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Transcript of Oxnard California s Groundwater Recovery … CALIFORNIA’S GROUNDWATER RECOVERY ENHANCEMENT AND...
OXNARD CALIFORNIA’S GROUNDWATER RECOVERY ENHANCEMENT
AND TREATMENT (GREAT) PROGRAM
Mary Vorissis, CH2M HILL, Thousand Oaks, CA
Jim Lozier, CH2M HILL, Phoenix, AZ
Paul Franks, CH2M HILL, Oakland, CA
Ken Ortega, Public Works Director, Oxnard, CA
Anthony Emmert, Water Resources Manager, Oxnard CA
Introduction
The City of Oxnard is a coastal community located in western Ventura County. The surrounding area,
known as the Oxnard Plain, supports a broad variety of land uses including agricultural, municipal, and
industrial. The Oxnard Plain is located approximately 60 miles northwest of downtown Los Angeles and
35 miles south of Santa Barbara.
As part of its water resources master planning process, The City of Oxnard, the largest municipality on
the Oxnard Plain, determined that additional, alternative water supply sources should be developed to
continue meeting the City’s goal of providing current and future residents and businesses with a reliable
and affordable source of high-quality water. Limitations on both the City’s local groundwater and
imported water sources, plus the increased cost of imported water, prompted the City to conduct an
advanced planning study of alternative water supply sources. The study resulted in the development of
the Groundwater Recovery Enhancement and Treatment (GREAT) Program, a water resources project
that combines wastewater recycling and reuse, groundwater injection, storage and recovery, and
groundwater desalination. The GREAT Program provides regional water supply solutions to water users
in the Oxnard Plain.
Project Drivers
Water supplied to the City of Oxnard comes from three sources; imported water from Northern
California, local ground water purchased from United Water Conservation District (UWCD) and local
groundwater pumped from City wells. These current water supply sources are insufficient to meet the
City’s growing demand and have limitations with respect to costs and reliability. In addition to the
increasing demand for water, there is also a need to manage the water resources in the Oxnard Plain due
to environmental impacts. Water users in the southern Oxnard Plain have relied on groundwater wells
mainly for irrigation of crops. Over time, groundwater recharge has not kept up with the rate of
withdrawal resulting in a water imbalance condition.
Since two sources of the City’s water supply are groundwater from the Oxnard Plain, the local
hydrogeology and history of groundwater use must be understood to comprehend the limitations of the
area groundwater sources.
Two regional aquifer systems occur beneath the Oxnard Plain and Pleasant Valley areas: the Upper
Aquifer System (UAS) and the Lower Aquifer System (LAS). These confined aquifer systems are
heavily used for regional water supply and are overlain by the Semi-Parched aquifer, an unconfined
water table aquifer that is not used for water supply because of its lower yield and poor water quality.
The UAS extends to a depth of approximately 400 feet and consists of the Oxnard and Mugu aquifers.
The LAS extends to a depth of approximately 1,600 feet and consists of the Hueneme, Fox Canyon, and
Grimes Canyon aquifers. Low-permeability aquitards occur between the individual aquifers of the UAS
and LAS. Except in the Oxnard Forebay, a clay cap overlies the UAS, which supports the Semi-Parched
aquifer. The clay cap and Semi-Parched aquifer are absent in the Oxnard Forebay.
Today, most recharge to the regional aquifer system occurs from artificial recharge performed by
UWCD in the Oxnard Forebay at the Saticoy and El Rio spreading grounds from Santa Clara River
surface water diversions (surface spreading). Historical over pumping of the UAS and LAS resulted in
groundwater levels depressed below sea level, coastal seawater intrusion, and land subsidence of up to
approximately 3 feet in some areas. Increased artificial recharge in the 1990s by UWCD has largely
mitigated the water imbalance conditions in the UAS and has begun to push back the intruded seawater
toward the ocean. The imbalance conditions continue in the LAS because the hydraulic connection from
the spreading ground area in the Oxnard Forebay to the underlying LAS is poor due to intervening
aquitards and a regional low-permeability zone separating the area of the Oxnard Forebay and the
southern Oxnard Plain in the LAS.
