TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
FIELD PUMPING TESTS
C-1. General. There are two basic types of pump-
(2) Nonequilibrium equations are directly applica-
ble to confined (artesian) aquifers and may also be used
ing tests: equilibrium (steady-state flow) and nonequi-
with limitations to unconfined aquifers (gravity flow
librium (transient flow).
conditions). These limitations are related to the per-
a. Equilibrium-type test. When a well is pumped,
centage of drawdown in observation wells related to
the water discharged initially comes from aquifer stor-
the total aquifer thickness. Nonequilibrium equations
age adjacent to the well. As pumping continues, water
should not be used if the drawdown exceeds 25 percent
is drawn from an expanding zone until a state of equi-
of the aquifer thickness at the wall. Little error is
librium has been established between well discharge
introduced if the percentage is less than 10.
and aquifer recharge. A state of equilibrium is reached
when the zone of influence has become sufficiently en-
c. Basic assumptions.
larged so that: natural flow into the aquifer equals the
(1) Both equilibrium and nonequilibrium methods
pumping rate; a stream or lake is intercepted that will
for analyzing aquifer performance are generally based
supply the well (fig. C-1); or vertical recharge from
on the assumptions that:
(a) The aquifer is homogeneous and isotropic.
equals the pumping rate. If a well is pumped at a con-
(b) The aquifer is infinite in extent in the hori-
stant rate until the zone of drawdown has become sta-
zontal direction from the well and has a constant
bilized, the coefficient of permeability of the aquifer
(c) The well screen fully penetrates the pervious
(d) The flow is laminar.
b. Nonequilibrium-type test.
(e) The initial static water level is horizontal,
(1) In this type of test, the value of k is computed
(2) Although the assumptions listed above would
from a relation between the rate of pumping Q, draw-
seem to limit the analysis of pumping test data, in
down H' at a point P near the well, distance from the
reality they do not. For example, most pervious forma-
well to the point of drawdown measurement r, coeffi-
tions do not have a constant k or transmissibility
cient of storage of the aquifer S, and elapsed pumping
T(T = k x aquifer thickness), but the average T can
time t. This relation permits determination of k from
readily be obtained from a pumping test. Where the
aquifer performance, while water is being drawn from
flow is artesian, stratification has relatively little im-
storage and before stabilization occurs.
(Courtesy of UOP Johnson Division)
Figure C-1. Seepage into an aquifer from an adjacent river.