Waste Disposal and Groundwater Quality in Jimeta- Yola 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'~a nd longitudes 12'23'~t o 12'33'~a~nd

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

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.