Karst information on the cheap: data for the Phase I investigation
Kochanov, William E., DCNR, Bureau of Topographic and Geologic Survey, 3240 Schoolhouse Road, Middletown, PA 17057-3534.
The Phase I investigation has been developed as a means of determining if hazardous materials have been released into the subsurface or in buildings on a site. It is a commonplace assessment that includes a thorough review of available historical records such as property titles, taxes, zoning status, and also topographic maps and aerial photography. A visual inspection of the site typically complements the background search. This inspection may reveal topographic features that provide clues to subsurface conditions. These may be the result of cultural activity but they may also be naturally occurring features. To the geologist or engineer, the background review and on-site assessment help to establish the basis of understanding that will guide a project through completion. It is therefore critical that the compilation of data be as comprehensive as possible.
Karstic conditions occur throughout central and southeastern Pennsylvania and present challenges regarding potential for subsidence and groundwater contamination. The Pennsylvania Geological Survey has ongoing geologic and karst-mapping programs that identify carbonate bedrock and karst surface features such as sinkholes, surface depressions, and caves. The data and associated publications form a base from which inferences regarding karst development and distribution can be used to evaluate the Phase I site. Decisions regarding site remediation and construction design can be evaluated in the early stages of a project rather than dealing with more costly subsidence and/or groundwater contamination problems in the future.
Karst is a unique geologic setting where standard land developmental practices generally do not apply. Although Phase I assessments are typically required for commercial projects, many karst problems are encountered in residential settings. When a problem occurs, it generally falls to the municipal government or perhaps to the property owner. Modification of local zoning laws to include a mandatory Phase I assessment for all residential development projects within karst areas could offer some protection to homeowners and municipalities. This assessment then becomes part of the history of a property and allows the homeowner to make an informed decision on accepting the risk associated with this geologic hazard.
Oral paper presented at the 2006 Philadelphia Annual Meeting (22–25 October 2006)