San Jose Trunk Sewer Inspection and Assessment

The San José Sanitary Trunk Sewer is a key component of the wastewater conveyance system that serves the San Juan metropolitan area. This trunk line conveys over 25 mgd of wastewater from the eastern, southeastern, and western portions of the metropolitan San Juan service area to the Puerto Nuevo Regional Wastewater Treatment Plant (WWTP). The last principal segment of the San José trunk sewer system is a 90 - inch diameter reinforced concrete pipe which passes under the former San Juan Landfill. The 90-inch diameter trunk sewer segment was installed in the 1950s and is approximately 700 meters long. This segment of the trunk sewer consists of a reinforced concrete pipe installed over wooden pile supports spaced at approximately 8 feet. The original ground surface consisted of alluvial soils from the bank of the Puerto Nuevo River, soil with limited structural capacity. For the past 20 years, the Puerto Rico Aqueduct and Sewer Authority (PRASA) has become increasingly concerned with the physical condition and hydraulic carrying capacity of this trunk line. During the 1970's, a sanitary landfill was constructed over the San José Trunk. Over the years, San Juan Landfill operations encroached upon the trunk sewer and the line was covered with, in some cases, in excess of 40 feet of refuse. The additional loading from the landfill was not considered in the original design of the concrete pipe. In the 1980's, PRASA obtained a Court Order to restrain the San Juan Municipality from continuing to deposit solid waste over the trunk alignment. Since the line is constructed of concrete and has been in service for over 50 years, there is also a significant concern that the effects of corrosive sewer gases and leachate may have compromised the structural integrity of the pipeline. Prior evaluations of the trunk sewer have suggested that the structural integrity of the line may have been compromised by the load of refuse and overburden on the portion of the trunk line that runs through the landfill. There was concern that the trunk line may have settled in areas under the landfill, which could result in lost hydraulic carrying capacity. Additionally, manholes within the landfill have been covered over and appropriate inspection of the line could not be conducted to ascertain the condition of this important infrastructure element.