The Ground Water Characterization Program

1. The Ground Water Characterization Program Helping Secure Virginia’s Ground Water Resources For The Future The DEQ Office of Ground Water Characterization is tasked with improving the understanding of Virginia’s ground water systems. One component critical to that effort is obtaining bore hole geophysical logs. Bore hole geophysical logging involves lowering electronic tools into wells and boreholes to measure different properties. The data collected is displayed graphically in vertical strip charts as shown at the right. DEQ stores, transports and operates their state of the art computer controlled bore hole geophysical logging equipment in a specially modified vehicle. The truck is climate controlled so it can be used in all weather, except lightning, and it is equipped with four wheel drive so it can reach almost any site a drill rig can access. The cable and draw works are capable of logging holes in excess of 2,500 feet deep. Once a sufficient number of bore hole geophysical logs have been collected in a given area, hydrogeologic cross sections are created that illustrate the underlying geology as shown below. The geologic conditions control the movement and occurrence of ground water and form the framework for computer models utilized to predict future ground water availability. These charts are then interpreted by DEQ Ground Water Geologists who identify and delineate the specific water bearing zones, called aquifers, from the non water bearing zones, called confining units, as shown above. This information also identifies the most productive areas within the aquifer allowing well screens to be placed in the best possible locations for obtaining water. Continuing growth in historically rural areas of Virginia’s Coastal Plain is causing concern over future ground water availability and expansion of the Ground Water Management Area is a possibility. Bore hole geophysical logs are required for ground water withdrawal permits issued in Virginia’s ground water management area and obtaining them at the time of drilling is easily done. For more information contact: Scott Bruce DEQ Groundwater Characterization Program Phone: (804) 698-4041 Email: taylor.bruce@deq.virginia.gov GWCP Fact Sheet 001-2010

2. Using geophysical logs to place well screens Case study: Five public water supply wells in Virginia’s Coastal Plain were drilled on a 75 foot by 100 foot parcel between 1960 and 2007. All 5 wells were logged by their respective drillers but only the most recent, well #5, was also logged with down hole geophysical logging equipment. The partial printout at the right illustrates how DEQ Ground Water Geologists utilized the data to identify the aquifers and confining zones underlying the site and selected the most productive water bearing zones within the aquifer (blue cross hatching) for well screen placements. You can see how the previous well screens missed the best positions in the aquifer with part of one screen even being placed in the overlying confining unit (red cross hatching). Nanjemoy/Marlboro Confining Zone Aquia Aquifer Well #4 Screens Upper Potomac Confining Zone Well #5 Screens Well #3 Screen Well #1 Screen Well #2 Screen Well #1 Specific Capacity 0.97 Upper Potomac Aquifer Well #2 Specific Capacity 2.75 Well #3 Specific Capacity 2.75 Well #4 Specific Capacity 3.53 Well #5 Specific Capacity TBD