ACHIEVING “ZERO LEAKAGE” ON GEOMEMBRANES
Based on several years of testing activities we deployed our SENSOR DDS® MIT Arc tester to test the integrity of leaking process ponds following an emergency call from a Client. With incredible ease the Arc tester detected all leaks even ones in areas not anticipated by the Client.
The need for the survey was generated because the geomembrane installers on the site could no longer continue. They had already installed three layers of geomembrane in attempts to abate leaking.
Despite this the ponds were still leaking and the contaminants always appeared under the newly placed geomembrane layer after use of the ponds. The lining installers work was excellent quality, the degree of CQA was usual and good enough to even convince the authorities to allow the ponds to be put into service. The result of the ponds being completely out of service would have been enforced stoppage of the client’s production processes which would have caused massive losses.
Thanks to excellent results using the SENSOR DDS® MIT Arc tester it was discovered that the problem was not because of improper or poor quality work by the geomembrane installers, but in fact careless work of other construction companies doing maintenance of related facilities, such as pipes and other construction work (dropping of hand tools, almost invisible holes due to sparks from mig welding of metal pipes, etc.).
During the survey of this facility we found surprising results – many small almost invisible holes. Analysis of the cause of the holes revealed a production fault within the material itself. Such leaks are unable to be seen by visual inspection or revealed by any other known conventional ELL system for exposed membrane testing. In addition any inspection by the dipole method when geomembrane is covered by material could also not have revealed such tiny and high density (by area) of holes.
Furthermore we also detected and located large amount of other holes of more classically known origin: faulty extrusion seams; faulty hot wedge seams; holes next by hot wedge seam created by high pressure between machine pinch wheels; overheated and burned out areas; punctures by sharp objects; and stones coming from poor subgrade conditions when geomembrane is placed over the top during its installation; etc, etc.
We also discovered damage due to wrongly stored rolls of geomembrane and holes as a result of their shipping and handling. The next interesting findings were leaks under drainage pipes created during pipe installations. Debris and small sharp stones and objects creates small punctures.
Based on expert opinion on site even such small holes can create significant leakage of productive material contaminating the subgrade. This is because of their position directly under drainage pipes where there is also usually a depression in the subgrade. Based on these findings such places were more carefully treated, cleaned and tested twice, once before placing a pipes and second time after their installation to ensure that no damage was left in these areas.
Other discoveries were the existence of many holes were created due to the frequent passage of people over already placed panels of geomembrane, moving small machineries during installation process or other additional construction works. Whilst other holes were as a result of accidents caused by strong wing and moving objects over the geomembrane surface.
Thanks to the Arc testing process all holes were detected, located successfully repaired allowing the site to reach the status of zero leakage.
Progressively from 2009 within next 4 years and in different countries (several within the EU plus, Turkey, Chile, Bolivia) and in different geomembrane applications (water ponds, municipal landfills, process ponds, mining sites, roofing, etc) we carried out many surveys covering nearly 5,000,000m2 on a variety of geomembranes types (HDPE, LLDPE, PVC, PP, fiberglass, PU liquid coatings, etc.) and over many different thickness from 0.6 – 5.0mm. The results far exceeded our expectation. More than 4,700 holes were detected. From these real life findings we created some statistics which are hereby presented. The image below shows the general analysis of all detected holes in relation to their size
The chart below shows the general analysis of all detected holes in relation to their size. Within the chart below is an analysis of all detected holes in relation to their causes. What is incredible looking at the data is the realization that without Arc Testing how many holes must stay undiscovered, creating potential places for leaks and contamination, or loss of production material.
In order to highlight the contribution of each ELL method in relation to amount of holes / leaks detected chart below was created. Inside this chart the both the Arc Test and Dipol method are compared. This comparison is linked through the sizes of detected leaks / holes so to be able to pinpoint their productive mutual complementarity. It should be noted that the overlapping area of size of leaks / holes (5.0 – 50.0 mm) is represented by diametrical opposing hole / leak types. In the case of Arc Testing it is mainly faulty seams and cuts in geomembrane. Whereas in case of SENSOR DDS® Mobile / Dipole method these are mainly tears and damage caused by heavy plant.
All presented data is based on real results from surveys completed over a total area of 6,820,020m2 which represent 6.98 holes / leaks per Hectare. Further conclusions can be drawn from the chart above as this shows the clear dominance of the Arc Testing method as a proportion of detected leaks which represents 92.98%of the 4,761 leaks / holes detected and located. The next conclusion that can be drawn from this chart is that the holes sized from 1.0mm to 50.0mm are predominantly found by Arc Testing. On the other hand it is necessary to say that within the interval of 10.0 – 50.0mm the dipole method is equally good at detection of leaks. In this case this is represented mainly by serious damage like tears or general damage caused by heavy machinery. Also it should be noted that, leak size interval of 1.0 – 50.0 mm by its very nature covers the majority of emerging breaches in the liner . The aforementioned interval represents 94.64% of all leaks detected and located within the survey analysis.
