Hyperion Treatment Plant 5-Mile Outfall Re-Ballasting Project

Abstract

Outfall StudyThe 5-mile outfall is inspected externally on a yearly basis, but was never inspected internally during its 50-year existence. To collect sufficient information to establish and evaluate the condition of the pipeline, the City of Los Angeles in conjunction with Parsons Corporation initiated a program to conduct field studies for evaluation of the outfall in mid 2007. Divers were sent into the outfall to assess its structural condition, evaluate its reliability, and identify potential trouble spots. The inspection consisted of several scientific and engineering exams, including internal inspection, external remote operated vehicle inspection with sonar, field studies, hydraulic analyses, pressure evaluations, geotechnical investigations, seismic hazard, and structural stability analysis that utilized a physical model designed and constructed at the Oregon State University.Concrete core samples were also taken from the outfall to determine concrete strength and rebar condition. Inspection ResultsThe inspection revealed that the outfall itself was structurally sound. The strength of the concrete had not deteriorated and the rebar was intact. In addition, the pipe joints were not leaking and did not indicate signs of wear. However, the inspection did reveal that the ballasting in several locations had either washed away or settled into the seabed floor. It was recommended that a project be initiated to reballast the outfall to ensure protection and continued successful operation. Proposed ProjectThis project will apply approximately 40,000 cubic yards of additional 8, 10, and 12-inch minus rock ballast from Stations 92+00 to 275+25 up to pipe's mid point. The ballast will consist of a four foot table with a 1 to 1.5 slope from that point to the sea floor ( Figure 3). This project consists of a 3758 WEFTEC 2011