WorldWide Drilling Resource

WorldWide Drilling Resource ® Environmental Monitoring by Thomas Kwader, Ph.D., P.G. How Many Wells Does it Take to Define the Hydrogeology of a Site? Although I have worked the majority of my 45-year career in hydrogeology in North Florida, I have also worked in various other areas of the United States and have observed a wide range of hydrogeologic conditions. I worked in areas where the geology was very consistent laterally for miles and water levels well beyond 100 feet in depth. I have also worked in water basins with first-magnitude springs flowing more than 100 cubic feet of water per second (750 gallons per second) or flowing more than approximately 45,000 gallons per minute. Many of my projects required a good working understanding of the site’s subsurface geology and hydrology for remediating a contaminated site, or for providing a reliable supply of potable groundwater. Sites varied tremendously in complexity, with some sites varying very little from one end to the other, while some sites that were relatively level in elevation varied greatly in both geology and hydrology from borehole to borehole. Even over very short distances, some sites showed significant strati- graphic variability less than ten feet between boreholes. Oftentimes, to develop a good understanding of how contaminated groundwater moves vertically and laterally at a particular site, collections of soil, sediments, and water samples are taken and analyzed for various physical and chemical characteristics. Drilling contractors often use various methods to collect “cores” of the subsurface soils to obtain information regarding the speed and direction of water moving below the site surface. The location, number, and depths of boreholes drilled depend upon the complexity of the hydrogeology beneath the site and how the hydrogeology varies across the site. The number of borings is also dependent upon how large the site is. Generally, at least three borings are necessary, and some sites may re- quire more than 100 borings because of the complex layering and source(s) of contamination. One of my “worst-case” sites is locat- ed in west central Florida and required more than 50 roto-sonic continuous cores with no two borings being alike. Ironically, the first three borings on the corners were similar on the 60-acre site; however, the more borings we collected, the more complex the site became. That site taught me a lesson in humility and reinforced the fact that hydrogeology (especial ly karst) can be extremely complex. Tom Tom Kwader may be contacted via e-mail to michele@ worldwidedrillingresource.com ENV 32 AUGUST 2019 Torquato Drilling Accessories provides a full range of roller cone rotary hole openers custom manufactured using the finest materials. Large, premium- quality roller cones are made in many thread connections and sizes up to 60 inches to meet job requirements and ensure dependable performance in a wide range of forma- tions. Available with tungsten carbide inserts or steel tooth, Torquato’s rotary hole openers are well-suited for vertical applications such as water well, geothermal, or gas and oil, and are also ideal for horizontal directional drilling. Torquato Drilling Accessories is a Valued WWDR Advertiser.