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Eastern San Joaquin Groundwater Basin Groundwater Management Plan 1 Introduction 1 .1 Background San Joaquin County is home to approximately 600,000 people and sustains a $1.34 billion agricultural economy. The population is expected to increase to approximately 1.1 million by 2030. Water demand in the county is approximately 1,600,000 acre feet per year, 60 percent of which is quenched by groundwater. The California Department of Water Resources (DWR) has declared the Eastern San Joaquin Groundwater Basin (Basin) "critically overdrafted," indicating that the current rate of groundwater pumping exceeds the rate of recharge and is not sustainable. (DWR, 1980) Based on the San Joaquin County Water Management Plan, the Basin is overdrafted by 150,000 of/yr on average. Long-term groundwater overdraft has lowered the groundwater table by 2 ft/yr in some areas to -70 ft (MSL) and has induced the intrusion of highly saline groundwater into the Basin from the west. Without mitigation, such intrusion will degrade portions of the Basin, rendering the groundwater unusable for municipal supply and irrigation. Failure to address water supply and management needs in Eastern San Joaquin County will ultimately result in severe economic disruptions to the County. Agriculture in San Joaquin County, valued at $1.34 Billion, is already stressed due to declining market prices, rising regulatory, labor, and energy costs, and can ill afford threats to its water supply—a fundamental component of its continued existence. Municipal and industrial users simply must have reliable, high-quality supplies to exist. Loss of supplies to saline intrusion, potential loss of basin yield due to subsidence or simply lack of reliability will translate into business flight, job loss, loss of revenue for public services and general economic decline. Individual agencies in Eastern San Joaquin County have long grappled with declining groundwater levels and unreliable supplemental water supplies. Conversely, long term overdraft has created opportunities for groundwater banking to the benefit of regional and statewide interest. Overuse of groundwater has depleted a substantial portion of stored groundwater in the Basin and has made available volume for potential regulatory storage. It is estimated that at least 1.2 million af, a volume equivalent to Folsom Lake, could be used to store wet year water for use in subsequent dry years. However, to do so would require the monumental task of overcoming the institutional, political, financial, and physical challenges of groundwater banking. Independently, agencies in Eastern San Joaquin County have found it difficult to wield the political and financial power necessary to mitigate the conditions of overdraft. County interests have come to realize that a regional consensus based approach to water resources planning and conjunctive water management increases the chance for success. Regional planning efforts such as the San Joaquin County Water Management Plan (adopted by the County Board of Supervisors in October 2002) and the Mokelumne Aquifer Storage, Recovery Study (MARS Study), and the South County Surface Water Supply Project have proven successful ventures. Since its formation in 2001, the Northeastern San Joaquin County Groundwater Banking Authority (Authority) has employed the consensus based approach in its goal to develop "...locally supported groundwater banking projects that improve water supply reliability in Northeastern San Joaquin County...and provide benefits to project participants and San Joaquin County as a whole." Collaboration amongst the Authority member agencies has strengthened the potential for broad public support for groundwater management activities as well as the ability to leverage local, State, and federal funds. Table 1-1 lists the member agencies of the Authority. Northeastern San Joaquin County Section 1 Groundwater Banking Authority 20 Introduction