Road runoffs were sampled from five highways and five urban roads located in the New Juaben Municipality during the late storm events in the month of November 2014 and the early storm events in January 2015. A variety of water quality parameters such as, pH, temperature, turbidity, electrical conductivity (EC), total suspended solids (TSS), total dissolved solids (TDS), aqueous concentrations of Chloride (Cl -), Phosphate ( ), Nitrate ( ) and Sulphate ( ) ions as well as the total concentrations of some selected heavy metals (Fe, Cu, Zn, Pb, Cd, Ni and Cr) were analysed for both periods. Although the results for the studied parameters, particularly the heavy metals varied for both sampling periods, the general trend indicated an increase in accumulation from November 2014 to January 2015. This was attributed to vehicular deposition as well as other natural and anthropogenic depositions on the road surfaces during the antecedent dry weather period between the two sampling months. The highest increase in pollutant loadings was associated with the heavy metals and some physico-chemical parameters such as TSS, TDS, EC and turbidity. Generally, EC, TDS, TSS and turbidity were above the permissible limits of the Environmental Protection Agency (EPA) of Ghana for both sampling periods. However, almost all the mean concentrations of heavy metals recorded for both road runoffs and the control samples were within the permissible limits of the Ghana EPA with some few exceptions.
Environmental pollution has always been a problem in Ghana, despite efforts to reduce pollutant loading from point and nonpoint sources. Examples of point sources are factories, power plants, sewage treatment plants, underground coal mines and oil wells [
Till now, very few studies have been conducted to assess the contribution of road runoffs, which is fast gaining grounds as one of the most important sources of surface water pollution in Ghana. The absence of any system to manage or treat road runoffs to a harmless level that meets the acceptable water quality standards is therefore likely to cause environmental and economic risks. It is in this light that the study aims at assessing the extent to which road runoff is a significant contributor to surface water pollution in the New Juaben municipality.
The New Juaben Municipal Assembly,
Aboabo and to Akwadum [
Runoff samples were collected for two different months,
The sampling locations differed in daily traffic flow and surrounding land use. Accessibility for runoff sampling was also considered during site selection. The first set of samples was collected in November 2014 and the second set of samples was collected in January 2015. The choice of these months was to capture the effect of the antecedent dry period brought about by the dry (harmattan) season on the quality of road runoff in the study area. Two rain water samples (one from the urban area and the other from the highway area), were collected directly about 3 meters above the ground level during the storm events and were treated as control samples.
The road runoff samples were collected directly into acid pre-cleaned 1.5 L polyethylene bottles and labelled with the appropriate sample site numbers and placed in an ice chest at a temperature of 4˚C. Necessary care was taken to avoid contamination of the samples in the course of transportation to the laboratory, storage and analysis.
Sampling dates | ||||
---|---|---|---|---|
Sample location | Sample code | 24-Hour traffic volume (vehs/day) | Late rainfall | Early rainfall |
Koforidua-Akwadum Highway | KAKD | 11,361 | 4th November 2014 | 20th January 2015 |
