Characterization of a Dipole Flow System Using Point Velocity Probes. Copyright 2010 Ian Reed Bowen B.S., University of Kansas, 2008

Transcription

1 Characterzaton of a Dpole Flow System Usng Pont Velocty Probes BY Copyrght 2010 Ian Reed Bowen B.S., Unversty of Kansas, 2008 Submtted to the graduate degree program Department of Geology and the Graduate Faculty of the Unversty of Kansas n partal fulfllment of the requrements for the degree of Master of Scence Dr. J.F. Devln, Char Dr. Jennfer Roberts, Commttee Member Dr. Don Steeples, Commttee Member Date Defended: November 22, 2010

2 The Thess Commttee for Ian Reed Bowen certfes that ths s the approved verson of the followng thess: Characterzaton of a Dpole Flow System Usng Pont Velocty Probes Charperson Dr. J.F. Devln Dr. Jennfer Roberts, Commttee Member Dr. Don Steeples, Commttee Member Date approved:

3 Abstract A drect groundwater velocty measurement tool, the Pont Velocty Probe, was developed to measure veloctes n the vertcal and horzontal drectons. The tool was desgned and tested n a low-cost laboratory flow-through tank. Followng testng, the tool was deployed n the feld surroundng a dpole well used to conduct an aqufer tracer test. The velocty data showed some devatons from modeled behavor and was used to characterze the heterogenety of the aqufer. The results from the flow and transport modelng suggest that the area very close to the well was extremely mportant to the behavor of tracers n the dpole flow system. Fnally, a smple model was developed to optmze hydraulc conductvty usng the velocty data wth good results.

4 v Acknowledgements I would frst lke to thank my advsor, Dr. Rck Devln, for the mentorshp, revew efforts, and all the other work over many years and several projects. However, t s your frendshp that I apprecate most, so thank you. I must also thank Dr. Nel Thompson, Unversty of Waterloo, for provdng me the opportunty to perform ths study. Ashley Matha and Kat McLean, also at the Unversty of Waterloo, deserve specal recognton for spendng countless hours n the feld collectng data. Thank you to Peter Schllg for all the help, tranng, tme and lfe savng advce. If t weren t for you, I wouldn t know how good I had t. One of these days we mght fnally buld that deck. Thank you to Alek McElroy for your help n laboratory testng of the mn-pvps. Many other people at the Unversty of Kansas provded assstance on ths project. I would especally lke to thank Dr. Jennfer Roberts for revewng, teachng, and mentorshp. I d also lke to thank Dr. Don Steeples and Dr. Legh Stearns for ther help revewng ths manuscrpt. Several other people at the Unversty of Waterloo deserve recognton. Bob Ingleton, Paul Johnson, Steve Cha, and Terry Rdgway helped assemble, nstall, and troubleshoot equpment and made my lfe much easer whle n Ontaro. Fnally, I must thank my wfe, my frends, and my famly for always beng there when I needed support. Ths work was funded by Dr. Nel Thompson at the Unversty of Waterloo.

5 v Table of Contents Abstract... Acknowledgements.. v Table of Contents... v Lst of Tables v Lst of Fgures x Chapter 1: Introducton 1 1.1: The mportance of Groundwater Velocty.1 1.2: The Scale Dependence of Groundwater Velocty Measurements : The Dpole Recrculaton Well and Reactve Tracer Test : Thess Objectves..7 Chapter 2: A Smple, Low Cost, Leak Resstant Flow Through Tank : Introducton : Methods : NeST Desgn : NeST Constructon and Packng : Tracer Tests : Porosty Estmaton : Results and Dscusson : Conclusons 15 Chapter 3: Development and Laboratory Testng of a mn-pvp : Introducton.25

6 v 3.1.1: Conventonal Estmaton of Groundwater Velocty : Materals and Methods : Expermental Procedure : Results and Dscusson : Conclusons 35 Chapter 4: Velocty Characterzaton of the DFRTT : Introducton : Ste Descrpton : PVP Constructon and Theory : PVP and Well Installaton : Dpole System : Feld Methodology : Dpole Operaton : Velocty Feld Characterzaton : Results and Dscusson : Conclusons 56 Chapter 5: Parameter Optmzaton Usng Velocty Data : Introducton : Model Development : Results : Conclusons...72 Chapter 6: Conclusons and Recommendatons : Conclusons...77

