RCAP's Drop of Knowledge: Article Roundup #6

Drop of Knowledge is a monthly digital article from Rural Community Assistance Partnership (RCAP.) The articles focus on topics like wastewater, drinking water, policy, and infrastructure in rural America. It contains how-to’s, tips, and guidance from more than 300 technical assistance providers (TAPs) across the country. Some featured articles are linked below:

• An Elementary Look at Water Pollution
• Colonias in Texas: Improving the Quality of Life One Flush At a Time
• Investigating Inflow & Infiltration
• Water and Wastewater Utility Asset Management: Vehicles
• Wastewater Maintenance: Drawdown Pump Test
• When the Going Gets Rural: Five Challenges Technical Assistance Providers Can’t Escape

Looking for something else? Find more articles and subscribe to A Drop of Knowledge.

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.