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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater Intrusion Control Using Recycled Water in Southern California. Boletín
Geológico y Minero, 125 (2): 143-155
ISSN: 0366-0176
Large-Scale Aquifer Replenishment and Seawater
Intrusion Control Using Recycled Water in Southern
California
R. Herndon and M. Markus
Orange County Water District, 18700 Ward Street, Fountain Valley, California 92708
RHerndon@ocwd.com
ABSTRACT
In 2008, eighteen years after determining that its Talbert Seawater Barrier required expansion, the Orange Cou-
nty Water District started up the world’s largest indirect potable reuse facility, the Groundwater Replenishment
System (GWR System). The GWR System provides a reliable potable-quality water supply to the Talbert Barrier,
which consists of 109 multi-depth injection wells. The Talbert Barrier began operation in 1976 with the completion
of Water Factory 21, the rst project in California permitted to inject recycled water into a potable-supply aqui-
fer. By 1990, as groundwater pumping increased, it was evident that the barrier’s original injection wells were
incapable of maintaining protective groundwater elevations to prevent seawater intrusion. Ten years of technical
planning and public outreach culminated in the decision to demolish the undersized Water Factory 21 and build
a state-of-the-art advanced recycled water treatment system and expanded barrier. Barrier expansion entailed
construction of over 20 new injection wells in key areas where seawater intrusion was observed. Flow modeling
indicated that average barrier injection needed to be doubled to 80 m
3
/min (30 mgal/day). Based on seasonal
groundwater pumping patterns, model simulations indicated that the barrier should inject up to 107 m
3
/min (40
mgal/day) in the summer/fall months and one-half that rate in winter/spring months to maintain a protective
hydraulic barrier. With a capacity of 187 m
3
/min (70 mgd), the GWR System provides all of the high-quality water
that the barrier requires, with the remainder conveyed to OCWD’s inltration basins in the city of Anaheim. Five
years after start-up, the expanded seawater barrier has met all expectations in terms of capacity and groundwa-
ter elevation maintenance using a reliable locally-produced water supply.
Key words: Articial recharge, California, hydraulic barrier, seawater intrusion.
Recarga articial de acuíferos y control de intrusión de agua de mar a gran
escala utilizando agua reciclada en el sur de California
RESUMEN
En 2008, dieciocho años después de llegar a la conclusión de que la Barrera Talbert contra la intrusión necesi-
taba una ampliación, el Orange County Water District puso en marcha la instalación más grande del mundo
para la reutilización indirecta de agua potable, el GWR System. Este sistema proporciona un suministro able
de agua de calidad casi potable a la barrera Talbert, que consta de 109 pozos de inyección de diferentes pro-
fundidades. La barrera Talbert comenzó a funcionar en 1976 con la realización de “Water Factory 21”, el primer
proyecto en California que posibilitó la inyección de agua reciclada en un acuífero que era utilizado para sum-
inistro de agua potable.. En 1990, como el bombeo de agua subterránea aumentó, se hizo evidente que los
pozos de inyección originales de la barrera eran incapaces de mantener la protección contra la intrusión del
agua del mar. Diez años de planicación técnica y la difusión pública culminaron en la decisión de demoler
la fábrica “Water Factory 21”, cuyo tamaño estaba infradimensionado, y construir un sistema técnicamente
avanzado de tratamiento de agua reciclada, así como de ampliar la barrera hidráulica contra la intrusión. Esta
ampliación implicaba la construcción de más de 20 nuevos pozos de inyección en áreas clave en las que se
observó un mayor avance de la intrusión marina. Un modelo de ujo indicó que la capacidad de inyección de
la barrera debía duplicarse hasta alcanzar un caudal de inyección de 80 m
3
/min. Basado en los patrones de
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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
VERSIÓN RESUMIDA EN CASTELLANO
Introducción
La costa sur de California depende en gran medida de agua que se transporta (o “importa”) desde varios
cientos de millas a través d eacuductos desde el norte del estado y desde el río Colorado (gura 1). Esta agua
supone aproximadamente la mitad de las necesidades totales para satisfacer la demanda de una población de
20 millones de personas en una región semi-árida. Las aguas subterráneas, las superciales y las recicladas
suministran la otra mitad de las necesidades. En los últimos 10 años, la normativa medioambiental en el norte
de California y la reducción de la aportación del río Colorado han ocasionado una disminución de la disponi-
bilidad de esta agua importadas, en una cuantía cifrada entre el 20 y el 25%.
Para hacer frente a estas reducciones sustanciales en las fuentes de suministro de agua tradicionales, las
agencias de agua del sur de California han tratado de fortalecer y diversicar sus carteras de agua, aumen-
tando la captura de aguas de tormenta, aguas residuales recicladas, la eciencia en el uso del agua y la de-
salación de agua de mar. Afortunadamente, una parte signicativa del sur de California están ubicada sobre
grandes cuencas de agua subterránea. El objetivo de las agencias regionales de agua es la gestión sostenible
de estas aguas subterráneas maximizando su producción y evitando su sobreexplotación a largo plazo, así
como la degradación de la calidad del agua, la intrusión de agua de mar y la subsidencia.
El range County Water District (OCWD) administra los recursos de agua subterránea en el norte del Conda-
do de Orange mediante actuaciones y programas que incluyen la recarga de acuíferos, el control de intrusión
de agua de mar, la protección de la calidad del agua, el reciclado del agua y la conservación del agua de lluvia.
