Effect of overburden confining stress on hydraulic performance of geosynthetic clay liners (GCLs).

Geosynthetic clay liners are a rapidly evolving geosynthetic product used in most hydraulic barrier applications in the geo-environmental industry. Continuous research has led to new insights to overcome the shortcomings faced in deploying GCLs in the field. These include shrinkage due to shear failure on side slopes, the effect of temperature variation, and inadequacy of minimum timely confinement to achieve optimum hydraulic performance. This paper presents previous experimental data and an additional dataset from this research gathered to observe the effect of overburden confining stress on GCL hydraulic conductivity and how the findings can be used to predict the performance of a geosynthetic clay liner for a given field application. An inverse power relationship is identified between these two parameters along with the reduction in the order of the degree of hydraulic conductivity depending on the permeant material passing through. A relationship is determined to estimate the GCL hydraulic conductivity as a function of the overburden confining stress, given that it is pre or post hydrated and the permeant liquid passing through the product. It is proposed that the relationship can be used to predict the GCL hydraulic performance in the field and provide guidance in improving the serviceability of hydraulic barrier designs.

Factors affecting the hydraulic performance of a geosynthetic clay liner overlap.

Geosynthetic clay liners (GCL) are increasingly being used as a major component of barrier systems replacing compacted clay liners due to their very low permeability and speed of installation. Researchers and practitioners have identified the critical role of the GCL overlap that presents constant challenges encountered in maintaining the designed hydraulic conductivity. This study presents a series of flow box tests conducted to evaluate and improve understanding of the combined effect of each of the four contributing factors, namely, overlap width, supplemental bentonite applied at the overlap, the overburden confining stress, and the hydraulic head acting on the GCL overlap. The findings reveal that the overlap width is the most significant parameter affecting the design hydraulic conductivity. The application of a minimum overburden stress to maintain the designed hydraulic performance is also recognised as important. The effect of confinement due to higher hydraulic heads is of interest to practitioners. The supplemental bentonite has the least effect on the GCL overlap hydraulic performance even though it enhances the function of the overlap seam. This knowledge addresses the inadequacy of published GCL overlap experimental data comparing the effect of different factors affecting its hydraulic performance. It also assists industry practitioners to design and specify the overlap criterion for a specific application depending on the product specifications and site conditions. The results of this research will help minimise failures of liner systems in barrier applications such as landfills, mines, tailing dams substantially to reduce the potential risk of groundwater contamination.

Molecular identification of mosquito species in the Anopheles annularis group in southern Asia.

The Anopheles annularis group of subgenus Cellia Theobald (Diptera: Culicidae) includes five currently recognized species in southern Asia: An. annularis Van der Wulp, Anopheles nivipes (Theobald) and Anopheles philippinensis Ludlow, which are widespread in the region, Anopheles pallidus Theobald, which is known in Sri Lanka, India and Myanmar, and Anopheles schueffneri Stanton, which occurs in Java and Sumatra. Identification of the four mainland species based on morphology is problematic. In view of the fact that the three widespread species are variously involved in malaria transmission in different parts of the region, we developed a species-specific polymerase chain reaction assay based on rDNA internal transcribed spacer 2 (ITS2) sequences to facilitate entomological and epidemiological studies of the four species. The method proved to be reliable when tested over a wide geographical area.

Experience with the oral iron chelator deferiprone in transfusion-dependent children.

OBJECTIVE: To establish efficacy and safety of deferiprone. DESIGN: Prospective study. SETTING: The Lady Ridgeway Hospital for Children, Colombo. PATIENTS: Transfusion-dependent children in the age group 1 to 15 years. INTERVENTION: Patients were given 75 mg/kg/day of deferiprone orally in divided doses. MEASUREMENTS: Efficacy of deferiprone therapy was assessed by 4 to 6 monthly serum ferritin (SF) assays. Safety of therapy was assessed by 4-weekly white cell counts and serum alanine aminotransferase (ALT) levels. The Z-score was used to assess the significance of the difference between the mean initial and final SF level. RESULTS: 82 patients received deferiprone therapy for a mean duration of 30 +/- 14 months. Initial SF levels ranged from 1115 to 12,165 micrograms/l with a mean of 5156 +/- 2631 micrograms/l. Final SF levels ranged from 312 to 15,285 micrograms/l with a mean of 2809 +/- 2380 micrograms/l (Z score 5.99; p < 0.001). Two (2.4%) children developed agranulocytosis which reverted to normal on discontinuation of treatment. 41 (50%) developed arthropathy and in 17 this was severe enough to require discontinuation of therapy. Serum ALT levels were raised in 35 (43%) patients but reverted to pretreatment values or lower despite continuation of deferiprone therapy. There was one death in a 9-year old child who developed diabetes mellitus and heart failure despite deferiprone therapy for 3 years. CONCLUSIONS: A final SF level < 2500 micrograms/l was achieved in 52% children. Severe arthropathy and agranulocytosis may necessitate permanent discontinuation of therapy.