ARCHIVED REPORTS_2015 - Laserfiche WebLink

Home Browse Search

As-Built CQA Report for the Construction of Area 2A at the Foothill Sanitary Landfill San Joaquin County,California • 9.0 LEAK LOCATION SURVEY Leak Location Services, Inc. (LLSI), as a subcontractor to R. J. Gordon, performed the leak location survey for the HDPE geomembrane, first on bare membrane and another after GDM and operations layer soil were placed. Two test methods were used: (a) water puddle method (ASTM D 7002) for primary and secondary bare geomembrane, and (b) dipole method (ASTM D 7007) for geomembrane with all the liner components in place including LCRS and operations layer soil. The water puddle leak detection technique consists of the application of a difference in electrical potential between the ground underneath the geomembrane and a water jet sprayed onto the surface. The HDPE geomembrane is non-conductive and prevents the flow of electrical current. In the event a leak is present, the water comes in contact with surface below the geomembrane, thus allowing the flow of electrical current.A current detector informs the operator via visual and audio signals of the presence of a potential leak. For this project, the GCL layer acted as the conductive layer below the geomembrane.The equipment was calibrated using the end of an 18 AWG insulated wire with the other end connected to earth ground.The calibration was performed at the beginning and at the end of each day. For the dipole method, a voltage potential is introduced to the soil above the non-conductive geomembrane and grounded to the earth beneath it. In the case of a hole in the geomembrane, • current exits through the hole location, causing an anomaly in the voltage potential field at that location. Measurements of voltage potential are taken in a grid pattern throughout the survey area. For this project, a calibration test was performed using a 0.25 inch diameter artificial leak to determine the maximum distance that the leak could be reliably detected. The leak detection distance was approximately 3.3 feet. The survey data was taken on 5-foot spacing, which means measurements were made within 2.5 feet of every point above the geomembrane. The introduced artificial leak was then repaired. LLSI performed the water puddle leak location survey between August 2, 2015 and August 4, 2015, and the dipole leak location survey between September 10, 2015 and September 16, 2015. No holes were detected during either survey. LLSI's leak location survey report is included in Appendix M. • PA14 Projects114-101(SJCDPW North County and Foothillffoothill CQA1Report\Final ReportToothill CQA Rport-Final.docx 34