[tag=NN] [lemma=surface] [lemma=consume | □=□] □
[tag=NN] [lemma=surface] [lemma=consume | word=□] □
[tag=NN] [lemma=surface] [lemma=consume | tag=□] □
Not only do they have the potential to put more lives at risk due to the number and proximity of aircraft operating on the airport surface , they also take place in a complex and dynamic environment where root causes are difficult to isolate . Mixed together and applied ( with elbow grease ) to the smooth marble surface , they can bring it to a high sheen . Due to the burial of the base some 60 cm or more below the substrate surface , they are difficult to collect without benthic suction apparatus . Once these pollutants are deposited onto road and parking surfaces , they are available for transport in runoff to receiving waters during storm events .