United States Department of the Interior

BUREAU OF RECLAMATION PO Box 25007 Denver, CO 80225-0007 I\/REI� ) Rl,M.R ro 86-68320 2.2.4.21 July 17, 2019 VIA ELECTRONIC MAIL

MEMORANDUM

To: Subbasin Liaison, Engineering Geologist, John Day, OR Attn: PN-1775 (Mark Croghan) From: Justine Overacker, Justin Rittgers Qf?-_ Geophysicists, Seismology, Geomor{hology, and Geophysics Group (86-68330)

Subject: Transmittal of Technical Memorandum 85-833000-2019-19

Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support: Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

Attached is a copy of the subject Technical Memorandum (TM). The TM presents the results and interpretations of reprocessed legacy Electrical Resistivity data originally collected forthe 1989 John Day Water Optimization Study near Prairie City, OR. This geophysical survey was originally conducted primarily to determine the existence, location, and geologic nature of an inferredburied ancient river channel, and additionally find the depth to bedrock and delineate hydrogeologic contacts. Reprocessing efforts were undertaken as part of renewed interest in using local aquifer resources to alleviate reliance on surface water resources forirrigation. Reprocessed geophysical data will serve to answer whether AEM surveys would be effectivein identifyingt he aquiferconditions in the John Day River Valley.

If you have any comments regarding this TM, please contact Geophysicists Justine Overacker at 303-445-2973 or via e-mail at [email protected] or Justin Rittgers at 303-445-3010 or via email at [email protected].

Attachment cc: Electronic Copy cc recipients (w/ att. to ea) [email protected] [email protected]; [email protected] -- Geophysicist Intern [email protected]; [email protected] -- Geophysicist [email protected] Liaison jgodaire@usbr:gov- Manager, Seismology, Geomorphology, and Geophysics Group

For Official Use Only

Technical Memorandum 85-833000-2019-19

Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support: Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

Columbia Basin Project Pacific Northwest Region John Day, OR

For Official Use Only

U.S. Department of the Interior Bureau of Reclamation Technical Service Center Seismotectonics, Geomorphology & Geophysics Group Denver, Colorado July 2019

Mission Statements

The U.S. Department of the Interior protects America’s natural resources and heritage, honors our cultures and tribal communities, and supplies the energy to power our future.

The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public

Technical Memorandum TM-$5-833000-2019-19

Geophysical Analysis- John Day River Basin AEM Surveying feasibility Support: Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data Columbia Basin Project Pacific Northwest Region John Day, Oregon

I Tne Ovtk ate eophysicist

Justin cLRt’gers Date Geophy’sicist

Peer Review by:

/fJ ZQ• .7 ichard D. Markiewicz Geophysicist

of the: US. Department of the Interior Bureau of Reclamation Technical Service Center Seismology, Geomorphology, & Geophysics Group Denver, Colorado TM-85-833000-2019-19 Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support

Table of Contents

I. Summary ...... 4

II. Background...... 5 A. Prior Work: 1989 Electrical Resistivity and Magnetics Survey ...... 5 B. Goals and Motivations for Geophysical Reprocessing ...... 7

III. Data Acquisition ...... 7

IV. Data Processing and Interpretation...... 10

V. Results ...... 12

VI. Conclusions ...... 17

VII. References ...... 18

VIII. Appendix A –Direct Current Resistivity Method ...... 19

List of Figures

Figure 1 – Overview of the resistivity survey transects (series of red points) located just south of Prairie City in Oregon, and the overall initially proposed AEM survey footprint (purple polygon) which encompasses the majority of the John Day River basin watershed...... 6 Figure 2 – Electrical resistivity survey lines (red lines) defined by corresponding 1D sounding locations (red dots). E to E’ is the magnetics transect that overlays Resistivity Line 1 and extends past A to A’...... 9 Figure 3 – Example diagram depicting a 4-pin resistivity survey measurement similar to survey geometries used in the 1987 surveys. Here, the four electrodes are centered on a given 1D sounding location, and the separation distances between the various electrodes can be increased to achieve a corresponding greater depth of investigation at the 1D sounding location. Typically, an alternating current is used, and the corresponding voltage signals are measured and averaged to produce a single apparent resistivity value (bottom plots)...... 10 Figure 4 Example of 1D electrical resistivity data for a single sounding. Apparent resistivity is plotted as a function of the half distance between “A” and “B” electrodes (left). Resistivity data can also be displayed at depth (right) as a layered model (red) or a smooth model (brown) for inversion...... 11 i

Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

Figure 5 Example of 2D ERT data (apparent resistivity values) plotted as a pseudo-section (top), the associated forward-modeled apparent resistivity data (center), and the associated recovered Earth resistivity model of “true” resistivity values (bottom)...... 11 Figure 6 – Resistivity Line 1 results. From 1989 John Day Site report (Top): Apparent resistivity values shown as numbers on the pseudo-section, plotted at the lateral location of each sounding station, and at pseudo-depths related to measurement geometries for each data point. Sounding locations are marked 1 through 13. Reprocessing and modeling results (Middle and Bottom): True resistivity values indicated by color, and elevation profiles are incorporated into model. 1D Inversion has sounding locations marked by black plus signs...... 14 Figure 7 – Resistivity Line 2 results. From 1989 John Day Site report (Top): Apparent resistivity values shown as numbers on the pseudo-section, plotted at the lateral location of each sounding station, and at pseudo-depths related to measurement geometries for each data point. Sounding locations are marked 1 through 11. Reprocessing and modeling results (Bottom): True resistivity values indicated by color, and elevation profiles are incorporated into model. Each 1D inversion has sounding locations marked by black plus signs. These symbols are plotted at the true depths of the center of each resulting model layer...... 15 Figure 8 – Resistivity Line 3 results. From 1989 John Day Site report (Top): Apparent resistivity values shown as numbers on the pseudo-section, plotted at the lateral location of each sounding station, and at pseudo-depths related to measurement geometries for each data point. Sounding locations are marked 1 through 11. Reprocessing and modeling results (Bottom): True resistivity values indicated by color, and elevation profiles are incorporated into model. Each 1D inversion has sounding locations marked by black plus signs. These symbols are plotted at the true depths of the center of each resulting model layer...... 16 Figure 9 – Resistivity Line 4 results. From 1989 John Day Site report (Top): Apparent resistivity values shown as numbers on the pseudo-section, plotted at the lateral location of each sounding station, and at pseudo-depths related to measurement geometries for each data point. Sounding locations are marked 1 through 11. Reprocessing and modeling results (Bottom): True resistivity values indicated by color, and elevation profiles are incorporated into model. Each 1D inversion has sounding locations marked by black plus signs. These symbols are plotted at the true depths of the center of each resulting model layer...... 17 Figure 10 – Various electrode array configurations commonly used in resistivity surveying...... 19 Figure 11 –Electrical Current Flow and charge accumulation schematic...... 21 Figure 12 – Generalized schematic of a dipole-dipole type 2D ERT electrode array configuration, and the sequential construction of a pseudo-section of apparent resistivity values (raw 2D resistivity data) as it is related to the dipole geometries used...... 22 Figure 13 – Overview of inverse modeling process...... 23

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TM-85-833000-2019-19 Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support

List of Tables

Table 1 – Latitude/Longitude coordinates (in decimal degrees) of start and end of each geophysical survey line...... 8

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Technical Memorandum No. 85-833000-2019-019 Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support: Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

I. Summary

During FY19, US Bureau of Reclamation (Reclamation) Technical Service Center (TSC) personnel performed reprocessing and inverse modeling of several one-dimensional (1D) electrical resistivity sounding surveys that were originally performed by a private geophysical contractor in 1987 for a John Day River Basin hydrogeologic study. These previously performed 1D resistivity soundings were collected at several stations established along four survey transects located approximately 2 miles south of Prairie City, OR. The four transects were originally surveyed in a site characterization effort for Reclamation to select exploration drill hole sites for groundwater, but only apparent resistivity values (i.e., raw data plotted with pseudo-depths) were presented in the 1989 report [1].