7 v 6.2: Recommendatons...79 References.81 Appendces 87

8 v Lst of Tables Table 2.1: Parts Requred n the Constructon of a NeST..16 Table 2.2: Summary of the velocty estmates acqured usng the NeST.17 Table 3.1: PVP Reproducblty 36 Table 3.2: Summary of PVP Results..36 Table 3.3: Comparson of PVP and Tracer Test Results...37 Table 3.4: Summary of Vertcal Velocty Data..37 Table 5.1: Hydraulc conductvty values used n velocty optmzaton.73

9 x Lst of Fgures Fgure 2.1: NeST Schematc 18 Fgure 2.2: Constructon of the NeST.19 Fgure 2.3: Complete NeST wth PVP 20 Fgure 2.4: Vsual Tracer Test.21 Fgure 2.5: Example PVP and Contnuous Tracer Breakthrough Curves...22 Fgure 2.6: Modeled Equpotentals of the NeST.23 Fgure 2.7: Comparson of Velocty Estmates.24 Fgure 3.1: Mn-PVP Schematc.38 Fgure 3.2: Example PVP Breakthrough Curves..39 Fgure 3.3: Expected and Measured Velocty Comparson 40 Fgure 3.4: PVP Orentaton for Vertcal Velocty Testng...41 Fgure 4.1: DFRTT Feld and Model Comparson 57 Fgure 4.2: DFRTT and Well Skn PVP Schematc..58 Fgure 4.3: Dpole Velocty Characterzaton Experment Desgn..59 Fgure 4.4: Comparson of Normalzed DFRTT Model and Feld Data Fgure 4.5: Velocty Results n Cross Secton...61 Fgure 4.6: Velocty Results n Plan Vew..62 Fgure 4.7: Hydraulc Conductvty Profle of Dpole Well 63 Fgure 4.8: Modeled Breakthrough Curves wth Dstal Heterogenety..64 Fgure 4.9: Hgh K near well Velocty Results n Cross Secton.65 Fgure 4.10: Modeled Breakthrough Curves wth Proxmal Heterogenety.. 66 Fgure 4.11: Comparson of Improved Model and Feld DFRTT Data...67

10 x Fgure 5.1: Locatons of PVPs wth Devatons from Ideal Behavor.73 Fgure 5.2: Model Doman Showng Hydraulc Conductvty Zones..74 Fgure 5.3: Optmzed Velocty Results Comparon.75.

11 1 Chapter 1: Introducton 1.1 The Importance of Groundwater Velocty n Aqufer Characterzaton Accurate ste characterzaton has always been a necessary step n contamnant remedaton. As technology has advanced, more detaled stespecfc data have become necessary. The rse of passve n stu remedaton strateges has placed an emphass on understandng groundwater velocty patterns at stes, and the role velocty plays n contamnant transport (Gavaskar, 1999; Labaky et al., 2007). Detaled groundwater velocty data can be obtaned wth the Pont Velocty Probe (PVP), whch s capable of drectly measurng groundwater velocty at the centmeter scale wthout a well (Labaky et al., 2007). Ths nvestgaton has centered on furtherng the development of the Pont Velocty Probe n the laboratory and feld. Frst, a laboratory testng apparatus, the Nested Storage Tank, was desgned and constructed to provde an nexpensve bench top devce for testng the PVP (Chapter 2). The Nested Storage Tank was used to laboratory test a new PVP desgn capable of measurng horzontal and vertcal flow (Chapter 3). Followng testng, the PVP was deployed around a pumpng well to characterze a dpole flow system (Chapter 4), and the velocty data measured were used to optmze hydraulc conductvty nformaton n a smple flow model (Chapter 5). 1.2 The Scale Dependence of Groundwater Velocty Measurements Characterzng groundwater velocty s very mportant for determnng contamnant transport pathways and resdence tmes n remedaton systems.

