2:00 PM - 2:15 PM
[HDS10-08] Assessment of water supply function and measures for chemical release accidents triggered by major earthquakes
Keywords:Chemical accidents, Water supply function, Major earthquake, Modeling, Natech
In recent years, natural disasters called Natech (Natural hazard triggered technological accident) has become a big issue around Europe. Also, in Japan, Natech becomes social issues by the recent major earthquake such as the Great East Japan Earthquake, in which highly concentrated toxic chemical substances was released due to tsunami or fire. Such an accident causes risks related to serious environmental contamination. However, chemical behaviors in the environments and degrees of the impact on the infrastructure after the accident have not been clarified especially under the unstable situation. In this research, we aimed i) to clarify the influence of toxic chemicals released into the environment due to the major earthquake and ii) to evaluate the efficiency of the countermeasure option, focusing on unintended releases of chemicals from manufacturing or on-site storage facilities to water.
As the research area, we selected Yodo River in Osaka, which is an essential water source that supports the infrastructure of Kansai area. On the other hand, there are growing concerns for the risks caused by seismic motion and liquefaction as there are many chemical factories with drainage pouring into Yodo River.
We selected 38 chemical substances with high risk such as acrylonitrile in addition to toluene and xylene that are used in large quantities. These chemicals are also included in Pollutant Release and Transfer Register (PRTR) which make it possible to grasp more actual discharge status. Among PRTR, these 38 substances have especially high toxicity for human (LD50 ≦300 mg/kg) (UN, 2015), and have difficulty to remove even in the water treatment process because of its high solubility in water (≧10,000 mg/L) and hydrophilic properties (octanol/water partition coefficients (Log Kow)≦ 1.5) (Ito et al., 2014). The prediction occurrence of chemical release accident caused by the earthquake was calculated as the expected value (Y) based on the statistical data in the world (Santella et al., 2011). Probability (Pn) of occurrence of the accident in Yodo basin area caused by Hanaore fault was calculated by the Poisson distribution. Subsequently, we calculated the maximum expected concentration of chemical substances at the water-intake points in the river after the accident using the hydrology-exposure analysis model (AIST-SHANEL ver. 3)(AIST, 2015). The accident date on the model was set for winter season since the streamflow is relatively low throughout the year from a factory which has the largest storage of target chemicals. Emergency shut-off valve was adopted as a countermeasure in this scenario. As judgement criteria for suspension of water supply, we evaluated subacute toxicity as a criterion (JCisubacute).
As a result of the model calculation, the concentration of acrylonitrile in the purified water was calculated to be 2.19×10-1 mg/L for a maximum. In this case, water supply system would stop, since it exceeds JCisubacute (=6.25×10-2 mg/L) based on the no observable adverse effect level (NOAEL) (Ministry of the Environment, 2003) obtained from rats. Furthermore, as it exceeds the predicted no effect concentration (PNEC) of aquatic organisms, 7.6×10-3 mg/L (Ministry of the Environment, 2003), intake of the water would also stop. On the other hand, if the Emergency shut-off valve works properly, the outflow rate is 2% or less of the storage tank, calculating from the length of pipe and tube diameter outside the valve (Osaka, 2013). In that condition, the concentration of acrylonitrile in the river is less than JCisubacute and PNEC, which suggested that outage of water supply function can be avoided. According to these analyses, we found that an emergency shut-off valve is a useful option as a countermeasure for an earthquake. Furthermore, it would be possible to implement more quick and proper responses applying the method of this study, even in the case that the released chemicals are not included in the criteria for tap water.
As the research area, we selected Yodo River in Osaka, which is an essential water source that supports the infrastructure of Kansai area. On the other hand, there are growing concerns for the risks caused by seismic motion and liquefaction as there are many chemical factories with drainage pouring into Yodo River.
We selected 38 chemical substances with high risk such as acrylonitrile in addition to toluene and xylene that are used in large quantities. These chemicals are also included in Pollutant Release and Transfer Register (PRTR) which make it possible to grasp more actual discharge status. Among PRTR, these 38 substances have especially high toxicity for human (LD50 ≦300 mg/kg) (UN, 2015), and have difficulty to remove even in the water treatment process because of its high solubility in water (≧10,000 mg/L) and hydrophilic properties (octanol/water partition coefficients (Log Kow)≦ 1.5) (Ito et al., 2014). The prediction occurrence of chemical release accident caused by the earthquake was calculated as the expected value (Y) based on the statistical data in the world (Santella et al., 2011). Probability (Pn) of occurrence of the accident in Yodo basin area caused by Hanaore fault was calculated by the Poisson distribution. Subsequently, we calculated the maximum expected concentration of chemical substances at the water-intake points in the river after the accident using the hydrology-exposure analysis model (AIST-SHANEL ver. 3)(AIST, 2015). The accident date on the model was set for winter season since the streamflow is relatively low throughout the year from a factory which has the largest storage of target chemicals. Emergency shut-off valve was adopted as a countermeasure in this scenario. As judgement criteria for suspension of water supply, we evaluated subacute toxicity as a criterion (JCisubacute).
As a result of the model calculation, the concentration of acrylonitrile in the purified water was calculated to be 2.19×10-1 mg/L for a maximum. In this case, water supply system would stop, since it exceeds JCisubacute (=6.25×10-2 mg/L) based on the no observable adverse effect level (NOAEL) (Ministry of the Environment, 2003) obtained from rats. Furthermore, as it exceeds the predicted no effect concentration (PNEC) of aquatic organisms, 7.6×10-3 mg/L (Ministry of the Environment, 2003), intake of the water would also stop. On the other hand, if the Emergency shut-off valve works properly, the outflow rate is 2% or less of the storage tank, calculating from the length of pipe and tube diameter outside the valve (Osaka, 2013). In that condition, the concentration of acrylonitrile in the river is less than JCisubacute and PNEC, which suggested that outage of water supply function can be avoided. According to these analyses, we found that an emergency shut-off valve is a useful option as a countermeasure for an earthquake. Furthermore, it would be possible to implement more quick and proper responses applying the method of this study, even in the case that the released chemicals are not included in the criteria for tap water.