Geology, hydrogeology, and geophysics often address subsurface conditions, i.e. the differences in rock or soil differences beneath the surface where they cannot be directly observed. Geology deals with the fabric of the subsurface, hydrogeology deals with the flow of water through the fabric, and geophysics deals with the physical properties of the rock/water system. Geophysical instruments (known by many as “black boxes”) can be used to measure physical properties in the subsurface such as velocity, magnetism, gravity, resistivity, and density. These properties are related to rock and soil strength, composition, and thickness, and are affected by the amount and type of water saturation in the rock.

Road cuts are a great boon to geologists because the rock formation composition, attitude, thickness, and water zones can be directly observed. In the eastern United States these water-bearing zones are often contained in fractures and faults. You have probably gone by a road cut and observed a series of fractures; perhaps water is only coming out of one of the numerous fracture systems occurring at the outcrop. But where is that same water bearing fracture 500 feet east of the road cut? Why do you care? Because you want to drill a good well on your property, which is located 500 (or 1,000 or 10,000) feet away from the road cut. Common sense tells you that you must find the same water-bearing fracture to drill a good water well, but the question is how to find the water bearing fracture if you can't see it?

Common tools used in subsurface investigation equipment include various types of drills, probes, and excavation machinery. These tools provide data point by point, and data between the points is “interpreted” from information gathered at the points. The more points you drill, the more information you have, and the greater chance that your interpretation will be correct (that is, you will drill at the right location to intercept the water-bearing fracture). Geophysics allows you to gather more data points than traditional methods at a lower cost.

Geophysical instruments were originally refined for use in oil and gas or mineral exploration. This industry had the economics to design, build, test, and improve the electronic, mechanical, and computer capabilities necessary to provide reliable geophysical data. During the last twenty years this technology has been gradually transferred to the environmental and groundwater industry. However, in many cases geophysical applications are misunderstood, leading to improper application and data interpretation.

Personnel at AA&E have been applying geophysics to groundwater and environmental projects since 1985. A geophysicist is an integral part of our support staff, so we can provide you with an integrated approach to geologic and hydrogelologic interpretations based on sound science, extensive local experience, and a synergistic approach.

Our expertise allows us to guide you in the proper application of geophysics to such problems as sinkhole mapping for site development, locating water wells in low-yield aquifers, finding buried drums and tanks, mapping contaminant plumes, and delineating buried dump areas. There is a lot more to this story; contact us if you have a difficult environmental problem – geophysics may lead to the solution.

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