A Statewide Assessment of Infiltration and Inflow in Municipal Collection Systems in Maryland

Maryland’s Smart Growth program focuses development where there is adequate utility system infrastructure. Excessive infiltration and inflow (I/I) can prevent the use of available capacity in wastewater collection systems. The Maryland Environmental Service (MES) conducted a project to evaluate collection systems across the State to determine the extent of I/I and the estimated costs needed to correct the deficiencies.The systems had an average of 50% available capacity when using dry weather flows, but after factoring in I/I flows, the actual available capacity was on average only 10%. The amount of I/I per kilometer of sewer line ranged from 5.6 to 17.9 cubic meters/km/day, with system rehabilitation costs from $5,600 to $17,300 per cubic meter of I/I. Extrapolating the cost factors to 45 other collection systems in Maryland gives a total estimated cost of $800 million.