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.

Figure 2. Project Study Area

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.