1. (a) Permanent methods for protecting water quality, including all stormwater management practices, shall be designed to:

   1. (1) Minimize the discharge of pollutants in accordance with Env-Wq 1507.03;
   2. (2) Recharge groundwater in accordance with Env-Wq 1507.04;
   3. (3) Protect channels in accordance with Env-Wq 1507.05;
   4. (4) Control peak runoff rates in accordance with Env-Wq 1507.06; and
   5. (5) Implement long term maintenance practices in accordance with Env-Wq 1507.07.

2. (b) No component of a stormwater management system shall be:

   1. (1) Constructed below the elevation of the 10 year floodplain for any project within the 100-year floodplain;
   2. (2) Located in an area of RSA 482-A jurisdiction, unless a permit that specifically allows the proposed impacts has been issued pursuant to RSA 482-A and Env-Wt 100 through Env-Wt 900; or
   3. (3) Located on lots in single family or duplex residential subdivision for the purpose of meeting Env-Wq 1503.19(b) or (c), unless the construction of the stormwater management practice is included as part of the permit and the practice is protected with an easement or deed restriction pursuant to Env-Wq 1504.07.

3. (c) Except as provided in (e) and (f), below, and any practice-specific requirement or exception, no stormwater management practice described in Env-Wq 1508 shall:

   1. (1) Receive stormwater from a high-load area, including but not limited to groundwater protection areas where the stormwater comes from one or more areas where petroleum products are dispensed or otherwise transferred for commercial or industrial purposes;
   2. (2) Receive stormwater from areas where the soil contains contamination, as defined in Env-Or 602.07, at levels greater than the soil remediation criteria of Env-Or 606.19;
   3. (3) Discharge stormwater into the ground where the groundwater contains contamination at levels greater than the ambient groundwater quality standards established in Env-Or 603.03;
   4. (4) Discharge stormwater where the soil contains contamination at levels greater than the soil remediation criteria of Env-Or 606.19; or
   5. (5) Discharge stormwater into areas with slopes greater than 15%, unless calculations are provided demonstrating that resulting seepage forces do not cause slope instability.
4. (d) Nothing in this section shall be interpreted to allow a party to cause or contribute to an ambient groundwater quality standards (AGQS) violation as defined in RSA 485-C:2, I, as reprinted in Appendix C.
5. (e) Practices that are not hydraulically connected to groundwater shall be exempt from (c), above.
6. (f) In areas where groundwater contains contamination at levels greater than the ambient groundwater quality standards established in Env-Or 603.03 or soil contains contamination at levels greater than the soil remediation criteria of Env-Or 606.19, a qualified geologist or engineer, experienced in contaminant fate and transport analysis, shall certify that the proposed design will not result in impacts to groundwater flow or quality that are detrimental to the environment or human health greater than those posed by current site conditions. Such impacts shall include, but are not limited to contaminating water supply wells, expanding contaminant plumes, or increasing vapor intrusion risks. The certification shall be signed, sealed, and dated by the New Hampshire-licensed professional engineer or geologist who performed the analysis.
7. (g) An overflow structure associated with a stormwater management system shall be designed to convey, in a controlled manner, any flows that exceed the system’s capacity.

Source. #9343, eff 1-1-09; ss by #12342, eff 8-15-17; ss by #14472, eff 1-19-26, EXPIRES: 1-19-36