OCWD cubre un área aproximada de 900 km
2
y tiene una población de 2,4 millones (Figura 2).
Abastecimiento con agua subterránea y gestión de la cuenca
El agua subterránea proporciona dos tercios de la demanda de agua en el área de servicio de OCWD, y el
tercio restante se obtiene a través del agua importada. El costa de la utilización del agua subterránea es de
aproximadamente la mitad del costo del agua importada.
La principal fuente de agua de recarga de la cuenca subterránea del Condado de Orange es el río Santa
Ana, cuyos caudales se componen generalmente de aguas residuales tratadas descargadas de plantas de
tratamiento de aguas residuales situadas aguas arriba del condado, y de caudales estacionales ligados a tor-
mentas. En promedio, OCWD puede detraer y recargar aproximadamente 185 hm
3
del río cada año. El distrito
también recarga aproximadamente 86 hm
3
por año de agua reciclada procedente del Sistema de Recarga de
Agua Subterránea (GWR System), que se describe más adelante. Por último, los acuíferos reciben un prome-
dio de 74 hm
3
por año de recarga natural procedente de la precipitación y la inltración del agua de riego. En
ocasiones, OCWD agua importada comprándola como fuente adicional de agua para recargar los acuíferos. El
agua subterránea se bombea desde aproximadamente 200 pozos de gran capacidad, que son propiedad y son
operados por las agencias locales que suministran el agua directamente a los usuarios (Figura 3).
Como su principal objetivo, OCWD se ha esforzado por aumentar la utilización de los acuíferos mediante
la ampliación de la capacidad de recarga de los mismos (Figura 4). Como históricamente se han sucedido
períodos de sequía e inundación, la cuenca se ha operado como un depósito para retirar o almacenar agua
(Figura 5).
Características hidrogeológicas
La cuenca de agua subterránea del Condado de Orange es una estructura sinclinal, con sedimentos que con-
tienen agua dulce que alcanzan profundidades de hasta 1.200 m. Cerca de la costa, una zona de falla ha creado
una barrera local contra la intrusión marina. Los acuíferos de la cuenca forman una compleja serie depósitos
bombeos estacionales de las aguas subterráneas, el modelos indica que la barrera debería inyectar hasta
107 m
3
/min en los meses de verano / otoño y la mitad en invierno / primavera de meses para mantener su ca-
pacidad de protección contra la intrusión marina. Con una capacidad de 187 m
3
/min, el Sistema GWR propor-
ciona toda el agua de alta calidad que requiere la barrera, y el resto es enviado hacia unas balsas de recarga
situadas en la ciudad de Anaheim. Cinco años después de su puesta en marcha, la nueva barrera hidráulica
ha cumplido todas las expectativas en términos de capacidad y de mantenimiento de los niveles de las aguas
subterráneas utilizando una fuente de agua able y producida en la misma zona geográca.
Palabras clave: Barrera hidráulica, California, intrusión marina, recarga articial.
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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
de arena y grava interconectados y con intercalaciones de arcillas y limos. En las zonas del interior, las capas
de arcillas y limos se vuelven más delgadas y más discontinuas, lo que permite un mayor ujo de agua en-
tre los acuíferos someros y los más profundos. Tres sistemas acuíferos más importantes de la cuenca están
hidráulicamente conectados, de froma que las aguas subterráneas pueden uir entre ellos a través goteo
procedente de los acuitardos intermedios o de discontinuidades dentro de los mismos (Figura 6).
Control de la intrusión marina
La entrada de agua salada en los acuíferos costeros del Condado de Orange se conoce desde 1930 y ha
constituido el factor clave para la explotación de los acuíferos. Cuatro barreras de intrusión de agua de mar
operan en el sur de California y consisten en una serie de pozos que inyectan agua dulce para crear un domo
hidráulico o “cresta” que impide el ujo hacia el interior de las aguas subterráneas salinizadas.
La barrera Talbert, del OCWD, lleva en funcionamiento desde 1976 y originalmente el agua que se inyec-
taba era una mezcla de aguas subterráneas profundas y agua reciclada procedente de Water Factory 21, que
fue el primer proyecto en California con autorización para inyectar aguas residuales tratadas en un acuífero
con agua potable para suministro (Figura 7). La barrera inicial estaba formada por 23 pozos de inyección de
diferentes profundidades ,con una capacidad de alrededor de 40 m
3
/min. El agua de mar puede intruir en
acuíferos profundos plegados, como consecuencia de que los mismos poseen conexión hidráulica con el
acuífero superior, el Talbert, que está en contacto directo con el Océano Pacíco. Los acuíferos más profundos
son fuertemente explotados mediante los pozos de producción situados hacia el interior, creando así fuertes
gradientes hidráulicos hacia los pozos (Figura 8).
