Cache is NOT at the posted coordinates unless you are working on your two minute drills! Work through the cache page and the actual coordinates should present themselves. BYOP...
The theme for my inaugural cache is groundwater, as a hydrogeologist it just made sense! More specifically it will give you a brief insight into the applied science of hydrogeology. Below are some of the more interesting facts on groundwater, I have kept it short so we can get down to the real deal.
- 40-50% of all the drinking water in the USA comes directly from groundwater
- Groundwater constitutes approximately 30% of the freshwater on the earth
- Surface water (lakes/rivers) makes up less than 1% of the freshwater on earth
- The USA uses 350 billion gallons of freshwater per day
- 53 billion gallons per day are used for irrigation
Part 1 - A Tribute to Henry Philibert Gaspard Darcy
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Darcy was a pioneering scientist that formed one of the most fundamental laws and scientific basis for the flow of fluid through the ground (permeability). In the mid-1800s the French engineer successfully quantified several factors controlling ground water movement. These factors are expressed in an equation that is commonly known as Darcy's Law. Using his law we can calculate the ground’s ability to transmit water when submitted to hydraulic gradient (known as hydraulic conductivity or K). For the purposes of this puzzle K will be represented in the units ft/day. Darcy’s Law is represented by the equation:
By rearranging Darcy's Law and solving for hydraulic conductivity (K) in common units we can get a sense of what hydraulic conductivity really represents.
Q = discharge (volume of water per unit time) = 277.33932 ft3/day
K = hydraulic conductivity = ft/day
A = cross-sectional area = 16 yd2
dl = distance = 20 ft
dh = change in head = 12 inches
dh/dl = hydraulic gradient = ft/ft
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Part 2 – So how much can we pump out of this well??
We can use the value of K that we calculated in part 1 to determine the specific capacity (Q) or the rate at which we can pump water from a well per unit of drawdown (we don’t want to pump the well dry!) We can do this by calculating the transmissivity (T) of the aquifer and apply it to the following equation for a confined aquifer:
T = Q/s*2000
If we assume the aquifer is approximately 80 ft thick it would give a transmissivity of 15,423.836 gpd/ft. For drawdown in the well of 10 ft (s) rearrange the equation and calculate the specific capacity (Q) of the well, or the rate at which a well can be pumped without the fear of running out of water!