Groundwater Leakage Research Articles

Fill dam leakage by network assessment

This paper describes a stochastic way of making a prediction of groundwater leakage through a fill dam and subsoils. The main point of this method is to construct a network for a geological structure within a flow region. It consists of some node points and branches. The node point gives an imaginary space coordinate of a soil deposit. The branch plays the role of a groundwater conduit in the model. It has substantial parameters for prescribing the groundwater flow, such as permeability, thickness and length of soil layer. All these values are given from boring and in-situ test results, which are usually found to be widely scattered even in the same soil layer. Monte Carlo simulation helped in taking into account those values.

Uranium in groundwaters of southeastern Manitoba, Canada

Anomalously high levels of naturally derived uranium have been found in groundwater samples from wells completed in overburden and bedrock aquifers in southeastern Manitoba. Uranium analyses were carried out on groundwater samples collected from 287 individual wells in a 15 500 km2 area. The mean U concentration in all samples was 58.3 μg/L; the maximum value was 2020 μg/L. Uranium concentrations were highest in samples from Precambrian rock aquifers, averaging 115.6 μg/L, and were lowest in samples from Paleozoic sedimentary rock aquifers, averaging 3.5 μg/L.Uranium concentrations up to 250 μg/L were found in groundwaters in or associated with Lake Agassiz clay deposits. These high concentrations are thought to result principally from release of U from the organic component of the clays, either by oxidation or desorption. Leakage of uraniferous groundwater from the clays appears to provide a significant source of U to underlying sand and gravel aquifers and to the Precambrian bedrock aquifer. Uranium within the bedrock is also being released to solution by oxidation of uraniferous hematite found as mineral coatings and fracture fillings in highly weathered zones. Uranium solubility in many Precambrian bedrock groundwaters is increased by recharge of these aquifers by ground waters from overburden materials that contain high [Formula: see text] concentrations.

Spring-related carbonate rocks, Mg clays, and associated minerals in Pliocene deposits of the Amargosa Desert, Nevada and California

The Amargosa Desert of Nevada-California is a spring-fed structural basin containing large amounts of Pliocene carbonate rocks and Mg clays deposited in playas, marshland, ponds, and flood plains. Pliocene basin-fill deposits dated at 2.4 to 3.2 Ma are subdivided into three lithofacies, designated “Tpa, Tld, and Tpl.” Tpa is chiefly limestone and was deposited, in marshland and ponds. Tld consists chiefly of limestone and montmorillonite claystone that were deposited in varied environments, including ponds and flood plains. Tpl is almost entirely Mg clays, limestone, and dolomite, which were deposited in playas and associated marshland. The largest area of playa sediments, termed East Playa, is in the east-central part of the basin. Limestone and dolomite seepage mounds and caliche-breccia musses were formed along zones of ground-water leakage within East Playa. Chemically precipitated Mg smectite and sepiolite form large deposits in Tpl. Sepiolite was formed in water of low salinity, whereas Mg smectite was formed in water of higher salinity. Authigenic celadonitic illite and K-feldspar are commonly associated with Mg smectite and are very likely reaction products of montmorillonite in saline, alkaline water. Silicic vitric ash layers were locally altered to phillipsite and K-feldspar in saline, alkaline water and to montmorillonite as a result of leaching by water of low salinity. Carbonate rocks are locally silicified along seepage zones. Carbonate minerals of the Pliocene deposits have stable isotopic compositions that vary with their lithofacies. Tpa limestones deposited in or near areas of spring discharge have low δ18O values averaging +16.6. Tld limestones recrystallized in the vadose zone have higher δ18O values, averaging +18.1. Carbonate minerals of Tpl are the most δ18O-rich, with calcite averaging +20.3 and dolomite +24.3, reflecting evaporative concentration in playas. Much of the dolomite is of replacement origin yet is in approximate isotopic equilibrium with the calcite it replaces. Relatively pure sepiolite has lower δ18O values than do Mg smectite clays, which fits with the lower salinity inferred for sepiolite precipitation. Sepiolite and Mg smectite disseminated in limestone fall outside the oxygen isotopic limits of the relatively pure clays, possibly because of diagenetic recrystallization. The Pliocene climate was wetter than that of the present, and springs were more widespread in the Amargosa basin. This dolomite may have formed in water isotopically and chemically about the same as that of the calcite, and dolomitization may have been chiefly a result of the differing crystallization kinetics of calcite and dolomite and of fluctuating water chemistry in a playa environment. The saline, alkaline water of East Playa resulted from evaporation of a mixture of alkali bicarbonate runoff from the volcanic terrane to the north with Ca-Mg bicarbonate water discharged in springs from the Ash Meadows ground-water system, whose recharge area is principally in Paleozoic carbonate rocks to the east and northeast. Seepage along fault zones in East Playa was initially of Ash Meadows type, low in silica, and changed to siliceous water, derived from volcanic rocks, resulting in silicification of carbonate deposits. Caliche breccias along the western margin of the basin record a similar change in the composition of ground-water seepage, which may be attributed to a period of decreased precipitation about 2.5 Ma which reduced recharge from nearby carbonate rocks relative to that from more distant volcanic rocks to the north and northwest.