En los años de la década de 1990, el aumento de bombeo superó la capacidad del acuífero Talbert para
hacer frente a la intrusión de agua de mar, como se indica por las concentraciones de cloruro que progresan
hacia el interior (Figura 9). Basándose en estas observaciones, OCWD comenzó investigaciones para ampliar
el sistema así inyección. Se desarrolló y calibró un modelo numérico de ujo, que posteriormente fue utilizado
para determinar las ubicaciones y las tasas de inyección de los pozos de inyección adicionales. Los resultados
mostraron que se necesitaría doblar la tasa media de inyección de la barrera hidráulica, alcanzando 80 m
3
/
min (30 Ml / día). Para lograr esa capacidad de inyección deseada, se construyeron nuevos pozos de inyec-
ción en 13 nuevas ubicaciones que se muestran en la Figura 9. Los pozos de Inyección fueron desarrollados
nuevamente, y actualmente se sigue haciendo lo mismo para eliminar los materiales nos acumulados en las
rejillas, que rodean el empaque de grava anular. Con estas operaciones se consigue restaurar la capacidad de
la inyección (Figura 10).
Agua reciclada – una fuente local de agua able
El suministro de agua a la barrera Talbert fue el impulso para el desarrollo y puesta en funcionamiento de
instalaciones para el reciclado de agua en el condado de Orange a nales de 1960 y principios de 1970. En
ese momento, el acceso al agua importada para los futuros pozos de inyección habría requerido la construc-
ción de un acueducto costoso para conectarse a la tubería principal de alimentación de agua importada más
cercana y habría creado una dependencia a largo plazo de las fuentes de agua que se encuentran a cientos de
kilómetros de distancia. Teniendo en cuenta estas cuestiones, OCWD decidió proseguir el tratamiento avan-
zado de aguas residuales procedentes del Orange County Sanitation District (OCSD) que eran descargadas al
mar. mediante la construcción de la infraestructura “Water Factory 21”.
Más de 25 años de experiencia operacional con Water Factory 21 y la barrera de Talbert sentaron las bases
para planicar una instalación de reciclado de agua mucho mayor y la expansión de la barrera hidráulica con-
tra la intrusión. En un maravilloso ejemplo de la colaboración interinstitucional, OCWD y OCSD encontraron
una solución común a sus respectivas necesidades: el Sistema GWR. El Sistema GWR se diseñó inicialmente
para producir 187 m
3
/min de agua reciclada con un tratamiento avanzado. Esto fue suciente para abastecer a
toda la barrera hidráulica de inyección, entregar otros de 107 m
3
/min para las balsas de inltración de OCWD,
y posponer la necesidad de OCSD para construir un emisario marino más grande (Figura 11). La microl-
tración fue seleccionado como método rentable de pre-tratamiento previo a la ósmosis inversa. Después de
la ósmosis inversa, el agua es tratada por oxidación avanzada mediante luz ultravioleta y peróxido de hidróge-
no. Estos procesos purican el agua hasta aportarle una calidad casi igual a la del agua destilada. Debido a
que la ósmosis inversa elimina casi todos los minerales del agua, es necesario añadir cal para estabilizar el
agua antes de su transporte a las instalaciones de recarga (Figura 12). El agua producto nal tiene una con-
centración de sólidos disueltos totales de aproximadamente 45 mg/L y supera todas las demás normas para
el agua potable del estado y federal, otorgándole la máxima calidad del agua de recarga disponible.
Un paso importante para llevar al Sistema GWR a buen puerto fue la obtención de la aceptación y apoyo
públicos. Se hicieron más de 1.000 presentaciones ante las organizaciones comunitarias, funcionarios elec-
tos, agencias reguladoras, grupos empresariales, cientícos y académicos, profesionales de la salud, edu-
cadores, y los grupos ecologistas. Además, el proyecto está supervisado por un panel asesor independiente
146
Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
Introduction
Coastal southern California is highly dependent on
water transported (or “imported”) hundreds of miles
through aqueducts from northern California and the
Colorado River (Figure 1). Imported water accounts
for approximately one-half the total supplies to meet
the needs of a population of 20 million in this semi-
arid region. Local groundwater, surface water, and
an increasing amount of recycled water comprise the
other half of the water supply. In the last ten years,
environmental regulations in northern California and
supply reductions on the Colorado River have de-
creased the volume of imported water delivered to
southern California by 20 to 25 percent.
Facing substantial reductions in their traditional
water supplies, southern California water agencies
have sought to strengthen and diversify their water
portfolios by increasing the amount of captured local
storm water, increasing the use of recycled wastewa-
ter, increasing water use efciency, and exploring sea-
water desalination. Fortunately, signicant portions of
southern California are underlain by large groundwa-
ter basins comprised of alluvial and marine deposits
of gravels, sands, silts, and clays. These groundwater
basins contain large quantities of potable-quality wa-
ter; however, their long-term groundwater production
yield depends on the supply of replenishment water.
The objective of regional water agencies is to sustain-
ably manage these groundwater basins by maximizing
Figure 1. Coastal southern California has a population of 20 million and re-
ceives 50 percent of its water supply from northern California and the Colo-
rado River via aqueducts.
Figura 1. La costa sur de California tiene una población de 20 millones de
habitantes, y recibe el 50% de su suministro de agua desde el norte de Cali-
fornia y el río Colorado a través de acueductos.
que proporciona una continua revisión cientíca periódica de las operaciones y el desarrollo del proyecto. El
resultado de esta campaña educativa multianual fue un abrumador apoyo público al Sistema GWR. Ahora
en su sexto año de funcionamiento, el GWR ha producido y recargado más de 370 hm
3
de agua. El coste de
producción es menor que la del agua importada, lo que demuestra la viabilidad económica del proyecto.
