Water Samplers Vacuum pump based automatic water samplers

Fundamentals of Automatic Water Samplers

Automatic water samplers collect samples from a water source without requiring human intervention each time a sample is needed. The samplers can be programmed to collect samples at different intervals for different durations. The collected water samples can be evaluated immediately onsite, or they can be stored and transported to a facility's laboratory for analysis.

Facilities in many industries use automatic water samplers to help meet their required water quality standards. These facilities have seen a trend in recent years toward more heavily regulated water quality governance, more detailed permit requirements, and more thorough water sampling documentation.

Automatic water samplers provide facilities with detailed sampling data that is reportable and defensible. In addition, facilities have discovered several other benefits of using automatic water samplers:

• Reduced costs through labor savings
• Minimized potential for human error in sampling technique
• Improved water sampling consistency
• Fewer safety risks to sampling personnel

By efficiently collecting and preserving water samples, automatic water samplers help provide accurate water quality data. This data aids facilities in making more informed decisions. Ultimately, these decisions can affect the safety and health of humans and other organisms that depend on water as a vital resource.

Manual vs. Automatic Sampling

Before reviewing the different types of automatic water samplers, it may be helpful to first understand how automatic water sampling is different from manual water sampling.

Manual sampling, sometimes referred to as performing a "manual grab," requires minimal equipment. Low-tech manual sampling is done by simply placing a sample container into a water source, or its flow, and collecting a sample. Manual sampling can be a cost-effective solution for a facility with short-term monitoring programs or very infrequent sampling.

Facilities that conduct frequent sampling in multiple, distant locations often find manual sampling to be inconvenient. Manual sampling requires trained sampling personnel to be available to collect samples. In addition, some site environments pose safety concerns to sampling personnel. In these situations, facilities often prefer automatic sampling.

Automatic sampling uses a preprogrammed powered water sampler to collect water samples on a time-based or event-triggered schedule. For example, a water sampler can be programmed to collect water samples every day at 6 a.m. and 6 p.m. (time based), or a sampler can be programmed to start sampling every time rain begins to fall (event triggered).

Because of the ability to program the sampling and the convenience offered, automatic sampling is often preferred to manual sampling. Automatic sampling offers the convenience of unattended, long-term monitoring, thereby reducing the time and cost associated with frequent manual sampling. In addition, automatic sampling minimizes the possibility of human error in sample collection.

Automatic Water Sampler Components

Automatic water samplers vary considerably in their technology and application, but they share the same components. These components are briefly described in the following sections.

Controller

The controller, or "brain" of the water sampler, is used to program and control the sampler. The controller usually has a keypad for programming the sampler and an LCD for providing status feedback.

Pump system

The pump system moves fluid from the water source into the water sampler to collect the samples. Water samplers commonly use either a peristaltic or vacuum pump.

Sample containers

Sample containers hold water samples until they are evaluated or analyzed. A water sampler may deposit samples into a single sample container (composite sampling) or into individual sample containers (discrete sampling).

Cooling chamber or refrigerator

If samples must be chilled, a portable sampler's cooling chamber or a stationary sampler's refrigerator is used.

Automatic Water Sampler Types and Characteristics

The following water sampler types and characteristics, as well as their advantages and disadvantages, are described in these sections:

• Peristaltic pump and vacuum pump technology
• Composite and discrete sampling
• Portable and stationary water samplers
• Chilled and non-chilled water samples

Peristaltic pump and vacuum pump technology

Automatic water samplers use either peristaltic pump or vacuum pump technology. Both pump technologies move fluid from the water source into the water sampler so that the fluid can be collected.

Peristaltic pump

In a peristaltic pump, the flexible tubing is squeezed to make the fluid flow through the tubing. The following are the steps used to measure and collect a water sample using peristaltic pump technology:

1. The pump rotates in the reverse direction. By pumping air through the system, the pump cleans the intake tubing of residual liquid and obstructions. Alternatively, personnel can manually switch the intake tubing from the water source to a container of clean rinsing water to purge the line. They can then switch the intake tubing back to the water source.
2. The pump rotates in the forward direction and pumps fluid from the water source into the intake tubing.
3. As the controller detects the fluid in the intake tubing, the controller determines how many pump revolutions, or "pump counts," are required to attain the programmed sample volume.
4. To reach the required sample volume, the pump rotates forward for each pump count. Each time the pump rotates forward, the pump tubing is squeezed to move the fluid along.
5. As the required pump counts are completed, the sample is deposited in the sample container.
6. The pump rotates in the reverse direction. By pumping air through the system, the pump cleans the intake tubing of residual liquid and obstructions. Alternatively, personnel can manually switch the intake tubing from the water source to a container of clean rinsing water to purge the line. They can then switch the intake tubing back to the water source.

