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Science of Water : Concepts and Applications

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<strong>Water</strong> Treatment Calculations 327<br />

Well yield is determined by using the following equation:<br />

Example 10.3<br />

gallons produced<br />

Well yield, gpm <br />

duration <strong>of</strong> test, min<br />

Problem:<br />

Once the drawdown level <strong>of</strong> a well stabilized, it was determined that the well produced 400 gal during<br />

a 5-min test.<br />

Solution:<br />

Example 10.4<br />

gallons produced<br />

Well yield, gpm <br />

duration <strong>of</strong> test, min<br />

400 gal<br />

<br />

5 min<br />

80<br />

gpm<br />

Problem:<br />

During a 5-min test for well yield, a total <strong>of</strong> 780 gal are removed from the well. What is the well yield<br />

in gpm <strong>and</strong> in gph?<br />

Solution:<br />

Then convert gpm fl ow into gph fl ow:<br />

Specifi c Yield<br />

gallons produced<br />

Well yield, gpm <br />

duration <strong>of</strong> test, min<br />

780 gal<br />

<br />

5 min<br />

156 gpm<br />

156 gal/min<br />

60/h<br />

9360 gph<br />

(10.2)<br />

Specifi c yield is the discharge capacity <strong>of</strong> the well per foot <strong>of</strong> drawdown. The specifi c yield may<br />

range from 1 gpm/ft drawdown to more than 100 gpm/ft drawdown for a properly developed well.<br />

Specifi c yield is calculated using the following equation:<br />

Specific yield, gpm/ft <br />

well yield, gpm<br />

drawdown, ft<br />

(10.3)

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