When Whitmarsh's Wells Turned Salty

The town of Whitmarsh sits on a low sandy point with the bay on three sides. About 12,000 people live there in winter. In July and August the number nearly triples, because the beach cottages fill and the two campgrounds open.

Whitmarsh gets all of its drinking water from four wells. The wells draw from a layer of sand and gravel that lies about sixty feet down. Rain soaks through the sand and collects in that layer as fresh water. Salt water from the bay seeps into the same layer from the sides. Fresh water is less dense than salt water, so it floats in a lens on top of the salty water below. The lens is thickest under the middle of the point and thinnest near the shore.

When a well pumps hard, it pulls water toward itself from every direction. That includes the salty water below. Hydrogeologists call this saltwater intrusion. Pumping gently draws mostly from the fresh lens. Pumping hard for weeks can lift the salty water high enough to reach the bottom of a well.

Three summers ago, people on the north side of town said their tap water tasted faintly salty. The water department sent samples to a laboratory. The results showed that chloride, the main dissolved part of sea salt, had climbed steadily in Well 3 since June. Well 3 sat closest to the shore. The department shut it down in the middle of August and reopened it in late October, after the summer crowd had gone and the fresh lens had rebuilt itself.

Shutting one well for two months worked that year, yet the town could not count on that fix every summer. The town needed another source, and the council spent a winter comparing three of them.

The first option was to drill new wells about two miles inland, where the fresh layer is thicker and the bay is farther away. The land there is a working cranberry farm, and the owner did not want to sell. New wells would also need a pipeline back to town and a new pump station.

The second option was to buy treated water from the city of Broadmere, twelve miles up the shore. Broadmere has a surface water plant and more capacity than it uses. A pipeline would cost less than most people expected. The contract would run for twenty years, and Whitmarsh would be depending on another community's council to keep selling.

The third option was a small desalination plant that would treat bay water directly. The bay never runs dry, so the supply would be certain. Removing salt from seawater takes a great deal of energy, roughly 11 to 15 kilowatt-hours for every 1,000 gallons treated, while treating and delivering fresh water takes about 1 to 2. Whitmarsh would be paying that difference every day for as long as the plant ran.

The council chose the Broadmere pipeline. It also did two things that had nothing to do with pipes. It set a summer limit on how hard each well may be pumped, and it passed a rule allowing lawn watering only twice a week from June through September.

None of the three options was created by the council. They were set by where Whitmarsh is: a narrow point of sand, a thin lens of fresh water, a bay on three sides, and a population that nearly triples in the same weeks the aquifer is under the most strain.

1. According to the passage, why does fresh water sit above salt water in the layer under Whitmarsh?
2. What did the laboratory results show about Well 3, and what did the water department do about it?
3. Name the three options the council compared, and give one drawback of each.
4. Why did shutting Well 3 for two months solve the problem that year but not for good?
5. The council set a pumping limit and a lawn watering rule in addition to choosing a pipeline. Explain why those two rules address the salt problem even though they add no new water.
6. The last paragraph says the options were set by where Whitmarsh is. Using details from the passage, explain how the town's geography narrowed its choices.