Water is precious and necessary for a sustainable economic development of an area as it is the next major support to life after air. In the urban areas where pipe-borne water, bore-hole water and hand-dug wells are available, it is an indication that water is a vital component of human existence. Groundwater is of major importance and is intensively exploited for private, domestic and industrial uses. 90% of the population depends largely on hand-dug wells. Rapid growth in urban populations and industrial activities and commercial and agricultural developments result in increase in the search and uses of potable water [1] -[3] .

A major source of groundwater abstraction for use is by means of a hand dug well. A well is a hole or shaft sunk into the earth for the purpose of obtaining water and other fluid from an underground supply. Such a hole can be constructed in different ways upon which wells are commonly classified as hand dug wells, borehole, among others. Hand dug wells are of vital importance as source of domestic water supply for the majority of Nigerians. Hand dug well water remain the major source of domestic (drinking) water in the city of Wukari. The quality of this hand dug well water across Nigeria is rarely analyzed nor treated before use. Until recently, most artificial wells in the country do not have pump. Hand dug wells are usually between 1 and 20 meter deep depending on the geological characteristics of the area, and lined with stone, bricks, and recently cemented rings [4] [5] .

The spilling, leaking, improper disposal, or intentional application of chemicals at the land surface can result in runoff that contaminates nearby streams and lakes, or infiltration that contaminates underlying aquifers. The type and severity of water contamination often is directly related to human activity, which can be quantified in terms of the intensity and type of land use in the source areas of water to streams and aquifers.

A relatively simple way to study the effects of land use on groundwater quality is to compare the predominant land uses within a given area to the concentrations of selected contaminants in water drawn from shallow aquifers within that area. Analysis of the relation between land use and the magnitude of contamination in a specific area primarily is based on the following two assumptions [6] :

First, it is assumed that contaminated groundwater at a well originated as uncontaminated recharge (precipitation) that passed through a contaminated area before reaching the well. The area from which a well derives its water (and associated contaminants) is known as the well’s groundwater “contributing area.” Land use and land cover largely determine the type and amount of contaminants entering streams, lakes, and underground pathways, including aquifers. Some contaminants occur and move naturally, whereas others are produced by human activities and their movement often is accelerated as a result of rainfall that accentuates runoff and infiltration. Second, it is assumed that the contaminants detected in groundwater were present within the well's contributing area and were transported by groundwater flow to the well. The source(s) of contaminants within a contributing area, such as buried septic systems and leaking underground fuel tanks, can be difficult to identify and locate. In many instances, these sources can be inferred from the type and intensity of land use within the contributing area. Factors that can affect the movement of contaminants from source areas to wells are:

・ The chemical nature of the contaminant;

・ The physical properties of the soil and aquifer material;

・ The amount and timing of recharge; and

・ The direction and velocity of groundwater movement.

Heavy metals are elements having some atomic weight between 63.54 and 200.59, and a specific gravity greater than 4. Although trace amount of some heavy metals are required by living organisms, any excess amount of these metals can be detrimental to life [3] . The solubility of these metals in soils and groundwater is largely controlled by pH [1] [4] [7] ; amount of metal and cation exchange capacity, organic carbon content and the oxidation state of mineral components as well as the redox potential of the system. Pollution of groundwater is an impairment of water quality by chemicals, heat or bacteria to a degree that does not necessarily create public health hazards, but does adversely affect such water for domestic, farm, municipal or industrial use. Trace elements are generally present in small concentration in natural water system. Their occurrence in groundwater and surface water can be due to natural sources such as dissolution of naturally occurring minerals containing trace elements in the soil zone or the aquifer material or to human activities such as mining, fuels, smelting of ores and improper disposal of industrial wastes [7] -[9] 2000 cited in: [2] .

Heavy metals such as iron, manganese, cadmium, mercury, lead, arsenic, chromium, copper, Nickel, zinc cause a number of hazards to humans; and are indeed cofactors as activator biochemical reactions. Heavy metals are natural components of the earth’s crust, as can neither be degraded nor destroyed. Through rivers and streams, the metals are transported as either dissolved species in water or as an integral part of suspended substances causing the most detrimental effects on aquatic life. Also, to a small extent, the metals enter the human bodies via food, drinking water and air. Though, some heavy metals (e.g. copper, selenium, zinc) are essential to maintain the metabolism of the human body, but their concentration above the desirable levels can be poisonous. Heavy metal poisoning could be from drinking-water contamination (e.g. lead pipes), high ambient air concentrations near emission sources, or intake via the food chain [2] .