The reprocessing and modeling of these data were performed using both 1D and two- dimensional (2D) inverse electrical resistivity tomography (ERT) modeling techniques. Modeling was performed to help reveal the “true Earth resistivity structure” beneath each transect using IX1Dinv by Interpex Software LLC and Res2Dinv by GeoTomo Software Inc1. These subsurface images were produced in support of a proposed airborne electromagnetic (AEM) survey in the John Day area to determine whether AEM surveys would be a viable option for mapping hydrogeology and deep aquifer resources throughout the John Day River basin. Local water entities are interested in evaluating the hydrogeologic properties of these aquifer resources and the potential to manage them to relieve pressure on surface water resources. The 1987 resistivity survey data provide a unique opportunity to evaluate the feasibility of AEM to achieve the current hydrogeologic study objectives, and more specifically, the desired depths of investigation and hydrostratigraphic differentiation throughout the proposed AEM footprint.

The immediate objectives for this effort included the following;

1) Reprocess historical data whose primary purpose was to determine the existence, location, and geologic nature of an inferred buried ancient river channel, and additionally find the depth to bedrock and delineate hydrogeologic contacts.

1 Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the U.S. Government. 4

TM-85-833000-2019-19 Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support

2) Answer whether AEM surveys would be effective in identifying the aquifer conditions for those areas.

II. Background

The John Day resistivity survey site is located in the John Day River Valley near Prairie City, Oregon at elevations between 3,465 and 3,900 ft (red points in Figure 1 and Figure 2). It is located upon a large mid-Pliocene to Pleistocene alluvial fan that forms extensive benchlands for about 30 square-miles south of the river, originating from the formerly glaciated Strawberry Range. The benches slope uniformly northwards, and are composed of fanglomerate, gravel, sand, clay, and tuff termed the Rattlesnake Formation. The site is bounded by volcanic flows, with the Columbia River Group basalt probably underlying most of the site west of Strawberry Creek, and the Strawberry Volcanics probably forming bedrock to the east.

A. Prior Work: 1989 Electrical Resistivity and Magnetics Survey

The John Day Site was chosen in 1989 study based on previous work performed by the US Geological Survey (USGS) that estimated the location of an ancient river channel hypothesized to be an excellent aquifer under artesian pressure [2]. A 1986 well drilled 0.75 miles south of the present-day river encountered 460 ft of gravel above bedrock, so the estimated location of the ancient channel was moved to 1.5 miles south of the present channel.

Electromagnetic and magnetic geophysical data was collected in an effort to locate and map the buried ancient river channel in the John Day River valley, determine approximate contacts between fine- and coarse-grained sediment in potential aquifers, and locate depth to bedrock. The data supported the existence of an ancient channel cut into bedrock in the survey area 1 to 1.5 miles south of the present-day river, but the secondary objectives involving quantitative analysis of deep resistivity to identify depth to bedrock and delineate aquifer contacts were less successful. The results are summarized in the 1989 report by Sprenke [1].

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Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

Figure 1 – Overview of the resistivity survey transects (series of red points) located just south of Prairie City, Oregon, and the overall initially proposed AEM survey footprint (purple polygon) which encompasses most of the John Day River basin watershed.

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TM-85-833000-2019-19 Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support

B. Goals and Motivations for Geophysical Reprocessing

The main goal of reprocessing the 1987 resistivity data was to be able to provide technical advice on whether or not electromagnetic surveys (e.g. airborne electromagnetics) would be effective in identifying the aquifer conditions for those areas. With the availability of the modeled resistivity data, the viability of an AEM survey in the same area can be generally determined. Here, both the lateral and vertical variations (e.g., contrasts) in electrical resistivity of various lithologic units and the overall resistivity value distributions are points to consider when evaluating how AEM will help to inform a greater groundwater study effort. Optimally, various lithologic units will have enough of a resistivity contrast to allow for development of a well-constrained 3D hydrostratigraphic model of the John Day River Basin. Additionally, the overall range of electrical resistivities should ideally be high enough as to not significantly limit the expected depth of investigation that would be achieved by AEM.

The reprocessed and modeled data could further be used to help define appropriate AEM system technical specifications required for contractors bidding on electromagnetic surveys for the John Day water optimization project. Additionally, the reprocessed data would serve as a comparison point for future electromagnetic surveys to avoid ending up with poor quality data or inadequate results (e.g., establish a “test-line” that can be used to verify the AEM system’s performance immediately prior to full data production efforts). For example, we would expect the resistivity signatures obtained by co-located AEM surveys to have resistivity values of a reasonably similar magnitude and distribution as the reprocessed results present here.

III. Data Acquisition

Data was collected for the 1989 John Day Water Optimization Study for Reclamation by consulting geophysicist Kenneth F. Sprenke. The data was originally collected to help Reclamation in selection of exploration drill hole sites as part of the study. To avoid crossing drainages, the survey lines were laid out to follow the ridges of the benchlands. The stations were 700 ft apart, and the approximate locations of all stations and survey lines are shown in the detailed site map presented in Figure 2. Details of the surveying parameters are provided in the following excerpt taken from Sprenke (1989):

The contract required the running of four 1.5-mile geophysica1 resistivity lines to a depth of investigation of about 700 feet. In addition, in order to aid in the interpretation of the resistivity results, a detailed magnetic profile was run across the entire valley basin (about 5 miles). Along each resistivity line, soundings were conducted using the Schlumberger electrode array. Current electrode spacings of 400 ft, 600ft, 900 ft, 1,500 ft, 2,100 ft, and 3,000 ft were employed. A rule of thumb for the Schlumberger array is the depth of investigation is about one quarter of the current electrode spacing. Thus, for each sounding, apparent resistivities were obtained for six different depths of investigation ranging from 100 ft to 750 ft. The potential electrodes used were of the non-polarizing type and were spaced 7

Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

symmetrically about the center of the array. A Scintrex IP8 1000-volt transmitter was employed which maintained a constant current to an accuracy of 0.01 amps. A high impedance digital voltmeter was used to measure potential differences to an accuracy of 0.1 millivolts. The 288 apparent resistivities obtained on the four 1.5-mile lines required laying out and picking up about 30 miles of geophysical cable. Figure 2 depicts the locations of the four resistivity survey lines (red lines) and magnetic line collected along the ridges of the benches south of the John Day river. Furthermore, the geographic coordinates for the starts and ends of each resistivity survey transect and the magnetic survey line can be found in Table 1.

Resistivity surveys generally consist of a series of measurements that are each recorded using two current injection electrodes (Electrodes “A” and “B” form a source dipole) and two measurement electrodes (Electrodes “M” and “N” form a receiver dipole). Each unique source/receiver dipole pair is referred to as a quadrapole measurement, which constitutes a resistivity data point/measurement. For each measurement/quadrapole, 1) the geometric location of each electrode (XYZ) is recorded, 2) the electrical current injected between A and B electrodes is recorded, and 3) the measured voltage between M and N electrodes is recorded. These values allow for the calculation of an “apparent resistivity” value for each measurement.

Figure 3 presents a generalized diagram of a single four-pin 1D sounding measurement configuration. A magnetic survey was also performed along one 5-mile line (Transect E-E’ on Figure 2) to tie the resistivity results to the geological structure of the overall river basin. These data were not reprocessed or modeled and are not presented or discussed further in this report.

Table 1 – Latitude/Longitude coordinates (in decimal degrees) of start and end of each geophysical survey line.

Line End Start LAT/LON (D.dd.) End LAT/LON (D.dd.)

Resistivity Line 1 44.44821, -118.677 44.42469, -118.674

Resistivity Line 2 44.45237, -118.692 44.4339, -118.682

Resistivity Line 3 44.44837, -118.715 44.43069, -118.703

Resistivity Line 4 44.43987, -118.735 44.42229, -118.713

Magnetic Line 44.44819, -118.677 44.38048, -118.668

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TM-85-833000-2019-19 Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support

Figure 2 – Electrical resistivity survey lines (red lines) defined by corresponding 1D sounding locations (red dots). E to E’ is the magnetics transect that overlays Resistivity Line 1 and extends past A to A’.

