Compton Hill Reservoir Replacement

COMPTON HILL RESERVOIR

In 1985 Reitz & Jens was retained by the City of St. Louis Water Division to perform a dam safety evaluation of the Compton Hill Reservoir. Our analysis determined that this reservoir, built in 1867, had been sited over several active sinkholes which were causing water loss due to seepage, resulting in several slope failures. To mitigate the seepage and stabilize slopes, a partial hypalon liner was installed inside the active reservoir, and interceptor sewers were installed at selected locations near the reservoir perimeter.

In 1994, the City proposed to replace the existing reservoir with two new tanks. Reitz & Jens was retained as a sub consultant to Black and Veatch to provide all geotechnical services associated with this project. Design phase services included a geotechnical investigation utilizing historical records, test borings, and a geophysical investigation. The investigation established the location of sinkhole throats, and determined the support capabilities of the underlying soils and bedrocks. The geophysical investigation was performed in the active reservoir utilizing seismic and gravity methodologies. Design phase services also included a geotechnical investigation to determine the soil coefficients for a seismic retrofit of the Compton Hill Water tower which is on the National Register of Historic Structures.

Two sinkholes needed treatment prior to construction of the new tanks. The largest of the sinkholes was treated by exposing the bedrock surface around the throat and installing a reverse graded crushed rock filter, a method which has successfully pioneered by Reitz & Jens in the early 1960s. In consideration of the construction sequencing, the second sinkhole will be isolated using a secant wall. Another unique feature of the site improvements was using construction demolition materials (primarily concrete) and specialized gradations of crushed limestone to place a 20 foot deep fill beneath the new tanks.

Presently, the large sinkhole has been treated, and the rock fill placed for the first tank. In 1997, the secant wall and fill for the second tank was constructed. Reitz & Jens provided field quality control inspection and testing during treatment of the first sinkhole and placement of all fill materials. Our firm also provided the same scope of services during installation of the secant wall and associated fills for the second tank. The first tank went on-line in August 1997, with the entire project completed in 1998.