Substantial differences have been found between measured and computed heat losses from a large in-ground thermal storage tank used for annual cycle heat storage. One suspected source of error in the computation was the neglect of the latent heat effects in the moist soil and efforts have been made to examine these. One of these effects, that was due to freezing and thawing of the soil moisture is discussed, and the results of some simulations of the effect in a numerical model are presented.