A GEOPHYSICAL INVESTIGATION OF THE HYDROGEQLOGICAL CHARACTERISTICS OF THE UD-ELL HILLS AREA, MANISTEE COUNTY, MICHIGAN Thesis Ior the Degree of M. S. MICHIGAN STATE UNIVERSITY Richard L. Kellogg ‘ 1964: III III I III I 1qu I I 11le IIIIZIIIIII I 3 1293 1 Ammms‘é :11 02 .04 ‘ mbc3 10312303 SEII I 1" {$9355 ABSTRACT A GEOPHYSICAL INVESTIGATION OF THE HYDROGEOLOGICAL CHARACTERISTICS OF THE UDELL HILLS AREA, MANISTEE COUNTY, MICHIGAN by Richard L. Kellogg A geophysical investigation utilizing the seismic refraction and earth resistivity geophysical techniques was conducted in the Udell Hills area of Manistee County, Michi- gan. The objectives of the study were to obtain character— istic seismic velocities and electrical resistivities of representive glacial drift materials, to determine the thickness of the unsaturated overburden, and to delineate the configuration of impermeable clay layers Known to occur in the area from drill hole information. A total of 45 seismic and 24 resistivity profiles were made. The electrical resistivity well-logging method was attempted in several wells in the study area, but only one test gave usable data. The seismic refraction method generally indicated a two layer earth consisting of a surface layer composed of dry, well sorted sand, and an underlying layer composed of saturated sand. Surface velocities vary from 600 to '2,000 feet per second with an average of 1,140 feet per second, while saturated layer velocitieszmnmgefrom A,000 to 6,750 feet per second with an average of 5,460 feet per second. RICHARD L, KELLOGG Electrical resistivities obtained from the Mooney and Wetzel curve matching method and the Barnes layer method vary from a few thousand to several million ohm-centimeters. The Mooney and Wetzel method indicated all saturated resis- tivities are less than 75,000 ohm-centimeters while a sig- nificant number of unsaturated layers also have resistivi- ties in this range. CflueBarnesnmthod of interpretation in- dicated that the majority of resistivities less than 75,000 ohm-centimeters fall within the saturated zone. Resistivi- ties in excess of 250,000 ohm—centimeters as determined by both methods of interpretation, occur within the unsaturated zone. The interpretation of both the seismic and resistivity data indicates a ground water mound, with a total relief of about 100 feet, associated with the Udell Hills. Seismic results were found to be 10% in error when compared with control data, while resistivity results aver- aged 14% in error. The geophysical methods employed in the study were unsuccessful in detecting the clay layers. This failure may be attributed to the low resolving power of the seismic refraction and earth resistivity geophysical methods. In this area, the seismic method gave the most precise and diagnostic results; however, the resistivity method con- tributed to the study in corroborating the seismic Observations. A GEOPHYSICAL INVESTIGATION OF THE HYDROGEOLOGICAL CHARACTERISTICS OF THE UDELL HILLS AREA, MANISTEE COUNTY, MICHIGAN By Richard L. Kellogg A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Geology 1964 ACKNOWLEDGMENTS I wish to express my sincere thanks to Dr. William J. Hinze for his invaluable guidance, helpful suggestions and criticisms, and thorough study of all phases and portions of this paper. Thanks are also due to Dr. Chilton E. Prouty, Dr. Harold B. Stonehouse and George B. secor for their interest and helpful suggestions pertaining to this study. This investigation was made possible by grants from the Lake States Forest Experiment Station of the U. S. Department of Agriculture, Forest Service and the National Science Foundation through the Institute of Water Research, Michigan State University. These grants are gratefully acknowledged. Special acknowledgment is due to Dean H. Urie, Research Forester of the Lake States Forest Experiment Station who is directly reSponsible for laying out the investigation sites and surveying them and helping wherever possible with the field studies. Finally, I wish to thank John N. Roth, geophysics graduate student, who assisted in drafting the illustrations used in this report. 11 TABLE OF CONTENTS ACKNOWLEDGEMENTS LIST OF ILLUSTRATIONS. LIST OF TABLES INTRODUCTION GEOLOGY AND GEOGRAPHY. SEISMIC REFRACTION METHOD Refraction Theory Field Equipment Selection of Sites GeOphone Layout REDUCTION OF SEISMIC DATA RESISTIVITY METHOD Resistivity Theory. Field Equipment Site Selection Spread Layout . Electrical Resistivity well— -Logging SEISMIC INTERPRETATION , Introduction . Velocities of Representative Glacial Drift Materials . Depth to Water Table Analysis of Errors RESISTIVITY INTERPRETATION Introduction . Theoretical Methods . Empirical Methods . . Moore' 8 Cumulative method Barnes Layer method 111 Page ii viii \OCDNIO O\ J: 11 14 14 15 18 18 20 21 21 21 31 38 40 4O 40 41 41 41 Page Resistivities of Representative Glacial Drift Materials . . . . . . . . . . . . 44 Depth to Water Table. . . . . . . . . . 57 Analysis of Errors . . . . . . . . . . 59 SUMMARY OF THE INTERPRETATION . . . . . . . 63 Representative Seismic Velocities and Electrical Resistivities . . . . . . . . . . . 63 Thickness of the Unsaturated Overburden . . . 64 Configuration of Impermeable Clay Layers . . . 65 CONCLUSIONS. . . . . . . . . . . . . . 72 BIBLIOGRAPHY . . . . . . . . . . . . . 74 iv Figure U) \DCDNICMU‘l-I: 10. ll. l2. l3. 14. 15. l6. 17. 18. 19. 20. LIST OF ILLUSTRATIONS Location of Area of Investigation TOpographic Map of Area. Configuration of Current and Potential Electrodes, Wenner Setup Lines of Current Flow in a Layered Earth .Location of Seismic Sites Two Layer Time—Distance Graph. Two Layer Time-Distance Graph. Two Layer Time-Distance Graph. Two Layer Time-Distance Graph. Three Layer Time-Distance Graph Three Layer Time-Distance Graph Three Layer Time—Distance Graph Three Layer Time-Distance Graph . Histogram of Surface Layer Velocities Histogram of Saturated Layer Velocities Elevations of the Water Table by the Seismic Method. . . . . Water Table Map by the Seismic Method Fence Diagram--Seismic Method Moore's Cumulative Curve Resistivity and Lithologic Log of Well G—50 V Page 16 17 22 23 24 25 26 27 28 29 3o 32 33 35 36 37 42 45 Figure 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. Location of Resistivity Sites Resistivity versus Electrode Separation Curves-—Stations 1 through 4 Resistivity versus Electrode Separation Curves—-Stations 5 through 8 Resistivity versus Electrode Separation Curves--Stations 9 through 12. Resistivity versus Electrode Separation Curves--Stations 13 through 16 Resistivity versus Electrode Separation Curves—-Stations l7, 18, 20, 21 Resistivity versus Electrode Separation Curves-~Stations 22 through 2 Resistivity versus Electrode Separation Curves—-Station 19 . Histogram of Layer Resistivities by the Mooney and Wetzel Method . Histogram of Layer Resistivities by the Barnes Layer Method . . . . Histogram of Layer Resistivities by the Mooney and Wetzel Method, 0-250,000 ohm-centimeters . . . . . Histogram of Layer Resistivities by the Barnes Layer Method, 0-250,000 ohm—centimeters . . . Water Table Map by the Resistivity Method Fence Diagram-—Resistivity Method Comparison Chart-—Stations 1 through 6 Comparison Chart-—Stations 7 through 11 Comparison Chart-—Stations 12 through 14. vi Page 46 47 48 49 Figure Page 38. Comparison Chart-—Stations 15 through 17 . 