Letter for Year 19: September 2010-August 2011

The Illinois State Water Survey (ISWS), under contract to the Imperial Valley Water Authority (IVWA), has operated a network of rain gauges in Mason and Tazewell Counties since August 1992 and a network of groundwater observation wells since 1994. The purpose of the rain gauge and groundwater observation well networks is to collect long-term data to determine the impact of groundwater withdrawals during dry periods and during the growing season, and the rate at which the aquifer recharges. This letter serves as the year end report for Year 19 which covers the time period from September 1, 2010 through August31, 2011.The groundwater observation well network consists of thirteen wells, MTOW-01 through MTOW-13. The observation wells are drilled wells between 2 and 6 inches in diameter. With the exception of MTOW-05 and MTOW-09, these wells are equipped with pressure transducers that electronically log the groundwater level data. In Year 15, a new well was drilled to replace MTOW-1. This new well, named Snicarte #2, or MTOW-1Ahastakenthe place of the original well (MTOW-01 or Snicarte #1) within the monitoring well network. In accordance with our agreement, each well, with the exception of MTOW-05 and MTOW-09, is visited by ISWS personnel during the first few days of the month during irrigation season and approximately bi-monthly during the non-irrigated portion of the year. A 25-site rain gauge network (Figure 1) with approximately 5 miles between gauge was established in late August 1992. The network was reduced to 20 sites in September 1996. The rain gauge network is maintained by a Mason County resident, Bob Ranson,hired to visit each site monthly. During these visits the charts are changed, data downloaded and other routine services performed. Champaign-based ISWS personnel visit the rain gauge network to perform major maintenance and repairs as needed.