INTRODUCTION

High explosives are usually employed in mining, seismic exploration, demolition and military warheads. They undergo detonation at rates of 1,000 to 9,000 meters per seconds ¹. High explosives are conventionally subdivided into primary, secondary and tertiary explosives. Primary explosives are sensitive to shock, friction and heat ². Secondary explosives also called base explosives are relatively insensitive to shock, friction and heat. They may burn when ignited in small, unconfirmed quantities, but detonation cannot occur. These are sometimes added in small amount to blasting caps to boost their power. Dynamite, Trinitrotoluene (TNT), Royal Demolition eXplosive (RDX) and Pentaerythritol tetranitrate (PETN) are secondary explosives. PETN is often considered a benchmark compound. Materials that are more sensitive than PETN are classified as primary explosives ³. Tertiary explosives also called blasting agents are so insensitive to shock that they cannot be reliably detonated but require an intermediate explosive booster of secondary explosive ⁴. Tertiary explosives are primarily used in large-scale mining and construction operations ⁵. Explosives degradation is a serious environmental challenge because it contaminates groundwater. Royal Demolition eXplosive (RDX) have been reported in fifteen monitoring wells; twelve of the wells had RDX above 2 ppm ⁶. In Massachusetts, a monitoring well installed approximately 750 feet from the centre of the demolition pit exhibited the highest concentrations of RDX (370 ppb)⁷. The groundwater contamination in the area extends to the down gradients at least one half mile to the west ⁷.

pH is the negative logarithm to base 10 of hydrogen ion concentration. The values of pH below 7 are said to be acidic, while values of pH above 7 are basic. When the concentration of [H⁺] and [OH^-] are equal, the pH of the solution is said to be neutral. It is necessary to determine the pH of water since it affects chemical coagulation, disinfection, water softening and corrosion. The pH also controls the oxidation of cyanides, dewatering of sludges, CO₂ corrosion, stability index and reduction of hexavalent chromium to trivalent chromium. Higher pH values may cause scale formation in boilers and inhibit the germicidal potential of chlorine. Carcinogenic compounds such as trihalomethanes are induced at higher pH ⁸.

Sagbama (Figure1) is located in Bayelsa state, Niger Delta Nigeria. The concession is in the Nigeria West Belt between latitude 10^o 00N and 14^o00N and longitude 39^o 00E and 42^o 50E. The vegetation of the area is high forest, generally dominated by dense rain forest with light shrub at the riverbank.

Figure 1. Map of Sagbama in Bayelsa, Niger Delta Nigeria (401 x 450)⁹

MATERIAL AND METHODS:

Uphole drilling

The uphole was drilled to 60m depth using the rotary method and flushed continuously for 20 minutes to enhance stability. Each hole was cased with perforated 6 inch PVC pipe. The uphole lithology was sampled every 5 m or at the change in lithology. The grain size analysis was accomplished using the sieve method for the sands. The result of the sieve analysis was used to calculate particle size, sorting, roundness and sphericity with the aim of estimating the porosity and permeability of the soil. No size analysis was carried out for the silt and clay. The source and receiver line number were used for identification of the uphole locations while the coordinates was verified using a handheld Global Positioning System (GPS) set. The Meridian Platinum GPS was used after calibrations. The elevations of the uphole points were determined using the same instrument (Table I).

Explosive detonation

The energy source was the high explosive dynamite (TNT) and 6m Electric Detonators loaded in 5 hole pattern source array. In dry areas, the holes were thumped to a depth of 4m while in flooded/marshy terrain they were flushed to a depth of 6 metres. Each pattern hole was loaded with 0.4kg/l seismic, electric detonators (1 shot point = 5x0.4kg/l caps for five hole pattern). A total amount of 116,3 49.2 kg dynamite was detonated in 60, 398 source point in an area of 771.26 square kilometers of Sagbama area.

