Blog & Recent Projects

The 7 Biggest Myths of Direct Sensing (Part II)

Posted by admin on Oct 3, 2012 1:07:12 PM

We hope you enjoyed our last blog post, The 7 Myths of Direct Sensing (Part I) outlining the three basic assumptions or principles we have in mind when deploying high resolution direct sensing tools, defining high resolution and direct sensing tools, and disclosing the first three myths related to site characterization projects.

Below are four additional myths related to detection levels, remediation programs, cost of direct sensing, and the need for real time data with the corresponding truths.


Myth 4: The detection levels of direct sensing tools like the Membrane Interface Probe (MIP) are not low enough

If you’re going off the basis that the contaminant levels at your site are too low for direct sensing tools, you’re probably should ask yourself do I really only have 10 ppb and if so, why do I still have 10 ppb? Direct sensing tools for contaminant profiling are first and foremost source area characterization tools. Published detection levels for VOCs using MIP are 1 ppm for petroleum and 200 ppb for select chlorinated compounds. LIF tools are used to characterize residual petroleum-based or PAH containing compounds – not dissolved phase. That said, direct sensing tools are also diagnostic tools for understanding the heterogeneity of the subsurface – often times more-cost effective than your other options. Consider the following questions. If you have 10 ppb everywhere (forever) might you have a source you have not found? Where in the large 3D geospatial volume are you going to sample to gain sufficient decision-making information? What technologies are going to get you a decent answer out of a tight clay, a flowing sand, a large vertical column, a large plume migration? Would not the high resolution information about the soil and hydraulic properties obtained from the Hydraulic Profiling Tool (HPT) provide a better basis for a sampling and analysis plan than conventional educated guessing? What’s it going to cost you to get those answers?

Truth: Low contaminant levels may exist on a site, but the source area, contaminant storage and transport zones must be defined to execute any cost-effective remediation.

Myth 5: Direct sensing can’t be used to monitor the progress of remediation programs

Effective remedial activities result in measurable changes in subsurface geochemistry, contaminant concentrations and distribution, soil structures, and biochemistry.  These interrelated changes are measurable with direct sensing tools and can be mapped in before and after images. Application of direct sensing technologies including Membrane Interface Probe (MIP), Laser Induced Fluorescence (LIF),  Hydraulic Profiling Tool (HPT), and the Membrane Interface Probe-Hydraulic Profiling Tool (MiHpt) provide lots of cost-effective information rapidly. These tools should be used when designing the project data quality objectives before during and after remedial activities.

Truth: MIP, LIF, HPT, and MiHpt have been used in many innovative ways to monitor the results of in-situ remediation efforts.

Myth 6: Direct sensing is more expensive than other sampling and analysis methodologies.

One of the reactions to a direct sensing approach that we often hear is that the costs are too high. When discussing site characterization costs, it’s critical to consider the reduction in remediation costs by 4-5x of the total investigation costs using a high resolution site characterization (HRSC) approach. There’s the response, “my client has decided to just do conventional sampling and screening and lab analysis.” Our first comment, “we wish them luck.” Our second comment, “if we keep doing this the same way we always have, we’ll keep getting the same results (and spending the same money).” This “penny wise pound foolish” demonstrates a lack of understanding that better information will lead to better success at a lower cost. One of the most important questions to consider is what will be the increased cost of remediation if you are off depth, too conservative in your engineering estimate, or simply miss?

Truth: The huge three dimensional geospatial volume of heterogeneous soil, water, and contaminant mixtures make accurate remedial design and implementation difficult.  Failure to attack this statistical hurdle mathematically generated by the data gaps will result in an expensive repetitive cycle  of field activities, lab analyses, wasted remediation resources, and expensive operation and maintenance costs.

Myth 7: I don’t need more data in real time

You may say to yourself, we don’t need real time information. My report is not due for several weeks and we’ll still have to wait for the lab data. Yes, your report may not be due, but your budget is going out the window at full speed. Let’s be honest. Aren’t you tired of finding out you’re right (or wrong) several weeks after the fact? Are you tired of blowing your budget and coming up short on conclusions and high on risk and uncertainty? If not, then you don’t believe in principle one, being firmly motivated in knowing the size, shape, and type of contaminant mass and soil structure.

Truth: Direct reading sensors provide data in real time. Having the real time information allows for visibility, control, and risk management enabling the involved stakeholders to reduce the uncertainty at the site and reduce the total project budget.

Hopefully these seven myths related to site characterization have sparked some discussion and raised questions regarding your understanding that frankly the heterogeneity rules,  and relying strictly on conventional sampling and monitoring wells alone results in a lot of uncertainty. Hopefully, we also have raised your awareness on the critical importance of real time information to visibility, control, and risk management. Direct sensing technologies belong in your toolbox and a strong case can be made that they are actually faster, better, and cheaper than conventional, lower data density approaches.

Using a high resolution approach provides you a better characterization and remediation optimization to:

  • Better assess liability in property transactions
  • Significantly reduce your monitoring, remediation, and legal liability costs, and
  • Receive a more complete, comprehensive site characterization

Keep us posted with your thoughts related to site investigation and remediation projects related to direct sensing and the seven myths which we’ve outlined.

Tags: Direct Sensing, High Resolution Site Characterization (HRSC), Hydraulic Profiling Tool (HPT), Membrane Interface Probe-Hydraulic Profiling Tool, Membrane Interface Probe (MIP), News, Site Characterization