It is important to determine soil type at the proposed site before construction begins. Soils in the area to be impounded must hold water with a minimum of seepage. Soils for an embankment pond must also be suitable for dam and spillway construction. Clay and silty clay are good soils for impounded areas, but some clay soils stay in suspension, causing water to remain muddy. Sandy clay is generally suitable, while sand, gravel and sand-gravel mixtures are unsuitable. Outcrops of shale, limestone, sandstone or other bedded materials should be avoided. These may contain crevices or channels that can cause excessive water loss or seepage from the pond. Detailed information on the suitability of various soils for pond construction is available from the Natural Resources Conservation Service.