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materials to prevent downward movement of surface water into the well from the top of the casing, or along the annular space. In a confined or artesian situation, sealing must prevent loss of pressure and/or return of water to the surface, or into a dry "thief'zone, or into a zone of less pressure head. PRE-DESTRUCTION ACTIVITIES The importance of obtaining specific hydrogeologic and well construction data increases with the complexity of well construction and the risk of aquifer contamination from known nearby sources. If a driller's log, geophysical log, and construction data are available these would be the primary sources of data to be consulted. However, for many old wells this type of information is not available. Static water levels and well depths can be directly measured. Well construction:details, such as placement of screens, can be determined by a downhole video survey, and other logs such as natural gamma, cement bond, casing inspection,;and fluid conductivity, can be completed in the well, to address specific local concerns (ie., flowing wells;threat of contamination)that may dictate destruction procedures. Any obstructions in the casing, such as debris, pumps, or junk should be removed, to the original total depth of the well, if known. It should be recognized that in some instances, such as in attempts to recover an old pump that has dropped to the bottom of the well or where casing has collapsed, such efforts may not be successful and the clearing of obstructions shall be required only to the extent possible. Additionally, the well should be pumped or bailed to clean any suspected foreign fluids, such as turbine oil, from the water column to the extent possible. RECOMMENDATIONS The California Groundwater Association recommends adopting the following on materials and procedures for the proper destruction of wells, as presented in this Article and summarized on the:accompanying Well Destruction Plow Chart. SEALING MATERIALS Sealing materials provide a '-water-tight" barrier to migration of water and any associated contaminants in the well bore. Recommended seating materials per Bulletin 74-81/90 include: neat cement, sand-cement, bentonite, or combinations of these materials. In some cases, additives are used to affect viscosity, setting time, and strength. It should be noted that make-up water chemistry may be important in determining the ultimate behavior of the sealing materials during placement and curing. The water quality of the make-up water should be checked before operations begin to ensure that the water is compatible with the sealing materials. Neat cement grout: Neat cement grout generally involves using a ratio of one 94-lb. Bag of Portland cement to no more than 6-1/2 gallons of water (which is equal to a 17-sack cement/water mix as available from a "ready-mix" source). A small amount of bentonite (up to 6 percent) may be added to make the mixture more "fluid" and reduce shrinkage. Special additives may need to be used in the mix to prevent deterioration of the cement column in areas subjected to sea-water intrusion,for example. Sand-cement matures: Sand-cement mixtures increase the "bulk" and might be used in such situations as filling a large-diameter hand-dug well. The recommended mixture is generally 2 parts sand to I part Portland cement by weight and about 7 gallons of water. High solids sodium bentonite: This type of"sealing grade" grout consists of 20 to 30 percent solids content by weight of sodium bentonite when mixed with water. Pumping in place is necessary for this bentonite, to ARTICLE 299—DESTRUCTION OF WATER WELLS —Page 2 of 8 (Revised 4/27/2013)