Permeability for the liner itself is as good as zero, but the permeability for the whole system has to be considered.This is because if you putting liners in that are going to cover acres of pond the joints in the liner can never be considered absolutely 100% water tight. There will be small holes , minor imperfections , faulty welds etc. There are various QA systems to check and test for this.
Spark testing of liners and vacuum and pressure testing of welds etc. With these tests and competent installers the leakage rate can be made very low.
I have included some standards below that i have used on a number of projects. Generally i have used 1.5mm smooth on the floor and 2mm textured on the walls. Textured or smooth is really a safety decision as the smooth gives a very slippery surface but is not a problem if it will never be walked on. I have used white HDPE on the walls as well but i am not sure whether this is of any advantage.
Density (geomembrane) Minimum 0.940 g/cm3 ASTM D1505
Tensile Properties (each direction) ASTM D6693
Strength at Break (N/mm-width) Minimum 43 Dumbell, 2 ipm
Strength at Yield (N/mm-width) Minimum 23
Elongation at Break (%) Minimum 700% G.L. = 51 mm
Elongation at Yield (%) Minimum 13% G.L. = 33 mm
Tear Resistance, (N) Minimum 187 ASTM D1004
Puncture Resistance, (N) Minimum 530 ASTM D4833
Carbon Black Content1, (%) Range 2.0% ASTM D1603
Carbon Black Dispersion Rating Note 1 ASTM D5596
Notched Constant Tensile Load, (hrs) Minimum 400 ASTM D5397
ASTM D 413 Tensile Properties strip tensile test
ASTM D 570 Moisture Content
ASTM D 638 Strip Tensile Properties – Plastics (>1mm)
ASTM D 696 Thermal Shrinkage
ASTM D 882 Strip Tensile Properties – Plastics (<1mm)
ASTM D 751
Coated Fabrics – Thickness, Grab Tensile, Strip Tensile,
Peel Adhesion, Seam Strength, Hydrostatic Resistance
and Blocking Resistance
ASTM D 1004 Tear Strength
ASTM D 1149 Ozone Resistance
ASTM D 1204 Dimensional Stability
ASTM D 1505 Density
ASTM D 1693 Stress Crack Resistance
ASTM D 1822 Impact Resistance
ASTM D 3083 Resistance to soil burial
ASTM D 4632 Grab Tensile – Geotextiles
ASTM D 4716 Transmissivity (longitudinal)
ASTM D 4833 Puncture Resistance
ASTM D 4885 Tensile Properties – Wide Strip Test
ASTM D 5199 Thickness – Optical Method
ASTM D 5397 Stress Crack Resistance (NCLT
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"