Water Smarts 2002

• Year: 2002
• Title: Water Smarts
• Author: Upper Arkansas Area COG USGS Pueblo Office
• Description: A well and septic system owner's guide to ground water in the upper arkansas area chaffee, custer, fremont, and lake counties, Colorado
• Publications - Doc Type: Other

granodiorite) and metamorphic
rocks (gneiss). They are
exposed at the surface in about
42 percent of the area. Water
occurs in fractures in these
rocks. Well yields from the
crystalline rocks generally are
less than 10 gallons per minute.
However, greater yields may
be obtained where the rocks are
highly fractured, particularly
along watercourses. Rocks in
areas that are faulted likely are
more intensely fractured than
those in areas that are not
faulted. Because ground -water
flow through fractures is
relatively rapid and soils are
generally thin, ground water in
fractured crystalline rocks is
susceptible to contamination
from the surface.
Upper Arkansas
Ground -Water Study
There are six generalized rock types in
the 3,673 - square mile Upper Arkansas
Area. Because the number and size of
the pores vary between and within
these rocks, the water storage and
transport abilities are highly variable.
Typical Aquifer
Water Holding Capacity
Sand & Gravel 5 gal
5 gallons of
sand & gravel 1 gal
can hold about
16 cups (1 gallon)
of water. �is
Fractured Rock 5 gal
An equal amount
of fractured rock 3 tsp
can hold about
3 teaspoons (0.01
gallon) of water.
Water - Holding Capacity
Generally, saturated sand and
gravel holds and yields more
water to wells per foot than do
silt and clay, sedimentary
rocks, or fractured bedrock. A
five - gallon bucket of sand and
gravel can hold about 16 cups
of water or about 20 percent of
the total volume is drainable
pore space. An equal amount of
fractured rock may hold and
yield about 3 teaspoons of
water or about 0.2 percent of
the total volume. While clay
may contain as much or more
water than sand and gravel,
water does not drain readily
from clay. Yields from
sedimentary rocks lie between
those of sand and gravel and
fractured rocks, depending on
the type of rock and the
presence of fractures or
solution openings.
Well Yields
Reported well yields,
including domestic, irrigation,
public supply, and stock wells,
in the area are highly variable,
ranging from 0.01 gallon per
minute to 4,620 gallons per
minute with an average
reported well yield of about 17
gallons per minute. Well
yields vary primarily as a result
of geology and well
construction.
Reported well yields for about
10,000 domestic and household
wells ranges from less than 1 to
1,500 gallons per minute with
an average of about 11 gallons
per minute.
Well Depths
The depths to which wells are
drilled vary greatly in the area.
Well depth is, in part, a
function of where the well is
located. Wells drilled on hills
or ridges generally need to be
deeper than those located in
valley bottoms. Reported well
depths, from records of 11,522
wells in the of the State
Engineer's database, range
from 2 feet to 3,000 feet below
land surface, with an average
depth of about 162 feet.
Average reported well depths
are less in Chaffee and Lake
5
Counties than in Custer and
Fremont Counties.
In the Upper
Arkansas Area
of Colorado, the
average depth to
the static water
level is about 67
feet. The
maximum
reported depth
of static water
level is 900 feet
and the
minimum is 1
foot, based on a
review of 9,947
well records
from the State
Engineer's
Office database.