Building on Lesson Learned for Expanding the Next Phase of the

Groundwater Replenishment System

William Dunivin

1

*, Mehul Patel, P.E

1

. and James H. Clark, P.E.

2

1

Orange County Water District

2

Black & Veatch

*

January 2008. During the first two and a half years of operations numerous issues were

identified with the initial plant design. These issues served as “lessons learned” and were able to

be addressed in the first planned expansion of the existing facility. The solutions to these issues

are discussed in detail and can serve as guidance to other utilities considering implementation of

a large scale reclamation facility.

KEYWORDS:

Advanced Water Purification Facility, Microfiltration, Reverse Osmosis, Ultraviolet Light, Flow

Equalization, Lime Post Treatment, Decarbonation

INTRODUCTION

GWRS is a water supply project constructed by the Orange County Water District (OCWD) and

Project Overview

GWRS was put into operation in January 2008. Located in central Orange County, the project

extends from Huntington Beach, Fountain Valley, and Costa Mesa near the coast to Santa Ana,

Orange, and Anaheim generally along the Santa Ana River. The GWR System consists of three

major components: (1) AWPF and pumping stations; (2) a major pipeline connecting the

treatment facilities to existing recharge basins; and (3) expansion of an existing seawater

intrusion barrier. The locations of the main project components are shown on Figure 1.

Figure 1. GWRS map.

Advanced Water Purification Facility

Figure 2. AWPF Process Flow Diagram.

OCSD clarified secondary effluent, normally disposed to the ocean, first goes through a

screening process prior to MF membrane treatment. MF is a low-pressure membrane process

that removes suspended matter from water. MF specifically is used to separate suspended and

colloidal solids including bacteria and protozoa from the OCSD secondary effluent. Sodium

hypochlorite is added to the MF feedwater to minimize MF membrane fouling. MF filtrate is fed

to RO, and MF reject streams are returned to OCSD’s Plant No. 1 for treatment. MF has

demonstrated exceptional effectiveness as a pretreatment for RO. Based on a design recovery of

approximately 89 percent, 326 MLD (86 mgd) of filtrate is produced by MF. Excess filtrate is

sometimes used to supplement tertiary non-potable reuse.

permeate is then directed to UV treatment. The RO concentrate or brine is discharged into the

ocean via the existing OCSD ocean outfall. Based on a design recovery of approximately 85

percent, the production rate of RO is 265 MLD (70 mgd).

Following RO, the RO permeate undergoes UV treatment. UV treatment involves the use of UV

light to penetrate cell walls of microorganisms, preventing replication and inducing cell death.

UV thus provides additional bacterial and viral inactivation and, combined with RO treatment,

increases removal efficiency. With the addition of hydrogen peroxide, UV light and the

hydroxyl radicals oxidize organic compounds for ultimate removal from water. UV and

peroxide treatment are used for N-Nitrosodimethylamine (NDMA) and other low molecular

weight organics removal. UV product water then undergoes additional chemical treatment prior

available by OCSD's new Steve Anderson Lift Station (SALS). Although the SALS facility

originally was planned for nighttime operation to make up for flow depressions, OCSD now

intends 24 hour a day operation to increase the overall supply of treated wastewater. Knowing

the GWR System treatment facility can operate at various flows, the expansion can include

greater capacity to accommodate the higher flows available during the day. In addition, OCSD

is currently under construction to expand its secondary treatment processes, which is expected to

be completed in late 2011 to provide an increased flow of secondary treated water to AWPF.

This 114 MLD (30 mgd) expansion could result in a minimum average increase of

approximately 60 MLD (16 mgd or 18,000 acre-feet per year [afy]) of production from the GWR

System. Expansion of the GWR system is a viable option based on the current success of the

production of up to 304 MLD (80 mgd or 90,000 afy). In addition, flow equalization of

secondary effluent is being evaluated to maximize the production of the GWR System to the full

379 MLD (100 mgd or 112,000 afy).

The OCWD Water Production Staff has been operating the GWRS since January 2008. The

experience gained during the first two years of operations was used to help improve the existing

treatment process and for the design of the expansion. OCWD staff has worked closely with

learned during the first two years of operation have been instrumental in the expansion design.

Additional MF, RO, and UV light treatment equipment will be purchased and installed. The

design also includes flow equalization, improvements to the lime stabilization process, additional

drawings allowing for these specific equipment manufacturers at an established price. The

equipment purchase was then assigned to the construction contractor. The same approach is

being used for the expansion.

While the treatment train remains the same, the expansion includes numerous challenges

associated with the design. In addition, construction sequencing to reduce downtime of an

existing operational facility is a huge factor to consider. Other design challenges include

updating the process control system (SCADA), improving the lime postreatment system for

varying flows, and accommodating for an ultimate build out of 493 MLD (130 mgd).