The Fox Canyon Groundwater Management Agency (FCGMA) was established in 1983 to manage the
groundwater basin. In an effort to manage the basin, FCGMA established allocations for water users and
developed a schedule to reduce the allocations over a 25-year period to reduce groundwater pumping to
a “safe yield” by 2010 (Fox Canyon Groundwater Management Agency Management Plan adopted in
May 2006). As a result, the impacts to Oxnard of increasing the groundwater supply from the present
sources could be significant because of special fees assessed by FCGMA to users who pump more than
their allocated quantity.
Like groundwater, imported water supplies from Northern California are limited, and supplies that
exceed current deliveries are expected to be increasingly costly in the future. Oxnard purchases imported
water from Calleguas Municipal Water District (CMWD). The CMWD supplies treated water from the
Metropolitan Water District of Southern California (MWD) at a contracted rate (Tier 1). Dependent
upon the volume purchased, a Tier 2 rate exists that is about 14% more expensive that Tier 1 and may
not be available in all years depending on drought conditions in the State. In addition, the all rates for
imported water are expected to increase. Thus, the future water rates for users in the Oxnard Plain are
unpredictable. Likewise, the reliability of the imported water source is uncertain. The imported water
comes from the Sacramento-San Joaquin Delta and environmental groups and other shareholders have
been active in protecting the Bay-Delta ecosystem. As a result, a long- term solution developed to
protect the Bay includes a reduction of water exports in average rainfall years with further reductions
during drought years. Also, water deliveries to Southern California could be seriously disrupted in the
event of an earthquake or failure of delta levees due to erosion, seepage and/or land subsidence
(California Department of Water Resources, The State Water Project Delivery Reliability Report 2007,
Draft).
Innovative Approaches
The GREAT Program is an innovative approach to managing water resources in the Oxnard Plain. It
provides a holistic solution to area’s water resource issues by focusing on water reuse, groundwater
recharge, potable water supply, wetland restoration and public education.
Water Reuse and Groundwater Recharge Treated effluent from the Oxnard Wastewater Treatment Plant (OWTP) is discharged directly to the
City-permitted deep ocean outfall and this discharge currently does not contribute to the benefit of the
region’s water resources. Reclaiming this lost resource is the foundation of the GREAT Program. The
Advanced Water Purification Facility (AWPF) provides further treatment of the secondary effluent from
the OWTP. The AWPF, currently under design by CH2M HILL, employs a multiple barrier treatment
train consisting of microfiltration/ultrafiltration (MF/UF), reverse osmosis (RO), and ultraviolet (UV)-
light-based advanced oxidation (AOX) processes to purify the secondary effluent as required to conform
to CA Department of Public Health (DPH) “Title 22” Recycled Water criteria for groundwater recharge.
By treating all recycled water to the most stringent criteria (groundwater recharge criteria), the City has
the flexibility to deliver recycled water for unrestricted reuse as well as groundwater injection. Also, the
production of a single water quality allows the City to create one distribution network to serve multiple
users and the injection wells.
The AWPF will be constructed along Perkins Road in the vicinity of the OWTP. Figure 1 shows a
schematic of the AWPF treatment process.
Figure 1. Schematic of AWPF Process
The main treatment processes of the AWPF are summarized in the following paragraphs.
The MF system is a low-pressure filtration process that is typically applied for the removal of particulate
and microbial contaminants, including turbidity, Giardia, and Cryptosporidium. As filtration occurs, the
accumulation of solids on the membrane surface increases the resistance to flow through the membrane.
