Storm Drain

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NPDES Phase 2 Post-Cosntruction


The Cities of Lathrop, Lodi, Manteca, Patterson, and Tracy, and portions of the County of San Joaquin (collectively Agencies) are each classified as Phase II Municipal Separate Storm Sewer System (MS4) communities. In 2013, the California State Water Resources Control Board (State Water Board) adopted a National Pollutant Discharge Elimination System (NPDES) general permit for Phase II MS4 communities to regulate stormwater and nonstormwater discharges from MS4s to waters of the United States. As part of the Phase II Permit, the Agencies are required to develop/update post-construction standards to address stormwater quality for regulated new development and redevelopment projects.

The Post-Construction Stormwater Standards Manual provides guidance for planning, implementing, and maintaining effective
control measures with the intention of improving water quality and mitigating potential water quality impacts, including hydromodification, from stormwater and non-stormwater discharges. The Manual provides tools to address the following objectives:


  • Establish the methodology to consider the effects of stormwater runoff from a new development or redevelopment project during the project planning phase;
  • Minimize contiguously-connected impervious surfaces in areas of new development and redevelopment, and where feasible, to maximize on-site infiltration of stormwater runoff;
  • Implement site design measures to preserve, create, or restore areas that provide important water quality benefits such as riparian corridors, wetlands, stream and buffers, and maintain, protect, and improve underlying soil quality;
  • Provide source control measures to minimize the transport of and/or eliminate potential sources of pollution to stormwater runoff or run-on into the MS4 and receiving waters;
  • Implement Low Impact Development (LID) control measures to reduce and/or eliminate the volume of stormwater runoff and pollutants leaving the project site;
  • Control post-construction peak stormwater runoff discharge volumes and velocities (hydromodification) to mitigate impacts from downstream erosion and to protect downstream habitat; and
  • Develop tools for effectively operating, managing, and maintaining stormwater
    control measures.
The Post-Construction Stormwater Standards Manual only applies to regulated projects in the NPDES Phase 2 Area. The State Water Resources Control Board has developed a tool called Post-Construction Water Balance Calculator to help developers recognize when they have achieved the volume reduction requirement.  For a map of the NPDES Phase 2 Area, the Post-Construction Standards Manual, and the Post-Construction Water Balance Calculator click on the appropriate links below.

NPDES Areas                 
Post-Construction Standards Manual                 Post-Construction Calculator for Small Projects


Applicability of the 2015 Post-Construction Stormwater Standards Manual

  • Small Projects - These are projects that create and/or replace at least 2,500, but less than 5,000 square feet of inoervious surface; or detached single-famility homes that create and/or replace a minimum of 2,500 square feet of impervious surface and are not part of a larger plan of development. 
  • Regulated Projects - These are projects that create and/or replace greater than or equal to 5,000 square feet of impervioud surface and LUPs that create 5,000 square feet or more of newly cosntructed contiguous impervious surfaces.
  • Hydromodification Management Projects - These are a subset of Regulated Projects that create and/or replace once acre or more of impervious surface.

LID techniques include:

  • Preserve natural hydrology;
  • Manage storm water close to the rain falls;
  • Minimize site disturbance and grading;
  • Retain vegetation;
  • Cluster development;
  • Reduce impervious surface;
  • Reforestation;
  • Bioretention systems;
  • Landscape with native plants;
  • Compost amended soils;
  • Pervious concrete;
  • Porous asphalt;
  • Permeable pavers;
  • Eco roofs (green roofs)


Links to LID Web Sites:


EPA's LID and other Green Design Strategies

EPA's Green Infrastructure


San Joaquin River


PO Box 1810 / 1810 East Hazelton Avenue, Stockton, California 95201    |    Phone  (209)  468 - 3055

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The Storm water Pollution Prevention Program is a Program of the

San Joaquin County

Public Works Department

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