Section Env-Wq 1508.14 - Pretreatment Practices: Pretreatment Swales Pretreatment swales shall comply with the following:
(a) Swales shall not be used in any of the areas identified in Env-Wq 1507.02(c)(1)-(4) unless the practice has an impermeable liner;(b) The swale length shall be at least 50 feet long;(c) Any portion of the swale that is in a roadside ditch which collects runoff from the adjacent roadway shall not count towards the minimum length specified in (b), above; (d) The bottom of the swale shall be no more than 8 feet wide;(e) The bottom of the swale shall not be within the SHWT;(f) The swale side slopes shall be no steeper than 3:1 and no flatter than 20:1;(g) The swale shall have a longitudinal slope between 0.5% and 2% without check dams or 2% to 5% with check dams;(h) The maximum flow depth in the swale shall be 4 inches at the WQF;(i) The swale shall be sized to discharge the 10-year, 24-hour storm; and(j) The swale shall be vegetated.N.H. Admin. Code § Env-Wq 1508.14
(See Revision Note #1 at chapter heading for Env-Wq 1500) #9343, eff 1-1-09
Amended by Volume XXXVII Number 32, Filed August 10, 2017, Proposed by #12342, Effective 8/15/2017, Expires 8/15/2027.Amended by Number 41, Filed October 12, 2023, Proposed by #13758, Effective 9/28/2023, Expires 9/28/2033 (formerly Env-Wq 1508.13) (see Revision Note #4 at chapter heading for Env-Wq 1500).