Procedures for aquifer tests


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Procedures for aquifer tests

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Title:
Procedures for aquifer tests
Creator:
Parker, Garald G. (Garald Gordon)
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Aquifers -- Hydrogeology -- Everglades (Fla.) ( lcsh )
Hydrology -- Florida -- Biscayne Aquifer (Fla.) ( lcsh )

Record Information

Source Institution:
University of South Florida
Holding Location:
University of South Florida
Rights Management:
The University of South Florida Libraries believes that the Item is in the Public Domain under the laws of the United States, but a determination was not made as to its copyright status under the copyright laws of other countries. The Item may not be in the Public Domain under the laws of other countries.
Resource Identifier:
032968560 ( ALEPH )
891343127 ( OCLC )
G16-00626 ( USFLDC DOI )
g16.626 ( USFLDC Handle )
3 ( Box number )

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Book

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PAGE 1

PROCEDURES FOR AQUIFER TESTS Pumping Test 1. Obtain all pertinent data about well(s) including depth, water level, pump setting, preliminary test data, time since last pumping, etc. 2. Measure and record over a one week period the depth to water in test well and in observation well(s) before test starts. Mark MP with paint. Measure WL periodically during day(s) before test to determine trend. Record barometer readings before, during, and after test. 3. Write in proper headings on notebook sheets or use our mimeographed forms. 4. Set stop watch and synchronize with pocket or wrist watch(es). 5. If electric measuring line is used, check its operation before test. Do not use steel tape to measure WL in pumped well while it is pumping except in wells of large diameter where the water surface can be observed during measurement. Do not lower any measuring device below the level of the bowls or the suction pipe while the well is pumping. 6. Measure distances from each observation well to the pumped well. Take bearings and sketch positions of all wells and pertinent landmarks. If. there is no record of the observation well(s) or if the record is in doubt, run slug test with two or more 5-gallon buckets of water to determine if well is open and will react to nearby pumping.

PAGE 2

7. Start pump on an even hour or half hour. If one of the first closely spaced measurements is missed, just catch the next one on your notebook list. If movement of needle on millimeter is sluggish, jiggle the line several feet up and down. If operator is running test alone and if an orifice meter with manometer is being used, tape the manometer to a folding carpenters rule in a position so that it can be read while water-level measurements are being made. If you are asing a Hoff meter or other device for measuring discharge, it may be necessary to check drawdown at less frequent intervals in order to get a proper number of discharge measurements. After measurements are being made at longer intervals, switch off the electric line between measurements to save batteries. In working along with pumped well and one or more observation wells, make first observations after pumping starts by checking the observation wells; after trend is established, alternate observations at pumped well (discharge and drawdown) with those at observation well(s). 8. Throughout the test, make detailed notes of all phenomena pertinent to the test, i.e. , condition and color of water, time and nature of any changes in color or quantity of sediment pumped, time and nature of any rapid fluctuations of discharge or water level, times of and length of any temporary shut downs, note any nearby wells that are pumping and obtain any data on them that may be useful in accounting for any anomalies that may appear in the results of your test, note any nearby ponding of discharge water and record distance and bearings, etc.

PAGE 3

9. At different times during test, usually at beginning and near end of test, take temperature and water sample or field conductivity, if practicable. Fill out QW tag and attach to sample. Keep sample from freezing. 10. Before test starts, fill out a complete well schedule on test well and observa-tion well(s). Such things as diameter and reductions in casing; number, type, and zones of perforations (or well screens); log of well; method and length of well development; and settings of bowls and suction pipe are especially important. Take particular care to identify each field and office sheet to avoid later confusion. Each field notebook sheet or mimeographed sheet should be marked with well number and name (if it is known by a particular __.....,, name), the date, the location, your name, and the project. For example: "Well 12-64-13ddd, Air Force Academy Project, fifth Dawson well, obs. well no. 2, 150 feet north of pumped well, tested June 6, 1941, by Rex "seegar" Smith and Paul "bauxite" Schneider. Be sure to label every sheet of field or office graph paper in a similar manner. If you don't, it may be impossible to identify any sheet that may later be lost from a pump-test folder. I 11. During the test, after first flurry of measurements, plot WL vs. time in minutes on semi-long paper to permit determination of progress of test. Use T = ~iQ for approximate value of T. 12. Do not operate pump at full throttle when test starts; use valve to throttle back the discharge (if possible). Later it may be possible to open the valve if discharge rate drops too low. Maintain some back pressure. Over pump-ing initially may result in bothersome surging and interruptions later in the test.

