In-situ groundwater flow measurements as a tool for hardrock site characterisation within the SKB programme.

Abstract

In many cases, groundwater flow governs hydrochemical conditions and transport of contaminants. Groundwater flow rates are also a very essential input to risk assessment and a general understanding of the hydraulic system, and Swedish Nucklear Fuel and Waste Management Co (SKB) has undertaken a considerable amount of technical develoment for in-situ groundwater flow measurements by the dilution method. In order to meet the requirments for performance assessment and construction engineering, equipment has been developed that make in-situ groundwater flow measurements possible for a range of borehole diameters and site conditions in fractured hard rock. The latter include surface boreholes down to 1000 m depth and high-pressure conditions in boreholes drilled from deep underground constructions. Results from more than ten years of development and measurements are a valuable tool for site characterisation in fractured hard rock, preferably combined with other hydraulic and chemical investigation methods. The dilution method is well suited for collection of basic groundwater flow data, which may be used for development and calibration of hydraulic models. If groundwater flow is measured both under natural conditions as well as during disturbances to the system, the result will contribute significantly to the conceptual hydraulic understanding of the site.