Chemical Grouting: A Solution to Infiltration

Editor's Note: We want to thank Avanti International for permission to use their photo as Figure 1 in this post.

Infiltration is defined as an excess of unwanted water entering a sanitary wastewater system from groundwater or storm water. More specifically, infiltration occurs when groundwater enters the sanitary sewer through defects in pipes and manholes (Figure 1). This excess water can cause damage to the collection system when sewers are forced to transport more flow than they are designed to handle. Increased effluent also raises wastewater treatment costs because the facility must treat harmless storm water and groundwater with the sewage. This added flow increases wear on equipment, electrical cost, and overall operation and maintenance expenses. In addition, if the capacity of the collection system or treatment plant is exceeded, untreated wastewater may be discharged into the environment.

Figure 1. Potential Sources for Infiltration

As with most utility problems, there are many potential solutions. For infiltration where defects are localized, some of these solutions include mechanical point repair, injection methods, or rerounding. A discussion of the chemical grout injection option is given below. 

The chemicals used for grouting have been available since the early 1960s. They are usually urethane based and when they come in contact with water react to form a polymer material that is a barrier to water flow. The conditions/steps required for grouting are:

1. A pipe or joint cannot be failing structurally
2. There must be a path for the grouting solution to flow out into the soil
3. The area must be free of debris such as roots, grease and other obstacles that may prevent proper application of the grout.
4. Application of the chemicals at a pressure higher than the water table of inflowing water.
5. Final testing of the repair (air pressure or visually).

A video providing an overview of this process using remotely operated equipment is given below.

Chemical grouting can also be applied manually and can stop the leak almost instantly. A video of manual grouting for a leak in sewer wall is shown below. 

In summary, chemical grouting technology for stopping infiltration is attractive because the chemicals are non-toxic to the wastewater treatment plant and can be applied using remote controlled equipment or manually for small localized defects. Chemical grouting is a flexible low cost option for infiltration repairing of sewer mains in addition to sewer laterals.

Featured Video: Sewer Dye Testing

A municipal sanitary sewer system is designed to collect and transport wastewater from homes, offices, businesses, restaurants and other sources to a municipal wastewater treatment plant for treatment and safe discharge into the environment. If other sources of water are allowed to enter the sewer system, the collection system and wastewater treatment plant can become over loaded allowing untreated water to be discharged. This is defined as sanitary sewer overflows, or SSO’s. One of the biggest sources of excess water is infiltration of storm water and groundwater into the sanitary sewers. A method to detect this infiltration is through dye testing.

Dye testing is a simple procedure where storm drains, yard drains, and the outside of the foundation walls of the house, or other areas are flooded with water to simulate a period of heavy rainfall. The colored water is pumped through the ground and storm water system and appears in the sanitary sewer collection system where leaks occur. This test is simple and complements smoke testing that may have been done previously.

The dye testing procedure can be accomplished in the following steps.

1. Isolating a section of the storm water network to test by plugging pipes at specific locations. 
2. Then, bright-dyed water is pumped into the storm water network until it reaches capacity. 
3. Remote CCTV cameras are deployed into the sanitary sewer system, where any points of storm water ingress are highlighted clearly by the dyed water.

Once the testing is completed, the locations of these sources of infiltration makes the process of repairing these leaks far more straightforward facilitating effective piping and system repairs which keep infiltration to a minimum.

A video showing how dye testing can be carried out is shown below: