The Villages Voice - August 2010

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Understanding Our Aquifer and Sinkholes

by Doug Tharp

Understanding Our Aquifer and Sinkholes

By Doug Tharp

As we go about our daily lives here in The Villages, most of us probably don’t stop to think about what’s right underneath us or why our region is characterized by sinkholes and springs.

First, let me give you a little geology lesson. Right underneath the ground is a landscape of dissolving lime rock. As slightly acidic rain falls and percolates into the ground, the acidic water slowly dissolves the limestone, which can cause sinkholes to form. This type of landscape is referred to by geologists as a karst terrain. Karst terrains are characterized by sinkholes, caverns and springs.

Within the limestone is the Floridan aquifer system, which is where we get our drinking water. It’s also the source of our region’s springs. The Floridan aquifer is very close to the land surface in our area and there is a close connection between surface waters and the underground aquifer.

In Florida, we receive about 53 inches of rainfall a year. In some areas of the state, only about six inches of rainfall actually percolates down through the soil and into the aquifer to replenish or recharge water supplies. In our area, 10 to 25 inches of rainfall recharges our aquifer annually due to the close connection to the Floridan aquifer.

However, while this close connection helps replenish the aquifer, it also can allow pollutants to easily enter our drinking water. The Southwest Florida Water Management District (District) has documented an increase in nitrates and a decrease in water quality in our area’s surface waters and springs over the last several decades. One of the major sources of nitrates is lawn fertilizers. Too much fertilizer applied to landscapes seeps past the root zone of the grass, plants or trees and into the aquifer, or runs off into streams, lakes and bays.

As I mentioned earlier, another part of living in our area means living with sinkholes. There are two types of sinkholes: subsidence sinkholes and collapse sinkholes. Subsidence sinkholes are caused when granules of sand cascade down to fill the voids and cavities created by dissolving limestone. These sinkholes are generally small in size and often appear as depressions in the ground. Collapse sinkholes form the same way, however, if the soil above the cavity is made up of sand and clay, it can collapse abruptly and potentially create a large sinkhole.

Unfortunately, sinkholes are a natural part of living in Florida and it’s important to know the warning signs. Some of the signs include structural cracks in walls, floors and pavement; cracks in the ground surface; slumping, sagging or slanting fence posts, trees or other objects; and doors and windows that fail to close properly. If you do see any of these signs on your property, you should provide for your personal safety, evacuating if necessary, and notify your insurance company or agent.

For more information on sinkholes, visit the District’s web site at www.WaterMatters.org/hydrology/sinkholes/. Additional information on aquifers can be obtained by visiting www.WaterMatters.org/publications and ordering or downloading a copy of the District’s “West-Central Florida’s Aquifers” brochure.

Doug Tharp is a member of the Southwest Florida Water Management District Governing Board and also serves as co-chair of the District’s Withlacoochee River Basin Board.