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    County of Maricopa

    The County of Maricopa has enacted a Stormwater Ordinance in order to establish minimum stormwater management requirements and controls to protect and safeguard the general health, safety, and welfare of the public residing in watersheds within this jurisdiction.  The County of Maricopa is the permitting authority for all land disturbing activities and requires the land owner to maintain all on-site stormwater control facilities and all open space areas (e.g. parks or “green” areas) required by the approved stormwater control plan. The County of Maricopa will only provide construction permits to projects that establish a plan to manage stormwater runoff occurring during the construction process. The County of Maricopa, under the NPDES program, also has the authority to inspect properties for noncompliance and can issue a notice of violation (NOV) for any deficiency or infraction onsite. Property owners are responsible for the maintenance of any stormwater facilities or practices located on the property. The County of Maricopa has the authority to inspect stormwater facilities and practices in order to ascertain that they are properly maintained and functioning.

    Maricopa County Stormwater Laws and Regulations

    Maricopa County regulations are compliant with its Arizona Pollutant Discharge and Elimination System (AZPDES) permit requirements for the county's municipal separate storm sewer system (MS4).

    Maricopa County is designated as a small MS4 and must obtain stormwater discharge permit coverage under the County of Maricopa Phase II Small MS4 General Permit AZG2016-002.

    To meet the minimum requirements of the Phase II permit, be aware of the Maricopa County Stormwater Quality Management and Discharge Control Regulations. This regulation prohibits non-stormwater discharges and illicit connections to the County's MS4. Runoff from construction sites, as well as long-term, permanent runoff control is also regulated by the County. 



    1101.0 - Introduction

    The goal of this post-construction Stormwater management program is to protect public safety and public infrastructure, reduce erosion on private properties and stream channels, and protect the quality of Waters of the U.S. to the maximum extent practicable. The goals are achieved by maintaining and/or restoring natural drainage patterns, minimizing grading and disturbance, and minimizing the extent of impervious cover, as well as encouraging the use of a variety of best management practices for reducing the pollutant loadings from newly developed and redeveloped sites. This will be accomplished by requirements to , among other things, reduce the magnitude and extent of impervious cover and site disturbance, remove pollutants from runoff prior to the introduction of Stormwater to the County MS4, and promote effective operation and maintenance of all Stormwater facilities.

    1101.1 - Applicability

    The post-construction requirements in this Chapter apply to permanent Stormwater management facilities, systems and/ or devices. Stormwater management during construction activities is regulated separately pursuant to Chapter 6 of this Regulation.

    1102.0 - Objectives

    In order to protect the health, safety and general welfare of the residents of Maricopa County, as well as to protect, sustain and enhance the quality of the Waters of the U.S. in and adjacent to the County, drainage and Stormwater management practices shall be utilized as directed herein to achieve the following objectives:

    • Accommodate site development and redevelopment in a manner that protects public safety and that is consistent with federal and state water quality requirements and the requirements of the Phase II Stormwater permit for the County.
    • Protect water quality to the Maximum Extent Practicable by removing and/or treating pollutants prior to the introduction of Stormwater to the County MS4 or any Storm Drainage System connected to the MS4 throughout the County.
    • Promote effective long-term operation and maintenance of all permanent Stormwater management facilities.
    • Treat and release Stormwater as close to the source of runoff as possible using a minimum of structures and maximizing reliance on natural processes.
    • Address certain requirements of the Municipal Separate Storm Sewer System (MS4) National Pollutant Discharge Elimination System (NPDES) Phase II Stormwater regulations.
    • Reduce the environmental impacts of Stormwater pollution from existing developed sites undergoing redevelopment while encouraging development and redevelopment in urban areas and areas designated for growth.

    1103.1 –Post-Construction Permits Required

    A post-construction permit is required for land disturbance equal to or greater than one acre in area except as otherwise provided per Section 1103.2 of this Regulation. Land disturbances of less than 1 acre constituting a part of a larger development plan are also regulated. Activities for which a post-construction permit is required include land development and redevelopment to include clearing or grubbing, leveling, construction of new or additional impervious or semi-pervious surfaces such as driveways, roadways, parking lots, recreation features; construction of new buildings or additions to existing buildings; and installation of permanent Stormwater management facilities or appurtenances thereto.

    1103.2 -Exemptions

    The following activities may be exempted by the Director from on-site Stormwater quality runoff control. An exemption shall apply only to the requirement for on-site permanent Stormwater management facilities, systems and/ or devices, in the application for a Stormwater permit. All other Stormwater management design elements, such as a storm sewer system, road culverts, erosion and sedimentation control and runoff quality, shall be required. All exemption requests must be filed with the Department.

