Pumps

(1) The test pump should be a centrifugal, or more preferably, a turbine or submersible pump. It should be capable of lowering the water level in the well at least 10 feet or more depending upon the characteris­tics of the formation being tested. The pump should preferably be powered with an electric motor, or with an engine capable of operating continuously for the duration of the test. The pump discharge line should be equipped with a valve so that the rate of discharge can be accurately controlled. At the beginning of the test, the valve should be partially closed so that back

pressure on the pump can be varied as the test pro­gresses to keep the rate of flow constant.

(2) During a pumping test, it is imperative that the rate of pumping be maintained constant. Lowering of the water level in the well will usually cause the pumping rate to decrease unless the valve in the dis­charge line is opened to compensate for the additional head or lift created on the pump. If the pump is pow­ered with a gas or diesel engine, changes in tempera­ture and humidity of the air may affect appreciably the operation of the engine and thus cause variations in the pumping rate. Variations in line voltage may similarly affect the speed of electric motors and thus the pumping rate. Any appreciable variation in pump­ing rate should be recorded, and the cause of the varia­tion noted.

(3) The flow from the test well must be conveyed from the test site so that recharge of the aquifer from water being pumped does not occur within the zone of influence of the test well.

c. Flow and drawdown measurements.

TEST WELL

Pumps

DRAWDOWNat P О Int p =H"= (h – h ) DRAWDOWN AT TEST WELL – H’=H -(h + h ‘)

 

U. S. Army Corps of Engineers

(1) The discharge from the well can be measured by means of an orifice, pitometer, venturi, or flow­meter installed in the discharge pipe, or an orifice in­stalled at the end of the discharge pipe, as described in appendix G. The flow can also be estimated from the jet issuing froma smooth discharge pipe, or measured by means of a weir or flume installed in the discharge channel. For such flow measurements, appropriate consideration must be given to the pipe or channel hy­draulics in the vicinity of the flow-measuring device. Formulas, graphs, and tables for measuring flow from a test well are given in appendix G.

(2) In thick aquifers, or in deposits where the material varies with depth, it may be desirable to de­
termine the permeability of the various strata of the formations in order to better determine the required length and depth or well screens of wellpoints for the design of a dewatering or drainage system. This permeability can be determined by measuring the vertical flow within the well screen at various levels with a flowmeter. The flow from the various strata can be obtained by taking the difference in flow at adja­cent measuring levels; the flow-meter, equipped with a centering device, is placed in the well before the pump is installed. Typical data obtained from such well-flow measurements in a test well are shown in figure C-4. These data can be used to compute the coefficient of permeability of the various strata tested as shown, The

Подпись: ELEVATION, FT MSL

100 80 Є0 40 І0 0

FLOW IN SCREEN, PERCENT OF TOTAL WELL FLOW

 

FLOW IN WELL AT VARIOUS DEPTHS IN PERCENTOFTOTAL FLOW

 

COEFFICIENT OF PERMEABILITY OF INDIVIDUAL SAND STRATA

 

Pumps

U. S. Army Corps of Engineers

correlation between Dio and kh shown in figure C-4 was based on laboratory sieve analyses and on such well-flow tests.