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SITE-94. Geochemical characterization of Simpevarp ground waters near the Aespoe Hard Rock Laboratory

Abstract

The present report analyzes the geochemical data in order to evaluate collection and interpretation techniques that will be used to site the repository and to assess its safety. Ground waters near the Aespoe Hard Rock Laboratory (HRL) may be grouped into five chemically and isotopically distinct water types, on the basis of their deuterium and chloride contents: 1) recent waters, 2) 5 g/L chloride waters, 3) deep waters, 4) seawater imprint waters, and 5) glacial melt waters. The sampled ground waters show a progressive change from a predominantly NaHCO{sub 3} composition at shallow depth to a CaCl{sub 2}-rich composition at depth. Despite the proximity of the Baltic, relatively few of the sampled ground waters contain any evidence of a seawater component. This finding, together with the rather shallow depths at which saline waters were found, indicates that Aespoe island is presently in a regional ground-water discharge area. The chemical and isotopic composition of the sampled waters also indicates that local recharge of dilute recent waters occurs only down to shallow depths (generally less than 100 in). The Aespoe ground waters are sulfidic and do not presently contain any dissolved oxygen. Measured E{sub H} values are generally near -300 mV, and  More>>
Authors:
Glynn, P D; Voss, C I [1] 
  1. US Geological Survey, Reston, VA (United States)
Publication Date:
Sep 01, 1999
Product Type:
Technical Report
Report Number:
SKI-R-96-29
Reference Number:
EDB-00:103092
Resource Relation:
Other Information: 161 refs, 53 figs, 7 tabs; PBD: Sep 1999
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; CHLORIDES; GEOLOGIC FRACTURES; GROUND WATER; RISK ASSESSMENT; SEAWATER; SITE CHARACTERIZATION; UNDERGROUND DISPOSAL
OSTI ID:
20043510
Research Organizations:
Swedish Nuclear Power Inspectorate, Stockholm (Sweden)
Country of Origin:
Sweden
Language:
English
Other Identifying Numbers:
Other: Project SKI-98291; ISSN 1104-1374; TRN: SE0000024005500
Availability:
Available from INIS in electronic form
Submitting Site:
SWDN
Size:
220 pages
Announcement Date:

Citation Formats

Glynn, P D, and Voss, C I. SITE-94. Geochemical characterization of Simpevarp ground waters near the Aespoe Hard Rock Laboratory. Sweden: N. p., 1999. Web.
Glynn, P D, & Voss, C I. SITE-94. Geochemical characterization of Simpevarp ground waters near the Aespoe Hard Rock Laboratory. Sweden.
Glynn, P D, and Voss, C I. 1999. "SITE-94. Geochemical characterization of Simpevarp ground waters near the Aespoe Hard Rock Laboratory." Sweden.
@misc{etde_20043510,
title = {SITE-94. Geochemical characterization of Simpevarp ground waters near the Aespoe Hard Rock Laboratory}
author = {Glynn, P D, and Voss, C I}
abstractNote = {The present report analyzes the geochemical data in order to evaluate collection and interpretation techniques that will be used to site the repository and to assess its safety. Ground waters near the Aespoe Hard Rock Laboratory (HRL) may be grouped into five chemically and isotopically distinct water types, on the basis of their deuterium and chloride contents: 1) recent waters, 2) 5 g/L chloride waters, 3) deep waters, 4) seawater imprint waters, and 5) glacial melt waters. The sampled ground waters show a progressive change from a predominantly NaHCO{sub 3} composition at shallow depth to a CaCl{sub 2}-rich composition at depth. Despite the proximity of the Baltic, relatively few of the sampled ground waters contain any evidence of a seawater component. This finding, together with the rather shallow depths at which saline waters were found, indicates that Aespoe island is presently in a regional ground-water discharge area. The chemical and isotopic composition of the sampled waters also indicates that local recharge of dilute recent waters occurs only down to shallow depths (generally less than 100 in). The Aespoe ground waters are sulfidic and do not presently contain any dissolved oxygen. Measured E{sub H} values are generally near -300 mV, and on average are only about 50 mV lower than E{sub H} values calculated from the sulfide/sulfate couple. Maintenance of reducing conditions, such as presently found at the Aespoe HRL, is an important consideration in assessing the performance of nuclear waste disposal sites. Measurements of dissolved radon and of uranium concentrations in fracture-fill materials were used to calculate an average effective flow-wetted surface area of 3.1 m{sup 2} per liter of water for the Aespoe site. Estimation of flow-wetted surface areas is essential in determining the importance of matrix diffusion and surface sorption processes for radionuclide release calculations. The Rn calculation technique shows promise in helping narrow the possible range of values that need to be considered. Tritium measurements confirm that the recent ground water type, originally identified on the basis of deuterium and chloride measurements, contains a significant proportion of recent, post-1950, water. Better tritium analyses, together with a greater number of carbon-13 analyses on dissolved inorganic carbon, would have helped interpret the carbon-14 analyses that were obtained primarily from relatively shallow ground waters (< 500 m depth). The SITE-94 Central Scenario climate model suggests that three glaciations may occur in the Northern Hemisphere during the next 120,000 years. If such glaciations do occur, possible climate-driven changes in ground-water geochemistry, particularly in redox conditions, could occur in the Fennoscandian shield. During two of these glaciations, 2- to3-km high ice sheets are predicted to form over the Fennoscandian shield, extending over Aespoe island and further south. Modeling of ground-water flow and transport suggests the possibility of deep and fast penetration of glacial melt waters during periods of glacial advance. The intruding melt waters have a median travel time of less than 100 years to 500 m depth. Ice composition data from the base of the Greenland ice sheet suggests that the melt waters will be highly enriched in dissolved oxygen, with concentrations at least 3 to 5 times higher than would be obtained at atmospheric equilibrium. The relative scarcity of fast-reacting pyrite in hydraulically conductive fractures, and the expected scarcity of organic carbon that would be exposed to the intruding melt waters, implies that Fe(II)-rich silicate minerals would be the primary reductants for the intruding dissolved oxygen. Current information suggests that the reaction rates would not be sufficiently fast to prevent penetration of oxygenated melt waters to a depth of at least 500 m. Despite clear evidence of past, deep, glacial meltwater penetration, convincing geochemical evidence remains to be found to prove or to disprove that deep penetration of oxygenated ground waters occurred during the last Pleistocene glaciation. Amorphous Fe-oxyhydroxides and goethites have been observed at great depths at several SKB sites in Sweden. These phases may have formed as a result of the intrusion of oxygenated glacial melt waters. The recommendations for future geochemical characterization of potential nuclear waste disposal sites made by the present report generally complement recommendations made earlier by Andrews based on the international program of hydrochemical work at the Stripa mine. In addition to better sampling techniques and protocols, future characterization efforts should place greater emphasis on the measurement of conservative constituents (Cl, Br, {sup 2}H, {sup 18}O) that may provide information on the origin of ground waters and also on the hydrologic disturbances induced by sampling, testing and excavation activities. (abstract truncated)}
place = {Sweden}
year = {1999}
month = {Sep}
}