Waste Disposal and Groundwater Quality in JimetaYola Area, Adamawa State, Nigeria

ABSTRACT. Waste disposal and groundwater quality studies were carried out in the Jimeta- Yola area. The area lies between latitudes 9'1 1'N to 9'20'~ and longitudes 12'23'~ to 12'33'~~ and covers an areal extent of about 305km2. Groundwater quality monitoring was carried out through the collection of water samples from hand-dug wells, boreholes and leachates beneath refuse dumps. These samples were analyzed chemically and bacteriologically using atomic absorption spectrophotometer (AAS), DW2010 spectrophotometer, titrimetric and membrane filtration methods. The acronym DRASTIC refers to the seven hydrogeologic parameters used in evaluating pollution potential of an area. The DRASTIC parameters were determined from borehole logs, borehole Lithologic sections, b soil and topographic maps, groundwater level map, and hydraulic conductivity values. The results of the analyses reveal that chromium hexavalent recorded increase in concentration of 63.6% and 75.8% in the hand-dug wells and boreholes respectively during the rainy season period. Copper recorded increase in concentration of 68.2% and 84.8%, iron was 59.1% and 64.5%, and nitrate was 57.9% and 42.4%. Dissolved oxygen also recorded increase in concentration during the dry season period by 72.7% and 84.4%in the hand-dug wells and boreholes, while the chemical oxygen demand and biochemical oxygen demand also recorded increase in concentration in the rainy season by 86.4% and 90.6%, and 85.7%and 87.5% in the hand-dug wells and boreholes respectively. The increase in total coliform number counts in the dry season was 55% and 51.6% in the hand-dug wells and boreholes; ammonium ion concentration level increased by 81.8% and 48.5% during the dry season period, while phosphate was 81.8% and 72.7% during the rainy season in the hand-dug wells and boreholes. The leachate plumes were delineated on the basis of chloride, ammonium ion and electrical conductivity. Chloride concentrations in the plume were 165.2mgll in the dry season and 590mgll in the rainy season periods respectively. Ammonium ion reveals values of 15.93mgll and 19.24mgll in the dump during the dry and rainy season periods respectively, while the electrical conductivity values were 2230mSlcm and 1380mSlcm at the source of the plume during the dry and rainy season periods respectively. Variation in the concentrations of the dissolved contaminants reveal that chromium hexavalent exceeded the recommended limit of WHO by 41% and 39.4% in the hand-dug wells and xviii boreholes, copper by 45.5% and 6.1 5; sodium 63.7% and 12.1%; chloride by 68.2% and 18.25; nitrate by 68.2% and 36.4%; phosphate by 72.7% and 62%; and TDS by 63.6% and 9.l%in the hand-dug wells and boreholes respectively. The total coliform counts were high in both the dry and rainy season periods. Values ranged from 5 to 77 in the dry season and 4 to 40 in the rainy season in the hand-dug wells, and from 3 to 65 in the dry season and 1 to 50 in the rainy season in boreholes. Values reveal increase in the coliform number counts in the dry season. The contaminant transport model for the unconfined aquifer in the study area indicates low, moderate and high travel time. The average values in the hand-dug wells ranged from 101 to 7438 years and from 257 to 201 18 years in boreholes. The unconfined aquifer has an average contaminant travel time (years) ranging from 179 to 13678 years. The computed values of the DRASTIC indices ranged from 1 1 1 to 193, and led to the classification of the area into low, moderate and high vulnerability zones. The study reveals that the shallow aquifer is more polluted, and can be better developed by drilling of interceptor wells along the Benue River and other areas of high vulnerability to pollution. Drilling of productive wells in the Alluvium aquifers should be to the depths of 140- 168 meters. Household and commercial wastes, sewage effluent from domestic wastes, and limited application of fertilizer at the outskirts are among the sources and causes of groundwater contamination/ pollution in the area.