12 2 The need for small-scale estmatons s partcularly mportant when n stu remedaton schemes are employed because contamnant mass dstrbuton wthn a plume s hghly varable spatally and temporally (Morkn et al., 2000; Gulbeault et al., 2005). Gulbeault et al. (2005) showed a 15 cm samplng nterval was necessary to characterze mportant centmeter scale features n several plumes. Whle these varatons are related to heterogenety, the heterogenety s equally related to hydraulc conductvty, K, and therefore groundwater velocty. Even f K can be measured and the dstrbuton defned at ths scale, other hydraulc parameters necessary to calculate velocty such as hydraulc gradent are unlkely to be fully measurable at the same scale. Ths has negatve mplcatons for remedaton desgn (Gerczak et al. 2006). As alluded to above, conventonal methods for determnng velocty are largely based on ndrect estmates usng Darcy s Law (Fetter, 2001). The method nvolves a calculaton requrng knowledge of the hydraulc gradent, the hydraulc conductvty and porosty for a ste (or specfc locaton). These parameters may be dffcult to estmate accurately and precsely for small areas such as those assocated wth contamnant transport and remedaton treatment zones. The ndrect technque s usually consdered lmted by the need for accurate aqufer K estmates (Ballard, 1996; Butler, 1997). Representatve K values are dffcult to obtan because ths property can vary by orders of magntude over short dstances, and values may also vary wth the type of measurement method used (Sudcky, 1986; Butler, 2005). K s typcally

13 3 estmated wth pumpng tests, slug tests, or laboratory core analyss. In a pumpng test, a large volume of aqufer s sampled and provdes a relatvely large scale average estmate of the K. However, aqufer tests do not provde the detaled nformaton about the varatons n K at a scale relevant to many contamnant transport nvestgatons (Butler, 2005). Slug tests estmate K close to a well, and hgh-resoluton slug tests are capable of provdng K profles at small ntervals (approxmately 10 centmeters) (Labaky, 2009). Aqufer materal obtaned from cores can also be used to provde very detaled K dstrbutons (usually centmeter-scale vertcal dstrbutons) (Sudcky, 1986). Whle the samplng ntervals of slug tests and core analyss are small enough to provde nformaton relevant to treatment zones, they requre an extensve samplng network to properly characterze heterogenety, and the K dstrbutons are nsuffcent on ther own to permt a velocty feld to be defned. Once K s well defned, the calculaton of veloctes may be lmted by the qualty of hydraulc gradent estmates. The error assocated wth the measurement of hydraulc heads may lmt the precson wth whch an hydraulc gradent can be determned. For example, Devln and McElwee (2007) reported work nvolvng a hghly conductve aqufer n whch the gradent could not be determned relably over a ~500 m 2 regon. The lmtatons of ndrect velocty determnaton can be overcome by drect velocty measurements. Whle the Pont Velocty Probe was selected for the work descrbed n ths thess, a number of other technologes exst that mght be useful n other stuatons. Examples that have receved notable attenton n the

14 4 past nclude the collodal borescope, borehole dluton, the VECTOR Groundwater Flowsensor, the Geoflo meter, and natural and forced gradent tracer tests (Ballard, 1996; Kearl 1997; Labaky et al., 2009). The technologes lsted above operate at a varety of scales. The PVP s dscussed n detal n Chapter 3 and operates at the centmeter scale. The collodal borescope velocty estmate could be averaged over a volume as small as 1 mm 3 as estmated by Ballard (1996), however f many measurements were averaged, the effectve scale could be larger (Kearl, 1997; Labaky et al., 2009). Borehole dluton has been used to determne velocty profles n wells at small ntervals (tens of centmeters), but s lmted to horzontal veloctes (Ptrak et al., 2007). The scale of the velocty estmates generated by the VECTOR Groundwater Flowsensor and the Geoflo meter are lmted by the szes of the nstruments, or the well screens n whch they operate. In the case of VECTOR Groundwater Flowsensor, the tool s 75 cm long. Ballard (1996) suggests that the VECTOR Groundwater Flowsensor provdes a velocty estmate averaged over a nearly 1 m 3 volume whch s contrasted wth a 1000 cm 3 volume for the Geoflo meter. Fnally, tracer tests nvolve the njecton of a tracer nto the subsurface and montorng ts transport due to ambent or forced groundwater flow. Ths type of test yelds veloctes that are averaged over the dstance between the measurement ponts (often 10s of meters)

