Sandy soil textures (USDA Soil Textures of loamy fine sand or coarser) have large pore space and water moves rapidly through the sandy textures. As a result it is difficult to reduce the iron in the soil to the gray colors normally found in wet loamy soils. Sandy soils are considered problem soil for hydric soil determination. Most field guides for hydric soils have different criteria for sandy soils. Make sure you document the soil texture.