Solinst Discrete Interval Sampler for Groundwater (Model 425 & 425-D)

  • Provides High Quality Samples
  • Easy to Operate and Transport
  • No Purge Sampling
  • No Mixing of Water from Different Levels Minimal Disturbance to the Water
  • Deep Water Version Available Representative water samples to submerged depths of up to 1200 m (4000 ft)
Product Options


The 425 Discrete Interval Sampler produces representative water samples from areas beneath layers of floating product (LNAPL). Discrete interval sampling is a form of no purge sampling and is also ideal for obtaining product samples directly (DNAPL). Additionally, the 425 Discreet Interval Sampler can be used to profile open bodies of water, screened wells, and open boreholes. Passive samples can also be collected from distinct levels or points of inflow. By causing only negligible disturbance, the mixing of water from different levels is reduced to minimal levels.

With the 425 Discrete Interval Sampler, purging and purged-water disposal can be easily avoided. By passive sampling from a specific depth directly, the water collected is highly representative of the groundwater surrounding the well at that level.

Discrete Interval Sampler

Made from stainless steel, the Solinst Model 425 is highly durable and extremely reliable. LDPE tubing is mounted conveniently on the Solinst reel, which also features a pressure attachment. A high-pressure hand pump can be inserted into the attachment and used to apply and release pressure on the sampler. Sample-release devices are included with each Discreet Interval Sampler.

Before being lowered into the well, the sampler is pressurised with the high-pressure hand pump, preventing water from entering before the sampling zone is reached. Once at the appropriate depth this pressure is released and hydrostatic pressure fills the sampler with water from the proper sampling zone. Water is unable to enter the tubing because of a floating checkball located inside the passive sampler, making tubing decontamination unnecessary.

Once filled, the passive sampler is pressurised again and returned to the surface. Then, the passive is decanted by the sample-release device, which regulates flow and minimises degassing.

When a product layer is located on the surface of the sampling source, the 425 Discreet Interval Sampler is able to obtain samples that are uncontaminated by the upper layer, making it perfect for groundwater sampling.

425-D Deep Sampling Discrete Interval Sampler

The NEW 425-D Deep Sampling Discrete Interval Sampler can sample from submerged depths as much as 1200 m (4000 ft). The stainless steel sampler connects to the same convenient tubing reel as the standard 425. Operation follows the basic principles of hydraulics. The sealed sampler is pressurized at depth allowing water to enter. The sampler is vented and sealed before retrieval to surface, maintaining sample integrity.

Discrete interval sampling is ideal for obtaining truly representative water samples and for obtaining samples of product (LNAPL and DNAPL). The DIS is ideal for groundwater sampling from below an oil/product layer on the surface of the water, as it allows a sample to be obtained which is untouched by the oil.

Discrete Interval Sampling is also used to profile open bodies of water, open boreholes and screened wells, and to collect samples from distinct levels or points of inflow. Mixing of water from different levels in the well is minimized.

Manufactured by: Solinst
Model: Solinst Discrete Interval Sampler for Groundwater (Model 425 & 425-D)

Services offered for this product

  • Sales
  • Rental
  • Installation
  • Calibration
  • Maintenance


Obtaining a representative groundwater sample from below oil/product layers
Discrete interval sampling in lakes, rivers and wells
Chemical profiling of wells
Sampling at points of inflow to well
LNAPL and DNAPL sampling


Recommended Operating Pressure
Submerged Depth
25 208148
50 3015217
100 5030364
200 9560660
300 14090 952
Operating Pressure = (Submerged Depth in feet x 0.43) + 10 psi
(Submerged Depth in meters x 9.8) + 70 kPa

Discrete Interval Sampler Capacity
English Units Metric Units
Size Capacity Size Capacity
1" x 2' 6 oz25.4 mm x 610 mm190 ml
1.66" x 2' 18 oz42 mm x 610 mm475 ml
2" x 2' 27 oz50.8 mm x 610 mm800 ml
1" x 4' 12 oz25.4 mm x 1220 mm365 ml
1.66" x 4' 32 oz42 mm x 1220 mm 1000 ml
2" x 4' 61 oz50.8 mm x 1220 mm1800 ml
Other diameters and lengths available, on request.

425-D Recommended Operating Pressure and Weights
Submerged Depth
Number of Weights
160 50 50 345 0
320 50 100 345 0
640 50 200 345 1
960 75 300 520 2
1280 100 400 690 3
1600 125 500 860 4
1920 150 600 1030 5
2250 175 700 1200 6
3250 200 1000 1380 9
The 1.66” ø x 2' (42 mm x 610 mm) Deep Sampling DIS has a capacity of 420 ml (14 oz). Sampling at deeper depths may be possible, contact Solinst to determine the suitability of your application.



A device that collects water samples at a specified depth without need for purging beforehand. Samples taken reflect only the specific water chemistry at the time and location where the sample was taken. It can also be referred to as an individual or catch sample. This type of sampling is recommended when standard purge sampling is impractical or not efficient. Groundwater sampling relies on the principle that groundwater is characteristic of the water outside the well at that depth.
Three different modifications of the grab samplers are offered by Solinst: the model 428 BioBailer which is single use and made of biodegradable PVC, the Model 429 Point-source Bailer which is reusable and made of stainless steel, and the Model 425 Discrete Interval sampler which is essentially a pressurised bailer. They are all modifications of the basic bailer.
The 428 BioBailer and 429 Point Source Bailer require a suspension line for raising and lowering the bailer. It is recommended you use a Solinst 103 tag line- this can be attached to the bracket at the top of the sampler. A sample release device is included with each bailer, and discrete interval sampler, to help with transfer to a sample bottle. The 425 Discrete Interval Sampler includes tubing, of a specified length, that is attached to the sampler for raising, lowering and pressurising the sampler. The tubing is on a reel with fittings to allow the sampler to be pressurised using a high-pressure hand-pump.
The Discrete Interval Sampler is the only sampler that collects a representative a sample of a particular depth without interference from other levels. This is because the sampler is pressure sealed for transport up and down through the water. In the 428/429 bailers, water passes through the body so this is not the case. The 429 has check balls at both ends of the bailer, so as the bailer is lowered, water flows through it until it reaches the required depth. But upon return to the surface the check balls are closed to prevent the water from mixing. However, if the check balls become dislodged there is still a risk of mixing. The 428 has one check ball at the bottom, therefore there is more risk of the sample mixing with water above. These bailers are not truly discrete as the samples from them can only be considered representative of a particular depth when used optimally. The check balls provide a good seal but it is not completely leak free. So if the models 428/429 are used past their maximum recommended depth, potentially the samples can be lost, if they are raised long distances above the water surface to the ground surface. Samples collected provide a snapshot of the water chemistry at a specific point in the well at that moment in time only. A more representative/average sample can be attained using sampling pumps that purge and then sample, drawing water from a larger area over a longer period of time.
Samplers should be slowly and gently lowered through the water column, to create as little mixing as possible, and the sample collected for the desired depth is representative of that depth. And in the case of the 428/429 bailers they should also be gently raised to avoid the check balls being dislodged and the sample contaminated. For all samplers it is recommended a sample release device is used.
  • Lower cost for instrumentation
  • Faster sampling
  • Little/no water agitation
  • Simple
  • Allows sampling in wells with small water volumes
  • Variety of sample sizes
  • Can be used to identify stratified layers of water chemistry in wells/boreholes
No, Solinst certifies that PFAS is not used, or knowingly present in the manufacturer, or production of their products.