69 39. Comparison Chart—-Stations 18 through 20 . 70 40. Comparison Chart——Stations 21 through 23 . 71 vii Table 1. LIST OF TABLES Analysis of Errors viii INTRODUCTION Present interest in the hydrogeological characteristics of the glacial drift aquifers of the Southern Peninsula of Michigan has focused attention on the application of geo— physical methods to the investigation of ground water condi— tions of this area. A detailed survey was undertaken in the Udell Hills area of Manistee County, Michigan, for the pur- pose of ascertaining the potential of geophysical methods in this application. The major objective of this study is the delineation of the subsurface geology and ground water drainage patterns of this area by the seismic refraction and surface resis- tivity geophysical methods. Specifically, the objectives of this study are as follows: 1. To obtain characteristic seismic velocities and resistivities of representative glacial drift materials, 2. To determine the thickness of the unsaturated overburden, 3. To determine the configuration of impermeable clay layers known to occur in the area from drill hole information. The area under study is located in the west-central part of the Southern Peninsula of Michigan, in Manistee 1 County (Figure 1). The area is roughly 3 miles in diameter and covers portions of sections 13, 14, 15, 22, 23, 24, 25, 26, and 27 of T21N, Rl5w in Manistee County. It lies roughly 15 miles east of Manistee, Michigan in the Manistee National Forest. A total of 45 seismic and 24 resistivity profiles were made. In addition, the electrical resistivity well—logging method was attempted in several wells in the study area, but only one gave usable data. UDELL EXPERIMENTAL FOREST / FIGURE I LOCATION OF AREA OF INVESTIGATION GEOLOGY AND GEOGRAPHY The Udell Hills rises to a maximum of 300 feet above the surrounding level sand plains. The feature has been interpreted as a glacial moraine of possible Valders age (Martin, 1955). The glacial drift in this area is believed $1 to be about 500 feet thick. The Udell Hills is composed I primarily of sand, but local gravel and boulder beds and clay lenses occur within it in no well defined pattern. The topography of the Udell Hills is rugged in com- parison to the surrounding area, with steep SIOpes occurring along the northwestern and southeastern flanks. The feature is marked locally by knob and kettle topography. Two promi- nent ridges occur, one along the northwestern perimeter and the other along the southeastern perimeter (Figure 2). A central valley of generally low relief occupies the depression between the ridges. The Udell Hills is forested except for occasional cleared fields. It is accessible by roads leading from State Highway 55 which connects the cities of Manistee and Cadillac. N 9.50.... .08. .83 . .08. .00 4<>mm.—.z_ map—.200 m<_2 o_In_._.ZDOU mmkm_z<_2 m.3_I DIED: .Z_NH .>> .3 .m .>> 9.x SEISMIC REFRACTION METHOD Refraction Theory In the seismic refractiOn method, the quantity observed is the time between the initiation of the seismic wave, and the arrival of the first wave at a series of detectors or geophones placed at measured distances from the shotpoint. The minimum time path, corresponding to the first arrivals is ordinarily considered in the theory. At detectors located close to the source of the seismic energy, the minimum travel path is a straight line in homo- geneous, isotropic material. For the case where a higher velocity mediumlhnderlies the surface material, a wave that has been refracted along the.interface will reach the sur- face at the same time as the direct wave at a distance from the shotpoint known as the critical distance. This occurs when the time lost in traveling the longer path is recovered by taking advantage of the higher velocity medium. Beyond the critical distance, the first arrival will be the wave that has been refracted along the surface of the underlying medium. These relationships may be readily extended to the case of two or more interfaces (Dobrin 1960, p. 74). Field Equipment The basic equipment used in the seismic refraction method consists of explosives for initiating a seismic wave, geophones which respond to the arrival of the wave, cables for carrying the electrical responses of the geo- phones, and a seismograph recorder which receives the impulses fromtfluageophones, amplifies them, and records them on film. The seismograph recorder used in this study was the Porta-Seis model manufactured by the Electro-Technical Laboratory Division of Mandrel Industries, Inc. Permanent records are made on Polaroid film which is readily devel- oped in the field. The instrument is a portable l2 trace unit with a built in blasting device which records the instant of detonation of the explosive charge on a separate trace. Timing marks interrupt each trace at 10 millisecond intervals. A 12.7 volt nickel cadmium battery supplies power to the galvanometer lamp. This battery was recharged following each days field operations. A truck mounted, general purpose seismograph was used where the required length of recording time was not avail- able on the Porta-Seis. Field operations with this instru— ment are time consuming and expensive; consequently it was used only when absolutely necessary. 