U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2004–3096

September 2004

A SMALL-DIAMETER SAMPLE PUMP FOR COLLECTION OF DEPTH-DEPENDENT 

SAMPLES FROM PRODUCTION WELLS UNDER PUMPING CONDITIONS

Printed on recycled paper

By John A. Izbicki

The U.S. Geological Survey, in cooperation with the manufacturer (1Besst 

In2c. http://www.besstinc.com), has modified a commercially available gas-displacement sample pump to collect water 

at selected depths within production wells 

under pumping conditions. The modified 

pump is about 6 inches long, less than 1 

inch in diameter, and is operated through 

repeated application and release of 

compressed gas. The pump is intended 

for use in production wells having limited 

access that prevents the use of traditional 

geophysical tools, such as wire-line 

bailers, used to collect depth-dependent 

water samples. In most cases, the production pump does not have to be removed 

or the well modified for insertion of the 

sample pump. Data collected at different 

depths within the production well reflect 

water quality at those depths under actual 

pumping conditions. If well-bore flow 

velocities are known, the quality of water 

in the aquifer between sample depths can 

be estimated.

DESIGN AND BASIC OPERATING 

PRINCIPLES OF THE SAMPLE PUMP

The modified sample pump consists 

of a series of one-way flow valves connected to the surface by two 1/8-inchdiameter Teflon tubes bonded together 

into a single hose. One tube serves as 

a pressure line, and the other serves as 

the sample line (fig. 1). After the pump 

is lowered into the well to the sample 

depth, water enters the pump, filling 

both Teflon tubes to the water level 

in the well (Initial conditions, fig. 1). 

The pressure line is pressurized using 

compressed gas, and water is displaced 

from this tube into the sample line 

(Pressure cycle, fig. 1). A one-way flow 

valve at the pump intake prevents the 

displaced water from flowing back into 

the well. Once the water is in the sample 

line, another one-way valve prevents 

the water from flowing back toward the 

sample pump after pressure is released 

(Release cycle, fig. 1). 

To force additional water into the 

sample line, pressure is alternately applied 

and released on the pressure line at the 

surface using compressed gas regulated 

through a control panel built by the U.S. 

Geological Survey. The column of water 

in the sample line can be forced upward to 

the surface through the sequential application and release of pressure. Alternately, 

when sufficient volume is accumulated, 

water in the sample line can be forced 

to the surface using compressed gas. 

With proper use, water from the pump is 

suitable for analysis for a wide variety of 

constituents, including volatile organic 

carbon and dissolved gasses. The pump 

is capable of lifting water from depths as 

great as 1,200 feet. The pump and hose 

are mounted on a motorized reel (fig. 2).

 Samples from different depths within 

production wells can be collected by 

sequentially moving the pump to a different sample-collection depth without 

retrieving the pump from the well after 

each sample is collected. The pump pro- Figure 1. Diagram showing schematic of smalldiameter pump and basic operating principles.

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Figure 2. Photograph showing a) hose-reel 

assembly and b) small-diameter sample pump.
concentrations increased with depth 

below the pump intake but remained 

below the U.S. Environmental Protection 

Agency proposed Maximum Contaminant Level for arsenic of 10 micrograms 

per liter (μg/L). 

Flow was downward in the well from 

the top of the screened interval to the 

pump intake (fig. 3). No samples were 

collected above the pump intake and the 

arsenic concentration of water yielded 

from the aquifer to the well above the 

pump intake was not calculated.

DISCUSSION

The small-diameter pump provides 

a means to collect depth-dependent 

water-quality data from specific intervals in long-screened production wells 

under pumped conditions. Coupled 

depth-dependent water-quality and velocity-log data have application to a wide 

range of hydrologic problems including seawater intrusion, brine invasion, 

naturally occurring trace-elements, and 

anthropogenic contamination. The smalldiameter sample pump described in this 

fact sheet enables more efficient collection of depth-dependent samples from 

production wells having limited access 

by increasing the ease with which water 

samples are collected (thereby reducing 

the time and cost) through eliminating the 

need to retrieve the sample pump from 

the well after each sample is collected.

vides an alternative to traditional samplecollection methods using wire-line bailers 

or sample-collection methods developed 

by Izbicki and others (1999), both of 

which require sample equipment to be 

pulled from the well to bring each depthdependent sample to land surface. 

DATA INTERPRETATION

Depth-dependent water-quality data 

collected within production wells under 

pumping conditions can be used to 

estimate the quality of water yielded to a 

well from a selected depth interval using 

the following equation:

Ca = (CiQi − Ci+1Qi+1)/Qa , (eq. 1)

where: 

C is the concentration of a given 

 constituent,

Q is the flow of water within the well 

 (either as volume per unit time, 

 as velocity, or as percent of total 

 discharge), 

i is the first sample collection and 

 flow measurement depth,

i+1 is the second sample collection and 

 flow measurement depth, and

 a is the interval between i and i+1.

(In this example, flow in the well is 

presumed to be upward toward the 

pump intake and the first sample-collection depth is shallower than the second 

sample-collection depth.)

Depth-dependent water-quality data 

collected from production well 4N/5W2H1 near Victorville, California, using 

this small-diameter sample pump are 

shown in figure 3. The well is screened 

between 600 and 836 feet below land 

surface, and the pump intake is at 685 

feet. The well was pumped at 1,000 gallons per minute. Flow was upward from 

the bottom of the well screen toward the 

pump intake. The deepest sample collected from the well is presumed to be 

representative of water in the aquifer at 

that depth. The next deepest sample is a 

mixture of water already in the well and 

water that entered the well between the 

two sample depths. The combination of 

velocity-log and depth-dependent waterquality data can be used to resolve the 

mixture within the well and estimate the 

concentration of a constituent in water 

contributed from the aquifer to the well at 

selected sample depths below the pump 

intake during pumping (fig. 3). Results of 

calculations show that, in general, arsenic 

Figure 3. Depth-dependent water-quality data collected from production well 4N/5W-2H1 near 

Victorville, California.

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REFERENCES CITED Izbicki, J.A., Christensen, A.H., and Hanson, R.T., 1999, U.S. 

Geological Survey combined well-bore flow 

and depth-dependent water sampler; U.S. 

Geological Survey Fact Sheet FS 196-99.

1. The use of trade names in this fact sheet is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.