Water sampling and analysis

The groundwater was sampled from 11 upholes in Sagbama. The sample locations were Geo-referenced using the survey coordinates of eastings and northings. The elevation of each sample location was determined by measurement of the Z-component of the coordinates. The water samples were taken from the boreholes at a depth of 12m to 15m (Table I).Water samples were collected and analyzed from each uphole before the commencement of dynamite detonation. The water samples were collected using small bottles using with a rope.

Determination of groundwater pH

The pH of the groundwater was determined using The American Water Works Association method ¹⁰ and Standard Methods for the Examination of Water and Wastewater ¹¹. The pH meter was switched on at least 30 minutes before the test. Buffer solution 4.0, 7.0 and 9.2 were prepared as follows. Buffer solution pH 4 was prepared by dissolving 10.12g of potassium hydrogen phthalate, KHC₈H₄O₉ in distilled water and dilute to 1 dm³. Buffer solution pH 7 was prepared by dissolving 1.361g of anhydrous potassium dihydrogen phosphate, KH₂PO₄, and 1.42g anhydrous disodium hydrogen phosphate, Na₂HPO₄, which was dried at 110°C. The solution was diluted to 1 dm³ using distilled water which has been previously boiled and cooled. Buffer solution pH 9.2 was prepared by dissolving 3.81GM borax, Na₂B₄O₇.10H₂O in distilled water, which has been previously boiled and cooled and dilute to 1 dm³. The pH meter was calibrated to 9.2 using the buffer solution pH 9.2 and by the adjustment of the calibration Knob. It was further calibrated to 7.0 using the buffer solution of pH 7.0 and by the adjustment of the calibration Knob. It was finally calibrated to 4.0 using the buffer solution of pH 4.0 and by the adjustment of the calibration Knob. The test samples were then read using the pH meter.

The results of the pH analysis before the commencement of dynamite detonation served as control. The water was subsequently sampled fortnightly, that is 14 days for an interval of 2 months after the seismic acquisition process has been completed. The results obtained from the analysis of the samples during and after acquisition were compared with the results obtained before detonation and also with standard values.

Table 1: Sagbama (SG) monitoring boreholes showing location x-y coordinates and elevation

Uphole No.	Uphole location	Easting	Northing	Elevation (Z)
SG1	2030/4070	397450.42	133107.70	18.70
SG2	270/4070	397850.88	129103.76	19.80
SG3	2110/4070	397450.72	125101.30	16.20
SG4	1950/4070	397451.30	121100.00	28.10
SG5	1790/4070	397450.50	117100.30	32.80
SG6	2430/4230	401451.50	133101.60	18.14
SG7	2270/4230	401450.82	129100.90	18.50
SG8	2110/4230	401452.74	125102.84	26.70
SG9	1950/4230	401450.50	121600.80	27.20
SG10	1790/4230	401448.80	117100.50	31.80
SG11	2430/4390	405450.82	133101.18	39.60

Measurement of permeability

Coefficient of permeability was measured using the constant head permeameter. Soil sample was placed in the cylinder. A measurement was taken between the two tapings in the cylinder connected to the manometers. Water from the reservoir was allowed to flow through the sample at a constant rate. As soon as the water begins to flow, the stop clock reading begins. Water flowing the sample was collected with the measuring cylinder. The differences of heads from the manometers were measured. The time was recorded using the stop clock. This was repeated for two other samples. Coefficient of permeability (K) was calculated using Darcy’s Law (eq.1)

, .

Soil porosity determination

The soil was placed into a mould of volume (V_T) = 1000 cm³. The weights of the sample and mould (M_t) were determined. The sample is then dried in an oven at temperature 105⁰C and re-weights (M_s). The weight of water M_w, weight of solid M_s, volume of voids V_v was determined based on eq. 2 and 3 respectively. . From these, porosity values were calculated from eq. 4

RESULTS AND DISCUSSION:

The dynamite detonation density was 150.86 kg/Km². The results of groundwater pH in Sagbama area are presented in Table 2. The water samples taken from the boreholes before detonation of dynamite served as control and were designated as day-zero samples. pH averages over the sampled period on is shown in Figure 2. Sagbama area borehole lithologic Log is presented in Figure 3 while Sieve analysis and grain size distribution curve, (13m depth) of Sagbamaarea is presented in Figure 4.

