Because the Sparta, as a confined aquifer, has relatively small storativity, the response of water levels to heavy pumping stress is substantial and occurs over a large area. Long-term pumping has resulted in regionally extensive water-level declines and change in location of potentiometric lows from natural groundwater discharge areas in pre-development years to pumping centers in northern Louisiana and southern Arkansas. (8)
Groundwater flow, potentiometric surface, and water level declines
In predevelopment times (around 1900) well water levels were well above the top of the Sparta Sand. (15) As early as the 1940's, substantial declines in water levels were documented in Union and Jefferson Counties in Arkansas. (1) Figure 16 shows simulated declines of greater than 260 foot over a century at the location of two Sparta wells in Louisiana.
In 1960, USGS, in cooperation with Louisiana Department of Transportation and Development, began reporting water withdrawals and usage data every five years (14), allowing analysis of trends. Declining potentiometric levels within the Sparta due to pumping have been plotted on maps for more than 35 years. (Ref. 12 and Sec. 7.a.1. of this paper) By 1965, withdrawals had formed cones of depression at Minden, Jonesboro-Hodge, Monroe, Bastrop, and Farmerville. (15) Since 1980, the deepening and expanding cones of depression in Monroe, Bastrop, and Farmerville have coalesced, forming a trough between El Dorado and Monroe regions. (6) Figure 17 shows average water level declines from one to four feet per year, increasing eastward.
Between 1980 and 2001, well water level declines greater than 30 feet were recorded in Claiborne, Jackson, Lincoln, Ouachita, and Union Parishes, most prominently in heavy pumping areas around Ruston, Monroe-West Monroe, and Jonesboro-Hodge. (2) In Lincoln, Ouachita and Union Parishes, water levels declined 10 to 15 feet between 1980 and 1989 and 30 to 35 feet between1989 and 2001; total decline was about 50 feet over 20 years. (2) Regionally, the range of Sparta well water level decline between 1990 and 2000 was 0.1 feet to 5.2 feet per year. (15)
Figure 18 is a USGS hydrograph of a Lincoln Parish Sparta well (L-26). Over 42 years (October 1967 to October 2009), the water level in L-26 declined 71 feet (an average of 1.7 feet per year). Water levels in two Ruston wells declined at a rate of 2.8 feet per year over 44 and 46 years; another declined 3.2 feet per year over 41 years. (2, p.26)
‘The effect of heavy pumping can be remarkable locally. An aquifer test near El Dorado resulted in an approximate 5.7 foot water level decline 2,400 feet from the pumping well after 3 days of pumping at a rate of about 460 gallons per minute.’ (1)
Dewatering and Potential Compaction of Sands
By 1997, the potentiometric surface in the Sparta aquifer was below the top of the Sparta Sand in much of Webster, Claiborne, Lincoln, Bienville, and Jackson Parishes, and parts of Ouachita, Union, and Bossier Parishes. (9) Figures 19 and 20
‘Excessive dewatering of the Sparta aquifer and overlying confining units can lead to irreversible compaction (subsidence), reducing its ability to be recharged and its water-yielding capacity….(and) reducing the rate at which water can move through the aquifer.’ (1)
A USGS Fact Sheet ‘The Sparta Aquifer: A Sustainable Water Resource?’ describes the process of compaction. ‘[The stress of rock and water mass acting downward] is borne by the granular skeleton of the aquifer matrix (effective stress) and the fluid pressure of water in the pore spaces. When the fluid pressure is reduced, the effective stress increases….If water level declines below the top of a confined aquifer, the aquifer becomes unconfined…at that location and the fluid pressure becomes zero transferring all the stress to the aquifer matrix. Aquifers and confining units containing significant amounts of fine-grained materials, as the Sparta aquifer does, are most susceptible to compaction.‘ (1) (Figure 21)
Notable subsidence had not been documented in the Sparta aquifer when the USGS Fact Sheet was published. (1) Interpretable data is required. Meyer, Meyer, LeCroix, and Hixson in the Sparta Groundwater Study remarked, ‘It is important for the long-term preservation of the aquifer to restore the water level to the top of the aquifer.’ (2)
Advance of the Freshwater/Saltwater Interface Westward and Upconing of Salt Water in the Sparta
When large scale pumping of water out of the Sparta reduces the hydrostatic pressure, saltwater can fill in, either upconing locally or moving the salt water interface westward into the freshwater region. (2)
The 'Water Quality' section of this paper (section 3.d.) describes increasing salt concentration in Sparta water. Briefly, over twelve years ending 2007, average chloride concentration rose from 85.8 mg/L to 126.5 mg/L in LDEQ monitored wells (5); in three of 14 wells, the chloride concentration exceeded the EPA secondary standard for drinking water (5); a 2009 study shows that chloride concentration of Sparta water along the freshwater/saltwater interface continues to increase (12). Figure 22 shows increasing chloride concentration in a Winn parish well over 30 years.
