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Development of Mineral Environmental Assessment Methodologies
Task 2 - Development of Mineral Environmental Assessment Techniques at the Watershed Scale

Development of Numerical Models

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Subtask Contacts: Raymond Johnson and Andrew Manning

Subtask Objectives

Subtask Statement of Work

Subtask Products


Subtask Objectives

Performing a mineral environmental assessment over a broad region would require an ability to estimate baseline water quality conditions in mineralized watersheds having little or no available water chemistry data. Knowledge of baseline (premining) water quality is essential in order to assess the potential environmental impacts of future mining. Previous work has identified numerous factors that might influence the natural generation of low-pH, metal-rich surface water and groundwater (acid-rock drainage, or ARD). This work has largely focused on lithology and hydrothermal alteration type, and suggests that these mineralogical factors are of primary importance. However, the relative importance of climatic, hydrologic, and geologic factors controlling the subsurface flow of water and oxygen essential for sulfide oxidation remains uncertain. The purpose of this subtask is to use numerical modeling methods to determine relative importance of the many variables controlling ARD production, and to identify a limited number of "super variables" of primary importance in predicting the occurrence of ARD on the watershed scale. Knowledge of these super variables would be critical in successfully performing a mineral environmental assessment because data are typically scarce, particularly over broad regions, demanding that efforts be focused on the acquisition of only the most essential data coverages.

  1. Identify numerical modeling codes best suited for simulating the generation and transport of natural acid-rock drainage (ARD) and for performing the required modeling experiments.
  2. Determine relative importance of the many factors potentially controlling ARD production using numerical modeling experiments. Emphasis will be placed on assessing climatic, hydrologic, and geologic factors that control the subsurface flow of oxygen and water as apposed to mineralogical factors, which have been studied far more extensively. Identify "super variables" of primary importance predicting the occurrence of ARD.
  3. Identify potential proxies or surrogates for super variables identified. Emphasis will be placed on those super variables for which direct measurements are rare, meaning that broad data coverages would be difficult or impossible to obtain.

Statement of Work

Model sensitivity studies will continue to be performed using primarily TOUGHREACT to obtain final model test results. A report will be drafted on results of the sensitivity studies. Modeling efforts with the incorporation of existing data from well-characterized sites will continue to help establish reasonable ranges for model inputs.

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