L&S Surveying Services Limited operates out of Trinidad and Tobago and Guyana, with 17 years of experience in the field of surveying and mapping. As a company, we observed a need for underground utility location and mapping in the twin island of Trinidad and Tobago (T&T) through research and interactions with many clients. Similarly, the technology proved beneficial to T&T since the main drivers
for the country’s economy is oil and natural gas. Therefore in 2009, L&S added a Sub-Surface Surveying Service to its portfolio where we are able to locate, demarcate (supply and install aboveground markers) and document/map metallic and non-metallic features underground.
A combination of tools are employed to locate these subsurface features including Ground Penetrating Radar (GPR), electromagnetic pipeline and cable/fault locator, Duck Rudder and ferromagnetic locator. While GPR is one of the leading subsurface investigative tools, other techniques are often employed because the soil profile of T&T is mostly clay and does not provide the ideal conditions for clear scan data to be captured by the GPR. Also, since many areas in T&T are susceptible to flooding from heavy rains, other options have to be explored because the
signal from GPR is usually lost in soil heavily saturated with water.
Specifically for waterborne pipelines and sewer lines, additional non-routine procedures for a fruitful location are required where the use of both technologies complement each other. A perfect example is where L&S was required to locate and map an existing water supply line known to supply a conveyor
system within an industrial steel plant. The line was both metallic and PVC at various points, and GPR and electromagnetic locators were used to locate the line for future design drawings in the plant’s maintenance department.
Other examples of jobs executed with the water/sewer theme are:
1. The locating and mapping of all the compound’s underground sewer and drainage network for a known bottling company in Trinidad. This included sewer tanks, portable water lines and concrete drains. The purpose of the job was to assist in the creation of an Environmental Management
Assessment (EMA) plan for certain health approvals to ensure that the client was not polluting the area.
2. Mapping of the underground infrastructure for the state’s water utility company. This was done to assist in updating the company’s Geographic Information System (GIS) records with old existing PVC major pipelines’ locations.
Similarly, T&T water and sewer infrastructure is not always metallic or have tracer wire add-ons. Therefore, a method using test pits to verify results along with the technician’s experience is adopted. Conversely, for jobs done without test pits, the confidence in the location data is lower than the typical metal pipeline location exercise and experience in viewing GPR scan data and deduction of existing surface features help in these locates.
Installation of aboveground markers is also just as important as locating these subsurface features because, in reality, some form of demarcation is the last line of defense. In the past in T&T, “digging before checking” was common and the results were not favorable. Therefore, L&S stresses the importance of demarcation and goes further to integrate the information surveyed with topographic
data. In other words, the underground information captured is overlaid onto a topographic map. This proves beneficial and acts as a future reference for clients, especially in scenarios where pipelines are to be relocated for various purposes.
Through the knowledge gained, we are able to spread awareness of the technology and its use as a damage prevention tool to our clients and society through demonstrations, conferences and career days. However, the following has been observed:
1. Since the mapping of pipelines was very poor throughout the years in T&T, the industrial side of T&T has embraced the technology. The same cannot be said for the private sector.
2. Demarcation of underground features is important for future reference since markers are really the last line of defense. Likewise, record preparation of the data collected overlaid onto topographic maps for future reference is also important, especially for asset management and the relocation of lines
for facility upgrades.
Nikita Morris is Project Assistant, Darryl Ragoopath is Survey Supervisor/Underground Utility Location and Mapping Expert, and Brendon Marchan is Assistant Survey Manager at L&S Surveying Services Limited (Trinidad). Visit lssurvey.com to learn more.