8 Two geophone cables were used in this study. The shorter has 12 geOphone take-outs at 20 foot intervals, and the longer 12 take-outs at 100 foot intervals. Geophones having a peak output frequency of 7—1/2 cycles per second were used, with the exception of detec- tors on the far end ofquXKJfoot profiles where four cycle phones were used. A commercial blasting agent, detonated by a Special primer, was used for a seismic energy source in the majority of the survey. An electric blasting cap was used to detonate the primer, and the blasting agent. Ordinarily 60% dynamite was utilized occasionally when the blasting agent could not be obtained. Shotholes were drilled with a hand powered bucket type auger which, with the aid of an extension handle, could reach a depth of 12 feet. Although drilling in sand pre- sented no problems, drilling in clay and coarse gravels was extremely difficult, and sometimes impossible. Selection of Sites A series of seismic Spreads were made along a traverse running generally northwest from the Manistee ski area well to the base of the northwest upland ridge near Well l-l (Figure 5). Additional profiles were established at acces— sible points in the interior basin. The Specific location of each seismic Spread was determined by the objectives of the survey as well as by accessibility, tOpography, vegetation, and proximity to control wells. The topography is an eSpecially important factor in Shallow refraction studies in view of the effect it may have on the precision of the seismic results. Every effort, consistent with the objectives of the survey, was made to locate the seismic Spreads on flat or constantly sloping surfaces. Genrally, sites with less than 20 feet of variation from a constant slope were selected, but this was not always possible in the uplands area. A topo— graphic correction was applied to Spreads located in areas that did not conform to a flat or constantly sloping surface. Geophone Layout Seismic Spreads varied in length between 140 and 1000 feet depending upon the objectives of the particular profile. To determine depths uniquely, the shotpoint and distant geo- phone were interchanged, and reversed records were obtained. At the onset of the seismic program, symmetrical geOphone Spreads were employed by means of which the operators could shoot at both ends of the Spread without the necessity of picking up and redistributing the cable. However, it soon be- came evident from time distance plots of these spreads, that there was a lack of coverage in the important region near the shotpoint because of the wide spacing of the detectors used in the symmetrical Spread. Accordingly, Spreads were adjusted to obtain maximum coverage near the shotpoint, and to obtain a 10 minimum 3f three arrivals on each recorded layer, wherever possible. This goal was accomplished at the price of a Slight decrease in the overall efficiency of the seismic field program. The Spreads and geOphone Spacings were varied to avoid artificially filled areas and loose gravel which might cause erroneous results. GeOphones were placed in shallow holes from which loose surface materials had been removed. Elevations were surveyed at 100 foot intervals along each Spread, and in areas of rapid changes in elevation, at closer intervals. REDUCTION OF SEISMIC DATA The seismic refraction record shows the time delays between the detonation of the shot and the arrival of the first wave at the geophones. The basic data of the refraction method includes the relative time measurements taken from the record, the elevation and spacing of the geophones and shotpoint, and the depth of the explosive beneath the surface. The seismic data was initially plotted in the form of a time—distance graph with time as the ordinate and I distance as the abscissa. Following this the effects of the elevation of the geOphones, and the depth of the shot hole were determined by a graphical technique, and applied to the observed time delays. The corrected data were then treated analytically on a high Speed digital computer to determine the number of, depth to, and velocity of each individual layer. Although the computations made by the computer are unique, the final results are subject to the interpreters experience and judgment in removing the parameters used in the computations from the time—distance graphs. In addition, the seismic refraction method is subject to a number of geo- logical and seismic limitations which are discussed and related to this survey below. 11 l2 1. The velocities in successive layers increase as the depth increases. This assumption generally was met in this survey, the exceptions occuring where high velocity clay materials overlaid low velocity unsaturated sand layers. 2. Each layer transmits seismic waves at a constant velocity regardless of the direction of propaga- tion. There is no evidence to suggest that this assumption was not met in the investigation. 3. Each layer is bounded top and bottom by planes. This assumption is a fair approximation over the short spread lengths used in this study. 4. Each layer is sufficiently thick to be detected at the surface. No doubt this assumption was not met in several Spreads recorded in the up: land area where time-distance plots indicate a layer at one end of the Spread where it is thick, but not at the other, where it is too thin to be detected, or missing altogether. The first two assumptions are the most important, since variations from the ideal frequently are unrecognized and lead to gross errors in the results. Assumption three was taken into account in this study in the data reduction process. The fourth assumption was also taken into account in the data reduction wherever seismic evidence indicated a discrepancy in the number of layers detected at the surface. 13 This was accomplished by inserting a layer of minimum thickness to be detected at the surface and of velocity suggested by the results from adjacent areas. RESISTIVITY METHOD Resistivity Theory In the surface resistivity method of surveying, a known current is introduced into the ground through two current electrodes, and the resulting potential differ- ence is measured between pairs of potential electrodes. The quantity actually measured in resistivity surveying is known as the apparent resistivity. The apparent resis- tivity is defined as that resistivity which would produce the same ratio of potential drop to impressed current for the same electrode configuration when used in a homogeneous semi-infinite medium whose resistivity is equal to the apparent resistivity. Thus, the apparent resistivity is a weighted average of whatever layer resistivities may exist in the region through which the current flows. The apparent resistivity may be calculated from the following formula which applies to the Wenner elec— trode configuration, in which the electrodes are equidistant and colinear (Figure 3). = 21rA (17.) p I Where: apparent resistivity in ohm-centimeters, ‘0 ll 11> II separation of adjacent electrodes in centimeters, l4 15 V = potential in volts between the inner or potential electrodes (C and D of Figure 3), I = current in amperes between the outer or current electrodes (A and B of Figure 3). Figure 4 Shows lines of current flow between two electrodes in a two layer earth with a high conductivity layer, 62, underlying a low conductivity layer, 51. The depth of investigation is changed by varying the separation between the current electrodes. For the Wenner electrode configuration, the depth of investigation is often assumed to be equal to the separation of adjacent electrodes. Field Equipment The basic field equipment used in the resistivity method includes a resistivity meter for making measure- ments of V and I or the ratio g, electrodes, and associ- ated cables. The instrument used in this survey was a portable direct current resistivity meter manufactured by Keck and Associates, Okemos, Michigan. The ratio of E is obtained directly from a null reading ohmmeter after a bucking po— tentiometer has been adjusted to eliminate Spontaneous earth potentials. The power system consists of 45 volt "radio B" batteries which can be connected in series, to- gether with an ammeter which permits the current in the circuit to be monitered. Additional batteries may be added or withdrawn as necessary to keep the current at approximately the same level. l6 CONFIGURATION OF CURRENT 8: POTENTIAL ELECTRODES IIII K R| * RZ—fi A A A1 /////// //////// A D 3 k——r. r2 FIGURE 3 N EN EN ¢ mmaoi \DiW// b- \\\\ .