Koforidua-Jumapo Highway | KJU | 10,160 | 4th November 2014 | 20th January 2015 |
Koforidua-Nkurakan Highway | KNK | 16,778 | 6th November 2014 | 26th January 2015 |
Kasajan Highway | KASJ | 8213 | 6th November 2014 | 21st January 2015 |
Adweso Highway | ADWE | 18,088 | 10th November 2014 | 26th January 2015 |
Nana Kwaku Boateng Street | NKB | 6852 | 10th November 2014 | 26th January 2015 |
Market Avenue | MAV | 2815 | 10th November 2014 | 26th January 2015 |
Old Library Road | OLR | 3309 | 10th November 2014 | 26th January 2015 |
Total 2 Road | TOT 2 | 19,409 | 10th November 2014 | 26th January 2015 |
Adu Sakodie Street | ADSK | 5362 | 10th November 2014 | 26th January 2015 |
Sampling sites | Sample codes | Sampling point 1 | Sampling point 2 | Sampling point 3 | |||
---|---|---|---|---|---|---|---|
Longitude | Latitude | Longitude | Latitude | Longitude | Latitude | ||
Market Avenue | MAV | W 0.2577˚ | N 6.0932˚ | W 0.2571˚ | N 6.0925˚ | W 0.2558˚ | N 6.0913˚ |
Old Lib. Road | OLR | W 0.2577˚ | N 6.0911˚ | W 0.2584˚ | N 6.0905˚ | W 0.2595˚ | N 6.0897˚ |
Nana Kwaku Boateng | NKB | W 0.2616˚ | N 0.0837˚ | W 0.2559˚ | N 6.0910˚ | W 0.2551˚ | N 6.0921˚ |
Total 2 Street | TOT 2 | W 0.2600˚ | N 6.0942˚ | W 0.2593˚ | N 6.0936˚ | W 0.2582˚ | N 6.0916˚ |
Adu Sakodie Street | ADSK | W 0.2564˚ | N 6.0947˚ | W 0.2570˚ | N 6.0945˚ | W 0.2578˚ | N 6.0933˚ |
Koforidua-Jumapo | KJU | W 0.2862˚ | N 6.1400˚ | W 0.2960˚ | N 6.1556˚ | W 0.3311˚ | N 6.1685˚ |
Koforidua-Akwadum | KAKD | W 0.3432˚ | N 6.1117˚ | W 0.3188˚ | N 6.1119˚ | W 0.2892˚ | N 6.1085˚ |
Koforidua-Nkurakan | KNK | W 0.2420˚ | N 6.1130˚ | W 0.2460˚ | N 6.1100˚ | W 0.2483˚ | N 6.1052˚ |
Kasajan Highway | KASJ | W 0.2760˚ | N 6.0823˚ | W 0.2802˚ | N 6.1078˚ | W 0.2821˚ | N 6.1239˚ |
Adweso Highway | ADWE | W 0.2610˚ | N 6.0559˚ | W 0.2500˚ | N 6.0781˚ | W 0.2539˚ | N 6.0869˚ |
All pH measurements were done using a digital pH meter (AB15 pH meter, Fisher Scientific, Hampton, NH). The instrument was calibrated for each set of measurements with standard buffer solutions. However, the temperatures of the road runoff samples were determined in the field using a thermometer. The TDS and the Electrical Conductivity were measured using a digital conductivity meter (Hanna instruments), calibrated with 0.01 M KCl solution. The argentometric method was used to determine the chloride concentration in the runoff samples while the absorptometric method was applied in the determination of the turbidity using the cybercan IR TB 100 turbidimeter. The sulphate ion concentrations were determined by the Automated Methylthymol Blue Method. However, ascorbic acid method was applied in the determination of phosphate.
The laboratory analysis of the runoff samples were done using VARIAN AAS 240FS-Atomic Absorption Spectrometer to measure the concentration of the selected heavy metals such as cadmium, copper, chromium, zinc, iron, nickel and lead. The runoff water samples were digested using concentrated nitric acid HNO3 and concentration of the selected heavy metals were determined. The essence of the digestion before analysis was to reduce the interference of organic matter and convert the metal to a form that can be analyzed by AAS.
Interpretation of the overall heavy metal concentrations in the sampled road runoff was drawn by using Mean, Standard Deviation, Skewness and Kurtosis. The results of the analyses were compared to the permissible limits set by the Environmental Protection Agency of Ghana for effluent discharge, as contaminated effluent affects man and his environment.