Conclusions
Los acuíferos costeros del sur de California han sido amenazados por la intrusión de agua de mar desde el
comienzo de su utilización hace más de 100 años. Barreras hidráulicas contra la intrusión marina requieren un
suministro continuo de agua cuya calidad esté próxima a la de potable. Como el agua importada se ha conver-
tido en una fuente de agua no segura y más cara, las agencias locales han desarrollado sus propias fuentes de
agua, utilizando agua reciclada altamente tratada. El sistema GWR, de OCWD, garantiza para el Condado de
Orange un suministro able, resistente a la sequía, y controlado localmente, de agua de la más alta calidad,
y ha revolucionado la forma que los consumidores tienen de percibir las aguas residuales - como un recurso
valioso que se debe cuidar y reutilizar.
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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
Figure 2. The Orange County Water District recharges the basin with
Santa Ana River water and recycled water at 400 hectares (1,000
acres) of inltration ponds.
Figura 2. El Orange County Water District realiza recarga articial
mediante balsas de 400 ha de supercie utilizando agua proceden-
te del río Santa Ana y agua reciclada.
groundwater production while avoiding long-term
overdraft, water quality degradation, seawater intru-
sion, and land subsidence.
This paper discusses some of the programs and
projects that have been implemented by the Orange
County Water District (OCWD or District) to improve
water supply reliability and protect against seawater
intrusion in a highly urbanized coastal groundwater
basin in southern California.
Institutional Setting and Climate
OCWD is a special governmental water agency that
was created by the state of California in 1933 to ma-
nage the surface water and groundwater resources in
northern Orange County for the benet of the public
within the District. District programs include aquifer
replenishment or recharge, seawater intrusion con-
trol, water quality protection and improvement, wa-
ter recycling, and storm water conservation (OCWD,
2009). OCWD is governed by a board of directors, se-
ven of whom are publicly elected and three of whom
are appointed by three cities. Employees number
approximately 220, including engineers, hydrogeolo-
gists, water system operations and maintenance staff,
public affairs specialists, chemists, biologists, accou-
ntants, and water quality specialists. Most revenue for
OCWD comes from an assessment that it charges on
groundwater pumped and a lesser amount from pro-
perty taxes.
OCWD covers an area of approximately 900 km
2
(350 mi
2
) and has a population of 2.4 million (Figure
2). The Mediterranean-type climate in Orange County
is generally mild, with annual rainfall of approximate-
ly 350 mm (14 in), and average monthly temperatures
ranging from 14 to 24
o
C (58 to 75
o
F). Most of the rain-
fall occurs in the months of December through March.
Groundwater Supply and Basin Operation
Groundwater supplies approximately two-thirds of
the total water demand within OCWD’s service area.
Most of the remaining water demand is met by im-
ported water. The cost of using groundwater is about
one-half the cost of imported water (OCWD, 2012).
Thus, the residents and businesses that overlie the
Orange County groundwater basin enjoy a tremen-
dous economic savings in water cost as compared to
areas, such as the city of San Diego, that are largely
dependent on imported water due to the absence of a
prolic groundwater basin.
The primary source of recharge water to the Orange
County groundwater basin is the Santa Ana River, the
longest river in southern California. The Santa Ana
River ows that arrive in Orange County are generally
composed of treated wastewater discharged from up-
stream sewage treatment plants and seasonal storm
ows. On average, the combined amount of river
ows that OCWD is able to capture and recharge in
its inltration basins is approximately 185 million m
3
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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
(150,000 acre-ft) each year. During periods of heavy
rainfall, high volumes of storm ow in the river may
greatly exceed the District’s recharge capacity and dis-
charge to the Pacic Ocean. The District also recharges
approximately 86 million m
3
(70,000 acre-ft) per year
of advanced treated recycled water from a landmark
project known as the Groundwater Replenishment
System that is described later. Lastly, the groundwa-
ter basin receives an average of 74 million m
3
(60,000
acre-ft) per year of natural recharge from precipita-
tion and inltration of irrigation water. Occasionally,
OCWD purchases imported water as an additional
source of water to recharge the groundwater basin.
Groundwater is pumped from approximately 200
large-capacity wells owned and operated by cities,
local water districts, and water companies that pro-
vide water directly to the water users (Figure 3). Water
users are primarily residences, industries, parks, and
golf courses, as very little agricultural land remains
in Orange County. A “typical” production well within
OCWD is 330 m (1,100 ft) deep, has an operating rate
of 8 m
3
/min (2,110 gal/min), and today would cost at
least $3 million to construct and equip with pump
and motor. Considering the cost differential between
groundwater and imported water, the cost of invest-
ing in a new well can be recovered in a short time
period.
As its primary goal, OCWD has strived to increase
the utilization of the groundwater basin by expand-
ing recharge capacity. Since the 1950s, groundwater
production from the basin has increased by more
than 50 percent (Figure 4). As periods of drought or
deluge have occurred historically, the basin has been
operated as a reservoir to withdraw or store water.
OCWD established a basin operating range based on
historical experience and observations, e.g., seawater
intrusion or shallow groundwater levels, such that if
groundwater storage approaches the low end of the
range, OCWD has the authority to provide nancial
incentives to well operators to reduce groundwater
pumping and shift more of their supply to imported
water. Alternatively, as the volume of groundwater in
storage approaches the high end of the range, OCWD
can allow groundwater pumping to increase (Sovich
and Herndon, 2007). Figure 5 illustrates the cycles
over the last 40+ years of increasing and decreasing
the volume of groundwater stored in the basin, de-
pending on water availability, e.g., drought.
