Bad Hydrogeology

Misconception: Groundwater flows in underground rivers.

Little groundwater flows in open channels beneath the surface. Most flows through fractures in the rock, through millimeter sized opening between layers, and between the grains of the rock.

Misconception: Groundwater flows great distances.

The vast majority of groundwater discharges back to the surface within a few miles of its point of recharge, usually to the closest stream. The origin of this misconception may stem from terms such as “Wisconsin Flow.” This term has been applied to the aquifer in downtown Pittsburgh. The general public interprets this to mean that the groundwater has flowed from Wisconsin. The origin of the term is that the valley-fill sediments comprising the aquifer were deposited from sediment laden meltwater released from the melting glacier in northwestern Pennsylvania during the Wisconsinan Stage of the Ice Age. The name Wisconsinan Stage is applied to this time period because sediments and effects of this glaciation were first studied in Wisconsin.

Misconception: Groundwater flows quickly.

Groundwater at different depths flows at different speeds. Even fast flowing groundwater at shallow depths flows very slowly compared to surface water. Precipitation falling on a hilltop may move through the ground as groundwater and discharge along the flanks of the hill within several days where conditions allow extremely fast groundwater flow. At great depths, it may take thousands of years for groundwater to flow to its discharge point. As opposed to surface water flow velocity, which is measured in feet per second, groundwater velocity is measured in feet per day, per year, or longer!

Misconception: Water dowsing / witching / divining.

Any success of water dowsing in Pennsylvania can probably be attributed to the fact that a well drilled almost anywhere in the state will probably eventually find some water.

Misconception: Groundwater and surface water are separate.

Groundwater, surface water, and atmospheric water are intimately related through the earth’s water recycling machine, called the hydrologic cycle. Water passes repeatedly through all three parts of the cycle. Groundwater provides 2/3 of the flow to streams in Pennsylvania. As groundwater levels drop, stream flow decreases.

Misconception: Groundwater is a non-renewable resource.

Groundwater is constantly renewed by passing from atmospheric or surface water to groundwater in the hydrologic cycle.

Misconception: There is less groundwater than surface water in the world (or Pennsylvania).

True if salt water is included, because 97% of the world’s water is in the oceans. However, groundwater accounts for 96% of the unfrozen fresh water in the world. All of the world’s streams, lakes, and wetlands make up most of the other 4%. A small fraction of a percent of the world’s unfrozen fresh water is in the atmosphere in the form of water vapor, clouds, and precipitation. In Pennsylvania, groundwater is about 32 times the amount of surface water.

Misconception: All groundwater is stored in, and flows through, aquifers.

Groundwater is stored in, and flows through, almost all rocks, but at different rates. Aquifers are merely the rocks and sediments that have sufficient permeability to transmit groundwater fast enough to supply what is needed for a specified use. Confining units are not impermeable, but also store and transmit groundwater, although they transmit it at a much lower rate than aquifers.

Misconception: All groundwater is suitable for drinking.

Although flow through the ground does have a purifying effect on water by filtering sediment, bacteria, and certain chemicals, the purification effect is limited. Large concentrations of chemicals may be too much to be completely removed, and certain chemicals may not be removed by the ground at all. Some groundwater is naturally unsuitable for drinking because of the minerals it has dissolved from the rock through which it flows.

Misconception: Water from springs is safe without treatment.

See previous comment.

Misconception: If the water tastes good, then it’s safe to drink.

Many contaminants cannot be detected by taste. Conversely, water that doesn’t taste great isn’t necessarily harmful. The way to tell for sure is to have a certified laboratory analyze the water quality.

Misconception: Groundwater contamination is usually extensive.

Groundwater contamination is usually fairly local. Most groundwater flow is in the shallow flow system and discharges fairly close to its point of recharge. Small amounts of groundwater in the local flow system penetrate to deeper flow systems and may carry contaminants greater distances. However, the groundwater contributed by one local flow system to a deeper system is usually an insignificant amount. Because the vast majority of groundwater flow is local, groundwater contamination is usually local. However, because groundwater contributes most of the flow to streams, groundwater contamination can pollute streams for long distances below the discharge.

Misconception: Artesian water is “better.”

Artesian water is of no better quality than non-artesian water. The term artesian has no relationship to water quality. It is water produced from an artesian aquifer, which simply means that it is under sufficient pressure to cause the water in a piezometer to rise above the level of the aquifer. This myth probably developed because artesian aquifers are often confined, and confined aquifers may be somewhat protected from surface contamination by the overlying confining unit. However, not all artesian aquifers are confined, and not all confined aquifers are free of contamination.

Misconception: The water level in wells is the water table.

The water level in wells is not the same as the water table. After all, the water table at the site of a flowing well is not above the ground. If it were, you would be standing in a lake. The water table is the boundary between saturated and unsaturated media. The water level in a well is at the water table only if the well is within a few feet of the water table. Upon deeper drilling, the water level in the well will either rise or fall, depending on whether the well is in a discharge area or a recharge area. At a particular site, the water level in the well will probably be different for different aquifers. This is especially true in fractured rocks, where the water level in a well is often the function of which and how many fractures were intercepted by the borehole.