Measurements of the ground motion spectrum [3] indicate that the amplitudes are well below 100 nm except for a 27 Hz/300 nm peak which however could not be reproduced in recent measurements [4]. Assuming a girder response factor of ten for certain eigenmodes the maximum excursion of the elements on the girder is determined to be 3 
m. Taking into account simulation results for the corresponding orbit response orbit excursions of the electron beam with rms values of up to 15 m [2] at the location of the experiments are expected for the vertical plane. This corresponds to 150% of the vertical beam sigma for an emittance coupling of 1% (It should be noted that this coupling factor is somehow arbitrary in the sense that much smaller coupling ratios are achievable utilizing a proper coupling compensation of the lattice [2]). This worst case estimate shows that it is necessary to introduce a fast orbit feedback system which attenuates the oscillations to the desired limit.
In this paper a concept for such a feedback system is presented. It is followed by a description of the actual implementation at the SLS storage ring. Requirements on corrector granularity and BPM noise are defined. Simulations will then show that a fast orbit feedback is capable of attenuating the residual oscillations such that the requirements of the experiments are fulfilled.