Go-ahead for 113,500 m³/d Orange County GWRS expansion
Orange County's world-renowned membrane-based Groundwater Replenishment System (GWRS) in California is to be expanded by another 30 MGD (113,500 m³/d) following approval by the board of the Orange County Water District (OCWD) on 30 March 2011.
Additional microfiltration (MF), reverse-osmosis (RO) and ultraviolet (UV) light treatment equipment will be purchased and installed. In addition, flow equalization of secondary treated effluent from Orange County Sanitation District (OCSD) will be provided by the construction of two 7.5 million gallon (28,400 m³) storage tanks.
The storage tanks will allow for the excess secondary effluent available in daytime hours to be stored and then fed to the GWRS during low night flow periods.
A significant portion of the infrastructure has already been constructed to accommodate an expansion. This includes the yard piping, pump stations, and the electrical backbone. When the GWRS was originally designed and constructed, all piping, facilities, electrical systems and the site were designed for an ultimate capacity of 130 MGD (492,000 m³/d).
Because the major processes (MF, RO and UV light) are modular systems, expansion will be relatively simple.
Five construction management companies - Butier/Tetra Tech/AECOM; Hill International; Kennedy/Jenks; MWH; and Parsons - had put in bids by 20 January 2011. A review committee ranked the Parsons bid the best followed by MWH and Butier/Tetra Tech/AECOM. It was also the least expensive.
Major work on the expansion would entail:
The project is estimated to cost US$ 156.2 million.
GWRS staff recommended prequalifying nine contractors for the project. These contractors would receive the plans and specifications to prepare construction bids with board approval. Only firms from the prequalified list would be allowed to bid on construction of the project.
The Mira Loma Recharge Basin is currently under design and will be in construction in the fall of 2011. Construction is expected to be completed in fall 2012, prior to completion of the proposed expansion of GWRS. It is projected that the basin could recharge 20,000 afy (24.7 million m³) of GWRS water.
The GWR system, a joint project of OCWD and OCSD, has been operating since January 2008 and is the world's largest water purification facility of its kind. Highly treated wastewater, originally destined for the ocean, is pretreated by Memcor submerged membrane modules at a rate of 86 MGD (325,000 m³/d) before entering the RO units, followed by UV and hydrogen peroxide disinfection.