ABSTRACT
Observation wells are engineered openings constructed through the solid earth, usually circular in crosssection, that are drilled or otherwise excavated to allow human access to specific zones of underground water for the purpose of measuring attributes such as water levels or pressure changes that would otherwise not be observable at the Earth’s surface. Wells constructed to sample groundwater quality have been called observation wells by some hydrogeologists, but common accepted practice restricts the term monitoring wells to wells from which water samples may be collected for chemical analysis.[1] Groundwater-level monitoring networks incorporate multiple observation wells, and maps constructed from these water levels allow hydrogeologists and engineers to determine the direction of the subsurface flow. Observation wells are occasionally called ‘‘piezometers,’’ although most hydrogeologists consider piezometers to be a special type of observation well in which a simple tube emplaced in an aquifer, open at the top for access and measurement and open at the bottom to allow communication with the aquifer.[2] No matter what the name used for these features, observation wells are windows to the groundwater system, and they allow us to collect in situ information from which we can develop an understanding of the degree of interconnection of openings in the aquifer, calculate the amount of water that is stored in the subsurface openings, and determine the hydraulic head and pressure gradients present in the subsurface which control groundwater flow and rates of movement.
BASIC CONSTRUCTION
