Case Studies of 1,4-Dioxane Releases, Treatment, and Drinking Water Contamination - Environmental Investigation and Remediation - page 400

presence of 1,4-dioxane as an impurity of surfactants in household sundries such as shampoos and
liquid detergents. This study provides a cautionary tale for planners of recycled water projects and
shows why it is important to test for and consider 1,4-dioxane when designing advanced wastewater
treatment projects. This case study is also a success story: OCWD is the gold-standard bearer for
recycled water projects and is the destination for engineers from across the globe to learn about
successfully transforming wastewater into a valuable water resource.
8.6.1 H ISTORY OF THE O RANGE C OUNTY W ATER D ISTRICT G ROUNDWATER
R EPLENISHMENT S YSTEM
OCWD was formed in 1933 to manage water supply and groundwater in a 360-square-mile area in
the lower Santa Ana River watershed, covering much of Orange County on the southern California
coast. OCWD is the water provider to about 2.3 million people in more than 20 cities, including
Newport Beach, Huntington Beach, and Seal Beach on the coast, Cypress and Fullerton on the
northern end, Anaheim and Yorba Linda to the east, and Santa Ana and Irvine to the south. The
groundwater basin is a 3000-ft-thick wedge of alluvium overlying bedrock formations; water sup-
ply wells extend as deep as 1000 ft. Under normal operating conditions, groundwater is the resource
for about 70% of the water provided by OCWD (Deshmukh, 2007). The alluvial basins are vulner-
able to seawater intrusion at several “gaps” where bedrock has been eroded by rivers to leave a
direct alluvial aquifer interconnection between the main groundwater basin and the Pacii c Ocean.
The 2.5-mile-wide Talbert Gap between the Newport and Huntington Mesas presents the greatest
seawater intrusion challenge to groundwater-basin operations in Orange County (OCWD, 2004).
To sustain the groundwater basin and prevent overdraft while managing seawater intrusion,
OCWD actively recharges the groundwater basin, primarily with water from the Santa Ana River
and to a lesser extent with imported water. Percolation ponds introduce water into the groundwater
basin in the upland cities of Anaheim and Orange. OCWD operates one of the oldest and most
sophisticated conjunctive use and groundwater protection programs in the world, sampling more
than 700 wells to collect more than 13,000 water samples and conduct more than 300,000 ground-
water analyses every year. The OCWD monitoring program analyzes more than 300 constituents,
including emerging contaminants beyond regulatory requirements (Yamachika, 2007).
Between 1945 and 1969, the basin went into overdraft because of increased pumping and pro-
longed drought conditions with only two intervening wet years during these three decades. An annual
overdraft of 100,000 acre-feet brought the water table to 15 ft below sea level, leading to seawater
intrusion into some aquifers; coastal wells soon began producing brackish water and had to be aban-
doned. OCWD increased its artii cial recharge using Santa Ana River water and, beginning in 1948,
water imported from the Colorado River. To pay for the imported water, OCWD assessed a pump tax
on all producers of groundwater and began the long-term process of replenishing the overdrafted
groundwater basin. By 1956, Orange County's population was booming, and the water level dropped
further; the cumulative overdraft grew to 700,000 acre-feet, and salt water invaded aquifers as much
as 5 miles inland. By 1964, the replenishment program caught up with extraction and began rei lling
the basin. During this timeframe, the Santa Ana River became increasingly unreliable as a source of
replenishment water. In the face of increasingly expensive imported water and less reliable local
surface water, OCWD turned to reclaimed wastewater, that is, recycled water (OCWD, 2008).
In 1965, OCWD began a pilot project to inject treated wastewater to create a hydraulic barrier to
seawater intrusion along the Talbert Gap in Huntington Beach. In 1971, ofi cials of the California
Department of Health Services approved a full-scale project after reviewing data from the pilot
project. OCWD drilled a series of 23 multipoint injection wells distributed across the 2.5-mile-wide
Talbert Gap. Construction on an advanced wastewater treatment system called Water Factory 21
began in 1972. Full-scale operation of the project started in 1976 (OCWD, 1996).
Water Factory 21 was dedicated in a 1977 ceremony that included serving punch made with
reclaimed water. The plant was very successful and won international acclaim. By 1991, OCWD