City of Phoenix / County of Maricopa


Maricopa County Stormwater Management Plan

2.0 Introduction

This Stormwater Management Plan (SWMP) was created in response to the Arizona Pollutant Discharge Elimination System (AZPDES) General Permit AZG2016-002. The SWMP is the principal means in which Maricopa County (County) has recorded programs and policies to demonstrate full permit compliance. Under the general permit, the County must implement actions and activities that demonstrate compliance with permit requirements. These actions are called Minimum Control Measures (MCMs) and include:

  1. Public Education and Outreach
  2. Public Involvement and Participation
  3. Illicit Discharge Detection and Elimination
  4. Construction Site Runoff Control
  5. Post-Construction Runoff Control
  6. Pollution Prevention & Good Housekeeping for Municipal Operations

The County has developed Best Managing Practices (BMPs) for each MCM. Each MCM and their corresponding BMPs are outlined and detailed in Section 6.0 of this SWMP.

6.5 Post Construction Stormwater Management

The County maintains a program to manage post-construction stormwater runoff controls that includes education and inspection. The post-construction BMP inspection program ensures that structural and non-structural BMPs are constructed/implemented as approved for use and ensures they are maintained over time. The County maintains a policy addressing maintenance responsibilities for post-construction structural BMPs as well as policies and procedures for routine inspections by the County staff. The program addresses two key components: assurance that the BMPs approved for each new or redevelopment project are built to standards and that the owner/operator of structures are maintained over time. Site inspections are conducted to ensure that, during development and redevelopment, post-construction stormwater management is being addressed through proper design, implementation, operation, and maintenance.

Existing Maricopa County regulations require that developments receive and retain stormwater volume generated by a two-hour, 100-year precipitation event. Retention basins are required to be located not less than 25 feet from septic systems. Runoff that has been retained onsite must be disposed of within 36 hours by percolation, dry wells, or drainage into an approved drainage way, not to exceed pre-development flows. Disposal of stormwater is considered essential for vector control. The drainage regulations also contain language designed to ensure stability and prevent erosion in hillside developments. An inventory of all post construction stormwater structures is maintained. This inventory fluctuates at properties and land are annexed over time.

City of Phoenix Stormwater Policies and Standards

(Sec. 3.9)

All drainage facilities and easements owned and/or operated by private entities, including Homeowner’s Associations, shall properly maintain their storm water management system to ensure that it will perform as designed. (City of Phoenix Storm Water Policies and Standards 3.9.5) This is especially important during monsoon season.

3.9 Maintenance

It is essential that maintenance be considered during the planning, design and construction of drainage facilities. Maintenance is provided so that the facilities can function as they were originally designed and constructed, and so that the service life of the facility is maximized. Common maintenance problems associated with drainage facilities include growth of unwanted vegetation, debris accumulation, sedimentation, erosion, scour, soil piping, soil settlement and structural damage. Culverts and bridges are to be designed to avoid impacts to existing sediment transport conditions. Provision for permanent drainage facility accessibility, including access for maintenance equipment into channels and culverts, is necessary for regularly scheduled maintenance activities.

3.9.5 Private Maintenance

All drainage facilities owned and/or operated by private entities, including Homeowner's Associations, shall be properly maintained to promote performance of the drainage facilities consistent with the original design intent.

Links

Maricopa County Stormwater Management Plan

City of Phoenix Stormwater Policies and Standards