WorldWide Drilling Resource

12 FEBRUARY 2021 WorldWide Drilling Resource ® Environmental Monitoring by Thomas Kwader, Ph.D., P.G. Owner, Qwater Well Developer and WorldWide Drilling Resource ® Hydrogeologist Trying to Avoid Drilling into Iron-Rich Groundwater I must tell you upfront, this story does not end well; however, it is important to know why this is a nearly impossible task. Almost all areas on this earth have a shallow water table consisting primarily of silt, sand, and gravel that will supply some volume of potable water to a small well. Exceptions may include hard rock strata areas where saline water is present at shallow depths. In my early years as a young hydrogeologist, I worked for a regional water management district in Florida. I received many phone calls asking, “How deep should I drill a new well to tap the best groundwater?” Sounds like a simple question if you have enough well data. Often, these wells were used for irrigation purposes or for a small domestic drinking water supply. Hydrogeologically, there is a shallow sand aquifer almost everywhere in Florida, often within the upper 50 feet depending on the depth to the water table. I began compiling hydrogeologic data for the surficial or sand aquifer for much of the state. The data shows that most areas have some potable water and are capable of yielding plenty of water for domestic and lawn irrigation purposes. (Note: Most of Florida has multiple aquifers down to 1000+ feet; however, deep wells are generally much more expensive.) The “problem” is iron - the fourth most abundant element in the earth’s crust (after oxygen, silicon, and aluminum). Iron is abundant and can render water to taste “bad” at concentrations less than 1 part per million and will stain everything it touches over a short period of time. Iron is relatively expensive to remove at volumes needed for domestic drinking water (a few hundred gallons per day). The iron concentration in groundwater can be affected by many factors including: Ph, oxygen available (Eh), iron content of the formation sediments, amounts of rainfall (dilution), organic matter content in the subsurface, etc. What I learned is concentrations of iron in groundwater are generally not mappable over even short distances - commonly tens of feet. My son often complains of high iron in his shallow well water, while his next-door neighbor has a similar depth well with no iron. Long story short, iron levels can commonly vary greatly over short distances and depths - more so than any other chemical compound. The only way to know the iron levels at a particular depth is to sample the zone before the well is com- pleted. Generally, iron levels at shallow depths are slightly less than at deeper depths, but that is not always the case. Tom Tom Kwader may be contacted via e-mail to ENV To be noticed, give us a call: (850) 547-0102 or e-mail: