Core Logging for Groundwater Investigations Using Graphical Shading Geologic Logs

This core logging lab was designed for an upper division undergraduate course on introductory physical hydrogeology.

It is helpful if students have taken an introductory geology course so they are familiar with basic geologic terms.

Having some familiarity with depositional processes from a sedimentology course (or similar) is also beneficial but not strictly necessary.

This is one of the first labs we do during our semester-long course. It is typically situated after we cover the basic properties of porous media (e.g., porosity, permeability, compressibility) in a lecture. Often times in hydrogeology courses we talk conceptually about aquifers and simplify their characteristics. I find it beneficial to have students interact with geologic materials early on in the course to provide an experience/and or a reminder that groundwater flows through geologic materials and that these materials are often quite complex.

The pre-lab lecture (50 min) is meant to provide them with some context for one of the primary reasons we log cores in hydrogeology (to inform interpretations of subsurface geology/hydrogeology) and show them the standard approach to logging in the environmental industry as well as describe some of its limitations.

The lab activity is taught in a 3-hour period. It generally takes between 2-2.5 hours to actually run the lab. It includes an introductory lecture (20-25 min). This is meant to describe how to use a graphical shading geologic log form and introduce standard classification systems used to describe geologic materials. If students are familiar with basic sedimentology, then often this lecture can be very brief (a refresher). Then students practice applying these classification systems while they log core. The students spend about 1-1.5 hours logging their cores and answering the lab activity questions.

There are four overall learning objectives for this lab in its current form.

1. Students should be able to describe, in general terms, how geologic data are used in hydrogeology studies.
2. Students should be able to explain the standard approach for collecting geologic data and list some of its limitations.
3. Students should be able to apply the classification systems presented in lecture to describe the basic sedimentological properties of core (at a beginner's level).
4. Students will gain experience recording their geologic observations using a graphical shading geologic log.

Practicing the translation of classification systems to real world materials. This translation requires making observations and then deciding how those observations fit into the idealized framework of the classification system.

Making basic geologic observations and then inferring hydrogeologic properties from those observations. This requires students to synthesize what they know about the solid particles to infer something about the space between those solid particles.

Gaining experience logging cores. Core logging is a skill required for many hydrogeology positions, particularly those at an entry-level.

In this activity, students collect basic geologic data from cores (i.e., they log the cores) using a graphical shading log form. This style of data collection has been designed to facilitate rapid collection of high-quality, highly-resolved sedimentological data from cores to support groundwater investigations.

The materials included in this contribution were prepared to be ready to use 'out of the box' or modified to meet the needs of individual courses and instructors. The instructional materials provided include:

• Instructor guide (pdf)
• Preparatory lecture (pptx)
• Lab lecture (pptx)
• Lab activity (docx)
• Graphical shading geologic log templates (xlsx, pdf)
• Core logging reference sheets (pdf)
• Virtual core (i.e., high resolution core photos) (jpg)
• Key for virtual core graphical shading geologic logs (pdf)
• Reference list (docx)

Instructor Guide -- educator-only file

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Preparatory Lecture (PowerPoint 2007 (.pptx) 22.2MB Aug21 25) and Lab Lecture (PowerPoint 2007 (.pptx) 13.1MB Aug21 25)
The lecture slides are provided as pptx files and use the generic PowerPoint theme to make reformatting and use of individual slides or the entire file as easy as possible. The existing slide background is white and all text is black. Only minimal animations are used. All images have been described with alternative text and the PowerPoint accessibility checker has been utilized to further ensure the accessibility of the lecture content. In addition, text providing additional context for the information on the slides has been provided in the notes pane for each slide.

Lab Activity (Microsoft Word 2007 (.docx) 29kB Aug21 25)
The lab activity is provided as a docx file. It includes a list of the materials required for the lab, a complete set of step-by-step instructions for the students, and a set of example lab questions. Answers to the example lab questions are provided at the end of this guide.

Graphical Shading Geologic Log Templates (Zip Archive 1.4MB Aug21 25)
A variety of graphical shading geologic log templates are provided. There are several versions of the template provided for unconsolidated sediments, each representing a different depositional environment (e.g., arid alluvial fans, glacial, marine-estuarine, fluvial, generic (base)). There are also templates provided for both carbonate and siliciclastic bedrock. Both xlsx and pdf versions of the templates are provided. The xlsx versions can be modified to remove parameters that are not needed or to add parameters that are needed depending on the particular cores being logged, the context of the course, and the time available for the exercise.

Core Logging Reference Sheets (Zip Archive 9.2MB Aug21 25)
Logging reference sheets designed to support logging of unconsolidated sediments, siliciclastic rock, and carbonate rock are also provided in pdf format. These sheets can be printed and provided to students along with other reference materials like grain-size cards and Munsell charts. It is often advantageous to laminate these sheets so they can be stored and re-used.

Virtual Core (Zip Archive 6.8MB Aug21 25)
A 'virtual core' (i.e., high-resolution core photos) has been provided to support the exercise for occasions where physical cores cannot be acquired. These photos cover two 10 ft intervals of a quaternary core collected in northwest Iowa. Making observations from photos is difficult, particularly for beginning loggers who are also not familiar with the materials. So, I have selected photos with clear changes in texture and color and some coarser intervals where very coarse sand and gravel can actually be visualized. Unfortunately, these cores do not include much in terms of sedimentary structures because of the depositional setting and the drilling method (rotosonic).

Key for Virtual Core Graphical Shading Geologic Logs -- educator-only file

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Reference List (Microsoft Word 2007 (.docx) 17kB Aug21 25)
A list of references used in the slides or throughout the development of the graphical shading geologic log templates and reference sheets are provided in a docx document. Also included in the document are examples of publications that provide guidance for core logging for a variety of purposes. There are also two references provided that describe how advanced stratigraphic assessment is used in contaminant hydrogeology projects. Hyperlinks are provided for all the publications in an online format.

Detailed notes and suggestions are provided in the instructor guide.

Assessment of the activity is based on student responses to questions at the end of the lab and their completed graphical shading geologic logs.

I generally focus my assessment of the actual core logs on 4 components:

• Appropriate resolution/detail
• Legibility
• Completeness
• Accuracy

A simple rubric for assessing the graphical shading geologic logs is provided in the Instructor Guide.

See detailed list of references added as an attached document.

There is a complementary short course designed for current professionals on this topic. The short course includes a series of short videos (<12 min) designed with engagement in mind. Some of those videos (or parts thereof) might be useful within the context of this exercise. The course is free and can be accessed with this link: Short Course on Improving Geologic Data Collection for Groundwater Remediation Projects.