Study On The Key Technologies Of Water Resouces Regulation By Groundwater Depression Cone In Daqing City

DaQing is a city that primarily based on the petroleum mining andpetroleum manufacture, and it plays an irreplaceable role in our nation'senergy supply. However due to the seriously limited surface water resource inthe DaQing petroleum mining area, groundwater has been the main watersupply. After 40 year's petroleum exploitation, to satisfy the water demand ofpetroleum production and city development & construction, the long termgroundwater over pumping has resulted in the formation of the eastern and thewestern regional groundwater depression cones. We take the westerndepression cone for example to study the water resource artificial regulation &storage in the depression cone area. This study is of great meaning in thecontrolling and improving of the geological setting, preventing the potentialenvironmental geological disaster and enhancing the water supply safety to thestudy area. Based on the analyzing of years of groundwater exploitation andutilization data of DaQing, we use the groundwater mathematical modelingtechnique and the hydrogeochemical modeling technique to study the keyproblem in underground reservoir artificial regulation & storage. This researchincludes: analyzing the condition of underground reservoir construction,dividing and determining the specific water level and specific reservoircapacity, modeling and analyzing of the groundwater resources artificialregulation & storage scheme and analyzing the groundwater quality changescaused by the groundwater artificial recharge. Through these studies, we drawthe following conclusions: (1). The western part of DaQing is much suitable for the undergroundreservoir construction: the reservoir area aquifer is composed of grit ofBaiTushan group ,Quaternary sediments and the TaiKang group, Tertiarysediments, which is of high water storability and water conductivity;theNenJiang river water, with plenty of water of good quality, is available for theunderground reservoir recharge;the boundary condition is suitable for waterstorage, and what's more, with the hydraulic structures foundation, theunderground reservoir construction would obvious bring social, environmentaland economic much benefit.(2). Build the groundwater mathematical model for the undergroundreservoir area in the western DaQing city. After the model's calibration andvalidation, we get the hydrogeological parameter subarea and the parametervalue for each subarea, and have a further acknowledgement about thehydrogeological setting and the groundwater flow character. This conditionsfor the specific reservoir capacity calculation and for the water resourcesartificial regulation & storage designing and modeling.(3). Similar to the surface reservoir dividing disciplinarian, we divide thespecific water level and reservoir capacity of the underground reservoir asfollow: dead water level and dead reservoir capacity, ordinary water level andregulating reservoir capacity, emptying reservoir capacity, occupied reservoircapacity and total reservoir capacity. What's more, we discuss thedisciplinarian of the artificial regulation & storage water level determinationof the phreatic aquifer and the confined aquifer.(4). Useing the TDS as the water quality index, by analyzing therelationship between the water quality evolve tendency and the groundwaterdynamic in a few water plants, we deduce that the threshold level ofgroundwater quality deterioration is 115m. Combining with the confinedaquifer upper board limitation, we determine dead level of the groundwaterartificial regulation & storage is 115m.(5). Calculating underground reservoir specific capacities under differentordinary water levels, considering the water exploitation condition in initialand the current confined water level, we determine the ordinary water level ofartificial regulation & storage is 132m. Base on this, we get the specificreservoir capacity as follow: total reservoir capacity, 1160.44×108m3, deadreservoir capacity 1159.30×108m3, regulating reservoir capacity1.14×108m3,available emptying reservoir capacity1.04×108m3 . The total reservoircapacity big or small doesn't suggest that the underground reservoir regulationis good or poor, but the emptying reservoir capacity determines the currentavailable storing space, the regulating reservoir capacity determines availablewater resources after underground reservoir construction.(6). If the exploitation keeps current (year 2004) condition (theexploitation rate is 1.30×108m3/a ), the groundwater level in the depressioncone centre (QianJin water plant , DuLitun water plant and the south waterplant) would have a little rise, then the water level would be 119~121m byyear of 2010;if the groundwater exploitation rate could cut down 5% per yearduring the underground reservoir construction period, then the groundwaterlevel of depression cone centre would be 121~123m by year of 2010. Theresult shows that if the exploitation rate keeps at current condition or just havea slightly cut down and the recharge depend only on the natural aquiferrecharge, the water level can't achieve the expected level.(7). Consider the situation of that from 2007, we artificially rechargegroundwater with the rate of 10×104m3/d, then, the groundwater level in thedepression cone centre would be132m till the end of 2010. For this case, theshape of depression cone would be blurry at the western water plant, theRangHulu water plant, DuLitun water plant and South water plant, and thenew groundwater depression cone centre would move to the XingShugangwater plant and the Xing'er water plant. The lowest water level would be126~127m, almost equal to the water level in the southern part of reservoir(127m). The whole underground reservoir would be under slightly depressingstate, and the water injected in could be well stored, and the water level wouldnearly reach the designed water level.(8). To guarantee the whole city's domestic and industrial water demand,the water lackage would be complement by the under ground reservoir water,in case of the NenJiang river water is seriously polluted or surface waterdiversion engineering breaks down,. If we take the water level in 2010 undercondition of simply exploitation cut down as the initial water level, after onemonth emergency water supply, the groundwater level of the main exploitationarea would descend to the dead level(115m);but if we take the water level in2010 under condition of artificial recharge as the initial water level, then aftertwo months, the water level in the main water plant would draw down to thedead level. That means the artificial recharge would prolong the undergroundreservoir emergency supply duration for a month.(9). Take the western water plant for example, according to the commonwater quality request for the artificial recharge groundwater, the suspendingsubstance content of the injected water ( LongHupao pipe line outlet surfacewater) is obviously over-standard, must be treated before injection. Both thecontent of cadmium (0.28mg/L) and arsenic (2.18 mg/L) in the injected waterexceed the drinking water standard (cadmium<0.01 mg/L, arsenic <0.05mg/L), but are obviously less than those of groundwater (cadmium 0.70 mg/L,arsenic 3.55 mg/L). So the artificial recharge won't degrade the groundwaterquality level, but it is much better to treat the water to the standard of thedrinking water before injection.(10). Adopt hydrogeochemical modeling technique to study the influenceof artificial recharge to the groundwater environment. The result shows that: ifwe ignore the water-rock interaction, assuming the injected water and thegroundwater is simply mixed together, without obvious chemical reaction,then the modeling result would in consistent with the experiment result. Thissuggests that the surface water and the groundwater have well water qualityconfluent ability. If we take the possible mineral reaction in the aquifer intoconsideration, the PH value of the mixed water would decline, and the calciumand the magnesium concentration would raise for some extent, the iron andmanganese concentration would have a slightly rise, and the concentration offluorin, chlorite, sodium and sulfur would commonly draw down. Watermixing won't change water quality obviously and the water quality will tendsto low mineralizion.