Hydrogeologic Setting
The Orange County groundwater basin formed in a
synclinal, northwest-trending trough that deepens as
it continues beyond the Orange-Los Angeles county
line. The Newport-Inglewood fault zone, San Joaquin
Hills, Coyote Hills, and Santa Ana Mountains form the
uplifted margins of the syncline. The total thickness
of sedimentary rocks in the basin surpasses 6,000 m
(20,000 ft), of which only the upper 600 to 1,200 m
(2,000 to 4,000 ft) contain fresh water. In the southeas-
tern area underlying the city of Irvine and along the
Figure 3. Groundwater accounts for two-thirds of the total water
needs within OCWD and is supplied by 200 production wells.
Figura 3. El agua subterránea aporta las dos terceras partes de la
demanda del OCWD, y es suministrada mediante 200 pozos de
bombeo.
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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
basin margins, the thickness of fresh water-bearing
sediments is less than 300 m (1,000 ft) (Herndon and
Bonsangue, 2006).
Structural folding and faulting along the basin
margins, together with downwarping and deposition
within the basin have occurred since Oligocene time.
The Newport-Inglewood fault zone, comprising the
most signicant structural feature in the basin from
a hydrogeologic standpoint, consists of a series of
faulted blocks which are generally up thrown on the
southwest side. Folding and faulting along the New-
port-Inglewood fault zone have created a natural re-
striction to seawater intrusion into the groundwater
basin (Herndon and Bonsangue, 2006).
Pleistocene or younger aquifers within the basin
form a complex series of interconnected sand and
gravel deposits. In coastal and central portions of
the basin, these deposits are extensively separated
by lower-permeability clay and silt deposits or aqui-
tards. In the inland areas, the clay and silt deposits
become thinner and more discontinuous, allowing
larger quantities of groundwater to ow more easily
between shallow and deeper aquifers (California De-
partment of Water Resources, 1967).
OCWD subdivided the groundwater basin into
three major aquifer systems based on vertical po-
tentiometric head differences measured regionally at
over 50 multi-depth monitoring wells. The three aq-
uifer systems, known as the Shallow, Principal, and
Deep, are hydraulically connected, as groundwater is
able to ow between them via leakage through the in-
tervening aquitards or discontinuities in the aquitards
(Figure 6). Over 90 percent of groundwater production
occurs from wells that are screened within the Princi-
pal aquifer system at depths between 60 and 400 m
(200 and 1,300 ft).
Figure 4. Groundwater production has increased since the 1950s
with the expansion of OCWD’s recharge facilities and increased re-
charge water supplies.
Figura 4. La producción de agua subterránea se ha incrementado des-
de la década de 1950 gracias al mayor número de instalaciones de
recarga del OCWD, así como a un mayor volúmen de agua recargada.
Figure 5. Groundwater storage varies depending on water supply
availability and precipitation, but is maintained within an accepta-
ble operating range.
Figura 5. El almacenamiento de agua subterránea varía dependien-
do de la disponibilidad de agua y de la precipitación, pero se man-
tiene dentro de un rango de operación aceptable.
Figure 6. Three hydraulically-connected major aqui-
fer systems form the conceptual hydrogeologic mo-
del of the Orange County groundwater basin.
Figura 6. El modelo hidrogeológico conceptual de la
cuenca subterránea del Condado de Orange lo for-
man 3 acuíferos principales conectados hidráulica-
mente.
150
Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
Seawater Intrusion Control
Incursion of saline ocean waters into Orange Coun-
ty coastal aquifers has been documented since the
1930s, several decades after the rst groundwater
production wells were constructed for agricultural
irrigation (Poland and Sinnott, 1959; California De-
partment of Water Resources,1966). Because of its
detrimental impacts to groundwater quality, seawa-
ter intrusion has been a major factor governing the
amount of groundwater that can be reliably pumped
from the Orange County groundwater basin.
Between 1953 and 1975, four seawater intrusion
barriers were constructed along coastal southern
California in Los Angeles and Orange counties. These
barriers consist of a series of wells that inject fresh
water to create a pressurized subsurface hydraulic
“mound” or “ridge” that prevents the inland ow of
saline groundwater within the affected aquifers. All
four barriers are currently supplied by at least 50 per-
cent advanced treated recycled water, the remaining
portion supplied by imported water.
OCWD’s Talbert Seawater Barrier has been in op-
eration since 1976 and was originally supplied with a
blend of deep groundwater and recycled water from
Water Factory 21, which was the rst project in Califor-
nia that was permitted to inject highly-treated waste-
water into a potable-supply aquifer (Figure 7). The
original barrier consisted of 23 multi-depth injection
well sites with 81 individual casings ranging in depth
from approximately 30 to 120 m (100 to 400 ft) and
had a total operating capacity of about 40 m
3
/min (15
mgal/day). Hydrogeologic studies found that seawa-
ter is able to intrude into folded deeper aquifers due
to their hydraulic connection with the younger, over-
lying Talbert Aquifer that is in direct contact with the
Pacic Ocean. The areas of hydraulic connection are
referred to as “aquifer mergence zones” (California
Department of Water Resources, 1966). The deeper aq-
uifers are heavily pumped by inland production wells,
thereby creating strong lateral and vertical hydraulic
gradients toward the wells (Figure 8). The Main Aqui-
fer is protected against seawater intrusion, because it
is hydraulically separated from the Talbert Aquifer and
is offset by the Newport-Inglewood fault zone, which
largely acts as an effective hydraulic barrier, based on
the lack of evidence of increasing salinity in the Main
Aquifer.
