ABSTRACT: The
Final Report: Technical Feasibility of Subsurface Intake Designs for the Proposed Poseidon Water Desalination Facility at Huntington Beach, California, Authored by the Independent Scientific Technical Advisory Panel Under the Auspices of the California Coastal Commission and Poseidon Resources (Surfside) LLC, Convened and Facilitated by CONCUR, Inc., October 9, 2014, document copy is embedded. Summary, Conclusions, and Recommendations for Phase 2 section, Chapter VI, is reproduced. Importantly, “
Only the seabed infiltration gallery and the beach gallery survived the fatal flaw analysis and both are deemed to be technically feasible at this site.” “The ISTAP evaluated nine types of subsurface intakes for technical feasibility at the Huntington Beach site. The subsurface feasibility options included: (1) vertical wells completed in the shallow aquifer above the Talbert aquifer, (2) vertical deep wells completed within the Talbert aquifer, (3) vertical wells open to both the shallow and Talbert aquifer, (4) radial collector wells tapping the shallow aquifer, (5) slant wells tapping the Talbert aquifer, (6) seabed infiltration gallery (SIG), (7) beach gallery (surf zone infiltration gallery), (8) horizontal directional drilled wells, and (9) a water tunnel.” “It is the collective opinion of the ISTAP that each of the other seven subsurface intake options for the desired hydraulic capacity range (100-127 MGD) had at least one technical fatal flaw that eliminated it from further technical consideration.”
Note: Final Report Becomes Part of the Public Record
REFERENCES:
POSEIDON
WATER
Public hearings needed about desal science, MONTEREY HERALD
— Kristina Baer, Monterey
POSTED:
10/26/15
Experiment a costly waste for Cal Am ratepayers, MONTEREY HERALD
— Roland Martin, Carmel
Authored by the
Independent Scientific Technical Advisory Panel
Under the
Auspices of the California Coastal Commission and Poseidon Resources (Surfside)
LLC
Convened
and Facilitated by CONCUR, Inc.
October
9, 2014
Chapter VI. Summary,
Conclusions, and Recommendations for Phase 2
The ISTAP evaluated nine types of subsurface intakes for technical feasibility at the Huntington Beach site. The subsurface feasibility options included: (1) vertical wells completed in the shallow aquifer above the Talbert aquifer, (2) vertical deep wells completed within the Talbert aquifer, (3) vertical wells open to both the shallow and Talbert aquifer, (4) radial collector wells tapping the shallow aquifer, (5) slant wells tapping the Talbert aquifer, (6) seabed infiltration gallery (SIG), (7) beach gallery (surf zone infiltration gallery), (8) horizontal directional drilled wells, and (9) a water tunnel.
The hydraulic design capacity for these subsurface intake types ranged from 127 MGD for the combined requirement of the proposed SWRO plant and RO concentrate discharge dilution, and 100 MGD, if the concentrate discharge dilution was unneeded (diffuser system used to reduce environmental impacts from the concentrate discharge).
The
ISTAP used a standard definition of technical feasibility as defined in the
California Coastal
Act
and carefully evaluated fatal flaws of each subsurface intake type considered
for application at the proposed Huntington Beach site. Only the seabed
infiltration gallery and the beach gallery survived the fatal flaw analysis and
both are deemed to be technically feasible at this site. The design of both
types of galleries is well understood, but construction challenges would be
expected for both due to their subsea/subtidal construction. The surf zone
(beach) gallery, in particular, was judged to have some potentially difficult
constructability challenges (and thus a lesser degree of technical feasibility)
related to construction in the high-energy surf zone. The ISTAP does not
consider the existing scale of use of any particular subsurface intake compared
to the capacity requirement at Huntington Beach to be a fatal flaw for
technical feasibility (e.g. the only existing seabed infiltration gallery has
an hydraulic capacity of 27 MGD versus the 100 MGD proposed at the Huntington
Beach site, and no large scale implementation of the beach gallery has been
constructed and operated to date).