The filtration process then stops for a membrane backwash. Membrane backwash time is generally
between 1 and 3 minutes, and is achieved by reversing the flow through the membrane to remove the
solids accumulation from the membrane surface. Intermittent backwash or backpulse procedures are not
100 percent effective at removing particulates and foulants that accumulate on the membrane
surface. For this reason, a chemical cleaning (i.e., clean-in-place) process is also needed. Typical design
practice is to design and operate the MF/UF system such that the chemical cleaning interval is 30 days
or greater. A chemical feed system continuously doses hypochlorite to the MF/UF system feedwater to
form chloramines (1.5 to 2.0 mg/L combined chlorine), which will minimize microbiological fouling. A
filtrate tank collects filtered flow (i.e., filtrate) from the MF/UF units. The filtrate tank has a dual
function: to provide water during cleaning cycles and to continuously feed the downstream RO system
by minimizing the flow fluctuations.
RO is a pressure-driven membrane-separation process that removes dissolved contaminants (i.e., TDS,
organic compounds) from water. Filtered water will continuously be pumped at elevated pressure to the
RO system by a set of high-pressure feed pumps. The required feed pressure varies depending on the
TDS of the feedwater (i.e., osmotic potential), as well as membrane properties and temperature. RO feed
pumps are equipped with variable frequency drives (VFDs) to allow constant flux operation. The RO
system will be designed for a finished water production capacity of 6.25 mgd for the AWPF Phase 1,
and 25 mgd for Phase 2. It will have three stages to allow water recovery of 80 to 85 percent, where
concentrate from the first stage will be applied to a second stage, and concentrate from the second stage
will be applied to a third stage. Permeate from the three stages will be blended into a final product water
and will constitute the feedwater to the UV/AOX system. Similar to the MF/UF system, the membranes
will foul with accumulation of particulates. Chemicals are used to routinely clean the membranes
therefore, a chemical system is necessary.
The UV/AOX process is used for both disinfection and advanced oxidation and reduction of
micropollutants at the AWPF. Reclaimed water destined for groundwater recharge, and agricultural and
landscape irrigation will normally undergo UV/AOX treatment at all times. However, in those instances
when only UV light disinfection is required, the AWPF will have the capability to apply a lower UV
dose required for disinfection of water for “unrestricted reuse,” also referred to as “disinfected tertiary
recycled water” or “Title 22 reclaimed water,” as defined by the CDPH.
The post-treatment systems include decarbonator towers and liquid lime injection downstream of the
UV/AOX process. Following UV/AOX, the water quality is projected to be very aggressive with an LSI
in the range of -3.3 to -2.5; also, the water will have high concentrations of carbon dioxide, up to
50 mg/L. Lime is needed to increase the pH and achieve an LSI of +2. A portion of the carbon dioxide
must be removed to reduce the lime dose needed for stabilization. If the water is not stabilized, it will be
very corrosive and will not be suitable for recycled water uses or groundwater recharge. In order to
remove carbon dioxide, water is distributed over media packed in the decarbonator towers. Air flow
through the media strips the carbon dioxide and other volatile compounds. Liquid lime is then dosed to
add calcium and alkalinity, thereby increasing the pH.
The finished water pump station pumps will provide the finished water to the groundwater
replenishment system and recycled water transmission lines. Initially, the finished water will supply
recycled water to local municipal and industrial users and several ASR wells. Ultimately, the finished
water system will have capability to serve M&I users, area agricultural users and groundwater injection
wells.
Potable Water Supply A large portion of the Oxnard Plain is cultivated and irrigated with groundwater pumped from private
wells as well as several developed piping and well systems. Figure 2 shows the existing water facilities
that could be considered for recycled water. If recycled water is delivered to the areas shown,
agricultural users would not need to pump groundwater from the LAS for irrigation. This would allow
groundwater levels to recover, which would help to reduce the regional effects of aquifer overdraft
conditions in this area. Recycled water used for irrigation would offset groundwater pumping for
irrigation and result in unused groundwater allocations that could be transferred from the growers to the
City.
In the winter, when agricultural irrigation demands are low, the recycled water would be recharged to
groundwater by direct injection into the LAS along the coastal areas of the southern Oxnard Plain. This
would cause a focused increase in groundwater levels along this coastal area, which would help to
reduce the effects of aquifer overdraft, especially seawater intrusion. In addition, this would result in
FCGMA storage credits to the City from groundwater injection.
