Flood Maps

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NPDES Phase II Permit

The National Pollutant Discharge Elimination System (NPDES) program, established under section 402 of the Clean Water Act of 1972, provided the framework to regulate point sources of pollutants to receiving streams. The NPDES program established a comprehensive two-phase approach to managing stormwater discharges. Phase I of the program required permits for municipal separate storm sewers (MS4s) serving populations greater than 100,000 people and for stormwater discharges associated with industrial activities. Phase II requirements of the NPDES program applied to all non-point source discharges of stormwater from small MS4s with populations less than 100,000 people. Implementation of the NPDES phase I and II permitting program was delegated to the N.C. Department of Environmental Quality (NCDEQ), which determined that Morrisville should be brought into the program as an owner of an MS4. Morrisville received their Phase II permit from NCDEQ in November of 2005, and the permit must be renewed every five years.

To meet the conditions of its Phase II permit, Morrisville was required to develop and implement a stormwater management program that includes the following minimum control measures (MCMs):

Public Involvement and Participation

Illicit Discharge Detection and Elimination

To report illegal dumping into streams or storm drains, call the Stormwater Hotline at 919-463-S0AK (7025).

The focus of the illicit discharge detection and elimination program is to detect and eliminate illicit discharges, including spills and illegal dumping. The Town must identify and address significant contributors of pollutants to the MS4, implement appropriate enforcement procedures and actions, and develop a storm sewer system inventory and overall map showing all outfalls and associated conveyances. The final program goal is to inform employees, businesses, and the general public of hazards associated with illegal discharges and improper disposal of waste.

The Town developed and adopted an ordinance to prohibit illicit discharges to the storm sewer system, which is included in the Town’s Unified Development Ordinance. Also, GIS mapping of the existing stormwater drainage system as of 2013 has been completed, and corresponding drainage areas have been delineated and receiving streams identified. New construction after 2013 is being added to the inventory using digital “as-built” files required during the construction process. The Town is also in the process of developing a stormwater outfall inspection program to detect dry weather flows and monitor erosion at system outfalls.

Construction Site Stormwater Runoff Controls

The primary goal of the construction site runoff control program is to reduce pollutants in stormwater runoff from construction activities disturbing one or more acres of land surface and those activities less than one acre that are part of a larger common plan of development. Additional objectives include providing procedures for public input, sanctions to ensure compliance, requirements for construction site operators to implement appropriate erosion and sediment control practices, reviews of site plans that incorporate consideration of potential water quality impacts, and procedures for site inspection and enforcement of control measures. Finally, the Town must establish requirements for construction site operators to control waste, such as discarded building materials, concrete truck washout, chemicals, litter, and sanitary waste at the construction site that may cause adverse impacts to water quality.

The Town of Morrisville relies on the Wake County Sediment and Erosion Control program to comply with this MCM. Additionally, the Town conducts random inspections of local land-disturbing activities that have a sediment and erosion permit issued by Wake County to see if the site is in compliance. The Town monitors the Wake County program for effectiveness in the permittee jurisdiction. Finally, potential problems at construction sites with sediment and erosion control permits are reported to Wake County, and any follow-up actions are monitored and documented. Potential sediment and erosion control violations should be reported to the Town through the Stormwater Hotline at 919-463-S0AK (7025) or through the online reporting system.  Report can also be made directly to Wake County Erosion Control staff.

Post-Construction Stormwater Management

The purpose of the post-construction stormwater management program is to manage stormwater runoff from new development or redevelopment that drains to the MS4 and disturbs an acre or more of land area for single family projects (a half acre for others), including projects less than an acre that are part of a larger common plan of development or sale. The program also is required to provide a mechanism to ensure long-term operation and maintenance of BMPs and to ensure that controls are in place to minimize the impact to water quality.

The Town adopted and approved a post-construction stormwater management ordinance, included in the Engineering Design and Construction Manual. The Town enforces and implements the requirements of the ordinance for post-construction stormwater management and only allows the use of stormwater quality BMPs designed in accordance with the NCDEQ Stormwater Design Manual. Additionally, the Town requires annual operation and maintenance reports for each BMP and is implementing long term operation and maintenance by legal documentation and maintenance security funds.

Pollution Prevention and Good Housekeeping

The aim of the pollution prevention and good housekeeping program is to prevent or reduce stormwater pollution from municipal operations.

As part of the program, the Town annually reviews and inventories activities that could result in potential pollutant runoff. This includes Town-owned facilities, operations, stormwater systems, and BMPs. A training program has been established to educate appropriate employees on clean water issues and workplace responsibilities to reduce or eliminate pollutants from stormwater.

In addition to the Phase II program, the stormwater division also implements the following programs:

• Riparian buffer program
• Floodplain management

Watershed Assessment

 In 2016, the Town completed a multi-phase watershed assessment. This study included an assessment of the existing condition of all streams and stormwater outfalls. It also included identification of potential restoration opportunities of streams, riparian buffers, outfalls, and stormwater control measures. Detailed hydrology, hydraulic, and flooding calculations and evaluations was not within the scope of this study. 

See the watershed assessment reports below: