"Life is neither good nor evil, but only a place for good and evil." - Marcus Aurelius
There is a movie that you may have seen called "Erin Brockovich", starring Julia Roberts in the heyday of her movie career. The location for the topic of the film was in Hinkley, California, and the point of the film was Erin's uncovering of documents related to groundwater pollution.
Below: Southern California. The arrow indicates the location of Hinkley. Las Vegas is at the top right and the Los Angeles metropolitan area is at the lower left.
Below: Closer in to Hinkley - town center is in the upper left quadrant. Outside of the town limits is an arrow. This marks the location of a what was a source of groundwater pollution - a compressor station along a natural gas pipeline. Yes, there is an aquifer filled with water underneath all that sand. Thus the farms - the green alfalfa circles.
Below: The close-up of the natural gas pipeline compressor station at Hinkley.
Between 1952 and 1966, this site had a wet cooling tower that blew down a portion of the cooling water to prevent scale build-up. This blowdown flowed into unlined evaporation ponds - an estimated total of 370 million gallons (1.4 billion liters), where a portion of this water seeped down into the soil, contaminating the groundwater underneath. As you can see in the above image, the ponds have since been fitted with impermeable liners.
Here is where we get to old-school cooling tower chemistry.
Back in those days, it was desirable to maintain the cooling water at a pH of 6.0 to 6.5 - in a slightly acidic condition. This slightly acidic condition allowed the cooling tower to be run at higher cycles of concentration. "Higher cycles" refers to the concentration of solids in the cooling tower compared to the concentration in the make up water. At some point, the concentration of solids will become high enough that the solids will precipitate and form scale. With an acidic solution, concentrations of alkaline solids could be higher without the risk of them coming out of solution, thereby scaling up the cooling tower or equipment that was cooled by the water.
The acidic condition would help ensure that these solids - carbonates of magnesium and calcium - remained dissolved in the mild acid. However, that mild acid also caused a different problem. It would also attack the metals that the cooling tower piping and equipment was made from.
Below: Graph of corrosion rate vs pH.
As you can see from the above chart, a pH of 6.0 to 6.5 is not ideal for the ferrous metals of piping and equipment, although it is a nice way to reduce water usage in the cooling tower. The additional sulfuric acid required to keep the pH this low was less expensive than the cost of all the water needed to operate the cooling tower at lower cycles. To reduce the corrosive effect of this low pH regimen, Chromium-based corrosion inhibitors were added to the cooling water. You can probably see where this is going...
The chromate-based corrosion inhibitor eventually percolated into the groundwater, along with the cooling tower blowdown water. Pacific Gas & Electric, the public utility that owned the gas compressor station, notified the local water board of the contamination in December of 1987.
The citizens of Hinkley were not amused. I'll quote Wikipedia here.
Residents of Hinkley filed a class action against PG&E, Anderson, et al. v. Pacific Gas and Electric (Superior Ct. for County of San Bernardino, Barstow Division, file BCV 00300).[1] LeRoy A. Simmons was the judge. In 1993, Erin Brockovich (a legal clerk for lawyer Edward L. Masry) investigated an apparent cluster of illnesses in the community which were linked to hexavalent chromium.[8] The case was referred to arbitration, with maximum damages of $400 million for more than 600 people. After arbitration for the first 40 people resulted in about $120 million, PG&E reassessed its position and decided to end arbitration and settle the case. It was settled in 1996 for $333 million, the largest settlement of a class action lawsuit in U.S. history at the time.[9][3][10]
Of interest: During the arbitration process, the plaintiffs had on their side a paper written in 1987 by a researcher in China named Zhang. This paper reported a strong link between Hexavalent Chromium and cancer. In 1997, against Zhang's written protest, the research paper was withdrawn - invalidating the earlier research. This was used by industry in the US to delay setting of minimum drinking water standards for Chromate, and to delay or stall further litigation.
Wikipedia again:
In 1997, an article was published in which Zhang retracted his 1987 research.[13] ChemRisk, a firm known to be working with PG&E since 1995, updated his analysis and published it in April 1997 Journal of Occupational and Environmental Medicine (JOEM, the official publication of the American College of Occupational and Environmental Medicine) as a retraction of Zhang's 1987 paper. It was published under Zhang's name (then a retired Chinese government health officer, and despite his written objection) and that of a second Chinese scientist, Shu Kun Li.[13] Peter Waldman, reporter for The Wall Street Journal, wrote that Zhang's son was "outraged" at "the idea that his father would willingly have invalidated his earlier award-winning work."[14][15] According to the Center for Public Integrity, "In contrast to the earlier article, the new one concluded that chromium wasn't the likely culprit. The revised study—which did not reveal the involvement of PG&E or its scientists—helped persuade California health officials to delay new drinking water standards for chromium."[7]
If you guessed that perhaps that Hinkley, California is not the only place in the world where drinking water has been contaminated by Hexavalent Chromium, you would be correct. There are a couple of other gas compressor stations along natural gas pipelines that also have this issue.
Heavy industry used chromates for corrosion control in many places - and at the time, there was no Clean Water Act to prevent them from disposing of it wherever they pleased. There are a lot of people around the globe who currently drink water contaminated with this carcinogen.
Erin, being a smart lady, followed the pipeline to the next compressor station, in Kettleman Hills, California, and initiated a second groundwater contamination lawsuit. A third lawsuit was initiated in Willits, California at a chrome plating operation. California is prime real estate for environmental class action lawsuits - and there are huge sums of money to be made litigating and defending such cases.
What's changed since then? Well, for one thing, toxic heavy metals are no longer used for corrosion control :)
Modern cooling tower chemistry is controlled differently. It's still necessary to add sulfuric acid for pH control, but the control band tends to be in the 8.5 to 9.5 region, so of course the water is much less corrosive to the ferrous piping. Even so, a mild corrosion inhibitor is helpful in reducing corrosion even further. This inhibitor is injected in trace quantities, and is usually an orthophosphate, polyphosphate, or sometimes a neutralizing amine. Phosphates are not good, obviously, but they are by far preferable to chromates.
Scale build-up is a little more difficult at the higher pH control ranges used in modern chemical control schemes, but it's possible. Cooling towers do need to blow down more water, and can't be cycled up quite as high as they were before. But there are some chemicals that can help keep some of the alkali salts in solution, even if they are not dissolved in a mildly acidic solution. The chemicals that keep these salts from precipitating and forming scale are called polymers.
Scale tends to begin in places where suspended solids drop out of solution in cooling tubes, restricting flow and creating an irregular place for salts to begin forming crystals. Other chemicals act as dispersants to prevent these solids from accumulating in the first place, and these chemicals are called phosphonates.
The final issue that cooling towers have is biological growth. Cooling towers are perfect for growing bugs, as they are warm and humid. It turns out there is a relationship between scale build-up and growth of "bugs". Preventing scale helps prevent microbio growth. The scale provides a "safe space" for films of polysachharide slimes to form, under which bio growth can begin to fester. If you prevent scale, you prevent runaway bio growth, but you don't eliminate it. Really, you never eliminate bio growth. Microbiological bugs surround us - they are in the air - and our cooling tower drafts in millions of cubic feet of air per hour. The best you can do is control it.
The best way to get rid of microbio growth is good old fashioned bleach. Sodium hypochlorite (NaClO), slightly stronger than what you use in your laundry, kills germs. We all know this, and bleach works amazingly well treating millions of gallons in a cooling tower as well. The bleach breaks down in the cooling tower into free chlorine, which literally burns the slimes and cell walls of bacteria that may have set up shop in the system.
Not-so-Fun fact: Legionnaire's disease was first discovered following an outbreak at an American Legion convention at a hotel in Philadelphia in 1976, with over 2000 members in attendance. 211 people became sick and 29 died. The CDC sprang into action - this was back when it was capable of such things - and quickly solved the epedemiological mystery. A pneumonia-causing bacteria was growing in the hotel's HVAC system.
Other not so fun facts:
- The same thing happened in 1985 in Stafford, England in a hotel, causing 28 deaths.
- In 1999, in Bovenkarspel, Netherlands 318 people were sickened and 32 killed by Legionella bacteria that had infected a hot tub at the Westfriese indoor flower exhibition.
- In 2001 in Murcia, Spain, over 800 were sickened by a cooling tower that was infected with Legionella bacteria.
The list of Legionella outbreaks is long, unfortunately.
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