Transferred groundwater allocations and the City storage credits gained by injecting recycled water
could be extracted for potable use at a combination of the City municipal wells and the UWCD wells.
These water supply wells are located on the northern Oxnard Plain and Oxnard Plain Forebay areas
(UAS) where groundwater levels are currently above sea level and the basin is more readily replenished.
The City currently blends local groundwater with imported water for potable use. The blending of water
sources is necessary to maintain TDS levels below 500 mg/l, thereby making the water more palatable to
local residents. Since additional potable water comes from groundwater sources, the GREAT Program
includes construction a regional brackish water desalting facility for removal of high TDS. The product
water form the desalting facility is blended with other groundwater sources to supply a consistent water
quality to the public.
Wetland Restoration The treatment process used in the AWPF produce a waste stream with high concentrations of salt and
other constituents. The potential to use this waste stream as a water resource to restore coastal wetlands
is being evaluated as part of the GREAT Program. A Pilot Wetlands Project, operated between 2003 and
2006, was a unique study that investigated the use of the following six natural treatment system
technologies to dispose of reverse osmosis concentrate while providing healthy wetland ecosystems:
• Surface flow (SF)
• High marsh (SFHM)
• SF low marsh (SFLM)
• Horizontal subsurface flow (SSF)
• Peat-based vertical upflow (VF)
• Submerged aquatic vegetation (SAV) systems.
At the conclusion of the study, it was observed that the systems did not accumulate salts or metals to a
degree that showed an adverse effect on the health of the plant communities. The results of this pilot-
scale work were used to design a demonstration wetlands system to accept membrane concentrate from
the GREAT Program AWPF. Ultimately, the City hopes to provide this water resource to restore and
maintain the Ormand Beach Wetland located on the Oxnard Plain.
Public Education Another concept in the GREAT Program is to create public friendly facilities that promote public
education of water resources. The AWPF and the desalting facilities are intended for public access to
view the treatment process. The process buildings include ramps and elevated walkways to promote
walking tours of the facilities. An innovative architectural design for a visitor’s center at the AWPF
includes interactive displays and an auditorium/assembly room. The Site for the AWPF is designed to
enable visitors to view the process equipment and stages of treatment as well as observe the
demonstration wetlands via pathways through the site.
Water Quality Challenges
The innovative nature of the GREAT Program has created challenges for the City. Some of the more
unique challenges are related to water quality associated with the AWPF and the associated
demonstration wetland.
AWPF Feed Water Quality The City of Oxnard wastewater treatment plant (OWTP) is a secondary, activated sludge treatment
system that is operated as designed for an average solids retention time (SRT) of approximately 2 days
to achieve biochemical oxygen demand (BOD) removal only. Low-SRT operation suppresses
nitrification, thereby causing a high ammonia concentration in plant effluent. Nonexistent nitrification
results in very minor changes in alkalinity during secondary treatment. In addition, low SRT operation
prevents oxidation of the slowly biodegradable organics, thereby contributing to relatively high organic
concentrations (dissolved organic carbon/total organic carbon [DOC/TOC]) in secondary effluent.
The quality of the effluent produced by the OWTP is based on sampling conducted over a 4-month
period in 2005 and 2006. The effluent is characterized by high levels of total and dissolved organic
carbon, inorganic ions (sulfate, chloride, sodium and total dissolved solids) and ammonia. Phosphorus
levels are only moderate due to the addition of ferric chloride at the headworks of the OWTP for odor
control. Ferric addition also aids in the coagulation of colloidal BOD in the raw wastewater.
The high levels of TOC and total nitrogen require a high level of removal of these constituents by the
RO process in order to meet the California Department of Public Health (CDPH) Title 22 Recycled
Water Regulations for groundwater recharge. To this end, bench testing was conducted during the
AWPF conceptual design phase to evaluate the use of in-line coagulation prior to MF in order to reduce
TOC loading on the MF and RO membranes and to decrease the MF fouling potential of the effluent.
