Water Well Journal
Issue link: http://read.dmtmag.com/i/655200
I t is overwhelming to think groundwater makes up an estimated 99% of all freshwater in the world. Yet groundwater is "out of sight, out of mind" for most here in the United States. However, the present threat of groundwater shortages in pockets of the nation has elevated the importance of this commonly undervalued resource. In times of drought or groundwater contamination—when people are noticeably affected—the value of water becomes clear. We're seeing it with the years-long drought in California and the water crisis in Flint, Michigan. The principle behind what Benjamin Franklin said two centuries ago remains true today: "When the well runs dry, we shall know the value of water." On the heels of National Groundwater Awareness Week, held March 6-12, Water Well Journal begins a three-part series examining major aquifers in the United States. Part one focuses on the Floridan aquifer system, which un- derlies the entire state of Florida as well as southern portions of Alabama, Georgia, and South Carolina. It covers 100,000 square miles and is the largest aquifer in the southeastern United States. ● ● ● Florida is no doubt a water state. The Floridan aquifer system was developed millions of years ago during the late Paleocene to early Miocene periods when Florida was underwater. The Floridan aquifer system has been divided into an upper and lower aquifer separated by a unit of lower permeability. The Upper Floridan aquifer is the principal source of water supply in most of north and central Florida. Currently, the Upper Floridan aquifer supports nearly 10 million people as their primary source of water—used for public, domestic, and industrial water supply with almost 50% of its water being used for irrigation. The state also draws water from the St. Johns River, the Suwannee River, and the Ocklawaha River. In the southern portion of the state, where it is deeper and contains brackish water, the aquifer has been used for the injection of sewage and industrial waste. Location is key when drilling a water well in the Floridan aquifer system as the geological formations vary across the state. It is comprised of a sequence of limestone and dolomite, which thickens from about 250 feet in Georgia to about 3000 feet in south Florida. Drilling Challenges The Upper Floridan aquifer can be as deep as 600 feet and as shallow as 200 feet in northeast Florida. "Knowing what you have to do to get to those depths and what you find above that formation makes it the challenging part," says Merritt Partridge, vice president of Partridge Well Drilling Co. Inc. in Jacksonville, Florida. "Whether there is an underlying rock bed above that, whether you lose drilling circulation in those formations above it, or you lose circulation in the Floridan aquifer system makes it challenging." Partridge Well Drilling, established in 1892 at a time when drill rigs had masts made of wood, drills by using mud rotary as far south as Key West and has completed several projects in Mississippi and Georgia. However, the majority of its work is done in northeast Florida. It also drills wells shallower than the Upper Floridan aquifer, but typically everywhere it drills, the Floridan aquifer system is present. The Upper Floridan aquifer poses a unique drilling chal- lenge: In some areas it is a confined artesian aquifer, which is an underground layer which holds groundwater under pres- sure. This causes the water level in the well to rise to a point where the pressure is equal to the weight of water putting it under pressure. Partridge says water level and artesian pressure are key factors to consider when drilling into the Floridan. Based on their well records, Partridge can estimate if the water level will be deep in the well or free flowing at the surface, which is not uncommon in certain areas. In parts of northeast Florida, AQUIFERS continues on page 18 (COVER STORY) (Left) A drone photo in August 2015 shows one of Partridge Well Drilling Co. Inc.'s smaller drill rigs drilling a 3-inch-diameter rock well to about 100 total feet in Jacksonville, Florida. They were able to pump more than 50 gpm out of the well. The top of the Floridan aquifer system in this area is about 450 feet. WWJ April 2016 17 Twitter @WaterWellJournl Part one of three: Floridan aquifer system By Mike Price Aquifers in the United States