The impacts of fertilizer manufacturing on groundwater in South Africa

English: As a result of the fertilizer industry’s rapid growth, and the increasing global awareness concerning environmental issues, fertilizer production facilities have come under growing pressure to comply with ever more stringent environmental regulations. There are numerous contaminants associated with the fertilizer industry. These may be released into the environment through dusts, fumes, air emissions, liquid pollutants, or solid wastes. Some of these contaminants pose serious potential health and environmental risks. Groundwater is one of the aspects of the environment heavily effected by the fertilizer industry, and the aim of this study is to provide more clarity on the extent of the pollution caused by the fertilizer industry on the quality of groundwater. The site investigated is located in the industrial area of Potchefstroom, South Africa, and includes Sasol Nitro Potchefstroom (SNP), the Kynoch Fertilizer Production Facility (KFPF), and the surrounding area. SNP is a hot and cold blend liquid fertilizer plant, and KFPF manufactured fertilizers on a full scale from 1967 until mid 2006. An in-depth investigation was conducted on the SNP site by the researcher, and data from the KFPF site were provided by SRK Consulting who carried out a study there in 2007. The predominant contaminants associated with the fertilizer industry, also found in significant concentrations the investigated area, are; nitrate (NO3), ammonium (NH4), phosphate (PO4), sulphate (SO4), fluoride compounds (F), chloride (Cl), cadmium (Cd), and zinc (Zn). Various other heavy metals and radionuclides posing potential health and environmental risks may be released into the environment during the processing of phosphate rock; the types and quantities of which depend on the content of the phosphate rock. In general, NO3 (the most predominant contaminant found throughout the site), Ca, Mg, Cl, and Mn are found predominantly in solution in the groundwater (i.e., not adsorbed to soil/rock) in the saturated zone, except where there is loading from the surface within the bounds of SNP, which means that they are present in the unsaturated zone as well and leach down to the saturated zone. SO4 and K were found in little more concentrations in solution than in soil samples (in the saturated zone), but in a lesser contrast than for example, NO3 and Ca. Zn and F were found predominantly in soil samples, and primarily in the upper layer of soil. PO4 was almost exclusively found in the upper layer of soil, as well as NH4, but to a lesser extent. The general distribution of contaminants on site is attributed to their respective solubility characteristics and their tendency to be adsorbed by soil/rock. Many of the contaminants show a consistent peaking at a depth of ca. 6m. This may be attributed to the fact that pH levels are mildly acidic within the first few meters of soil, after which it increases rapidly to approximately neutral values throughout the depth of the site. Contaminants’ solubility that are pH dependant (lower pH increases solubility) would hence dissolve and leach through the first layer of soil/rock and precipitate where pH values increase. Significant chromium (Cr) concentrations were found in all the water samples taken from the boreholes on the eastern side of the site, ranging between 0.4 – 1.925mg/l. The main source of chromium was found to be the site on the southern boundary of the SNP plant, which was the location of a tannery in the past. Due to the evidence of the effectiveness of plants reducing contaminant concentrations in the northeastern corner of the site, phytoremediation is recommended as a viable option to rehabilitate the area.