Table 2 : Borehole water pH analysis results in Sagbama (SG) area

Day	SG1	SG2	SG3	SG4	SG5	SG6	SG7	SG8	SG9	SG10	SG11	Mean
0.00	7.87	8.25	6.77	7.64	6.72	8.28	8.46	8.00	7.80	8.32	7.29	7.76
1.00	7.57	5.78	6.78	7.69	6.31	8.28	8.46	7.80	7.80	8.38	7.38	7.48
15.00	7.67	7.39	7.10	7.65	5.81	8.18	8.46	8.00	7.90	8.32	7.57	7.64
29.00	6.97	6.82	7.11	7.69	6.77	8.08	8.56	8.00	7.80	8.38	7.78	7.63
43.00	6.57	6.84	7.89	7.67	6.65	7.79	8.46	8.00	7.80	8.31	7.87	7.62
57.00	7.43	5.75	7.80	7.61	5.97	8.18	8.46	8.00	7.80	8.38	7.64	7.55
71.00	6.61	8.28	6.75	7.68	5.91	8.28	8.46	8.00	7.90	8.35	7.65	7.62
85.00	6.47	7.12	6.80	7.69	6.67	7.28	8.46	7.90	7.80	8.31	7.72	7.47
99.00	7.45	8.02	7.20	7.67	6.65	7.28	8.46	7.90	7.80	8.38	7.48	7.66
113.00	8.47	7.19	7.56	7.19	7.12	7.28	8.46	7.89	7.90	8.37	7.29	7.70

Figure 2: pH averages over the sampled period on Sagbama area

Figure 3: Sagbama Area Borehole Lithologic Log

Figure 4: Sieve analysis and grain size distribution curve, 3m depth, Sagbama Area

The average pH value of the control (groundwater before detonation) was 7.76. On the first day after dynamite detonation, the average pH value was 7.48 (Table II, Figure 2). The range of pH values of the groundwater remained almost unchanged from day-15 to day-71 post dynamite detonation in the area. The highest recorded average value of 7.98 was obtained on day-71 after the dynamite detonation. The pH decreased on day-81 to 7.47 post dynamite detonation. Thereafter the average pH value increased to 7.70 on day-113. These variations of the control are not significant enough for dynamite to be said to have impacted on the pH value of the groundwater. The control and test values are both within 6.5 – 8.5 compliance limit of the Federal Ministry of Environment, Housing and Urban Development (FMEnv,H&UD).

The representative lithology of Sagbama area (Figure 3) as revealed by the borehole logging consists of 0-2m clayey sand, 2-5m silty and fine sand, 5- 13m medium sand, 13 -27m medium to coarse sand, 27 – 60m medium to coarse sands and gravelly mix (Figure 3). These litho-types are mainly non-plastics also categorized as cohensionless sands. The presence of silty sands at 4 to 5m depths could be an obstruction to infiltration of contaminants from dynamite detonation. Sieve analysis results from Sagbama (Figure 4) showed average to 7% passing for grain size 0.075mm, 8% passing for 0.15mm grain size, 39% passing for grain size 0.03mm, 77% passing for grain size 0.6 mm, 96% passing for grain size 2.36mm and 100% passing for grain size 5.00mm.

The Coefficient of permeability, K, at a depth of 3m (Figure 4) was 3.24 cm/sec. Permeability is the ability of a soil or rock type to conduct or discharge water (and effluents) under a hydraulic gradient. It depends on soil density, degree of saturation, viscosity and particle size. Infiltration capacity of soil depends on permeability, degree of saturation, vegetation, amount of rainfall and duration of rainfall ^12,13. Coefficient of permeability of unconsolidated sand is affected by the fluid viscocity, grain size, grain sorting, grain shape and packing ¹².

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

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Received on 02.10.2016 Accepted on 08.12.2016

Int. J. Tech. 2017; 7(1): 01-06

DOI:10.5958/2231-3915.2017.00001.3