Temperature
The study revealed that mean temperature ranged from a minimum of 25˚C at sites KAKD and KASJ to a maximum of 27.3˚C at site MAV in November 2014,
Electrical Conductivity (EC)
The study revealed that mean EC ranged from a minimum value of 804.40 μS/cm at site KAKD to 2850.10 μS/cm at site NKB in November 2014,
Urban roads | Highways | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
PARAMETER | MAV | OLR | NKB | TOT 2 | ADSK | KJU | KAKD | KNK | KASJ | ADWE |
pH | 6.60 | 6.71 | 6.57 | 6.67 | 6.63 | 7.33 | 7.12 | 6.78 | 6.88 | 6.80 |
Temperature (˚C) | 27.30 | 25.60 | 26.50 | 26.10 | 26.10 | 25.10 | 25.00 | 25.10 | 25.00 | 25.10 |
EC (μS/cm) | 2620.30 | 1580.67 | 2850.10 | 2340.30 | 2532.78 | 1204.50 | 804.40 | 1325.40 | 1000.12 | 1459.00 |
TSS (mg/L) | 98.15 | 64.95 | 104.43 | 71.67 | 69.88 | 56.07 | 38.33 | 66.33 | 47.10 | 68.67 |
TDS (mg/L) | 1654.80 | 1074.23 | 2010.93 | 1740.10 | 1520.40 | 818.67 | 594.31 | 776.10 | 648.40 | 940.20 |
Turbidity (NTU) | 108.22 | 78.33 | 156.40 | 104.35 | 98.10 | 92.73 | 46.15 | 81.17 | 59.40 | 72.78 |
Chloride (mg/L) | 33.40 | 26.33 | 38.48 | 31.08 | 29.78 | 15.40 | 17.93 | 21.47 | 20.43 | 22.60 |
Sulphate (mg/L) | 49.73 | 36.67 | 58.31 | 34.52 | 54.17 | 17.88 | 14.48 | 24.67 | 18.67 | 21.08 |
Phosphate (mg/L) | 2.31 | 0.41 | 3.09 | 0.04 | 1.44 | 10.78 | 8.67 | 6.67 | 5.67 | 6.48 |
Nitrate (mg/L) | 18.88 | 11.21 | 22.33 | 14.67 | 17.40 | 4.40 | 10.28 | 12.06 | 9.12 | 13.73 |
Urban roads | Highways | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
PARAMETER | MAV | OLR | NKB | TOT 2 | ADSK | KJU | KAKD | KNK | KASJ | ADWE |
pH | 5.03 | 5.66 | 5.47 | 5.52 | 5.57 | 6.02 | 5.78 | 5.67 | 5.77 | 5.59 |
Temperature (˚C) | 28.60 | 26.70 | 28.10 | 27.60 | 27.40 | 26.10 | 26.40 | 26.90 | 26.20 | 27.10 |
EC (μS/cm) | 7196.13 | 3466.15 | 6820.98 | 6740.88 | 6510.02 | 1749.05 | 2496.78 | 2854.23 | 1978.17 | 4310.09 |
TSS (mg/L) | 212.67 | 180.31 | 242.21 | 205.35 | 327.35 | 158.52 | 137.43 | 179.33 | 162.95 | 201.02 |
TDS (mg/L) | 4792.73 | 2241.99 | 4570.08 | 4488.02 | 4542.40 | 1435.65 | 1670.65 | 1864.21 | 1370.13 | 2870.78 |
Turbidity (NTU) | 279.67 | 242.05 | 299.48 | 261.67 | 397.96 | 224.06 | 152.08 | 190.13 | 201.67 | 243.47 |
Chloride (mg/L) | 96.88 | 58.88 | 104.13 | 82.43 | 77.67 | 43.08 | 46.21 | 53.41 | 56.47 | 72.40 |
Sulphate (mg/L) | 172.15 | 72.92 | 148.48 | 112.33 | 120.07 | 51.67 | 58.10 | 68.40 | 69.73 | 94.67 |
Phosphate (mg/L) | 11.75 | 13.67 | 3.93 | 2.78 | 16.33 | 18.67 | 37.40 | 28.10 | 11.93 | 5.67 |
Nitrate (mg/L) | 87.33 | 37.33 | 64.12 | 76.40 | 42.67 | 25.92 | 27.52 | 35.67 | 30.67 | 58.40 |
Minimum | Maximum | Mean | Std. Dev. | Kurtosis | Skewness | Control sample | |
---|---|---|---|---|---|---|---|
pH | 6.57 | 7.33 | 6.81 | 0.24 | 1.14 | 1.31 | 6.51 |
Temperature (˚C) | 25.00 | 27.30 | 25.70 | 0.78 | 0.11 | 0.96 | 24.10 |
EC (μS/cm) | 804.40 | 2850.10 | 1771.76 | 743.25 | −1.69 | 0.27 | 576.78 |
TSS (mg/L) | 38.33 | 104.43 | 68.56 | 20.33 | 0.11 | 0.53 | 3.51 |
TDS (mg/L) | 594.31 | 2010.93 | 1177.76 | 509.18 | −1.45 | 0.45 | 381.40 |
Turbidity (NTU) | 46.15 | 156.40 | 89.76 | 30.53 | 1.80 | 0.91 | 9.16 |
Chloride (mg/L) | 15.40 | 38.48 | 25.69 | 7.38 | −0.85 | 0.33 | 13.10 |
