Oak Island Archaeology Update: Does the water analysis show that there is silver buried on Oak Island?

On Season 8 Episode 24 of Curse of Oak Island (COOI), environmental scientist Ian Spooner and Chemist Matt Lukeman, both professors at Acadia University, unveil the results of a study of groundwater contamination on Oak Island, arguing that high levels of copper and zinc may indicate “a Gerhardt dumptruck’s” worth of silver is buried on the island. This, of course, would go a long way toward increasing the team’s confidence that the treasure they are looking for is indeed on Oak Island. In brief, the argument is that since old silver coins often contain zinc and copper, finding elevated levels of those elements in groundwater on Oak Island could indicate the presence of buried silver coins.

I will note that I am straying a bit outside my area here. Archaeologists use environmental data such as this for our analyses, but I am looking at this very much as a consumer and not a producer. However, we still have to know how to interpret this data, and we have to know when it is surprising and suggestive, and when it isn’t.

Let’s consider what the results of the study actually tell us, and what they don’t. First, I must commend the COOI team for making this particular study more transparent than previous ones. We get much more information about method, for example, than for the DNA study of the alleged human bones. I suspect this new and welcome spirit of scientific openness may have something to do with Lukeman’s involvement. He was actually given an award in 2017 for his efforts at educating the public about pseudoscience.

Figure 1: Elemental concentrations in groundwater samples from Oak Island (Lukeman and Spooner)

The results are presented fairly clearly, although it would be nice to get a level of confidence with the results. These would normally be reported not as single values, but as ranges, or at least as averages and standard deviations around the mean of many readings. The real issue, as always, is the interpretation of the results. We definitely get numbers this time, in the form of micro-grams per liter (µg/L) of water (Figure 1), and a spatial distribution of the shafts from which the samples were drawn (Figure 2). What we don’t get, is an idea of whether and how surprising the numbers actually are, and what they might mean.

Figure 2: Map of sample locations (Lukeman and Spooner)

It is very difficult to interpret the numbers without some idea of a local baseline, or expected value. This could easily be generated by doing a similar study on nearby islands with a similar settlement history, and by looking at some mainland sites, including water wells, of which there must be many in the area. Even samples drawn from other places on the island, farther away from the money pit would be helpful.

Without this comparative information, we have to rely on general information about what we might expect in terms of silver, copper, and zinc content in groundwater if there were indeed a buried treasure on Oak Island. In the episode, Spooner relies heavily on the reading of 777 µg/L of zinc in one of the shafts. Just how surprising is that value? Is it high? Is it low? Without a local baseline, we don’t know, and we have to rely on more general information.

The World Health Organization (WHO) reports that while “In natural surface waters, the concentration of zinc is usually below 10 µg/litre, and in groundwaters, 10– 40 µg/litre”, zinc concentrations in tap water and domestic wells can reach between 1100 and 2400 µg/L.

As for copper, for which the highest value in the Oak Island study is 342 µg/L, WHO reports normal environmental values between 3 and 19 µg/L. For domestic water supplies, the values can range from 5 to 30 000 µg/L.

For both copper and zinc, the major source of increased concentration in domestic supply is plumbing. Water Ph level and hardness are also factors. Given these values, we have to ask ourselves how surprising it is to find a few hundred micrograms per litre of zinc and copper in water at the bottom of shafts in an area that has been heavily settled for at least 250 years, and where treasure searchers have no doubt used and discarded (and buried) tons of equipment over the years, much of which could have contained significant copper and zinc. Copper and zinc, after all, are the major components of brass, an alloy much favoured in marine environments for all kinds of tools and fittings, both domestic and industrial.

But what about silver itself, which is the ultimate target of the study? Knowing that the silver values are very low (trace at most) in all samples, how likely is it that silver is in the ground on the island? The ever helpful WHO reports that “The most recent measurements of silver in rivers, lakes, and estuaries using clean techniques show levels of about 0.01 µg/litre for pristine, unpolluted areas and 0.01–0.1 µg/litre in urban and industrialized areas”, which is consistent with the Oak Island study, with the caveat that we don’t actually know the detection limit of the method used by the COOI team.

For sites in which we might expect higher silver concentrations, WHO reports values of up to 300 µg/L for water near photo-processing plants, which in the old days at least, used silver oxide. The WHO report does note that the highest values were found before the development of “ultra-clean metal sampling, which began in the late 1980s, [and] should be treated with caution”. Still, they give us an idea that dumptrucks full of silver might very well increase silver concentration in ground water around them to some detectable level.

In summary, in the absence of local comparative data on zinc, copper, and silver concentration in ground water, and therefore relying on generally available information and on the history of the island, the values found by Lukeman and Spooner don’t immediately seem surprising, and there is no reason to assume that they indicate the presence of a silver hoard buried on Oak Island. There are alternative sources of copper and zinc that need to be examined first, and the absence of detectable concentrations of silver itself is notable (and that is how I would write the concluding paragraph of a paper review for a scholarly journal, in case you ever wondered what those look like).

References:

World Health Organization 1996. Zinc in Drinking-water: Background document for development of

WHO Guidelines for Drinking-water Quality, in Guidelines for drinking-water quality, 2nd ed. Vol. 2. Health criteria and other supporting information. Geneva.

World Health Organization: Copper in Drinking-water Background document for development of WHO Guidelines for Drinking-water Quality

World Health Organization, 2002. Concise International Chemical Assessment Document 44: Silver and silver compounds, environmental aspects. Geneva.