WEBVTT Kind: captions Language: en 00:00:11.000 --> 00:00:12.000 [Narrator] 00:00:12.000 --> 00:00:14.450 Today is environmental site managers have many tools to choose from when conducting 00:00:14.450 --> 00:00:17.610 site characterization and remediation. 00:00:17.610 --> 00:00:21.000 Geophysical tools can provide noninvasive ways to see inside the earth, much like how 00:00:21.000 --> 00:00:25.070 medical imaging lets us see inside the human body. 00:00:25.070 --> 00:00:29.730 The USGS Scenario Evaluator for Electrical Resistivity (or "SEER") is a quick and simple 00:00:29.730 --> 00:00:34.280 tool practitioners can use to assess the likely outcome of using two-dimensional electrical 00:00:34.280 --> 00:00:39.140 resistivity imaging for site characterization and remediation monitoring. 00:00:39.140 --> 00:00:42.730 Electrical resistivity imaging is a widely used geophysical method for environmental 00:00:42.730 --> 00:00:44.630 site management studies. 00:00:44.630 --> 00:00:49.260 The method is sensitive to fluid conductivity, interconnected porosity, saturation, clay 00:00:49.260 --> 00:00:51.350 content, and metallic materials. 00:00:51.350 --> 00:00:55.520 But is 2D electrical resistivity imaging the right tool for your project? 00:00:55.520 --> 00:00:59.220 This depends on the site properties, the goals of the survey, and the survey design. 00:00:59.220 --> 00:01:03.949 The Scenario Evaluator for Electrical Resistivity, or SEER, is a spreadsheet-based tool that 00:01:03.949 --> 00:01:09.180 allows the user to simulate conceptual site models for electrical resistivity imaging. 00:01:09.180 --> 00:01:12.300 Usually when you go into the field, you have an idea of what you are looking for, and you 00:01:12.300 --> 00:01:15.840 know something about the site geology and hydrogeology. 00:01:15.840 --> 00:01:20.340 With this information, you can use SEER as a type of quick geophysical feasibility study 00:01:20.340 --> 00:01:23.960 to see if electrical resistivity imaging is the right tool for the job. 00:01:23.960 --> 00:01:28.590 First, you use your site conceptual model to create a model of the anticipated electrical 00:01:28.590 --> 00:01:30.930 resistivity conditions at the site. 00:01:30.930 --> 00:01:35.580 Then, you use this to create a hypothetical dataset, like what you would expect to collect 00:01:35.580 --> 00:01:38.030 in the field, which is called a forward model. 00:01:38.030 --> 00:01:42.159 Next, you analyze the hypothetical dataset as if it were actual data collected in the 00:01:42.159 --> 00:01:46.900 field, giving an inverse model that provides a realistic idea of the best obtainable result 00:01:46.900 --> 00:01:49.520 from a geophysical survey in the field. 00:01:49.520 --> 00:01:53.040 Although you might assume the inverse model would always match the true resistivity model 00:01:53.040 --> 00:01:56.670 we created based on our conceptual model, it inevitably will not. 00:01:56.670 --> 00:02:01.369 Unlike in popular movies, real-word geophysical surveys donít provide magical 20/20 vision 00:02:01.369 --> 00:02:06.159 of the Earthís subsurface, but instead provide images that can be blurry and imperfect yet 00:02:06.159 --> 00:02:07.210 still useful. 00:02:07.210 --> 00:02:11.440 Letís see how desktop feasibility studies with SEER can help you decide whether electrical 00:02:11.440 --> 00:02:16.510 resistivity imaging surveys are a go/no-go for a particular environmental investigation. 00:02:16.510 --> 00:02:21.160 The SEER spreadsheet allows the user to select a survey design to model, Using dropdown menus, 00:02:21.160 --> 00:02:24.290 the user can: Select from common study scenarios, such as 00:02:24.290 --> 00:02:29.870 delineating dense nonaqueous-phase liquid (DNAPL) or light nonaqueous-phase liquid (LNAPL) 00:02:29.870 --> 00:02:33.920 releases in the subsurface or imaging an underground storage tank; 00:02:33.920 --> 00:02:40.319 Select electrode spacing and survey geometry; Estimate measurement errors, to give us something 00:02:40.319 --> 00:02:45.560 close to real-world results; and Decide whether to add borehole electrodes. 00:02:45.560 --> 00:02:49.980 Then you click on "simulate" to compare the true resistivity model and the predicted inversion 00:02:49.980 --> 00:02:52.680 results. 00:02:52.680 --> 00:02:56.290 This will give you a sense of whether your target is likely to be resolved using a given 00:02:56.290 --> 00:02:57.810 survey design. 00:02:57.810 --> 00:03:02.290 In another example, you can experiment with a survey design to detect a conductive DNAPL 00:03:02.290 --> 00:03:03.290 plume. 00:03:03.290 --> 00:03:06.650 First, model a survey using only surface electrodes. 00:03:06.650 --> 00:03:11.300 Next, model the same target and survey, but add borehole electrodes. 00:03:11.300 --> 00:03:15.040 This example shows that, in this scenario, you might want to add borehole electrodes 00:03:15.040 --> 00:03:20.420 in order to develop a more accurate model of the subsurface conditions to inform remediation. 00:03:20.420 --> 00:03:25.750 However, our project sites are more complex and electrically heterogeneous than the simple 00:03:25.750 --> 00:03:27.930 example models shown so far. 00:03:27.930 --> 00:03:32.980 That is why SEER allows you to freely manipulate resistivity values in cells of the worksheet. 00:03:32.980 --> 00:03:37.200 You can change the target shape, extent, and depth, or the electrical resistivity of the 00:03:37.200 --> 00:03:41.810 surrounding earth materials, and immediately view the effect on the predicted results. 00:03:41.810 --> 00:03:45.760 Detailed help files provide instructions on how to use SEER, as well as background information 00:03:45.760 --> 00:03:51.120 on electrical resistivity surveys and modeling. 00:03:51.120 --> 00:03:55.210 SEER can provide environmental site managers with a quick and easy mini feasibility study 00:03:55.210 --> 00:04:00.129 to assess realistic outcomes from electrical resistivity imaging for site investigations 00:04:00.129 --> 00:04:03.140 and remediation monitoring. 00:04:03.140 --> 00:04:06.090 SEER and additional documentation are available from the USGS web site. 00:04:06.090 --> 00:04:07.090 https://doi.org/10.5066/F7028PQ1 00:04:07.090 --> 00:04:08.090 [CREDITS]