conditions. Studies
are needed to determine the extent of the Dune Sand Aquifer, the water quality and quantity of the Dune Sand Aquifer, the
extent and thickness of the Salinas Valley Aquitard and the extent of the 180-Foot
Aquifer. Second, the effects of the MPWSP on the Basin need to be
evaluated. Specifically, a series of test boring/wells would be needed to assess the
hydrogeologic conditions at the site. Aquifer testing would also be needed to establish accurate baseline conditions and determine the pumping effects on both the Dune Sand
Aquifer and the underlying 180-Foot Aquifer.
Aquifer tests should mimic proposed pumping rates. Third, updated groundwater modeling is needed to evaluate
future impacts from the MPWSP. Specifically,
modeling scenarios are necessary to predict changes in groundwater levels, groundwater flow direction, and changes
in the extent and boundary of the seawater intrusion front. Additional studies are also necessary to determine how any extracted fresh water is replaced, whether through re-injection wells, percolation basins, or through existing recharge
programs. The studies will form the basis for a plan that avoids injury to other groundwater
users and protects beneficial uses in the Basin.
EXECUTIVE SUMMARY
Introduction
The California Public Utilities Commission (Commission)
asked the State Water Resources Control Board (State Water Board) whether the California Monterey
Peninsula Salinas
Valley Groundwater Basin (SVGB or Basin) near or beneath Monterey Bay
Technical Conclusions
There are gravity and pumped well designs proposed for the
MPWSP, as well as several well locations. Well design and well location will need testing to provide design/site specific information needed for complete
technical and legal analysis. The conditions in the aquifer where MPWSP feedwater would be extracted could be either confined or unconfined however; there is currently not
enough information to determine what type of conditions exist at the location of the MPWSP
wells. Effects from confined aquifer pumping would be observed over a larger area than if
extraction occurred from an unconfined aquifer. Previous studies done in the one of proposed MPWSP well locations indicate that there would be an approximate 2-mile
radius zone-of-influence if groundwater was pumped from an unconfined aquifer. It is unknown what the effects would be if water was pumped from a confined aquifer with
different hydrogeologic conditions.
The aquifers underlying the proposed extraction locations
have been intruded with seawater since at least the 1940’s. The impairment means that there is little or
no beneficial use of the water in the intruded area. Groundwater quality at the site of the proposed MPWSP wells will play an important role in
determining the effects of extraction on the other users in the Basin.
The Basin is in overdraft.
Groundwater extractions and outflows to the ocean needed to repel seawater intrusion exceed groundwater inflow into the
Basin. The overdraft condition is important because it limits the availability of
fresh water supplies to Basin users.
Legal Conclusions
To appropriate groundwater from the Basin, the burden is on
Cal-Am to show no injury to other users. Key factors will be the following: (1) how
much fresh water Cal-Am is extracting as a proportion of the total pumped amount, to
determine the amount of treated water considered as desalinated sea water, available for export as developed water; (2) whether pumping affects the water table level in
existing users wells and whether Cal-Am can mitigate any lowering of water levels
through monetary compensation for increased pumping costs or upgraded wells;
(3) how Cal-Am should return any fresh water it extracts to the Basin to prevent
injury to others; and (4) how groundwater rights might adjust in the future if the
proportion of fresh and sea water changes both in the larger Basin area and the immediate area
around Cal-Am’s wells.
Both near and long-term, a physical solution that protects
legal users in the Basin from harm would permit Cal-Am to extract groundwater. Even if overdraft conditions continued in the Basin following imposition of the solution,
Cal-Am could legally continue pumping brackish water so long as the quantity and
method of extraction are not detrimental to the conditions in the Basin and other
Basin users’ rights, taking into account replacement water provided as part of the
project. So long as overlying users are protected from injury, appropriation of water consistent
with the principles discussed in this report should be possible. Cal-Am should have the
opportunity to show any desalinated water it produces is surplus to the current
needs of the Basin, replacement water methods are effective and feasible, and the MPWSP can
operate without injury to other users.
Recommendations
Additional information is needed to accurately determine
MPWSP impacts on current and future Basin conditions regardless of whether the
extraction occurs from pumped or gravity wells. First,
specific information is needed on the depth of the wells and aquifer conditions. Studies
are needed to determine the extent of the Dune Sand Aquifer, the water quality and quantity of the Dune Sand Aquifer, the
extent and thickness of the Salinas Valley Aquitard and the extent of the 180-Foot
Aquifer.
Second, the effects of the MPWSP on the Basin need to be
evaluated. Specifically, a series of test boring/wells would be needed to assess the
hydrogeologic conditions at the site. Aquifer
testing would also be needed to establish accurate baseline conditions and determine the pumping effects on both the Dune Sand
Aquifer and the underlying 180-Foot Aquifer.
Aquifer tests should mimic proposed pumping rates.
Third, updated groundwater modeling is needed to evaluate
future impacts from the MPWSP. Specifically,
modeling scenarios are necessary to predict changes in groundwater levels, groundwater flow direction, and changes
in the extent and boundary of the seawater intrusion front. Additional studies are also necessary to determine how any extracted fresh water is replaced, whether
through re-injection wells, percolation basins, or through existing recharge
programs. The studies will form the basis for a plan that avoids injury to other groundwater
users and protects beneficial uses in the Basin.
NOTICE OF OPPORTUNITY FOR PUBLIC COMMENT, April 3, 2013
ADDENDUM:
CALIFORNIA AMERICAN WATER COMPANY'S MONTEREY PENINSULA
RELATED NEWS ARTICLE:
Board says Cal Am can seek to prove wells won't hurt other
users
By JIM JOHNSON Herald Staff Report, 04/03/2013
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