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Groundwater Recharge Rules

The live source corpus grounds groundwater-recharge compliance in N.J.A.C. 7:8-5.4 together with the calculation assumptions in N.J.A.C. 7:8-5.7 and the technical workflow in BMP Manual Chapter 6.

Structured citation evidence for this page lives in the sibling claim manifest.

Regulatory Summary

N.J.A.C. 7:8-5.4 requires the design engineer to demonstrate that a major development maintains 100 percent of the average annual pre-construction groundwater recharge volume for the site, unless an exemption within the rule applies.

The live source set also confirms two important limits on recharge claims:

  • projects in an urban redevelopment area are outside the base recharge requirement
  • stormwater from areas of high pollutant loading shall not be recharged

Calculation Framework

The recharge workflow in the live source set depends on N.J.A.C. 7:8-5.7 and BMP Manual Chapter 6. A key starting assumption already normalized in the citations layer is that the pre-construction land cover is presumed to be wooded land use in good hydrologic condition unless another condition is properly documented.

BMP Manual Chapter 6 then carries that rule framework into the NJGRS and related recharge-calculation workflow.

NJGRS allocation details

Chapter 6 is more specific than many of the older recharge summaries. In the BMP Calculations worksheet, the NJGRS defaults Vdef and Aimp from the sitewide annual-recharge worksheet. That default only works when a single recharge BMP receives runoff from the site's full impervious area.

If a recharge BMP receives runoff from only part of the impervious area, the designer has to replace the default Aimp with the exact impervious area routed to that BMP. If more than one recharge BMP is used, Chapter 6 requires the designer to assign each BMP its own exact Aimp and Vdef and to use a separate NJGRS spreadsheet for each BMP.

Engineering Interpretation

The safest authored summary is:

  1. start with the recharge requirement in N.J.A.C. 7:8-5.4
  2. use the calculation assumptions and factors in N.J.A.C. 7:8-5.7
  3. use BMP Manual Chapter 6 for the technical workflow and supporting calculations
  4. screen for recharge prohibitions before claiming infiltrated volume

The current citations layer does not support several of the older shorthand statements that tried to convert recharge eligibility into a single HSG table or a single blanket GI-only slogan.

BMP Implications

In the live source set, recharge credit is tied to BMPs and configurations that actually infiltrate into subsoil and are not prohibited by the recharge exclusions in the rule. The practical implication is that recharge analysis must stay coordinated with:

  • soil testing
  • SHWT separation
  • groundwater-mounding review
  • pollutant-loading screening

Chapter 6 also narrows what counts in the recharge-BMP drainage area. Only directly connected impervious area can be used as Aimp for recharge-BMP calculations. For subsurface recharge BMPs, runoff from parking lots, driveways, roads, and similar on-grade impervious surfaces must be pretreated to remove 80 percent TSS before the runoff is routed into the recharge system.

Cross References