Solinst 425-D Deep Sampling Discrete Interval Sampler

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