Sulphate (mg/L) | 14.48 | 58.31 | 33.02 | 16.23 | −1.43 | 0.49 | 17.90 |
Phosphate (mg/L) | 0.04 | 10.78 | 4.56 | 3.64 | −1.05 | 0.34 | 0.04 |
Nitrate (mg/L) | 4.40 | 22.33 | 13.41 | 5.19 | 0.01 | 0.08 | 2.10 |
Minimum | Maximum | Mean | Std. Dev. | Kurtosis | Skewness | Control Sample | |
---|---|---|---|---|---|---|---|
pH | 5.03 | 6.02 | 5.61 | 0.25 | 2.77 | −0.95 | 5.57 |
Temperature (˚C) | 26.10 | 28.60 | 27.10 | 0.80 | −0.04 | 0.78 | 25.63 |
EC (μS/cm) | 1749.05 | 7196.13 | 4412.25 | 2195.82 | −2.01 | 0.16 | 1837.78 |
TSS (mg/L) | 137.43 | 327.35 | 200.71 | 53.76 | 3.02 | 1.52 | 11.34 |
TDS (mg/L) | 1370.13 | 4792.73 | 2984.66 | 1453.81 | −2.12 | 0.23 | 1219.67 |
Turbidity (NTU) | 152.08 | 397.96 | 249.22 | 68.02 | 1.81 | 0.97 | 25.54 |
Chloride (mg/L) | 43.08 | 104.13 | 69.16 | 21.01 | −1.02 | 0.45 | 28.67 |
Sulphate (mg/L) | 51.67 | 172.15 | 96.85 | 40.52 | −0.49 | 0.78 | 35.64 |
Phosphate (mg/L) | 2.78 | 37.40 | 15.02 | 10.90 | 0.69 | 1.01 | 0.65 |
Nitrate (mg/L) | 25.92 | 87.33 | 48.60 | 21.65 | −0.83 | 0.73 | 16.30 |
1749.05 μS/cm at site KJU and a maximum value of 7196.13 μS/cm at site MAV,
Total Dissolved Solids (TDS)
Analysis of water samples of the study area showed that the mean TDS ranged from a minimum of 594.31 mg/L at site KAKD to a maximum of 2010.93 mg/L at site NKB in November 2014,
Total Suspended Solids (TSS)
The study revealed that the mean TSS ranged from a minimum of 38.33 mg/L at site KAKD to a maximum of 104.43 mg/L at site NKB in November 2014,
Turbidity
Turbidity in water arises from the occurrence of very finely divided solids which are not filterable by routine methods in solution. The observed values of mean turbidity ranged from a minimum of 46.15 NTU at site KAKD to a maximum of 156.40 NTU at NKB in November 2014,
pH
The study revealed that, with the exception of sites KJU and KAKD which recorded mean pH values of 7.33 and 7.12 respectively in November 2014,
Chloride
The observed values of the mean concentration of chloride ranged from a minimum of 15.40 mg/L at KJU to a maximum of 38.48 mg/L at NKB in November 2014,
Sulphate
The mean values for sulphate ranged from a minimum of 14.48 mg/L at site KAKD to a maximum of 58.31 mg/L at NKB in November 2014,
Phosphate
The analysis of road runoff samples of the study area showed that the mean values for phosphate ranged from a minimum of 0.04 mg/L at site TOT2 to a maximum of 10.78 mg/L at site KJU in November 2014,
Nitrate
The study revealed that the mean values for nitrate ranged from a minimum of 4.40 mg/L at site KJU to a maximum of 22.33 mg/L at site NKB in November 2014,
Heavy Metals
Analysis of road runoff samples from the study area,
Trace metals | Urban roads | Highways | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
MAV | OLR | NKB | TOT 2 | ADSK | KJU | KAKD | KNK | KASJ | ADWE | |
Fe (mg/L) | 0.008 | 0.063 | 0.136 | 0.115 | 0.007 | 0.351 | 0.09 | 0.172 | 0.400 | 0.561 |
Cu (mg/L) | 0.135 | 0.020 | 0.165 | 0.038 | 0.151 | 0.016 | 0.017 | 0.014 | 0.023 | 0.047 |
Cd (mg/L) | BDL | BDL | BDL | 0.003 | 0.002 | 0.005 | 0.075 | 0.005 | 0.008 | 0.004 |
Pb (mg/L) | 0.104 | 0.083 | 0.150 | 0.095 | 0.152 | 0.029 | 0.009 | 0.023 | 0.060 | 0.101 |