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Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

Figure 3 – Example diagram depicting a 4-pin resistivity survey measurement similar to survey geometries used in the 1989 surveys. Here, the four electrodes are centered on a given 1D sounding location, and the separation distances between the various electrodes can be increased to achieve a corresponding greater depth of investigation at the 1D sounding location. Typically, an alternating current is used, and the corresponding voltage signals are measured and averaged to produce a single apparent resistivity value (bottom plots).

IV. Data Processing and Interpretation

Modeling was conducted for all resistivity datasets by performing both independent 1D modeling for each sounding/station location, and by means of merging individual 1D soundings and performing 2D tomographic inversions for a given survey transect. Below is a brief description of the general steps performed. The elevation data was not recorded during the initial field work, so it was approximated with digitized topographic maps and Google Earth’s elevation profile tool. Additionally, geographic coordinates for soundings were approximated using Google Earth.

Apparent resistivity data, along with electrode geometry of each measurement is the final input data for the iterative inverse resistivity modeling process. The inversion process seeks to minimize the difference between the recorded and recovered data while obtaining some “meaningful” or “geologically reasonable” model (e.g., smooth model with reasonable model parameter values expected for a given site’s geology/conditions). An example 1D inversion is presented in Figure 4, and an example tomogram is presented in Figure 5.

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TM-85-833000-2019-19 Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support

Figure 4 – Example of 1D electrical resistivity data for a single sounding. Apparent resistivity is plotted as a function of the half distance between “A” and “B” electrodes (left). Resistivity data can also be displayed at depth (right) as a layered model (red) or a smooth model (green) for inversion.

Figure 5 – Example of 2D ERT data (apparent resistivity values) plotted as a pseudo-section (top), the associated forward-modeled apparent resistivity data (center), and the associated recovered 2D tomography (Earth resistivity model) of “true” resistivity values (bottom).

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Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

Resistivity data were reprocessed using IX1Dinv software. This was done to determine the “true Earth resistivity” values compared with the original “apparent resistivity” values (raw data). IX1Dinv uses the distance half-length of the current electrodes, distance between the measurement electrodes, and apparent resistivity to build each 1D sounding. Elevation, cardinal directions, and azimuthal data was also input for each sounding location. An estimated layered model of resistivities was then input to a depth of 400 meters, and a smooth model was run using 30 layers for each 1D sounding along a given survey line. Both models were input into the multiple iteration inversion ran for each 1D sounding location. The resulting models were then used to build the final 2D resistivity cross-section for survey transects A through D (see Figure 2) shown in the results section.

Resistivity data reprocessing was tested using Res2DInv software for resistivity Line 1, but the inversion results did not show promise compared to the 1D inversion. The tested 2D inverted tomogram showed laterally-continuous homogenous apparent resistivity layers, very different than the pseudo-section and 1D cross-section results (see Figure 6). This is attributable to the difference between 1D and 2D inversion methods. 1D inverted cross-sections are modeled based on a layer-cake Earth model. 2D inversion, in contrast, is built by inverse modeling of adjacent gridded cells, which generally requires denser data coverage. The historical resistivity data did not provide adequate coverage along each transect to constrain the 2D inversion process well during the test, so that method of reprocessing was discontinued for the other three lines.

V. Results

The modeling results along Resistivity Line 1 through Resistivity Line 4 are presented in Figure through Figure 9, respectively. In these cross-sections, more electrically conductive (low resistivity) regions such as water-saturated weathered bedrock and soils, are indicated by cool colors (e.g., dark and light blues), while less conductive (more resistive) materials such as solid bedrock or dry sandy alluvium are indicated with warmer colors (e.g., yellows and reds). It should be noted that each 2D cross-section is presented with a common color-scale to help visualize variations in resistivity across the entire study site. Each cross-section figure is plotted using line stationing (lateral distances in units of meters) relative to the location of the first sounding for each transect. Therefore, these cross-sections are viewed as though the reader is nominally looking eastward. Note that each independent cross-section is presented with absolute elevations in units of meters above mean sea-level, and the elevations change based on the location of the sounding along each survey line.

When looking at the results, it is important to remember that these cross-sections represent the average resistivity for the depth range beneath each survey transect and are the product of modeling relatively noisy data collected with now antiquated field instruments. Therefore, the resulting cross-sections are presented to help visualize an approximate spatial distribution of true resistivity values within the subsurface, and there is some uncertainty associated with the models. In general, however, the RMS error for each of the soundings was quite low—usually under 5 percent— and a high level of confidence is placed on the various 1D inversion models used to generate the 2D cross-sections presented here.

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Resistivity Line 1 (see Figure 6) is unique amongst results because it includes both 1D and 2D inversion models. In the case of 1D inversions, each sounding is inverted independently and then graphically “stitched” together to create a 2D cross-section of spatial resistivity variation. In contrast, the 2D inversion approach performs tomographic inversion, and the input data along a given transect was generally insufficient to help support and constrain this approach to inverse modeling. Therefore, the 2D inversion results differ significantly from the 1989 pseudo- sections. While 2D tomography modeling was also carried out for resistivity Lines 2-4 in this way, this report presents and focuses on results obtained from the 1D inversion approach, as this was deemed the most appropriate given the nature of the input data.

There are positive similarities between the 1989 pseudo-section and the resulting Line 1 cross- section. Near the center of both models is an area of higher conductivity capped by an area of higher resistivity. The south sides of each transect feature a layer of highly resistive material in the shallow subsurface. Both models also feature a large resistivity area overlain by a more conductive material to the north. The apparent resistivity values are, in general, of the same order of magnitude between the two models. Areas of the model where there is a difference in magnitude can be attributed to the inversion process and are a consequence of resistivity values being averaged through the depth of investigation.

Modeling results for resistivity Line 2 (Figure 7) also corroborate the results from the 1989 report. Near the shallow subsurface across the tomogram is a layer of higher resistivity material underlain by more conductive layers, particularly between soundings 4 and 6. On the south side of the transect are distinctive high resistivity layers that appear to dip southward from soundings 6 to the end of the transect. The magnitudes of the resistivities are of similar value as well.

Resistivity Line 3 (Figure 8) is well-corroborated with the original report results. To the north there is a dipping area of high resistivity over top an area of conductivity (labeled as a possible topographic effect in the original pseudo-section). High resistivity values abound in the upper layers of the tomogram and are juxtaposed by highly conductive layers beneath them. There are two artifacts of the inversion process shown as white spots between soundings 7 and 8, and 10 and 11 capping a very resistive section that does not appear in the original report soundings. This area of difference is attributable to higher variability in the inversion model.

Inverted model results for resistivity Line 4 (Figure 9) are also encouragingly like the pseudo- section results. High resistivity values are layered over a conductive layer that starts about midway down in the tomogram. The area of greatest resistivity in the shallow subsurface is located near sounding 3 for both models. There is an area of higher resistivity underlaying the conductive layer near the center, unlike the pseudo-section, but this is likely a consequence of the averaging process when measuring apparent resistivity.

To reiterate, these results study do not seek to re-interpret the geological results from the 1989 study, only to address whether the data supports the viability of using electromagnetic geophysical survey methods, like AEM, in the future to develop groundwater resources. These results can, however, be used in such surveys to help design appropriate technical specifications and serve as a comparison point for quality control.

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Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

Figure 6 – Resistivity Line 1 results. From 1989 John Day Site report (Top): Apparent resistivity values shown as numbers on the pseudo-section, plotted at the lateral location of each sounding station, and at pseudo-depths related to measurement geometries for each data point. Sounding locations are marked 1 through 13. Reprocessing and modeling results (Middle and Bottom): True resistivity values indicated by color, and elevation profiles are incorporated into model. 1D Inversion has sounding locations marked by black plus signs.