Groundwater leakage into tunnels and storage caverns. A documentation of factual conditions at 73 caverns and tunnels in Sweden : Bergman, S M Proc 1st International Symposium on Storage in Excavated Rock Caverns (Rockstore 77), Stockholm, 5–8 Sept 1977, V2, P267–273. Publ Oxford: Pergamon Press, 1978

Groundwater leakage into tunnels and storage caverns. A documentation of factual conditions at 73 caverns and tunnels in Sweden : Bergman, S M Proc 1st International Symposium on Storage in Excavated Rock Caverns (Rockstore 77), Stockholm, 5–8 Sept 1977, V2, P267–273. Publ Oxford: Pergamon Press, 1978

肝属川周辺の水理地質の研究

In studying the hydrologic balance such area that permeable materials like sand, gravel or ash and weakly welded pumice flow of the Quarternary, cover impermeable bedrocks, it is extremely important to check whether the specified geological conditions, which will cause the watershed leakage from one river basin to another exist or not.Generally speaking, the underground divide does not necessarily coincide with the topographic divide in such area due to the relief of bedrocks underlain by permeable materials. Consequently, a part of groundwater which infiltrated in the permeable materials flow across the topographic divide along the surface of the bedrocks.This report describes a result of investigation on the hydrologic balance in the Kimotsuki River basin (about 450km2) by taking into consideration of all possible items relating to the hydrologic balance, especially to the watershed leakage.Dr. K. Ogasawara investigated the hydrologic balance of this river basin based on the statistics for three years, 1967 to 1969, and confirmed that the average amount of annual flow (2350mm) is in excess of the average amount of the estimated rainfall (2107mm). However, the amount of loss by spontaneous evaportaion is assumed to be approximately 300mm (i. e. actual annual rainfall of this area comes to 2407mm). This is the reason why Dr. K. Ogasawara suggested the possibility of the watershed leakage of groundwater from another river basin area into the Kimotsuki River basin.A field investigation by the authors and various published geological data showed the following properties in this area and its vicinity.1) In the Kimotsuki River basin and its vicinity, pumice flows (20 to 50m in thickness, and probably pleistocene in age) which is commonly known in Japan as “Shirasu” distribute unconformably covering the Nichinan formation which is mainly composed of sandstones and shales in alternation. No doubt, the “Shirasu” has a much higher permeability compared with the Nichinan formation.2) Former topographic divide of the old Kimotsuki River basin which is composed of the Nichinan formation and is now covered by “Shirasu” may possibly act as a groundwater divide. In the left bank area of the Kimotsuki River basin, such groundwater divide which can be geologically estimated exists within the Hishida and Tabaru River basin across the topographic divide.3) The area which may possibly supply groundwater to the Kimotsuki River basin by the watershed leakage is estimated about 47km2; 34km2 in the Hishida River basin and 13km2 in the Tabaru River basin respectively.Considering above mentioned hydrogeological data, satisfactory results on the hydrologic balance were obtained. That is, if the estimated amount of the watershed leakage from the Hishida and Tabaru River basin is added to the amount of flow, it comes to approximately coincide with the amount of rainfall in the Kimotsuki River basin.On the contrary, in the Hishide River basin, the estimated amount of flow from corrected area of this river basin (sabtract 34km2 from actual river basin area) might be abequate judging from available amount of river water during irriration season.

A NEW METHOD OF CHEMICAL GROUTING TO SOLIDIFY LOOSE GROUND

Cement grouting has been commonly used to solidify loose ground or to check ground-water leakage in the course of excavation or other types of construction work. In cement grouting, however, cement particles in the grout form a kind of so-called suspension; and the grout can penetrate neither into tiny seams of rock that are smaller than the cement particles, nor effectively into sand.A means to be used successfully in such a case is chemical injection in which suitable chemicals that are originally in a prefectly liquid state are injected and made to coagulate after the injection to effect the purpose of solidification.Heretofore, a combination of sodium silicate (Na2SiO3) and calcium chloride (CaCl2) has been used for this purpose. But this method has a drawback concerning the procedure of injection. As the two chemicals react each other very rapidly, the solution of sodium silicate must be injected first, and, after cleaning the pipes and the pump free of the first chemical, the second chemical is to be injected. Thus, the injection of two chemicals must be carried out alternately, and this process not only is a troublesome operation but also has a drawback that the chemicals react each other and coagulate near the injection-pipe outlet to stop the passage of the second chemical, the deeper penetration of first chemical thus being not fully utilized.Therefore, it is essential to inject both chemicals simultaneously through one injection pipe either by mixing them before pumping or by using two pumps. Moreover the time that shall pass after the two chemicals have been mixed together until they start to coagulate (coagulation time), should be able to be easily controlled to accord properly with the purpose of the work.For instance, in case where a considerably large area or mass is to be solidified, the coagulation time should be maintained longer. On the other hand, for checking leakage of water, the chemicals should coagulate as quickly as other working conditions permit.In order to develop higher strength of the solidified layers, a more concentrated solution of sodium silicate will be required. The viscosity of sodium silicate solution becomes higher at a great rate as the density increases, so it becomes more difficult to effect a satisfactory penetration in narrow voids. This has been another problem in injection of chemicals that consist mainly of sodium silicate. It is necessary to reduce the viscosity without affecting the strength and other properties of the chemicals. Various studies have been done in this respect.Chemicals Proposed by the Authors:As a mean to solve the above-mentioned problems, the author devised a method of using a combination of sodium silicate and sodium aluminate, adding, according to the necessity, a certain amount of NaOH in order to stabilize the reaction of these chemicals.Sodium aluminate is an intermediate product in the process of manufacturing alumina. The proportion of its two components, Al2O3 and Na2O, can be changed as is desired. In addition to this, the viscosity of this solution does not increase with the degree of its concentration at so great a rate as in case of sodium silicate (Fig. 1.).Consequently, the mixture of sodium aluminate and sodium silicate solutions is far less viscous than sodium silicate alone. This is to say that the added sodium aluminate has a role of lowering viscosity while it itself acts as one component of the chemical reaction.On the Coagulation Time:The most influential factor in using these chemicals is the temperature of the solution. Fig. 9 shows the relation between the temperature and the coagulation time. The coagulation time flactuates also with the change in mixing proportion of these two chemical solutions as well as the proportion of the two components of each solution. In general, the coagulation time becomes sho