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(A) Underground stormwater management systems may be permitted in all zoning districts upon city staff approval to accomplish stormwater retention and percolation requirements provided those systems are designed for the prevention of clogging by fine material and for ease of cleaning with conventional sewer cleaning equipment.
(B) Design criteria:
(1) Underground stormwater management systems shall be designed by a licensed professional engineer.
(2) Underground stormwater management systems shall be designed to meet the treatment and hydrologic criteria of a retention treatment system as outlined in § 1 Table 1, and § 3(D)(1)(a) of this appendix with the exceptions noted herein.
(3) A system overflow outfall shall be required.
(4) The bottom of the underground stormwater management system shall be constructed a minimum of one foot above the estimated high groundwater elevation. The estimated high groundwater elevation and a modeled recovery analysis shall be performed by a licensed geotechnical engineer.
(5) Filtration media shall consist of clean, crushed, angular stone with a nominal size distribution between three quarters of an inch to two inches in diameter.
(6) Non-woven geotextile fabric shall be provided around the filtration media to prevent the migration of the media into the surrounding subgrade soils.
(7) A pretreatment structure shall be incorporated to remove all debris and sedimentation from the stormwater runoff prior to entering the ex-filtration system.
(8) Proper inspection and maintenance access ports/manholes shall be installed on all structures and ex-filtration termination points. Inspection ports shall also be installed at minimum every 20 feet along the length of the system.
(9) The design shall meet such site or project specific additional criteria as the Director of Public Works may require.
(10) Upon initial construction completion, an “as-built” drawing confirming that the stormwater management system was constructed according to the city approved drawings shall be signed and sealed by the engineer of record and submitted to the City Public Works Department.
(C) Inspection and maintenance criteria.
(1) Inspection, maintenance, and testing procedures, including report forms, shall be provided by the engineer of record and submitted to the city with the site construction plans, and be approved by the city, before a permit is issued.
(2) A volume test shall be performed on the underground stormwater management system and an engineer certified volume test report, satisfactory to the city, submitted as part of the final site inspection for certificate of occupancy, and every four years thereafter, to the City Public Works Department.
(3) Biannual inspections shall be performed by responsible party and findings logged on the report form for the life of the treatment system. Inspection records shall be kept on site for a period of four years and made available to the city for review when requested by the city.
(4) Routine maintenance and cleaning operations shall be performed and logged on the report form. Maintenance and cleaning records shall be kept on site for a period of four years and made available to the city for review when requested by the city.
(Ord. 1525, passed 5-7-15)