The testing showed that marginal (<10%) TOC removal could be obtained with ferric chloride at a dose
of 30 mg/L (as product). The ferric addition improved MF filterability to a small degree and increased
projected flux rate by 10 percent. However, these improvements were not consider sufficient to justify
the space required for ferric bulk storage and feed systems as well as piping necessary to provide
sufficient contact to ensure complete ferric chloride hydrolysis and floc formation prior to the MF
system.
AWPF Finished Water Quality Finished water from Oxnard AWPF will be used for agricultural and landscape irrigation (during dry
seasons) and ground water recharge. In each case, the filtered and disinfected wastewater must meet
California’s Water Recycling Criteria, Title 22, Division 4, Chapter 3, of the California Code of
Regulations unrestricted reuse criteria summarized in Table 1.
Table 1. California Title 22 Requirements for Unrestricted Reuse
Turbidity1 ≤ 0.2 NTU, 95% of the time within 24 hr period
No higher than 0.5 NTU any time
Pathogens
Virus
Total Coliform
A chlorine disinfection process following filtration that provides a
CT (The product of combined chlorine residual and modal contact
time measured at the same point) value of not less than 450
milligram- minutes per liter at all times with a modal contact time
of at least 90 minutes, based on peak dry weather design flow; or
Minimum 5 log (99.999%) inactivation of MS-2 or Poliovirus
≤ 2.2 MPN/100 mL, at 7-day period
≤ 23 MPN/100 mL, in 30-day period
Does not exceed 240 MPN/100 mL any time
1 Applies filtration processes using membrane technology
In addition to the turbidity and disinfection requirements specified in Table 1, the treated wastewater must
meet federal and California Drinking Water Standards for inorganic, organic, disinfectants and disinfection
by products (DBPs) and CDPH notification (action) level chemicals according to Ground Water Recharge
Reuse Criteria (April, 1 2007).
The DPH draft requirements include the stipulation for projects that recharge the aquifer with more than
50 percent recycled water that AOX treatment must be provided (subsequent to any RO membrane
treatment provided) to achieve at least a 1.2 log10 reduction of NDMA and 0.5 log10 reduction of
1,4-dioxane. In March 2002, CDPH established an action level for NDMA of 0.01 µg/L in drinking
water.
Additional elements of the draft CDPH regulations for groundwater recharge reuse address injection and
extraction of the water, nitrogen concentrations (≤10 mg/L as total nitrogen at AWPF effluent), TOC
concentrations (≤1 mg/L at AWPF effluent), sampling, and reporting requirements. Of particular
interest, during the first year of operation, it is proposed that sampling and analyses include the
following:
• Quarterly: Unregulated chemicals, Priority Toxic Pollutants, chemicals with state notification levels,
and other chemicals that DPH has specified including n-nitrosodiethylamine (NDEA) and
n-nitrosopyrrolidine (NYPR).
• Annually: Pharmaceuticals, endocrine disrupting chemicals, and other chemical indicators of
municipal wastewater presence as specified by DPH based on a review of the engineering report and
the affected groundwater basin(s). Currently, DPH has listed the following for monitoring for
information purposes only:
− Hormones: Ethinyl estradiol, 17-B estradiol, estrone.
− “Industrial” endocrine-disrupting chemicals (EDCs): Bisphenol A, nonylphenol and nonylphenol
polyethoxylate, octylphenol and octylphenol polyethoxylate, polybrominated diphenyl ethers.
− Pharmaceuticals and other substances: Acetaminophen, amoxicillin, azithromycin, caffeine,
carbamazepine, ciprofloxacin, ethylenediamine tetra-acetic acid (EDTA), gemfibrozil, ibuprofen,
iodinated contrast media, lipitor, methadone, morphine, salicylic acid, and triclosan.
Demonstration Wetland Water Quality The RO process produces a concentrate that could be a valuable resource for maintaining coastal
wetlands. The Membrane Concentrate Pilot Wetlands Project (Project) was conducted between 2003 and
2006 by CH2M HILL and the City of Oxnard as part of a program to desalinate brackish local
groundwater for potable water service. The Project assessed the feasibility of using reverse osmosis
membrane concentrate to restore local coastal wetlands and investigated water quality effects of
different wetland types on contaminants present in the concentrate. The Project consisted of twelve 1 m2
wetland tanks with two replicates of six different wetland types, including both treatment and natural
marsh habitat systems.
