Stanislaus and Tuolumne Rivers Groundwater Basin Association Groundwater Sustainability Agency


Since 1994, STRGBA members have worked cooperatively to provide coordinated planning to make the best use of available water resources of the Modesto Subbasin in order to meet the needs of the agencies.

The purposes of STRGBA are:

  • To determine and evaluate the subbasin’s groundwater supply.
  • To promote coordination of groundwater management planning activities, including the preparation of the Groundwater Sustainability Plan.
  • To develop a hydrologic groundwater model of the groundwater basin.
  • To determine the subbasin's need for additional or improved water extraction, storage, delivery, conservation, and recharge facilities.
  • To provide information and guidance for the management, preservation, protection, and enhancement of groundwater quality and quantity in the subbasin.

In September 2014, Governor Jerry Brown signed The Sustainable Groundwater Management Act of 2014 (SGMA) . SGMA sets the framework for statewide sustainable groundwater management by local agencies. SGMA requires, among other things, the formation of Groundwater Sustainability Agencies (GSA) and the preparation of Groundwater Sustainability Plans (GSP).

In 2017, member agencies of the Stanislaus and Tuolumne Rivers Groundwater Basin Association (STRGBA) - City of Modesto, Modesto Irrigation District, City of Oakdale, Oakdale Irrigation District, City of Riverbank, City of Waterford and Stanislaus County – formed as a GSA. STRGBA GSA has the authority and responsibility to manage the groundwater basin. Many groundwater basins in the San Joaquin Valley have experienced heavy groundwater pumping – especially during the recent drought. Several are now in a condition of critical overdraft. The Modesto basin isn't considered to be critically overdrafted, but since most of the cities within our basin rely solely on groundwater, we're considered a high-priority basin. Due to that designation, SGMA requires that we adopt and begin implementation of a GSP by January 31, 2022.

STRGBA GSA obtained a $1 million grant from the Department of Water Resources (DWR) and hired Todd Groundwater, Inc. to prepare a GSP for the basin. The GSP will help to identify areas within the basin that need better groundwater monitoring and provide a path to preventing undesirable results over the next 50 years.

The Modesto Subbasin and STRGBA GSA

Map of Modesto Subbasin Agencies

Modesto Subbasin Agencies

The seven agencies covering the Modesto groundwater subbasin formed the Stanislaus and Tuolumne Rivers Groundwater Basin Association Groundwater Sustainability Agency (STRGBA GSA). The member agencies all rely on groundwater for some or all of their water needs. These agencies share the groundwater resource and, through STRGBA, provide coordinated planning to make the best use of groundwater to the mutual interests of the participating agencies. The Tuolumne County GSA is responsible for the small section of the Modesto Subbasin that falls within Tuolumne County. The STRGBA GSA and Tuolumne County GSA are coordinating to develop a single GSP for the Modesto Subbasin.


The STRGBA GSA meets on the second Wednesday of each month at Modesto Irrigation District's downtown office - 1231 11th Street, Modesto. The meetings usually begin at 1:30 p.m. and the public is always invited and encouraged to attend.

Read STRGBA's Memorandum of Understanding.