\\\\\\\\\\\\\\\\\\\ 20:.0mm ommmbj < z_ 30...“. hzmmmno no mmz... \\\K 18 The electrodes were 4 foot lengths of 1/2 inch cold rolled steel. Electrodes were connected to the resistivity instrument by cables marked for positioning the electrodes at predetermined intervals. Site Selection Resistivity sites followed the same general traverse as the seismic Sites, with additional stations located in the interior valley. Selection of sites for the resistivity study was determined by the objectives of the study as well as accessibility, vegetation, topography, and proximity to control wells. Although tOpography probably affects the resistivity method less than the seismic method, there is no satis— factory way of correcting for terrain effects in resis- tivity surveying. Spread Layout The Lee modification of the Wenner electrode system was employed in this study. The Lee configuration utilizes an additional potential electrode E, placed at the center of the Wenner spread shown in Figure 3. With this arrange— ment, the sum of the potential drop between electrodes C and E and D and E will equal the potential drop measured between C and D if there are no horizontal variations in resistivity, dipping beds, or errors in the measurements. 19 Observations of the ratio of potential drOp to impressed current were made at a succession of decreasing electrode separations around a central electrode. Measure— ments generally were made beginning at a 280 foot separation between adjacent electrodes and decreasing to a 20 foot separation in increments of 20 feet. A 10 and a 5 foot Spacing completed the observations at each station. Measure— ments were made at each separation between the two outer potential electrodes as well as between the center and each outer potential electrode. A second set of measurements was then made with the current flowing in the opposite direction at each separation. In most areas, the earth immediately adjacent to each current electrode was saturated with a brine solution. This technique was necessary to decrease the contact resistance between the earth and the electrode, deSpite the fact that up to 580 volts was applied to the current circuit. An additional method for deCreasing contact resistance occa— sionally was employed. This technique involves replacing each current electrode with a ”multi point" electrode sys— tem in which a number of electrodes are connected together with jumpers. When using this technique, care was taken to arrange the electrodes so that they approximate a single large circular electrode, because a circular arrangement of electrodes produces a minimum distortion of the current lines (Jakosky 1960, p. 523). 20 Electrical Resistivity Well Logging Electrical resistivity well-logging was conducted with an instrument similar to that used in the surface resistivity studies plus a hand Operated well probe which was manually raised and lowered in the well. An electrode arrangement was employed in which one pair of current and potential electrodes is placed on the surface while the other pair is placed in the well. The pair of electrodes in the well were separated by 2.5 foot intervals, and readings were observed at 2.5 foot intervals as the probe was raised from the well. SEISMIC INTERPRETATION Introduction The interpretation of the results of the seismic portion of this survey includes the determination of the number of layers, the velocity of these layers, and the depth to the interfaces, as determined from calculations performed on the observed data. The interpretation, which is considered in terms of the Specific objectives of the survey, should be tempered by an understanding of the assumptions made in seismic refraction theory. These assumptions have been discussed and related to this study under the section "Seismic Method." Velocities of Representative Glacial Drift Materials The location of the seismic sites is shown on Figure 5. Two layers generally were detected by the seismic method. This is illustrated in Figures 6 through 9 which are examples of typical time—distance graphs obtained in the area. The first linear segment of the graph repre- sents travel times via the direct path through the surface layer. Beyond the critical distance, the second linear segment correSponds to travel times for the wave that has taken advantage of the higher velocity medium beneath the surface layer. 21 .Z_NH n 9.50.... bow. .oo_or. .oo_o~ [Sci mmtm oimfim .Iozz .>._.z:oo um._.m_z> 3.x 23 @ mesa.“— Iadmo woz<._.m_o.m> m2... owhommmoo ._. mun. I woz m2: owhommmoo bwwml woz<...m.a r [f I O m C 1 O E! . x\\\ x .\ I / .\ / / SGNOOBS-BWLL CON. 25 0 meGE Im m2; QMbommm—oo hum"... I moz<...m.o 0v. 0m. 00. om 00 0*. ON 0 x _ 4 _ H _ _ \0 .\. I /../ .80. 1 /// . \\\ -owo. x o I \ . loco xVA X \.\ /X/x \.\. /x L . _ . L t 00.. TIME - SECONDS .080?- 26 .060 '- .O40" I .020“ // L i I 40 80 I20 I60 DISTANCE - FEET CORRECTED TIME VS. DISTANCE FIGURE 9 I 200 GRAPH 27 0... . or. 6. mass... {$8 32596.? us: 35350 hmmm Iwoz<._.m_o a.” .o .o. ..0 ..¢ .. .. I 000. 100.. 0mm. 10cm. 00¢. SONOOBS-BWIJ. 28 _ . 9.30.“. 755.0 moz<.._.m.o.m> m2... omhowmmoo hwwn. I moz<._.m.o 000 00¢ 00m 00m 00. _ _ d _ a - / X/fl / . .\ ./. / O Q Q SONOOES-BWIJ. 0N_. 00.. 