To reduce infiltration into the existing wastewater collection system, you should

• A. Enforce ordinances that require roof drains to be discharged to street gutters or storm drains
• B. Insert plastic liners into sewer pipes
• C. Replace multi-holed manhole covers with no-hole covers
• D. Use higher pressures in force mains

Answer: (B)

Reducing infiltration means stopping groundwater from seeping into the sanitary sewer through cracks and joints. The most direct and effective way to do this in existing pipes is to rehabilitate the interior with a plastic liner. This liner creates a new, seamless inner surface that seals cracks and joints, so less groundwater can enter the system. It also tends to improve flow because the interior becomes smoother and less prone to seepage.

Other approaches either address inflow (like directing roof drainage away from the sewer, which reduces stormwater entering the system) or don’t specifically stop water from seeping through the pipe walls (changing manhole covers or increasing force main pressure). The lining method targets the actual leakage pathways, making it the best fit for reducing infiltration.