Roof Rainwater Quality Treatment And Hydrochemical Variation Of Fracture Karst Groundwater

With the rapid development of economy and increase of population, shortage of water resource and water enviroment deterioration increasingly become two questions faced by human beings. Many northern cities of China use fracture karst water as water supply source. In order to satisfy increasing demand to water supply, some cities blindly overexploit groundwater, which results in regional groundwater level descending, forms regional cone of depression, induces ground sedimentation and wells and springs exhausted and seawater encroachment and water quality deterioration of groundwater and so on; but on the other hand, with the urbanization process speeding up, cities are extended and constructed, area of impenetration is increasing year after year, which makes many seriously short of water city wasting water resource by losing rainwater runoff. At the same time, because of rainwater on the hardened ground can not infiltrate naturally, large amount of rainwater runoff can not discharged rapidly by drainage system, so which lead to road water logging and even flood, there bring harm to society, city environment and people's life.Therefore, if urban rainwater is utilized to recharge groundwater, it not only can supply decreasing groundwater resource and elevate groundwater level and prevent ground sedimentation and keep drinking water supply and protect spring, but also can reduce drainage network pressure and expense of function and investment to drainpipe in city by distributing some rainwater and lessen flood and water logging disaster at rainstorm. Whereas being influenced by environment pollution and influx material characters, urban rainwater is polluted in some degree. If this polluted rainwater is filled to ground, it must pollute groundwater. Therefore, how to control contamination in rainwater is a knotty problem in technology of manual recharge groundwater. Roof provides a natural place to collect rainwater and the roof rainwater quality is relatively good compared with road runoff, so there has a high value of utilization; in addition, with large permeability coefficient of fracture karst aquifer, the aquifer will provide a good condition for infiltration, which is conducive to the implementation of groundwater recharge. Aiming at the questions and advantages above, the paper researches the water quality characteristics and influencing factors of roof runoff in Jinan City, puts forward the pollution problem happened in the initial stage of precipitation and the initial storm water discard and how much to discard, explores a simple and feasible measure to deal with roof runoff, studies ground hydrochemical variation at recharge area, which all will provide important basic data and scientific basis for the next step of implementation of groundwater recharge and the study of the influence on water quality of fracture karst aquifer by recharge water and risk control. Specific studies are as follows:1. The major pollutants in roof rainwater runoff in flood season conclude color, turbidity, NH₃-N, NO₂-N, volatile phenol, SS and originate from cumulative dust, fossil fuel combustion and vehicle exhaust. Roof rainwater runoff quality is influenced by rainfall duration, rainfall density and season and so on.2. By the study of correlation of cumulative pollutant loads and cumulative discharge, the first ush phenomenon in rainfall process have been found and the first ?ush of storm runoff is usually the most polluted; according to variation of roof rainwater quality and considering pollutant control purpose and economy and safty of subsequent treatment process, 6mm of initial rainwater discard volume have been determined.3. In the filtration test by sand column system and sand filtration-activated carbon system, purification effect of roof rainwater by these two filtration systems are studied and compared with classâ…¢of groundwater environmental quality standard. From the experiment results, sand filtration system was effective to remove turbidity, color, volatile phenol, and metal ions and so on. However, it had a bad effect on removing ammonia nitrogen, nitrite nitrogen. Sand-activated carbon filtration system was effective to remove ammonia nitrogen, but it can not reach classâ…¢of groundwater environmental quality standard, and also it had a bad effect on removing nitrite nitrogen.4. In flood season in 2010, precipitation, water level, temperature, pH value, conductivity, total dissolved solid, turbidity and salinity were monitored, and under rainfall condition the response characteristics of underground hydrochemical variation by precipitation were studied, so hydrochemical variation of fracture karst aquifer and water-rock interaction mechanism were known for further.