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Groundwater Replenishment System Final Expansion Feasibility Study

Entrant: Orange County Sanitation District/Orange County Water District
Engineer in Charge: Rob Thompson, P.E.
Location: Fountain Valley, California
Media Contact: Eros Yong, OCSD

Entrant Profile

Orange County Sanitation District (OCSD) is a publicly-owned water resource recovery facility that provides wastewater collection, treatment, and disposal services for approximately 2.6 million people in central and northwest Orange County, California. OCSD has two treatment plants that treat residential, commercial, and industrial wastewater; Plant No. 1 in Fountain Valley and Plant No. 2 in Huntington Beach. Together both plants currently treat nearly 185 million gallons per day (mgd).

The Orange County Water District (OCWD) is an internationally recognized leader in the water industry and its international reach is growing. OCWD manages and replenishes the region's groundwater basin, ensures water reliability and quality, prevents seawater intrusion, and protects Orange County's rights to Santa Ana River water. OCWD takes the limited water supply found in nature and supplements it to provide water for 2.4 million people in Orange County, California.

For the past 18 years, OCSD and OCWD have partnered to enable the Groundwater Replenishment System (GWRS) to provide a drought-proof water supply for Orange County. OCSD currently delivers all Plant No. 1 secondary effluent to the OCWD GWRS facility which produces 100 mgd of potable reuse water. The potable reuse water is injected into a seawater barrier and pumped to recharge basins where it naturally percolates into the groundwater basin.

By supporting the GWRS Final Expansion, OCSD and OCWD will be able to recycle all current reclaimable wastewater flow in OCSD's service area.

Project Description

Since 2008, the Orange County Sanitation District (OCSD) and the Orange County Water District (OCWD) have partnered to enable the Groundwater Replenishment System (GWRS) to provide a drought-proof and sustainable water supply for Orange County. GWRS currently produces 103,000 acre-feet per year (AF/Y) of replenishment water for the OCWD-managed groundwater basin in north and central Orange County. In addition to GWRS purified water, OCWD uses Santa Ana River base flows, storm flows, and, as needed, imported water from Metropolitan Water District (MWD) as additional sources of groundwater replenishment water. OCSD and OCWD jointly embarked on a feasibility study as part of their planning for the GWRS Final Expansion, which supports OCSD's strategic goal of maximizing water recycling and OCWD's goal to produce up to 134,000 AF/Y of purified water. By supporting the GWRS Final Expansion, OCSD will be able to recycle most of the wastewater generated in its service area.

Currently, the 100 million gallon per day (mgd) GWRS advanced water purification facility (AWPF) is supplied with effluent water from OCSD's Plant 1. OCSD has maximized the available reclaimable wastewater treated at Plant 1 and therefore, secondary effluent from Plant 2 will be required to achieve the targeted 134,000 AF/Y.

One of the main issues to be considered with reclaiming water from Plant 2 is water quality. The Santa Ana River Interceptor (SARI) carries domestic wastewater along with industrial inflows and brackish desalter concentrate streams. SARI influent is not currently permitted to be reclaimed and has historically been diverted to and treated at Plant 2. Sidestream flows generated from the biosolids processing at Plants 1 and 2 are not currently being reclaimed and are not planned to be reclaimed through GWRS due to the high nitrogen and the presence of NDMA pre-cursors that exist in the polymers that could impact GWRS water quality. These sidestream flows are currently treated at Plant 2. In order for Plant 2 water to be recycled, the SARI and sidestream flows need to be separated from the reclaimable flows, treated separately, and discharged directly to the ocean rather than being sent to GWRS.

The primary goal of the Study was to identify what improvements were required to allow Plant 2 water to be recycled to produce the additional 31,000 AF/Y of purified water for groundwater replenishment.

Integrated Environmental Approach

This Study supported OCSD/OCWD's long-term objectives of maximizing water reuse. This final expansion will further increase a reliable water source for Orange County while reduces the amount of treated wastewater that is discharged to the Pacific Ocean, which also eliminates OCSD's need for increasing its ocean outfall capacity. The benefits of GWRS extend beyond Orange County. Statewide, lowering the demand on non-sustainable water supplies reduces the environmental impact to Northern California water sources.

Continuing this commitment to integrating environmental benefits into the program, GWRS expansion alternatives were evaluated based on a variety of objectives that considered impacts to water quality, maximizing water recycling, greenhouse gas emissions, and land use requirements. The Study identified ways to re-purpose existing infrastructure including modifications to the existing headworks to segregate SARI and sidestream flows at Plant 2, designating existing primary and secondary treatment trains for non-reclaimable flows, and slip-lining an existing pipe to minimize impacts within the plants' footprints and outside of the plant boundaries.

