration is included in routing the larger design storms; no adopted standalone TSS credit for the forebay PDF | Required when exfiltration is included in routing the larger design storms; no adopted standalone TSS credit for the forebay PDF |
Dry Well¶
| Criterion | Earlier chapter collection | 2026 chapter collection |
|---|---|---|
| Minimum subsoil design permeability | Minimum design 0.5 in/hr; governing tested minimum 1.0 in/hr before factor of safety 2 PDF | Minimum design 0.5 in/hr; governing tested minimum 1.0 in/hr before factor of safety 2 PDF |
| SHWT separation | At least 2 ft from dry-well bottom to SHWT and bedrock PDF | At least 2 ft from dry-well bottom to SHWT and bedrock PDF |
| Drawdown time | Maximum 72 hours PDF | Maximum 72 hours PDF |
| Foundation setback | Setback established by local ordinance or applicable review agency; no universal 10 ft criterion in Chapter 9.2 PDF | Setback established by local ordinance or applicable review agency; no universal 10 ft criterion in Chapter 9.2 PDF |
| Septic system setback | Setback established by local ordinance or applicable review agency; no universal 10 ft criterion in Chapter 9.2 PDF | Setback established by local ordinance or applicable review agency; no universal 10 ft criterion in Chapter 9.2 PDF |
| Required infiltration test method | Preconstruction methods per Chapter 12; convert percolation to conductivity. Fractured-bedrock basin flooding is pass/fail. Postconstruction methods must not require a hole in the soil layer PDF | Preconstruction methods per Chapter 12; convert percolation to conductivity. Fractured-bedrock basin flooding is pass/fail. Postconstruction methods must not require a hole in the soil layer PDF |
| K_design calculation | min(slowest eligible tested rate / 2, 10 in/hr), subject to practice criteria and hydraulic-impact assessment PDF | min(slowest eligible tested rate / 2, 10 in/hr), subject to practice criteria and hydraulic-impact assessment PDF |
Cistern¶
| Criterion | Earlier chapter collection | 2026 chapter collection |
|---|---|---|
| Storage capacity / sizing method | WQDS volume without overflow; restore capacity within 72 hours based on lowest three-consecutive-day demand PDF | WQDS volume without overflow; restore capacity within 72 hours based on lowest three-consecutive-day demand PDF |
| Chapter 14 volumetric reduction credit | Storage and reuse retention already present in Chapter 9.1; no Chapter 14 PDF | Chapter 14 adds the volumetric-reduction framework, including retention through reuse PDF |
Grass Swale¶
| Criterion | Earlier chapter collection | 2026 chapter collection |
|---|---|---|
| Maximum side slope | Maximum 3H:1V; 4H:1V recommended PDF | Maximum 3H:1V; 4H:1V recommended PDF |
| Maximum longitudinal slope | Maximum 10%; below 2% requires tested rate at least 1 in/hr and SHWT separation at least 2 ft PDF | Maximum 10%; below 2% requires tested rate at least 1 in/hr and SHWT separation at least 2 ft PDF |
Green Roof¶
| Criterion | Earlier chapter collection | 2026 chapter collection |
|---|---|---|
| Growing media depth (extensive) | Extensive media depth 6 in or less in prose; intensive 6 in or greater; apply actual assembly criteria at overlapping boundary PDF | Extensive media depth 6 in or less in prose; intensive 6 in or greater; apply actual assembly criteria at overlapping boundary PDF |
| Volumetric reduction credit (Ch. 14) | Retention and evapotranspiration already described; other BMPs may help retain the entire WQDS PDF | Chapter 14 adds volumetric framework; dry wells, cisterns, rain gardens or pervious paving are possible combinations, not a universal cistern requirement PDF |
Infiltration Basin¶
| Criterion | Earlier chapter collection | 2026 chapter collection |
|---|---|---|
| Minimum Ksat | Minimum design 0.5 in/hr; tested minimum 1.0 in/hr before factor of safety 2 PDF | Minimum design 0.5 in/hr; tested minimum 1.0 in/hr before factor of safety 2 PDF |
| SHWT separation | At least 2 ft below basin bottom to SHWT PDF | At least 2 ft below basin bottom to SHWT PDF |
| K_design calculation | min(slowest eligible tested rate / 2, 10 in/hr), subject to practice criteria and hydraulic-impact assessment PDF | min(slowest eligible tested rate / 2, 10 in/hr), subject to practice criteria and hydraulic-impact assessment PDF |
Pervious Pavement¶
| Criterion | Earlier chapter collection | 2026 chapter collection |
|---|---|---|
| Surface and storage porosity | Specified asphalt/concrete surface porosity 15–25%; aggregate porosity 40% is an example assumption to substantiate, not a universal void ratio PDF | Specified asphalt/concrete surface porosity 15–25%; aggregate porosity 40% is an example assumption to substantiate, not a universal void ratio PDF |
| SHWT separation | SHWT or bedrock at least 1 ft below storage-bed bottom for underdrained systems; at least 2 ft for infiltrating systems PDF | SHWT or bedrock at least 1 ft below storage-bed bottom for underdrained systems; at least 2 ft for infiltrating systems PDF |
Rain Garden¶
Rain garden is a bioretention application described on Chapter 9.7 p2. Chapter 9.7.