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Figure 7 – Resistivity Line 2 results. From 1989 John Day Site report (Top): Apparent resistivity values shown as numbers on the pseudo-section, plotted at the lateral location of each sounding station, and at pseudo-depths related to measurement geometries for each data point. Sounding locations are marked 1 through 11. Reprocessing and modeling results (Bottom): True resistivity values indicated by color, and elevation profiles are incorporated into model. Each 1D inversion has sounding locations marked by black plus signs. These symbols are plotted at the true depths of the center of each resulting model layer.

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Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

Figure 8 – Resistivity Line 3 results. From 1989 John Day Site report (Top): Apparent resistivity values shown as numbers on the pseudo-section, plotted at the lateral location of each sounding station, and at pseudo-depths related to measurement geometries for each data point. Sounding locations are marked 1 through 11. Reprocessing and modeling results (Bottom): True resistivity values indicated by color, and elevation profiles are incorporated into model. Each 1D inversion has sounding locations marked by black plus signs. These symbols are plotted at the true depths of the center of each resulting model layer.

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Figure 9 – Resistivity Line 4 results. From 1989 John Day Site report (Top): Apparent resistivity values shown as numbers on the pseudo-section, plotted at the lateral location of each sounding station, and at pseudo-depths related to measurement geometries for each data point. Sounding locations are marked 1 through 11. Reprocessing and modeling results (Bottom): True resistivity values indicated by color, and elevation profiles are incorporated into model. Each 1D inversion has sounding locations marked by black plus signs. These symbols are plotted at the true depths of the center of each resulting model layer.

VI. Conclusions

There is a high level of confidence in the modeling results and interpretations presented here for the following reasons:

1. Relatively low RMS errors (e.g., data misfits) for each inversion.

2. Overall corroboration between patterns observed in resistivity modeling results and the original 1989 report’s pseudo-sections.

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Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

3. Overall corroboration with field observations of local topography and surface water saturation levels.

Based on the modeling results presented in this report, TSC analysts conclude that the resistivity structure at the John Day Site is conducive to AEM surveys. There is evidence that AEM would be able to image the hydrogeologic structure and support the desired depths of investigation throughout the proposed AEM footprint shown in Figure 1. Specifically, the modeled resistivity values do not indicate that the area investigated in the 1989 resistivity surveying is not so electrically conductive that an AEM survey’s depth of investigation would be severely hindered. Additionally, the hydrogeologic structures interpreted in the resistivity data indicate that there is adequate contrast from one geologic unit to another, such that an AEM survey would be able to successfully differentiate and map these units in three dimensions. Hence, the more spatially comprehensive resistivity information that an AEM survey would provide would allow for the construction of a basin-scale hydrogeologic model for sake of informing surface-groundwater interactions, and related water management strategies.

It is important to note, however, that these conclusions assume the four transects are representative of the entire proposed AEM footprint, extrapolating historical data from an area roughly 5 square-miles to an area 50 times larger and extending over 40 miles west of the historical survey area. Based on the previous geological work outlined in the 1989 report [1] and remembering that these transects were located on the benchlands rather than the river valley, there are likely subsurface structural variations not accounted for in this assumption that might affect the quality of AEM data collected. Therefore, the conclusions discussed herein should be taken with some measure of flexibility when it comes assessing the applicability of an AEM survey throughout the proposed area.

VII. References

[1] Sprenke, K. F., 1989. Geophysics Survey of the John Day Site, Upper John Day Water Optimization Study, Order Number 9-PG-10-14220, U.S. Bureau of Reclamation, Boise, Idaho.

[2] Thayer, T. P., 1972. Potential Ground-water Resources of the upper John Day River Valley, Grant County, Oregon, U.S. Geological Survey, Washington, D.C., available at: https://pubs.usgs.gov/of/1972/0376/report.pdf

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VIII. Appendix A –Direct Current Resistivity Method

A single direct current (DC) resistivity measurement is most commonly executed by directly passing electrical current through the subsurface with two electrodes (A and B) and measuring the resulting voltage on the surface with two other electrodes (M and N) located in the vicinity of the current electrodes. There are several electrode configurations that can be employed for making resistivity measurements, as depicted in Figure .

Figure 10 – Various electrode array configurations commonly used in resistivity surveying.

In a Wenner-type array configuration, each measurement is achieved using two electrode pairs, where all electrodes spaced equidistantly with the voltage measurement pair centered between the current electrode pair, as seen in Figure 11. Similarly, a Dipole-Dipole type electrode array configuration also makes use of two electrode pairs, except that the current dipole and the measurement dipoles are placed adjacent to one another (as opposed to centered on one another). In a Dipole-Dipole survey, both the dipole sizes and the inter-dipole spacings are varied in order to achieve varying depths of investigation, as depicted in Figure . Spacing between electrodes can range from inches to hundreds of feet apart. Depth of investigation and resolution of models are directly related to the electrode geometries used, where smaller spacings result in shallow

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depths of investigation and higher resolutions, while larger electrode spacings result in greater depths of investigation at the expense of resolution (more material is averaged).

Electrodes themselves are 16 inch long stainless steel rods, about a ½ inch in diameter. These rods are inserted into the ground 6 to 12 inches deep. The direct current resistivity concept is based on changes in voltage observed at the ground surface caused by varying electrical current flow at different locations in the subsurface. These changes in current flow are caused by the presence of relatively higher or lower resistivity anomalies surrounded by a fairly uniform half- space, or subsurface.

In the case of a four-electrode measurement, the current passes from the source, A electrode, into the subsurface finding the path of least resistance. Flowing through lower resistivity anomalies and flowing around higher resistivity anomalies, it then passes back up to the surface sink created by the B electrode (see Figure 11). The M and N electrodes measure the voltage at the ground surface. By using the equation V=IR, the instrument uses the electric current applied and the voltage measured to identify the resulting resistance. Resistance is automatically converted into an apparent resistivity value computed by the instrument based on the geometry of the given measurement (by convention, half-space geometry is applied for surface measurements, and whole spaces are used for down hole surveys). In the case of a surface-based resistivity measurement made on a homogeneous half-space with electrical resistivity , the generalized equation for the expected measured voltage for a given resistivity measurement is given by the following: 𝜌𝜌 𝑉𝑉 1 1 1 1 = + 2 𝜌𝜌𝜌𝜌 𝑉𝑉 � − − � Here, is the measured voltage difference𝜋𝜋 𝐴𝐴𝐴𝐴���� �(volts)𝐵𝐵���𝐵𝐵� between� 𝐵𝐵𝐵𝐵���� electrodes𝐴𝐴���𝐴𝐴� M and N, is the injected current (amps) between electrodes A and B, is the electrical resistivity of the infinite half- space.𝑉𝑉 The expression in the square brackets is equal to , where is referred to𝐼𝐼 as the 𝜌𝜌 “Geometric Factor” defined by , , , and (the1 distances between the respective 𝑘𝑘 electrode pairs). In the case of a dipole-dipole array configuration,𝑘𝑘 this generalized equation for apparent resistivity reduces to the𝐴𝐴𝐴𝐴��� �following� 𝐵𝐵���𝐵𝐵�� 𝐵𝐵𝐵𝐵��� �expression:𝐴𝐴���𝐴𝐴�

= ( + 1)( + 2) 𝑉𝑉 𝜌𝜌𝑎𝑎𝑎𝑎𝑎𝑎 𝜋𝜋𝜋𝜋𝜋𝜋 𝑛𝑛 𝑛𝑛 Here, is the apparent resistivity, is 𝐼𝐼the common dipole length that is also referred to as the = = “A-spacing”𝑎𝑎𝑎𝑎𝑎𝑎 (e.g., ), and is an integer multiplier ≥1 that defines the number of A-spacings𝜌𝜌 (i.e., distance) between the𝑎𝑎 center of the dipole pairs. Finally, the calculated apparent resistivity𝑎𝑎 values,�𝐴𝐴��𝐴𝐴� along𝑀𝑀𝑀𝑀���� �with the𝑛𝑛 associated electrode geometry for each value, are used as the input into inverse modeling software. The inverse modeling process generally involves an iterative process that seeks an earth conductivity model that describes/explains the data collected in the field, and tries to minimize the difference between that recorded field data and the forward-calculated data (using finite difference and/or finite element modeling of related physics to predict expected data) while recovering a reasonable conductivity model (e.g., smooth model with reasonable resistivity values expected for a given site/material). Figure provides a general overview of the inverse modeling process. 20

TM-85-833000-2019-19 Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support

Figure 11 –Electrical Current Flow and charge accumulation schematic.

