“Classification of a dam” means “classification of a dam” as defined in RSA 482:2, I, namely, "the potential hazard classification placed on a dam by the department based on the potential threat to life and the potential extent of property damage in the event of accidental damage to, or failure of, the dam structure. The classifications shall be "non-menace," "low hazard potential," "significant hazard potential," or "high hazard potential" defined as follows:

1. (a) “Non-menace structure” means a dam that is not a menace because it is in a location and of a size that failure or misoperation of the dam would not result in probable loss of life or loss to property, or it is located on a great pond with a maximum height of less than 6 feet;

2. (b) “Low hazard structure” means a dam that has a low hazard potential because it is in a location and of a size that failure or misoperation of the dam would result in any of the following or meets other parameters set-forth below:

   1. (1) Overtopping of any road, excepting unmaintained class VI roads and recreational trails or crossings, accessing property other than the dam owner’s which could render the road impassable or otherwise interrupt public safety services, is classified at a minimum as a “low hazard structure”;
   2. (2) A dam that is 6 feet in height or greater and stores a maximum volume of 50 acre-feet or greater, or that is 25 feet in height or greater and stores a maximum volume of 15 acre-feet or greater, is classified at a minimum as a “low hazard structure”;
   3. (3) A dam that creates a surface impoundment for liquid industrial or liquid commercial wastes, septage, or sewage, or that is known to impound contaminated sediment, regardless of height or storage capacity, is classified at a minimum as a “low hazard structure”;
   4. (4) Any flooding to a developed structure on a property other than the dam owner’s that is not normally occupied; or
   5. (5) Any dam that is part of or integral to a local or private roadway accessing property other than the dam owner’s is classified at a minimum as a “low hazard structure”.

3. (c) “Significant hazard structure” means a dam that has a significant hazard potential because it is in a location and of a size that failure or misoperation of the dam would result in any of the following or meets other parameters set-forth below:

   1. (1) Flooding between the lowest contact of the foundation with the ground surface and up to one foot above the lowest finished floor elevation of a normally occupied residential, commercial, or industrial structure;
   2. (2) Up to one foot of flooding above ground surface at any point under or immediately adjacent to a normally occupied ground supported residential, commercial, or industrial structure;
   3. (3) One foot or more of overtopping to a class I or II route located downstream of the dam which could render the road impassable or otherwise interrupt public safety services; or
   4. (4) Any dam that is part of or integral to a class I or II route is classified at a minimum, as a “significant hazard structure”.

4. (d) “High hazard structure” means a dam that has a high hazard potential because it is in a location and of a size that failure or misoperation of the dam would result in probable loss of human life or meets other parameters set-forth below:

   1. (1) One foot or more of flooding above the lowest finished floor elevation of a normally occupied residential, commercial, or industrial structure;
   2. (2) One foot or more of flooding above ground surface at any point under or immediately adjacent to a normally occupied ground supported residential, commercial, or industrial structure;
   3. (3) Failure of a structurally attached, normally occupied habitable residential, commercial, or industrial structure;
   4. (4) Campsites receiving any level of flooding due to a dam failure; or
   5. (5) Any other circumstance which would more likely than not cause one or more deaths.

Source. #1716, eff 2-20-81; ss by #2207, eff 12-13-82; ss by #2900, eff 11-7-84, EXPIRED 11-7-90 New. #5080, eff 2-22-91; ss by #6462-A, eff 2-21-97; ss by #8288, INTERIM, eff 2-21-05, EXPIRES: 8-20-05; ss by #8412, eff 8-20-05; ss by #10508, eff 1-22-14; ss by #13979, eff 5-24-24 (formerly Env-Wr 101.06) (see Revision Note at chapter heading for Env-Wr 100)