Groundwater-level and storage-volume changes in the Equus Beds aquifer near Wichita, Kansas, predevelopment through January 2015

Abstract

Development of the Wichita well field began in the 1940s in the Equus Beds aquifer to provide the city of Wichita, Kansas, a new water-supply source. After development of the Wichita well field began, groundwater levels began to decline. Extensive development of irrigation wells that began in the 1970s also contributed to substantial groundwater-level declines. Groundwater-level declines likely enhance movement of brine from past oil and gas production near Burrton, Kansas, and natural saline water from the Arkansas River into the Wichita well field. Groundwater levels reached a historical minimum in 1993 because of drought conditions, irrigation, and the city of Wichita’s withdrawals from the aquifer. In 1993, the city of Wichita adopted the Integrated Local Water Supply Program to ensure that Wichita’s water needs would be met through the year 2050 and beyond as part of its efforts to manage the part of the Equus Beds aquifer Wichita uses. A key component of the Integrated Local Water Supply Program was the Equus Beds Aquifer Storage and Recovery project. The Aquifer Storage and Recovery project’s goal is to store and eventually recover groundwater and help protect the Equus Beds aquifer from oil-field brine water near Burrton, Kansas, and saline water from the Arkansas River. Since 1940, the U.S. Geological Survey has monitored groundwater levels and storage-volume changes in the Equus Beds aquifer to provide data to the city of Wichita in order to better manage its water supply. Groundwater mostly flowed from west to east in the shallow and deep parts of the Equus Beds aquifer in January 2015. A large area of declines greater than 10 feet in the shallow part of the Equus Beds aquifer from predevelopment (before substantial pumpage began in the area in September 1940) to January 2015 covered most of the central part of the study area, where the city of Wichita well field is located, and extended beyond it. Groundwater-level rises of greater than 10 feet from 1993 (the historical minimum groundwater levels) to January 2015 covered most of the central part of the study area in the shallow and deep parts of the Equus Beds aquifer; rises of greater than 20 feet mostly were within the north-central part of the study area. The 1993 to January 2015 recovery of storage volume previously lost from predevelopment to 1993 was about 46 percent (55,200 acre-feet) for the central part of the study area and the percentage recovery was larger than the 31 percent (59,800 acre-feet) recovery for the entire study area. Groundwater-level rises and the larger percentage recovery of storage volume in the central part of the study area was most likely a result of the city of Wichita adopting the Integrated Local Water Supply Program strategy which reduced Wichita’s pumpage from the Equus Beds aquifer in 2014 to the smallest amount since 1940. January 2015 storage volumes were about 96 percent (3,057,000 acre-feet) and 94 percent (960,000 acre-feet) of total aquifer storage for the study area and the central part of the study area, respectively. Groundwater levels from January 2014 to January 2015 in the central part of the study area rose about 3 feet in some places, probably because Wichita reduced its withdrawals from the aquifer in 2014 by more than 50 percent. Groundwater levels probably recovered less than anticipated because of decreased recharge and net groundwater flow and increased agricultural pumpage. A volumetric water budget for the central part of the study area between 2013 and 2014 showed that the substantial decrease in total pumping (10,412 acre-feet) did not result in an increase in storage volume because it was more than offset by decreased recharge (6,502 acre-feet; artificial and from precipitation) and an even greater decrease in net groundwater flow (11,710 acre-feet).