UTILIZING WATER WELL LOGS FOR SOIL PARENT MATERIAL MAPPING IN THE MID-ATLANTIC COASTAL PLAIN

Abstract

The mapping of soil units formed in Marlboro Clay regolith has been identified by the USDA Natural Resources Conservation Service as a high priority due the importance of this mapping unit for risk assessment by county planners and the difficulty of mapping these soils using a soil landscape model. The objective of this study was to evaluate the use of water well logs to map outcrops of the Marlboro Clay formation in Prince George's County, Maryland. Water well logs were acquired (n = 799) and their locations were estimated using MDProperty View. The bottom elevation and thickness of the formation were interpolated using five interpolation methods. The inverse distance weighted (IDW) method proved to be the best for interpolating the bottom elevation variable with a cross validation root mean square error (RMSE) of 13.5 m, while the global polynomial method was the best for the thickness variable (cross validation RMSE of 2.9 m). The mean thickness of the formation was 6.0 m. There were 17 logs in the northern portion of the study area with thicknesses ranging from 14.3 to 32.6 m. Therefore a conservative maximum thickness method was also applied. The interpolated thickness method was effective at predicting non-outcrop locations, but failed to identify outcrops. The maximum thickness method accurately predicted outcrops, but was not appropriate for soil mapping. Due the uncertainty regarding the thickness of this formation, soil survey may not be an appropriate method for urban planning risk assessment of the location of Marlboro Clay outcroppings.