29 I j ' l .200[\ X \x \‘ . .IGO- . - ./ . m \ D 2 .I20” / x E O 0 DJ ‘1’ \ “2’ .osor— - .: .040 +- / . - o x\ 0 6-———§-‘————"— 4 \J I 0 00 300 400 50 DISTANCE - FEET CORRECTED TIME VS. DISTANCE GRAPH FIGURE l2 3O .I20 I I I I .080r .060” TIME-SEC. .040 - .020 - 5C l00 IUD 500 250 DISTANCE - FEET CORRECTED TIME VS. DISTANCE GRAPH FIGURE I3 3O .IZO I I I I .I00 .080 .060 TIME-SEC. .040 .020 0 5'0 To?) Elia—3200 250 DISTANCE - FEET CORRECTED TIME VS. DISTANCE GRAPH FIGURE I3 31 The surface layer consists of a dry, well sorted sand throughout most of the study area. The material beneath the surface layer is primarily saturated sand. In the interior basin and in the uplands, an intermediate layer was frequently detected by the seismic method. This layer is indicated on time-distance graphs (Figures 10 through 13) by the segment of intermediate Slope between the direct arrivals and the refractions from the saturated layer. This zone of intermediate velocity probably is a result of lithologic variations in the unsaturated material. The unsaturated layers excluding intermediate layers in this zone, have an average velocity of 1,141 feet per second, and a range of 600 to:2,000feet per second (Figure 14). The average velocity of the intermediate velocity layers is 2,140 feet per second. The saturated sand shows a velocity range of‘4fixx3to 6,750 feet per second, with an average velocity of 5,461 feet per second (Figure 15). Anomalously high velocities were occasionally recorded for both the unsaturated and saturated layers. These veloci— ties may be due to an increase in the clay content of the layers. Depth to Water Table The indentification of the water table was made on the basis of the results of the seismic survey guided by 32 .v. maze—n. .86 \.E >._._oo._m> mafia... mm“. mm. mmm. mm. mmm. mmm \\% \\ . N. \\\\ \ \\\\\\\\\\\\‘ \\\\\ ¢N l mu ILCILIODUJZO> NM I mw> 33 I5 FIGURE VELOCITIES - SATURATED LAYER \\\ \\\1§§ \\\\\\\1§§ \\\\\\\\ \1§§ \\\\\\\\I§§ \\\\\\I§§ LLIIUJODUJZO> b Jr I I I I I J I In IN ‘0 In v- to N - 0 I01- 9 VELOSCITY5 FT./SEC. 34 water table depths from well data. Figure 16 Shows the elevations of the water table obtained from the results of the seismic method, together with the elevations of the water table in each control well. The water table map prepared from the results of the seismic method and drilling data indicates a ground water mound associated with the Udell Hills centered in section 23 (Figure 17). 'This mound displays a total relief of about 100 feet over the area of investigation. A minor water table depression is indicated in the northwestern quarter of section 24. A fence diagram (Figure 18) isometrically projected N 45° W is useful for observing the Spatial relationships of the results of the seismic study. In particular, the relationship between the surface tOpography and the water table surface is evident from an examination of the diagram. The solid black line represents the horizontal datum from which elevations were measured. Surface elevations are Shown as dashed lines, while the water table is represented as alternating dots and dashes. Individual layers in the unsaturated zone have been omitted from the diagram. Each of the columns of the diagram represents a point of seismic depth determination. The ground water mound, previously noted, is evident from the diagram. In other areas, the water table generally follows the surface topography. :53 w. manor. 7 . booc .Z_NH .ooon .ooo~ _ a north! 0.2050 MI... >m meE. cut“; ..._0 mzo...<>m..m .122 .Czaoo $5.252 m._.__: .38: mm mm hm «mac ovk. . .1. EL. .8 :1 . «ch. . Ne». 1: at. n s «91 no? I . 2: r. .4 ans. ofiévo 3 v3 0'“. g. cos. 2:. oi. v2 0 n3 ~-v 5Q 02 . ~_o. m2. . $5.“... 1: m _ 55!. 3:. V N m N N N at. mph. :Ko of .86 8... v2... 313% . 0 m2, won. or.» am: o9. of. a: . — Sh Nch 5050 2!. 0n rvbno v2. . E, o: _ . 2L. . 02 at. 3-6 A: wt. I I oh m2 . c: SA. 5. a: m2 0!. DQN .0 .3 .>>¢_.m 50 h.meoE F . _ 5 ~ 25. o .QSv .68 Q3 . .o. .355. «858 81km: o.2m.mm m4: m...m<... mmbas hm .) . .2 .N H «A one). Q V N N .>> .v. .m .>> 0.x 3'! o. manor... F + 93250 20:03 .8. mm. .o... M. mIaom .205 owqdom 43.20580... .005 Ju>m4 um...z:00 mmhm_z<2 0.3.... 4.500 T II III /- I. I. ,- I. /// // /I. /. I. I ’- II' I. IIIIIII IL, 3 . .. . ,_ x . w x. I. I z / . . \ I\\ ‘ lfl.'.' \\ \ ‘ q'. \. . .. x x .\ . X A U'Ul' . ,L I, II % . . ll rIIIII_IIIII_‘\ . . . . . . .. rIII IJ 38 Analysis of Errors An analysis of the error between the interpolated and calculated depth to the water table for Spreads adjacent to seven control wells is given in Table 1. Linear interpola- tion between two wells was used to obtain the projected water table elevation at the position of the geophysical measurement (third column). The per cent error for the seismic observations is given in the final column. The average per cent error for the five cases in which seismic and geological conditions were amenable to the detection of the water table is 10%. The remaining two cases failed to detect the water table. This is probably due either to insufficient Spread length or to the existence of a low velocity zone. Several factors contribute to the percentage of error. First, the control wells are located a minimum of 100 feet, and a maximum of 740 feet from the points of seismic observation. Secondly, the linear interpolation process used to obtain the water table elevation of the seismic site may be in error. In addition, errors may arise because of the departure of the subsurface conditions from the assumptions which are made in seismic theory. TABLE I ANALYSIS OF ERRORS KIIAIISISGH JOJJH % otwsteg JOJJH % quewaanseew {eotsfiudoeg JO uotquetg adagang uotqueIH quem Jeqem fiatAIISIseH uotqueIg GIQQL Jeiem otwsteg eqeq 118M woas uotqueta etqet Jelem IIeM JO uotqueIH eoejans {ISM pue queweanseew teotsfiqd -oeg ueemqeg eoueistq uotqeufitseq 119M 23 14 29 17 24 764 806 952 863 900 886 733 756 720 733 767 736 752 741 762 NR NR 722 746 740 748 730 726 714 758 763 855 968 786 904 862 740 600 300 710 -R3 No. l 667 MSA Well G—5l Well 1—1 0-54 812-8 802—R 753 COLE [\CD Lf\_:r [\ [\ 815 100-S 540—R Lf\ Lfl 14% 10% Average Error RESISTIVITY INTERPRETATION Introduction The interpretation of the resistivity portion of this survey includes locating the depths of the interfaces between layers of contrasting resistivities, determining the number of layers, and obtaining resistivity values for these layers. All pertinent well data were integrated into the interpreta— tion, which is considered in terms of the specific objectives of this study. Various interpretive procedures have been develOped for mapping lithologic and structural variations from resis— tivity data. Interpretative methods employed in this study were of two basic types; theoretical and empirical. Theoretical Methods Theoretical methods employ some form of master curve computed from theoretical considerations. The field curve is superimposed on families of theoretical curves until a match is found. From the matched curves, resistivities and depths may be obtained. Only the Mooney and Wetzel theoretical curves were employed in this study (Mooney and Wetzel, 1956), because the various theoretical curve matching methods will give approximately equivalent results. 