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3 Mr. Scarlett talked about the different methods of testing. He does not feel that geophysics can be used solely to characterize sites. Geophysical techniques are almost invariably indirect. These techniques measure characteristics and responses that are caused by what is in the subsurface but not directly looking at what is there. These indirect methods lead to non-unique solutions. Correlative data, along with experience and common sense is used to construct the models which lead to interpretation. He pointed out. that the quality of data has a lot more to do with conditions than the operator. He referred to the letter from Aquaterra giving all the techniques. He noted that they all can provide an answer but none can give all the information needed to make a decision. They use the date from borings and geophysics together so that they can take their known points and extend that to cover a lot more area. Chair Carey asked Mr. Scarlett to review the different geophysical techniques and to indicate if any of these methods will provide enough information to exclude some sites before going to more invasive type testing. Mr. Scarlett noted that with the exception of airborne geophysics and over water geophysics there are no non-invasive geophysical techniques. To get geophysical data, entry is required to the site. A survey must be done and paths must be cut and markers will have to be left. This is less invasive but not non-invasive. MAGNETIC PROSPECTING would look at the variations in the earth's magnetic field. This technique provides information on the distortion to the magnetic field. Certain rocks which have more iron in them will cause more distortions to the magnetic field. The critical issue is how fine a net will be used. If looking for small features, this would require close gritting over a hugh area and the cost could be as much as $600 an .acre. In his opinion magnetic prospecting has a place but not at the front end of site evaluations. ELECTRICAL RESISTIVITY SOUNDINGS has been used for decades. It is labor intensive. Wires are run from a central location at increasing intervals and the response of the earth is measured to an applied voltage which then can be backtracked through to give the electrical properties of the subsurface. This would provide a vertical profile to the earth's resistance. It varies according to water content, rock type, etc. Interpretation tends to be more subjective than other techniques. It will give a good idea of vertical distribution of resistivity which can identify the location of ground water and bedrock but does not normally end up being very accurate. Supporting data would be necessary with this type of testing. Electrical resistivity can give some information on soil or rock depth. It will not provide information on characteristics or type of rock. It will have some applications but is not something he would use in differentiating sites. Unless there is one site that is tremendously different from the others, this type of testing will not provide conclusive data from which to make a decision.