Perched Water Table
Perched Water Table
(OP)
Does anyone have experience dealing with a perched water table?
Situtation: Low lying area which is typically "dry". After significant storm events(several inches of rain), the depression fills with runoff. The runoff is retained for extensive periods of time (weeks to a couple of months).
With no positive outfall and a permitting nightmare to construct one, I'm looking for a way to increase percolation and decrease the time until the depression returns to a normal state.
I'm thinking their is a confining layer that significantly slows the percolation. What would be the drawback to punching several "holes" through the confining layer to more quickly draining soils?
Situtation: Low lying area which is typically "dry". After significant storm events(several inches of rain), the depression fills with runoff. The runoff is retained for extensive periods of time (weeks to a couple of months).
With no positive outfall and a permitting nightmare to construct one, I'm looking for a way to increase percolation and decrease the time until the depression returns to a normal state.
I'm thinking their is a confining layer that significantly slows the percolation. What would be the drawback to punching several "holes" through the confining layer to more quickly draining soils?





RE: Perched Water Table
RE: Perched Water Table
"An aquifer in which a ground water body is separated from the main ground water below it by an impermeable layer (which is relatively small laterally) and an unsaturated zone. Water moving downward through the unsaturated zone will be intercepted and accumulate on top of the lens before it moves laterally to the edge of the lens and seeps downward to the regional water table."
Your surface water doesn’t fit the definition as perched as it isn’t an aquifer. As mentioned, your problem may potentially be classified as a wetland and there are definite ramifications if the development of wetlands is regulated in your area. Your local permitting agency should be able to help with this. Additionally, let me add that perforating an aquitard is commonly frowned upon by most regulatory agencies as aquitards tend to protect drinking water supplies from surface contamination. Your test holes (as you put it) could potentially be classified as injection wells and constructing/operating injection wells without permits could lead to major legal problems.
Now on a more positive side; your proposed solution of draining through the underlying aquitard is an interesting one. Much of your proposed solution would depend upon the depth to the aquitard and its thickness, as well as the ability of the underlying strata to accept the water. If the aquitard is shallow and thin enough, you may be able to build a drain system using trenches. A test boring logged by a geologist would provide the information you are looking for.
RE: Perched Water Table
RE: Perched Water Table
mitchell54, your past trouble is one thing that concerns me. This area is significantly lower than the surrounding terrain and I think could potentially have the problem you suggest.
If I get a drill rig out to punch a deep hole, what's the likelihood that just in testing, I create a bigger problem than what already exists?
Again, thanks for everyone's input.
RE: Perched Water Table
RE: Perched Water Table
RE: Perched Water Table