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Casing depths and solute travel times to wells
Author(s) -
Kirkham Don,
Sotres M. Olga
Publication year - 1978
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/wr014i002p00237
Subject(s) - aquifer , streamlines, streaklines, and pathlines , casing , phreatic , geology , hydraulic conductivity , water table , radius , dimensionless quantity , hydrology (agriculture) , geotechnical engineering , soil science , groundwater , mechanics , petroleum engineering , physics , computer security , computer science , soil water
Travel times are computed for a solute moving by assumed piston flow in a steady state along streamlines in a phreatic (water table) aquifer in which a tube well is located to determine the influence of unscreened casing depth on travel time. Flow nets are first computed by potential theory and then travel times along sets of streamlines for 18 geometries. Parameters varied are unscreened casing depth, well radius, and thickness of aquifer, all for a fixed radius of influence. For a well radius of 10 ft (3.05 m), a radius of influence of 500 ft (152 m), an aquifer thickness of 100 ft (30.5 m), a depth of the unscreened (impervious) casing below the water table of 25 ft (7.62 m), a hydraulic conductivity of 100 ft/d (30.5 m/d), a head difference across the system of 5 ft (1.52 m), and an aquifer porosity of 0.25 the longest travel time for a solute entering at the water table is 89.3 yr , and the shortest, which is for flow along the well casing, 0.500 day. Corresponding travel times for the same geometry, except that the unscreened depth of casing is doubled from 25 ft (7.62 m) to 50 ft (15.24 m), are 106.4 yr and 2.38 days. Other times may be determined conveniently from charts that give dimensionless times t ′ that are to be multiplied by a factor [ƒ/( KH )] b 2 , where ƒ is aquifer porosity, K is hydraulic conductivity, H is pumping drawdown depth, and b is radius of influence. The computed travel times should be useful in well design and protection from solutes, such as nitrates and acids originating from agriculture, industry, strip mines, sanitary landfills, or other groundwater pollution sources near wells. Supplementary appendix (computer program) is available with entire article in microfiche. Order from American Geophysical Union, 1909 K Street, N.W., Washington, D.C. 20006. Document W78‐001; $1.00. Payment must accompany order.