    • Emergency Exemption: Emergency maintenance work performed for the protection of public health, safety and welfare. A written description of the scope and extent of any emergency work performed shall be submitted to the Department within two (2) calendar days of the commencement of the activity. If the Department finds that the work is not an emergency, then the work shall cease immediately and the requirements of this Regulation shall be addressed as applicable.
    • Maintenance Exemption. Any maintenance to an existing Stormwater management system made in accordance with plans and specifications approved by the Department.
    • Gardening. Use of land for gardening for home consumption.
    • Irrigation return flows and other agricultural and non-agricultural activities excluded by 40CFR 122.3.
    • Improvement–related Exemption. A Stormwater management system will not be required for any net increase of impervious surface of less than one thousand square feet where the cumulative total square feet of all impervious surfaces does not exceed the impervious surface standards of the applicable zoning district. However, where the net increase in impervious surface exceeds one thousand square feet but the total disturbed area is less than five thousand square feet pursuant to a soil erosion and sediment pollution control plan /or a grading plan, the Applicant shall demonstrate compliance with this Regulation for the increased impervious surface.

    1104.0-General Requirements

    A. The management of Stormwater on site, both during and upon completion of the land disturbances described in Section 1101 shall be accomplished in accordance with the standards and criteria of this Regulation and the requirements of the Maricopa County Drainage Policies and Standards, the Maricopa County Drainage Regulations, the Subdivision Regulations for Maricopa County and the Floodplain Regulations for Maricopa County. The design of any temporary or permanent facilities and structures and the utilization of any natural drainage systems shall be in full compliance with this Regulation and any other applicable Regulation.

    B. The intent of these design standards is to encourage environmentally sound Stormwater management practices that provide necessary drainage facilities while protecting the hydrologic characteristics and water quality of the site and watershed. Development shall be required to incorporate Stormwater management control.

    C. Applicants shall refer to the most recent version of the Maricopa County Drainage Policies and Standards and the Maricopa County Drainage Design Manual, Vol. III, Erosion Control Handbook, or other appropriate references for guidance in the design of Stormwater management facilities, system and/ or devices, most appropriate to individual site conditions. The objectives are to achieve water quality improvement at the source or during conveyance, prior to the introduction of Stormwater into the County MS4 or any Storm Drainage System connected to the MS4.

    D. The Stormwater management system shall not create an adverse impact on Stormwater quality in either upstream or downstream areas. Offsite areas, which drain to or across a site proposed for development, shall be addressed in the Stormwater Management Plan prepared for the development. No Stormwater Management Plan shall be approved unless it provides information sufficient to assure that the runoff from the project shall not adversely impact water quality in downstream areas.

    E. Where deemed necessary by the Director, the applicant shall construct storm drains to handle on-site runoff to the maximum extent permitted under the County Planning Code, provide on-site/off-site drainage easements, and provide for the conveyance of off-site runoff to an acceptable outlet in the same watershed.

    F. Any Stormwater management facilities regulated by this Regulation that would be located in or adjacent to Waters of the U.S. or wetlands shall continue to be subject to approval by the U.S, Army Corps of Engineers (USACOE) or other agencies through their permit processes. Proof of approval by the USACOE shall be provided by the applicant prior to the start of construction.

    G. Any Stormwater management facility or part thereof regulated by this Regulation that will be located in Maricopa County Department of Transportation, Flood Control District of Maricopa County, or other County-owned rights-of-way or that will drain across or onto MCDOT, Flood Control District or other County-owned rights-of-way shall be subject to written approval, licensing or permitting by the appropriate authority. Excluding the USACOE approval process detailed in paragraph 6 above, documentation of such aforementioned approval, licensing or permitting shall be provided by the applicant at the time of application.

    H. At the time of application for a building permit for any approved lot created by a subdivision and/or improved as a land development project, issuance of the permit shall be conditioned upon adherence to the terms of this Regulation.

    I. Stormwater drainage to impaired waters or unique waters may be subject to additional performance criteria or may need to utilize or restrict certain Stormwater management practices.

    1105.0 –Permanent Stormwater Management Design Standards

    Design standards for post construction design and maintenance are contained in the most recent version of the Maricopa County Drainage Policies and Standards as adopted by the Maricopa County Board of Supervisors and the Board of the Flood Control District of Maricopa County. Standards for the application of Best Management Practices are found in the most recent version of the Maricopa County Drainage Design Manual, Volume III, Erosion Control. Other design requirements are found in the most recent versions of the Maricopa County Drainage Design Manuals Volume I, Hydrology, and Volume II, Hydraulics. Applicants shall refer to the version of the manuals in effect at the time the application is made.