By the 1990s, increased production of groundwater
caused coastal aquifer groundwater elevations to de-
cline below sea level, thus exceeding the Talbert Bar-
rier’s ability to prevent seawater intrusion. Chloride
concentrations in groundwater, an excellent indicator
of saline intrusion, also showed increases progress-
ing inland and beginning to “ank” around both ends
of the barrier (Figure 9). Based on these observations,
OCWD began investigations to expand the seawater
barrier injection well system to reverse the seawater
intrusion. A numerical groundwater ow model was
developed, calibrated, and used to determine the lo-
cations and ow rates of additional injection wells
(Camp Dresser & McKee, 2000). Ultimately, using as-
sumptions of anticipated future groundwater produc-
tion, it was determined that the average barrier injec-
Figure 7. OCWD’s Talbert Seawater Barrier injects 42 million m
3
/yr
(34,000 acre-ft/yr) of recycled water, most of which ows inland to
replenish the groundwater basin.
Figura 7. La barrera Tablbert contra la intrusión, del OCWD, inyecta
42 hm
3
/año de agua reciclada, la mayor parte de la cual se mueve
hacia el interior y recarga la cuenca subterránea.
151
Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
tion rate would need to double to 80 m
3
/min (30 mgal/
day). Observed cyclical groundwater level changes
based on seasonal pumping patterns dictated the
need for higher injection in the summer/fall months
of heaviest pumping and signicantly less injection in
the winter/spring months of lowest pumping. Based
on these seasonal patterns, the model simulations
indicated that the barrier should inject up to 107 m
3
/
min (40 mgal/day) during the summer/fall months and
only one-half that rate in the winter/spring months.
The model simulation results turned out to be amaz-
ingly accurate based on subsequent operational ex-
perience.
To increase injection capacity, 13 new injection well
sites, comprising 28 individual multi-depth casings,
were constructed between 1998 and 2006 at the west
and east ends of the original barrier as well as to the
south (Figure 9). As with the original injection wells,
the new wells were screened in several aquifers that
are susceptible to seawater intrusion; however, eight
of the new wells were constructed into the deeper
Main Aquifer for the sole purpose of aquifer recharge,
as it was explained previously that this aquifer is not
impacted by seawater intrusion. Each well casing was
installed in a separate borehole with a cement-ben-
tonite annular seal above the well screen to reduce
the potential for leakage of pressurized injection wa-
ter within the annulus. Specications for the new in-
jection wells included 30.5-cm (12-in) diameter Type
316L stainless steel casing and wire-wrapped screen.
Each new well is equipped with pressure-reducing
valves and ow meters at the wellhead, down-hole
Figure 8. Injection wells maintain a “pressure mound” in multiple
aquifers to counteract the hydraulic gradient that drives seawater
intrusion toward production wells.
Figura 8. Los pozos de inyección mantienen la “presión en el domo
de recarga” en múltiples acuíferos, para contrarrestar el gradien-
te hidráulico en función del cual la intrusión marina penetra en el
acuífero.
Figure 9. OCWD doubled the capacity of the Talbert Seawater Ba-
rrier by constructing 28 new injection wells to reverse inland migra-
tion of saline groundwater.
Figura 9. OCWD ha doblado la capacidad de la barrera contra la in-
trusión Talbert construyendo 28 nuevos sondeos de inyección cuyo
objetivo es revertir la entrada de agua del mar hacia el interior del
acuífero.
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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
pneumatic ow-control valves to maintain a full col-
umn of water (prevents injection of air if well is turned
off and put back on-line), and telemetry. The telemetry
system monitors and transmits water level/pressure
and ow data to the central operations data manage-
ment system for performance tracking.
Typical operational ow rates of the older, original
injection well casings range from 0.2 to 1.1 m
3
/min
(50 to 300 gal/min). Typical ow rates of the newer
injection wells range from 0.8 to 4.5 m
3
/min (200 to
1,200 gal/min). The difference in the ow rates be-
tween older and newer wells is likely a function of the
age, smaller diameter (15 cm/6 in), and shorter screen
length of the older wells relative to the newer wells.
Injection well redevelopment and back-ushing
are performed periodically to remove accumulated
ne particulate materials from the well screens and
surrounding annular gravel pack and thereby restore
injection capacity (Burris, 2012). Redevelopment of
the older injection wells is typically performed every
other year and consists of air-lift pumping and surg-
ing, which requires the disassembly and reassembly
of the wellhead piping. More frequent redevelopment
of the older injection wells would be preferable; how-
ever, the labor and mobilization of well development
equipment is time-consuming and costly and, thus,
must be considered when determining an accept-
able frequency (Figure 10). The newer injection wells
are equipped with 10-cm (4-in) diameter “sound-
ing” tubes that join the blank well casing above the
screen. OCWD staff use a mobile air compressor to
air-lift pump the injection wells through the sounding
tubes on an approximate monthly basis. No wellhead
disassembly is required, so this process can be ac-
complished quickly and more frequently to maximize
injection well performance by minimizing the effects
of clogging.
