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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. B. Gradients. Where possible,a well shall be located up the ground water 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 (page 28 of Bulletin 74-81), or by other influences. C. Flooding and Draina e. 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, Siting 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. D. 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." Section 9. Sealing the Upper Annular Space. Note: Sealing requirements are also described in Appendix B, page 67 of Bulletin 74-81. Section 9 (page 29 of Bulletin 74-81) has been revised to read as follows: "The space between the well casing and the wall of the drilled hole, often referred to as the annular space, shall be effectively sealed to prevent it from being a preferential pathway for movement of poor-quality water, pollutants,or contaminants. In some cases,secondary purposes of an annular seal are to protect casing against corrosion or degradation, ensure the structural integrity of the casing, and stabilize the borehole wall. -13-