Zn (mg/L) | 0.084 | 0.033 | 0.167 | 0.035 | 0.233 | 0.017 | 0.027 | 0.018 | 0.031 | 0.044 |
Ni (mg/L) | BDL | BDL | 0.002 | BDL | BDL | 0.003 | BDL | 0.002 | 0.005 | 0.006 |
Cr (mg/L) | BDL | BDL | BDL | BDL | BDL | BDL | BDL | BDL | BDL | BDL |
Trace metals | Urban roads | Highways | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
MAV | OLR | NKB | TOT 2 | ADSK | KJU | KAKD | KNK | KASJ | ADWE | |
Fe (mg/L) | 2.311 | 2.581 | 2.578 | 0.695 | 1.175 | 3.212 | 4.270 | 2.731 | 2.744 | 4.906 |
Cu (mg/L) | 1.474 | 0.243 | 2.205 | 1.256 | 0.261 | 0.141 | 0.117 | 0.198 | 0.135 | 0.199 |
Cd (mg/L) | 0.081 | 0.018 | 0.018 | 0.015 | 0.016 | 0.009 | 0.067 | 0.282 | 0.027 | 0.021 |
Pb (mg/L) | 2.345 | 0.429 | 1.788 | 1.105 | 0.835 | 0.084 | 0.039 | 0.035 | 0.039 | 0.656 |
Zn (mg/L) | 2.256 | 0.851 | 2.205 | 1.623 | 1.622 | 0.797 | 0.783 | 0.729 | 0.405 | 1.594 |
Ni (mg/L) | 0.085 | 0.448 | 0.437 | 0.422 | 0.423 | 0.618 | 0.772 | 0.492 | 0.524 | 1.623 |
Cr (mg/L) | 0.274 | 0.492 | 0.456 | 0.328 | 0.312 | 0.676 | 0.718 | 0.602 | 0.656 | 0.738 |
Minimum | Maximum | Mean | Std. Dev. | Kurtosis | Skewness | Control sample | |
---|---|---|---|---|---|---|---|
Fe (mg/L) | 0.007 | 0.561 | 0.190 | 0.19 | 0.119 | 1.056 | 0.005 |
Cu (mg/L) | 0.014 | 0.165 | 0.063 | 0.062 | −1.061 | 0.985 | 0.004 |
Cd (mg/L) | 0.002 | 0.075 | 0.015 | 0.027 | 6.887 | 2.618 | BDL |
Pb (mg/L) | 0.009 | 0.152 | 0.081 | 0.050 | −1.083 | 0.02 | 0.001 |
Zn (mg/L) | 0.017 | 0.233 | 0.069 | 0.073 | 2.002 | 1.712 | 0.002 |
Ni (mg/L) | 0.002 | 0.006 | 0.004 | 0.002 | −2.231 | 0.567 | BDL |
Cr (mg/L) | BDL | - | - | - | - | - | BDL |
Minimum | Maximum | Mean | Std. Dev. | Kurtosis | Skewness | Control sample | |
---|---|---|---|---|---|---|---|
Fe (mg/L) | 0.695 | 4.906 | 2.72 | 1.252 | 0.202 | 0.156 | 0.212 |
Cu (mg/L) | 0.117 | 2.205 | 0.623 | 0.745 | 0.794 | 1.419 | 0.018 |
Cd (mg/L) | 0.009 | 0.282 | 0.055 | 0.083 | 7.749 | 2.716 | BDL |
Pb (mg/L) | 0.035 | 2.345 | 0.736 | 0.805 | 0.267 | 1.082 | 0.008 |
Zn (mg/L) | 0.405 | 2.256 | 1.287 | 0.656 | −1.41 | 0.298 | 0.081 |
Ni (mg/L) | 0.085 | 1.623 | 0.584 | 0.404 | 5.727 | 2.078 | 0.011 |
Cr (mg/L) | 0.274 | 0.738 | 0.525 | 0.177 | −1.694 | −0.267 | BDL |
control samples recorded values of 0.005 mg/L and 0.212 mg/L in the respective months,
Total copper (Cu) concentrations in highway and urban road runoffs is derived in part from its use in automobile brake pads for some types of automobiles and can exceed water quality standards [
Cadmium (Cd) is released into the environment from mining and metal processing operations, burning fuels, making and using phosphate fertilizers, and disposing of metal products. Cd is also used for electroplating and for pigments present in paint, printing ink, and plastics [
The study revealed that the mean concentration of cadmium determined ranged from 0.002 mg/L at site ADSK to a maximum value of 0.075 mg/L at site KAKD but was not determined at sites MAV, OLR and NKB in November 2014,