Recycled Water – A Reliable Local Water Supply
Supplying water to the Talbert Seawater Barrier was
the original impetus for the development of recycled
water treatment facilities in Orange County in the late
1960s and early 1970s. At that time, access to impor-
ted water to the future injection wells would have re-
quired the construction of a costly pipeline to connect
to the nearest major imported water feeder pipeline.
In addition, the use of imported water for barrier in-
jection would have created a long-term dependency
on water sources that are hundreds of miles away.
Considering these issues, OCWD made the bold and
innovative decision to pursue advanced treatment of
secondary-treated efuent from the Orange County
Sanitation District (OCSD) that was being discharged
to the ocean. California’s Department of Public Health
and Regional Water Quality Control Board permitted
Water Factory 21 as the rst research and demons-
tration project to treat and inject wastewater into a
drinking water aquifer. Water Factory 21’s treatment
processes included lime clarication, multimedia l-
tration, and either carbon adsorption and chlorination
or reverse osmosis. The recycled product water was
blended with deep aquifer water and/or imported wa-
ter so that the wastewater component never excee-
ded two-thirds of the total blend prior to injection. To
make way for the expanded recycled water treatment
facility, Water Factory 21 was demolished in 2004.
The successes and lessons learned from over 25
years of operation of Water Factory 21 and the Talbert
Figure 10. Redevelopment of the older injection wells requires heavy equipment and more time (left photo), whereas air-lift pumping of the
newer injection wells can be done quickly using a mobile air compressor and dedicated sounding tubes (right photo).
Figure 10. El re-desarrollo de los viejos sondeos de inyección requiere equipos pesados y más tiempo (foto de la izquierda), mientras que
el bombeo mediante air-lift en los sondeos nuevos se puede hacer rápidamente utilizando un compresor de aire comprimido portátil y
tubos (foto derecha).
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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
Barrier laid the foundation for planning of a much larg-
er advanced treated water recycling facility to supply
the expanded seawater barrier as well as inltration
basins 13 miles inland. As OCWD was considering
the need for a larger water supply to the expanded
seawater barrier, OCSD (a separate governmental
agency responsible for the collection, treatment, and
disposal of sewage) was facing the prospect of con-
structing a larger ocean outfall pipe to accommodate
larger volumes of treated sewage disposal resulting
from projected population growth. The ocean outfall
pipe would have cost approximately $200 million and
would have been subject to substantial environmen-
tal review and potential opposition by coastal envi-
ronmental groups. In a wonderful example of inter-
agency partnership, OCWD and OCSD found a com-
mon solution to their respective needs – the Ground-
water Replenishment System (GWR System). A joint
funding agreement was signed in 1997, wherein OCSD
agreed to supply secondary-treated efuent to OCWD,
and the $481 million in total project construction costs
would be shared between the two agencies.
The GWR System was initially sized to produce 187
m
3
/min (70 mgal/day) of advanced treated recycled
water. This rate of production was sufcient to sup-
ply all of the seawater barrier injection water, deliver
an additional 107 m
3
/min (40 mgal/day) to OCWD’s
inltration basins, and postpone OCSD’s need to
construct a larger ocean outfall pipe (Figure 11). Ear-
ly in the project design, microltration was identied
as a cost-effective alternative to lime clarication
and conventional ltration pre-treatment prior to re-
verse osmosis. Several microltration systems were
pilot tested by OCWD for several years beginning in
1995. After microltration, the next step in the treat-
ment process is reverse osmosis, followed by ad-
vanced oxidation consisting of ultraviolet light and
hydrogen peroxide. Pilot testing of these processes
together demonstrated that this technology could
purify wastewater to near-distilled quality. Because
the treatment process, reverse osmosis in particular,
removes nearly all minerals from the water, lime is
added back to the product water in order to stabilize
it prior to conveyance to the recharge facilities (Figure
12). The nal product water has a total dissolved sol-
ids (TDS) concentration of approximately 45 mg/L
(Burris, 2012). This compares favorably to the TDS
concentrations of imported water and Santa Ana Riv-
er water, approximately 500 and 600 mg/L, respec-
tively. The GWR System water also exceeds all other
state and federal drinking water standards, making it
the highest quality recharge water available.
One of the biggest potential challenges in bringing
the GWR System to fruition was obtaining public ac-
ceptance and support. Although OCWD had an estab-
lished track record of performance over 25 years with
Water Factory 21, implementation of a recycled water
recharge project on such an unprecedented scale war-
ranted an aggressive public outreach program. Over
1,000 presentations were made to dozens of commu-
Figure 11. The GWR System provides approximately one-fourth of
the total recharge to the Orange County groundwater basin. The
highly-treated recycled water is recharged via seawater barrier in-
jection wells and surface inltration basins.
Figura 11. El sistema GWR aporta aproximadamente una cuarta
parte del total de agua que se recarga en la cuenca subterránea
del Condado de Orange. El agua reciclada, con un alto grado de
tratamiento, se recarga a través de la barrera contra la intrusión y
también mediante balsas.
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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
nity organizations, elected ofcials, regulatory agen-
cies, business groups, scientists and academicians,
health care professionals, educators, and environ-
mental groups. In addition, the project is overseen by
an independent advisory panel that provides on-go-
ing periodic scientic peer review of the project oper-
ations and performance. The result of this concerted,
multi-year educational campaign was overwhelming
public support for the GWR System, including over
$92 million in local, state, and federal grant funding
as well as $85 million in operational subsidies from
the Metropolitan Water District of Southern California
because the project reduces dependence on imported
water supplies.