21

Reprocessing of 1989 Water Optimization Study Electrical Resistivity Data

Figure 12 – Generalized schematic of a dipole-dipole type 2D ERT electrode array configuration, and the sequential construction of a pseudo-section of apparent resistivity values (raw 2D resistivity data) as it is related to the dipole geometries used.

22

TM-85-833000-2019-19 Geophysical Analysis- John Day River Basin AEM Surveying Feasibility Support

Figure 13 – Overview of inverse modeling process.

23

Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

EDUCATION & TRAINING: • Ph.D., Geophysics- Colorado School of • Wilderness First Aid/CPR Certified (2019) Mines, Golden CO., 3.87/4.0 GPA with • Defensive Drivers Training (2019) minor: Science Technology Engineering • General Mine Safety Training (2008) Policy • ATV Safety Training (2009) • B.S. Geophysical Engineering- Colorado • Leadership Training (CLFP- 2018) School of Mines, Golden CO., 3.4/4.0 GPA • Sexual Harassment, Civil Treatment, and with specialization: Geological Engineering Diversity Training (2018) • OSHA 40- hour training (2009)

GENERAL PROFESSIONAL BIO: I am currently a full-time US Bureau of Reclamation geophysicist stationed at the Technical Services Center in Denver Colorado. I specialize in basic and applied research and the application of geophysics for addressing complex geological engineering, civil engineering and infrastructure-related investigations and challenges, as well as for hydrogeologic, water resources characterization and management studies, groundwater exploration, canal/levee/dam-safety, environmental, corrosion, and archeological applications. I have extensive experience in project management, geophysical survey design, geophysical instrumentation and monitoring, geophysical data collection, data processing, data analysis, digital signal analysis, coding in various object oriented and scripting languages, database creation and management, forward and inverse numerical modeling, geophysical and geologic data/product interpretation, technical writing and verbal communication, and visualization and presentation of results to large and small audiences in a variety of meaningful and useful ways for use by engineers, program/project managers, stakeholders and non-geoscientists alike. I have an extensive multidisciplinary geoscientific background in a wide variety of state-of-the-art geophysical methods and analytical techniques, an extensive background in geology and geologic and civil engineering applications of geophysics, all with an emphasis on maximizing the value of information contained within geophysical data. I have published several peer-reviewed journal articles, and presented invited talks and posters at numerous technical conferences and workshops. I am proficient in virtually all near-surface geophysical methods (including surface-based, downhole logging, surface-to-downhole, crosshole, and most airborne techniques).

SPECIALIZED EXPERTISE AND WORK EXPERIENCE: I have extensive expertise in the data collection, data processing, data analysis, and forward and inverse modeling of the following geophysical data types: Seismic reflection/refraction, active and passive seismic surface wave interferometry, crosshole/downhole seismic profiling, surface-to- downhole and crosshole tomography, sonic logging and tomography, resistivity and spontaneous potential logging, self-potential mapping, electrical resistivity soundings, electrical resistivity tomography, ground penetrating radar imaging, magnetics, time-domain and frequency-domain electromagnetics mapping and profiling, acoustic emissions monitoring and source localization, gravity, induced polarization, and various non-destructive testing techniques such as impact-echo, SASW, slab- impulse response, etc. Much of my specific expertise involves 1D/2D/3D implementations of geophysical techniques, as well as time-lapse (4D) and joint time-lapse (5D/n-dimensional) techniques for data analysis and modeling. Additionally, I have experience in the use of semi-empirical analytic models of petrophysical relationships to aid in data/model interpretations, experience in developing data fusion and attributes analysis algorithms, anomaly detection and characterization algorithms, and semi-automation of data processing and interpretation workflows with the use of machine learning algorithms. I also have experience with wireless geophysical sensor network prototype development and testing for the application of long-term infrastructure monitoring using open-source Arduino-based distributed wireless sensor networks (WSNs) and commercial systems.

Rittgers, Justin B. 2019 Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

February, 2016 – June, 2018 (present): Geophysicist GS-11, US Bureau of Reclamation After completing a Ph.D. in Geophysics in December of 2015, I was converted to a full-time duty as a professional geophysicist (pay-grade GS-11) for the US Bureau of Reclamation. Since February of 2016, official Reclamation-duties and activities and non-Reclamation related outside professional activities and experience have included the following:

1) Designing, leading and/or participating in numerous Reclamation and federal inter-agency research projects as either a critical team-member or project manager: both Dam Safety-funded Technology Development projects, and Research and Development (R&D) Science and Technology (S&T) Program-funded research projects. - Specific research project details/roles/duties available upon request 2) Designing, leading and carrying out numerous Reclamation mission-related and federal inter- agency (MIPR) geophysical projects related to water resources management, canal and dam- safety issue evaluations, comprehensive facilities reviews, and modification design-related activities as geophysics project manager, managing large field crews and all travel, field, and office-related geophysical project logistics related to survey design, budget planning, acquisitions, contracting, data collection/analysis/interpretation/reporting and overall project execution. When not assigned project manager duties/role, my role as a technical team- member typically involves providing specialized technical support for various aspects of engineering, environmental, hydrologic, geologic, and canal and Dam safety-related projects and research across the country. Virtually all of my Reclamation and inter-agency geophysics projects have been completed ahead of schedule and under budget with no injuries. - Specific project details/roles/duties available upon request 3) Conducting teleconference calls with Military and National Security Agency officials, and site visits to meet one-on-one with regional Natural Resource Specialists and preparing associated documents and technical information for sake of completing Categorical Exclusion Checklists (CEC) and acquiring required permits/site access permissions for proceeding with mission- based project work. 4) Providing numerous technical peer-reviews and technical inputs for Reclamation documents and presentations, including technical conference proceedings abstracts, technical conference presentations given by TSC colleagues, geophysical Technical Memorandums and reports/deliverables, summaries for R&D annual Regional Directors Meetings about S&T Water Infrastructure projects, summaries for Best Practices Guidelines, Operations and Maintenance (O&M) Exams Guidance documents, Water Operations and Maintenance/Summer Bulletins, S&T Bulletins, as well as research proposals, technical presentations, technical drawings and plots, and data interpretations/results produced/drafted by Reclamation and federal inter- agency colleagues. 5) Providing critical expertise in the formulation and drafting of technical contract requirements to be included in Performance Work Statement, including required geophysical system specifications, required proof of bidding companies’ technical proficiencies, and required scopes of work for qualification of contract bids for large geophysical surveying contract/project (~$750,000 services contract, ~$1-million Dollar Reclamation project budget). 6) Organizing and leading in-person Reclamation project team meetings at TSC, Area Offices, Water District Offices, and stake-holder offices/meetings in order to discuss and present project- related planning, technical information, project updates, and geophysical survey results. 7) Organizing and leading Web-based Reclamation project team meetings and Teleconference calls with fellow TSC colleagues, Area Offices, Water District Offices, and other non- Reclamation stake-holders and clients in order to discuss and present project-related planning, technical information, and geophysical survey results.