15 5 1.3 The Dpole Recrculaton Well and Reactve Tracer Test The feld test of the new PVP desgned n ths work nvolved mappng the velocty feld around a dpole recrculaton well. A dpole well s one that both njects water to the subsurface and wthdraws t, so flow recrculates through the aqufer around the standppe. To create the dpole well used n ths work, packers were used to solate two sectons of a contnuous well screen so that water could be njected through one and extracted from the other. Ths resulted n a recrculatng system wth both horzontal and vertcal components to flow n the surroundng aqufer. Such flow systems are dffcult to characterze expermentally because the flow pattern s both complex and concentrated n a relatvely small volume. Unless flow rates are substantal, conventonal methods of trackng groundwater movement,.e., usng hydraulc head measurements, are lkely to be nadequate n a system lke ths. Therefore, the dpole flow system provded an deal locaton to test PVPs. Practcal uses of the dpole packer apparatus nserted nto a well nclude the acquston of K profles wth depth, and the assessment of mcrobal actvty n an aqufer through the use of reactve tracers (Reha, 2006; Roos, 2009). Wth the latter use n mnd, a flow model was created to smulate and match conservatve and reactve tracer breakthrough curves from a feld test termed the Dpole Flow and Reactve Tracer Test, DFRTT. In prelmnary work, the results of DFRTTs at the CFB Borden ste, n Ontaro, Canada, suggested that a homogeneous aqufer model was nsuffcent to replcate the expermental breakthrough curves. The DFRTT breakthrough data showed earler arrval

16 6 tmes than expected from the model, as well as dscrepances n the tal of the breakthrough curves (Roos, 2009). Determnng the area of nfluence of a dpole well s a common goal of studes nvolvng these technologes. The results of prevous work are mxed, but most suggest the area of nfluence s dffcult to characterze and usually smaller than predcted usng groundwater models (U.S. EPA, 1999; U.S. EPA, 2000; Johnson and Smon, 2007). Factors contrbutng to ths nclude ansotropy and heterogenety of the formaton that are not properly taken nto account n the models. However, lmtatons n the numercal models themselves may also contrbute to these dsagreements (EPA, 1999; Johnson and Smon, 2007). At least one prevous study has reported drect measurements of groundwater velocty surroundng a dpole well (Johnson and Smon, 2007). In that case, the veloctes were measured wth the VECTOR Groundwater Flowsensor, whch operates by relatng temperature dstrbutons on a 0.75 m to 1 m long heated, cylndrcal probe to groundwater velocty. The Vector Flowsensor was not able to relably measure vertcal veloctes and therefore much of the flow system n that work could not be adequately defned (Su et al., 2006; Johnson and Smon, 2007). The authors remarked on the ther dsappontment n the qualty of the drect velocty measurements, and the nablty of the flow system mappng to establsh a hydraulc connecton between the extracton and njecton portons of the capture zone. At least some of the problems assocated wth ths attempted mappng exercse may have been due to the scale of the velocty measurements.

