Insect parts, muddy water, and new sinkholes: Not necessarily fatal flaws to water well permitting in karst

Content Provider	Scilit
Author	Hubbard, David A. Mcthenia, Andrew W.
Copyright Year	2020
Description	Book Name: The Engineering Geology and Hydrology of Karst Terrains
Abstract	A significant karstland dilemma is tapping quantitatively and qualitatively adequate groundwater resources. In the relatively impermeable Paleozoic carbonate rocks of the Appalachian Valley and Ridge physiographic province, most groundwater occupies solutional conduits formed along faults, fractures, and partings. Virtually all of these conduit (natural plumbing) systems developed as a result of bedrock dissolution by infiltrating meteoric or surface waters. Many of these conduit (cave) systems have accumulated partial- to full-passage fills of authigenic and allogenic sediments. The degree of mechanical and adsorptive filtering provided by these fills varies from system to system and through time. The detection of insect parts, or more broadly invertebrate parts, in a water well sample may be mistakenly assumed to demonstrate the direct influence of surface water. These conduit (cave) systems have evolved aquatic and vadose zone terrestrial ecosystems. In Virginia alone, there are approximately 130 cave-limited species, whose presence does not demonstrate the direct influence of surface water. Turbid waters occur in karst groundwater via two mechanisms. When turbid surface water enters subsurface conduits at sink points and is not adequately filtered by sediment fills, such turbidity demonstrates the direct influence of surface water on groundwater. Fine-grained sediments may be entrained from sediment fills within the subsurface conduit systems under high flow conditions generated during extreme precipitation events or by water well drilling and pumping. Such in-conduit entrainment does not demonstrate surface water influence, but may indicate that existing natural sediment filters are eroding and the conduit system eventually may open to the direct influence of surface water. The higher the pumping rate, the greater the probability of sediment filter entrainment and potential conduit opening to the surface and possibly to surface waters. New sinkholes form naturally in karst as a result of rapid groundwater fluctuations, especially when such fluctuations de-water voids at the bedrock-soil interface in covered karst. The actual progression of the void through overlying soils to the surface, is usually associated with precipitation events. These natural sinkhole forming processes can be triggered during de-watering by water well drilling and pumping rates exceeding normal conduit flows. The formation of new sinkholes may open conduits to the direct influence of surface water. Because sinkholes are under-drained by conduits, they are entry points through which contaminants may access karst groundwater. The determination of qualitative adequacy of karst groundwater is a site specific problem, as are most karst hazards, especially with regard to insect parts, turbidity, and sinkhole formation.
Related Links	https://api.taylorfrancis.com/content/chapters/edit/download?identifierName=doi&identifierValue=10.1201/9781003078128-30&type=chapterpdf
Ending Page	238
Page Count	4
Starting Page	235
DOI	10.1201/9781003078128-30
Language	English
Publisher	Informa UK Limited
Publisher Date	2020-11-24
Access Restriction	Open
Subject Keyword	Book Name: The Engineering Geology and Hydrology of Karst Terrains Geography Conduit Surface Water New Sinkholes Well Drilling Karst Groundwater Flows Bedrock Drilling and Pumping
Content Type	Text
Resource Type	Chapter