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## Conceptual models > Unconfined aquifer >## Aquifer of infinite lateral extent |

Aquifer of infinite lateral extent

Assumptions:

✓aquifer is unconfined, of infinite lateral extent, isotropic or anisotropic on the vertical plane;

✓pumping well may be fully penetrating or partially penetrating;

✓drawdown can be estimated in the observation well (fully penetrating or partially penetrating) or in the piezometer at any distance from the pumping well;

✓allowance for storage capacity of the pumping well, skin effect and storage capacity of the observation well (see Moench’s solution accounting for pumping well storage capacity) is made.

a b

c d

e f

Conceptual hydrogeological schemes (cross-sections) of unconfined anisotropic aquifer of infinite lateral extent.

a – partially penetrating pumping well and piezometer; b – partially penetrating pumping and observation wells; c – fully penetrating pumping well and piezometer; d – fully penetrating pumping and observation wells; e – fully penetrating pumping and observation wells in the unconfined leaky aquifer; f – confined-unconfined aquifer.

Fundamental equations:

1) Neuman’s solution for average drawdown in observation well and drawdown in piezometer in anisotropic aquifer; pumping well as well as penetrating well may be fully penetrating or partially penetrating;

2) Boulton’s solutions for average drawdown and water table drawdown in fully penetrating well in isotropic aquifer;

3) Moench’s solution for average drawdown in observation well and drawdown in piezometer in anisotropic aquifer; pumping and observation wells being fully penetrating or partially penetrating;

4) Moench’s solution for average drawdown in observation well and drawdown in piezometer in anisotropic aquifer; pumping and penetrating wells being fully penetrating or partially penetrating; allowance is made for pumping well and piezometer storage capacity, skin effect in the pumping well and shape factor of the piezometer;

5) Moench’s solution for drawdown in fully penetrating or partially penetrating pumping well in anisotropic aquifer with account for pumping well storage capacity and skin effect;

6) Theis’s solution for water table drawdown for fully penetrating well in isotropic aquifer;

7) Hantush’s solution for water table drawdown for fully penetrating well in isotropic leaky aquifer;

8) Moench–Prickett solution for confined-unconfined aquifer.

Pumping regimes:

One well pumped at a constant rate

Pumping

Recovery

One or several wells pumped at a variable rate

Pumping

If Moench’s solution is applied some additional parameters should be specified such as: casing radius of the pumping well, skin hydraulic conductivity, skin thickness and, if needed, shape factor of the observation well or piezometer.

References

Barlow P.M., Moench A.F. WTAQ version 2 - a computer program for analysis of aquifer tests in confined and water-table aquifers with alternative representations of drainage from the unsaturated zone // U.S. Geological Survey. 2011. Technique and Methods 3-B9.

Boulton N.S. Analysis of data from non-equilibrium pumping tests allowing for delayed yield from storage // Proceedings of the Institution of Civil Engineers. 1963. Vol. 26. P. 469–482.

Boulton N.S. The drawdown of the water-table under non-steady conditions near a pumped well in an unconfined formation // Proceedings of the Institution of Civil Engineers. 1954. Vol. 3, N 3. P. 564–579.

Moench A.F. Computation of type curves for flow to partially penetrating wells in water-table aquifers // Ground Water. 1993. Vol. 31, N 6. P. 966–971.

Moench A.F. Flow to a well in a water-table aquifer: an improved Laplace transform solution // Ground Water. 1996. Vol. 34, N 4. P. 593–596.

Moench A.F. Flow to a well of finite diameter in a homogeneous, anisotropic water table aquifer // Water Resources Research. 1997. Vol. 33, N 6. P. 1397–1407.

Moench A.F., Prickett T.A. Radial flow in an infinite aquifer undergoing conversion from artesian to water table conditions // Water Resources Research. 1972. Vol. 8, N 2. P. 494–499.

Neuman S.P. Analysis of pumping test data from anisotropic unconfined aquifers // Water Resources Research. 1975. Vol. 11, N 2. P. 329–345.

Neuman S.P. Effect of partial penetration on flow in unconfined aquifers considering delayed gravity response // Water Resources Research. 1974. Vol. 10, N 2. P. 303–312.

Neuman S.P. Perspective on «Delayed yield» // Water Resources Research. 1979. Vol. 15, N 4. P. 899–908.

Neuman S.P. Supplementary comments on «Theory of flow in unconfined aquifers considering delayed gravity response» // Water Resources Research. 1973. Vol. 9, N 4. P. 1102–1103.

Neuman S.P. Theory of flow in unconfined aquifers considering delayed gravity response // Water Resources Research. 1972. Vol. 8, N 4. P. 1031–1045.