In order to control pollution of water resources, the owner or person responsible for the development area shall use conservation planning and practices to maintain the level of conservation established in the following standards.
(a) Standards and Specifications: Post-Construction runoff practices used to satisfy these standards shall meet the standards and specifications in the current edition of the Rainwater and Land Development manual, NRCS Field Office Technical Guide for the local county, or the Ohio EPA, which ever is most stringent.
(b) Water Quality Basins:
(1) Pool Geometry: The minimum length-to-width ratio for the pond is 3:1 (the length will be three (3) times the width).
(2) Riser in Embankment: The riser shall be located within the embankment for purposes of maintenance access. Access to the riser will be by manholes.
(3) Water Drains: Each retention basin shall have a drainpipe that can completely drain the pond. The drain shall have an elbow within the pond to prevent sediment deposition from plugging the drain, and prevent sediment deposition from draining into the nearby waterways.
(4) Adjustable Gate Valves: Both the Water Quality and the Storm Water Management Basin drains shall have adjustable gate valves. Valves shall be located inside of the riser at a point where they will remain dry and can be operated in a safe and convenient manner. During the annual inspections the valves shall be fully opened and closed at least once, and the certifying official shall attest to this on the inspection form. To prevent vandalism, the handwheel shall be chained to a ringbolt or manhole step.
(5) Principal Spillway: Each principal spillway shall be designed in accordance with the Natural Resources Conservation Service (NRCS) standards and specifications for the office serving the local county. Each principal spillway shall have the capacity to pass the 100-year design storm flows. The inlet or riser size for the pipe drops shall be designed so that the flow through the structure goes from weir flow control to pipe flow control without going into orifice control in the riser. The crest elevation of the primary spillway shall be no less than one foot below the emergency spillway crest. Premium joint pipe is required and a removable trash rack shall be installed at each location. Anti-seep collars shall be provided for all pipe conduits through an embankment.
(6) Emergency Spillway: An emergency spillway shall be provided on each Water Quality and Storm Water Management basin. Emergency spillways shall convey flood flows safely past the embankment, and shall be designed in accordance with NRCS standards and specifications for the office serving the local county. Emergency spillways shall have a 100-year design storm capacity unless exempted in writing by Engineering Director and/or his or her designees.
(7) Embankments: Each dam embankment shall be designed in accordance with the NRCS standards and specifications for the office serving the county that the project is located in. Anti-seep collars shall be provided for all pipe conduits through an embankment.
(8) Safety Features:
A. The primary spillway opening shall not permit access to the public and other non-maintenance personnel.
B. The perimeter of all water pool areas that are deeper than three (3) feet shall be surrounded by benches that meet the following:
i. A safety bench, with a maximum slope of 3%, which extends outward, on dry land, from the shoreline. This bench will be a minimum of 25 feet wide to provide for the safety of individuals and maintenance vehicles that are adjacent to the water pool. The safety bench may be landscaped, without the use of structures, to prevent access to the water pool.
ii. Side slopes between the safety bench and the aquatic bench shall not be steeper than 3:1 (3 feet horizontal for every 1 foot vertical).
iii. An aquatic bench that extends inward from the shoreline far enough to ensure public safety and has a maximum depth of 15 inches below the normal water surface elevations. The aquatic bench may be landscaped to prevent access to the deeper water pool. The aquatic bench may also be incorporated into the Post-Construction Water Quality Plan.
iv. Side slopes beyond the aquatic bench and below the permanent water level shall not be steeper than 2:1 (2 feet horizontal for every 1 foot vertical).
v. The contours of the pond will be designed and managed to eliminate drop-offs and other hazards. Side slopes getting to the pond shall not exceed 3:1 and shall terminate on a safety bench.
(9) Water Quality Basin: If a Water Quality Basin is needed and can not be incorporated into an existing or planned Detention or Retention Basin then a separate Water Quality Basin will need to be planned, designed, constructed and maintained into perpetuity.
A. Water Quality Basins will not be constructed in any permanent or intermittent stream channel.
(10) Flexibility: These standards are general guidelines and shall not limit the right of the Engineering Director and/or his or her designees to impose at any time additional and/or more stringent requirements nor shall the standards limit the right of the Engineering Director and/or his or her designees to waive, in writing, individual requirements.
A. If the Engineering Director and/or his or her designees waives, in writing, individual requirements the owner will provide the Engineering Director and/or his or her designees with the information and documentation required to assure Ohio EPA that the waived requirement will not degrade water quality.
(Ord. 2009-75. Passed 6-22-09.)