‘Not sound practice’
Recent failure of herring and smelt fisheries are warnings of more to come
Your May 16 editorial “A simmering hot potato” doesn’t question how P.E.I.’s groundwater affects the ocean. From my first letter to the editor I stated, “Don’t drill into confined aquifers, municipal wells not excluded,” and “we risk turning the ocean into a salt water desert.”
The P.E.I. aquifer has alternating layers of thick aquitards and thin aquifers. The aquitards are consolidate sandstone which basically lie in a horizontal plane. Aquitards pass water at a low flow rate.
Sandwiched between two aquitards is a thin horizontal aquifer of unconsolidated sand, mud, gravel and water. Water is forced in a horizontal direction through the aquifer and is eventually discharged offshore in the ocean.
The study of groundwater motion models the forces of gravity and pressure as equipotential surfaces; the aquifer’s vertical equipotential surface (field of force) drives the horizontal water flow (field of flow).
When a well is drilled, a record called a drill log is kept: depth drilled, rock type encountered, static water level and sudden flows of water are recorded. When a confined aquifer is penetrated water can rise five meters and the well is said to be producing water; rising water in the well is doing work against gravity and the aquifer is said to be doing pV work — pressure volume work.
In drilling from 35 to 100 metres, assume four aquifers are encountered; one aquifer will stand out as having the highest water level; call this aquifer the dominant aquifer. The other three aquifers I call sub-dominant. The dominant aquifer will suppress water flow in the three sub-dominant aquifers completely. Additionally, water flow through the aquitards will also be completely suppressed.
Here’s how. The nature of a deep water well is the same as a column of water in a fresh water lake: the water pressure increases one atmosphere as the depth is increased by 9.8 meters, the pressure increase is uniform and the well’s equipotential surfaces are horizontal planes. When a deep water well is drilled each of the three sub-dominant aquifers is overridden by the increased pressure of the dominant aquifer and the aquifer’s former vertical equipotential surfaces become horizontal equipotential planes — the groundwater flow to the ocean stops.
An argument using the uniform increase of hydrostatic pressure applies to the aquitards as well — all aquitards become static.
All the foregoing is why deepwater wells are so deadly to the ocean.
If you seal the wells with cement then the dominant aquifer’s pressure is removed from the three sub-dominant aquifers and the horizontal equipotential planes will become vertical again, hence groundwater flow to the ocean will resume. All deep-water wells should be filled with cement.
Now we see the effects of the pressure death of the P.E.I. aquifer, this perpetual water machine of gluttony that is destroying terrestrial, aquifer and marine ecosystems.
The recent failure of the herring and smelt fisheries are warnings.
Hydrogeologists warn that drilling into confined aquifers is “not sound practice.” Killing the host is always a bad idea.