GROUNDWATER FEATURES MAP – A DERIVATIVE MAP PRODUCT FROM STATEMAP MAPPING EFFORTS IN CHATHAM COUNTY, NC

Detailed geologic mapping in Chatham County, North Carolina by the NC Geological Survey, with partial support from STATEMAP, has identified multiple diabase dikes, faults, and fracture zones. These geologic structures can be areas of increased groundwater permeability and preferred groundwater flow and can have important ramifications to groundwater resources and pollutant transport. The majority of drinking water in Chatham County is provided by private or community wells within fractured bedrock aquifers. Anticipated growth in the county has heightened the awareness of long-term sustainability of groundwater resources in the county by various stakeholders.

In 2019, we developed a preliminary simplified map (at approximately 1:90,000-scale) with accompanying explanatory text and associated GIS data of compiled diabase dikes, faults, and fracture zones - named Preliminary Groundwater Features Map of Chatham County. Chatham County government welcomed the map and are in the early stages of evaluating if this information can be incorporated into their unified development ordinances and how the information could be used in vulnerability-based methods for delineating groundwater protection areas.

In a continued effort to assist Chatham County staff, a derivative 1:24,000-scale Groundwater Features Map was prepared as a prototype. Included on the map are: 1) station locations of diabase and quartz (possible indicators of brittle faults); 2) interpreted diabase dike and brittle fault lines; and 3) interpreted geomorphic lineaments from Hillshade elevation data from LiDAR. LiDAR interpreted lineaments easily visible at 50,000- to 100,000-scale (major lineaments) are identified on the Groundwater Features Map. Multiple unmarked geomorphic lineaments are visible when viewed at 10,000- to 50,000-scale (minor lineaments). Minor lineaments that extend for short distances (100’s to 1000’s of feet) are not indicated on the map but may have important implications on a site-specific investigation. To avoid leaving out pertinent groundwater features, we present the map with the Hillshade elevation data from LiDAR image. It is hoped that this information will provide scientifically defensible data for county staff and other stakeholders in Chatham County in their decision-making processes.