The former use of lead as an additive in gasoline as an anti-knock agent caused highway and urban road runoffs to contain higher concentration of lead. Despite the phasing out of leaded gasoline, naturally occurring lead in gasoline can be on the order of 15 mg/L which might cause highway and urban road runoffs to contain sufficient concentration of lead in violation of water quality standards. Pb is of greatest concern because lead in soluble form is very stable, most toxic and difficult to eliminate [
Zinc (Zn) has lots of use including galvanization of steel, preparation of negative plates in electric batteries, vulcanization of rubber, wood preservatives, antiseptics and in rat and mouse poison (Zn-phosphide). Very low amount of the Zn may cause loss of appetite, decreased sense of taste and smell, slow wound healing and skin sores [
The study revealed that the mean concentration of nickel (Ni) determined ranged from 0.002 mg/L at sites NKB and KNK to a maximum value of 0.006 mg/L at site ADWE but was not determined at sites MAV, OLR, TOT2, ADSK and KAKD in November 2014,
Chromium was not detected at all sampling sites as well as in the control samples in November 2014. However, in January 2015 the sampling sites recorded incredible high concentrations of chromium with mean values ranging from a minimum of 0.274 mg/L at site MAV to 0.738 mg/L at site ADWE. The chromium concentration in the control samples fell below detection limit. An overall mean value of 0.525 ± 0.177 mg/L was recorded for all the sampling sites in January 2015. Higher concentrations of Cr in sampled road runoffs might be due to vehicular depositions and also the fact that a lot of building constructions are on-going along the highways since chromium is used in metal alloys and pigment for cement [
Statistical Analysis
The statistical summary of the physico-chemical parameters of highway and urban road runoff water samples for the November 2014 and the January 2015 sampling periods are presented in
The negative value of kurtosis recorded for the parameters temperature, EC, TDS, chloride and nitrate in January 2015,
The pH values of both control sample and the road runoffs were acidic, which is mainly due to a high concentration of
The statistical summary of heavy metals in the highway and urban road runoff water samples for the November 2014 and the January 2015 sampling periods are presented in
Based on the location analysis of the quality of road runoffs, it is observed that site KAKD recorded the least overall mean concentration of heavy metals (0.018 mg/L) while site ADSK recorded the highest overall concentration of heavy metals (0.193 mg/L) for the road runoffs sampled in November 2014. The January 2015 road runoff analysis showed site ADWE recording the highest overall mean concentration of heavy metals (1.391 mg/L) while KASJ gave the least overall mean concentration of heavy metals (0.647 mg/L). The road runoffs sampled in January 2015 recorded relatively higher concentrations of heavy metals which indicate that there was accumulation of heavy metals as a result of depositions from vehicles and other automobiles during the antecedent dry weather period. However, the highly acidic nature of the early rains in January 2015 also contributed to the high levels of heavy metals in the sampled road runoffs since they are able to wash off most of the heavy metal contaminants from the road surfaces.
