per Geology and Soils Manual, Missouri State Highway Commission, 1962, p.77-90.
These neighborhoods, as most of the City of St. Louis beyond the downtown area, were developed between the mid 19th Century and mid 20th Century, before many geologic soil studies and classifications were conducted. The natural overburden (soil above bedrock) is best described in the above-referenced manual. This silty/clay soil predominating the City is described as being any one or a combination of the following: Memphis, Clinton, and Marion silt loams (wind-deposited soils which became clayey due to downward percolating water and compaction). These loams are characterized by yellowish-brown to brown to light grayish-brown silty clay.
Because of their silty character, these loams are susceptable to capillary water movement (pulling water up from the natural water table surface), thus mainitaining a higher than usual water table. This is especially significant in areas that are not topographically high (at a low elevation). In such areas, groundwater would be encountered closer to the surface. These neighborhoods do not have such areas, except those areas of neighborhoods noted below that lie within floodplains. Any digging conducted to normal project depths would not be expected to encounter water.
With respect to construction projects, these loams are considered somewhat elastic: left exposed, will slump when wet and dust (erode) when dry. Without proper compaction, this soil will sink and form depressions in areas where used as backfill.
Migration of percolating water (as well as contaminants) through these loams are relatively slow and move downward to the capillary fringe (upper water table). Thus, property and basements in this area, unless immediately near hazardous sites, are well above and away from potential contaminants. As in all neighborhoods developed for over 50 to 100 years, the natural overburden has been criss-crossed with utility lines, trenches, pipes, and impervious fill sands and materials, all of which serve as conduits, speeding the migration of any contaminants more quickly and further away from their source(s) than allowable through the natural overburden.
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