Data from the pilot study indicated the following conclusions:
• Membrane concentrate supported healthy plant communities for over three years; deleterious effects
on plants were not observed.
• Both metals and nutrients were effectively removed in many of the wetland system types.
• Concentrations of key constituents such as nitrate and selenium decreased to levels at or below
toxicological thresholds in some wetland types.
• Due to significant evapotranspiration water losses through all wetland types, significant mass
removals were observed for virtually all chemical constituents including salts.
• Discharge from the wetlands was less toxic to indicator organisms than raw concentrate.
• Salts and other contaminants did not accumulate in plant tissues and sediments outside of ranges
found in natural ecosystems and it is expected that a full scale system would have a lifespan
comparable to other common natural treatment systems.
Table 2. Removal Rate Values During Phase 1 in Peat-based Vertical Flow Wetlands
Nutrient
Trace
Metals Salts
Parameter Units NO3 Se Fe TDS Chloride
Influent concentration mg/L 54.4 0.022 0.30 2350 274
Effluent concentration mg/L 9.5 0.007 0.05 2695 300
Percent reduction (concentration) % 83% 67% 82% -15% -10%
Mass removal g/m2/y 237 0.09 1.31 8068 953
Percent reduction (mass) % 96% 93% 96% 76% 77%
The best-performing wetland type was the peat-based, vertically flowing wetland system; this will be the
cornerstone of a larger scale demonstration wetland facility to be constructed in the near future. Results
from the Pilot Study have been used to design a larger scale demonstration system at the AWPF. The
demonstration wetlands will be 1.2 acres in size and treat a portion of the concentrate stream from the
AWPF.
Summary of GREAT Program Elements
Comprised of several elements, the major GREAT Program components include recycled water
treatment, potable water treatment, conveyance, and groundwater injection and consists of several
projects that will be constructed in two phases. The proposed projects under Phase 1 and Phase 2
Buildout are described below.
Phase 1
• Construction of an Advanced Water Purification Facility (AWPF) capable of delivering 6.25 million
gallons per day (mgd) of product water with quality suitable for groundwater injection, agricultural
irrigation, and other M&I recycled water applications.
• Construction of a demonstration wetland, at the AWPF site, and evaluate the use of waste
concentrate to preserve coastal wetlands.
• Construction of recycled water conveyance facilities including slip-lining of an abandoned trunk
sewer for M&I recycled water uses, and construction or modification of an existing pipeline to
injection well locations.
• Construction of a pilot aquifer storage and recovery (ASR) well, which is a dual purpose injection
and extraction well that is used to inject water into the basin and extract water from the same well,
and potentially three to five ASR wells.
• Construction of a 5.00 mgd Regional Desalter Facility that will be used to recover those created
groundwater credits from, 1) injection of recycled water and, 2) reduced pumping by agricultural
pumpers who use recycled water instead of pumping from the groundwater basin.
Phase 2–Buildout
• Expansion of the AWPF to deliver 25 mgd of product water with quality suitable for groundwater
injection, agricultural irrigation, and other M&I recycled water applications.
• Expansion of recycled water conveyance facilities to include piping to agricultural irrigation systems
in the southern Oxnard Plain and piping to ASR well locations.
• Construction of additional ASR wells to form a complete seawater intrusion barrier.
• Expansion of the Regional Desalter Facility to 10 mgd.
• Potential use of waste concentrate to preserve the Ormand Beach wetland on the Oxnard plain.
The culmination of projects that form the GREAT Program have unique aspects and some, such as the
AWPF and demonstration wetlands, are innovative solutions to water resource challenges faced by
many communities. However, it is the holistic nature of the GREAT Program that is its most notable
innovation. The approach to address water needs of a community by understanding natural recycling
that occurs within the water cycle and applying those principals to water resources planning is truly a
GREAT Program.