Hydrology and Water Quality CEQA Mitigation Measures

Summary

The California Environmental Quality Act (CEQA Overview) requires that state and local agencies consider and disclose the potential environmental impacts of a proposed project. CEQA states that projects should not be approved as proposed if there are feasible alternatives or feasible mitigation measures available which would substantially lessen the significant environmental effects of such projects (PRC § 21002).

Part of the CEQA process involves determining the type of environmental impacts likely to result. For hydrology and water quality, the CEQA Handbook defines impacts as the need to assess whether the project will affect surface and groundwater resources (including aquifer characteristics and water quality), whether runoff will be generated, that could affect flooding or drainage characteristics, or whether flooding from storm events or dam failure inundation might result.

The hydrology and water quality section of an environmental impact report should also include information on the hydrological characteristics of the site prior to any proposed project.

The availability of water supplies and infrastructure to serve project demand are addressed in the [Public Services and Utilities and Energy] section of the CEQA Handbook.

Standards of Significance

Thresholds of significance must be determined for the following potential hydrology and water quality environmental impacts.

Will the proposed project:

• Violate any water quality standards or waste discharge requirements;

• Substantially deplete groundwater supplies or interfere substantially with groundwater recharge such that there would be a net deficit in aquifer volume or a lowering of the local groundwater table level (i.e., the production rate of pre-existing nearby wells would drop to a level which would not support existing land uses or planned uses for which permits have been granted);

• Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, in a manner which would result in substantial erosion or siltation on- or off-site;

• Create or contribute runoff water which would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff;

• Otherwise substantially degrade water quality;

• Place housing within a 100-year flood hazard area, as mapped on a federal Flood Hazard Boundary or Flood Insurance Rate Map or other flood hazard delineation map;

• Place structures within a 100-year flood hazard area that would impede or redirect flood flows;

• Expose people or structures to a significant risk of loss, injury or death involving flooding, including flooding as a result of the failure of a levee or dam; or

• Inundation by seiche, tsunami, or mudflow

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