17 7 Most of the methods avalable for makng groundwater velocty estmatons provde an estmate of velocty averaged over a scale too large to be helpful n characterzng flow around the DFRTT. The PVP s a promsng tool that provdes measurements at the centmeter scale usng a low-cost, easy to nstall probe that s able to return velocty estmates n a reasonable tme frame (wthn 1 day) (Labaky et al., 2007; Devln et al., 2009). Ths tool s one of the few capable of measurng vertcal and horzontal veloctes at the centmeter scale allowng the characterzaton of a dpole nduced flow system n unprecedented detal. 1.4 Thess Objectves The objectves of ths thess are to: 1. Desgn, construct, and test a smple, nexpensve, and leak resstant apparatus sutable for creatng a controlled flow system n a porous medum at the benchtop scale. The apparatus s to be used n achevng objectve 2, below. 2. Desgn, construct, laboratory test, and feld-test a prototype PVP capable of measurng horzontal and vertcal flow. 3. Desgn, construct, and feld-test a devce capable of measurng groundwater velocty n the well skn of an operatng dpole well. 4. Characterze the flow system around a dpole well to assst n the smulaton of tracer movement n the aqufer durng a DFRTT wth a numercal model.

18 8 Chapter 2. A Smple, Low-Cost, Leak-Resstant Flow Through Tank 2.1 Introducton Laboratory nvestgatons nvolvng flow and transport are essental for understandng many groundwater systems because they provde a controlled envronment n whch to study flow and transport (Sllman, 1998; Danqugny et al., 2004). The most mportant benefts to of these tests are that the boundary condtons and propertes of the porous medum can be hghly constraned and smplfed, or at least characterzed n great detal (Sllman, 1998). Laboratory models allow selected processes to be solated and studed under controlled, repeatable condtons and are less expensve than feld experments (Sllman, 1998; Danqugny et al., 2004; Close et al., 2008). The purpose of ths work was to develop a low-cost benchtop tank system to study flow and transport, hereafter referred to as the Nested Storage Tank (NeST). Many laboratory-scale aqufer models have been developed snce Darcy s (1856) column experments. Flow and transport experments are stll commonly conducted n one-dmensonal columns (Sternberg et al., 1996; Watson et al., 2002; B et al., 2009), but for some nvestgatons one-dmensonal flow s nsuffcent to meet the expermental needs. For example, two-dmensonal physcal models, often used to vsualze flow systems, have been used to study the effect of heterogenety on transport (Sllman et al., 1998; Barth et al., 2001). There have also been physcal models developed to study radal flow around

19 9 wells (Smpson et al., 2003). Fnally, A varety of tanks to study threedmensonal flow have been developed. Most are of benchtop scale (Danqugny et al., 2004), such as the one presented n ths artcle, but there are also several large smulated aqufers reported n the lterature (Close et al., 2008; Lee et al., 2008; Kobus et al. 1996). A drawback to the use of benchtop tanks s that they are not commercally avalable, except for some small teachng kts. Custom bult tanks are moderately costly to buld, and are often subject to leakage. In some tank desgns, unform flow s not acheved (Patterson et al., 2010). The NeST, whch can be easly constructed for about $50 from readly avalable parts, usng common tools, was demonstrated to create a hghly unform flow system, and was used to compare and contrast several methods of estmatng average lnear veloctes n porous meda. 2.2 Methods NeST Desgn The NeST uses a three-compartment system consstng of two open water reservors and an ntermedate porous medum contaner. In the experments performed for ths project, water was pumped at a constant flow rate between the open-water reservors, creatng an hydraulc gradent and consequently flow through the porous medum. The frst compartment conssted of a tall plastc storage contaner n whch hgh water levels could be mantaned. The second compartment, later packed wth a porous medum, was connected to the frst wth

20 10 9 short, plastc rrgaton fttngs dstrbuted evenly over the entre upgradent sde of the contaner. The frst two compartments were seated nsde the thrd, whch receved flow from the porous medum compartment through about 400 small holes drlled nto the downgradent end of that contaner (Fgures 1 and 2). Sand was contaned wthn the second compartment by lnng the rrgaton fttngs and the effluent end of the compartment wth Ntex mesh. Because all the compartments were made of sngle peces of molded plastc, the potental for leakage was very low NeST Constructon and Packng The NeST desgn makes use of nexpensve, readly avalable plastc storage bns, rrgaton ppe-fttngs, and screen (Table 1), and constructon of the tank requres lttle more than a drll and handsaw. The upgradent compartment (1 n Fgure 3) was connected to the porous medum compartment (2 n Fgure 3) by cuttng away the rm of the latter to allow contnuous contact between the compartment sdes. Holes were then drlled for the rrgaton fttngs (Fgure 2), whch were fastened n place wth a garden hose washer and nut so that the two compartments were held tghtly together. A small amount of slcone caulkng between the fttngs and the holes was sometmes necessary to assure a good seal. Nytex mesh was placed nsde the nuts to prevent sand from enterng the frst compartment through the fttngs. Next, the downstream end of the sand compartment was perforated wth about 400 1/16 holes, usng an electrc drll. The frst and second

