Umshini wokuthungatha amapayipi ochungechunge lwe-NPD ulungele kakhulu izimo ze-geological ezinomfutho ophakeme wamanzi angaphansi komhlaba kanye ne-coefficient ephezulu yokungena kwenhlabathi. I-slag embiwe ikhishwa emhubheni ngendlela yodaka ngokusebenzisa ipompo yodaka, ngakho inezici zokusebenza kahle okuphezulu kanye nendawo yokusebenza ehlanzekile.