Rittgers, Justin B. 2019 Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

8) Organizing and conducting in-person technical presentations to Dam Safety University (DSU) Technical Training audiences in order to present dam safety-related geophysical techniques and to update TSC program managers and engineers about the Geophysics Team’s current technical capabilities for providing “in-house” geophysical services and technical support for Dam Safety Office related projects and challenges. 9) Organizing and conducting in-person and web-based (DOIRSWG) presentations and discussions on the use of remote sensing and airborne geophysical survey technologies for helping to solve water-related challenges. 10) Participating as a critical team member in the organization, definition, drafting and implementation of S&T Program Prize Challenge Competitions, and subsequently participating on judging panels, and carrying out next-steps research related to winning submitted solutions. 11) Participating as a critical researcher and technical expert in the organization, definition, drafting and implementation of geophysics and remote sensing-related S&T program infrastructure- related research initiatives and priorities, presenting and participating in annual S&T infrastructure workshops. 12) Participating as a critical researcher and technical expert in the organization, definition, fostering and implementation of interagency collaborative research initiatives, priorities, relationships, and specific collaboration endeavors for the S&T Program with the US Army Corps of Engineers and other fellow DOI Agencies, presenting and participating in annual S&T infrastructure workshops. 13) Enabling, empowering, and leading fellow geophysicist colleagues at TSC by means of providing informal training and experiential learning opportunities for best practices in implementing geophysical survey design, data collection and processing, as well as using data processing codes/scripts and workflows that I have developed for efficient geophysical data analysis, modeling, and figure/results generation. 14) Testing, maintenance, and upgrading of Reclamation’s geophysical survey equipment. 15) K-12 outreach via judging at Regional Science Fairs, presenting at annual engineering career day workshops/luncheons, and class demonstrations/lessons about the geosciences as a career option. 16) Invited presentations at the Colorado School of Mines at various workshops, meetings, and student professional society luncheons. 17) Serving as Member at-Large Graduate Thesis Advisory Committee Member for thesis-based Master’s of Science degree candidates within the Computer Science program, and the Geophysics program at the Colorado School of Mines (2016-2018). 18) Conducting formal technical-reviews of submitted articles to peer-reviewed journals by- invitation as Geophysics technical subject matter expert (e.g., Journal of Applied Geophysics). 19) Pursuing intermittent and short-term external employment opportunities by providing private geophysical consulting services to pre-approved and non-prohibited external sources/clients through my single-member LLC, JR Geophysics LLC as the Principal Geophysicist.

Rittgers, Justin B. 2019 Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

June, 2011 – February, 2016: Geophysicist Internship (SCEP/Pathways) GS-11, US Bureau of Reclamation Worked as a part-time geophysicist (pay grade GS-11) for the US Bureau of Reclamation participating as a critical team-member in various federal inter-agency research projects, mission-related and inter- agency geophysical projects, and providing specialized technical geophysical support (including peer- reviews, geophysical survey design, work-related travel, data collection, data analysis and interpretation, technical writing of reports/Technical Memorandums, etc) for various types of engineering, environmental, hydrologic, geologic, and Dam safety-related projects across the country, while pursuing a Ph.D. at the Colorado School of Mines. Most duties performed during this timeframe (with the exception of project-management roles) were similar or identical to those continued as a full-time geophysicist for Reclamation (See above).

May, 2006 – September, 2010: Project Geophysicist – Zonge Geosciences, Inc., Lakewood, CO. Worked as a full-time professional geophysicist for Zonge Geosciences, Inc, after graduating from the Colorado School of Mines in 2006, applying several geophysical methods including resistivity tomography, surface-based/downhole/crosshole seismic imaging, seismic surface waves, IP, SP, magnetics, electromagnetics and GPR to the solution of a variety of complex engineering, environmental and geologic problems. Experience includes noninvasive subsurface geologic mapping, characterization of earthen dams and levees, natural and sub-concrete void detection, UBC building/bridge site classifications, grout injection and compaction-related ground improvement monitoring, ground water exploration, landfill delineation, Federal and State transportation agency studies, bedrock rippability studies, slope stability and landslide studies, vibration monitoring, UXO detection, UST detection, EPA superfund site studies, and archeological investigations. Performed geophysical investigations for government and industry entities throughout the U.S., including several projects in Alaska, Hawaii and international work in Greenland and South Africa.

RELEVANT EMPLOYMENT HISTORY: (Reference Contacts Available Upon Request) May 2018 – Present: Owner, Principal Geophysicist, JR Geophysics LLC February 2016 – Present: Full-time Geophysicist, GS-12, USBR, Seismology, Geomorphology and Geophysics (SGG) Group June 2011 – February 2016: Part-time Geophysicist Intern (Pathways), GS-11, USBR, Seismology, Geomorphology and Geophysics (SGG) Group August 2013 – December 2015: NSF PIRE Research Assistant August 2011 – August 2013: NSF SmartGeo Fellow August 2011 – May 2014: CSM: Materials of the Earth Lab Teaching Assistantship August 2010 – December 2011: CSM: Advanced Seismic Processing Teaching Assistantship May 2006 – September 2010: Project Geophysicist: Zonge Geosciences, Inc. Lakewood, CO May 2005 – May 2006: Project Assistant: USGS Crustal Imaging Group, Denver, CO May 2005- August 2005: Lab Assistant: Colorado School of Mines Rock Properties Research Lab; December 2004 – May 2005: UXO Research Project Assistant: Colorado School of Mines, CGEM

SPECIFIC RECLAMTION RESEARCH AND PROJECT EXPERIENCE EXAMPLES:

2011 – Present: Geophysicist, Principal Investigator, Project Manager – A multitude of Reclamation and inter-agency (MIPR) projects related to Dam-Safety, Applied Research, Technology Development, Water Exploration, Aquifer Characterization, Water Reuse and Storage, Pipeline Projects, Canals, etc. Specific examples available upon request.

Rittgers, Justin B. 2019 Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

NON-RECLAMTION DAM/LEVEE/WATER-RELATED PROJECT EXPERIENCE EXAMPLES:

2009: Project Geophysicist – Trinity Levee, Dallas, Texas: Client: Fugro Consultants, Inc. Evaluation of levee structure using electrical resistivity, seismic refraction tomography and multi-channel analysis of seismic surface waves (MASW). Prepared integrated report on lateral material variations (parallel to axis using all methods applied) for more than six miles along this urban levee. Project was completed on time, on budget, with no injuries or safety issues.

2008 – 2009: Project Geophysicist – Eagle Mountain Dam and Levee, Lake Worth, Texas: Client: PB Americas Evaluation of the main dam and spillway levee structures using SP, electrical resistivity, time-domain electromagnetics, magnetics and seismic refraction tomography. Prepared integrated report on location and lateral extent of sheet piling (parallel to axis of each structure using magnetics), lateral material variations and locations of concentrated flow paths (along each structure using SP, electrical resistivity and time domain electromagnetics) and on location and lateral extent of cutoff wall (at spillway levee using seismic refraction tomography). Two separate projects completed on time, on budget, with no injuries or safety issues.

2009: Project Geophysicist – Warm Springs Dam: Client: U.S. Army Corps of Engineers Emergency mobilization and evaluation of severely leaking dam using SP. Prepared integrated report on lateral material variations and locations of concentrated flow paths for this embankment structure. Project conducted on short notice, completed on time, on budget, with no injuries or safety issues.

2009: Project Geophysicist – Cove Fort Reservations, Cove Fort, Utah: Client: Natural Resources Consulting Engineers Inc. Evaluation of a normal-fault basin structure and mapping of perched aquifers associated with subcropping faults and basaltic sills within basin sediments near Cove Fort, Utah, using large-loop Time Domain Electromagnetic (TDEM) soundings. Prepared integrated report on the basin structure as well as location, depth, lateral extent and lateral variations in conductivity associated with the presence of perched and compartmentalized fresh water aquifers within the basin sediments. Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection, interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2008: Project Geophysicist – City of Flagstaff, AZ Water / City of Show Low, AZ Water: Client: HydroSystems, Inc. Evaluation of a deep basin structure and aquifer near the cities of Flagstaff and Show Low, AZ, using the Controlled Source Audio Magneto-telluric (CSAMT) technique. Mapped the basin thickness/geometry as well as depth, lateral extent and lateral variations in conductivity associated with the presence of ground water within the basin sediments. Was responsible for shipping/travel/personnel/field logistics and data collection. Two separate projects completed on time, on budget, with no injuries or safety issues.

