The park facility has been in operation since 1983, and receives an average of 70,000 gallons per day of primary treated effluent derived from campground and beach bathhouses. The effluent is discharged to eight RIBS that are located on a coastal sand dune that ranges in thickness from 35 feet under the RIBS to a featheredge at the discharge location in a freshwater swamp. Depth to ground water ranges from nearly 30 feet under the basins to ground surface in the swamp. Dune sands are very uniform in size (1.2 +/- 0.57 mm) and mineralogy (> 98 % quartz).
Effluent is dominated by organic N (0.1 - 28 mg/L) and ammonium N (0.5 - 5 mg/L). Comparison of effluent with ground-water quality data from 18 standard, and three, seven channel CMT wells indicate that N mineralization and nitrification are nearly complete in the vadose zone, and there is little attenuation of N in the vadose zone. Nitrate-nitrogen concentrations > 25 mg/L occur nearly 250 feet downflow of the RIBS in wells and swamp discharge areas despite sub-oxic to anoxic conditions. These findings indicate current RIBS design assumptions may not be appropriate for the mid-Atlantic region. Significant vertical variations in water quality call into question current requirements for permit compliance monitoring.