21 11 compartments, now held together wth the fttngs, were placed nto the thrd. Nytex screenng was then draped over the downgradent sde of compartment 2, coverng the holes and preventng the porous medum from escapng compartment 2 nto compartment 3. Fnally, compartment 2 was wet packed wth a porous medum sand n the case of the experments reported n ths work. Wooden braces, held n place wth clamps, were used to prevent the tank from deformng due to the pressure of the saturated porous medum (Fgure 3). After packng the tank, a perstaltc pump moved water out of compartment 3 and nto compartment 1. Ths created an hydraulc gradent across the porous medum n compartment 2, and flow ensued Tracer Tests Three types of the tracer tests were performed to estmate the average lnear velocty nsde the NeST, and to permt an assessment of the degree of unformty of the flow system generated. The measured veloctes were compared to velocty estmates derved from equaton 1: where Q s the flow rate (Volume/Tme), n (dmensonless) s the porous medum (sand) porosty, and A (Length 2 ) s the cross sectonal area of compartment 2. Q v = (1) An In the frst tracer test, the water level n compartment 2 was rased to fully saturate the sand medum wthout creatng any pondng on the surface. A dye

22 12 (blue food colorng) was appled to the sand surface and ts transport was tracked vsually (Fgure 4). The second test conssted of a constant-source salt tracer experment. A concentrated NaCl soluton was added to compartment 1 to nstantaneously ncrease the salt concentraton enterng compartment 2 from <50 mg/l to about 1000 mg/l NaCl, ncreasng the conductance of the water accordngly. Conductvty detectors were nstalled n the NeST durng packng and used to montor arrval tmes of the tracer. Veloctes were estmated by fttng the breakthrough curves wth a model based on the Ogata-Banks (1961) soluton to the advecton dsperson equaton (Fgure 5a). The thrd test for velocty estmaton was performed usng a pont velocty probe (PVP), as descrbed by Labaky et al. (2007). The PVP determnes velocty by montorng tracer transport around a cylndrcal probe (see Chapter 3 for detals). Brefly, ths test also produced breakthrough curves, whch were modeled to determne the average lnear velocty of water n compartment 2 (Fgure 5b) Porosty Estmaton It s apparent from equaton 1 that velocty estmaton depends upon a reasonable knowledge of the porous medum porosty. Two methods for measurng porosty were used n ths work. Frst, an approxmately 15 cm core of sedment was collected from the NeST after the tracer tests were complete. The core was weghed wet and later dry, and the porosty estmated gravmetrcally.

23 13 Snce core collecton can deform the sample, basng porosty measurements, a second method was also used. The sand was wet packed nto a 600 ml beaker n a fashon smlar to the packng procedure n the NeST. Agan the porosty was determned gravmetrcally. 2.3 Results and Dscusson The software sute, Vsual MODFLOW PRO, was used to assess the dstrbuton of non-unform flow near the nlet, due to the presence of 9 dscrete entry ponts for flow. Constant-head boundary locatons were used to represent the rrgaton fttngs, as well as the open water column at the downgradent end of the sand compartment (Fgure 6). No-flow boundares were used to surround the rest of the model doman. The smulatons ndcated that rregulartes assocated wth the rrgaton fttngs on the upgradent boundary were lmted to no more than 10 cm from the boundary. Boundary effects were mnmal n the center of the box where the PVPs were located. Experments were performed at varous flow rates to evaluate the comparablty of the varous tracer test methods (Fgure 7, Table 2). In general, the estmated veloctes agreed qute well, wth nearly all measurements wthn ±25% of one another. Ths s encouragng because the tests operate on dfferent prncples wth slghtly dfferent scales of measurement. The velocty obtaned from equaton 1 was based on relatvely certan knowledge of the flow rate and cross sectonal area of the tank. The porosty of

