GSI recently completed a scope of work in Delaware that included water sampling to 100′ below ground surface (BGS) and installation of prepack monitoring wells to 75′ BGS. The scope was follow-up sampling to fill data gaps from previous investigations GSI has assisted with at the same site.

The initial task consisted of vertical profiling at three locations by collecting a grab water sample from every 10′ to a depth of 100 feet. Static water level was between 6 and 8 feet. GSI utilized the Geoprobe Screen Point sampler(SP16). GSI used one of their Geoprobe 7822 machines to drive the closed SP16 sampler to the 100′ depth and then exposed the stainless sample screen. A peristaltic pump was used to purge the interval until the groundwater ran clear. Once the sample was collected the SP16 was pulled up 10′ to the next interval and again purged to remove water from the previous interval and produce clear formation water for a sample. This process was repeated until a sample from the shallow 6 to 10′ interval was collected. The three 100′ borings were completed on schedule in 1 1/2 days.

The next task consisted of installing nine (9) 1 1/2-inch prepack wells ranging from 45′ to 75′, with five of the nine specified for the 70 to 75′ range. Continuous soil cores were collected from each of the five deep well locations for logging the lithology. The more shallow wells were nested with a deep well and installed by driving closed casing to the target depth (45′-55′). Each well was completed with 10-foot prepack well screen and a 2-foot bentonite sleeve. Wells were then sealed with cement-bentonite grout placed through the drill casing . By grouting through the casing, GSI could be sure the wells were continuously sealed throughout the entire borehole. Wells were finished with flush mount covers and pumped for development. All wells were completed on schedule in about 5 days.

The photo below shows grouting the prepack wells through the casing and collection of the displaced water.