Groundwater Supply Availability January 2014

The Arkansas Water Plan Update Requires Assessment of Current And Future Water Supply Availability Groundwater Availability Groundwater Availability Groundwater Quality Fish and Wildlife Flows Quality Surface Water

What Constrains our Ability to Supply Water? Available Supply Water Law/Regulatory Physical Availability Infrastructure

Mississippi Alluvial/Sparta Ozark Aquifer; Springfield Aquifer Arkansas River Alluvial Aquifer Ouachita Mountain Aquifer

Arkansas Groundwater Demand Data Trends Updated Demand Data Added from ~ 13% increase

Comparison of Demand and Achievable Pumping Rate

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Groundwater Modeling Scenarios Scenario 1 and 2: Minimum water elevation equal to the bottom elevation of both unconfined and confined aquifers for wet and dry climate conditions Scenario 3 and 4: Minimum water elevation equal to half the aquifer thickness in the alluvial aquifer and the top of formation in the confined aquifer for wet and dry climate conditions

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Interior Highlands of Northern and Western Arkansas Qualitative Evaluation of Water Supply Availability Groundwater use has declined and surface water use has increased dramatically, and the vast majority of the population in northern Arkansas is served by surface water Various aquifers generally occur in shallow, fractured, well-indurated, structurally modified bedrock Many formations are capable of supplying volumes sufficient for small community-supply sources of water

Northern Interior Highlands Aquifers Springfield Plateau Aquifer Widely used throughout its extent in northwestern Arkansas Numerous domestic and livestock wells, although surface-water systems have replaced the aquifer as a general source of water supply Ozark Aquifer Primary use of the Ozark aquifer is for public supply; 76 MGD was withdrawn for public supply in 2010 Irrigation use was about 20 MGD from the Ozark aquifers in 2010; 70% of irrigation occurs in counties in the aquifers far eastern extent, where row crops like cotton, rice, and soybeans are commonly grown Depth to water in most of these wells is approximately 100 ft

Southern Interior Highlands Aquifers Arkansas River Valley Alluvial Aquifer Irrigation pumpage is small Municipal supply withdrawals induce recharge from the river Ouachita Mountains Aquifer Should not be considered as a source of supply for municipal growth and economic development unless the required quantity was small Western Interior Plains Confining System Well yields sufficient only for household, small municipal, and non- irrigation farm use.

Groundwater Quality

Groundwater Quality Analyses Groundwater quality information provided by USGS

Groundwater Quality Methodology Water quality data from approximately 8,000 groundwater sites: 7000 from the ANRC and USGS database 1,000 from the ADEQ database Statistical analyses and spatial distribution maps for chemical constituents associated with 16 aquifer systems in Arkansas. Major ions (calcium, magnesium, sodium, potassium, chloride, sulfate, and bicarbonate) and selected trace metals (iron, manganese, and arsenic).

Drinking Water Standards Water quality of drinking water will be compared to: US EPA drinking water standards (Maximum Contaminant Levels (MCL)) Health advisories Secondary drinking water regulations for cosmetic effects (such as tooth or skin discoloration) or aesthetic effects (such as taste, odor, or color)

East Regional Planning Area Mississippi River Valley alluvial aquifer Water quality generally is good Elevated iron concentrations in most areas prevent use for commercial, industrial, and municipal without treatment Elevated salinity additionally occurs in different areas of eastern Arkansas Cockfield aquifer Principal aquifer in southeast Arkansas In outcrop area, lower pH values and dissolved solids but higher nitrate and iron concentrations Downdip higher pH and dissolved solids; lower concentrations of nitrate and iron 23

East Regional Planning Area Sparta aquifer Second highest of volume of use Generally is of very high quality Isolated areas contain slightly elevated chloride concentrations Downdip increases in dissolved solids and decreases in iron and nitrate Cane River, Carrizo, Wilcox, Nacatoch, Ozan, Tokio, and Trinity aquifers Increasing salinity at various distances downdip from the outcrop areas that renders the groundwater unusable for most purposes. 24

North Regional Planning Area Ozark and Springfield Plateau aquifers Rapid influx of surface-derived contaminants, especially nitrogen, in karst landscape Nutrients, bacteria, and other surface-derived contaminants associated with agricultural activities pose the greatest threat to groundwater quality 25

West-central, South-central, and Southwest Regional Planning Areas Ouachita aquifer and the Western Interior Plains Dominant changes in geochemistry were attributed to rock type, residence time along individual flow paths, and resultant rock- water interaction Elevated iron and manganese concentrations and production of methane Nutrients, bacteria, and other surface-derived contaminants pose the greatest threat to groundwater quality 26