3 August 1998
b. Sampling and analysis. It is mandatory to review the stipulations contained in the
current U.S. Environmental Protection Agency's drinking water standards and state/local
regulations as interpreted by the Surgeon General of the Army/Air Force and to collect
chemically analyze samples as required for the determination of all constituents named in the
drinking water standards. The maximum chemical concentrations mandated in the drinking
water standards are given in TM 5-813-3/AFM 88-10, Vol. 3. Heavy metals and arsenic are
rarely encountered in significant concentrations in natural ground waters, however, they may
be of concern in areas with metamorphic rock. Radioactive minerals may cause occasional
high readings in granite wells.
a. Definitions. The following definitions are necessary to an understanding of well
- Static Water Level. The distance from the ground surface to the water level in a well
when no water is being pumped.
- Pumping Level. The distance from the ground surface to the water level in a well when
water is being pumped. Also called dynamic water level.
- Drawdown. The difference between static water level and pumping water level.
- Cone of Depression. The funnel shape of the water surface or piezometric level which is
formed as water is withdrawn from the well.
- Radius of Influence. The distance from the well to the edge of the cone of depression.
- Permeability. The ease of which water moves through the rock or sediment.
- Hydraulic Conductivity. Also called coefficient of permeability. The rate at which water
moves through the formation (gallons per day per square foot. It is governed by the size and
shape of the pore spaces.
b. Well Discharge Formulas. The following formulas assume certain simplifying conditions.
However, these assumptions do not severely limit the use of the formulas. The aquifer is of
constant thickness, is not stratified and is of uniform permeability. The piezometric surface is
level, laminar flow exists and the cone of depression has reached equilibrium. The pumping
well reaches the bottom of the aquifer and is 100 percent efficient. There are two basic
formulas (Ground Water and Wells) one for water table wells and one for artesian wells.
Figure 5-3 shows the relationship of the terms used in the following formula for available yield
from a water table well.
1055 log (R/r)