40 41 Empirical Methods Empirical methods used in this study include Moore’s Cumulative method and Barnes' Layer method. Meore's Cumulative method.--Moore's Cumulative method, which has no theoretical basis, involves plotting a summa- tion of resistivities at equal electrode intervals, against electrode separations. Straight lines are then drawn through as many points of accumulated resistivity as possible. Because earth materials usually consist of layers having different resistivities, two or more straight line segments ordinarily will be required to connect these points. The electrode separation at the point of intersection of two adjacent segments may be interpreted as the depth to an interface between materials of contrasting resistivities. The Moore's Cumulative method is essentially a graphical integration of the apparent resistivity curve. The method does not give layer resistivity values. It was applied in this study through separate interpretations with electrode intervals of 10 and 20 feet. Figure 19 is an example of a Moore's curve with an indicated depth of 94 feet. Barnes Layer method.-—The Barnes Layer method assumes that layers of earth material are analogous in behavior to a number of parallel connected resistors. Each resistor represents a Specific layer of earth material equivalent 42 I o I -< -I—<—-Iu>—mrn:0 7 ITI<—--II>I‘C§C3001>_ CUMULATIVE RESISTIVITY PLOT 94 FT.\\ 0 I- 0 0 0.5 h" ’36 P I l I, l I J l l I l l l, I 0 40 80 I20 I60 200 240 ELECTRODE SEPARATION (FT) FIGURE I9 280 43 in thickness to the separation of adjacent electrodes. The method essentially modifies the Wenner formula to remove the effect of the current flowing through the layers above. Values of resistivity obtained from the Barnes' method are relative to the true resistivity of each horizon. The resistivity of a Specific layer may be obtained from the following relationship (Barnes, 1954): Vn = 2nA ‘—————- pL In " Vn , Rn—l Where: I p = resistivity in ohm—centimeters of any individual L layer, A = separation of adjacent electrodes or thickness of layer in centimeters, In = current in amperes through the outer or current electrodes, Vn = potential in volts measured across the inner or potential electrodes, fin-l = average resistance in ohms of the layers lying between the surface of the earth and the bottom of the layer just above the layer being investigated, N = number of any individual layer. The interpretation of the Barnes' resistivities was based on the detection of Significant trends in the data. The values of Y used in calculating the Barnes' data were I obtained from Wenner curves smoothed to minimize the effects from near surface variations in resistivity. 44 Resistivities of Representative Glacial Drift Materials Electrical resistivity well—log measurements were attempted at several wells that had not reached the water table. However, the very high surface resistivities and limited current capacity of the instrument prevented usable data from being obtained except at well G—50 where the surface material is clay. Figure 20 is the electrical resistivity and lithologic log of well G—50 from a depth of 10 to 42 feet. The resistivities range from 80,000 to 260,000 ohm—centimeters. The geographic location of the resistivity Spreads is shown in Figure 21. Profiles of apparent resistivity versus electrode separation are Shown in Figures 22 through 28. In general, the curves Show high surface resistivities, and as the water table is encountered or the percentage of clay minerals increases, the apparent resistivity decreases. Electrical resistivities obtained by the Barnes' and Mooney and Wetzel methods of interpretation varied from a few thousand ohm—centimeters to values in excess of 2,500,000 ohm-centimeters. The higher values are associated with dry near surface sand, deficient in moisture. Lower resistivities are related to materials containing a greater percentage of moisture and/or clay minerals. The results of this portion of the study are presented in the form of a series of histograms. Figures 29emui30 Show 45 ts -I0 I l 8 a -IrrIrn-n z— I-I'omo I N OI I 01 0 ~35 RESISTIVITY OHM-CENTIMETERS x I0“ 6 8 I0 I2 I4 I6 IS 20 22 24 26 I I I I I I I I I I I WELL G-50 ELECTRICAL 8 LITHOLOGIC LOGS 2'3 3'0 0 SANDY CLAY REDDISH if CLAYEY SAND ~ I8 "-‘3' REDDI SH SAND 2| FIGURE 20 46 _~ #8.... 7 . . i .003 .88 .008 .000. o mmtm >..._>_...m.mm.m .10.: .Czsoo H.524: _ _ 3...: .33: 1mm: new: Am- _ _ .. _ _ _ I9: . 1%: Imml IAN- . _ .>>.u_.m vw. .>> m3”. IChuflfi 14 HI! I ‘ C ‘ MN 950.... .v I. mo....>..rm.mwm ‘CCCJ‘ d d d d d 1 00.0.2. @032 ‘q‘dI‘ 1 1 ‘ «413d 4 4 ‘11I11 1 II I dddll\1d.MI1 d~ diiqidJ q I 0mm .l..l..l n \ ../. ‘. L0?“ 6-6 832% \ .. _. II 00m 00. 4 0m. 4 .l 00 \ / Ill—ILLICI-m OOH-l mma...:>_»m_mum 4133‘ 4 1 fidddd ‘1 1 1 I I o o9... . . moi. e2... Iqu I I I I .IIII I N70 mot>;m__mmm D L b \ \—-— ‘ ‘. .0 \ ' ' m“fi'::---: 00... d_,e ~ -_ '\ \ '\ \ \\,~ ‘~ ~ '\ \‘ S \. .0...“ - —~———_——— J-g.—~ N \ . O¢N u.I-' ? A 00. ON. mqmor-moow mums! mm...— 02 . - O a) .0? a2.. .2... DU 32......m— .Il ..... D— Illnv_ mm manor.— 5‘ a d 4J4: q u a 0mm .Lo 5 3 0m. 0N. cm i ‘- nl ..... l”— \u 2..». 352% x .2. K x. \. .\.. w. 00‘. \\\ x z i x o .. \ x _ .... .\ ... x q. x. m N M ... m m w m. 1 x. ..T F m \T . E : . w 2; ..... u E u ..C \\x \.\.x. v ...... \\\..xxx ..... ...mmmkmzfizmouzxo C.>:m_mmm - n p p 00—”_. p p p n u p . DO—h—p . p L . . p . ¢°_h_. . . . n n p n ‘ qq¢dq 1 q q Jq<¢qq u.‘ a .\ qufiu-J 1 “II -¢¢¢uq d J . om” om manor. .\ ..2. \ .l.l.l....ON .\ x \ -----m. N M W \ .l..'..l..lb— _ \.. \ .N.ON.0_.N_ wo._._>_._.m_mwm O . . tonal... . - I ' I I I I dI I fi‘ T1 ‘ d I. 00.5 . ooh... I- . ‘ . - 2...... ..2 ...-.- . :1..- 08 III! 2. 2 In!- mw 2.~ ”.228: 2.. 22 ..... INN u ¢~-- mo2._>_.2.m_mwm O ..I. . - - m2022.2. I . - 2.20222. 2202.222 2\U .U \\ 514 mm>m30 Jthm>>2m 26200.2 >m mm.._._>_._.m_mmm mm><4 mm mmDGE mo. .2 mmmhwgkzuolZIo >2._>_.rm_mmm A m¢N.N mam; mVB mat. m¢N._ mmm. \\\3 \\3'1. mmm><12 owh 55 cor-PMS. mm><4 mmzmm mm_._._>_._.m_mmm mm><4 on Nana—“2 A gum-N mam. O. x mmwhmszkzmolzro ».E>_.rm_mmm @ mt... mmi. m¢N._ mm . vs. mm m v N. O $2222 .\.\\\..