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GCSD: New Wells Being Tested

Shared by Roni Lynn Rudy

The Groveland CSD’s primary water source is the Hetch Hetchy Reservoir located in Yosemite National Park on the Tuolumne River. Hetch Hetchy is also the principal water source for theCity and County of San Francisco and a number of other utilities in the San Francisco Bay Area served by the City and County of San Francisco. Water flows from Hetch Hetchy through the Mountain Tunnel, a tunnel just south of Groveland into Priest Regulating Reservoir. GCSD

obtains water from the Mountain Tunnel prior to and upstream of Priest Regulating Reservoir at two locations. These locations are the Big Creek Shaft (the most upstream) and the Second

Garrotte Shaft.

The water source from the Mountain Tunnel is relatively pristine and, as a result, GCSD has

been able to avoid filtration of that source. The City of San Francisco Public Utilities

Commission (SFPUC) prepared an application for “filtration avoidance” in 1993. The conclusion was that the Hetch Hetchy water source met all of the eleven criteria for EPA filtration avoidance as of June 29 1993. SFPUC has provided routine monitoring of the watershed and has avoided the need to provide filtration ever since.

During severe drought conditions, SFPUC is able to introduce water from Cherry Reservoir into the Mountain Tunnel through the Lower Cherry Aqueduct. This Cherry Reservoir source of water can supply 200,000+ acre-ft of water but eliminate the filtration avoidance granted in

1993. The last time that Cherry Water was introduced in the Mountain Tunnel was during the

2014 drought.

Since GCSD water supply comes from the Mountain Tunnel downstream from the discharge

point from Cherry Reservoir, filtration would be required in order to produce potable water. In

2014, GCSD installed a new water filtration system at the Second Garrote Shaft. However, the

capacity of the filtration system at Second Garrote is unable to meet the District’s Maximum

Day Demand.

In addition to the primary water source, GCSD also has a secondary or Alternative Water

Supply (AWS) source. The AWS water source is Pine Mountain Lake. The District installed in

2003 a trailer mounted water treatment plant in PML to be able to provide water to the

Community during outages of the Mountain Tunnel. The AWS Water Treatment Plant (WTP) was intended to be a portable WTP.

During severe drought conditions, the Second Garrote WTP and the AWS WTP would not have enough capacity to supply water to the entire service area during maximum day demand. For this reason, the Groveland CSD is proposing a new groundwater well that will supply water to the Big Oak Flat and Tank 5 service areas during severe drought conditions. The introduction of this groundwater well will reduce the demand that has to be supplied from Second Garrote and the AWS systems and will increase fire resiliency.

The GCSD Board of Directors authorized staff to publicly bid the Hardrock Groundwater Test Well Project to drill and test two sites to determine where final wells will be permanently

constructed. Once constructed, the well(s) will provide sufficient redundancy during severe

drought conditions to ensure the Groveland CSD can continuously provide potable water to

the service area.

Construction costs for the Hardrock Groundwater Test Well Project are estimated to cost

approximately $140,000.00. The costs for the proposed Project will be covered in full by an

Urban Multibenefit Drought Relief Grant from the State of California Department of Water


The Urban Community Drought Relief Program is one of three Department of Water

Resources’ (DWR’s) Drought Relief Grant Programs that offers financial assistance to address

drought impacts. Funding for the Program was authorized by the Legislature amending the Budget Act of 2021; DWR was allocated $200 million for Urban Communities, $75 million for Conservation for Urban Suppliers, and $75 million for Turf Replacement. The same Budget Act also authorized $100 million for the Small Community Drought Relief Program. An initial phase of awards was released on February 2, 2023. Subsequent awards were released on April 6, 2023.

The GCSD Team is consistently focused on the future needs of the community and strives to

source as many grant programs as possible to take as much of the burden of the cost of

improvements as possible off of its customers.

GCSD staff is always happy to answer questions directly. Please contact the District by phone

or email with questions, concerns and compliments for the dedicated staff.

PHONE: 209.962.7161


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