Small Scale Sand Filter¶
Infiltrating GI; underdrained sand filters are excluded and belong to Chapter 11.4. Chapter 9.9.
Subsurface Gravel Wetland¶
Non-GI; no GI, quantity or recharge use; 90% TSS quality use requires waiver or variance. Chapter 11.5.
Tree Trench¶
Street trenches and enhanced/continuous tree pits are described on Chapter 9.7 p2. Separate basin designs require their own demonstrated chapter match. Chapter 9.7.
Vegetated Filter Strip¶
GI quality 60–80% depending on vegetation; quantity and recharge uses not allowed. Chapter 9.10.
Ch10 Large Bioretention¶
| Criterion | Earlier chapter collection | 2026 chapter collection |
|---|---|---|
| Contributing drainage area | Use Chapter 10.1 and the applicable rule eligibility; the Chapter 9.7 small-scale limit is 2.5 acres PDF | Use Chapter 10.1 and the applicable rule eligibility; the Chapter 9.7 small-scale limit is 2.5 acres PDF |
Constructed Wetland¶
GI; recharge not allowed; quality use requires waiver or variance; quantity for online systems. Chapter 10.4.
Extended Detention Ch10¶
Non-GI; no GI or recharge use; quality and quantity uses require waiver or variance. Existing URL does not change classification. Chapter 11.2.
Infiltration Trench¶
Editorial design entry point; actual configuration must meet Chapter 10.2 before its criteria or credits apply. Chapter 10.2.
| Criterion | Earlier chapter collection | 2026 chapter collection |
|---|---|---|
| SHWT separation | If Chapter 10.2 applies: at least 2 ft from SHWT or bedrock to lowest basin bottom; use sand-layer bottom for surface basins PDF | If Chapter 10.2 applies: at least 2 ft from SHWT or bedrock to lowest basin bottom; use sand-layer bottom for surface basins PDF |
Sand Filter Ch10¶
Infiltrating GI; recharge and quality uses require waiver or variance; quantity for online systems. Chapter 10.3.
Wet Pond Ch10¶
GI requires native-vegetation buffer at least 10 ft wide along at least 50% of shoreline AND retention for beneficial reuse. No recharge; quality use requires waiver or variance. Chapter 11.6 covers non-GI wet ponds. Chapter 10.5.
Blue Roof¶
Non-GI; quantity use requires waiver or variance; no quality or recharge use. Chapter 11.1.
Dry Detention¶
Detention application, not a separate chapter; use Chapter 11.2 eligibility. Chapter 11.2.
Extended Detention Ch11¶
Non-GI; no GI or recharge use; quality and quantity uses require waiver or variance. Chapter 11.2.
Hydrodynamic Separator¶
Hydrodynamic separation is a named Chapter 11.3 type. Actual certificate and configuration control eligibility. Chapter 11.3.
Manufactured Treatment Device¶
Chapter 11.3 covers non-GI devices; GI devices are addressed in 9.5. Actual certification and configuration control. Chapter 11.3.
Membrane System¶
Generic product label; no device-specific approval established. Require actual certificate and configuration before classification or credit. Chapter 11.3.
Oil Grit Separator¶
Generic product label; no device-specific approval established. Require actual certificate and configuration before classification or credit. Chapter 11.3.
Underground Detention¶
Subsurface vault, pipe and stone-bed arrangements appear in Chapter 11.2, p12; non-GI eligibility applies. Chapter 11.2.