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Post-Construction Site Requirements

In undisturbed areas, 50% of precipitation infiltrates into the ground, with 0-10% going to surface runoff. In urban areas, as much as 50% of precipitation goes to runoff, while only 20% infiltrates. In recent years, increased development has led to an increase in the amount of impervious surfaces, increasing the amount of runoff, degrading the overall quality of our waters.

To lessen stormwater impacts from new developments, best management practices to treat, store, and infiltrate water onsite before it can affect water quality downstream can be used. Examples of post-construction best management practices include Low Impact Development, grassed swales, and bioretention.

The objectives of Maricopa County’s Stormwater Quality Management and Discharge Control Regulation include protecting water quality to the Maximum Extent Practicable by removing and/or treating pollutants prior to discharge and promoting long-term operation and maintenance of all permanent stormwater management facilities.

To achieve these objectives, a Post-Construction Permit is required for land disturbances equal to or greater than one acre, or disturbances less than one acre if part of a larger plan of development. Activities for which a 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 stormwater management facilities. Post-construction design should incorporate permanent structural and/or non-structural best management practices and long-term operation and maintenance responsibilities. For submittal requirements and applicable fees, please refer to the Forms/Applications page or the Fee Schedule.

Standards for post-construction design and maintenance can be found in the Drainage Policies and Standards Manual for Maricopa County. Best management practices and additional design requirements can be found here:

For more information on Maricopa County’s Stormwater Program, please E-mail us at or call (602) 506-5557.

For regulation related comments or questions, please e-mail us at