    1106.0–Construction and Operation Responsibilities

    1106.01 –General Responsibilities

    A. Large developments shall address Stormwater quality on a unit/phased basis as part of their drainage plans required by the Maricopa County Subdivision Regulations and Section 2.4 of the Maricopa County Drainage Policies and Standards. Large developments include those which require a Development Master Plan per Section 206 of the Maricopa County Subdivision Regulation are typically those greater than 640 acres in size as defined in the Maricopa County Zoning Ordinance, or any significant local developments divided into units or phases which may be considered as a large development, even if less than 640 acres in size.  Stormwater quality must not be left for the final phase of a development.

    B. The owner of permanent Stormwater management facilities shall be responsible for the proper operation and maintenance of those facilities during and after construction. All permanent on-site BMPs shall be operational prior to the use by any development or phase of development dependent on those BMPs. An Operation and Maintenance Plan consistent with the requirements of Section 1109 shall be prepared for review and approval by the Director and shall be executed and signed by the Department and the owner.

    C. The owner of permanent Stormwater management facilities for a tract shall be responsible for the proper installation and function of those facilities in accordance with the approved Stormwater permit. All temporary soil erosion and sedimentation control measures shall be removed or converted to their permanent configuration in accordance with an approved erosion control plan. This requirement in no way precludes the authority of the Director to determine when sufficient stabilization has occurred on a site in order to convert to the permanent Stormwater management facilities.

    1106.02 –Report with Application

    For all post-construction activities governed by this Regulation the Applicant shall submit with their Stormwater permit application a report which shall contain the information necessary to allow the Department to review the application. It may be necessary for some applications covering large areas to have the report prepared by a professional licensed by the State of Arizona. The information in the report may include, but is not limited to, the following:

    • A suitable map of the watershed for all named streams within which the project is proposed with existing and proposed development areas presented on the map. A United States Geological Survey quadrangle map is sufficient.
    • Suitable maps and drawings showing all existing natural and constructed drainage facilities affecting the subject property.
    • Hydrologic watershed and water feature boundaries including all areas flowing to the proposed project, existing streams (including intermittent and ephemeral streams, and other bodies of water within the project area).
    • Sufficient topographical information with elevations to verify the location of all ridges, streams, etc. Two foot contour intervals are acceptable within the project’s boundaries and for proposed off-site improvement. For slopes greater than fifteen percent (15%), five (5)-foot contours are acceptable.
    • Notes pertaining to, and locations of existing standing water, areas of heavy seepage, springs, wetlands, streams, and hydrologically sensitive areas.
    • General type of soils with Hydrologic Soil Group noted, estimated permeability in inches per hour, and location and results of all soil tests and borings.
    • Description of current and proposed ground cover and land use. The total area and percent of impervious cover shall be noted.
    • A plan of the proposed Stormwater drainage system attributable to the activity proposed, including runoff calculations, Stormwater management practices to be applied both during and after development, and the expected project time schedule.
    • The design computations for all proposed Stormwater drainage systems, including storm drain pipes, inlets, runoff control measures and culverts, drainage channels, and other features, facilities, and Stormwater management practices.
    • A grading plan, including all areas of disturbance, of the subject activity. The total area of disturbance shall be noted in square feet and acres.
    • A plan of the erosion and sedimentation procedures to be utilized as required by the Maricopa County grading and drainage requirements.
    • A delineation of the pathways of all concentrated flow (that is, flow other than overland sheet flow.)
    • An operation and maintenance plan consistent with the requirements of Section 1108. Such a plan should clearly explain how the proposed facilities operate and the functions they serve.
    • The name of the development, the name and address of the property owner and applicant, and the names and address of the individual or firm preparing the plan.
    • A north arrow, submission date, scale and revision dates as applicable shall be included on each page of all plans submitted.
    • Complete delineation of the flow paths used for calculating the time of concentration for the pre-developed and post-developed conditions.
    • Construction details sufficient to express completely the intended Stormwater design components consistent with this Regulation.

    1107.1 -Ownership

    All Stormwater management facilities, systems and/ or devices identified within an approved Stormwater permit shall be owned and maintained by one, or a combination of, the following entities:

    • An individual for his or her own on-lot Stormwater management facilities not constructed as part of a subdivision and/or land development plan.
    • Where individual on-lot Stormwater management facilities, system and/ or devices are proposed in a subdivision or other development greater than one acre, the subdivision and/or land development plan and plat shall contain a note in a form satisfactory to the Department designating the entity responsible for operation and maintenance of the on-lot facilities consistent with an approved operation and maintenance plan.
    • An entity that owns or has a perpetual right to access the land on which the Stormwater management facilities, system and/ or devices are located. The operation and maintenance obligation runs with the land and is binding upon the initial grantees of each lot and his, her, or their heirs, administrators, successors or assigns. Stormwater management facilities, systems and/ or devices or the ownership of the land on which they are located may not be deeded or dedicated to the County or the Flood Control District.