Now in its sixth year of operation, the GWR Sys-
tem has produced and recharged over 370 million m
3
(300,000 acre-ft) of high-quality water, which is equal
to the annual amount of groundwater pumped from
the basin. In 2009-10, the unit cost of producing wa-
ter from the GWR System, including amortized capital
and operation and maintenance costs, was $0.72/m
3
($887/acre-ft) excluding all subsidies. This cost is less
than that of imported water, demonstrating the pro-
ject’s economic viability.
A key issue that OCWD faced soon after project
start-up was the need to modify the facility opera-
tion to account for diurnal uctuations in the supply
of secondary efuent from OCSD. The GWR System
had to be run at higher ows during the day and low-
er ows at night to coincide with efuent availabil-
ity. This operation was not anticipated during project
design, but it was accommodated successfully by
OCWD operations staff. The facility is operated such
that the demand of the seawater barrier injection
wells is met rst, and the remainder of the product
water is conveyed to the inltration basins. This pro-
cedure is followed because it is difcult to constantly
raise and lower ows to a series of highly-metered
and controlled injection wells which are best oper-
ated at a generally constant pressure.
Another nding after operating the project for sev-
eral months is that the injection wells continue to
clog and require regular redevelopment. By install-
ing and visually monitoring cartridge lters at dif-
ferent locations along the barrier injection system,
OCWD staff discovered that very ne particulates
were being conveyed and deposited on the lters,
which also meant that these particulates were being
delivered to the injection well screens and surround-
ing gravel pack. Staff analyzed the particles and
found that they are predominantly composed of cal-
cium carbonate, iron oxide, and aluminum silicate.
Current hypotheses for the sources of these parti-
cles are: 1) undissolved lime that is added after the
treatment processes, 2) impurities in the lime, and
3) dissolution or erosion of the mortar lining of the
barrier supply pipeline. While OCWD staff continues
to investigate these issues, it has found that regular
redevelopment and back-ushing are successful in
removing particulate matter and restoring and main-
taining injection well capacity.
Building upon the successful rst phase implementa-
tion of the GWR System, OCWD has embarked upon
an expansion of the project to add 80 m
3
/min (30 mgal/
day) of treatment capacity. The expansion will cost ap-
proximately $143 million and provide enough additio-
nal recharge water to the groundwater basin to meet
the needs of 250,000 Orange County residents each
year. In order to utilize nearly all remaining available
secondary efuent from OCSD, the expansion inclu-
des the construction of two large reservoirs to store
and balance the diurnal efuent ows from OCSD.
Construction is scheduled to be completed in 2015.
Further details of the GWR System and its on-going
expansion can be found at: http://www.gwrsystem.
com/about-gwrs.html
Figure 12. The GWR System’s state-of-the-art multi-stage treatment
process removes or destroys pathogens, nutrients, metals, phar-
maceuticals, and trace organic compounds such as 1,4-dioxane and
N-nitrosodimethylamine.
Figura 12. El estado del arte del tratamiento multiproceso que se
lleva a cabo en el sistema GWR muestra la desaparición o destruc-
ción de patógenos, nutrientes, metales, productos farmacéuticos
y compuestos orgánicos traza, como el 1,4-dioxano y el N-nitroso-
diometilamina.
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Herndon, R. and Markus, M. 2014. Large-Scale Aquifer Replenishment and Seawater… Boletín Geológico y Minero, 125 (2): 143-155
Conclusions
Coastal groundwater basins in southern California
have been threatened by seawater intrusion since
they began to be heavily utilized over 100 years ago.
Seawater intrusion barriers, consisting of injection
wells, have protected the coastal basins; however
they require a continuous supply of potable-quality
water. As imported water, the traditional supply to
the barriers, has become a threatened and more ex-
pensive source of water, water management agencies
such as OCWD have developed their own sources of
highly-treated recycled water. Following in the foots-
teps of Water Factory 21, OCWD’s GWR System gua-
rantees Orange County a reliable, drought-resistant,
locally-controlled supply of water of the highest qua-
lity, and reduces southern California’s reliance on wa-
ter supplies from northern California and the Colora-
do River. Additionally, producing GWR System water
costs less than and uses one-half the energy of impor-
ted water. Prior to the GWR System, water/wastewa-
ter agencies treated wastewater to tertiary levels for
non-potable uses such as landscape and agriculture.
In an era of distrust in government, OCWD and OCSD
successfully partnered to build a potentially contro-
versial water project that garnered overwhelming
public support and overcame the “toilet to tap” mis-
perception. The GWR System has revolutionized how
consumers look at wastewater – as a valuable resour-
ce they should take care of and reuse.
Acknowledgements
The authors wish to thank Mr. José Antonio de la Or-
den Gómez and the Instituto Geológico y Minero de
España (IGME) for inviting and making it possible for
Mr. Herndon to present the subject of this paper at the
International Water Resources Association Workshop
on Articial Recharge for Groundwater Management
in Palma de Mallorca, Spain, on October 20-23, 2009.
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Recibido: mayo 2013
Revisado: agosto 2013
Aceptado: agosto 2013
Publicado: junio 2014
