From the GMA Techline
Subject: Geocell application I would like to know the suitability of geocell as slope surface protection on acidic soil conditions. Can we apply geocell directly on top of the slope surface?
Reply: Geocells are regularly used in exactly the type of application you describe. A geotextile is generally placed on the prepared subgrade and then the geocell is deployed in the customary manner. If the slope is very steep, steel tendons can be used, passing through the geocells extending to the top of the slope where they are connected to an anchorage block. The infill of the geocells can be soil, stone, or concrete depending on the conditions and anticipated service life.
Regarding the acid conditions you mention, the HDPE will not be affected nor will an underlying PP geotextile. If, however, you are concerned about the acidity getting through the system thereby polluting a stream or waterway, you should consider placing a geomembrane on the slope before the geocell is placed. This particular application has been accomplished in several locations.