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Overview
Background of Stormwater Regulations In 1972, Congress passed the Clean Water Act, which required a National Pollutant Discharge Elimination System (NPDES) program to be put in place to control stormwater pollution. Although Congress authorized the Environmental Protection Agency (EPA) to enforce compliance of the Clean Water Act, the agency delegated authority to the states to allow specific legislation, programs, and enforcement. In North Carolina, the regulatory oversight for the the Clean Water Act is handled by the Department of Environment and Natural Resources (NCDENR) but specifically through the Division of Water Quality (DWQ). For detailed information, see the Division of Water Quality website on stormwater and runoff pollution. Phase I of the stormwater regulations - enacted in 1990 - required a stormwater permitting program for large or medium-sized municipalities that had populations of 100,000 or more. Phase II of the NPDES stormwater program became law in December 1999, which required smaller communities to comply as well by creating small municipal separate storm sewer systems (MS4s). However, it wasn't until 2006 that the final Phase II permitting regulations were put into place in North Carolina. Compliance with the Phase II stormwater regulations is measured against six major goals:
Who must comply and how? The stormwater regulations apply to both new development and redevelopment. For new development, the regulations apply to earth-moving activity or site preparation greater than one acre. The exception to the rule is for development that disturbs less than one acre as long as the house or project isn't part of a larger development that is more than one acre. For redevelopment, stormwater regulations also apply to commercial and residential construction. The overall goal is of the stormwater regulations is that the post-development runoff should meet the regulatory standard, which is to control the runoff from the first 1.5" of rain. The tricky part is that often there is no measure or metric of whether the post-development measures meet the mark. For instance, the Oak Island ordinances do not require the builder or homeowner to demonstrate or quantify how well the system is working. To further complicate matters, some engineered solutions that are fine when first installed may fill up with silt over time and lose their ability to control runoff. For example, pervious concrete may become as impervious as regular concrete if it's not installed correctly or maintained (e.g., prevent it from filling up with silt and sand). French drains around homes can fill up with silt and dirt, quickly losing any buffering or filtration capacity. Or the homeowner may remove a tree from the side yard and reduce the buffering capacity to soak up runoff. This is partly why the BMPs are constantly evolving. The Division of Water Quality has a model ordinance that clarifies how the regulations could be managed as part of a larger Stormwater Management Plan, a plan that is required by each stormwater permit under Phase II rules. A key part of the Stormwater Management Plan is a design manual that details what BMPs are acceptable, which can be structural or non-structural measures. The local municipal government can then pick and choose which designs to implement into their local building codes. There can be conflicts of local codes to stormwater BMPs such as:
However, there is a "Rehab Code" in place that provides North Carolina municipalities adjusted building code standards that allow better harmonization with current stormwater regulations. When a new project receives a stormwater permit, that is essentially obligating the contractor or homeowner to ensure the design, installation, and construction, of a stormwater management and control system for that site. One weakness in the current regulations is that they do not provide for any continued evaluation of the stormwater system after construction is completed. So, a planned urban development (PUD) could pass the initial stormwater inspection and get the certificates of occupancy (CO) but years later have lots of problems because the systems were not maintained properly. That ends up costing the town and homeowner's associations plenty to fix it (e.g., South Harbour). Thus, the trend is to move away from structural BMPs like French drains and pipes to ways of increasing the non-structural BMPs such as expanded pervious buffers or vegetated swales in between impervious surfaces. For example, instead of allowing a contractor to back fill a lot and elevate the house with underground pipe and a French drain system, the new BMPs might require a maximum footprint on the size of the house and total impervious surface; no additional back fill; and grade the site to a low spot on the lot where a rain garden will be placed. Or the grading of the site might require the runoff go to an area that is pervious instead of the street. Some of the key development standards in the Division of Water Quality model ordinance include:
Overview of Stormwater System & Phase II Permit The typical stormwater system is designed to handle the volume of rain from a storm that occurs once every 10 years; a 10-year storm will generate approximately 8 inches of rain within a 24-hour period. The stormwater system is engineered to handle this volume of water such that there is no standing flood water remaining on site for longer than a day. Since the amount of stormwater from a hurricane or a tropical storm far exceeds the normal capacity of the system it's expected that there may be significant flooding after a major storm. For instance, Hurricane Floyd in September 1999 dumped 20 inches of rain in some parts of coastal North Carolina, which easily overwhelmed stormwater systems for municipalities at a higher elevation than the Cape Fear region. In order to accomplish this, all development should be able to control runoff of the first 1.5 inches of rainfall or less from all impervious surfaces on site.
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