Water Well Standards

Part II Construction

Section 8. Well Location With Respect to Pollutants and Contaminants, and Structures.

  1. Separation. All water wells shall be located an adequate horizontal distance from known or potential sources of pollution and contamination. Such sources include, but are not limited to:

    • sanitary, industrial, and storm sewers;
    • septic tanks and leachfields;
    • sewage and industrial waste ponds;
    • barnyard and stable areas;
    • feedlots;
    • solid waste disposal sites;
    • above and below ground tanks and pipelines for storage and conveyance of petroleum products or other chemicals; and,
    • storage and preparation areas for pesticides, fertilizers, and other chemicals.

    Consideration should also be given to adequate separation from sites or areas with known or suspected soil or water pollution or contamination.

    The following horizontal separation distances are generally considered adequate where a significant layer of unsaturated, unconsolidated sediment less permeable than sand is encountered between ground surface and groundwater. These distances are based on present knowledge and past experience. Local conditions may require greater separation distances to ensure groundwater quality protection.

    Potential Pollution
    Contamination Source
    Minimum Horizontal
    Separation Distance Between
    Well and Known or
    Potential Source
    Any sewer (sanitary, industrial, or storm; main or lateral) 50 feet
    Watertight septic tank or subsurface sewage leaching field 100 feet
    Cesspool or seepage pit 150 feet
    Animal or fowl enclosure 100 feet

    If the well is a radial collector well, minimum separation distances shall apply to the furthest extended point of the well.

    Many variables are involved in determining the "safe" separation distance between a well and a potential source of pollution or contamination. No set separation distance is adequate and reasonable for all conditions. Determination of the safe separation distance for individual wells requires detailed evaluation of existing and future site conditions.

    Where, in the opinion of the enforcing agency adverse conditions exist, the above separation distances shall be increased, or special means of protection, particularly in the construction of the well, shall be provided, such as increasing the length of the annular seal.

    Lesser distances than those listed above may be acceptable where physical conditions preclude compliance with the specified minimum separation distances and where special means of protection are provided. Lesser separation distances must be approved by the enforcing agency on a case-by-case basis.

  2. Gradients. Where possible a well shall be located up the groundwater gradient from potential sources of pollution or contamination. Locating wells up gradient from pollutant and contaminant sources can provide an extra measure of protection for a well. However, consideration should be given that the gradient near a well can be reversed by pumping, as shown in Figure 3, or by other influences.

  3. Figure 3

  4. Flooding and Drainage. If possible, a well should be located outside areas of flooding. The top of the well casing shall terminate above grade and above known levels of flooding caused by drainage or runoff from surrounding land. For community water supply wells, this level is defined as the:

    "...floodplain of a 100 year flood..." or above "...any recorded high tide...", (Section 64417, Sitting Requirements, Title 22 of the California Code of Regulations.)

    If compliance with the casing height requirement for community water supply wells and other water wells is not practical, the enforcing agency shall require alternate means of protection.

    Surface drainage from areas near the well shall be directed away from the well. If necessary, the area around the well shall be built up so that drainage moves away from the well.

  5. Accessibility. All wells shall be located an adequate distance from buildings and other structures to allow access for well modification, maintenance, repair, and destruction, unless otherwise approved by the enforcing agency.

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