Springs and Aquifers EarthCache

(Question information area) There are two different types of aquifers, confined and unconfined. Unconfined aquifers are those into which water seeps from the ground surface directly above the aquifer. Confined aquifers are those in which an impermeable dirt/rock layer exists that prevents water from seeping into the aquifer from the ground surface located directly above. Instead, water seeps into confined aquifers from farther away where the impermeable layer doesn't exist. A spring is an aboveground or underground water source. A spring is formed when the pressure in an aquifer causes some of the water to flow out at the surface. In this case this a seepage spring. Seepage springs are springs in which the water seeps out of sand or gravel; they differ from general seepage only in being restricted to a small area. Such springs are usually marked by abundant vegetation at their points of emergence, and their waters are often colored or carry an oily scum due to the decomposition of vegetable matter or the presence of iron. The scum is frequently mistaken for petroleum. Petroleum is a thick, flammable, yellow-to-black mixture of gaseous, liquid, and solid hydrocarbons that occurs naturally beneath the earth's surface. The waters of the seepage springs commonly come from no great distance beneath the surface and are not usually very cold. Seepage springs may emerge along the top of an underlying impervious bed, but more commonly they occur where valleys are cut downward into the zone of saturation of a more or less uniform water bearing deposit. Under favorable conditions the seepage from sands gathers into channels and forms streams of considerable size, some of them flowing 5,000,000 gallons or more daily. Seepage springs, as in the cases cited, are commonly of the gravity type, but where channels or fissures emerge beneath beds of sand or gravel seepages not infrequently result from true artesian springs.

This area of Michigan was formed during the Devonian period. Types of rocks like limestone and old red sandstone form underground. Waters occur in limestone mainly in open channels, caverns, etc., dissolved in the rock by the water itself. The water originally probably followed joint or bedding planes which were gradually enlarged by solution into the caverns that now exist. The occurrence of caverns and passages within the limestone is very irregular, and their location can seldom be predicted. Most deep wells which are drilled in limestone regions, however, encounter one or more such passages at a relatively slight distance below the surface. Wells in limestone, even where only a few feet apart, may nevertheless obtain very different results, as a difference of a foot or two may mean the missing of a certain channel. The waters in limestone are generally hard but are not commonly otherwise mineralized. The Old Red Sandstone describes a suite of sedimentary rocks deposited in a variety of environments during the Devonian but extending back into the late Silurian and on into the earliest part of the Carboniferous. The body of rock, or facies, is dominated by alluvial sediments and conglomerates at its base, and progresses to a combination of dunes, lakes and river sediments. The familiar red color of these rocks arises from the presence of iron oxide but not all the Old Red Sandstone is red or sandstone — the sequence also includes conglomerates, mudstones, siltstones and thin limestones and colors can range from grey and green through red to purple.

• http://aquadoc.typepad.com/files/usgs_publication_meinzer_1923_cover_and_page_9.pdf
• https://water.usgs.gov/edu/watercyclesprings.html
• https://pubs.usgs.gov/wsp/0255/report.pdf
• https://en.wikipedia.org/wiki/Old_Red_Sandstone