NDLI: Glacio-lacustrine stratigraphy, aquifer characterization and contaminant transport: a case study in South Lake Tahoe, California, USA

Content Provider	Springer Nature Link
Author	Morgan, Craig W. Kent, Graham M. Seitz, Gordon G. vak, Michaela
Copyright Year	2008
Abstract	A hydrogeologic model that has been used by many researchers and consultants to describe an area of South Lake Tahoe, California, USA impacted by MTBE contamination describes a relatively homogeneous unconfined aquifer comprised of poorly sorted glacial outwash deposits, within which water-supply wells are able to exert significant alteration in natural groundwater flow. A re-examination of the area’s hydrogeology is presented, which supports a layered heterogeneous aquifer system constructed of alternating fine and coarser-grained glacio-lacustrine depositional units. This re-evaluation was accomplished through a review of lithologic logs across an area of approximately 1 km$^{2}$, combined with observations of significant hydraulic head differences and knowledge of the depositional environments controlled by Pleistocene Lake Tahoe high stands. Many of the fine-grained units observed at depths from 6 to 15 m, although relatively thin, are generally continuous and serve as significant barriers to groundwater flow. The vertical migration of contamination across these fine-grained units to deeper groundwaters was facilitated by cross-screened monitoring wells installed as part of site investigation activities. This conclusion highlights the importance of geologic characterization and proper monitoring well construction at contaminated site investigations.Un modèle hydrogéologique qui a été utilisé par de nombreux chercheurs et consultants pour décrire une région du Lac Tahoe Sud, Californie, Etats Unis, touchée par une contamination au MTBE dépeint un aquifère libre relativement homogène formé de dépôts d’épandage glaciaires peu classés, au sein duquel les puits d’alimentation en eau sont aptes à provoquer une modification significative de l’écoulement naturel de l’eau souterraine. Un réexamen de l’hydrogéologie de la région est présenté, qui rend compte d’un système aquifère hétérogène stratifié formé de couches de dépôts glacio-lacustre à granulométrie fine et plus grossière en alternance. Cette réévaluation a été réalisée à partir d’une compilation de logs lithologiques à travers une région d’environ 1 km$^{2}$ , associée à l’observation de différences de pression hydraulique significatives et à la connaissance de l’environnement des dépôts contrôlés par des niveaux élevés du Lac Tahoe au Pléistocène. De nombreuses couches à grain fin observées à des profondeurs de 6 à 15 m, quoique relativement minces, sont généralement continues et font office de barrière significative à l’écoulement de l’eau souterraine. La migration verticale de la contamination à travers ces couches à grain fin vers des eaux souterraines plus profondes était facilitée par des puits d’observation entièrement crépinés installés dans le cadre des activités de recherche sur le site. Cette conclusion souligne l’importance de l’identification géologique et de la construction correcte des puits pour des recherches sur un site contaminé.Un modelo hidrogeológico que ha sido utilizado por muchos investigadores y consultores para caracterizar un área del Lago Tahoe Sur, California, USA, que sufre el impacto de contaminación por EMTB (éter metal tert-butílico), describe un acuífero libre relativamente homogéneo compuesto de depósitos de deshielo glaciar escasamente seleccionados, dentro del cual los pozos de abastecimiento de agua ejercen una alteración significante del flujo subterráneo natural. Se presenta una re-evaluación del la hidrogeología del área, con un sistema de capas acuíferas heterogéneas con alternación de sedimentos finos y gruesos de origen glacio-lacustre. Esta re-evaluación comprendió una revisión de perfiles litológicos en un área de aproximadamente 1 km$^{2}$, combinada con observaciones de diferencias significativas del nivel del agua subterránea y los ambientes de deposición controlados por las mayores elevaciones durante el Pleistoceno del Lago Tahoe. Muchas de las unidades de granometría fina, halladas a profundidades de 6 a 15 m, son relativamente delgadas, aunque son continuas y constituyen barreras relevantes al flujo subterráneo. La migración vertical de contaminantes a través de las unidades de grano fino hacia aguas más profundas se facilitó por pozos de monitoreo rasurados que se instalaron como parte de las actividades de investigación. Esta conclusión destaca la importancia de la caracterización geológica y el monitoreo adecuado de la construcción de pozos en sitios de estudio contaminados.
Starting Page	981
Ending Page	994
Page Count	14
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	16
Issue Number	5
e-ISSN	14350157
Language	English
Publisher	Springer-Verlag
Publisher Date	2008-06-06
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	USA Conceptual models Contamination Cross-screened wells MTBE Waste Water Technology Water Pollution Control Water Management Aquatic Pollution Geology Hydrogeology
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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