The Ground Beneath the Valley: SGMA, Subsidence, and Who Pays When the Water Runs Out

The San Joaquin Valley sits on one of the most productive agricultural aquifers in the world — and one of the most depleted. For most of the 20th century, farmers drew groundwater freely, with no state-level regulation and no requirement to account for what was taken. In some areas of the valley, the land itself began to sink: a phenomenon called subsidence, measured in feet per decade rather than inches, documented repeatedly by NASA satellite data showing the ground dropping as much as two inches per month in peak drought years.

In 2014, California passed the Sustainable Groundwater Management Act — SGMA — a framework requiring local groundwater sustainability agencies to develop plans bringing overdrafted basins into balance by 2042. For San Joaquin County, the law created both a mandate and a political flashpoint. The county's primary groundwater basin, the Eastern San Joaquin Subbasin, includes the urban cores of Stockton, Lathrop, and Manteca, along with tens of thousands of acres of farmland that has relied on unmetered pumping for generations.

What the Numbers Actually Say

The Eastern San Joaquin Subbasin Groundwater Sustainability Plan, adopted in 2022, identified the basin as "critically overdrafted" under state definitions — meaning extractions consistently exceed the basin's natural recharge. The plan projects that reaching sustainability will require reducing total groundwater pumping while simultaneously expanding water recycling infrastructure and surface water deliveries.

For cities, the math is complicated by growth. Lathrop and Manteca are among the fastest-growing cities in California by percentage. Both have approved large residential and industrial developments in recent years. Every new home, warehouse, and distribution center adds to urban water demand — demand that must ultimately be met from a combination of Delta surface water deliveries through the State Water Project and groundwater that, by law, must now be managed to avoid further decline.

Stockton's Position

Stockton, as the county seat and largest city, occupies a distinct position in the groundwater equation. The City of Stockton obtains a significant share of its municipal supply from surface water delivered through the Delta — the Sacramento-San Joaquin River Delta that forms Stockton's western boundary. The city has invested in water recycling infrastructure over the past decade, and its utilities are active participants in the regional groundwater sustainability governance structure.

But Stockton's relationship with water has never been purely technical. The city's poorest neighborhoods — many of them in south and east Stockton — have historically faced water quality concerns distinct from groundwater quantity. Agricultural runoff, legacy industrial contamination, and aging distribution infrastructure have produced documented cases of elevated contaminants in tap water in parts of the county. Those issues are separate from the SGMA sustainability framework, but they share the same geography of inequity.

"You cannot separate the water quantity question from the water quality question, and you cannot separate either from the question of who built the Valley and who was left to absorb its costs."

The Farm-City Tension

SGMA's most consequential practical effect may be the tension it has created between agricultural and urban water users. In the San Joaquin Valley, agricultural interests have historically dominated groundwater governance at the local level. Growers in San Joaquin County pump groundwater for crops ranging from almonds and walnuts to dairy operations. Many hold senior water rights dating to the 19th century.

SGMA did not eliminate those rights. It created a framework — managed by locally constituted groundwater sustainability agencies — to balance them against the long-term health of the basin. Critics of the local implementation have argued that growers hold disproportionate influence over the very agencies meant to regulate them, and that plans approved so far rely too heavily on optimistic projections about future surface water availability — availability that climate change is making increasingly uncertain.

Supporters of the local approach argue that the alternative — state intervention under SGMA's probationary provisions — would be more disruptive and less calibrated to local conditions.

What Lathrop and Manteca Are Building Toward

Both Lathrop and Manteca have made significant investments in water infrastructure to support their growth trajectories. Lathrop operates its own treated surface water plant and has expanded recycled water distribution for landscape irrigation. Manteca receives treated surface water through regional wholesale agreements and has been developing additional water supply reliability projects.

The challenge is that growth projections embedded in both cities' General Plans continue to increase total demand. Developers seeking entitlements must demonstrate water supply availability — a requirement under California's Senate Bill 610 — but critics have noted that supply analyses often rely on water supply availability that has not yet been secured or infrastructure not yet built.

The growth will continue. The question being contested in water board meetings, sustainability agency hearings, and state oversight reviews is who bears the cost of making it work — and whether the aquifer the Valley has drawn on for a century will still be there when the accounting comes due.

DFP's Coverage Commitment

Dismal Freedom Press covers San Joaquin County water governance as part of its Environment desk. We attend groundwater sustainability agency meetings, file public records requests with water districts, and track state oversight correspondence. If you have a tip, a document, or a concern about water quality or groundwater management in the 209, we want to hear from you.

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