A New Approach for Sewer Mapping

A 3.603Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

As Surveyors in Government we are very familiar with surveying the infrastructure that provides the conveniences we’ve come to assume in the United States of America. I’m talking about paved roads, water, electric, communication lines, storm drainage and sanitary sewer disposal. All of these infrastructures have limited service life. Some of them may be repaired to extend that service life and some must be replaced. Surveyors and Mappers provide the topographic surveys that are used to design plans. I would like to share a new surveying and mapping technology (new to me) with you this month.

Many memories of climbing in and out of storm and sanitary manholes are still fresh in my mind due to difficulty, dangerous, humorous and less than sanitary conditions! Such as climbing down iron steps built into the brick walls of sanitary manholes. The paste squeezed out between your fingers as your grabbed the metal wrongs on your way down. The roaches never bothered me much as we used to catch the biggest ones we could get for fish bait while growing up. However some surveyors nearly danced into cars trying to avoid the little bugs as they scattered across the street after being dislodged by removing the sewer manhole lid. Alright I’ll stop.

Years went by attitudes and principles changed and climbing into sewers became unacceptable! Tools were invented to measure pipe sizes and manhole diameters from the surface. Safety has become the rule and when climbing into sanitary sewers must take place we are required to use retrieval devices, oxygen sensors, wear special suits and wear respirators. We must be trained and certified in order to perform these tasks.

The equipment necessary to meet OSHA safety guidelines is very expensive and the oxygen sensing units must be frequently serviced and calibrated. The equipment is cumbersome to store and transport. Using all of the required equipment and following the procedures required by OSHA, state and local government rules and regulations is very time consumptive and adds tremendously to the labor costs. These are some of the reasons we are trying a different approach regarding the infrastructure data collection on this survey project.

The project being surveyed is a sanitary sewer system and two lanes of the four lane roadway above it. The roadway mapping must take place but that mapping isn’t part of the subject I’m talking about. The technology is laser scanning. The new to me application is scanning sanitary sewer manholes and structures. "Necessity Is the Mother of Invention" (I love proverbial expressions). The roadway over the manholes in the failing sewer system had been widened many years ago. Some of the manholes were moved laterally without moving the pipe and main structure. Their cones were reconstructed making entering the structures extremely difficult. Our consultant is using a small sized laser scanner combined with and a reversed polarity tripod system to collect detailed spatial data inside the sanitary sewer structures.

We believe using this methodology will be a win-win situation for us. The amount of data collected will far surpass manual measurements. The man-hours necessary to collect the data are expected to be far less than those required to make manual measurements. By not requiring staff to enter these structures we’ve avoided retrieval gear, hazardous suits and most of all, avoid most of the life threatening risks incurred performing the manual measurements. The only reason I use the word most is surveyors must still work in a busy roadway and a good traffic plan must be in place.

I am excited as we wait for the results of this survey and if successful we look forward to using this mapping technology in storm sewer infrastructure data collection in the future. We believe it will change the way routine infrastructure mapping as well as as-built surveys are performed in the future. If you’re interested in the results of this survey or would like to share your common experiences please feel free to contact me at Joe.stokes@cityoforlando.net

Joe Stokes is the City Surveyor for the city of Orlando in Florida.

A 3.603Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE