¹Cooper, H.H., and C.E. Jacob,1946, A generalized graphical method for evaluating formation constants and summarizing well field history, Am. Geophys. Union Trans, Vol. 27, pp.526-534.

where:

s = drawdown measured in a monitoring well (m)
Q = discharge from pumping well (constant) (m³/d)
KD = transmissivity of the aquifer (m²/d)
r = distance between the monitoring well and pumping well (m)
S = storativity of the aquifer (dimensionless)
t = time since pumping started (days)

1. The aquifer is confined.
2. The aquifer has an infinite areal extent.
3. The aquifer is homogeneous, isotropic and of uniform thickness over the area influenced by the test.
4. Prior to pumping, the piezometric surface is horizontal over the area that will be influenced by the test.
5. The aquifer is pumped at a constant discharge rate.
6. The well is screened over the entire thickness of the aquifer ensuring entirely horizontal flow.
7. The flow to the well is not at steady-state.
8. The values of u are small (u<0.01), i.e., r is small and t is sufficiently large.

References:

¹Cooper, H.H., and C.E. Jacob,1946, A generalized graphical method for evaluating formation constants and summarizing well field history, Am. Geophys. Union Trans, Vol. 27, pp.526-534.
²Kruseman, G.P. and N.A. de Ridder, Analysis and Evaluation of Pumping Test Data (Second Edition), Publication 47; International Institute for Land Reclamation and Improvement, Wageningen, 1994.