Pumping Test Results for Wells Within
Potrero Canyon, Morongo Band of Mission
Indians Reservation, California
By M. Isabel Pimentel,
and Allen H. Christensen
U.S. GEOLOGICAL SURVEY
Open-File Report 02-228
Sacramento, California 2003
Prepared in cooperation with the Morongo Band of Mission Indians
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This
is an oversize poster showing lithology, well construction, and pumping tests
at several wells within Potrero Canyon on the Morongo Band of Mission Indians
Reservations during February 27 to March 2, 2001 (1.2 MB PDF)
The
text below provides the alternative text for this graphic image.
Introduction
Wells in Potrero Canyon are the main source of water for the Morongo Band of Mission Indians, located near Banning, California. A series of pumping tests were completed on four water-supply wells in the Canyon during February 27 to March 2, 2001. The purpose of the tests was to determine the productivity of each well and the interference (drawdown or water-level decline) each pumped well produced in surrounding wells.
During each pumping test, a well was pumped at a fairly constant rate for several
hours and drawdown was measured in the pumping well; nearby production wells (mostly
idle) were used as observation wells. Productivity of the pumping well, specific
capacity in gallons per minute per foot of drawdown (gal/min/ft), was determined
from time-drawdown data in the pumping well. The range of specific capacities
from these tests were 29.9 gal/min/ft, measured in well 24P3 (2S/1E-24P3) to 12.8
gal/min/ft in well 25H1. A specific capacity of 34.4 gal/min/ft was reported (Constant
Flow Test notes by McCalla Bros.) for well 24N1. The amount of the drawdown in
the observation wells during each pumping test was used to determine the interference
between wells.
Methods
In this report, wells are arranged as clusters A, B, and C based on well proximity and similarity of water-level elevations (see Potrero Canyon map in "Methods"). For tests performed in Potrero Canyon, wells 3, 4, 5 and 6 were used as pumping wells and wells 1, 2, 3, 4, 5 and 25R2 were used as observation wells. Wells 6 (24N1) and 25R1 (location shown only in "Methods") could not be measured due to obstructions in the wells.
Time-drawdown data were collected using 10 and 50 psig (pounds per square inch, gauged) pressure transducers and dataloggers. Transducers were set at a depth of about 25 feet below static water level in observation wells and approximately 80 ft below static water level in pumping wells. The transducers were calibrated prior to use and had an accuracy of ± 0.03 ft for the 10 psig and ± 0.3 ft for the 50 psig transducers. Approximately 14 hours of background data were collected for wells 1, 2, and 5 prior to start of the first test.
Water-level measurements were made manually using a calibrated electric measuring
tape to verify the accuracy of transducer readings. Each well was manually measured
before initial testing and approximately every hour throughout the duration of
each test. On average, each well was pumped for approximately 8 hours and was
allowed to recover overnight for about 15 hours before pumping tests of other
wells. No manual water-level measurements were made during the recovery period.
During the pumping test at well 3, well 6 was pumped intermittently to meet water
supply demands.
Summary
Pumping test results showed that wells 5 and 6 within Cluster A have the highest
specific capacities and the lowest interference between wells within the same
cluster. Wells in Cluster A had an average specific capacity of 32 gallons per
minute per foot [(gal/min)/ft] of drawdown and a maximum interference of 6.4 ft
in surrounding wells. Wells within Cluster B, had an average specific capacity
of 14 gallons per minute per foot [(gal/min)/ft] of drawdown, about one half of
the value for wells in Cluster A, and a maximum interference value of 37.3 ft
in nearby wells, more than double the value for wells in Cluster A. Note that
the highest interference is observed between wells 3 and 4 in Cluster B, even
though they are farther apart (about 75 ft more) than wells 5 and 6 in Cluster
A. Therefore, concurrent pumping of wells 5 and 6 within Cluster A would produce
a higher yield and less drawdown than pumping wells 3 and 4 within Cluster B.
No specific capacity values were calculated for Cluster C wells; well 25R1 was
not used for pumping or observation and well 25R2 was used only for observation.
Water levels observed during all pumping tests showed that pumping a well in one
cluster resulted in no drawdown in wells in other clusters. These results suggest
that the hydraulic interaction between Clusters A, B, and C is limited. Boundaries,
such as faults or buried outcrops, could significantly limit ground-water flow
and the hydraulic response between wells on opposite sides of such boundaries.
Further studies would be needed to determine the type and location of potential
boundaries located in Potrero Canyon.
Water Resources of California
