Sewage lines identified as needing up-sizing in the 1980 master plan have been completed. Flows today remain low and the existing system is not being hydraulically overloaded.
Area of Concern
An area of concern is the hydrogen sulfide degradation of concrete manholes installed during that era. Because of the low flows, the sewage turns septic in the sewer lines and begins to produce hydrogen sulfide gas. This compound converts to sulfuric acid and forms on the manhole walls. The sulfuric acid attacks the cement and turns it into a powdery substance and diminishes the strength of the concrete.
Protective coatings or non-corrosive construction materials were not being used in the construction of the manholes and now they are slowly decaying from the hydrogen sulfide. Manholes constructed out of red brick seem to resist the decay, but the cement grout used to bind the bricks is brittle in some areas.
Problem Identified & Addressed
The Utilities Department has identified this problem and is currently rehabilitating the manholes utilizing an alumina silicate concrete, (this material returns the structural strength) and an epoxy coat that is applied to the interior of the manholes to give them a corrosive resistant coating.
City of Roswell 425 N Richardson Roswell, NM 88201