Upconing of brackish water because of extreme drawdowns has resulted in increased chloride concentrations in some Union County, Arkansas Sparta wells (1) and possibly a Union Parish well (OU-205) that had a chloride concentration of 351 ppm in 2006. (5)
Summarizing results of their flow model of the Sparta aquifer in southern Arkansas and northern Louisiana and simulated response to withdrawals, McKee, Clark, and Czarnecki wrote in 2003 and 2004 (immediately before three El Dorado industries converted to river water use): ‘Historically, the Sparta aquifer has provided abundant water of good quality. In recent years, however, the demand for water in some areas has resulted in withdrawals from the Sparta aquifer that substantially exceed recharge to the aquifer. Considerable drawdown has occurred in the potentiometric surface, and water users and managers question the ability of the aquifer to supply water for the long term. Continued heavy withdrawals in the Sparta aquifer, where alternative water sources are not considered or available, will result in continued expansion of the cones of depression as well as increased drilling and pumping costs, decreased aquifer yield, and reduced water quality.’ (Ref.9, p. 2) ‘Continued pumping at withdrawal rates representative of 1990 - 1997 rates cannot be sustained indefinitely without causing hydraulic heads to drop substantially below the top of the Sparta Sand in southern Arkansas and north-central Louisiana.’ (Ref. 8, p. 1) top
Increased costs of heavy pumping, which can become prohibitive for public and industrial supply, may occur in a number of ways (Figure 23):
Wells must be deepened or replaced when the head falls below the screened (open) intervals of the well.
Well yields decrease because of reduced amounts of water in storage.
Pumping costs increase because of the increase in the vertical distance that groundwater must be lifted to the surface and because of reduced hydrostatic pressure.
Water treatment costs increase as poorer quality water is drawn from greater depths in the aquifer. If water becomes saltier, treatment (reverse osmosis or distillation) costs may be prohibitive.
Less Sparta water is available when sands become compacted; reduced aquifer capacity may be permanent.
Salt content of drinking water must be counted as salt intake, which may be especially important for individuals on a low salt diet.
The taste of water declines as poorer quality water is drawn from greater depths of the aquifer. If water becomes saltier, the saltiness may be appreciated at a concentration of chloride about 395 mg/L. (18)
Corrosion occurs more rapidly as water becomes saltier, necessitating early replacement of industrial equipment, public utilities equipment, and domestic plumbing fixtures and water-using appliances. (18)
In 1968, researchers, estimating costs of corrosion as water becomes saltier, found that using water with TDS concentration of 1750 mg/L compared with 250 mg/L decreased the service life by 70 percent of toilet flushing mechanisms and by 30 percent of washing equipment, adding 50 cents per1000 gallons to the cost of water used. (18) LDEQ reported that, in 2007, the TDS concentration in water from five of six sampled wells in Morehouse, Ouachita, and Union Parishes exceeded 1000 mg/L. (5) There are anecdotal reports that in Union Parish near the Arkansas border, where the chloride concentration exceeded 350 mg/L in one well in 2006 (Un-205-Ref. 5), equipment warranties are not offered because of corrosion problems.
Water in streams and lakes may be reduced, particularly in and near an aquifer outcrop area.
