Equipment

The most important piece of equipment required to complete groundwater sampling is our van. The 4x4, V-10 van allows us to travel throughout the state and carries every piece of equipment we might need. Fully equipped with custom shelving and an elaborate bungee system, the White Whale can hold more than your average old van. The van is also equipped with two marine batteries and a power inverter which produces alternating-current (AC) to power some of our pumps.

When dealing with more specific equipment, the collection of groundwater pumps is at the top of the list. We have a wide variety of pump options, depending on numerous factors such as well construction, depth to water, and well recharge rate. The most defining feature is pump type: submersible versus peristaltic. Submersible pumps are pumps that function when placed underwater within the well. Peristaltic pumps are pumps that sit outside of the well, while tubing is lowered into the well to extract the water. We typically use submersible pumps because they tend to have more power.

Our largest pump is a 1½ HP submersible pump on an 800-foot reel capable of pumping 20 gallons per minute. This pump is housed on a trailer and has an electric reeling system so it can be lowered into and raised out of a well with ease. The Groundwater Monitoring (Quantity) team uses the pump trailer to develop, or flush out, newly-installed wells or rehabilitate older wells. We will sometimes use the pump trailer if we have several wells requiring a purge volume greater than 400 gallons each at one site.

A more manageable-sized pump setup that we have used regularly is a ¾ HP, 150-foot submersible pump that is more easily transportable than the pump trailer. Sometimes we have a well that needs 1,000 or more gallons purged before sampling! This pump can be great for those instances since it can pump out water much faster than our smaller options. However, we tend to avoid using this pump because the effort required to use it and decontaminate it. This is a heavy pump! And with no pump trailer to reel it in and out, we get a good workout when using this pump.

We have two mid-size submersibles that are 150 and 250 feet long. These pumps are each setup on a reel with a convenient rolling cart and are easily hand cranked to maneuver the pump in and out of the well. These two pumps are used most commonly since they can handle most well volumes and are easy to transport. Each pump has its own separate controller that requires AC power, which we get from either the power inverter in the van or a separate small generator.

The last submersible option we have are plastic submersible pumps with names that like to show off how much power they have, i.e. Hurricane, Monsoon and Typhoon. We are currently using Monsoons, which can handle pumping up to 120 feet from below the ground level. We like to use these especially when there is risk for high turbidity in shallow wells because they can pump water at a slower rate using a low-flow controller.

The last type of pump we use is a peristaltic pump. It is used when the depth from ground surface to water level is less than about 30 feet. We use a peristaltic pump primarily with shallow wells or wells with smaller diameters and/or slow recharge rates. This type of pump is very useful when dealing with contaminated wells since the water only comes in contact with tubing, which can be replaced with each well. Luckily we do not usually encounter contamination at our sampling sites!

That’s all for pumps! The next piece of equipment is generally the first thing we get out once arriving at a site: a water level meter. A water level meter (or indicator) is basically a tape measure that has a sensor on the end that beeps when it comes in contact with water. Taking an initial water level reading lets us compare past water levels to confirm that an outside source is not over-pumping in the area. This reading also allows us to determine the volume of the water in the well, which changes depending on the water level. We also use the diameter and total depth of the well for this calculation. Three well volumes ≈ 0.123d2h, where d is well diameter (inches) and h is water column height (feet), which is calculated from subtracting the depth to water from the total depth of the well. We also use the water level meter to measure drawdown while we are purging the three well volumes before sampling. This ensures that we maintain a water level above the pump intake.

While the samples are delivered to the DWR chemistry laboratory for analysis, we get a few field parameters that tell us about the water while sampling. A water quality monitoring device, typically a hand-held YSI ProDSS, is used to measure multiple parameters like temperature, pH, dissolved oxygen, specific conductivity, oxidation-reduction potential (ORP) and turbidity We use the meter to determine when the water passing through the pump has stabilized and represents the true water in the aquifer.

Once we purge three well volumes and the parameters have stabilized, an additional set of tools come into play. After filling the various bottles for the lab, several analyses require a preservative to be added in the field to prevent various reactions from occurring, such as metals precipitation, microbial growth, and chlorine reactions. Once filled and preserved, the bottles are placed in coolers with ice, which is also another preservation method. Keeping the samples below about 4 °C is one of the most common and simple ways to preserve samples. This prevents/slows the sample degradation process.

In addition to total metals analysis, we collect samples for dissolved metals analysis, which requires the water to be passed through a 0.45 µm filter in the field. Filtered samples give us a better idea of the “truly” dissolved metals in the water (particulates will be caught in the filter).

A less common tool we can use for sampling is a bailer. Bailers are slim tubes with check valves that only allow water inside as the bailer is lowered. They are lowered into the well on a line to the desired sampling depth. The weight of the water in the full bailer closes the check valve, which gives a composite sample. This method of sampling can be especially useful for shallow wells that have a slow recharge rate and might be over-pumped with the submersible pumps.

Our newest pieces of equipment to join the team are for PFAS sampling. We have recently started sampling our network of wells for PFAS, which requires special equipment to prevent introduction of any kind of contamination. We use a “Hydrasleeve” which is a polypropylene tube-shaped bag, similar in shape to a bailer, that is attached to a rope or tether with a weight on the bottom. The Hydrasleeve remains closed and flat as it enters the well and is lowered to the desired sampling depth. When the Hydrasleeve has reached the desired depth, a slow and steady upward pull on the tether allows the check valve to open and water to enter. Once the Hydrasleeve has filled with the water, the check valve closes and remains closed during retrieval to the surface. A major benefit of using this method is that it requires no purging, so it saves a lot of time and effort.

We work very closely with the Groundwater Monitoring (Quantity) staff, who maintains the sites and monitors water levels and chloride levels for the monitoring well network. Water levels are recorded hourly, and data is downloaded quarterly. Chloride values are measured every two years. Site maintenance is an ongoing, never-ending task.

To obtain the daily water level readings without visiting all 700+ wells each day, the team uses data loggers called HOBOs. The frequency of measurements can be adjusted to any interval but we set it to record one per hour. One well at each site will have an additional HOBO to measure the atmospheric pressure at the site. Having this information is crucial for calculating accurate water levels.

Chloride sampling is done by collecting a sample from the screened portion of the well using a very technical piece of equipment: an electric fishing reel with a bailer attached to the end of the fishing line. The bailer is then lowered into the well to the well screen to collect a sample. After sample retrieval, the team then uses a chloride test kit to get a measurement right away. They also use a hand-held YSI meter to take field parameter measurements. The chloride measurements are used to map saltwater intrusion in the coastal plain of North Carolina.

A well video logging camera is used to observe downhole conditions in a well. The camera is used primarily when newly acquired wells were not installed by DWR and well construction or condition is uncertain or when there is believed to be an issue within a well (e.g. collapsed screen, sediment buildup, obstruction in well, etc.).

Solinst Telemetry System (STS) recording units have been installed in sixteen wells that are included in the Drought Indicator Well network. They consist of one pressure transducer, one barometer (corrects for air pressure), and are powered by a twelve-volt battery. Data is collected by a controller unit that stores hourly readings. Readings are sent to the DWR web page server every 3 hours via cell phone modem. DWR uses the STS system on the Drought Indicator Well network in place of monthly visits. They are serviced every quarter or semiannually depending on battery life. STS data is especially helpful in keeping the Drought Indicator Well water levels up to date.