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Central Contra Costa Sanitary District
Controls Corrosion with a Master Plan

In July 1978 the Central Contra Costa Sanitary District (CCCSD) retained corrosion consultants Corrosion Engineering and Research Company (CERCO, Concord , California ) to conduct a system checkout on the isolation of pipelines, the integrity of insulating flange kits and the proper installation of a cathodic protection (CP) system on the construction of the CCCSD’s Wastewater Treatment Plant.  CERCO determined that the CP system was not ready to be energized because some of the pipes had not been bonded and the proper wiring for the impressed current system had not been installed.  In October 1980, L.P. Sudrabin, a consultant, and V&A Consulting Engineers (V&A) conducted an evaluation of the four rectifiers and buried piping on the CCCSD treatment plant property. 

Initial Investigations
In February 1981, V&A, in conjunction with Metcalf & Eddy Engineers, reported that the soils were highly corrosive, with a pH between 6.0 and 6.8.  Soil resistivities ranged from 1,700 to 12,000 ohm-cm and high concentrations of sulfates were found to be between 100 and 1,389 mg/kg dry weight.  Additionally, many piping systems were found to be shorted across insulating joints or to the reinforcing bar of building structures.  Most of the 1-inch to 78-inch diameter piping systems consisted of coal tar-coated steel pipe, cement mortar steel pipe, cast iron pipe, steel pipe with thermal insulating jackets, and ductile iron pipe.  Four excavations were made to expose ductile iron pipe, cast iron pipe, and steel pipe with a coal tar enamel or X-Thru-Coat®.

The initial investigation revealed that some corrosion had already occurred on the cast iron pipe and a small hole in the X-Thru-Coat® had resulted in the loss of some metal in the pipe wall.  Similarly, the coal tar enamel-coated steel pipe showed some graphitization and loss of metal.

Photos 1 and 2 show some of the deficiencies in the cathodic protection system found during the initial investigation.

Photo 1. Hole in X-Thru-Coat on cast iron pipe.	Photo 2. Broken conduit containing anode wires.

The four impressed-current systems were found to be protecting only a small amount of pipe due to (1) the lack of electrical continuity across pipe joints and (2) unnecessary shorting to other pipes, resulting in stray current corrosion.

As a result of the investigation, V&A presented three alternatives for CCCSD to consider:

Alternative A.  Complete the work proposed by the existing construction team but require isolation of the existing piping systems from each other and from building structures, and require that all unprotected pipes be bonded.

Alternative B.  Divide the piping systems of the treatment plant into four different zones according to the type of pipe and soil properties, so that each system can be protected with a cathodic protection system in the most suitable, cost-effective manner.

Alternative C.  Do nothing to the existing piping system and repair/replace as needed.

After evaluating all the alternatives, it was apparent to the owner that Alternative A would not work, since there were too many deficiencies in the protection of the piping system since the report was written.  Alternative C would be too costly (due to the number of repairs likely to be required) as well as extremely inefficient use the existing cathodic protection system.  Alternative B would be the CCCSD’s best option for fixing the existing deficiencies and protecting any future piping systems.

Master Plan Development
Ultimately, Alternative B was selected by the District and a Corrosion Control Master Plan was proposed by V&A.  The master plan would be implemented in two phases which included the following:

Identify locations where test stations were needed to monitor the existing piping systems.
Prepare plans and specifications for the installation of test stations. 
Prepare a construction cost estimate for planned test station installation. 
Design and install anode beds that would be used during field testing during Phase II.

In August 1985 V&A reported the overall strategy for implementing Phase I.  This included the isolation of certain buried piping in sections, based on pipe material, size of piping, existing electrical shorts to other structures and ease of isolation.  Zone 1 consisted of an impressed current system on steel piping buried outside the east side of the operations building.  Zone 2 consisted of isolating fuel oil supply/return lines and high pressure water lines.  Zone 3 consisted of isolating natural gas, liquefied petroleum, and atmospheric air from reinforcing bar in building structures.  After they were isolated, a galvanic anode system was installed on the piping system of Zone 3. 

Due to the unforeseen effects of the CP systems on the other three zones, the investigation of Zone 4 was postponed until everything else had been isolated and protected.  That way the effects of the CP systems from Zones 1, 2, and 3 on the ductile iron and cast iron pipe could be investigated.  Figure 2 is a general site map, showing the six different zones of the wastewater treatment plant.  A total of 45 test stations, three anode beds, and 27 bond stations were designed for installation within all four zones.  Photos 3 and 4 show the installation of an anode.

Photo 3. An auger is used to drill the hole.	Photo 4. The anode is lowered down into the hole.

Based on the success of Phase I, V&A was retained to complete Phase II of the CCCSD Cathodic Protection Design.  Like Phase I, it included field testing on the installed anode beds, test stations, and isolation of pipelines from building structures.  After the data was collected and analyzed, the size and quantity of additional CP systems would be selected.  Drawings, specifications, and cost estimates were created and updated at 10%, 50%, and 90% submittals before being finalized for construction.  A total of eight rectifiers, eight mid-depth anode wells, 84 anodes, and 13 junction boxes were designed for installation within all six zones. 

Master Plan Implementation and Results
CCCSD’s corrosion master plan has been in operation for approximately 15 years, and has been highly effective during that time.  The success of the CP systems in prolonging the life of the piping systems subsequently persuaded CCCSD to expand the corrosion control program to include pump stations, reclaimed water pipes, sewer force mains, and water mains.  Currently V&A conducts “as needed” cathodic protection surveys to monitor the condition of these pipelines and structures.  The systematic, conscientious use of a corrosion control program, preceded by a comprehensive master planning process, can enable Districts to maintain the integrity of their pipelines and avoid expensive repairs. 

Figure 1. Boundaries of the six cathodic protection zones within the CCCSD wastewater treatment plant.

If you would like more information on a corrosion control management program please contact us at 510-903-6600.