"What it looks like is, the mercury that was already there in the aquifer or sand is being mined out when the groundwater goes anoxic," said Lamborg. Mercury that has been stored in the ground for several thousands of years is being drawn out and is now on the move.
Along the Ashumet Valley, a 3-kilometer depression between the towns of Falmouth, Sandwich, and Mashpee, Mass., mercury continues to accumulate and move downstream in a plume ending in Green Pond in East Falmouth.
According to Lamborg, it's a community-wide problem. Because the soil on Cape Cod is sandy, waste dumped into the ground disappears quickly. Although it may seem out of sight and out of mind, the contaminants such as mercury accumulate and resurface in the ponds and ocean.
"This is just one really big example, but it's happening in a small way through everybody's backyard septic system, which leaches a little bit of mercury out of the aquifer and accumulates. You don't need a really big industrial scale thing for this to happen. It's happening everywhere," Lamborg said.
"These findings should help guide future studies evaluating potential groundwater contamination with mercury," said Doug Kent, a U.S. Geological Survey hydrologist, who collaborated on this research.
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Woods Hole Oceanographic Institution