2008: Project Geophysicist – Alcoa Hydroelectric Development- Greenland: Client: PB Americas/Alcoa Mapping of depth to bedrock, rock quality, VS-30, elastic moduli and permafrost detection along approximately 9 miles of proposed dam, spillway and power tunnel structures in remote locations of Greenland. Proposed borrow pit sites were also evaluated. Project implemented frequency-domain electromagnetics, seismic p-wave refraction tomography and passive (ReMi) and active (MASW) surface wave soundings, and involved extremely challenging travel, safety logistics and terrain. Prepared integrated report on bedrock topology, potential locations and lateral extent of permafrost and zones exhibiting poor rock quality (parallel to axis of each proposed structure). Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection, data processing, interpretation, report

Rittgers, Justin B. 2019 Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

generation, presentation of final results and follow-up with client. Successfully evaluated proposed borrows locations. Project completed on time, on budget, with no injuries or safety issues.

2007: Project Geophysicist – Fort Knox Tailings Impoundment, Fairbanks, AK: Client: Fairbanks Gold Mining, Inc. Mapping lateral and vertical extent of seepage through the south abutment of the tailings impoundment with the use of Self Potential (SP) and time-domain electromagnetic (TDEM) soundings. Was responsible for survey design, shipping/travel/personnel/field logistics, data collection, data processing, visualization and interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2007: Project Geophysicist – Bay Harbor, Petoskey, Michigan: Client: Barr Engineering Evaluation of an EPA superfund site via 3D mapping of top of clay/shale bedrock affecting pollution-plume migration using large-loop Time Domain Electromagnetic (TDEM) soundings, seismic p-wave refraction tomography and seismic surface wave techniques. Helped to prepare an integrated report on bedrock topography and location of paleo-channels to aid in placement of pollution mitigation/interception wells. Was responsible for survey design, shipping/travel/personnel/field logistics, data collection, data processing, visualization and interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2006: Project Geophysicist – A.V. Watkins Dam, Box Elder County, Utah: Client: Bureau of Reclamation Emergency mobilization and evaluation of severely leaking dam using SP. Prepared integrated report on lateral material variations and locations of concentrated flow paths for this embankment structure. Project conducted on short notice, completed on time, on budget, with no injuries or safety issues.

2006: Project Geophysicist – Grant Ranch, Colorado: Client: Lottner Rubin Fishman Brown & Saul, P.C. Mapping of top of clay/shale bedrock and investigation of the presence of a suspected subcropping shear- zone affecting groundwater flow using the Dipole-Dipole technique of the Direct Current Electrical Resistivity (ERT) method, and seismic surface wave techniques. Helped to prepare an integrated report on bedrock topography and engineering properties of the bedrock. Was responsible for shipping/travel/personnel/field logistics, data collection, data processing, visualization and interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

ADDITIONAL RELAVENT NON-RECLAMATION PROJECT EXPERIENCE EXAMPLES:

2010: Project Geophysicist – Saddle Road Realignment Project, Hawaii, HI: Client: Geolabs, Inc. / Central Federal Lands and Highways Administration Mapping of depth to bedrock and regions of potentially problematic soft soils along several miles of a proposed Saddle Road realignment locations with the use of 2D passive (ReMi) and active (MASW) surface wave profiling and 2D seismic p-wave refraction tomography. Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection, data processing, visualization and interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2010: Project Geophysicist – HAVO-HALE, Hawaii and Maui, HI: Client: Geolabs, Inc. / Central Federal Lands and Highways Administration Mapping of geology and near surface voids beneath existing roadways and parking areas along several miles within the Hawaii Volcanoes National Park in Hawaii and the Haleakala National Park in Maui. The projects the use of a multi-channel and duel-frequency Ground Penetrating Radar (GPR) system. Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection,

Rittgers, Justin B. 2019 Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

data processing, visualization and interpretation, report generation, presentation of final results and follow- up with client. Two separate projects completed on time, on budget, with no injuries or safety issues.

2009: Project Geophysicist – Honolulu HHCTCP, Honolulu, HI: Client: Geolabs, Inc. / Central Federal Lands and Highways Administration Mapping of depth to bedrock and regions of potentially problematic soft soils along several miles of a proposed high-speed light-rail transit system with the use of 2D passive (ReMi) and active (MASW) surface wave profiling. Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection, data processing, visualization and interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2010: Project Geophysicist – Thurston Lava Tube, Hawaii Volcanoes National Park, Hawaii, HI: Client: YEH and Associates, Inc. / Central Federal Lands and Highways Administration Site evaluation and mapping of fractures and problematic/unstable regions of bedrock beneath the Thurston Lava Tube Overlook area for consideration during proposed remediation efforts. Project implemented 3D Ground Penetrating Radar (GPR) and 3D seismic p-wave refraction tomography. Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection, data processing, visualization and interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2009: Project Geophysicist – Old Stapleton Airport, Denver Colorado: Client: Mortenson Construction Conducted total field magnetic mapping methods (MAG) at the Filing 32 project area at the old Stapleton Airport in order to identify magnetic anomalies indicative of the presence and location of any deep structural foundation caissons left in-place and obscured by regraded fill during demolition of the original Stapleton Airport terminal and surrounding structures. Several in-place significant subgrade foundation components where identified throughout the site, helping the client avoid costly contracting change orders and other issues due to encountering unknown subsurface features during the planned construction phase of the development project. Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection, interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2009: Project Geophysicist – Guanella Pass Landslide Characterization, Georgetown Colorado: Client: YEH & Associates, Inc. Geophysical investigations conducted across an active landslide located above Guanella Pass road, in order to image and characterize the geometry and dimensions of the landslide lobe, and detect the depth and shape of the subsurface slip-plane for informing mitigation efforts. Was responsible for survey design, proposal preparation, travel/personnel/field logistics, data collection, interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2008: Project Geophysicist – Former Firestone Property, Lakewood, Colorado: Client: Terracon, Inc. Geophysical investigation conducted to detect the presence of any large underground metallic bodies or rebar reinforced structures which might be consistent with the presence of an underground storage tank (UST). To meet the project objectives time-domain electromagnetic (EM) and total-field magnetic gradiometery mapping techniques were employed. Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection, data processing, interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

Rittgers, Justin B. 2019 Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

2008: Project Geophysicist – Highway 6 and Highway 119, Jefferson County Colorado: Client: Yeh and Associates Geophysical investigation conducted above the intersection of Highways 6 and 119 near Blackhawk, Colorado, using 2D seismic p-wave refraction tomography for mapping the depth to bedrock, and assessing lateral and vertical variations in rock quality along the cliffs overlooking this intersection to aid in design of a bridge for animal migration over the highways. Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection, data processing, interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2008: Project Geophysicist – Wind Energy Facility 1, West Coast Region, South Africa: Client: Black & Veatch Corporation Evaluation of proposed wind turbine generator sites at a remote location in South Africa, mapping depth to bedrock, lateral and vertical distribution of shear-wave velocity, determination of small-strain elastic moduli and vertical distribution of electrical resistivity beneath select test sites to aid in foundation and grounding mat design. Was responsible for survey design, proposal preparation, shipping/travel/personnel/field logistics, data collection, data processing, interpretation, report generation, presentation of final results and follow-up with client. Project implemented 1D passive (ReMi) and active (MASW) surface wave soundings, 2D seismic s-wave refraction tomography and 1D electrical resistivity soundings.

