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Drought allowing saltwater to creep westward toward drinking water wells By Neil Santaniello Staff Writer
May 7, 2001
Lantana water plant chief Ana Blanco watches clear water gush from a 2-inch pipe in the median of East Central Boulevard, dips a few fingers into the stream and licks them.
The taste makes her grimace: It has a lightly salty flavor, a bad sign. But "it's not burning your tongue yet," she says.
Her worry is what old brochures dubbed "the silent intruder" -- saltwater intrusion, the slow subterranean advance of ocean water into underground water reserves. The march of salt water can lengthen in a drought. If forceful enough, it can contaminate wells for years, decades or permanently.
A lab test an hour later shows the raw water coming from that 150-foot-deep groundwater monitoring well was saturated with 3,864 parts per million of chloride -- salt water from the Atlantic Ocean creeping inland below the surface.
That's almost 15½ times the saltiness that federal and state regulators permit in drinking water that's suctioned out of production water wells and piped off to treatment. Fortunately, the production well has a far lower level, within acceptable limits.
A taste test of water from a second well a block away meets Blanco's approval. "It tastes sweet to me ... compared with the other one," she said.
The South Florida Water Management District views saltwater intrusion as one of the worst-case consequences of the region's acute water shortage.
Under district orders, water utilities deemed "at risk" have stepped up checkups of their sentinel wells from four times a year to once a week.
"It's not something that sneaks in overnight, and it's suddenly there and you tremble," said Scott Burns, water-use department director for the water district. "This is something everyone has been managing for many years."
So far during the current drought, only two monitoring wells from Jupiter to Key West have seen chloride levels climb enough to concern water managers. One is Lantana's East Central Boulevard well and the other a well in Lake Worth at Palm Way and Fifth Avenue South.
Both protect wells that deliver water to treatment plants but are not currently being contaminated by too much salt water.
Salt water in South Florida might move underground at a rate of a few feet a year to as much as 80 feet, Burns said.
"A turtle would be a sprinter in comparison," Burns said. "That's the good news. The bad news is once salt water gets into a well it is even slower to get out."
Saltwater intrusion is an ever-so-gradual advance of salinity through porous aquifer rock.
It has been aided by development that drained lands from the coast to the lip of the Everglades and lowered water tables. Storm water that once seeped into the earth and bolstered the flow of fresh water from west to east now rolls off concrete and asphalt into drains that send it directly into the sea.
At the same time, fresh water is siphoned out of the ground and sent to faucets and showerheads for an ever-growing number of homes and businesses cramming into South Florida.
Salt water can move inland in a uniform wedge. Denser than fresh water, it displaces ground water by sliding under it. The invader crawls fastest through the most porous portions of the Biscayne Aquifer, where that limestone sponge is most absorbent.
Replacing a contaminated well with one farther from the salt water front can cost "a half-million or a million dollars" per well, said Hollywood Public Utilities Director Whit Van Cott.
Saltwater intrusion has long threatened public water wells. In 1988 four Hallandale Beach wells were closed and two shelved for emergency use only, said the town's deputy director of public works, David Pritchard.
During the past 20 years individual wells -- but not entire well fields -- have been shut down by the water district all along the seaboard: Jupiter, Jupiter Island, Riviera Beach, Delray Beach, Boynton Beach, Boca Raton, Deerfield Beach, Pompano Beach, Hollywood, unincorporated Broward County, North Miami Beach and Miami Springs.
During the 1971 drought, saltwater intrusion cost Miami-Dade County some wells, Burns said.
Older wells nearest the coast are usually in the most danger because of their proximity to intermingling of salt and fresh water in the aquifer. They were dug "where the original population density was," said district Water Conservation Officer Bruce Adams.
Helping to blockade saltwater intrusion are coastal gates installed on South Florida's major flood control canals. They carry fresh water from the west to the coast and hold it there to saturate the aquifer and boost groundwater levels.
But some coastal wells lie east of those canal salinity barriers.
To cope with saltwater intrusion, coastal cities have drilled new wells farther inland. They have pumped those harder and relied less on their eastern wells, usually tapping them only in wet periods. Some towns put their endangered wells on standby.
But coastal towns are reluctant to abandon coastal wells altogether.
Coastal wells deliver "our very highest quality water," said Roy Reynolds, Broward County water management director.
The water that bleeds into them has moved much farther through geological filters, including fine-grained sand, and is clearer than water in western wells, he said.
Western water is darker, more tea-colored, from soaking through Everglades muck and organic matter. It costs more to clean because there is more color to strip out.
Wells closer to the coast are more productive, too, because their aquifer rock can absorb and transmit more water with less pumping. Lake Worth can yank a million gallons a day out of wells east of Interstate 95; it can pull maybe half that from wells near Lake Osborne, said Michael Thew, the city's water-systems superintendent . "The aquifer to the west just doesn't deliver as much water."
But Lake Worth had to cut back on coastal water by 75 percent because of rising salt levels in monitoring wells to the east, he said.
One of those, a 170-foot deep sentinel between Federal Highway and the Intracoastal Waterway, saw chlorides leap from 275 parts per million in January to 800 ppm in April, Thew said. The drinking water standard is 250.
"We're not sure what's going on," but it could be an effect of the drought, he said.
One Achilles heel in the defense against saltwater intrusion is southeastern Broward County, Reynolds said.
Development in southwest Broward gouges more deeply into former Everglades than to the north, sucking up a lot of fresh water that used to flow toward Hollywood and Hallandale Beach and protect against saltwater intrusion.
"That's why we're suffering," said Pritchard, whose town of Hallandale Beach is preparing to build a $15 million, more-sophisticated treatment plant so it can clean up water it must draw from western Broward County wells.
Southeast Broward is at a disadvantage, too, because it lacks a network of canals to bring surface water from the west toward the coast or at least to Interstate 95, Reynolds said. It also is lower-lying.
"We can't raise [water tables] because we'd cause flooding," he said.
It appeared salt water might push inland there a month ago, before rains lifted a dropping aquifer, he said.
Water managers fear that Lake Okeechobee, South Florida's backup reservoir, might remain so low even after summer downpours that groundwater tables could be in worse shape next winter.
"I don't think it's very likely we are going to see a significant problem this year," Burns said "We're turning our sights to a potentially significant problem next year."
Reynolds said: "We're just scraping by. We're on the edge of OK."
Neil Santaniello can be reached at email@example.com or 561-243-6625.
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