future water supplies

Long term water supplies in California are quite limited if we continue to use water at present rates and the population grows.  The engineers and regulators know this, and theoretically so do the farmers and politicians.  We’ve already overallocated the Colorado River, such that it vanishes into the sediments at its mouth, no longer flowing directly into the Gulf of California.  And wet years for the Sacramento-San Joaquin River watershed doesn’t mean as much for the river flowrate as it does for the downstream farmers in the Central Valley who want to irrigate as much of their land as possible, or for the southern California utilities who want to store the extra water for drought conditions.

On top of expected in trends in population growth, climate change could potentially decrease the precipitation and/or streamflow in most of the southwest.  Furthermore, environmental concerns are pushing water regulators to scale back the allotted flows in the California and Colorado River aqueducts.  If you were the water manager for the city of Los Angeles, what would you do?  The net balance of your inflows is likely to decrease, while the delivery people demand is increasing…

There are a couple of options for new water supplies.  One is to build massive desalination plants, at a high energy cost and a high environmental cost for the disposal of brine waste.  In California you also run into the problem that necessary locations on the shoreline have really high property values and a bunch of neighbors screaming NIMBY.  Another is to look for temporary solutions like underused groundwater basins or watersheds.  Las Vegas is in the process of shipping groundwater from a remote valley of ranchers along the Nevada-Utah border to its water supply.  There’s also a project to mine a groundwater basin in the Mojave Desert in California, between Joshua Tree and Death Valley, for water supply to the L.A. basin.

But to me, the most reliable long-term option is indirect water reuse, which is already in place in Orange County, a relatively conservative portion of southern California.  I am slightly skeptical of direct reuse of wastewater effluent, even when treated beyond normal potable water standards, just because of the lack of a buffer or factor of safety if anything goes awry at the wastewater/water treatment plant.  But indirect potable reuse makes a lot of sense: treated wastewater is injected into a storage basin, most often an aquifer, and then after some flow distance, it is re-extracted as raw water for drinking water supply (i.e., it gets treated again after extraction).  During its travel in the subsurface, the water is filtered naturally by the soil and mixes a little bit with the native groundwater.  Quite a few cities employ this system with lakes, notably Las Vegas, Milwaukee, and Berlin (Germany), but there’s a lot more mixing and dilution in lakes than in groundwater.

To be honest, the indirect reuse in Europe, which has been working in some cases for over 120 years (see Berlin), is very convincing to me.  Water recycling could regenerate roughly 50% of the water supply of the entire L.A. basin (a lot of water is lost to outdoor uses like pools and lawns), and would make water supply as reliable as the wastewater supply.  An odd concept, perhaps, but in the case of Los Angeles this would be less wasteful than all the treated wastewater currently discharged to the ocean.  Given the right geology, water recycling would also require far less infrastructure than desalination plants or large water pipelines.

Would the public go along with this, if properly informed?  Sydney, Australia provides an example of the PR gone wrong – after a contentious public debate, they built a massive desalination plant.  But again, Orange County is already employing this successfully, so we should be able to point to them as a model.  As Orange County goes, so goes the country?  It’s not something I would normally expect to hold.

recycling water to save money

San Diego is in a tough spot when it comes to water.  It’s at the far end of the pipeline when it comes to imported supplies from the Colorado River and the California aqueduct, and the Metropolitan Water District (MWD) subsequently charges the San Diego County Water Authority extra for pumping over the extra distance.  It gets less annual rainfall than the LA Basin (10.3 inches in San Diego, 15.1 inches in LA) and has no significant natural rivers (the San Diego River has a flow an order of magnitude lower than the two biggest rivers in the LA Basin, the Los Angeles River and the San Gabriel River), so in some ways it needs imported water even more than Los Angeles.  On top of that, its main wastewater treatment plant, Point Loma, is likely to have its waiver from Secondary Treatment requirements of the Clean Water Act not renewed.  The cost of the required Point Loma upgrades for a 2015 permit could be $1.2 billion.

So a new study for the City of San Diego proposes a way to kill two birds with one stone: recycle treated wastewater into the drinking water supply.  The wastewater discharged to the ocean would decrease, as would the delivery of imported water.  The idea seems to be amenable to the public – a 2011 survey found that two-thirds of the respondents favored adding highly treated recycled water to the drinking water system – and depending on rate increases from MWD, the cost could eventually be lower than imported water.

