Surface Water Quality Trends in the Tarkwa Mining Area: 1993 – 2013

Abstract Tarkwa is characterised by a tropical and humid climate, as well as Birimian quartzites, sandstones, schists, phyllites, and conglomerates. The mining area is located in the Ankobra River Basin, bounded to the west, north, and south by the Ankobra, Huni, and Bonsa Rivers. Huni and Bonsa tributaries include Ahumabru, Teberebie, Bediabewu, Achofe, Awonabeng, Abekoase, Esumang, and Subri. This study presents 1993, 2002 and 2013 data. From 1993–2013, pH, conductivity, TDS, Alk, Ca, Mg, Na, K, Cl, SO₄², NO₃, Fe, Cu, Hg, Pb, Cr, Al, and Mn were studied. This paper compares early 1990s baseline data from Ghana Australian Gold (GAG), now AngloGold Ashanti Iduapriem Limited (AAIL), and Gold Fields Ghana Limited (GF), to recent data from the Tarkwa Nsuaem Municipality (TNM) mining area. Descriptive statistics and paired t-tests were used to calculate K-values and 20-year trends. For 20 years, pH, TDS, Cl, Mg, Na, SO₄², and NO₃ did not change significantly; Cu, Pb, and Conductivity did. Between 1993 and 2002, Fe, Ca, K, Alkalinity, and Mn increased, but not between 2002 and 2013. From 1993–2013, the pH, Cond, TDS, Cl, SO₄², NO₃, Ca, Al, Na, Fe, Cu, and Pb were all lower than the EPA's maximum mine effluent discharge limit.