A. Private utilities installed beneath retention/detention basins (if permitted) shall have a minimum of 30 inches of cover. B. Drywells are required for any depth of retention in excess of one (1) foot and retention basins that have a volume greater than 1,000 cubic ft. Basin bottom percolation shall not be used to reduce the volume used for drywell requirement calculations. C. Dual chamber drywells are required for all storm water retention applications. D. Drywells shall be installed according to ADEQ E. Drywells shall be installed according to ADEQ guidelines and shall be registered with ADEQ by the installer. F. Drywells shall be maintained by the land owner or the association formed by the owner. G. For drywells associated with surface retention basins, a maximum design percolation rate of 0.5 cubic feet per second (cfs) per drywell shall be used in calculating the number of dry well required. For drywells associated with underground storage systems, a percolation rate of 0.1 cfs per drywell shall be used. H. The drywell volume shall not be considered in the design calculation for sizing retention/detention. I. Multi-chamber drywells such as Envibro System or approved equal are required for fueling stations. A maximum percolation rate of 0.1cfs may be used for these systems. J. Drywell rim elevations shall be set a minimum of 0.3 feet above finish grade of basin bottom. K. Drywell depth varies based on location. The maximum depth will not exceed 120 feet.
