5 Assessment of Groundwater Quality in Sri Lanka …
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districts, while 4% is covered by water (Climate Change Secretariat Sri Lanka—
Ministry of Mahaweli Development and Environment 2016). The island consists
mostly of flat to rolling coastal plains, with mountains rising only in the south–central part. In the lowlands (altitude of 100–150 m), the mean annual temperature varies
between 26.5 and 28.5 °C, with an annual temperature of 27.5 °C. In the highlands,
the temperature falls quickly as the altitude increases. It is 15.9 °C in Nuwaraeliya.
Sri Lanka is influenced by the monsoons, allowing four distinct seasons, as a result of
lying in the equatorial and tropical zone. Therefore, monsoons and inter-monsoons
are considered as the major rainfall pattern experienced by different regions of Sri
Lanka. Rainfall patterns divided Sri Lanka into major three climatic zones; wet zone
(annual rainfall >2500 mm), dry zone (annual rainfall 1200–1900 mm) and semi-arid
zone (annual rainfall >1200 mm).
5.2.2 Sampling and Data Collection
Groundwater sampling was conducted in 1262 sampling wells distributed in 25
administrative districts and all climatic zones in Sri Lanka from 2010 to 2013. The
wells were randomly selected, and the locations were identified by GPS. Samples
were filtered on-site and then stored in pre-washed polyethylene bottles using membrane filtering technique (pore size of 0.45 µm) to separate suspended particulate
matter from the fluid and soluble component. Thereafter, they were sent to Japan for
analysis. Distribution of sampling locations is shown in Fig. 5.1.
The pH value of the water was measured on-site by glass electrode method using
a pH metre (Beckman Coulter, Inc. Model 260) with the STAR electrode 511,070.
Electrical conductivity (EC) was measured by using a conductivity metre (HORIBA
B-173; detection limit is 1–19.91 µC/cm). Major anions, fluoride, chloride, nitrate
and sulphate were determined by using ion chromatography (For anions: DIONEX
ICS 2000, Separation column ionPac AS18, Eluent KOH 23–40 mmol/L (gradient),
Suppressor; ASRS 300 4 mm). Cations such as sodium, magnesium and calcium were
also measured by using ion chromatography (For cations: DIONEX IC-1500, Separation column ionPac CS12, Eluent MSA 30 mmol/L (isocratic), Suppressor; CSRS
500 4 mm). Detection limit of fluoride is 0.2–2.0 mg/L, while it is 1.0–10.0 mg/L
for chloride, nitrate and sulphate. The limit is 0.5–10.0 mg/L for the above anion.
Concentration of metals in well water including aluminium (14.1–99.00), cadmium
(0.7–7.5), lead (2.4–25.1), zinc (6.9–47.0), nickel (2.6–24.9), copper (5.2–49.9),
arsenic (1.5–15.0), chromium (5.0–49.9) and iron (46.7–756.9) were determined by
using ICP-OES (Perkin Elmer Optima 5300) or ICP-MS (Agilent 7700) with the
detection limits as mention in the brackets in µg/L.
119
districts, while 4% is covered by water (Climate Change Secretariat Sri Lanka—
Ministry of Mahaweli Development and Environment 2016). The island consists
mostly of flat to rolling coastal plains, with mountains rising only in the south–central part. In the lowlands (altitude of 100–150 m), the mean annual temperature varies
between 26.5 and 28.5 °C, with an annual temperature of 27.5 °C. In the highlands,
the temperature falls quickly as the altitude increases. It is 15.9 °C in Nuwaraeliya.
Sri Lanka is influenced by the monsoons, allowing four distinct seasons, as a result of
lying in the equatorial and tropical zone. Therefore, monsoons and inter-monsoons
are considered as the major rainfall pattern experienced by different regions of Sri
Lanka. Rainfall patterns divided Sri Lanka into major three climatic zones; wet zone
(annual rainfall >2500 mm), dry zone (annual rainfall 1200–1900 mm) and semi-arid
zone (annual rainfall >1200 mm).
5.2.2 Sampling and Data Collection
Groundwater sampling was conducted in 1262 sampling wells distributed in 25
administrative districts and all climatic zones in Sri Lanka from 2010 to 2013. The
wells were randomly selected, and the locations were identified by GPS. Samples
were filtered on-site and then stored in pre-washed polyethylene bottles using membrane filtering technique (pore size of 0.45 µm) to separate suspended particulate
matter from the fluid and soluble component. Thereafter, they were sent to Japan for
analysis. Distribution of sampling locations is shown in Fig. 5.1.
The pH value of the water was measured on-site by glass electrode method using
a pH metre (Beckman Coulter, Inc. Model 260) with the STAR electrode 511,070.
Electrical conductivity (EC) was measured by using a conductivity metre (HORIBA
B-173; detection limit is 1–19.91 µC/cm). Major anions, fluoride, chloride, nitrate
and sulphate were determined by using ion chromatography (For anions: DIONEX
ICS 2000, Separation column ionPac AS18, Eluent KOH 23–40 mmol/L (gradient),
Suppressor; ASRS 300 4 mm). Cations such as sodium, magnesium and calcium were
also measured by using ion chromatography (For cations: DIONEX IC-1500, Separation column ionPac CS12, Eluent MSA 30 mmol/L (isocratic), Suppressor; CSRS
500 4 mm). Detection limit of fluoride is 0.2–2.0 mg/L, while it is 1.0–10.0 mg/L
for chloride, nitrate and sulphate. The limit is 0.5–10.0 mg/L for the above anion.
Concentration of metals in well water including aluminium (14.1–99.00), cadmium
(0.7–7.5), lead (2.4–25.1), zinc (6.9–47.0), nickel (2.6–24.9), copper (5.2–49.9),
arsenic (1.5–15.0), chromium (5.0–49.9) and iron (46.7–756.9) were determined by
using ICP-OES (Perkin Elmer Optima 5300) or ICP-MS (Agilent 7700) with the
detection limits as mention in the brackets in µg/L.