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Eastern San Joaquin Groundwater Basin Groundwater Management Plan Northeastern San Joaquin County Section 5 Groundwater Banking Authority 89 Groundwater Monitoring Program 5 Groundwater Monitoring Program Marked changes in groundwater levels and groundwater quality during the 1960’s prompted the DWR to initiate a groundwater investigation in Eastern San Joaquin County. Completed in 1967, DWR Bulletin No. 146 San Joaquin County Groundwater Investigation recommended that a groundwater monitoring program be established to track changes throughout the Basin. In the fall of 1971, the San Joaquin County Flood Control and Water Conservation District (County) initiated the collection and management of groundwater data and the production of semi-annual groundwater reports. In December of 2000, Montgomery Watson Harza (MWH) performed an evaluation of the County’s groundwater monitoring program and recommended improvements to better assess groundwater level conditions and saline intrusion and to develop measurement and sample collection protocols. Since that time the County has continued to implement the recommendations of the evaluation and will work closely with and meet the monitoring needs of the Authority. 5.1 Current Groundwater Monitoring Program The current groundwater level monitoring program includes semi-annual groundwater level measurements of over 550 wells (exact number varies from year to year) of which approximately 300 are measured by County staff. Water level measurements are taken in October and April in order to capture groundwater levels after and before peak groundwater pumping occurs. According to the MWH evaluation, both the frequency of measurement and the spatial adequacy of the monitoring well network are sufficient to determine regional groundwater trends throughout the Basin. The data collected is stored electronically in a database for further analysis. DWR posts a portion of the data on the internet at http://wdl.water.ca.gov/gw/admin/main_menu_gw.asp. In 2003, San Joaquin County Public Works Staff, in conjunction with Kennedy/Jenks Consultants, reformatted the database to facilitate advanced analysis of groundwater data in a Geographic Information System (GIS). Future upgrades include electronic data collection and the availability of the groundwater database and analysis capabilities over the internet. As documented in Section 2, saline intrusion from the west threatens the health of the underlying Basin. The County supports a limited effort groundwater monitoring program which includes the annual groundwater quality sampling of approximately 40 municipal and domestic supply wells (exact number varies from year to year) measured by County staff or obtained from the various urban water purveyors. The analysis typically includes chloride, electrical conductivity (EC) and total dissolved solids (TDS). Water quality sampling occurs in October when chloride levels are generally highest during the year. According to the MWH evaluation, the spatial adequacy of the monitoring well network is not sufficient to determine the source, aerial and vertical extent, and the rate of migration of saline groundwater. The data collected is stored electronically in a database for further analysis. 5.1.1 San Joaquin County Groundwater Data Center The San Joaquin County Groundwater Data Center (GDC) is a Countywide centralized interactive groundwater information vehicle that provides access to groundwater data collected and shared by agencies throughout San Joaquin County. Over half of the water used in San Joaquin County comes from groundwater. It is vital that we protect and ensure the long-term health and sustainability of the underlying groundwater basin. The San Joaquin County GDC is the foundation for Countywide groundwater management efforts pursued by its water interests.