Advantages

• Typically, a peristaltic pump sampler requires less power to run than a vacuum pump sampler.
• Because no wires stick out from a peristaltic pump sampler, the sampler has a tidy appearance.
• Peristaltic pump samplers may be less expensive than vacuum pump samplers.

Disadvantages

• Repeatedly squeezing the tubing to move the fluid through a peristaltic pump sampler causes the tubing to wear out, the squeezing to become less tight, and the sample volumes to vary. Consequently, a precise sample volume cannot be guaranteed from one sample to the next.
• When the pump tubing is squeezed in a peristaltic pump sampler, any suspended solids in the sample can be squeezed, and altered, as well. The solids can also stick to the lining of the tubing. Thus, the sample may not be truly representative of the water source at the time of sampling.
• Many peristaltic pump samplers are not compatible with larger tubing. When smaller tubing is used, it can become blocked by any large suspended solids in the fluid, or the large solids may be screened out.
• Peristaltic pump samplers typically provide less velocity than vacuum pump samplers. With less velocity, particles are not held in suspension as well and may settle, causing the water sample to not be truly representative of the water source.

Vacuum pump

In a vacuum pump, negative pressure creates a vacuum that makes the fluid flow. The following are the steps used to measure and collect a sample using vacuum pump technology:

1. A non-invasive, high-pressure purge of air is used to clean the intake assembly of residual liquid and obstructions.
2. Using the vacuum, fluid from the water source is drawn through the intake hose and into the metering chamber.
3. After the metering chamber is filled, the system is pressurized. Excess fluid is released until the correct sample amount is obtained.
4. The sample, now at its correct volume, is deposited into the sample container.
5. A non-invasive, high-pressure purge of air is used to clean the intake assembly of residual liquid and obstructions.

Advantages

• A vacuum pump sampler's metering chamber helps ensure that sample volumes are precise and repeatable from sample to sample. If the control volume is set at a level that does not greatly exceed the required sample volume, the suspended particles do not settle and affect the sample's representativeness of the water source.
• Because the tubing in a vacuum pump sampler is not squeezed repeatedly, it does not wear out as quickly as the tubing in a peristaltic pump sampler. In addition, because there is no squeezing, any suspended solids in the fluid are not altered.
• Unlike peristaltic pump samplers, vacuum pump samplers are typically compatible with larger tubing. Larger tubing allows larger suspended solids to pass through. Smaller tubing, on the other hand, may become blocked by larger solids.
• Compared to peristaltic pump samplers, vacuum pump samplers typically provide greater velocity. Greater velocity holds particles in suspension better and provides a more representative sample.
• The cleansing air pumped through a vacuum pump sampler is under higher pressure than the air pumped through a peristaltic pump sampler. The higher-pressure air may provide more thorough cleaning and less chance of residual liquid from a previous sample.

Disadvantages

• Typically, a vacuum pump sampler requires more power to run than a peristaltic pump sampler.

Composite and discrete sampling

Automatic water samplers can collect either composite or discrete samples over time. In composite sampling, individual sample volumes are deposited into a single large sample container. In discrete sampling, individual sample volumes are deposited into individual small sample containers.

Composite

Composite sampling can provide a representative water sample for a certain period. Over time, a composite sampler deposits individual sample volumes into a single large sample container. The size of the sample container can vary. For example, a composite sampler could be used with a single 9 L container or a single 20 L container.

Advantages

• A composite sampler is able to produce a water sample that represents the average water quality for a specified period.
• A composite sampler is less expensive than a discrete sampler.

Disadvantages

• Because multiple water samples in a composite sampler are combined in a single sample container, sampling personnel cannot pinpoint and track changes in a water source as precisely as with a discrete sampler.

Discrete

Discrete sampling is used to acquire multiple, distinct water samples over time. A discrete sampler deposits each sample volume into its own separate sample container. A stepper with distributor arm rotates among the sample containers and fills them one at a time.

The sample containers used in a discrete sampler are available in a variety of sizes, but a discrete sampler typically contains a set of sample containers that are uniform in size. For example, a discrete sampler could use a set of 0.5 L containers, a set of 1 L containers, or a set of 2 L containers. Because the space to hold the sample containers is finite, either many smaller containers or fewer larger containers can be used.

A variation on discrete sampling is multi-composite sampling. Multi-composite sampling uses a discrete sampler to deposit multiple sample volumes into a single sample container. The distributor arm then rotates to fill the next container in the same manner.

Advantages

• Because water samples in a discrete sampler are kept separate, sampling personnel can more precisely pinpoint and track changes in a water source than they can using a composite sampler.

Disadvantages

• Because of the multiple sample containers used, a discrete sampler requires more maintenance to collect, clean, and change out the sample containers.
• A discrete sampler is more expensive than a composite sampler.

Portable and stationary water samplers

Automatic water samplers are either portable or stationary. A portable water sampler can be moved easily from one site location to another. A stationary water sampler is designed to remain at a fixed installation. Both types of water samplers can be used to collect either composite or discrete samples.

