Ogallala Formation containing High Plains Aquifer Deposited over

Ogallala Formation (containing High Plains Aquifer): Deposited over 10 million years ago Coarse-grained sand, gravel, fine clay, silt, and sand 174, 000 square miles and 3. 270 billion acre-feet of water as of 1990 (65% NE, 12% TX, 10% KA, 4% CO, 3. 5% OK, 2%SD, 2% WY, 1. 5% NM) Source: High Plains Water District #1

• X% of aquifer showing water level changes. • More in southern half because farmers started using groundwater for irrigation in Texas in 1940’s, and trend moved north. • Average water level decline from 1940 -1980: 0. 25 feet/year. Source: USGS, 1996

Decrease in rate of water level decline from 0. 25 ft/yr to 0. 11 ft/yr after 1980. • Precipitation amounts above average • More efficient irrigation technology • Regulations on groundwater withdrawals • Decline of agricultural commodity prices and increased production costs leading to less agricultural production Source: USGS, 1997 Source: USGS, 1996

These maps from 1980 data show a relationship between irrigated land aquifer water level declines in the southern part of the High Plains Aquifer. Percentage of irrigated land in 1980 Source: USGS, 2001 c Source: USGS, 1996

These maps from 1997 data show a relationship between saturated thickness and depth to the water table, especially in the northern part of the High Plains Aquifer. Depth to water table in 1997 Saturated thickness in 1996 --97 Source: USGS, 2001 c Source: USGS, 2000

• Projected well yields for High Plains Aquifer for 1980 -2020. • Based on current economic trends and government policies –no new conservation measures. Source: USGS, 1988

High Plains Aquifer Recharge Precipitation is the primary cause of recharge to the High Plains Aquifer Source: USGS, 1999 Source: USGS, 2000 b

• • • High Plains Aquifer Recharge PRECIPITATION Seepage from streams, canals, and reservoirs, and irrigation return flow. Rate (from precipitation and irrigation) is 0. 25 -0. 50 inch/yr in the western portion of the High Plains region to 4 -6 inches in the eastern portion of the High Plains region. High Plains Aquifer Discharge • Evapotranspiration where the water table is near the land surface. • Seepage where the water table intersects the land surface. Chart source: USGS, 2002 Discharge > Recharge: because of human-induced discharge from wells for irrigation, leading to water table level decreases. Source: USGS, 1997

This graph shows the ages of the rocks that make up the High Plains and Madison Aquifers. About 10 MYA About 340 MYA Source: http: //seaborg. nmu. edu/earth/Life. html Chart source: USGS, 2001

Madison Limestone Black Hills, South Dakota • Madison limestone deposited about 300 mya as the bottom of a great inland sea. Source: USGS, 2001 • Black Hills uplift 50 mya, erosion eventually exposing older igneous rocks in center. • Now Madison limestone is exposed around the perimeter of the Black Hills. • The thickness if the Madison Formation increases from south to north and ranges from 0 -1, 000 feet. (USGS, 2001 b)

Madison Aquifer Potentiometric Surface Figure 26, USGS, 1984 Potentiometric surface • Madison Aquifer extends 210, 000 square miles into ND, NE, WY, MT and SD. • Confined

A significant amount of recharge to the Madison Aquifer comes from stream flow losses over limestone outcroppings. Source: Journal of Hydrology, 1999 The Madison Aquifer is confined above and below by layers of rock with much lower hydraulic conductivity. Below the Madison Aquifer there is one other aquifer and there are three above it. These aquifers are composed of sandstone and/or limestone and they were deposited roughly 530 -130 mya (http: //seaborg. nmu. edu/earth/Life. html). Below all the aquifers are confining layers of impermeable igneous and metamorphic rocks. Source: USGS, 2001

Madison Aquifer Flow Paths, Recharge Areas and Discharge Areas Source: USGS, 2001 The Madison Limestone is hydraulically connected to the Minnelusa Formation in the eastern most part of the Madison Aquifer, in the Dakotas. Here groundwater discharges from the Madison to recharge the Minnelusa Aquifer. (USGS, 1984)

Hydrologic Budget for Madison Aquifer Source: USGS, 2001 Madison Aquifer Recharge • Stream flow losses and precipitation at limestone outcroppings • Leakage from adjacent aquifers • Ground water inflows • • Total: Madison Aquifer Discharge Artesian and headwater spring flow Leakage to adjacent aquifers Ground water outflows Well withdrawal for municipal and personal consumptive uses Source: USGS, 2001 b

Source: USGS, 2001 Water levels in the Madison Aquifer were falling from 1987 -1992, but they have been rising since about 1993 all over the Black Hills. (USGS, 2001)

Major differences between High Plains and Madison Aquifers High Plains Madison • Unconfined • Confined • Recharge through infiltration and groundwater flow • • Rate: • Recharge through stream flow losses and precipitation at limestone outcroppings Rate: • Used primarily for agricultural irrigation • Used primarily for municipal and private consumption • Water level falling • Storage level stable and rising locally