Abstract: A cavity is excavated in the earth with preferably sloping sidewalls and a first impervious barrier or layer is placed on the surface of the excavation, such as a layer of plastic film or sheet. One or more self-starting pumps are placed at intervals along the slope and embedded in a pervious layer, such as sand, of from one to three feet in thickness. An inner impervious layer which, in a preferred embodiment, is substantially thicker than the outer or first impervious layer is layed over the sand and then a final layer or cap of clay is applied over the inner impervious plastic layer. Any seepage or leakage through the inner impervious layer caused by a tear or imperfection in the plastic, flows down to the self-starting monitoring pumps which, upon sensing the flow, turns itself on. The invention includes sensing the time of operation of the self-monitoring pump to determine the degree of seepage.