Interpreting land-use history by integrating aerial photographs, near-surface geophysics, and field observations into a digital database

Near-surface, non-invasive field geophysics was used to investigate the lan d-use history of a 60-acre former industrial site in Lancaster, Pennsylvani a. A proton-precession magnetometer and a Geonics EM31 non-contacting elect romagnetic conductivity meter were used to measure eleven profiles across t he site. Based on all the available data, four major land-use areas are dis tinguished: building foundation areas, excavated areas (clay mining), landf ills and background areas. The geophysical data show distinct signatures fo r these land-use classifications, The conductivity readings can be characte rized by their median values and standard deviations within each of these c lassifications: a) sports fields (background), 7.5 +/-2.8 millisiemens per meter (mS/m); b) excavated areas, 4.6 +/-3.4 mS/m; c) building foundations, 7.7 +/-4.0 mS/m; and d) landfill areas: 34.0 +/-30.8 mS/m, For magnetics, the median (with background subtracted) and standard deviation within each classifications are: 1) sports fields (background), -0.9 +/-8.7 nanoteslas (nT); 2) excavated areas, -0.8 +/-10.8 nT; 3) building foundations, -96.2 /-291.0 nT; 4) landfill areas, 37.7 +/-473.9 nT. Both conductivity and magn etics show similar patterns, although conductivity provides clearer visual discrimination between land-use types. The in-phase conductivity data are c onsistent with the land-use patterns determined from the aerial photographs and the other geophysical data. Zero (negative) readings occur over areas with high metal content such as the buildings foundations area and the land fill area. Clay pit areas show uniformily low readings consistent with the lack of metallic objects in these areas. All the data, including historical aerial photographs, historical land-cove r information, geophysical data, topography, hydrology, and existing buildi ngs and infrastructure were integrated into a digital database. Data such a s historical aerial photographs provided temporal (past) information about the land-use history of the site, while the geophysical data provided curre nt information about the type and spatial distribution of land use. The int egration of the geophysical data with other data in a digital database is a n effective tool for interpreting landuse history and understanding present environmental conditions.