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Influence of cover slab diameter on solute travel time to wells
Author(s) -
Kirkham Don,
Sotres M. Olga
Publication year - 1979
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr015i004p00941
Subject(s) - aquifer , streamlines, streaklines, and pathlines , slab , phreatic , casing , geology , hydraulic conductivity , radius , groundwater , water well , soil science , hydrology (agriculture) , geotechnical engineering , geomorphology , mechanics , geophysics , physics , computer security , computer science , soil water
Travel times are computed for solute, moving by assumed piston flow, in steady state along streamlines in a phreatic (water table) aquifer in which a tube well is located to determine the influence of a well cover slab on the travel times. Flow nets are first computed by potential theory; then travel times along sets of streamlines are derived for 12 geometries. Parameters are cover slab radius, screened and unscreened casing depth, thickness of aquifer, well radius, and radius of influence. For example, for a well of cover slab radius 1.8 m, screened casing depth 0.5 m, unscreened casing depth 1.5 m, thickness of aquifer 6 m, well radius 0.6 m, and radius of influence 30 m, hydraulic conductivity 35 m/d, head difference across the system 0.15 m, and aquifer porosity 0.25, the travel time for solute injected at the edge of the cover slab to reach the well is 5.4 days, whereas solute introduced at the top of the aquifer next to the well pipe with no cover slab is 0.17 day (4.1 hours). The longer travel time, 5.4 days versus 0.17 day for ‘no cover slab,’ provides a longer time for biochemical and biophysical degradation of the solute, which may be pollutants as nitrates and acids originating from agriculture, industry, strip mines, sanitary landfills, or other groundwater pollution sources near a well.