Environmental Enlightenment #156
By Ami Adini - Reissued March 22, 2016

This is a SHORT, LIGHT and SIMPLE newsletter. Its purpose is to rekindle in the initiated terminology they have once learned, and enlighten the uninitiated on terms they may have heard but never known the meaning of.

The Groundwater Monitoring Well

We monitor the condition of groundwater by collecting groundwater samples from monitoring wells.

This is a groundwater monitoring well:


First, we bore a hole in the ground:

In the borehole we insert a PVC pipe.

Most wells are made of a pipe that is 2 or 4 inches in diameter.

At the bottom of the pipe we connect a screen made of PVC slotted pipe:

     


The screen extends from the bottom of the well to about 10 feet above the water table.

Next, we fill up the space around the screen with loose sand.

It’s called a “filter pack.”  The filter pack acts to prevent loose sediments from entering the well.

We pour sand into the space between the PVC pipe and the borehole.

Typically, the borehole diameter is 4 to 6 inch larger than the well diameter. This gives a minimal annulus of 2 inches in width.

We raise the sand pack 2 feet above the screen.



The aquifer must be protected against intrusion of foreign substances through the well hole. We place a plug (seal) above the filter pack. The plug is made of 5 feet of bentonite chips which are hydrated with water. The hydration expands the bentonite and tightly seals the annulus, separating the active bottom of the well from the upper environment.

Bentonite is essentially a high swelling clay mineral whose name was derived from the location of the first commercial deposits mined at Fort Benton, Wyoming U.S.A.  Geologically, bentonites are mainly of volcanic origin and can date to the period of ammonites and dinosaurs.

At the surface, the well is completed with a box and traffic-rated cover

 

Next we develop the well.  The purpose of well development is to allow water to flow more freely toward the well.  Well development removes fine sediments along the well screen-aquifer contact and some distance into the formation.

We do it by MECHANICAL SURGING:

  • water is forced to flow in and out of a screen by raising and lowering a plunger apparatus within the well casing
  • apparatus called a surge block (see figure)
  • the surge block is attached to PVC pipe and raised and lowered causing water flow through the well screen
  • sediment must be removed from the well by bailers, other pumps or air lifting.

You can find past issues of "Environmental Enlightenment" at www.amiadini.com Wealth of information about environmental site assessments in the real estate transactions and issues concerning assessment and cleanup of contamination in the subsurface soil and groundwater.

Call me if you have any questions. There are no obligations.

Ami Adini
Ami Adini & Associates, Inc.
Environmental Consultants
Underground Storage Tank Experts
818-824-8102; mail@amiadini.com
www.amiadini.com

Ami Adini is a mechanical engineer, California Registered Environmental Assessor, Level II (Exp.), and president of AMI ADINI & ASSOCIATES, INC. (AA&A), an environmental consulting firm specializing in all phases of environmental site assessments and rehabilitation of contaminated sites. AA&A specializes in practical solutions to environmental concerns using the highest standards of ethics and integrity while providing its clients with maximum return on their investments.