Absolutes do not exist, and values get established only by comparisons.

Suppose I said, “Three hundred.” Your immediate response could probably be, “Three hundred what?

• Fish?
• Avocado?
• Light years?”

Suppose I said, “Three hundred dollars.”

Now we have a value that can be compared. We can buy so many almonds, rent a car for so many days, finance a date with a loved one, or do many other nice things. And when we look at the opportunities that three hundred dollars afford us, we shall undoubtedly arrive fast at the conclusion that five hundred dollars is more.

A “bench mark” is term used in the field of land surveying.

In establishing elevations of land features, the surveyor indicates feet above mean sea level. As it is impractical to run back and forth to the ocean every time we take a measurement, various bench marks are located throughout the land to indicate the altitude at their locations.

A typical bench mark is made of a round disk of metal embedded in a small monument of concrete with a punched point on the disk. The surveyor measures the elevations of the land features in that area relative to the known elevation of the point on the bench mark.

A “base line” is any line forming a side (A—B) of a triangle so that when the adjacent angles (alpha and beta) are measured, the relative position of a third point (C) (the tip of the triangle opposite the base line) is determined.

The principle of base line is used in land surveying and in navigation to locate various positions on the surface.

The concepts of bench mark and base line are same: establishment of an agreed-upon (arbitrary) value from which other, relative values are determined.

Certain real estate transactions take place in properties where subsurface contamination already exists or where an operation is planned that may cause contamination.

For example, an operator of refueling facility enters a lease agreement on the facility, or an industrial operation takes over a property.

In such cases, it would be prudent for all sides involved to establish an environmental base line (or bench mark) on the presence of pollutants in soil, soil-vapor, groundwater, sometimes indoor air, at the property. 

A base line is established by collecting samples from certain locations and depths and analyzing for the chemicals of concern.

At the end of the lease, or in any time in the future, repeat samples can be taken, analyzed and compared.

The repeat sampling should be done in the same locations as the base line sampling.

There could be reasons for future sampling in other locations and analytical tests for other chemicals, as in the case where different operations enter the property, but such sampling does not belong in the context of base line sampling.