The abundance order,
Correlational analysis,
According to Göbel et al. [
(Zn and Cd), steel part abrasion (Ni, Cr and Fe), brake drums (Fe), wear of bearings and bushing (Cu), wire corrosion and break lining abrasion (Pb, Cu and Zn) radiator fluid (Cu) [
In the absence of any major industry within the municipality, it can be concluded that automobiles contribute many important heavy metals to road surface particulates which are carried by storm water as runoffs and finally into receiving surface waters. The results obtained confirm that highway and urban road runoffs carry large amounts of pollutants that contribute to the degradation of the environment as a result of commercial activities and indirect depositions of pollutants by vehicles that carry various solid materials from construction sites and dirty roads onto the highways and urban roads within the municipality.
The urban roads recorded very high concentration relative to the highways for most of the measured parameters which was probably due to the high traffic intensity and commercial activities in the urban region of the municipality. Generally, the road runoffs recorded high values relative to the control samples for all measured constituents. Comparing the road runoff constituent loads with the recommended maximum values for permissible effluent discharge limits, it is found that a sizeable number of the runoffs were polluted with dissolved solids which accounted for the high values of EC recorded for both sampling periods. Highways and urban roads were
highly polluted in terms of solids because the TSS values recorded were above the levels of permitted wastewater discharge limits defined by the Ghana EPA.
Iron (Fe) recorded the highest overall mean concentration of heavy metals for both sampling periods. Cr was not detected at all the sampling sites during the November 2014 sampling period but surprisingly recorded an overall mean value of 0.525mg/L for the road runoffs sampled in January 2015 and this might be due to brake pad abrasions as well as steel part abrasions onto the road surface during the antecedent dry period. However, Cd recorded the least overall mean heavy metal concentration of 0.055mg/L for the January 2015 sampled road runoffs.
Furthermore, the measured concentrations for Ni and Cr for the entire highway sites were above the Ghana EPA limit for the road runoff sampled in January 2015, but none of the urban roads in both periods recorded any mean value above the Ghana EPA set limit. Moreover, the mean concentrations for Zn and Cu for all the sampling sites for both periods were within the Ghana EPA limits. The mean concentration for Cd recorded for the various sites for both periods were all within the Ghana EPA limit except for site KNK which recorded a mean value above the limit for the road runoffs sampled in January 2015. Pb on the other hand recorded mean values within the set Ghana EPA limit for all the sites in both periods with the exception of the urban road sites in January 2015. Surprisingly ADWE was the only highway site that recorded a mean value for Pb above the Ghana EPA limit and this might be due to the fact that it was the only highway site which was located within the urban region of the municipality.
There was a substantial increase in the concentration of all the studied constituents in both the runoff and the control samples during the January 2015 as compared to the November 2014 sampling period. This general trend could be attributed to the dry depositions of pollutants onto the road surface as a result of the harmattan during the antecedent dry weather period between the sampling periods.
Louis KorblaDoamekpor,RichmondDarko,Raphael KwakuKlake,Victus BobonkeySamlafo,Lord HunuorBobobee,Cornelius KwameAkpabli,Vincent KodzoNartey, (2016) Assessment of the Contribution of Road Runoffs to Surface Water Pollution in the New Juaben Municipality, Ghana. Journal of Geoscience and Environment Protection,04,173-190. doi: 10.4236/gep.2016.41018