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Watershed Protection Division
Watershed Protection Division

Construction and stormwater

An excavator digging dirt on a construction site

Construction activities are a major source of stormwater pollution. Sediment, or soil, disturbed during clearing, grading and excavation, and stockpiling can contaminate our storm drain system when loose materials migrate off from a site. Additionally, concrete and mortar wash-out and other associated construction debris are common contaminants in stormwater runoff at construction sites. Storm drains carry runoff directly to local creeks, streams, and rivers with no treatment or filtration.

Developers, contractors, and DIYers can prevent stormwater pollution by taking the following steps:

  1. Comply with stormwater permit requirements.
  2. Maintain required erosion and sediment control using Best Management Practices (BMPs), and properly manage the construction site to prevent the release of chemicals and debris.
  3. Plan and design erosion control measures prior to breaking ground on your construction site. Schedule excavation and grading activities for dry weather periods. For more information, consult the erosion control page operated by the County's Department of Planning and Development.

All of these prevention measures should be indicated in your construction plans and/or Stormwater Pollution Prevention Plan (SWPPP).

Requirements for construction projects

State of California requirements

Construction and/or demolition projects that disturb one acre or more of land must comply with State requirements to control the discharge of stormwater pollutants. Prior to the start of construction or demolition projects, a Notice of Intent (NOI) to comply with the Construction General Permit Requirements must be filed with the State Water Quality Control Board. A Stormwater Pollution Prevention Plan (SWPPP) must be developed and maintained during the project and it must include the use of Best Management Practices (BMPs)

A fiber roll wrapped around a storm drain inlet for sediment control

 to protect water quality until the site is stabilized.

County of Santa Clara requirements

All construction and demolition projects must also comply with the County’s Grading Ordinance, which requires the use of erosion and sediment controls to protect water quality while the site is under construction. Prior to the issuance of a permit for grading activity that occur during the rainy season (October to April), an Erosion Control Plan must be submitted to the County of Santa Clara Land Development Engineering (LDE) office detailing Best Management Practices to prevent the discharge of stormwater pollutants.

Stormwater inspections and enforcement

The County regularly inspects construction sites to ensure that projects are properly implementing water quality BMPs. Construction sites that are out of compliance with the County’s BMP Requirements must immediately correct deficiencies or be subject to fines.

Copper roofs and other architectural copper

Copper can harm aquatic life in the San Francisco Bay. Water that comes into contact with architectural copper may contribute to the impacts on water quality, especially during installation, cleaning, treating, or washing. Protect water quality by using these best management practices when using architectural copper in your projects.

Resources for construction site managers

  • The CASQA BMP Handbook Portal provides general guidance for selecting and implementing BMPs to eliminate or reduce the discharge of pollutants from construction sites. The Handbook/Portal also provides guidance on developing and implementing Stormwater Pollution Prevention Plans (SWPPPs).
  • For information on the State Construction General Permit and how to file a Notice of Intent, please visit the State Water Resources Control Board Construction Program website.

For guidance on how to design and install construction site BMPs, please use the following references: