ASTM C13.06 working to develop a new standard.
By Eric Carleton, P.E.
For the past five decades, municipalities have made installing watertight sanitary sewers a priority. The movement toward achieving a tighter system originated from the Environmental Protection Agency when it provided federal grant money for the upgrade of municipal sewage treatment plants and collection systems. It actively promoted the concept that groundwater infiltration or stormwater inflow equated to unnecessary treatment expenses and needed to be greatly reduced or eliminated. As a result, it became a prerequisite for project funding.
To verify required leakage criteria compliance, municipalities relied on standard infiltration testing if the water table surrounding the installed sewer was high enough. Physical measurements of incoming water were taken using a V-notch weir. If the sewer was above the water table, an exfiltration test was used. This required filling the sewer and manholes with large volumes of water from an outside source and again physically measuring the pressure of water that would leave the tested sewer section.
Positive air pressure
In the 1960s, many prominent researchers including Roy Ramsier, William Chase, George Riek, Harvey Duff and others devised testing protocols that used compressed air. This research helped develop standard testing protocols by ASTM International and others and using air instead of water became the primary means of sewer line acceptance.
However, when it came to testing the various manhole structures within the collection system, positive air testing had a drawback. With positive air pressure testing for pipelines, the system could be plugged off and properly restrained to resist the horizontal pipe movement the testing pressures exerted against the pipe (3-5 psi).1 Restraining the vertical movement of the various manhole components proved problematic since low air pressures provided enough force to physically lift flattops, cone reducers or casting frames. Consequently, manhole leakage testing was limited to visual inspections or water infiltration and exfiltration testing.
Negative air pressure
During the late 1980s, Peter Glazier of P.A. Glazier Inc. was the first to solve the positive pressure problem with manhole testing by using a vacuum, or negative pressure. Glazier proceeded to develop a simple portable testing apparatus, which could be used to seal the manhole top – whether it be a precast cone, flattop or even a casting frame – along with a portable, powered vacuum pump. He also hired a professional engineer, Michael J. Burke, to analyze the vacuum testing criteria and develop specific recommended testing vacuum limits and holding times related to current accepted positive air pressure testing methods. To gain wider acceptance of this novel testing approach, Glazier used Burke’s recommendations, but simplified the calculated holding times by promoting only a fixed value based on a manhole bury depth exceeding 30 feet.
A new standard emerges
The acceptance of vacuum testing for manhole structures gained national recognition, but without a national standard, the specific testing vacuum and holding times varied widely.2 In many cases, unreasonable criteria led to “testing failures” for manhole structures, which were found to be in compliance with infiltration/exfiltration limits established by the sewer authority.
In late 1990, ASTM Subcommittee C13.06, Manholes and Specials, requested a consensus-based standard for vacuum testing manholes. After three years of research, committee discussions and ballot processing, the final criteria for testing went back to the original analysis developed by Burke, which used a variable holding time requirement based on the tested manhole interior diameter and depth. The committee also agreed to maintain the initial test vacuum at 10 inches of mercury, with an allowable drop to 9 inches within the allotted time restraint. In 1993, ASTM C1244, “Standard Test Method for Concrete Sewer Manholes by the Negative Air Pressure (Vacuum) Test,” was published and Glazier’s original concept gained greater national acceptance.
Issues with backfilled manholes
But despite the new standard, an unexpected result occurred during the testing of manholes installed deep and backfilled in an area with a high water table. The combination of the manhole internal vacuum test pressure and the external hydrostatic pressure of the water table exerted pressures exceeding the limits on the resilient rubber connectors for the pipes entering the manhole. Consequently, manholes without defects were not only failing the test, but had damaged connectors in difficult water conditions that needed repair.3
To alert the public about this issue, ASTM International – after a ballot process – revised the title and scope of C1244 to “Standard Test Method for Concrete Sewer Manholes by the Negative Air Pressure (Vacuum) Test Prior to Backfill,” which was published in 2002. Though there are many valid technical reasons to revise this test, it did not answer the sewer agencies’ need to provide assurance that the completed manhole structure, including backfill placement, was in compliance to design requirements.4
In response to this need, ASTM C13.06 has a work item and task group in place to develop a new standard, which will address the appropriate concrete manhole vacuum testing criteria and issues of completed and backfilled manholes. If you are interested in participating and learning more about the ASTM task group or standards development, please contact Eric Carleton at [email protected] or at (317) 208-6431.
Eric Carleton, P.E., is NPCA’s director of codes and standards. He also is an ASTM Award of Merit recipient and currently serves as vice-chairman of ASTM C13, Concrete Pipe.
- Know When to Restrain Pipe, Michael Miller, MC Magazine, September/October 2004
- Vacuum Testing Provides Simple Method of Demonstrating Manhole Quality, Michael Miller, MC Magazine, Summer 1998
- Vacuum Testing Precast Concrete Manholes, Precast Solutions, Spring 2007
- Vacuum Testing Backfilled Manholes, Claude Goguen, P.E., LEED AP, Precast Solutions, Spring 2011