RESULTS

Using Lesson Learned for the Design of the GWRS Initial Expansion

OCWD began operating the 265 MLD (70 mgd) GWRS in January 2008. At the time, OCSD

had not completed the construction of the SALS to bring more water into its treatment plant

during the daily low flow period. There was enough treated secondary effluent during the hours

of 9 am to 10 pm to operate the AWPF at the design flow of 265 MLD (70 mgd). However,

night time flows dropped to as low as 95 MLD (25 mgd) between the hours of 10 pm and 9 am.

time to maintain process recovery and efficiency. One of the biggest challenges was learning to

control the RO product water decarbonation and lime stabilization process.

In an effort to proceed with the design of the GWRS Initial Expansion, OCWD staff met

internally with engineering and operations and maintenance staff to discuss what was learned

during the original design and construction and operation of the AWPF. The review included the

design engineer selection process as well as what staff learned during the first two years of

operations. A list was also developed of issues or improvements desired for the existing facility.

These improvements were to be incorporated into the design of the 114 MLD (30 mgd) initial

expansion.

One of the first steps was the selection of the design. The original design of the GWRS was a

approach to detail development, and general design approach, design firms were producing

conflicting designs within the same areas. It was learned that the best approach was to make sure

one firm handled the civil design; one firm handled electrical design, and so on. With the design

of the expansion, the level of effort is much smaller yet it was important to maintain consistency

across the various disciplines.

When the GWRS was designed and constructed, all piping, facilities, electrical systems, and the

site were designed for an ultimate capacity of 493 MLD (130 mgd). Because the major

processes (MF, RO, and UV light) are modular systems, adding additional equipment to increase

treatment capacity should be relatively simple.

Equipment Pre-selection

Specific to the MF and UV equipment, a pre-selection approach is being employed, as was done

for the original design. Based on demonstration testing performed at OCWD prior to the original

For the initial expansion of the GWRS, it was important to match existing MF and UV

equipment due to the existing system equipment configuration, ease of stocking spare parts, and

meeting regulatory compliance issues. Because consistency in the plant expansion design is

preferred, OCWD entered into pre-selection agreements with the same manufacturers or

suppliers. While the purchase of the equipment is assigned to the contractor at the time of

construction, OCWD entered into agreements with both suppliers for equipment design. The

contracts are between OCWD and the MF or UV equipment supplier. This contract enabled the

treatment plant expansion design team to prepare the work required to design the facilities

necessary for the MF and UV systems.

Maximize RO Energy Efficiency

Energy recovery devices (ERD) was incorporated into the design of the new RO skids for the

initial expansion. Each new RO skid will have its own dedicated ERD to reduce overall energy

consumption of the RO system. In addition, the ERD will be integrated with a booster pump to

boost feed pressures to the 2

RO stages and operational flexibility to prolong membrane life. Preliminary estimates indicate

(HMI) graphic displays for monitoring and controlling the process.

network. In addition to the process control network, two field device networks are provided:

Foundation FieldBus and DeviceNET. The Foundation FieldBus communication network is used

System includes greater capacity to accommodate the higher flows available during the day. The

current Preliminary Design Report evaluated an expansion that would result in approximately an

additional 114 MLD (30 mgd) of production out of the GWRS. A concept to equalize secondary

effluent flow has been completed, which would help increase daily production to the full 379

MLD (100 mgd) production capacity by storing wastewater during the day when it is available

and feeding the plant at night during low flow periods. The existing OCSD treatment plant site

is heavily developed with limited opportunities for construction of new process facilities. There

are advantages to development of primary effluent equalization. However, after further analysis

and review of the plant site, it was concluded that primary equalization was not feasible. This

facilities.

mgd). The expanded AWPF will only be able to treat to its design production capacity during the

Table 1. Typical day total flow available to the GWR System.

17:00

23:00

404

106.50

52.50

13.04

Backwash waste flows from the MF system and reject from the RO membranes are returned to

the OCSD plant. MF backwash flow is recycled to the head of the west side primary

sedimentation basins for subsequent treatment. The RO reject is not recycled; it is returned under

residual pressure to the downstream side of primary effluent distribution box (PEDB) 2, from

to Plant No.1.

Decarbonation and Lime Stabilization

The GWRS post-treatment facilities stabilize RO permeate using decarbonation and lime

addition. Challenges were experienced during the first year of operation in achieving the pH and

alkalinity targets and led to tailored, multi-approach changes developed during the Initial

Expansion Project to increase dose accuracy and reduce overall pH variability. The RO

permeate pH and the post-treatment target adjustments as shown in Table 2.