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n 1)[,L N,) r'Or6M 1 ANCY R 0 Box 2165 m Livermore California 94551 • 510-373-9211 OPERATIONAL DEFINITION CONSTANT RATE AQUIFER TESTS Well pump tests in which the flow rate is held reasonably constant (+/- about 5% ) or and that have a duration longer than a few hours are referred to either as constant rate aquifer tests or by a name suggesting a typical duration_ Typical test names are: 24-hour pump test, 72-hour pump test, etc However, in order to qualify as an aquifer test, the response in at least one observation well must be monitored in addition to that in the pumping well . Aquifer tests are not always conducted for the same reasons , although most tests have many of the same ob)ectives. Tests conducted without observation wells are an extended duration variety of sustained yield testing. If properly conducted, sustained yield testing of any duration can yield useful aquifer hydraulic information . Aquifer tests are performed to determine the hydraulic properties of aquifer systems, fundamentally, the transmissi.vity and the storage coefficient of the aquifer material near the monitored wells . Proper aquifer test design is essential to the successful determination of aquifer system properties . Aquifer test design, and later data analysis and evaluation require a knowledge of the geological characteristics of the subsurface; the type of aquifer and confining beds, including thickness and lateral extent; the type and nature of the boundaries to the aquifer system, data on the groundwater flow system, including horizontal or vertical flow, water table or potentiometric surface gradients, and regional trends in groundwater levels; and an understanding of other wells in the aquifer system. Aquifer test design should include the performance and interpretation of a step drawdown test. Performing successful aquifer tests require, at a minimum: 1 . ) A determination of the pre-pumping and post-pumping water- level trend; 2 . ) A carefully controlled and monitored constant pumping rate; 3 . ) Accurate water level measurements made at precisely known times during the drawdown and recovery periods in both the pumping well and an one (preferably three) or more observation wells . Analyzing and evaluating aquifer test data is based on theoretical models that the hydrogeologist must understand in addition to the thorough investigations into the geology of the area, as alluded to above. Because different types of aquifers can exhibit similar drawdown