Little Known Facts
about Small Diameter Wells and Direct Push Sampling

Filter packs need to be only two to three sand grains thick to retain and control the formation, according to Fletcher Driscoll, author of "Groundwater and Wells."

Although they are more difficult to manufacture, we provide the maximum internal screen diameter possible while minimizing the outside diameter of our PrePak Screens to fit inside standard drive casing. This provides several advantages, including better communication with the aquifer, larger diameter usable sampling tools, substantially reduced shipping costs, and more durable products. The narrower design also facilitates installation of small diameter wells to greater depths.

A well using a 0.010" slotted screen and the finest filter sand possible will not reduce turbidity resulting from silt and clay size particles.

Sand fine enough to retain silt size particles will pour through the slots of a 0.010" screen. The UltraFine (100x120 mesh) sand used in the GeoInsight Plus 10 PrePak Screens* and PrePak Jackets* can retain silt size particles and will reduce well turbidity by orders of magnitude. All GeoInsight PrePak intake devices come preassembled - so you don't waste expensive rig time filling with sand in the field.

Recent advances in the sensitivity of laboratory instrumentation have made it possible for select labs to cut sample volume requirements by 90% and still satisfy regulatory reporting limits.

A 3/4" well using PrePak Screens installed inside 2" direct push casing contains approximately 1/20th (5%) of the quantity of water in the saturated filter pack and casing as the same 2" well installed using a hollow stem auger.

This means less purge volume and faster stabilization of indicator parameters (pH, DO, EC, etc.). Sampling teams often find it faster to sample small diameter wells, while generating far less purge water than 2" and larger wells sampled on the same site. Because of their close contact with the aquifer, small diameter wells normally stabilize faster than 2" and larger drilled wells when monitoring indicator parameters for low flow sampling.

Recently, miniature bladder pumps that fit inside 3/4" wells have become available as sampling tools.

This makes it easier to perform low flow sampling and collect pumped samples from deep water table conditions using small diameter wells. Other downsized tools available to fit in 3/4" wells include interface probes, pressure transducers, bailers, and water level indicators.

A comprehensive, multi-well study conducted by the US Navy confirms that there is no statistical difference between samples collected from small diameter direct push wells and wells installed using hollow stem augers.

* Patent pending