GUSTINE — With Gustine expected to nearly double in size over the coming decades, city officials held a workshop last week to review a sweeping update to the community’s Water Master Plan — a technical blueprint that outlines how the city must overhaul and expand its water system to keep pace with growth, aging infrastructure and long‑term groundwater challenges.

The plan, prepared by Gouveia Engineering, replaces the city’s 2002 water master plan and uses the 2025 zoning map, the county’s 2024–32 housing element and the city’s annexation plans to project future needs. According to the report, Gustine’s water service area is expected to grow from about 870 acres today to roughly 1,825 acres at full buildout. Population within that area is projected to rise from 6,138 residents in 2024 to about 11,616 — an increase of nearly 90 percent.

That growth will drive a sharp rise in water demand. Average‑day demand is projected to more than double, from 1.63 million gallons per day to 3.41 million, while maximum‑day demand is expected to increase from 2.45 million gallons per day to 5.11 million. Annual water production would need to climb from 1,148 acre‑feet per year to 2,392 acre‑feet.

Aging wells and water quality concerns

Gustine currently relies entirely on groundwater drawn from four municipal wells — all of which face age, capacity or water‑quality issues. Well 4, built in 1996, has long struggled with sand intrusion and elevated nitrate levels. Well 5 consistently produces water with total dissolved solids above state standards. Wells 6 and 7 also show elevated nitrate levels, and Well 7’s actual production falls short of its rated capacity.

Together, the wells can produce about 3,200 gallons per minute, a supply the report says will not be sufficient as the city grows.

All of Gustine’s wells draw from the Delta‑Mendota Subbasin, which the state has designated as “critically overdrafted” under the Sustainable Groundwater Management Act. The designation reflects long‑term declines in groundwater levels, land subsidence and other impacts tied to pumping that exceeds natural recharge. Gustine is one of 23 Groundwater Sustainability Agencies in the subbasin, which recently completed a single basin‑wide groundwater plan now awaiting state review.

Major upgrades needed for the existing system

Engineers told the city that several significant upgrades are already needed just to reliably serve current customers. The plan recommends:

– Drilling two new groundwater wells capable of producing 850 gallons per minute each – Constructing two 0.5‑million‑gallon storage tanks with new booster pump stations – Replacing about 14,000 feet of aging and leaking water mains along Highways 33 and 140 – Replacing 3,900 feet of undersized 4‑inch pipelines on Wallis, Ash and Carnation avenues and in two alleys – Replacing aging valves, hydrants and other components throughout the system

Groundwater expansion recommended over surface water

To meet long‑term demand, the plan evaluated two expansion strategies: relying solely on new groundwater wells or adding treated surface water to the system. While a surface‑water option would provide the most flexible supply, the report estimates it would cost about $60 million in today’s dollars and would require securing a reliable surface‑water source.

Because of those challenges, engineers recommended the city pursue the groundwater‑only option. That approach would require three new 620‑gallon‑per‑minute wells, three 1‑million‑gallon storage tanks with booster stations, and about 43,000 feet of new 12‑inch pipelines.

Altogether, the master plan outlines about $96.4 million in capital improvements needed through buildout. Roughly $37.9 million of that total is tied to fixing and upgrading the existing system, while $58.5 million would support future development.

Climate change and long‑term reliability

The report notes that the groundwater basin beneath Gustine can likely support about 2,400 acre‑feet of pumping annually — enough to meet buildout demand — but several factors could affect long‑term supply reliability. Those include legal and environmental constraints, water‑quality changes, groundwater levels and climate‑driven variability.

Engineers cautioned that climate change may introduce new uncertainties, particularly during drought cycles. The plan recommends the city continue monitoring long‑term trends and consider strategies such as water‑efficient landscaping, conservation technologies, reduced groundwater pumping and conservation‑focused development policies.

In the near term, the report concludes that Gustine can continue relying solely on groundwater. But if water‑quality issues worsen or SGMA restrictions tighten, the city may eventually need to diversify its supply through conjunctive use — blending groundwater with treated surface water from the California Aqueduct or the Delta‑Mendota system.