The objectives of this study are 1) to proposed the optimal analysis methods for NORM(natural occurring radioactive material) 2) to research hydrogeochemistry and NORM charateristics according to the distribution of rock(geology) 3) to reveal the distribution NORM by Province 4) to research the gross-α and 226Ra properties.
In this study, liquid scintillation method was proposed as the optimal analysis one for 222Rn and 226Ra, and gas proportional method for gross-α.
A total of 247 samples were collected from groundwater to investigate the hydrogeochemical and NORM properties according to the distribution of rock(geology) were collected from groundwater. In-situ analysis of groundwaters resulted in ranges of 5.9~8.5 for pH, 13.7~25.1℃ for temperature, 66~820 μS/cm for EC, 33~591 mV for Eh, and 0.15~9.44 mg/L for DO. Major cation and anion concentrations of groundwaters were in ranges of 4.2~279.3 mg/L for Ca, 0.1~100.1 mg/L for Mg, 0.9~227.6 mg/L for Na, 0.2~9.3 mg/L for K, ND~3.3 mg/L for F, 1.8~779.1 mg/L for Cl, 0.3~120.4 mg/L for SO4, 15.3~372.1 mg/L for HCO3, and ND~27.4 mg/L for NO3-N. 222Rn and 238U concentrations in natural radioactive substances were detected in ranges of 18~15,953 pCi/L and N.D~131.1 μg/L, respectively. For the groundwater samples exceeding USEPA MCL level (30 μg/L) for uranium concentration, their pH ranged from 6.8 to 8.0 and Eh showed a relatively low value(86~199 mV) compared to other areas. Most groundwaters belonged to Ca-(Na)-HCO3 type, and groundwaters in metamorphic rock regions exhibited the highest concentration of Ca, Mg, Na, Cl,
NO3-N, U, and those in plutonic rock regions showed the highest concentration of HCO3 and Rn. Uranium and fluoride from granite areas did not show any correlation. However, uranium and bicarbonate displayed a positive relation of some areas composed of plutonic rocks(R2=0.3896). Groundwaters containing high ranium concentrations (>30 ug/L) were detected mainly in the granitic rock regions, especially in Cretaceous granite, Jurassic biotite granite, Jurassic two mica granite, and Precambrian granitic gneiss region. High radon-bearing groundwaters (>4,000 pCi/L) were found in the regions with various rock types including Cretaceous
volcanic rock, Jurassic biotite granite, Jurassic two mica granite, Jurassic pegmatitic granite, and Cretaceous sedimentary rock region, and so forth.
Also, in order to reveal the characteristics of the NORM distribution in nine provinces, uranium and radon in 681 samples of groundwater were analyzed. Most uranium concentrations in each province were less than 10 μg/L, and Jeonnam, Gyeongnam, Jeju provinces did not have any groundwater samples exceeding the US EPA drinking water MCL (30μg/L) of uranium. The percentatge of radon values exceeding US EPA drinking water AMCL (alternative maximum contaminant level, 4,000 pCi/L) was 22.6% (154/681) and Gyeongnam and Jeju provinces had no groundwater samples exceeding the AMCL. Uranium and radon concentrations of groundwaters in Gyeonggi, Chungbuk, Jeonbuk, Chungnam mainly composed of the Mesozoic granite and the Precambrian gneiss were relatively high, but their concentrations in Gyeongnam and Jeju widely comprised of the sedimentary rock and the volcanic rock were relatively low. A weak correlation between uranium and radon values was shown in Gangwon, Chungbuk, Gyeonggi provinces.
226Ra values of 19 groundwater samples having gross-α concentrations of more than 5 pCi/L ranged from ND to 1.18 pCi/L(ND: ≤ 0.1 pCi/L). Geologic settings of the 19 areas are composed of granitic rocks of Pre-Cambrian and Jurassic and Cretaceous, gneiss (schist) of Pre-Cambrian, and volcanic rocks of Cretaceous. No relationship was shown among 226Ra concentrations and in-situ water quality data, and uranium, radon, and gross-α concentrations.
To identify the characteristics of gross-α, groundwaters were sampled from 730 wells during 2007-2009. These samples were analysed using a gas-flow type GPC (Gas Proportional Counter) according to the USEPA method (900.0). A gross-alpha counting TDS (total dissolved solid) efficiency curve (Y = 0.0017X2 ? 0.3122X + 19.165, X = TDS, Y=efficiency, R2=0.9734) using natural uranium standard were obtained to get gross α value of the samples. The gross alpha values ranged from MDA (minimum detectable activity) to 14.88 pCi/L and 429 samples showed values higher than MDA (< 0.9 pCi/L). Correlations of the uranium values with the total alpha values and the gross-alpha values indicate that uranium values have significant effects on gross-alpha values. Groundwater samples of study areas were classified into four regions according to the rock types; plutonic (granite) rock region (427 areas), metamorphic rock region (181 aeras), sedimentary rock region (70 areas), volcanic rock region (52 areas). Groundwater of Cretaceous granite presented the highest gross-alpha value. Gross alpha in groundwaters showed no relationship with uranium in terms of the geological ages, rocks and minerals.