Quality

The purpose of this Study was to determine an implementation plan to support the GWRS Final Expansion. To accomplish this, all alternatives evaluated had to be adequately developed and the ranking of alternatives had to be transparent. Alternatives rankings were presented in a manner which allowed trade-offs to be easily seen and understood, and consensus to be reached on the best ranking alternatives.

Originality and Innovation

GWRS is one of the largest water reclamation plants in the world, and has been the "first" in many aspects of water recycling. In fact, most regulatory agencies view the treatment technology developed under this project as the "standard" for indirect potable reuse projects. They have been able to adapt to water quality changes, an evolving regulatory climate, and advancements in technologies. Therefore, it was critical that this Study provide for that continued flexibility to adapt to future conditions. This Study also investigated if a secondary, high recovery reverse osmosis (HRRO) system could be used to increase the overall GWRS recovery, increasing the product water capacity by blending HRRO permeate with RO permeate and reducing the required primary RO expansion capacity.

Complexity

Understanding the current and potential flows and water qualities is important to providing water for the GWRS Final Expansion because the effluent water quality from Plant 2 is different from the effluent water quality from Plant 1, which could impact the plant operations at both OCSD and OCWD. Segregation of SARI flows and other non-reclaimable flows from reclaimable flows that will be sent to GWRS also requires OCSD to evaluate their entire treatment process at Plant 2 to ensure that a high level of treatment can be provided while still having the flexibility to change plant operations to accommodate peak flow events.

Social and Economic Advancement

As part of the study, the capital costs for producing the additional 31,000 AF/Y of purified water was estimated at $253 million. The unit cost of producing this additional replenishment water (which includes the capital costs and the operation and maintenance (O&M) costs) is approximately $968/AF. This GWRS Final Expansion unit costs will increase on average with inflation for the operation, maintenance and electricity costs. In comparing this GWRS Final Expansion unit cost to imported water, currently at $1,000/AF, the GWRS Final Expansion costs are slightly less. However, the treated imported water rates are projected to increase by 4.5% each year. Therefore, the benefits of the less costly GWRS Final Expansion replenishment water can be passed on to the water agencies and cities which pump approximately 75% of their potable water from the north and central Orange County groundwater basin over the life of the project.

Click images to enlarge in separate window.


Aerial Image of Orange County Water District (OCWD) and Orange County Sanitation District (OCSD) Plant No. 1 and Plant No. 2.	Aerial Image of OCWD and OCSD Plant No. 1 in Fountain Valley, CA. OCSD currently delivers all Plant No. 1 secondary effluent, 115-125 mgd, to the OCWD GWRS facility which produces 100 mgd of purified water.

Aerial Image of OCSD Plant No. 2 in Huntington Beach, CA. Plant No. 2 currently treats between 62-72 mgd and all treated effluent is discharged to the Pacific Ocean.	OCSD Plant No. 2 Headworks Facility. The GWRS Final Expansion Feasibility Study recommended modifying the Headworks to treat two flow streams – reclaimable flows and non-reclaimable flows.

OCSD Plant No. 2 Pure Oxygen Activated Sludge Facility. The GWRS Final Expansion Feasibility Study recommended utilizing the Pure Oxygen Activated Sludge Facility for flows that are not permitted for use by GWRS.	OCSD Plant No. 2 Trickling Filter Solids Contact Facility- Secondary Clarifiers. The GWRS Final Expansion Feasibility Study recommended utilizing the Plant No. 2 Trickling Filter Solids Contact secondary treatment system for GWRS Final Expansion flows.

OCWD Flow Equalization Tanks for GWRS Initial Expansion. The GWRS Final Expansion Feasibility Study recommended building a new six-million-gallon flow equalization tank, similar to ones shown, at Plant No. 2 to store secondary effluent during peak flow hours.	OCWD GWRS Facility.

OCWD GWRS Microfiltration Facility	OCWD GWRS Reverse Osmosis Trains

OCWD GWRS UV Center	Current Orange County Groundwater Basin Water Supply and Projected after GWRS Final Expansion is complete.

Aerial Image of OCWD and OCSD Plant No. 1 and Plant No. 2 showing recommended projects for the GWRS Final Expansion. Most of the new facilities will be located at OCSD Plant No. 2.