There is an interesting note about GIS model for illegal dumping occurrence prediction. Researches had an assumption that high accessibility of the site and its low visibility will determine the probability of illegal dumping occurrence. They reported that unfortunately this assumption was wrong and there are no significant influence of these factors on illegal dumping.
Actually such result is not a surprise for me. Most of the huge dumping sites in St. Petersburg and Leningrad region I'm aware of do not have very high accessibility, I would say that their accessibility is somewhat moderate. Relatively low accessibility affects "visibility" of the dumping sites and I think that these two parameters are correlated. Also it isn't clear if researchers defined the amount of waste that separates illegal dump from just litter. It seems that they haven't used such parameter so their studies could be affected by litter, which can be found almost anywhere.