Reclaiming Wastewater in Southern California

The United States’ southwest has seen its share of water use dilemmas: explosive population growth, increased agriculture and an already-arid climate nearly always strain the groundwater supply. In addition, southern California must address seawater infiltration into fresh ground water aquifers; when too much groundwater is taken from the aquifers, the pressure of the nearby seawater is too great to resist and saltwater seeps into the aquifer. To address the latter problem, Orange County has for years been injecting freshwater into a ‘pressure ridge’ that effectively creates a barrier against seawater infiltration.

In a project that has the potential to address the issue of seawater infiltration and the water availability situation at the same time, the Orange County Water District has proposed to ‘recycle’ the wastewater generated by its customers. The project, called the Groundwater Replenishment System (GWR), takes highly-treated sewer water though an additional series of processes that purify it to a drinkable standard. From there, about half of the reclaimed water is to be injected into the county’s seawater barrier – the fresh water ‘pressure ridge’; the remaining water is to be pumped into the county’s recharge lakes.

Orange County makes a credible case for this undertaking. County officials predict that the population will grow by approximately 20 percent by 2020 with water use roughly matching that figure. Like most counties in southern California, much of Orange County’s water has been purchased from outside the region; while this has been a system that has worked for decades, it is costly and Orange County’s allotment is expected to decrease over the period from 2010 to 2020. Additionally, the energy costs to divert water to the region are considerable. The GWR system aims to provide a locally-controlled, renewable source of water that is more resistant to drought and climate fluctuations than reservoirs.

The system starts with treated sewer water; initially passing the fluid through a micro-filtration system; in this step, low-pressure water passes through a membrane system that effectively removes suspended solids and bacteria from the water. From there, the water is processed through a reverse osmosis system; removing salts, viruses, pesticides and minerals. Finally the water is treated with hydrogen peroxide and exposed to ultraviolet light; the combination of the UV and peroxide creates an oxidation reaction that breaks down any remaining compounds in the water. At the end of this process, the water is ‘drinkable’ by any of the quantifiable standards that are used around the world today.

Rather than pipe the reclaimed water directly to homes and businesses, it has one final filtration step. The reclaimed water is pumped to one of two destinations, the freshwater barrier or a recharge lake. Once at either of these locations, the water gradually works its way through the clay, sand and rock until it reaches the groundwater aquifer; essentially following the same path that rainwater and run-off take to the County’s water supply system.

Orange County officials estimate that the GWR System supplies water more cost effectively than other means. The water supplied by GWR costs approximately what it costs to import water to the region, currently; with significant population growth predicted for the entire southwest United States, those imported-water prices are predicted to rise in the coming years. The cost of GWR water also compares favorably to desalinated water; GWR produces water for approximately $525 per acre-foot while desalination costs range from $800 to $2000 per acre-foot. Independent cost studies have confirmed that the GWR System is indeed the most cost-effective solution for Orange County at this time. Also of note is that compared to the current importation scheme, the GWR System uses approximately one-half the energy per acre-foot of water supplied. All told, the system can provide approximately 10 percent of the county’s water-needs over the next few decades.

The system is not without its detractors, though. Many are uneasy with the idea of drinking sewer water – purified or not. These groups and individuals point to historic water quality issues that resulted from previously unknown or poorly understood contaminants. They have argued against the system from the start; asking, “Why take the chance?” Lining up on the side of the GWR, however, is a long list of community and religious leaders, politicians and large numbers of the voting public.

Unfortunately the real ‘chance’ that is on the table is the chance that southern California will not have a sustainable drinking water solution. Now that it has come online, the GWR System should be studied carefully over the next few years; longitudinal health studies should examine the ‘before’ and ‘after’ health of Orange County residents. If the detractors are correct, the problem demands remediation. If, however, there are no health or water-quality issues, GWR-type systems should be evaluated for use around the world; these systems may be an effective way to maintain groundwater supplies everywhere.