Jane Wagner-Tyack: Groundwater draft plan reaches milestone

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An important but not widely-publicized local planning process reached a milestone with the July release of the draft Groundwater Sustainability Plan for the Eastern San Joaquin Subbasin. This is the public’s first chance to see how groundwater in this region may be managed for the next 20 years.

Californians rely on groundwater more than we usually realize. In a drought, up to 40% of the water used by cities and agriculture comes from underground, not from rivers we can see. About half of Lodi’s water supply is groundwater. All the water delivered to Lodi residents was groundwater until 2012, when the Lodi Surface Water Treatment Plant became operational and the City was able to take advantage of an agreement with Woodbridge Irrigation District (WID) for Mokelumne River water to which WID holds rights. (The East Bay Municipal Utility District — EBMUD — is the other major holder of Lower Mokelumne River water rights.)

Groundwater is not inexhaustible. Particularly in arid agricultural regions south of us with little or no surface water supplies, groundwater pumping increases and wells must be deepened when surface water transfers decrease, as they do in years when there is less water for all users, including fish, to share. In the southern Central Valley, groundwater overdraft in response to drought conditions has actually caused the land to drop, or subside, damaging the canals built to deliver water from Delta watersheds.

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