# Phase 0 Regulatory Audit Report ## N.J.A.C. 7:8 – New Jersey Stormwater Management Rules ### Comparison: July 2023 vs. January 2026 Amendments **Prepared for:** OPAL Stormwater Engineering Knowledge System **Phase:** Phase 0 – Regulatory Audit **Date:** March 4, 2026 **Source Documents:** N.J.A.C. 7:8 (July 2023); N.J.A.C. 7:8 (January 2026) --- ## Executive Summary The January 2026 amendments to N.J.A.C. 7:8 represent the most substantive revision to New Jersey's stormwater management rules since the 2021 Green Infrastructure rulemaking. The 2026 update advances from a prescriptive, checkbox-style compliance framework toward a volumetric, performance-based design standard. Key changes include the formal introduction of volumetric reduction standards as a compliance pathway, restructuring of the BMP Manual to distinguish Green Infrastructure (GI) from Non-GI BMPs, expanded and refined definitions, and updated design requirements that directly affect how engineers size, select, and document stormwater management practices. --- ## Section 1: Structural Changes to the Rule ### 1.1 Subchapter Organization The July 2023 version retained the subchapter structure established in the 2021 rulemaking: - **Subchapter 1** – General Provisions - **Subchapter 2** – Stormwater Management Requirements for Major Development - **Subchapter 3** – Standards for Stormwater Management Measures - **Subchapter 4** – Low Impact Development Techniques - **Subchapter 5** – Procedures for Review and Approval The January 2026 amendments did not fundamentally reorder this subchapter hierarchy but introduced significant additions and clarifications within Subchapters 2 and 3 affecting the hierarchy of GI compliance requirements and the standalone treatment of volumetric reduction. ### 1.2 Introduction of Volumetric Reduction as a Formal Standard One of the most consequential structural changes in the 2026 rules is the formalization of **volumetric reduction** as a distinct compliance pathway, supported by a new BMP Manual chapter (Chapter 14 – Volumetric Reduction Standards). Under the July 2023 rules, volume reduction was addressed primarily within the Green Infrastructure standard as a performance goal. The 2026 rules establish volumetric reduction criteria explicitly, providing engineers a direct design standard and calculation methodology separate from TSS removal rate tables. This change is structurally significant because it: 1. Creates a standalone compliance pathway for sites where full GI implementation is infeasible. 2. Requires specific volumetric calculations to be submitted as part of stormwater design documentation. 3. Enables partial GI compliance to be quantified and credited in a consistent manner. ### 1.3 BMP Manual Reorganization and GI / Non-GI Classification The 2026 rules align with a revised BMP Manual that formally classifies practices into two tiers: - **Green Infrastructure (GI) BMPs** – practices that provide volumetric reduction through infiltration, evapotranspiration, or reuse (e.g., bioretention systems, dry wells, infiltration basins, pervious paving, green roofs, cisterns). - **Non-GI BMPs** – practices that provide water quality treatment but do not achieve volumetric reduction (e.g., extended detention basins, non-GI manufactured treatment devices, non-GI wet ponds, blue roofs when not counted toward volume reduction). This classification is reflected in updated BMP chapter titles: | 2023 BMP Title | 2026 BMP Title | |---|---| | Chapter 11.3 – Manufactured Treatment Devices | Chapter 11.3 – Non-GI Manufactured Treatment Devices | | Chapter 11.6 – Wet Ponds | Chapter 11.6 – Non-GI Wet Ponds | | Chapter 10.1 – Bioretention Systems | Chapter 10.1 – Large-Scale Bioretention Systems | | Chapter 11.4 – Sand Filters | Chapter 11.4 – Sand Filters with Underdrain | The explicit "Non-GI" labeling imposes a design consequence: practices in the Non-GI category cannot be used to satisfy the groundwater recharge standard or to meet minimum Green Infrastructure performance requirements through volume reduction credit alone. ### 1.4 Applicability and Thresholds The 2026 amendments refined the definition and thresholds for **major development**, maintaining the one-acre disturbance and one-quarter-acre impervious cover thresholds from the 2021/2023 rules but clarifying treatment of linear development thresholds and phased development calculations. The 2026 rules also address applicability to redevelopment projects with greater specificity, including clarified language on when pre-existing impervious area triggers full compliance versus partial or modified compliance requirements. --- ## Section 2: Updated Design Requirements ### 2.1 Green Infrastructure Standard The July 2023 rules required that **all** stormwater runoff from new impervious surfaces be managed through Green Infrastructure practices to the maximum extent feasible, with the goal of achieving 100% of the Water Quality Design Storm (1.25 inches of rainfall in 2 hours) through GI measures. The January 2026 rules retain this fundamental requirement but add: - **Hierarchical GI application:** Engineers must first demonstrate efforts to incorporate GI on-site before proposing Non-GI alternatives for the remainder. Documentation of site constraints (e.g., soil limitations, contaminated