24 14 the sand was estmated to be 0.52 ± 0.13, whch was prmarly responsble for the uncertanty n velocty estmated ths way. The vsual tracer test and constant source tracer test were conducted n smlar fashons. They both yelded an average velocty between the source and a montorng locaton and, as expected, agreed well. It s possble that small bases were ntroduced n the vsual tracer test due to varablty at the sand surface, snce t represents a boundary. The PVP operates at the centmeter scale, and the velocty was therefore not averaged over a dstance as t was n the other tests. Veloctes measured at sngle ponts are expected to exhbt more varablty than spatally averaged veloctes, lke those estmated n the vsual and constant source tests, even though the pont measurement are collected wth hgh precson. Nevertheless, the PVP veloctes agreed well wth those estmated by the other methods. The unformty of flow n compartment 2 was ndcated two ways. Frst, the progress of the vsual tracer was remarkably even across the tank, showng that no domnant preferred flow path exsted, at least near the surface. Second, the reasonable agreement n velocty estmates from the varous methods whch were based on flow n dfferent parts of the tank suggests that flow n the NeST apparatus was qute unform and well behaved. On ths bass, the NeST s judged to be capable of creatng and sustanng a unform flow feld through the porous medum compartment. Although hydraulc gradents were not measured n ths work, t was noted n several experments (data not shown) that the top of the saturated zone n the

25 15 sand was vsble through the translucent sdes of the compartments. Therefore, the possblty exsts for experments to be performed, n homogeneous materal, utlzng drect gradent measurements n addton to the methods descrbed above. 2.4 Conclusons The results of ths work demonstrate that the NeST system s an nexpensve, functonal apparatus for bench-scale flow and transport experments. Three ndependent tracer tests yelded very smlar estmates of the average lnear velocty n a sandy medum, ndcatng the NeST could produce a nearly unform flow feld n the tank, and that the system consttutes a relable benchtop apparatus for expermental work. The NeST s smple to buld, nexpensve, and not prone to leaks. The system s therefore sutable for teachng applcatons as well as research purposes.

26 16 Table 2.1: Parts requred n the constructon of a NeST Part Name Quantty Irrgaton Fttngs 9 Large Storage Contaner 1 Medum Storage 1 Contaner Tall Contaner 1 Hose Washers 18 Nytex Mesh 6 ft 2