Heavy metals are dangerous because they tend to bioaccumulate. Bioaccumulation results when there is an increase in the concentration of a chemical in a biological organism over time, compared to the natural concentration of chemicals in the environment. Heavy metals may enter a water supply from industrial and household wastes, or acidic rain resulting in the breakdown of soils and releasing heavy metals into streams, lakes, rivers, and groundwater [8] . Investigation of heavy metals is very essential since slight changes in their concentration above the acceptable levels, whether due to natural or anthropogenic factors, can result in serious environmental and subsequent health problems. This study therefore seeks to investigate heavy metal concentration in hand dug wells in Wukari, with a view to ascertain whether this source of domestic water supply is safe for human consumption.

In order to achieve the aim and objectives of the study, the methodology that was employed in this study is sub- divided into the following themes:

1) Reconnaissance survey.

2) Materials.

3) Methods and procedures of data collection.

4) Statistical analysis.

Magnesium: The amount of magnesium in the hand dug well water samples as obtained from the laboratory analysis is as follows: sample A, B, C, and D are 17.09, 20.76, 15.87 and 20.76 respectively as shown in Table 1. These values are higher than the NSDWQ*MPL and [12] effluent permission-able limit of 2.0 mg/l required for drinking water quality as shown in Table 2. High content of magnesium and calcium results to hardness of water. Magnesium has also been known to be essential for plants growth and development [2] .

Copper: The amount of copper in the hand dug well water samples as obtained from the laboratory analysis is as follows: 0.09 mg/l, 0.07 mg/l, 0.12 mg/l and 0.02 mg/l for samples A, B, C and D respectively as shown in Table 1. There is consistency in the values obtained from laboratory analysis and these values fall below the permissible limit of 1.0 mg/l set by NSDWQ*MPL and [12] as shown in Table 2.

Source: Field survey (2014).

Source: Field survey (2014). NSDWQ*MPL = Nigeria Standard for Water Quality and Minimum Permission Limit. FEPA = Federal Environment Protective Agency.

Though still within permissible limits, some people who drink water containing copper in excess of the action level in short term may experience gastrointestinal distress while those with long-term exposure may experience anemia, liver or kidney damage. People with Wilson’s disease should consult their personal doctor if the amount of copper in their water exceeds the action level. Also, long term exposure to water that contains copper can cause irritation of nose, mouth and eyes which can lead to headache, dizziness, vomiting and diarrhea among other health hazards [13] .

Iron content: The amount of iron in sample A hand dug well water is 0.30 mg/l , while samples B, C and D have values of 0.05 mg/l, 0.05 mg/l and 0.00 mg/l respectively as shown in Table 1. The beneficial effects of iron include; chlorophyll synthesis, oxidation-reduction in respiration, constituent of certain enzymes and proteins. Excess concentration of iron has a negative effect as it can cause gastrointestinal irritation and enhance the growth of iron bacteria that affects the water taste. The high concentration values of iron has the potential of staining laundry, metal pipes for reticulation and scaling in pipes. It can also result in gene mutation leading to haemochromatosis whose symptoms include fatigue, weight loss, joint pains and ultimate heart disease, liver problems and diabetes [13] . The iron concentration of the sample ranges between 0.00 - 0.30, when compared to NSDWQ*MPL and [12] limit, it is within the permissible limit of 0.3 mg/l as shown in Table 2.

Potassium: The concentration in the collected samples range between 9.5 - 24.0 as shown in Table 1. The values are quite below the NSDWQ*MPL and [10] recommended limit of 200mg/l as shown in Table 2.

Manganese: The manganese concentration of hand dug well water samples was 0.6, 0.5, 0.2 and 0.3 mg/l for sample A, B, C and D respectively as shown in Table 1. The values obtained far exceed SDWQ*MPL and [12] permissible limit of 0.05 mg/l as shown in Table 2.