Ground-water pumping can alter how water moves between an aquifer and river, stream, or wetland by intercepting groundwater flow that naturally discharges into the surface-water body or by increasing the rate of water movement from the surface-water body into an aquifer. (One consequence may be)… the lowering of water levels below the depth that streamside or wetland vegetation needs to survive.’ (19)
Sparta Withdrawals by Parish (Figure 11) and Withdrawals by Use (Figure 12) in 2004
The Sparta aquifer is pumped in a large area of north central Louisiana and a narrow band through Natchitoches and Sabine parishes. (2) ‘Currently (2004), more than 1760 wells are screened in the Sparta aquifer in Louisiana and Arkansas.‘ (8) Figure 13 shows locations of Sparta-Louisiana water wells identified from USGS data in 2000 for the Sparta Groundwater Study. (2)
‘The earliest known withdrawals from the Sparta (in southern Arkansas and Louisiana) began in 1898 in Pine Bluff, Arkansas.’ (8) In 1906, as many as six municipalities in south Arkansas and north Louisiana were pumping from the Sparta. (2)
Heavy industrial pumping began in the 1920's, with pulp and paper mills in Bastrop (1921), West Monroe (1930), Hodge (1931), and Springhill (1938). (2) By 1940, total pumpage exceeded 69.6 million gallons per day (mgd), which was considered more than the Sparta aquifer could recharge. (2-authors refer to McWreath et al-Ref. 27b)
In 1980, total Sparta pumpage was about 64.98 mgd. The next year, an International Paper mill in Morehouse Parish ceased pumping the Sparta (this paper, sec. 6.b.2.), but Sparta pumping elsewhere continued to increase. In 1994, total Sparta pumping reached a peak of about 72.73 mgd. (2) From 1994 to 1999, the Smurfit-Stone Container plant in Jonesboro-Hodge developed a Sparta recycling project (this paper, sec. 6.b.3.), which led to the saving of a significant amount of Sparta water. But, once again, some savings were lost to continuing increase of pumping elsewhere in the Sparta. In 2000, total Sparta pumpage was about 69.84 mgd.(2) Pumpage has remained relatively stable since then (2000 through 2009). After 1990, public supply withdrawals began to increase relative to withdrawals by industry. (6) By 2000, public supply use had exceeded industrial usage. (15)
New Demand for Water in Northern Louisiana
In 2002, Meyer, Meyer, LeCroix, Hixson, in their Sparta Groundwater Study, predicted an increasing water demand in the Sparta region because of projected growth in population and industry. (2)
Recently, the Louisiana Department of Natural Resources Office of Conservation (DNR) has permitted Sparta water use in horizontal drilling and hydraulic fracturing (‘frac well’) operations and two million gallons per day for a period of four or more years to leach a salt dome for storage of natural gas. (17) This action is part of expanding natural gas production in northwest Louisiana, which has come about because of advances in horizontal drilling and hydraulic fracturing, processes that are used in most natural gas wells in the United States today (16a).
Much of the Sparta region lies within the oil and gas producing North Louisiana Salt Basin. Figure 14 In 2006 and 2008 respectively, 444 and 511 oil and gas wells were permitted by DNR in the nine major Sparta using parishes. (17) Approximately two-thirds of the permitted wells were active and producing during those years. (17) Vertical drilling of a new well may require as much as one million gallons of water. (16b)
The multi-stage hydraulic fracture operations used in ‘frac wells’ may require 2 to 4 million gallons of water per well. (16b) Figure 15 One author provides perspective: this water use is less than that for coal, oil, and ethanol production; a golf course consumes about five million gallons of water per twenty-five days. (16c)
At the time of this writing, most ‘frac wells’ in North Louisiana are being drilled in the natural gas-rich Haynesville/Bossier Shale. This play lies within the Sabine Uplift, most of which is located just west of the Sparta region (16d) Figure 14
While Sparta water use for natural gas production is projected to be small relative to surface water and Wilcox aquifer use for most Haynesville/ Bossier Shale operations, it is recognized that ‘because the development of shale gas is new in some areas, these water needs may challenge supplies and infra-structure’. (16b) Any new Sparta water demand emphasizes the need to prepare for the region’s future water requirements.