Study On Water Quality Risk Assessment Of The Aquifer Recharge With Multi-water Resources In Yufu River,Jinan

At present, Jinan city has formed the multi-water supply pattern, including karst groundwater, the reservoir water from the southern mountain region, the Yellow River from the northern Plain Reservoir, urban reclaimed water and the Yangtze River water, to maintain municipal water. But how to supply high-quality groundwater for life and ensure the spring perennial gushing are still great challenges, so the groundwater recharge with the multi-water resources is one of the key measures to solve protection of spring and water supply safety.The upstream of Yufu River was selected as the project area. The riverbed mainly consists of sand gravel and developed fissures to make surface water directly infiltrated into the underground. The karst aquifer in the western Jinan provides huge storage space. Through the existing pipelines and pumping stations, the recharge water from Wohushan Reservoir,Yuqing Lake Reservoir and Tianshan Electric Pumping Station can be diverted to the upstream of Yufu River. These conditions lay the foundation for the groundwater recharge.But compared with the local groundwater, there probably have some risks to infiltrate source water with poorer water quality into the underground. Hence, by reviewing the related literature, collecting the hydro-geology data and historical water quality monitoring data of source water and groundwater before the recharge, conducing the field investigation to find out the surrounding land-use type and monitoring the physical and chemical indicators of source water and groundwater during the recharge, the water quality risk assessment of the aquifer recharge with multi-water resources in Yufu River was carried out according to the MAR guidelines of Australia?NRMMC–EPHC–NHMRC 2009a?, including entry-level assessment, commissioning investigation and research, maximal risk assessment and risk management. The study results are as follows:?1? Entry-level assessment consisted of feasibility assessment and difficulty assessment.Among them, feasibility assessment revolved round water demand, adequate water, the aquifer, water treatment site and management ability and the results indicated this artificial groundwater recharge project was basically feasible. Difficulty assessment results showed this project generally had a lower difficulty level. But based on the particularity of karst aquifer,the safety of source water recharged to the underground should be taken into consideration.?2? In commissioning investigation and research phase, six deep wells and three shallow wells were firstly arranged by the field survey of the upstream. Through comparing water quality indicators of source water and the groundwater before the recharge with the III grade of quality standard for surface water?GB 3838-2002? or ground water?GB/T 14848-93?,some monitoring indicators were determined, including total hardness, NO₄^-N, NO₂^-N,NO₃^-N, total nitrogen, fluoride, chloride, sulfate, bicarbonate, potassium, sodium, calcium,magnesium, TOC, BOD₅ and CODMn. In addition, to study the hydrogeochemical change during the recharge, other physical and chemical indicators such as pH, TDS and turbidity also needed to be monitored. Then, descriptive statistics was adopt to broadly analyze the monitoring indicators of shallow wells and deep wells for different source water recharge and the results showed that except for turbidity, other indicators basically met the III grade of quality standard for ground water and were roughly similar to the microcosmic ion correlation analysis. Three-line diagram was used to express the hydrochemical type changes of the groundwater and the results showed that during the Wohushan Reservoir and Yellow River recharge, the hydrochemical type changes respectively changed HCO3-Ca into SO4·HCO3-Ca·Mg or SO4·HCO3-Ca and SO4·Cl·HCO3-Ca·Mg?·Na?, SO4·HCO3·Cl-Ca·Mg·Na or SO4·HCO3·Cl-Ca?·Na?. Besides, geochemical assessment applied ion ratio coefficient method and the results indicated that the recharge generally posed no threat to the stability of the aquifer. The land-use risk assessment found that after the treatment, domestic and industrial waste water around the project area met the I-II grade of national sewage comprehensive emission standard?GB 8978-1996? and only the turbidity and CODMn exceeded the standards for drinking water quality?GB 5749-2006?. Moreover, because of much farmland and large fertilizer amount, three nitrogen intakes should be controlled. Clogging assessment displayed that during the recharge, the aquifer probably existed physical and chemical clogging, but the water-rock interaction between source water and the aquifer could help relieve clogging.?3? Combined with the results of commissioning investigation and research,semi-quantitative method was applied to conduct the maximal risk assessment of different source water recharge. Evaluation indicators came to twelve items, such as pathogen, salinity,inorganic compound, organic compound and nutrient. Among them, the evaluation principleof the first seven indicators mainly involved sustaining human health and protecting the environment. Specifically, from the point of considering the impact on human health, the groundwater quality indicators of different source water, shallow water and deep water should be compared with the standards for drinking water quality; from the environmental protection perspective, the different source water should be compared with the III grade of quality standard for ground water. The evaluation principle of other five indicators mainly learned from the relevant MAR provisions about the impact of the pollutant on the aquifer or biosphere. After integrating the maximal risk assessment results of different source water,turbidity and sulfate were finally determined to be the biggest risk items and critical control points. In addition, the Yellow River recharge still noticed the salinity risk; the Wohushan Reservoir water recharge needed control the risks of three nitrogen, BOD5 and CODMn.According to the land-use risk assessment, the pollutant transportation in the aquifer had a lower risk. Moreover, other six indicators were all proved to be low-risk items by looking up the historical data of the hydrogeologic prospecting and water quality monitoring data of source water and groundwater.?4? After analyzing the results of entry-level assessment, commissioning investigation and research and maximal risk assessment to determine high-risk indicators or potential pollutants, to improve safety and sustainability of the project operation, risk management planning not only considered the pre-treatment of high-risk indicators, but also attached importance to the later-period management, such as enhancing real-time monitoring and evaluation of the recharge water quality, controlling the recharge volume, accelerating the construction and operation of sewage discharge network in the upstream of Yufu River.