It is the collective opinion of the ISTAP that each of the other seven subsurface intake options for the desired hydraulic capacity range (100-127 MGD) had at least one technical fatal flaw that eliminated it from further technical consideration. The shallow vertical wells would create unacceptable water level drawdowns landward of the shoreline and could impact wetlands and cause movement of potential contaminants seaward. The deep vertical wells would have a significant impact on the Talbert aquifer that would interfere with the management of the salinity barrier and the management of the interior freshwater basin. The combined shallow and deep-water wells would adversely impact both the shallow aquifer and Talbert aquifer, and in addition, would produce waters with differing inorganic chemistry, which would adversely affect SWRO plant operation. Radial collector wells constructed into the shallow aquifer would have to be located very close to the surf zone which would make them susceptible to damage during storms and would be impacted by the projected sea level rise. Slant wells tapping the Talbert aquifer would interfere with the management of the salinity barrier and the management of the freshwater basin, and further, would likely have geochemical issues with the water produced from the aquifer (e.g., oxidation states of mixing waters). The recently-collected offshore hydraulic conductively data shows that the use of HDD wells is technically questionable and the largest capacity system in Spain is currently not operating at its original design capacity. The water tunnel constructed in the unlithified sediment at Huntington Beach would have overwhelming constructability issues.
The ISTAP recommends in Phase 2, further consideration be given solely to seabed infiltration galleries (SIG) and beach gallery intake systems. For clarification, the ISTAP believes that the remaining subsurface intake system deemed to be technically feasible could meet the seawater extraction goals of either 100 or 127 MGD.
It is important to stress that the ISTAP interpreted its Phase 1 charge relative to the Terms of Reference to be the evaluation of the technical feasibility of subsurface intake technology linked to a proposal. Consistent with that approach, the Phase 1 Panel considered nine technologies keyed to a potential project in the range 100 to 127 mgd. The Panel did address the broad issue of downward scalability where they saw relevance, but did not consider a full or parsed range of scale options for any of the nine technologies as this task exceeded the agreed upon scope defined in the TOR. Scalability issues could be addressed in subsequent assessments of other feasibility factors at the mutual agreement of the conveners.
Further, it was not the charge of the Phase 1 ISTAP to evaluate the economic considerations of using a subsurface intake versus a conventional open-ocean intake in this phase. The ISTAP recommends that the Phase 2 Panel give considerable analysis to the constructability of the seabed infiltration and beach gallery intake systems, because this greatly affects the economic viability of their potential use. However, the ISTAP recommends that in the Phase 2 evaluation of the subsurface intake options that a detailed lifecycle cost analysis should be provided to the succeeding committee. This lifecycle cost analysis should contain at least four scenarios, including: (1) the lifecycle cost using the appropriate operating period duration obtaining the 127 MGD of feed water from a conventional open-ocean intake without considering the cost of potential environmental impacts of impingement and entrainment, (2) the lifecycle cost using the appropriate duration of an operating period obtaining the 127 MGD of feed water from a conventional open-ocean intake and considering the cost of potential environmental impacts of impingement and entrainment, (3) the lifecycle cost using the appropriate duration of an operating period obtaining the 127 MGD of feed water from a seabed gallery intake system (or beach gallery intake system) using the same pretreatment design as used in treating open-ocean seawater, and (4) the lifecycle cost using the appropriate duration of an operating period obtaining the 127 MGD of feed water from a seabed gallery intake system (or beach gallery intake system) using a reduced degree of pretreatment, such as mixed media filtration followed by cartridge filters.
In each of these scenarios, the ISTAP recommends that the selected design hydraulic capacity match both the minimum and maximum flow rates consistent with the desired production rate of a 50 MGD desalination facility using the SWRO technology. The definition of an “appropriate” operating period should follow accepted industry standards for such lifecycle cost analyses. Typically, a period of 30 years is used, but given concerns on the potential for sea level rise impacts, analysis over a longer operating period (e.g. 50 years) may be desirable. In addition, the ISTAP questions the need for the use of seawater to dilute the concentrate discharge given the well-known use of diffuser outfalls to meet ocean discharge requirements.
The ISTAP also recommends that “Technical Feasibility” should continue to be defined by generally recognized factors as documented in the California Coastal Act of 1976.
(Section 30108 of the California Public Resources Code)
