Geotextiles prevent downward migration of smaller particles in to larger aggregates, and slump of heavier particles into finer underlying courses.
The formation of biofilm on geotextiles has also been shown to improve water quality:
- By degrading petroleum hydrocarbons
- By reducing organic pollutant and nutrient concentrations 
When installing geotextiles an overlap of 150 - 300 mm should be used.
Material specifications should conform to Ontario Provincial Standard Specification (OPSS) 1860 for Class II geotextile fabrics.
- Fabrics should be woven monofilament or non-woven needle punched.
- Woven slit film and non-woven heat bonded fabrics should not be used, as they are prone to clogging.
In choosing a product, consider:
- The maximum forces that will be exerted on the fabric (i.e., what tensile, tear and puncture strength ratings are required?),
- The load bearing ratio of the underlying native soil (i.e. is the geotextile needed to prevent downward migration of aggregate into the native soil?),
- The texture (i.e., grain size distribution) of the overlying and underlying materials, and
- The suitable apparent opening size (AOS) for non-woven fabrics, or percent open area (POA) for woven fabrics, to maintain water flow even with sediment and microbial film build-up.
|Percent media passing 0.075 mm (#200 sieve)||Non-woven fabric apparent opening size (AOS, mm)||Woven fabric percent open area (POA, %)||Permittivity (sec-1)|
|50 - 85||≤ 0.3||≥ 4||0.1|
|15 - 50||≤ 0.6||≥ 4||0.2|
|5 - 15||≤ 0.6||≥ 4||0.5|
|≤ 5||≤ 0.6||≥ 10||0.5|