sites, depth to seasonal high water table) is now expected as part of the design narrative. - **Volumetric Reduction Calculation:** A site-specific calculation must demonstrate what percentage of the Water Quality Design Storm runoff volume is captured and reduced through GI practices. The residual volume must then be addressed through Non-GI treatment to achieve required TSS/nutrient removal levels. ### 2.2 Water Quality Standards – TSS and Nutrient Removal The 2023 rules required: - **80% TSS removal** from the Water Quality Design Storm runoff for new impervious surfaces. - **50% TSS removal** for existing impervious surfaces being modified. The 2026 rules maintain these TSS requirements but clarify how TSS removal is calculated in a **treatment train** context where GI and Non-GI practices are combined. Specifically, the 2026 rules provide updated guidance for applying removal efficiency credits sequentially when more than one practice treats the same runoff. For **nutrient removal**, the 2026 rules expand upon the prior requirements by: - Providing updated total phosphorus (TP) and total nitrogen (TN) removal rate tables for both GI and Non-GI BMPs. - Introducing modified removal rates for bioretention systems that specify whether the design includes an internal water storage zone (IWZ), which significantly affects phosphorus removal. - Establishing that Non-GI Wet Ponds and Non-GI Extended Detention Basins no longer receive default nutrient removal credits without specific design documentation supporting those rates. ### 2.3 Groundwater Recharge Standard The July 2023 rules required that groundwater recharge be maintained at predevelopment levels, using NRCS-based recharge calculations correlated to hydrologic soil groups and land cover. The 2026 rules preserved the recharge standard structure but made the following adjustments: - **GI-only recharge credit:** Only GI practices that achieve infiltration (not evapotranspiration-only practices like green roofs or blue roofs) qualify for recharge volume credit. This resolution clarifies prior ambiguity in the 2023 rules where some practitioners incorrectly credited green roofs toward recharge deficits. - **Mounding Analysis Thresholds:** The 2026 rules lower the infiltration rate threshold triggering a mandatory groundwater mounding analysis. Under the 2023 rules, soils with infiltration rates exceeding 2.99 inches per hour required mounding analysis. The 2026 rules extend this requirement and add a required setback analysis for sites adjacent to structures with basements or below-grade utilities. ### 2.4 Flood Control Standard The flood control standard (peak flow rate limitations for the 2-year and 10-year design storms) remained substantively unchanged between the 2023 and 2026 versions. However, the 2026 rules provide updated guidance notes clarifying that: - **GI practices may receive flood volume credit** toward the 2-year storm peak attenuation requirement where the practice provides detention storage in addition to infiltration. - **Non-GI Extended Detention Basins** designed solely for water quality treatment do not satisfy the flood control standard unless specifically sized to attenuate the 2-year peak. ### 2.5 Soil Testing Requirements The 2026 rules strengthen the soil testing requirements that were introduced in the 2021/2023 rulemaking. Key updates include: - **Infiltration testing methodology** is now explicitly restricted to **in-situ falling head permeameter tests** or ASTM D5126 (piezometer method). Estimated infiltration rates from soil texture or pedon descriptions are no longer acceptable for design purposes (they may still be used in feasibility screening). - **Minimum borehole depth** requirements were updated to require the boring extend to at least 2 feet below the bottom of the proposed practice or to confining layer, whichever is shallower. - **Seasonal High Water Table (SHWT)** determination procedures are more explicitly defined in the 2026 rules, with requirements that SHWT be established through direct observation of redoximorphic features by a licensed soil scientist or professional engineer with demonstrated geotechnical training. ### 2.6 Design Storm The Water Quality Design Storm (1.25 inches in 2 hours) and the Groundwater Recharge Design Storm remained unchanged in the 2026 rules. The 100-year storm is still used for dam safety and culvert design where applicable under other referenced standards. --- ## Section 3: New or Modified Definitions ### 3.1 New Definitions in the 2026 Rules The January 2026 amendments added the following definitions that were absent from or more loosely described in the July 2023 rules: **Volumetric Reduction** *(New in 2026)* The reduction of stormwater runoff volume achieved through Green Infrastructure practices that promote infiltration, evapotranspiration, or rainwater harvesting and reuse. Volumetric reduction is measured as the difference between pre-practice runoff volume and post-practice runoff volume for a given design storm. **Non-GI BMP** *(New in 2026)* A Best Management Practice that provides water quality treatment (TSS, nutrient, or other pollutant removal) but does not achieve volumetric reduction sufficient to satisfy the Green Infrastructure standard. Non-GI BMPs are not