A saltwater intrusion could be “hydrologic disaster” for Lamoine

by Willem Brutsaert, Ph.D, Lamoine resident. (As published in the Ellsworth American 1/3/2018).

Dear Editor: Thank you for publishing my commentary, “Lamoine’s hydrologic gamble,” in The Ellsworth American of Dec. 20, despite its length.

Because of space constraints, I refrained from technical details, especially when dealing with the negative impacts on groundwater quality by removing the hill, i.e. Cousins’ Hill.

One such detail, apart from the removal of its filtering effect, relates to the fact that this hill, in groundwater hydrology context, is in close proximity to a saltwater body, namely Jordan River, and this makes that part of Lamoine’s sand and gravel aquifer by definition a “coastal aquifer” vulnerable to “seawater intrusion.”

Seawater intrusion is a natural phenomenon whereby saltwater occurs as a “wedge” below freshwater in coastal aquifers.

Freshwater being lighter than saltwater will “float” like a bubble on top of saltwater near the shore, according to the hydraulic principle of buoyancy (remember Archimedes’ “Eureka”). Infiltration from precipitation will keep the saltwater at bay. During extended periods of drought, the groundwater table will drop and this will cause the saltwater wedge to move (intrude) farther inland. This wedge will be “flushed” back again when the groundwater table rises during the wet season.

Due to this moving back and forth of the wedge, a mixing zone will exist between fresh- and saltwater. And here comes the big “however.” If we now remove the whole hill, permanently lowering the regional groundwater table, as explained in my commentary, the saltwater wedge will now permanently intrude farther inland below the freshwater. Add to that the fact that, due to global warming, seawater level will rise, and we may have a real hydrologic disaster on our hands: Salt water occurrence at much shallower depth and farther inland than is now the case.

No need to say that many household wells in the area will be affected. Based on the elevation of the water table with respect to mean sea level, and the density difference between freshwater and saltwater, one can calculate the approximate depth to saltwater before drilling a well, but that is a story for some other time.

Again, should Lamoine really gamble with its groundwater resources by removing the hill?

Willem Brutsaert Lamoine

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