The purpose of this policy is to provide clarification for Ground Water Quality Rule (IDAPA 16.01.11, 1997) implementation as it regards the use of storm water management practices and methods for ground water quality protection.

The policy only applies to storm water management practices and methods associated with ground water quality protection. Furthermore, the policy is limited to the use of these management practices and methods at the planning, design, or pre-construction stage. This policy is not intended for existing storm water systems which have been constructed without prior knowledge of ground water quality protection requirements under the Ground Water Quality Rule, although it can be applied to the maintenance of existing systems where such maintenance is necessary for continued ground water quality protection. This policy does not direct regional office staff to conduct plan and specification reviews of underground injection wells.

As stated in the Ground Water Quality Rule, IDAPA 16.01.11 (1997), any activity with the potential to degrade the quality of a General Resource aquifer must be managed at least to maintain the existing ground water quality through the use of best management practices (BMPs) and best practical methods (BPMs), to the maximum extent practical (IDAPA 16.01.11.301.02.a). Land development with the resulting storm water runoff represents an activity that could degrade ground water quality. Therefore, BMPs or BPMs designed to protect ground water quality, from contaminants that are often found in storm water, must be incorporated into land development activities where practical.

Also as stated in the Ground Water Quality Rule, any activity with the potential to degrade the quality of a Sensitive Resource aquifer must be managed at least to maintain the existing ground water quality through the use of best available methods (BAMs) and BMPs (IDAPA 16.01.11.301.01.a). Therefore, BAMs or BMPs designed to protect ground water quality, from contaminants that are often found in storm water, must be incorporated into land development activities that may impact a Sensitive Resource aquifer.

Ground water quality in General Resource aquifers shall be protected from contamination associated with storm water runoff through the use of BMPs or BPMs to the maximum extent practical. The practical approach includes preventing ground water contamination by incorporating appropriate or suitable storm water BMPs or BPMs at the design stage of an activity and the maintenance of existing and new BMPs and BPMs to ensure continued ground water quality protection.

Ground water quality in Sensitive Resource aquifers shall be, at a minimum, protected from contamination associated with storm water runoff through the use of BAMs or BMPs. This includes preventing ground water contamination through storm water BAMs or BMPs at the design stage of an activity, and maintaining existing and new BAMs and BMPs to ensure continued ground water quality protection.

Implementation of this policy will include notifying agencies and individuals that may be involved with storm water system design, review, or approval of the need to incorporate BMPs, BPMs, or BAMs, associated operation and maintenance of these systems, into the planning and design process for ground water quality protection. Notification will include correspondence from the DEQ to agencies and individuals to make them aware of their ground water quality protection responsibilities as defined by the Ground Water Quality Rule and this policy. The correspondence will point out that failure to include BAMs, BMPs or BPMs for storm water control in site development plans could delay a project, as well as lead to future contamination problems requiring corrective actions to protect ground water beneficial uses. The correspondence will also identify the Rathdrum Prairie as the only aquifer categorized as a Sensitive Resource.

To provide uniform implementation assistance, the above correspondence will include reference to the Catalog of Storm Water Best Management Practices , that includes site design techniques for controlling storm water runoff associated with land development activities. The ground water quality BMPs found in the Catalog could be used to comply with the criteria in the Ground Water Quality Rule and this policy. It will be noted that the Catalog is not intended to supersede local requirements or other recognized BMPs, BPMs, and BAMs that effectively protect ground water quality. The Catalog instead provides a consistent set of additional ground water quality protection options.

The correspondence will also point out that the Catalog is available from DEQ Regional Offices, and that any questions regarding the implementation of practices or methods for storm water control may be directed to a DEQ Regional Office.

Although the above correspondence informing agencies and individuals of this policy may take some time to develop and distribute, the policy shall become effective immediately.

This policy shall be effective immediately.

DATED: 1998.

WALLACE N. CORY, P.E.
ADMINISTRATOR