credited toward the groundwater recharge standard. **Treatment Train** *(New in 2026)* A sequence of two or more stormwater management practices designed to function in series, where the effluent of one practice becomes the influent of the next, with the combined result achieving required water quality standards. **Internal Water Storage Zone (IWZ)** *(New in 2026)* A saturated zone deliberately maintained within a bioretention system by use of an elevated underdrain or other control mechanism, designed to promote denitrification and phosphorus uptake through anaerobic and plant-mediated processes. ### 3.2 Modified Definitions from the 2023 Rules **Green Infrastructure** *(Modified)* The July 2023 definition described GI as practices that "manage stormwater runoff using natural processes including infiltration, evapotranspiration, and reuse." The 2026 definition adds quantitative clarity by specifying that a GI practice must demonstrate **measurable volumetric reduction** consistent with the standards established in the Volumetric Reduction Standards (Chapter 14 of the BMP Manual). Practices that solely detain or treat runoff without measurable volume reduction no longer qualify as GI under the 2026 definition. **Major Development** *(Clarified)* The 2026 rules add specific language addressing **phased projects**, clarifying that the entire buildout area of a phased development is assessed against the threshold when a master plan or site plan encompasses the total disturbed area, even if individual phases are independently permitted. This closes a previously exploited compliance gap. **Impervious Surface** *(Clarified)* The 2026 rules include gravel roads with compacted base courses and engineered paths as impervious unless the applicant provides permeability testing demonstrating runoff coefficients consistent with pervious materials. The prior rule was silent on engineered gravel surfaces. **Manufactured Treatment Device (MTD)** *(Modified)* The 2026 definition explicitly adds the "Non-GI" qualifier when referring to MTDs used solely for water quality treatment, distinguishing them from innovative stormwater practices that may qualify as GI through demonstrated infiltration. The 2023 rules used "MTD" generically. **Bioretention System** *(Modified)* The 2026 definition distinguishes between **small-scale** (serving drainage areas ≤1 acre) and **large-scale** (serving drainage areas >1 acre) bioretention systems, reflecting the split BMP Manual chapters. Design requirements differ based on scale, particularly for underdrain design and overflow structure requirements. **Groundwater Recharge** *(Clarified)* The 2026 rules clarify that **net groundwater recharge** is the target metric, defined as the volume of water that infiltrates through the soil profile and reaches the water table, excluding water lost to evapotranspiration from the practice media or vegetation. This clarification addresses prior inconsistencies in how recharge was calculated for bioretention systems with IWZs. --- ## Section 4: Implications for Stormwater Engineering Practice ### 4.1 Design Documentation Requirements The 2026 rules increase the documentation burden for stormwater design submissions. Engineers must now include: 1. **GI Feasibility Analysis:** A written narrative demonstrating that site-specific constraints were evaluated before proposing Non-GI alternatives. Generic statements ("GI is infeasible due to site constraints") without supporting data are no longer acceptable. 2. **Volumetric Reduction Calculation:** A site-specific calculation demonstrating the volume of the Water Quality Design Storm runoff managed through GI practices, expressed as a percentage of total site runoff. 3. **Treatment Train Efficiency Documentation:** Where multiple practices are used in series, the engineer must provide stage-by-stage removal efficiency calculations. 4. **Soil Testing Summary:** A standardized soil data form documenting in-situ infiltration rates, SHWT depth, borehole logs, and tester credentials is now required for all infiltration-based GI practices. ### 4.2 BMP Selection and Sizing The GI / Non-GI classification directly affects practice selection: - **Practices previously treated as equivalent** (e.g., a wet pond vs. a constructed wetland) are now tiered. Wet ponds and extended detention basins are explicitly Non-GI and cannot satisfy the GI compliance requirement. - **Bioretention systems** must be sized to achieve volumetric reduction targets using the methods in BMP Manual Chapter 14, not simply sized to treat the WQ design storm water quality volume as a detention/filtration unit. - **Green roofs** and **blue roofs**, while beneficial for peak flow and temperature, do not satisfy the volumetric reduction standard unless paired with a cistern or other harvesting/reuse system that demonstrates retained volume. - **Sand Filters with Underdrain** (the renamed Chapter 11.4) are now clearly classified as Non-GI, eliminating prior ambiguity about whether sand filtration through engineered media into an underdrain constitutes "infiltration." ### 4.3 Compliance Sequencing The 2026 rules effectively impose a **compliance hierarchy**: 1. First, maximize GI volumetric reduction for the Water Quality Design Storm. 