PAGE 4

13. If anticipated value of u (see previous test data) is too large (i.e. , w 0. 02), plot log-log curves. 14. If recorders are used, check times frequently and make small "ticks" on chart by flipping cable. Label data and recorder sheets for each well. 15. In making recovery test, it is as critical to obtain closely spaced measurements during first few minutes after pump is shut off. Generally, because of screen loss and other factors, the points will not fall on the straight-line semi-log plot and, hence, are useless. This is particularly true when dealing with non-artesian aquifers. After the recovery measurements become more widely spaced, plot t /t' vs. residual s on semi-log paper (t /t' on logarithmic scale) to see trend of recovery curve. Under most watertable conditions, such as in coarse alluvial gravel where the recovery _is rapid, this curve will determine when you can stop making recovery measurements. When water level approaches the static level and points start straying from a straight line, you may as well pack up and go home for all succeeding points will fall off the line and will be useless. With artesian wells and slow recovery, this "rule of thumb" may not apply. 16. If there are no suitable existing observation wells near the pumped wells, and wells have to be put down for this purpose, certain rules of location, spacing, and depth should be followed. A minimum of three observation wells is very helpful for it is very comforting to have three plotted points determine a straight line rather than two. Except for very thick aquifers, do not locate nearest observation well closer than distance m (thickness of saturated part

PAGE 5

of aquifer) from pumped well. Convenient spacings for three observation wells are m, 2m, and 4m; use of these spacings allow equal spacing of plotted points on logarithmic scale. 17. If aquifer is rather thick and fairly homogeneous, the three observation wells should terminate at about the mid-depth of the saturated part of the aquifer where they will reflect about the average head. If the pumped well penetrates only part of the saturated zone, or if the aquifer is known to be lentic-ular or otherwise heterogeneous, three pairs of observation wells are recom-mended, each pair to comprise (1) a shallow well ending a few feet below the pumping water level at the particular distance r, and (2) a deep well ending within a few feet of the base of the aquifer at the same distance r. s2 s2 Try Jacob's drawdown correction (s' = s-2 m) and if the correction ( 2m) amounts to 0. 01 foot or more, the corrections should be made. Plot the corrected drawdowns for each of the 6 observation wells at a particular time t, on semi-log paper and, if the 6 plotted points appear to be reasonably good, plo_ t graphic (or arithmetic) averages, --and connect (or attempt to connect) the three average points by means of a straight line. If one plotted point of any pair of points is obviously in error (owing to clogged observation well, etc,) disregard this point, rely mainly on remaining two average points. 18. Avoid running recovery tests only on wells in unconfined aquifers unless such aquifers are so coarse-grained and relatively homogeneous that they may be expected to drain rapidly. If observation wells are available for measurement of water levels , recovery tests should be made in conjunction with pumping

PAGE 6

tests regardless of type of aquifer. In applying either the Thiem or Theis method to data obtained from unconfined aquifers it is safest to consider t a constant and let r (t) be the variable, unless the pumping test is run for a sufficient length of time to insure reasonably complete drainage and approximate steady-state flow or unless computations are required to determine boundaries. 19. If determination of specific yield of an unconfined aquifer is desired, plan for a long period of pumping, and at say, 24-hour intervals, plot S against t, thus: s t The first approximations of S, thus plotted, should approach asymptotically the probable real value of S. If pumping has to be stopped before successive equal values are obtained, a slight extrapolation may give the probable value. A second approximation of Smay then be obtained by Jacob's suggested method: s = (m-s (average) ) s. m 20. Suggested equipment: a. Steel tape of adequate length and with lead weights and chalk. b. Electric tape of adequate length and with extra electrode(s) and

PAGE 7

electricians tape. c. Stop watch, with wrist band if desired. d. Flashlight with extra batteries and bulb. e. Semi-log paper and ordinary graph paper and mimeographed pumptest forms. f. Crescent wrench, pliers, and other tools. g. Pocket or wrist watch. h. Notebook, Indija ink pen, triangle, scale, slide rule. i. Brunton compass. j. Data and curves from similar previous test. k. Hoff meter, flume, weir plates, bucket, barrel, or other water-measuring device, if needed. 21. Suggested publications: Selected procedures for analyzing aquifer-test data -Brown. Ground water -E. W. Bennison Water management manual -U.S. B. R. Water well handbook -M0.. Well Drillers Association Water system handbook -Deming Co. Measurements of water flow through pipe orifice with free discharge -Layne Bowler Co. :& Water Supply Paper 887 -Wenael Notes on determining permeability by pumping tests under watertable conditions -Jacob

PAGE 8

Partial penetration of pumping well, adjustments for -Jacob Rational drawdown test of artesian well elucidates specific capacity -Jacob g~ . l..~ t (!'.)k l " ho Ma, Notes from ground-water short course, UV\l\/er3i., 0 • " Feb. Z 8 t~'=>.._,_ 1"'1,,1.,,., &l., t-l'SI::>. I


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