Shallow seismic data are typically recorded with multiple source impacts per shot gather, with individual impacts stacked in the recorder to economize storage. Don Steeples has observed that in some cases, separately recorded impacts at the same shot point share similar spectra at ground roll frequencies, but differ at higher signal frequencies. This observation suggests that multiple source gathers at a single station can be subtracted to remove ground roll and preserve signal. First attempts to suppress ground roll, using an extrapolation filter to fit source gathers, show interesting but ambiguous results. Additional study requires new data.