Getting the Most Out of a Test Pit Program for a Preliminary Investigation on the Puerto Nuevo Effluent Pipeline

Abstract

The Puerto Rico Aqueduct and Sewer Authority (PRASA), owns and operates the Puerto Nuevo and Bayamon Wastewater Treatment Plants which serve37 % of the sewer service in the island). Primary treated effluent is discharged to the Atlantic Ocean through an effluent pipeline that is shared between the Puerto Nuevo and Bayamon WWTP and the Bacardi Corporation WWTP which extends approximately 10 kilometers to an ocean outfall. The effluent pipeline is deemed to be a critical asset, whereby service cannot be interrupted. Discharge of any effluent from the pipeline would be in violation of EPA regulations. Much of the pipeline is located in environmentally sensitive areas where the pipeline runs adjacent to natural waterways and traverses wetlands The effluent pipeline was constructed in the 1970's and 1980's using prestressed concrete cylinder pipe (PCCP) manufactured in accordance with AWWA Standard C301. The pipeline ranges in size from 72-inches to 120-inches in diameter. Although there have been no failures on the effluent pipeline, PCCP used in the construction of PRASA's nearby Super Aqueduct pipeline have failed in the past. Usually, these pipes last a long time without service problems; however, there are variables that if not addressed properly during the design, installation and maintenance, can lead to corrosion of the prestressing wire. Under certain conditions, hydrogen sulfide gas may accumulate in air pockets that form at high points in wastewater force mains. The gas can oxidize into sulfuric acid and damage the top of the pipe wall. Conversion of the gas to sulfuric acid requires an aerobic or oxygen-supplied condition - such as that provided by an air pocket. To better understand the condition of the effluent pipeline and to minimize the risk of future failure, CH Caribe Engineers/PSC (CH-Caribe) and Openaka (a division of Pure Technologies) performed a preliminary investigation of the pipeline. The investigation focused on selected pipe sections that were readily accessible, where the scope of work included visual inspection, sounding, continuity testing of prestressing wire, sampling and analysis of prestressing wire and cement mortar coating, sampling and analysis of surrounding soil and groundwater, ultrasonic testing to measure wall thickness, etc. This paper addresses the procedures of the investigation, testing protocols, inspection and laboratory results, findings and recommendations.