\\ \ awh 56 layer resistivities obtained with the Mooney and Wetzel theoretical curves and the Barnes' Layer method reSpectively. In both cases, saturated layers have resistivities of less than 250,000 ohm—centimeters. The unsaturated layers diSplay a considerably greater range. The differentiation of the saturated and unsaturated resistivities was based upon the interpretation of the data guided by results from the seismic method and well data. Figure 31 is a histogram of layer resistivities constructed by dividing the first interval of Figure 29 into subintervals of 25,000 ohm—centimeters. All of the saturated resistivities except one zone are confined to an interval of 75,000 ohm-centimeters or less. A significant portion of the unsaturated layers also have a resistivity of less than 75,000 ohm—centimeters. A similar situation pertains to the layer resistivities obtained with the Barnes' Layer method. The result of dividing the first interval of Figure 30 into subintervals of 25,000 ohm-centimeters is shown in Figure 32. The majority of the saturated resistivities are less than 75,000 ohm—centimeters. All of the resistivities less than 25,000 ohm-centimeters fall in this category. The detection of the clay layers, and hence the deter- mination of characteristic electrical resistivities of these layers, generally was not possible. The limited thickness in relation to the depth of these layers is believed to be responsible for this condition. 57 mu>m30 ..thmz, 2m >w2002 >m mmFSFmfiwm mw>2._>_.2.m.mum mde 8a.. @222... mm?— m¢N2 0mm. 922-. mmv. 92m 0 \\\ \\\ \\\ is. \ MM omk 58 0022.522 «553 mmzmm mm_._._>_.2.m_mmm cub: Nn manor. no. xmmwhmghzwolizo >2._>_._.w_mmm mmtm 923 m8. ms... $22.2 9%.. 8m. $2.. a.“ mew. o I 0 § E \\2 m. 822222.52: H 22 I o $2.2m 92222 89 92.: 8222 mHN. mmm. mi. 82.. mam. o I o m 7 /~// / u m 9:22.233 7 / Wm m V ILKUJCDLIJZU> 1 D... qJ - T4 ..........0_ ....... m. mm Mann-vi IIIIv2 I. ..... im— an. mc2._>.._.m_mmm o .. . - ..w-.i.. . .14.... no.2. 3...... 51¢ mm>m30 JMNHMBw >MZOOE >m mm_._._>:.m_mwm mw><12 mN mmeE 00. x mmMnghzonZIO >h2>2hw2mwm A m¢N.N mag 935 mm»: mVN._ mmm. 9K. 09». m2vN. O S \\Q mmw> 55 DOIkms. mm>m mm_._._>_._.w_mmm mm><4 Om ”mm—30$ mo. 2. wmmhmszhzonZIO »._._>_.2.m_mwm A m¢~.~ 82 22.2 $3 3.0... moxm.\\\mww. mmv 3%. o no §§ \\\\ H. \\\ M. 8:25:52: \\ MN. \\ no. no awkwZOOs. >m mm.._._>_._.m_mmm «mi: .0 mmnwfi O. xmmmhwghzwo 12:0 >h_>_hm.mmm .0. .mm“\\ $3 mew mew 82 m¢~\2 mam. a“ mac. mew o n o H \\ \\ \\ g \ H. H 3.255sz M 2. E . . 7272 owk 58 oozhms. tub: mmzmm wu_._._>_._.m_wmm_ mw><12 Nn muse—.... O. xwmwhmghzwolizo >C>_._.w_mmm 3% 93 mom. 9:... name. $2 26. we... 8V mew. o u o \g E \x w. 822.34sz M c I m 82.2 9.3 mam. mi... 83 Ha. mam. mi. 8.. New. 0 I o M Z a/ /A ///.. H. I I e H // /V / H. m 3:22.326 Hy// / mm m 7 H... l ‘2’ LLOEUJO‘DLIJZU>- 59 Depth to Water Table Figure 33 is a contour map of the water table prepared from the results of the resistivity method, together with well data. The map is constructed on the basis of the interpretation of the data as guided by the results of the seismic method and well control information. All of the methods of interpretation were used in preparing this map. However, the Barnes' Layer method was used most frequently because the results from this method were more compatible with seismic and well control data. A ground water mound is centered in section 23. This mound and the small depression in the western portion of section 24 are similar to features previously noted on the seismic map. The ground water mound has a total relief of about 80 feet over the area of study. Figure 34 is a fence diagram, isometrically projected N 45° W and constructed from the same results as those used for the contour map of the water table. The datum and symbols used in this figure are the same as those employed in the seismic fence diagram. The ground water mound is apparent from an examination of the diagram. In other areas, the water table generally follows the relief of the surface elevation. Analysis of Errors An analysis of the error between the predicted and calculated depths obtained from resistivity mapping is mm NEG-m 2 2 2 E .82. boom .88 .08. o .o. .2392. .259on oozhms. >.:>:.m.mmm n32 w..m<._. «H.222 .Io_s_ SFZDOO MMFQZS). @242: .2160: cm >/ ...N .Z_N.._. m2 v NN .>> 3.x <2 259$ 61 vn M259... X mcuzmoo 20.58 H on. .00. F .88 ..w I... m4u.. umg .. ........... 32... 5:43 ZO_._.<.2.mmn_mqu_ >.:>_._.m_mmm .1022 $22300 mmkm_z<2 $.32: 4.2mm: ...!Iiiiii...‘ 62 given in Table l, for seven profiles adjacent to control wells. The average per cent error for the resistivity determinations is 14%. This compares favorably with the average per cent error of 10% obtained for the seismic depth determinations. Depths obtained in resistivity surveying may be affected by a number of factors which should be considered in evaluating the accuracy of the method. First, the resistivity data are subject to uncertainties which are inherent in the subjective nature of the interpretation process. Further, as eXplained previously, the depth of current penetration is dependent upon the relative con— ductivities of the materials included in the zone of measurement. Therefore, the relationship may not be one to one between the depth of current penetration and the electrode separation. Finally, lateral variations in the conductivity near the surface may produce changes in the apparent resistivities which may be mistaken for major resistivity variations at depth. SUMMARY OF THE INTERPRETATION Representative Seismic Velocities and Electrical Resistivities The seismic refraction method generally detected a two layer earth. The surface layer is composed of dry, well sorted sand, while the material beneath the surface layer is believed to consist of the same material in a water saturated state. The seismic study frequently detected a third layer in the uplands and the interior basin. This layer may be attributed to minor lithologic variations in the unsaturated layer. Seismic velocities of the unsaturated layer, excluding intermediate velocity materials in this layer, range from 600 to 2,000 feet per second with an average velocity of 1,140 feet per second. The average velocity of the intermediate layers is 2,140 feet per second. The saturated materials range from.4,000 to 6,750 feet per second with an average velocity of 5,460 feet per second. Three methods of interpretation were employed in the resistivity study. These included the Mooney and Wetzel curve matching method, the Moore's Cumulative method em- ploying both 10 and 20 foot increments, and the Barnes' Layer method. Electrical resistivities obtained from the Mooney and Wetzel and Barnes' methods of interpretation vary from 63 64 a few thousand to several million ohm—centimeters. The Mooney and Wetzel method of interpretation indicated all of the saturated layers except one have resistivities of less than 75,000 ohm-centimeters. A significant number of unsaturated layers also have resistivities confined to this range. The Barnes' method of interpretation yielded results that are more definitive than the Mooney and Wetzel method. All resistivities less than 25,000 ohm-centimeters fall within the saturated zone. The majority of resistivities less than 75,000 ohm—centimeters also fall within this zone. Resistivities in excess of 250,000 