1. Field of the Invention
This invention pertains broadly to sensing instruments and more particularly to instruments designed to sense the nature of underground constituents. In greater specificity, this invention relates to a sensor designed to detect chlorinated hydrocarbons and hence pollutants in underground formations.
2. Description of the Related Art
As man and woman have become increasingly conscious of the fragile nature of their environment, a focus has been made upon pollutants, where they exist, their real and potential effects, and how to be rid of those already in place. Such thoughts are relatively new to all of us.
At times in the history of the United States as well as in other countries crash efforts were undertaken in pursuit of what were then considered to be worthy goals. For example, in the former Soviet Union as well as prior Eastern bloc countries, rapid and radical efforts were made to transform these nations from relatively agrarian states into highly industrialized societies. A similar transformation occurred in the U.S. in the days of the Industrial Revolution. In many of these efforts the effects on the environment were either ignored or not addressed at all.
In other efforts, such as those of national defense, tremendous environmental catastrophes were permitted to occur and were simply considered a necessary expense. For example, in the nuclear armament industry of the U.S.A., the former Soviet Union, and other countries, tremendous compromises in the delicate balance of nature were allowed to be made. Even in non-nuclear defense industries, industrial by-products were often dumped on land, in the air or in the water.
Because of the recent turn in world events, industrialized nations have been able to turn away from their focus on national defense and instead concentrate on environmental considerations. Such is the case in the United States where tremendous sums are being spent and allocated to "clean up" the waste sites created in the past.
At both defense and privately held hazardous waste sites efforts are being made to quantify and map specific chemical contaminants. A method of doing this is by installing monitoring wells at the sites. The installation of the wells is a costly and slow process. In order to guide placement of such wells an in situ technique of determining specific contaminant levels is needed. Presently, chlorinated hydrocarbon ratios of contaminated soil are determined by digging up core samples of the soil and bringing these to a laboratory for analysis. Such a process is, of course, costly and time consuming.
The oil industry has devised a number of techniques for analyzing soil content. For example, devices have been designed that provide underground resistivity, formation porosity and formation density. Some of these oil-related sensors give off neutrons whose interaction with adjacent soil formations is sensed to determine the nature of the surrounding soil.
In one scheme neutrons are pulsed by way of a rotating member interfacing with a reacting stator. In another case, a neutron generator is simply switched on with the generator providing neutron output until its source has expired.
The nonswitchable neutron generators have been considered undesirable where controlled cessation of neutron generation is desired either to minimize personnel hazards or to prevent excess underground radiation. These devices are used after a bore hole has been drilled and may be part of what is known as the drill string or may be sent down independently. In either case, a relatively large and expensive drill hole is required.
As previously explained, the drilling of wells at hazardous waste sites can be costly and time consuming. In addition, the drilling of such wells creates the possibility of contaminant release through the drill hole itself.
A device known as a cone penetrometer has been used to measure ground hardness as well as the electrical sensitivity of the ground. Cone penetrometers are relatively small in diameter, varying from approximately one to two inches and are typically made up of 1 meter sections that are simply pushed into the ground one section at a time. Such cone penetrometers have been known to reach depths of approximately 150 feet. When the penetrometer is drawn from the ground, the ground fills in the hole made so that, for example, when used in a toxic waste dump minimal toxic emission will occur through the penetrometer's earth penetration point.