Eleven well-established, swine waste lagoon systems in the lower coastal plain of North Carolina were examined for evidence of seepage losses to the superficial aquifer. The sites were selected to represent three major soil systems in the areas of North Carolina with the highest swine populations. Elevated ammonium concentration was the strongest indicator of seepage. Estimated seepage losses were small on 45% of the systems studied. On the remaining sites, estimates of total nitrogen export indicated moderate to severe seepage losses. Several of these were near surface waters that probably served as discharge points, minimizing the likelihood of extensive impact on groundwater quality. No assessment was made of effect on the receiving surface waters. There was no apparent relationship between seepage loss rates and major soil system or style of construction. Rather, the dominant factor appeared to be the soil materials used in construction.