Water reuse also requires infrastructure, with costs of $2.7 – $3.4 billion over 50 years projected by the report, but the cost savings in required Point Loma upgrades (cost scales with the volumetric flow rate of water treated) could result in a very favorable cost-benefit ratio.  If San Diego pursues this strategy, it could be on the cutting edge of water management in the US.

recycling isn’t everything

I thought I should post this, after my enthusiasm for recycling in my last post: sometimes turning a waste stream into a marketable resource is a bad idea.  In fact, sometimes it’s a disaster.  Turns out, chemical companies thought about this a lot over the years, especially in the pre-regulation days.  In the 1940s and 1950s, Dow Chemical and Shell produced plastics from allyl chloride, and one of the by-products was a chemical called 1,2,3-trichloropropane (TCP).  Side research suggested that this compound could be added to a popular fumigant (Shell’s was called D-D, Dow’s was called Telone) without ill effects.  A Shell memo from 1981 suggests that the company made $6.3 million in fumigant sales, and saved $3.2 million in disposal costs for TCP.  In effect, the companies were able to use this waste as “filler” in a marketable good — perfect!

Originally the companies claimed that TCP was effective at killing nematodes, but subsequent research was unable to prove these claims.  In the meantime, the fumigants were used extensively in California’s Central Valley, where the compounds most resistant to degradation entered the groundwater, and the EPA, Clean Water Act, Safe Drinking Water Act, and Superfund law all came into effect.  Furthermore, we know today that TCP is a carcinogen, and more than 200 water wells across the Central Valley have elevated levels of TCP.  Although Shell stopped selling D-D in the 1980s and Dow changed its Telone formula in the 1990s, TCP will persist in affected groundwater for years.  This means that there are quite a few lawsuits out there to force these two companies to pay for additional treatment for existing water supplies and for external water supplies where treatment is unavailable.   The companies already settled with one small municipality for $13 million, which suggests that there are a few more settlements headed their way…

So to be clear, recycling works when you’re not dealing with hazardous material that may become a human health risk in the future.  It does not work when you try to hide toxic materials in useful products.

the wave of the future

There are people out there studying global cycling and reserves of elements.  Carbon cycling is well known, from climate research, but there are headlines now and again about trace elements that we might run out of — tantalum, neodymium, germanium, gallium — that play a role in industrial products or processes.  But the really scary numbers are for phosphorus, if you believe the USGS estimate of current reserves: peak production by 2030 and exhaustion of the global reserves by 2100.  Remember, phosphorus (along with nitrogen) is responsible for revolutionizing our agricultural yields in the mid-1900s, and farmers throughout the developed world use it heavily.

The reason why I think phosphorus scarcity is a good thing, is that there’s another obvious source of phosphorus in the world: human and animal wastes.  When the price of newly mined phosphorus gets high enough, projects to recover phosphorus from wastewater treatment plants or feedlot manure piles will be economical.  This type of “recycling” phosphorus is, in my humble opinion, more sustainable in the long term than the typical “use it and throw it away” thinking we have about, well, everything we use.

It’s refreshing to see that my line of thinking is shared by those in the Encina Wastewater Treatment Plant in Carlsbad, California.  They performed a pilot study last year and have begun evaluating the cost-effectiveness of implementing a full-scale system to recover phosphorus in little pellets to be used as fertilizer.  The pellets are composed of phosphorus, nitrogen, and magnesium in a mineral called “struvite”.  Researchers at Eawag have found that struvite precipitates more readily from urine than mixed wastes, and they have therefore pushed for “source separation”.  (Side note: It wasn’t the best thing to be the subject of their urine collection system while I worked there.)

Think about some of these trends, though.  Wastewater treatment has historically been about meeting some minimum level of treatment so that wastes could be dumped into our waterways.  Between the biogas recovery and fertilizer production, there is a shift towards viewing wastewater as a potential resource instead of a waste stream.  Any way to recycle these “wastes” back into productive use will lead to not only greater sustainability for wastewater treatment, but also larger profits for the treatment plants.  I will post more about this when it comes to the Los Angeles water balance, but it is worth noting that most of what exits a wastewater treatment plant is water.  If we could recycle this, too, wastewater treatment could be a huge boon to the energy, agricultural, and water needs of our society.  Now that’s impressive.