This clearly confirms that the dominant quantity of leaks are created during the geomembrane installation period and within a time period when the geomembrane is not yet covered. So far we could only intuitively think about it, but now we have very clear tangible evidence of this incredible issue. Of course on other side this is confirmation of the necessity of use of ELL methods to control the integrity of geomembranes after covering and in the end to have sites free of leaks. Again we can authoritatively state based on the chart above that the Arc testing method creates a logical pairing with the SENSOR DDS® Mobile Dipole method.
That further highlights the indispensability and suitability of the Arc Testing method for exposed geomembranes and its application before being covered. The assumption that the Dipole method is enough to detect and reveal every hole / leak including the ones described above detected by Arc Test is wholly incorrect because the principle and character of the Dipole method does not enable it to detect such geomembrane damage. Notwithstanding that the combination of Dipole with Arc Testing significantly moves meaningful ELL work to the pinnacle of a “Zero Leak” geomembrane installation. The Arc Tester under appropriate boundary conditions is able to detect 100% of all existing leaks in exposed geomembranes and the Dipole method contributes through the detection of leaks created during subsequent processes such as placement of drainage and protective layers on top of geomembrane. This is extraordinary and productive combination of ELL methods.
In fact similar findings were published by authors Forget, Rollin and Jacquelin(2005), whose analysis reached similar findings but based on water based method applications along with Dipole application. The clarity of need for such a unique combination of testing methods (exposed geomembrane testing and covered geomembrane testing) and creation of one logical set for achieving leak free installation is documented by Beck, A. (2012) whose paper describes the application of a conductive geomembrane tested by spark test and followed by Dipole method after covering, showing that in this combination of ALR 0.00001% can be achieved.
To obtain another very valuable findings we included within the analysis three sites where the pairing of an Arc Testing with Dipole testing was applied. We named them generically site “A”, site “B” and site “C”. These three sites were chosen due to the relatively large scale of their surveys in order to ensure statistically better and more relevant data. Standard CQA was applied as a matter of course. With regards to geomembrane installation sites B and C deployed an LLDPE 2,0mm double textured material whereas site A was constructed using LLDPE 1,5mm in a combination smooth and textured materials. In the case of site A the installation was done in portion of 40% of steep and gentle slopes. In case of sites B and C these were mainly flat areas with slight and general site gradient.
Total surveyed area of site “B” was 230,400m2 by both methods Arc Testing and Dipole testing. The results are given in the chart and table below. Of special note is finding that 58.82% of all leaks are within the size interval 1.0-50.0mm. It can be seen from the chart that there is a very sharp boundary between intervals of leak sizes to 10.00mm for Arc testing and above 10.0mm for Dipole testing. The explanation of this finding is that leaks detected by SENSOR DDS® MIT Arc Testers were mainly caused by faulty seams and cuts and punctures by small stones. On the other side the leaks sizes above 10.0mm detected solely by Dipole method were created by heavy machinery / plant (tears and larger punctures by stones) during placing of covering layers. Holes / leaks of sizes under 10.0mm did not appear during dipole testing. According to these results it can be stated that the presented character of leak division between Arc testing and Dipole testing as logical and with justification.
Total surveyed area of site “C” was 411,102m2 by both methods Arc Testing and Dipole testing. The results are given in the chart and table below. Of special note is finding that 89.25% of all leaks are within the size interval 1.0-50.0mm. Again evident from the chart that there is a very sharp boundary between intervals of leak sizes to 10.00mm for Arc testing and above 10.0mm for Dipole testing. The explanation of this finding is that leaks detected by SENSOR DDS® MIT Arc Testers were mainly caused by faulty seams and cuts and punctures by small stones. Of special note is detection of production faults inside geomembrane – almost invisible perforation at many places represented by leaks were purely from placing layers of stone by heavy machines (tears and wheel tracks). Leaks sizes of below 10.0mm did not appear in this construction period. According to these results it can be stated that the presented character of leak division between Arc testing and Dipole testing as logical and with justification.
The sum of Arc Testing together with Dipole Testing (or Permanent Monitoring) is greater than its individual parts. This seemingly incredible statement is backed by analysis of results from a sample size 6,820,020m2 and also by the analysis of the Arc testing method contribution to overall leak testing methodologies.
Simplicity, effectivity and most importantly the sensitivity of the Arc tester gives us the keystone to what is in biblical literature known as the “Holy Grail” and in our microscopic world of Geosynthetics applications known is as „Zero Leak”.
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