2007: Project Geophysicist – US Highway 412 and US 64, Oklahoma: Client: Terracon Consultants, Inc. Detection of voids and karst limestone bedrock under existing and proposed alignments of Highway 412 and US 64 in Oklahoma using the Dipole-Dipole technique of the Direct Current Electrical Resistivity (ERT) method. Prepared interpreted geoelectric cross-sections correlated to borehole geology, and an integrated report on the location, depth, lateral extent of highly resistive features associated with the presence of large air-filled voids and/or extensive karst bedrock. Was responsible for survey design, shipping/travel/personnel/field logistics, data collection, data processing, visualization and interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2007: Project Geophysicist – Grover Wind, Grover, Colorado: Client: Ground Engineering Consultants, Inc. Ascertain elastic coefficients to depth of 100 feet to aid in foundation design for a large wind turbine farm. Used seismic p-wave & s-wave refraction tomography (and general reciprocal method analysis) and surface wave testing to derive 2D seismic velocity profiles to depth in order to compute elastic constants and provide VS-30 values. Work included furnishing data at 30 different sites and calculations of material properties to a depth of 100 feet. Was responsible for shipping/travel/personnel/field logistics, data collection, data processing, visualization and interpretation, report generation, presentation of final results and follow-up with client. Project completed on time, on budget, with no injuries or safety issues.

2005: Project Assistant – USGS Crustal Imaging and Characterization Team, Denver, CO: Supervisors: David L. Wright and Chuck Oden Assisted in the construction and field/lab testing of a low-frequency Ground Penetrating Radar (GPR) prototype system. Deployed the system at a prove-out site and performed utility location at various decommissioned nuclear reactors at the Idaho National Laboratory (INL). Was responsible for system fabrication and testing, data acquisition, data processing, data visualization.

Rittgers, Justin B. 2019 Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

MISCELLANEOUS EXPERIENCE:

2006 - 2010: Data Processing and System/Software Testing/Development – (Zonge) Processed several 3D seismic p-wave refraction tomography and 3D Electrical Resistivity Tomography (ERT) data sets applied to time-lapse resin injection/ground improvement monitoring, reactivated landslide evaluation and bedrock topology/slope stability analysis.

Testing of prototype seismic p-wave data acquisition system hardware/software. Evaluation of prototype seismic p-wave first arrival auto-picking and wave-domain tomography inversion software, providing feedback and results to developers.

2011-Present: Software Development – (Colorado School of Mines and Reclamation) -3D Straight-Ray Cross-Well Tomography software capable of synthetic velocity model generation, survey design, forward modeling, linear inversion and non-linear LP-Norm inversion. -Non-linear inverse approach to stable reduction-to-pole of magnetic data collected at low magnetic latitudes. -Seismic first-arrival auto-picker algorithms -Code for downhole seismic profiling -Code for processing and visualizing borehole deviation data -Code for crosshole seismic/Vs30 processing and crosshole tomography -Code for visualizing GPR data in tunnels and conduits -Code for calculating towed streamer locations versus time from GPS/offset data -Inversion software for 3D time-lapse (4D) modeling of self-potential data and redox potential imaging -Development of a new 4D acoustic emissions/seismic source localization algorithm -Development of a new Structural Joint Inversion Scheme referred to as automatic joint constraints (AJC) -Acoustic wave propagation code for developing full waveform inversion capabilities

Numerous Additional Project and Experience Examples Available Upon Request.

HONORS AND AWARDS: 2017: Reclamation Employee Performance Award 2006: CSM Phillip R. Romig Award 2016: Reclamation Employee Performance Award 2015: Mendenhall Award 2015: Invited researcher, TU Delft, NL 2003 – 2006: CSM Dean’s List 2011: Fullbright Scholarship Offer 2004 – 2005: Devon Energy Scholarship 2006: National Dean’s List 1997: Eagle Scout 2006: CSM E-Days Engineer Award

PUBLICATIONS: Rittgers, J.B., Butler, D., Sirles, P., 2008, Subsurface Void Detection in Oklahoma Evaporite Deposits Using Geophysical Methods, In Proc. of the 59th Annual Highway Geology Symposium: Santa Fe, New Mexico, May 6-9, 2008, pp. 445-468.

Rittgers, J.B., Thomas, M., Kelly, H., 2010, Detection of Structural Components and Seepage Zones at the Eagle Mountain facility Using Geophysics, In Proceedings of the 2010 Annual Association of State Dam Safety Officials Conference (ASDSO): Seattle, Washington, September 19-23, 2010.

Homan, M., Sirles, P., Rittgers, J., 2010, Geophysical Methods to Map Subsurface Evaporite Features to Aid Roadway Geometric Design, Prepared for Proceedings of the 61st Annual Highway Geology Symposium: Oklahoma City, Oklahoma August 23-26, 2010.

Rittgers, Justin B. 2019 Justin B. Rittgers 720-278-8160 | 422 S. Alkire St., Lakewood CO, 80228 | [email protected] | [email protected] | [email protected]

Rittgers, J.B., Sirles, P., Morelli, G., Occhi, M., 2010, Case history: Monitoring resin injections with the aid of 4D geophysics. In Proc. of Symposium on the Application of Geophysics to Environmental and Engineering Problems (SAGEEP), Keystone, Colorado (USA), April 11-15, 2010, pp. 379-390.

Rittgers, J. B., Revil, A., Karaoulis, M., Mooney, M., Slater, L., Atekwana, E., 2011, Self-potential signals generated by the corrosion of buried metallic objects with application to contaminant plumes, Geophysics, 78 (5), EN65-EN82, DOI: 10.1190/GEO2013-0033.1

Rinehart, R.V., Parekh, M., Rittgers, J., Mooney, M., Revil, A., 2012, Preliminary Implementation of Geophysical Techniques to Monitor Embankment Dam Filter Cracking at the Laboratory Scale, Proc. 6th Intl. Conf. Scour and Erosion, Paris, France, Aug. 27-31, 2012.

Ikard, S.J., Rittgers, J., Revil, A., Mooney, M., 2013, Geophysical Investigation of Seepage Beneath an Earthen Dam, GroundWater, Published Online, DOI: 10.1111/gwat.12185

Ikard, S., Revil, A., Rittgers, J.B., and Schaeffer, K., 2013. Time-lapse self-potential monitoring of advective NaCl migration to delineate seepage paths in a heterogeneous earthen dam. GroundWater.

Mooney, M.A., Parekh, M., Lowry, B., Rittgers, J.B., Grasmick, J., Koelewijn, A., Revil, A., Zhou, W., 2014, Design and Implementation of Geophysical Monitoring and Remote Sensing during a Full Scale Embankment Internal Erosion Test, Proc. Geocongress 2014, Atlanta, GA, Feb. 23-26, 2014, in press.

J.B. Rittgers, A. Revil, T. Planés, M.A. Mooney, A.R. Koelewijn, A., 2015, 4D imaging of seepage in earthen embankments with time-lapse inversion of self-potential data constrained by acoustic emissions localization, Geophysical Journal International, 200, pp. 758-772, doi: 10.1093/gji/ggu432.

Rittgers, J.B., Revil, A., Mooney, M.A., Karaoulis, M., Hickey, C., and Wadajo, L., 2015. Time-lapse joint inversion with automatic joint constraints, submitted to Geophysics Journal International.

Rittgers, J.B., 2015. Active and Passive Electrical and Seismic Time-lapse Monitoring of Earthen Embankments, Ph.D. Thesis, Colorado School of Mines, Golden, Colorado.

T. Planés, M.A. Mooney, J.B. Rittgers, et al., 2015. Time-lapse monitoring of internal erosion in earthen dams and levees using ambient seismic noise. Géotechnique, DOI: 10.1680/jgeot.14.P.268.

T. Planés, J.B. Rittgers, M.A. Mooney, et al., 2015. Monitoring the tidal response of a sea levee with ambient seismic noise. Submitted to Applied Geophysics.

T.L. Wahl, R.V. Rinehart, M.J. Klein, J.B. Rittgers, 2016. Visual and Photogrammetric Observations of an Internal Erosion Failure. Submitted to 6th International Symposium on Hydraulic Structures, Portland, OR, 27-30 June, 2016.

Rittgers, Justin B. 2019