Studies of the Ra isotopic content of groundwater from a Coastal Plain aquifer adjacent to the Fall Line in South Carolina, USA, show that elevated 228Ra and 226Ra concentrations are associated with the aquifer. There is little seasonal variation in the concentration of either Ra isotope for a single well but up to an order of magnitude variation among wells within a 4 km2 area (228Ra activities range from 4.71-11.9 pCi/l; 226Ra activities range from 2.71-26.53 pCi/l). The 228Ra/226Ra activity ratio among wells ranges from 0.23-3.0 and is inversely proportional to 226Ra content. These results are contrary to the assumption in the USA Environmental Protection Agency drinking water regulations which state that 228Ra rarely exceeds 226Ra and thus require 228Ra measurements only when 226Ra exceeds 3.0 pCi/l. It is unknown whether these results are typical for all Fall Line aquifers of the southeastern USA, which extend from Alabana to Maryland and supply water to many small towns. These results, which show that the 226Ra concentration does not parallel 228Ra concentration in this geologic region, call for a reexamination of the EPA regulation.