THE USE OF GROUND PENETRATING RADAR TO FACILITATE THE DEVELOPMENT OF A SUB-SURFACE CONSERVATION PLAN AT AN URBAN HISTORIC SITE – THE THOMAS CLAPP HOUSE, DORCHESTER, MA

The Thomas Clapp House, located in Dorchester, MA, is one of the three historic properties owned by the Dorchester Historical Society. The Clapp House serves as the headquarters for the Society and is open for public tours. The Society has been active in conserving and preserving the historical aspects of the building and the remaining grounds associated with the original Clapp Estate. Presently, the nearly 40-acre estate consists of the main house, a 1806 neoclassical mansion of William Clapp; the 1701 and 1767 constructions of Lemuel Clap; one carriage house; one barn; and the remains of a second barn.

Presently, the Society is undertaking a major landscape restoration project. Their goal is to restore the grounds to align with the appearance of the property in the early-mid 1800s. In order to aid the Dorchester Historical Society in preserving historic subsurface features of the Estate, the research team planned a detailed study of the site using ground penetrating radar (GPR). The goal was to create a survey of subsurface features of the property and to determine their relevance to the environmental history of the estate. Through this survey, the team intends to reveal the location and change over time of property features such as wells and outbuildings in order to gain a more detailed understanding of the site's historical uses.

The survey consisted of nested GPR lines of 100, 500 and 800 MHz coupled with a real-time kinematic global positioning system (RTK-GPS). The 100 MHz served to establish the regional geologic framework and identify areas of disturbance and large-scale features. The 500 and 800 MHz arrays were deployed following analysis of the 100 MHz data to develop a better understanding of site specifics in areas highlighted by the 100 MHz survey. The GPR data were seamlessly integrated the RTK-GPS data stream to establish position of the GPR to within 10 cm in the vertical and horizontal. The RTK-GPS data stream also provided for the construction of a detailed digital terrain model of the site for use in site management.

The data collected during this survey will be used to create a subsurface conservation plan for the Clapp family property. The plan will become an integral part of Dorchester Historical Society's landscape restoration project to prevent unnecessary disturbance of cultural subsurface features on the site.