Manganese impacts a bitter taste to water, stains cloths and metal parts and precipitate in foods when used for cooking and it also promotes the growth of algae in reservoirs [2] .

Zinc: The amount of zinc in the hand dug well water samples as obtained from the laboratory analysis is as follows: 0.00 mg/l, 0.00 mg/l, 0.00 mg/l and 0.00 mg/l for samples A, B, C and D respectively as shown in Table 1. The laboratory values obtained all fall within the permissible limits of 5 mg/l as stipulated by [12] and NSDWQ*MPL as shown in Table 2.

Chromium: The amount of chromium in the hand dug well water samples as obtained from the laboratory analysis is as follows: 0.01 mg/l, 0.01 mg/l, 0.01 mg/l and 0.00 mg/l for samples A, B, C and D respectively as shown in Table 1. The laboratory values obtained all fall within the permissible limits of 0.05 mg/l as stipulated by [12] and NSDWQ*MPL as shown in Table 2. Since it is still below the permissible limit for drinking water quality, it shows that it has no implication on people who drink from the source. Water containing chromium in excess of the set limit may have an erythropoietin effect such as increased occurrence of goiter among humans and animals [1] .

The findings from this study shows that the concentration of copper, iron, potassium, zinc and chromium in Wukari hand dug well water are all within the set permissible limit of [12] and NSDWQ*MPL as shown in Table 2. This confirms the findings of [2] which is supportive of the fact that heavy metals concentration in ground water in Obajana and environs are within the set limit of [12] and NSDWQ*MPL.

Also, the findings shows that the concentration of manganese and magnesium in Wukari hand dug well water exceeds the set permissible limit of [12] and NSDWQ*MPL, which corroborate the findings of [1] [3] [13] -[15] that asserts that ground water in some selected Nigerian settlements shows some elevated levels of toxic metals. This they observe is a source of worry considering the fact that typical settlementin Nigeria is devoid of basic infrastructure that makes life worth living.

Statistical analyses using ANOVA single factor was conducted to test the null hypothesis that there is no significant variation in heavy metal concentration in hand dug well water from four different land uses of abattoir, waste dump site, residential and commercial in Wukari town. The summary of ANOVA single factor statistics is shown in Table 3. Using ANOVA single factor with a specified rejection level at α 0.05, the result indicates that the calculated value (F calculated) is 0.21, while the table value at P < 0.05 is 2.76 as shown in Table 4. This result is insignificant which implies that there is no significant variation in heavy metal concentration in hand dug well water from land uses A (abattoir), B (waste dump site), C (residential) and D (commercial) in Wukari town.

Table 3 shows the summary of ANOVA single factor analysis.

Using ANOVA single factor as shown in Table 4 with a specified rejection level at α 0.05 the result is insignificant. The calculate F value is less than the table F value, thus, the Null hypothesis is to be accepted (There is no significant variation).

The result of the laboratory analysis shows that the concentration of iron, copper, chromium, zinc, potassium in hand dug well water in Wukari falls within the permissible limits of NSDWQ*MPL and [12] ; while the concentration of manganese and magnesium far exceeds the permissible limits of NSDWQ*MPL and [12] . The results indicate that the drinking water quality is becoming deteriorated because most of the heavy metals tested for are found to be at minimum satisfactory level except for manganese and magnesium, which are found to be at unsatisfactory level because they are found to be at high levels in concentration. For now, it can be concluded that hand dug wells in Wukari Town are fit for domestic use, but that efforts should be made to reduce the magnesium and manganese concentration by having control on the anthropogenic factors (domestic waste water, agrochemicals, fumigation, local industries effluents) that lead to such high concentration levels or else, soon this source of water may become unfit for domestic use. The conclusion also is that there is no significant variation of heavy metal concentration in hand dug well water from land uses of abattoir, waste dump site, residential and commercial in Wukari town.

Kehinde T.Oyatayo,Godwin A.Songu,Greatest A.Amos,ChristopherNdabula, (2015) Assessment of Heavy Metal Concentration in Hand Dug Well Water from Selected Land Uses in Wukari Town, Wukari, Taraba State, Nigeria. Journal of Geoscience and Environment Protection,03,1-10. doi: 10.4236/gep.2015.39001