ASSESSING THE IMPACT OF WASTE ROCKS ON GROUNDWATER QUALITY IN THE ABANDONED COAL MINE OF JERADA CITY (NORTH EASTERN MOROCCO)

摘要

The exponential growth of urban dwellers calls for an increased awareness of urban ecosystems and appropriate, long-term management practices. Especially the water supply needs to be secured, both in terms of quantity and quality. In Morocco, numerous urban mine sites were abandoned regardless rehabilitation strategy. Consequently, mining activity contributes massively to deteriorate air, soil and water quality, to degrade natural ecosystems and to menace public health. The abandoned coalmine of Jerada is located in north east of Morocco, in horst zone, in the productive geological formation of Westphalian C. The mining activity has generated along 65 years (1936-2001), 15 to 20 millions tons of washery waste rocks, cumulated principally in urban center. The groundwater (n=30) and waste rock (n=7) sampling was led in the middle of May 2008, which presents in local climatic context the end of rainy season and the beginning of sec season. Waste rocks are exhaustively black schist, with a paucity in pyrite (anthracite debris contain between 2 to 5% of synergic pyrite) and predominance of calcareous minerals essentially as dolomite. Consequently, the majority of waste rock samples are not acid generators. The pyrite oxidation produces sulphuric acid, which will be quickly neutralized by carbonates. The alkaline tendency of pH classifies Jerada abandoned coal mine in circum neutral mining drainage type (NMD). The leaching through unsaturated and saturated zone will be facilitated due to a big pore size and a breaking tectonic having fractured Jerada coal basin. The deformed black schist alternative to sandstone permits a good water circulation. The massive product of mining drainage and the major pollutant of groundwater is undoubtedly S-SO4 (27/30 exceed WHO guideline). The spatial correlation between S-total and salinity illustrates the deterioration of groundwater quality due to pyrite oxidation. The alteration of schist and halite dissolution contribute to enrich groundwater in chloride (26/30 exceed WHO guideline). The quasi-absence of sewage disposal contaminates groundwater in N-NO3 (18/30 exceed WHO threshold). Metallic pollution of groundwater is geographically very restrained (1/30 to 3/30 exceed slightly WHO guidelines), due to the precipitation of metallic elements under hydroxide form. The recourse of groundwater use as drinking water in 7/30 of cases constitutes a real menace for public health (purgative effect due to S-SO4 and methemoglobinemia due to N-NO3); making sensitive Jerada population proves to be an urgent necessity.