    1108.0 –Operation and Maintenance Plans

    An Operation and Maintenance Plan shall be prepared to identify the ownership, operation and maintenance responsibilities and as-built conditions for all Stormwater management facilities. At a minimum, the operation and maintenance plan shall include the following:

    • Any obligations concerning perpetuation and/or maintenance of natural drainage or infiltration facilities, and other facilities identified within the Stormwater permit.
    • A description of the permanent Stormwater management practices on the site, explaining how each practice is intended to function and operate over time.
    • All drainage and access easements shall be depicted and any site restrictions to be recorded against the property shall be identified on the plan. All such easements and restrictions shall be perfected to run with the land and be binding upon the landowner and any successors in interest.
    • Ownership of and responsibility for operation and maintenance of Stormwater management facilities, including names and contact information, shall be required.
    • A description of all Stormwater management facilities, written in a clear manner, consistent with the knowledge and understanding of the intended user.
    • A general description of operation and maintenance activities and responsibilities for facilities held in common or on-lot, including but not limited to: lawn care, vegetation maintenance, clean out of accumulated debris and sediment (including from grates, trash racks, inlets, etc.), liability insurance, maintenance and repair of Stormwater management facilities, landscaping and planting, payment of taxes and construction of any kind associated with the use, benefit and enjoyment of the facilities by the owners.
    • A description of routine maintenance actions and schedules necessary to ensure proper operation of Stormwater management facilities.
    • Written statement by owner giving assurances that no action will be taken by any lot owner to disrupt or in any way impair the effectiveness of any Stormwater management facilities, setting forth in deed restrictions the ability but not the duty of the Department to take corrective measures if it is determined at any time that stipulated permanent Stormwater management facilities have been eliminated, altered, or improperly maintained, including the ability of the Department to cause the work to be done and lien all costs against the property should the required corrective measures not be taken by the lot owner, following written notification, within a period of time set by the Director.
    • An explanation of how the parties responsible for the long-term operation and maintenance of Stormwater management facilities shall make records of the installation and of all maintenance and repairs, and shall retain the records until the site use changes and new permits and operation and maintenance plans are requested and approved. These records shall be submitted to the Department as established by the Operation and Maintenance Plan or if otherwise required by the Department.

    1108.1 –Recording of Operation and Maintenance Plans

    The owner of any land upon which permanent Stormwater management facilities and/or BMPs will be placed, constructed or implemented as described in an approved Stormwater permit and the Operations and Maintenance Plan, shall record the following documents with the Maricopa County Recorder within 15 days of approval of the Operations and Maintenance Plan by the County:

    • The Operations and Maintenance Plan, or a summary notice thereof;
    • Any necessary Operations and Maintenance Agreement(s); and
    • Necessary access and/or drainage easements. Items and/or conditions may be required to be included in any Operation and Maintenance Agreement where determined necessary by the Department to guarantee the satisfactory operation and maintenance of all permanent Stormwater facilities, system and/ or devices. The Agreement shall be subject to the review and approval of the Department.

    1109 –Drainage Provisions and Flood Control Regulations

    A. Provisions for on-site Stormwater retention/drainage and off-site Stormwater drainage both entering and leaving the property may be required by the Maricopa County Department of Planning and Development and Flood Control District of Maricopa County. This Stormwater Regulation and all amendments hereto shall be consistent with and subject to the regulations and provisions of the Drainage Regulation for Maricopa County and the Floodplain Regulations adopted by the Flood Control District of Maricopa County.

    B. Erosion Control measures should be in conformance with BMPs identified in the most recent version of the Maricopa County Drainage Design Manual , Volume III, Erosion Control or other EPA, ADEQ or locally approved method.

    C. Stormwater pollution prevention is to be addressed through the use of BMPs to the maximum extent practicable to comply with federal, state, county or local regulations or ordinances.

    D. The Flood Control District has established a minimum level of control for new development discharging into District owned or operated structures. This minimum standard is “First Flush” and consists of retaining or treating the first 0.5 inches of direct runoff from a storm event. The technical details for calculating “First Flush” and an example application are found in the most recent version of the Maricopa County Drainage Policies and Standards at Standard 6.4.1. As stated in Section 1104, written approval in the form of a license, permit or easement to drain into Flood Control District-owned structures is required.


    Maricopa Stormwater Quality Management and Discharge Control Regulation

    Maricopa Stormwater Page