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Table 1 Modified degree of contamination gradation

From: Effects of columbite/tantalite (COLTAN) mining activities on water quality in Edege-Mbeki mining district of Nasarawa state, North Central Nigeria

Modified degree of contamination (mCd) According to [Abrahim and Parker 2008]
mCd < 1.5 Nil to very low degree of contamination
1.5 < mCd < 2 Low degree of contamination
2 < mCd < 4 Moderate degree of contamination
4 < mCd < 8 High degree of contamination
8 < mCd< 16 Very high degree of contamination
16 < mCd > 32 Ultra-high degree of contamination
mCd< 32 Extremely high degree of contamination