Tannins (humic acid) are found in waters which have passed through large quantities of decaying vegetation. There composition is varied dependant on the type of vegetation that the water comes in contact with.
High tannin levels are found mostly in surface water supplies where large quantities of vegetation have decayed. For example slow moving ponds and some shore and dug wells.
In some parts of Manitoulin Island, Tannins are found in deep wells because of the lack of soil structure and fracturing of the rock beneath the surface. We have found Tannin in drilled wells from 50 to 350 feet deep. These wells usually have little to no soil at the surface. The ground usually is composed of almost entirely rock with sparse vegetation.
In addition, the fracturing of rock on Manitoulin Island also permits for Tannin to move beneath the surface and show up seasonally during periods of melting and runoff. We have tested and found Tannins in drilled water supplies across all areas of the Island.
Tannins will cause water to be faint yellow to a dark tea colour. The concentration can range from 0 to greater than 5 ppm. They are often variable within a water source depending on the time of year.