Portable

As the term "portable" implies, a portable sampler is one that can be moved easily from one sampling site to another. (If required, however, a portable sampler can remain at a single site.) Because of their smaller size, portable samplers may also be used at space-restricted locations.

Advantages

• A portable sampler can be moved easily among multiple sites that require infrequent sampling.
• Portable samplers are smaller and weigh less than stationary samplers. Portable samplers may be appropriate for sampling sites that have space restrictions, such as manholes, or sites that require strapping a water sampler to a pole.
• Because a portable sampler requires less power than a stationary sampler, a portable sampler may be able to use solar power, batteries, or both.

Disadvantages

• Because a portable sampler uses ice rather than a refrigerator to chill samples, samples cannot be kept chilled for an extended period without frequent replacement of the ice. Consequently, sampling personnel need to replace the ice routinely or retrieve the samples before their temperature increases significantly due to ice melt.
• If a portable sampler is inactive for extended periods, an additional power source may be needed to ensure future sampling operation.
• Because of its portability, a portable sampler may be stolen.

Stationary

As the term "stationary" implies, a stationary sampler is designed to remain at a particular sampling site for an extended period. Although a stationary sampler is often considered a permanent fixture, it can be moved from a site.

Advantages

• A stationary sampler can be equipped with a locked cabinet to deter tampering with the controller or sample containers.
• If a stationary sampler has a refrigerator (powered by an ac power source), the sampler preserves chilled samples for an extended period without the need for sampling personnel to replace ice. 
• A stationary sampler can be left unattended, at a site that requires frequent sampling, with less likelihood that it will be stolen.

Disadvantages

• A stationary sampler cannot be easily transported to many sites.
• A stationary sampler typically requires an ac power source. If desired, a backup battery may be used as well.

Chilled and non-chilled water samples

Automatic water samplers may or may not be used to chill their collected water samples. Chilling options are available using either a portable or stationary sampler; however, the samplers' methods for chilling samples are different.

Chilled

Chilling water samples significantly reduces the rate at which chemical reactions and biological phase changes occur in the samples. Consequently, water samples are more accurate and representative of their water sources.

Stationary samplers typically chill samples using a refrigerator. When a refrigerator, powered by an ac power source, is used in a water sampling system, samples can be kept chilled for months. Water samples are typically kept at a temperature of 4 degrees Celsius (39 degrees Fahrenheit).

Portable samplers typically chill samples using ice placed in a cooling chamber. Many portable samplers are equipped with a cooling chamber in their base. The cooling chamber has an insulated cavity that can be filled with cubed or crushed ice. The use of ice can keep samples chilled for up to 24 hours prior to the samples' collection for analysis.

Advantages

• A refrigerator or cooling chamber can help prevent samples from undergoing significant biological or chemical change due to temperature change. Consequently, the samples' integrity is maintained, providing a more accurate representation of the water source.
• A refrigerator or cooling chamber may be used to meet a governing body's sampling requirements for maintaining a sample at a specific temperature prior to analysis.

Disadvantages

• When ice is used in the cooling chamber of a portable sampler, sampling personnel need to replace the ice or collect the samples before the samples' temperature increases significantly due to ice melt. In addition, sampling personnel may need to replace the ice in preparation for the next sampling round.
• A stationary sampler with a refrigerator requires an ac power source.
• Due to its size, a stationary sampler with a refrigerator may exceed the dimensional limitations of a sampling site.

Non-chilled

Stationary samplers without a refrigerator, as well as portable samplers used without ice, do not chill their water samples. Consequently, the water samples may be more susceptible to biological or chemical changes caused by changes in the ambient temperature.

Advantages

• Chilling is not necessary for certain water sample substances that are unaffected by temperature changes. Chilling is also unnecessary when water sample evaluation or analysis is conducted immediately after the sample collection.
• When samples do not need to be chilled, it is not necessary to purchase ice or a refrigerator.

Disadvantages

• If a chilling method is not used, a consistent water sample temperature may not be maintained. A change in water sample temperature may cause water samples to undergo significant biological or chemical change. Consequently, non-chilled samples may no longer serve as an accurate representation of the water source.

In Review

The intention of this section is to provide a general overview of automatic water samplers. More information, including answers to common questions, can be found in the other tabs at the top of this page.

Representatives from Campbell Scientific, may also be queried via phone or email.

Links

The following list provides some additional resources regarding water sampling and automatic water samplers:

• Campbell Scientific Vacuum Pump Water Samplers (video)
• Campbell Scientific Waste Water Samplers for WWTP Effluent Sampling (video)
• Superfund Program Representative Sampling Guidance Volume 5: Water and Sediment Part 1 – Surface Water and Sediment (PDF document)
• Superfund Program Representative Sampling Guidance Volume 5: Water and Sediment Part II – Ground Water (PDF document)