After 20 years in enviromental sampling and analysis we have come to believe in direct sensing as a means of providing the most rapid and comprehensive information about the distribution and composition of soil and groundwater contamination. Ever evolving, today’s direct sensing tools for remediation focused site characterization projects continue to add a greater range of high resolution information on subsurface conditions including hydrology, lithology and contaminant distribution to support environmental liability decision.
Although direct sensing approaches are used throughout the environmental industry supporting cleanup and closure efforts, there are still several myths associated in applying these methods to site investigation and remediation projects.
There are three basic assumptions or principles we have in mind when deploying high resolution direct sensing tools with as near real time decision-making information:
- The consumer of our services is firmly motivated in knowing the size, shape, and type of contaminant mass and soil structure.
- They believe better information will reduce the uncertainty, risk, and the cost of gaining that knowledge, and
- They believe that being approximately correct with a huge data set is far better than being precisely wrong with a limited data set.
Before we outline the 7 biggest myths of direct sensing related to site characterization, let’s define high resolution and direct sensing tools:
- Tools that can provide a lot of data points in a limited period of time
- Operate with as consistent of a measurement process as possible
- Are accurate in the measurement of depth beneath the surface
- Allow for measuring of multiple parameters such as soil structure, permeability, and contaminants simultaneously
- Preferably do not require the retrieval of a sample of soil, water, or vapor – a process that introduces a range of variables and therefore uncertainty
Below are the first three myths related to regulatory acceptance of data, sites with a long investigation history, and comparison to monitoring well data with the corresponding truths.
Myth 1: Regulators won’t accept direct sensing data
Regulators clearly understand the value of more data and information. Extensive training and education is underway to provide regulators and practitioners a number of best practice guidance documents. Today’s resources such as EPA’s Contaminated Site Clean-Up Information (CLU-IN) and Interstate Technology and Regulatory Council (ITRC) provide podcasts, workshops, and guidance documents to learn about industry best practices. Warning, if your client is trying to say “let’s only do the minimally, regulatory approved procedures to keep the agency happy” then they don’t pass the first principle of wanting to know the right answer using the most cost effective approach.
Truth: Regulators nationwide are motivated to get to the right answer with the least liability and embrace the use of high resolution tools to provide an abundance of risk mitigating information.
Myth 2: Direct sensing is not for sites with a long investigation history
There’s the assumption that direct sensing is not for sites with a long investigation history that have already been extensively characterized through traditional means. The typical pushback is “we’ve already characterized the site and we want to move onto remediation.” Unfortunately the length of investigation and resources consumed frequently does not yield the density of information required for cost effective remediation. We are often called up to support remedial designs and optimization on sites that have years of monitoring well, soil and groundwater data, and yet yield surprises in terms of data gaps, source zones, and pathways that escaped traditional investigation tools and protocols.
Truth: Better, more complete high resolution data collected in a systematic fashion provides for improved site conceptual models (SCM) and enable more effective remedial design and execution.
Myth 3: Direct sensing won’t tell me what a group of monitoring wells will
The myth is that direct sensing does not provide defensible data such as that available from sampling monitoring wells specifically in terms of static hydraulic head level, groundwater flow direction, and contaminant speciation and concentration. However, monitoring wells through their inherent placement and construction are subject to numerous sources of variation and uncertainty include well construction, heterogeneity of the subsurface lithology, heterogeneity of the groundwater flow direction, seasonality of groundwater, sampling methodologies, sample transport and holding times, laboratory handling and analyses, fouling, and plume dynamics over time. Fortunately, the high resolution characteristic of direct sensing tools frequently identify defects in the placement of monitoring well screens laterally and more importantly vertically.
Truth: Direct sensing tools provide the critical information on soil permeability, groundwater transport zones, contaminate distribution, and aquitard regions necessary for proper placement of monitoring well screens.
Want to learn more? Make sure to visit our blog in two weeks on Wednesday, October 3rd for Part II to discover the remaining four myths as a follow up for The 7 Biggest Myths of Direct Sensing.
