The National Clay Pipe Institute (NCPI) was recently called upon to aid the Costa Mesa Sanitary District (CMSD) of Southern California in an investigation into possible causes of an unknown material building up in some of its gravity sewer lines. As a non-profit technical resource for design, installation and operation of vitrified clay pipe (VCP) sewer systems, NCPI has assisted the engineering community with research and education since 1944.
CMSD manages the sewer collection system in the City of Costa Mesa, Calif., as well as sections of Newport Beach, and unincorporated areas of Orange County. The district has taken a front-line position in the development and maintenance of sustainable and efficient infrastructure since 1953 when its first VCP sewer lines were installed. The district maintains some of the longest-running VCP sewer lines in Southern California, and is committed to utilizing clay sewers today because of VCP?s long-term cost-benefit relationship and environmental friendliness.
Rob Hamers, District engineer for CMSD, contacted NCPI after maintenance personnel discovered a consolidation of an unidentified material on the inside of numerous VCP lines operating throughout the district. Most of the sewer pipe in question was installed in 1963. Initial video inspection of the lines was performed in 1992, and most recently in 2006. The video showed deposits extending out from the pipe wall in stalactite form, above the flow line of the effluent. The deposits were banded in color with larger white and smaller black layers.
Hamers and others within the district were unsure of the material?s origin, but were concerned about the apparent acceleration in consolidation from 1992 to 2006. ?The 1992 video showed only black and white spots with a slight white film on the inside of the pipe above the flow line, while the 2006 video showed significant growth of deposits,? Hamers said. ?In many cases, the buildup already impeded the hydraulic performance of the system and there was fear of the possibility for eventual blockages and overflows.?
Thomas Fauth, assistant manager for the District added, ?We tried to remove the material, but it was extremely dense and resistant to chemical or mechanical removal.?
NCPI began its investigation by gathering as much data as possible using as-built documentation, original installation and construction standards and relevant ASTM standards. CMSD staff provided samples of the sewer effluent and subject material for laboratory analysis. A review of video inspection history was also performed to develop a timeline for development of the material present. To assist in the chemical analysis of the removed build-up material and effluent, NCPI solicited the services of Dr. David Jenkins, Professor Emeritus of environmental engineering at the University of California-Berkeley, as well as E.S. Babcock and Sons Inc. Environmental Laboratories in Riverside, Calif., and West Coast Analytical Services in Santa Fe Springs, Calif.
Laboratory examinations showed elevated levels of calcium and magnesium in the effluent and high levels of calcium and magnesium in the solid material. Additional tests were performed on the solid material by R.J. Lee Group of Hayward Calif., using X-ray diffraction (XRD) and scanning electron microscopy. The results of the Lee Group analysis were forwarded to Dr. Alain Manceau (LGIT, University of Grenoble, France) for verification of results and interpretation of XRD spectra of minerals.
To better understand the condition of the consolidated deposits, NCPI arranged for the excavation and replacement of 15 linear feet of the affected pipe. NCPI?s examination of the excavated pipe, affected site conditions and adjacent manholes corroborated Jenkins? initial findings. Jenkins theorized that ingress of groundwater brought additional mineral content into the effluent. Subsequent findings also showed, through cross-sectional analysis and hydrostatic testing, the formation of the material was the result of a plating or evaporative deposition process. The testing further proved that material consolidation could not have been the result of water infiltration through the VCP itself. It was later determined that infiltration was occurring at manholes. All laboratory results and external interpretations were sent to Jenkins for final review and analysis.
Jenkins? report provides a simple explanation as to the origin of the material in the system, stating: ?The banded structure of the scale is explained by the seasonal variation of the groundwater level. Successive layers of scale are laid down as the groundwater rises and falls during the wet and dry seasons. The whitish calcium carbonate precipitates first because its precipitation relies solely on the pH change encountered when the groundwater is exposed to the lower carbon dioxide content of the sewer atmosphere. The manganic oxide precipitation occurs later because it requires the development of a microbial community capable of oxidizing the manganous salts in the infiltrated ground water to manganic salts.?
Since NCPI completed this initial study of the now described ?Calcium Buildup,? other Southern California cities have indicated that their pipelines have been affected by the same condition, including systems using PVC and concrete pipe. NCPI is currently working to further study the environmental conditions that contribute to calcium buildup. This includes area soil testing and review of USGS Topographical data for the entire southern Orange County area for water migration and subsurface consolidation patterns. Additional laboratories are looking at the pipe wall density and hydraulic conductivity for verification of true pipe density. NCPI has also recruited the help of Dr. Thomas Garrett, chemist and director of research of Mission Clay Pipe Industries Inc., to oversee the continued development and field-testing of a new chemical methodology for use in the removal and maintenance process. This process was developed by NCPI Southern California and Garrett to minimize the effect on normal treatment processes and support regular maintenance activity.
Mike VanDine, NCPI president, said: ?The National Clay Pipe Institute has always attempted to marshal the best resources available for any research. This project is an example of our commitment to the industry and to the development of truly sustainable sewer system with VCP.?
Joe Parker is Vice President of Tech Services, Southern California, NCPI. Garrett Richardson is Sales Representative for Mission Clay Products.
