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California of widespread water quality deterioration are in coastal ground water basins that have been subjected to seawater intrusion. Inadequately constructed or improperly "abandoned" wells are not the sole cause of water quality degradation in a California ground water basin. A small quantity of contaminants enteri15 one well may not have far-reaching effect. However, (1 the construction of thousands of new wells in California each year, (2) the fact that marry are - - becoming more closely spaced, and (3) the growing number of ® --- wells being neglected or indiscriminately abandoned indicate WELL 6TANK that the potential for impairing ground water quality is growing. Then, when pollutants move along the lines of natural water movement, the effects will be long-lasting and difficult, if not impossible, to correct. IIEPTIC TANK DISPOSAL a Inadequately constructed or improperly destroyed wells facilitate the impairment of ground water quality (see J, Figures 1 and 2) in five principal ways: 1. When the well is located too close to sources of pollution or contamination or downstream from them so that the well can be directly affected by flow from these sources (Figure lA). Ironically, sometimes the source of pollution l is a nearby abandoned well. 2. When the surface portion of the well is A.WELL LOCATED Too CLOSE B. ENTRY THROUGH PUMP VASE constructed without protective features so that contaminated TO POLLUTION SOURCE or polluted waters can flow directly into the well through one or more of several possible openings in or under the pump. Usually under these circumstances only the water in or adjacent to the well is affected (Figure 1B and 1C). 3. When the annular space (the space between the rp outside of the casing and the wall of the hole) lacks an adequate vertical seal and surface water or shallow sub- surface water.flows into the well along the outside of the casing. (Note that although the annular space may be filled with granular filter material, i.e., the familar "gravel- BOREHOLE pack", no seal exists and undesirable water can move downward or laterally.) This e of defective well is particularly susceptible (Figure 1DDto contamination. 4. When, during well construction (or the CASING destruction of abandoned wells), aquifers that produce poor quality water are ineffectively sealed off, allowing the interchange of water with one or more aquifers and thus significantly impairing the quality of water in those , _A d aquifers. The well now provides a physical connection between these aquifers (Figure 2). ❑ v ` 5. When the well is used intentionally, acciden- tally, or carelessly for the disposal of waste allowing r direct contamination of the ground water to occur. Such C. ENTRY BENEATH PUMP r D. VIA THE ANNULAR SPACE disposal is prohibited by law except under specially approved circumstances. Figure 1. AVENUES OF ENTRANCE FOR POLLUTANTS TO WELLS