Subsidence Fracturing of Stream Channel from Longwall Coal Mining Causing Upwelling Saline Groundwater and Metal-Enriched Contamination of Surface Waterway

Abstract

This study investigated a small waterway that had been impacted by upwelling groundwater due to recent geological strata fracturing caused by subsidence activity from longwall coal mining. Documents from the coal mine report that subsidence has undermined and fractured the stream channel for more than 10 years prior to this study. Mine documents also report many years of variably degraded water quality (salinity, elevated metals) in the reaches affected by fracturing. In this study, water quality of the stream was monitored over an 11-month period with water flow dominated by ground water upwelling through fractures in the creek channel. The upwelling water caused extensive modifications to the creek's surface water quality relative to unmined reference sites. The mean electrical conductivity increased by seven times from 230 μS/cm at reference sites to 1833 μS/cm below the upwelling. Dissolved oxygen in the upwelling groundwater was extremely low (2.7% saturation) and was mildly acidic (5.8 pH). Alterations to the ionic composition included sevenfold increases in magnesium, sodium, and chloride concentrations. Heavy metals iron and manganese increased by more than ten times, with nickel by more than 60 times compared to the reference sites. The alteration to ionic composition was inferred to be saline groundwater intrusion. The ecological impacts of such large modifications to surface stream water quality would be hazardous for integrity of downstream aquatic ecosystems.

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