When a number of IEG-MLSW systems are used at a site, they allow a very detailed three-dimensional soil and groundwater contamination profile to be developed, at a reasonable cost, since fewer boreholes are required, which itself reduces well purging and sampling time on site, at a much reduced cost. The patented modular system can be customised for the needs of each project, depending on the findings of a geoenvironmental investigation, or alternatively based on predetermined depths of interest. This IEG MLSW can be removed from the monitoring well.
Advantages
The system offers significant time and cost savings over multiple conventional fully-screened wells and allows very high quality data to be provided to facilitate risk assessments and accurate targeting of remediation system design.
- The number of monitoring boreholes required is less than conventional techniques.
- Less drilling means less disruption to ongoing site activities.
- The number of sampling horizons installed in the saturated and unsaturated zones is practically unlimited.
- Since the samples are removed without lowering the groundwater table or creating a cone of depression, the natural flow conditions of the aquifer remain undisturbed.
- Vertical flow in the sampling area which could result in distorted values therefore is almost entirely prevented.
- Material and personnel cost for this method are by far lower than conventional sampling with piezometers or nested wells, since only one person is needed to operate the hand pump, activating all sampling horizons at the same time.
- No distorted analysis results caused by “relocating“of contaminants during sampling, since all components making contact with groundwater or soil air are firmly mounted inside the MLSW.
- Sampling procedure can be reproduced, repeated, providing consistent, accurate readings.
System
The IEG MLSW system is used for the recovery of multiple high-quality samples of soil gas and groundwater from numerous isolated horizons in a single standard borehole. The system is also used to accurately delineate contamination profiles in three dimensions, which is vital for the design, installation and monitoring of a remediation system. Specifically, the MLSW can be used to identify areas of very little or no contamination, or to pinpoint the top or base of a plume, whilst simultaneously facilitating the accurate determination of high levels of contamination in the unsaturated and saturated zones, as well as the often highly-contaminated capillary fringe.
The MLSW consists of a groundwater sampling well (I.D. 100mm) with screened intervals (500-1000mm in length) positioned at specific depths in the saturated and unsaturated zones, dependent on field visual and olfactory assessments made during drilling. On completion of drilling, standard 100 mm I.D. HDPE well screen and casing is inserted into the borehole. The annulus around the screened intervals is filled with clean silica sand filter pack, whilst the annulus around the cased pipe sections between the screened sections is sealed with bentonite. These sealed sections between the horizontal sampling layers are designed to prevent vertical flow of soil gas and/or groundwater during the sampling, thereby assuring more accurate readings for the sampling at specific depths of the aquifer and/or the unsaturated zone.
Method of operation
The MLSW will be delivered to site as ordered. The MLSW consists of a single piston drive, to which are attached pre-assembled double lip-packers which are positioned between the desired horizontal sampling horizons. Stainless-steel sampling chambers consisting of a piston operating inside a cylinder, the number depending on the total of horizontal sampling areas desired, are positioned between the sealed sampling areas. The piston drive can be operated manually or by an electrical drive.
Soil-air and/or groundwater samples are withdrawn into pre-determined sample vessels via the dedicated and discrete stainless-steel sampling ports. Simple up- and downward motion of the piston head causes each of the sample cylinder chambers to fill with soil air or groundwater, depending on the particular depth of the sample intake. A strategically placed check valve controls the in- and outflow for an individual cylinder. The discrete samples can be brought to the surface without creating negative pressure, a situation frequently leading to distorted analysis results.