Agenda - 08-26-1991 - Laserfiche WebLink

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59 jurisdiction within a designated surface water supply watershed then they must protect it in a manner consistent with the state minimum requirements. Waters classified for future water supply use will carry the same requirements. • What is meant by an "engineered stormwater control structure "? Are there standard methods for designing these structures? What types of structures are acceptable? An engineered stormwater control structure is a man -made facility designed to intercept and treat stormwater runoff to remove pollutants that may be carried in the runoff water. Methods for the design of these structures can be found in the Stormwater Runoff Disposal Rules, 15A NCAC 2H .1003. Studies have demonstrated that wet detention ponds are the most effective device for pollutant removal. These structures provide a number of removal mechanisms (biological removal, removal through sedimentation, etc.) while also containing removed particles to avoid resuspension in future storm events. In some cases it will be difficult to always maintain a pool of water in the structure, never the less the device should be designed according to wet detention pond criteria. A technical guidance document is being developed by the state to provide more specific information on designing stormwater control structures. • Are local governments required to allow engineered stormwater controls in water supply watersheds where the state minimum criteria would allow them? No, for all water supply classifications where engineered stormwater controls are allowed, local governments may choose the "low density" option and control pollution sources by limiting minimum lot sizes. The "low density" approach is the preferred method of stormwater control if a watershed is to be developed. This option would allow local governments to allow a "safe" level of development without the responsibility for engineered stormwater controls. They also have the option of-allowing engineered stormwater controls in some portions of their jurisdiction, but requiring low density in the other portions of their jurisdiction. • What are the requirements for a local government which chooses to allow high density development and thus must ultimately be responsible for engineered stormwater controls? The local government must inspect each control structure at least annually. (A copy of an inspection sheet for local government use can be found along with the draft model ordinances.) The inspection does not have to include water quality or quantity sampling and analysis. The inspection, instead, is intended to ensure that the structure is functioning properly. If the structure is large, however, a boat may be needed to verify that the appropriate structural depth is being maintained. A local government that already has 13