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Artificial filters are desirable when the aquifer has a Water Well Drillers' Reports "uniformity coefficient"f of less than 2.5 (some authorities recommend a value of less than 3), or in poorly consolidated Detailed and comprehensive knowledge of the occur- rock, i.e., rock that tends to cave when pumping occurs. rence and quality of California's ground water resources is vital to protecting, conserving, and properly developing Detailed information on the design of intake them. The data obtained during the construction of water sections, including the selection of well screen aperture wells are primary sources of geologic and hydrologic informa- openings and artificial filter materials, will be found in tion. In 1949 the Legislature concluded that such informa- most publications dealing with ground water and water wells, tion would be invaluable in the event of underground a number of which are listed in Appendix E. pollution, and would provide a fund of geologic information regarding the State's ground water resources. As a result, Incomplete Development. Well construction causes legislation was passed requiring the filing of a report with compaction of unconsolidated material about the walls of the the Department. The report is called the Water Well Drillers' drilled hole and drilling fluid also invades these walls, Report and its submittal is also a requirement of these forming a mud cake. In consolidated rocks, cuttings, fine standards (see Chapter II, Section 7 "Reports"). Additional particles and mud can be forced into joints and fractures. information about the report is presented in "Guide to the Thus, the borehole walls become clogged reducing the Preparation of the Water Well Drillers' Report", Department potential yield and causing the drawdown to be increased. of Water Resources, October 1977. Proper well development breaks down the compacted walls (or opens fractures) and draws the material into the well where Comments and Public Hearings on Draft Edition it can be removed. Obviously,the more thorough the develop- ment the better the well will perform. Adequacy of develop- Where a publication is of general interest or its ment is largely a matter of experience and judgment. The subject is one on which there can be a diversity of opinion, success of development can be measured by the amount of sand it is the policy of the Department of Water Resources to produced during interrupted pumping and the final specific issue it in preliminary form and solicit comments from capacity of the well. interested organizations and individuals and the general public. Since the standards for the construction of wells Testing for Sand. The sand content should be and the destruction of abandoned wells recommended herein are tested after evelopment and performance (pump) testing. for application throughout the State, and because they are Sand production should be measured by a centrifugal sand specified by many counties and cities (in ordinances or sampled or other acceptable means. Following development regulations),. a draft edition was prepared and distributed for (i.e., stabilization of the formation and/or gravel pack) comment (April 14, 1981). In addition, four public hearings and pump testing, the sand content should not exceed a or meetings (of an informal nature) were held to obtain the concentration of 5 ppm (parts per million) by weight views of persons interested in, or concerned with, the 15 minutes after the start of pumping. construction and use of water wells. These hearings were conducted in cooperation with the Department of Health Sand production exceeding this limit indicates that Services represented by its Sanitary Engineering Section the well may not be completely developed or may not have been since this report contains provisions which pertain to the properly designed. In that event, redevelopment may be public health aspects of water well construction. The hear- appropriate or as an alternative, a sand separator installed. ings were held during June 1981 at Berkeley, Fresno, Redding In existing wells should this value be exceeded significantly, and Los Angeles. In response to a number of requests, the rehabilitation (redevelopment) or repair is probably needed. comment period was extended to September 1981. Again, as an alternative, a sand separator may need to be installed. Fifty-five persons representing 33 individuals and organizations attended the four hearings. Five formal (written) statements were presented and 16 persons commented verbally. In addition, written comments were received from 1 The uniformity coefficient is a ratio that describes the 33 other organizations and individuals. Those submitting I variation in grain size of granular aquifer material. It written comments are listed in Table 5. Copies of the is defined as the ratio of the particle size of a material written comments are available for inspection in the at which 60 percent of the particles are finer and Department's file in Sacramento. 40 percent are coarser (called D ) to the "effective" grain size (i.e., the particle si9e of the material at All comments were carefully reviewed and considered. which ten percent of the particles are finer and 90 percent As might be expected, opinions differed on the applicability are coarser) (D ). The value of the uniformity coeffi- of certain standards, guidelines, and procedures. There is, cient for a matggial of one grain size is unity; for a of course, some validity in each point-of-view, which forms heterogeneous sand it might be 30. the basis for reconsideration. Many comments were incorpo- Such a device is described in the Journal of the American rated in this final draft. Others were not used for various Water Works Association, Volume 46, No. 2, February 1954. reasons. Most of the comments dealt mainly with (1) the