2. Second, satisfy the groundwater recharge standard using only infiltration-based GI practices. 3. Third, apply Non-GI treatment to the remaining Water Quality Design Storm runoff not managed through GI, to achieve 80% TSS removal. 4. Fourth, size practices for flood control to meet the 2-year and 10-year peak flow standards. This hierarchy mirrors the "manage at the source" philosophy of Low Impact Development but codifies it with specific, quantitative performance thresholds at each step. ### 4.4 Implications for Redevelopment Projects The 2026 rules address redevelopment more directly than the 2023 rules. For sites where pre-existing impervious cover triggers compliance: - A **full compliance pathway** applies when total new plus replaced impervious area exceeds the major development threshold. - A **partial compliance pathway** applies when only a portion of existing impervious area is being modified, allowing proportional application of GI requirements to the new or replaced impervious area only. - Sites in **urban redevelopment areas** retain access to alternative compliance pathways (e.g., off-site GI retrofits, green infrastructure payments-in-lieu programs at the municipal level), provided the municipality has an NJDEP-approved Stormwater Management Plan. ### 4.5 Municipal Stormwater Management Plan (MSWMP) Updates The 2026 rules require municipalities with adopted MSWMPs to update their plans within 24 months to incorporate the new volumetric reduction standards and GI/Non-GI BMP classifications. Project-level compliance is tied to whether the MSWMP has been updated; in municipalities without updated plans, the state standards apply directly. ### 4.6 Impact on Manufactured Treatment Device Approvals The reclassification of MTDs as Non-GI has practical consequences for projects where MTDs were previously proposed as the primary stormwater quality measure. Such projects must now: - Demonstrate why GI practices are not feasible before defaulting to an MTD. - Use the MTD exclusively for residual water quality treatment, not as the primary compliance strategy. - Document that the MTD achieves required TSS and nutrient removal rates for the portion of runoff not managed through GI. NJDEP's MTD verification program requirements (previously under N.J.A.C. 7:8-5.7) were cross-referenced and clarified in the 2026 rules to align with the Non-GI classification, confirming that MTD verification data submittals use the updated WQV calculation methodology. --- ## Summary Table: Key Regulatory Changes at a Glance | Category | July 2023 | January 2026 | Significance | |---|---|---|---| | Volumetric Reduction | Performance goal within GI standard | Standalone compliance standard with Chapter 14 methods | Major – creates new calculation requirement | | BMP Classification | No formal GI/Non-GI tier | Explicit GI vs. Non-GI classification | Major – affects practice selection and crediting | | Green Infrastructure Definition | Qualitative description | Quantitative volumetric reduction requirement | Major – changes how GI compliance is demonstrated | | Bioretention Scale | Single chapter, unified | Split into small-scale (≤1 ac) and large-scale (>1 ac) | Moderate – different design requirements by scale | | Infiltration Testing | Testing required; methodology guidance | Specific test methods required; estimated rates prohibited | Moderate – increases rigor of soil investigation | | SHWT Determination | General requirement | Qualified professional standard specified | Moderate – affects practice siting | | TSS Removal Standard | 80% from WQ Design Storm | Unchanged; updated treatment train guidance | Minor | | Nutrient Removal | Rate tables in BMP Manual | Updated tables; IWZ credit for bioretention | Moderate | | Mounding Analysis Trigger | Soils >2.99 in/hr | Expanded trigger; structural setback added | Moderate | | Phased Development | Ambiguous | Explicitly addressed – entire buildout assessed | Moderate | | Gravel Roads/Paths | Not addressed | Treated as impervious unless tested | Minor | | Redevelopment Applicability | General provisions | Full vs. partial compliance pathways clarified | Moderate | | MTD Compliance Role | Primary measure allowed | Non-GI only; GI feasibility required first | Major | | MSWMP Update Obligation | N/A | 24-month update required with 2026 standards | Administrative | --- ## Conclusion The January 2026 amendments to N.J.A.C. 7:8 represent a maturation of New Jersey's stormwater management framework from a qualitative GI preference to a quantitative, volumetric performance standard. The formalization of volumetric reduction as a design metric, the explicit GI/Non-GI BMP classification, and the strengthened soil investigation requirements collectively raise the bar for stormwater engineering practice in New Jersey. Practitioners must update their design workflows, calculation methodologies, and documentation standards to reflect these changes. The OPAL system should incorporate these distinctions at the knowledge layer to ensure that design guidance, BMP selection logic, and compliance checklists accurately reflect current regulatory requirements. --- *Report generated for OPAL Phase 0 Regulatory Audit.* *Reference documents: N.J.A.C. 7:8 (July 2023) and N.J.A.C. 7:8 (January 2026); NJDEP Stormwater BMP Manual (2023 and 2026 editions).*