ohm—centimeters as determined by both methods of interpretation occur within the unsaturated zone. Thickness of the Unsaturated Overburden The interpretation of both the seismic and resistivity data indicates a ground water mound associated with the Udell Hills. The mound is centered in section 23 and has a maximum relief of about 100 feet over the area of study. A minor depression is indicated in the northwestern quarter of section 24. In the resistivity study, all three methods of inter— pretation were employed to obtain the final map. However, the Barnes' Layer method was emphasized in the final inter— pretation, because the results from this interpretational technique were in better agreement with the seismic results 65 and well control data. A series of comparison charts are presented in Figures 35 through 40, which show the results of each method of interpretation together with the seismic results in the final column. The seismic results were found to be 10% in error when compared to well control information at five sites. The average per cent error for the resistivity interpreta- tion at seven control well sites was 14%. Configuration of Impermeable Clay Layers The geophysical methods employed in this study were unsuccessful in detecting the clay layers that are known to exist in this area from drill hole information. This failure can be attributed to the limited resolving power of the seismic and resistivity methods in detecting layers of limited thickness. The resolving power of these methods is a function of the ratio of the thickness of the layer to its depth beneath the surface. In the Udell Hills, this ratio is too small to permit detection of the clay layers. MOONEY a WE ZEL II I7 33 5xl 06 5x 4.5m4 PEI—I SM Lax IO 5.7xlo" l1 % 7I9xlo5 L9xlo“ NO FIT no 4.5xlo5 1.3x Io4 STA 6 UI N0 leo5 “’18 I.5*IO N04 AAAAAAAA A vav 30H F.— W EH AAAAAAAA 22 24 AA AAu‘AA 66 432— 34 48 30 30 AAAAAA‘A‘ 90‘ 22 V2=550€ 30 28 i VI=|O3O V2=5691 Vl=ll 90 =5050. W l - . ELEVATION 764 764 772 770 772 792 FIGURE 35 - 5 STAT lxIO 5.25.6" STAB ‘ I W 2.5on6 very low resistivitfl v‘vv VVVV I4 I4 27 IN I 3| {I I 28 I I ifl I6 I l i 20 ‘W 67 fl MOONEY 8 WETZEL MOORES IO MOORES 20 AA‘AAAAAA I57 'vvvvvvv AAAAAAAAAA‘ 32‘ 72‘ 23 m '0 afi— vu=|227 5.5M04 3° .5xlo4 32 no , V2=555| 2.0x I05 2x Io4 me F_. I.5x l06 E :on5 3M04 I5 2 30. I LZXIO" 24x :05 4x I04 VVVVVV 30 VI; l098 V2=48Ifl r___. Vl= II82 V2=54l8 {— M Vl= I467 32 V2=5l42 VVVVVVVV W FIGURE SURFACE ELEVATION 794 8|3 8|5 806 800 36 68 ‘ MOONEY" a""w"'E_—3"TZEL MO RES Io macaw—W20 ARNE I Ic “'2 8ms 2.6“05 ELEVATION II 5 '0 BIG 2., Ix I0 34 9on5 VI=II90 4 XI 5 3 0 Ion 49 vwwwvw 67 7c vz=5472 , 5on4 M 93 '50 3on4 WNVJ W 7W STAIS *——w —-'3 5.6xlo5 .0 Agni VI=9II 85" 5 I.9xI0 4M0 I9 27 5 64 30—— vaneg 5.6xI0 25XI05 50I'————'I WI MW 95—— :"VA'A'A'A’v 5 V 3 .. I32~—— 23"0 LAME? Bolasnoa' 90‘ LZSJIIO5 W W I50 AAAAAAAA STA I4 ,_ + , 5 6"0 6.7on 4 3on 50—4 [WNW IIc 3.3;”05 tS-fiSBI 90I———~- 9c soy—1+ Wm 2"0 W W I89 W I70 5 Ion 230W FIGURE 37 7on 69 P 7x Io‘5 I3 2.3on5 40 7x I05 8O 80 A--- -- - v--- ,; Vvvvvvv I.5on5 74.7on5 4.?! l06 4.7x Io4 AAAAAAAA VV v‘vvvv MOONEY 8 WETZEL MOORES IO 37 57 97 MOORES 20 '""“" 6| 28 AAAAAAA v vvvvvvvv AAAAAA A- BARNES 6.5M?" 31! I05 2M05 70 230 MW I I05 “ 4.5on ' 4x I05 W 'W' l5 2x Io6 230 AAAAAAAA 'vvvva“ "_5‘ Em... 20 2.5on5 5.5x Io5 90 3.8m? 2 .5x Io5 I30 I..25qu5 23G 7x Io4 SEISMIC SURFACE ELEVATION VI= 978 904 25 2=224l I57» vs: Vl=lll5 I 953 25 V2=2552 W Vl=l360 363 II2 v2=540 FIGURE 38 STAZO 55 28%— 7.4x I0“ 46» EAL?" l.7!l06 4 4 23“ WHO L71: l05 7U I.7on“ W STA I9 NO FIT 5 7.4" IO 2.5on5 7.4“ I7 23 70 MOONEYBIWETZEL MOORES Io M MOORES 20 Iszlfi IIjI BARNE S 1.3x Io6 3.7x I05 m . 3x Io“ I sz I06 6on I70 30 IIO 250 Son“ I I.5Xl04 ‘ I 9on5 4x I05 I I 5.? <2 IIJI 7.5x Io‘5 7M0“ ‘ FIGURE 39 I5 22 I76 I= I492 V2=2l75 V36'M6 AA AAAAAAA v vvvvv SE'ISMIC SURFACE I' ELEVATION 7 8 8 808 865 71 STA 2| 2| 83 MOONEY Q I.2x Io6 4u I05 V'vvvvv §TA 23 73‘ AAAAAA V'Vvvvv 2.6m” TZEL MOORES IO 34 ‘— 79 NMAAAA V'Vvvvv BARNES MOORES 20 I.5on6 2x I05 74» 9O 6.5 " IO I I 40 Am“‘- vvvvvvvv YVV‘V‘VV I89 —-—— AAAAAAAA V'Vvvv “A‘AAAAA A‘AAMAAA‘ 65———1 SEISMIC VI= I29I 34 94 VZ=2400 AAA‘AA‘A Vvvvvv VI=II46 26 V2=2I9I V326“ AA‘AAAA‘A Vvvvvv VI= IBSOI ‘AAAAA“AA FIGURE 40 Vvvvvvvvvv SURFACE ELEVATION 900 886 8I2 CONCLUSIONS The seismic refraction and electrical resistivity geophysical methods were successfully applied to the determination of representative seismic velocities and electrical resistivities, and to the depth of the unsaturated overburden. The methods failed to detect the impermeable clay layers. The results of the seismic velocity study indicate a marked difference between the velocities of unsaturated and saturated layers. The electrical resistivities of saturated materials differ from the unsaturated layer values, but their ranges sflunv considerable overlap. A ground water mound with approximately 100 feet of relief was found associated with the Udell Hills. The peak of the mound is centered in section 23 and a minor depression is located in the northwest quarter of section 24. In this area, the seismic method gave the mostpmecise results when interpreted in conjunction with control well information. The resistivity method, the interpretation of which is generally more subjective than the seismic method, nevertheless contributed to the study and supplemented the seismic observations. 72 73 The seismic and resistivity geOphysical methods in conjunction with control well information, was an effective tool for determining the thickness of the unsaturated over- burden and delineating the ground water divides in the Udell Experimental Forest. BIBLIOGRAPHY BARNES, H. E. (1954) Electrical subsurface exploration simplified: Roads and Streets. DOBRIN, M. B. (1960) Introduction to Geophysical PrOSpecting, New York, MCGraw-Hill. JAKOSKY, J. J. (1960) Exploration Geophysics, Trija Publishing Company. JOHNSON, R. B. (1954) Use of the refraction method for differentiating Pleistocene deposits in the Arcola and Tuscola quadrangles, Illinois: Illinois State Geol. Survey; Report of Investigations No. 176. LINEHAN, D. (1952) Seismology applied to shallow zone research: Am. Soc. for Testing Materials, Spec. Tech. Pub. No. 122,;uL 156-170. MARTIN, H. M. (1955) Map of the surface formations of the Southern Peninsula of Michigan: Geological Surviy Division, Department of Conservation. Pub. No. 9. MOORE, R. w. (1945) An empirical method at interpretation of earth resistivity measurements: "Geophysical Prospecting 1945, "Trans. Am. Inst. Min. Met. Eng., vol. 164,;ux 197-214. ROMAN, I. (1951) Resistivity reconnaissance: Am. Soc. for testing Materials, Spec. Tech. Pub. No. 122, pp. 171-220. 74 "IIIIIIIIIIIIIIIIIIIII