27 17 Table 2.2: Summary of the velocty estmates acqured usng the NeST. The uncertanty represents one standard devaton for each flow rate and type of measurement. Test Type Dscharge (ml/mn) Measured Velocty (cm/day) Expected Velocty from Equaton 1 (cm/day) PVP 3.5 ± ± 4 16 ± 2 PVP 2.3 ± ± 4 4 ± 1 PVP 4 ± ± 4 13 ± 2 PVP 4.1 ± ± 4 14 ± 2 PVP 3.3 ± ± 4 12 ± 2 PVP 11 ±.5 44 ± 2 37 ± 6 PVP 12 ±.5 48 ± 2 42 ± 6 PVP 10.6 ±.5 43 ± 2 38 ± 6 PVP 10.4 ±.5 42 ± 2 40 ± 6 PVP 17 ±.5 68 ± 6 59 ± 9 PVP 18 ±.5 72 ± 6 73 ± 11 PVP 18.2 ±.5 73 ± 6 71 ± 11 PVP 18 ±.5 72 ± 6 69 ± 11 PVP 62 ± ± ± 57 PVP 62 ± ± ± 57 PVP 62 ± ± ± 57 PVP 62 ± ± ± 57 PVP 70 ± ± ± 57 Contnuous Salt Tracer 3 ± ±.3 12 ± 2 Contnuous Salt Tracer 3 ± ±.3 12 ± 2 Contnuous Salt Tracer 3 ± ±.3 12 ± 2 Contnuous Salt Tracer 3 ± ±.3 12 ± 2 Contnuous Salt Tracer 11 ±.5 35 ± 6 38 ± 6 Contnuous Salt Tracer 11 ±.5 25 ± 6 38 ± 6 Contnuous Salt Tracer 11 ±.5 37 ± 6 38 ± 6 Contnuous Salt Tracer 11 ±.5 40 ± 6 38 ± 6 Contnuous Salt Tracer 11 ±.5 41 ± 6 38 ± 6 Contnuous Salt Tracer 17 ±.5 41 ± 5 62 ± 6 Contnuous Salt Tracer 17 ±.5 50 ± 5 62 ± 6 Contnuous Salt Tracer 17 ±.5 48 ± 5 62 ± 6 Contnuous Salt Tracer 67 ± ± ± 54 Contnuous Salt Tracer 67 ± ± ± 54 Contnuous Salt Tracer 67 ± ± ± 54 Vsual Tracer 3 ± ± 3 12 ± 2 Vsual Tracer 3 ± ± 3 12 ± 2 Vsual Tracer 3 ± ± 3 12 ± 2 Vsual Tracer 3 ± ± 3 12 ± 2 Vsual Tracer 3 ± ± 3 12 ± 2 Vsual Tracer 3 ± ± 3 12 ± 2 Vsual Tracer 11 ±.5 47 ± 7 38 ± 6 Vsual Tracer 11 ±.5 39 ± 7 38 ± 6 Vsual Tracer 11 ±.5 34 ± 7 38 ± 6 Vsual Tracer 17 ±.5 38 ± 3 62 ± 6 Vsual Tracer 17 ±.5 36 ± 3 62 ± 6 Vsual Tracer 17 ±.5 35 ± 3 62 ± 6 Vsual Tracer 17 ±.5 40 ± 3 62 ± 6 Vsual Tracer 17 ±.5 33 ± 3 62 ± 6 Vsual Tracer 67 ± ± ± 54 Vsual Tracer 67 ± ± ± 54 Vsual Tracer 67 ± ± ± 54 Vsual Tracer 67 ± ± ± 54

28 Fgure 2.1: Schematc of the NeST system shows how the upgradent, porous meda, and downgradent compartments are connected. 18

29 19 A) upgradent B) downgradent Fgure 2.2: Constructon of the NeST system. The frst and second (porous medum) compartments are connected wth rrgaton fttngs, and the second and thrd compartments (thrd not shown) are connected va drlled holes on the downgradent end of the second compartment.

30 Fgure 2.3: The completed NeST wth a pont velocty probe deployed. Compartments are labeled n a fashon consstent wth the text.

31 Fgure 2.4: Tracer test conducted at 3 ml/mn pumpng rate resultng n a velocty of 17 cm/day. Ths result s near the 12 cm/day calculated usng Equaton 1. Furthermore, the tracer test shows that flow s qute unform laterally wth a 3 ml/mn pumpng rate. 21

32 Fgure 2.5: Example breakthrough curve data from the contnuous salt tracer tests and PVP tests at a pump rate of approxmately 3 ml/mnute and 67 ml/mnute. As seen here, the models were n good agreement wth the measured data and the velocty estmates agreed well wth expected values and other velocty estmates. 22

33 Fgure 2.6: Modeled equpotentals assocated wth flow n a NeST constructed as descrbed n ths artcle. Unform flow s predcted to occur wthn 10 cm of the nlet end of the porous medum compartment. The unts n the x and y drectons are meters. 23

34 Fgure 2.7: Comparson of velocty estmates usng the four technques dscussed n the text. The uncertanty represents the relatve standard devaton of each technque and flow rate. 24

35 25 Chapter 3. Development and Laboratory Testng of a Mn-PVP 3.1 Introducton Detaled ste characterzaton s hghly desrable, and sometmes absolutely necessary, to understand and solve hydrogeologc problems assocated wth groundwater contamnaton. The effort s often amed at determnng groundwater velocty through drect or ndrect means (Ballard 1996; Gavaskar, 1999; Labaky et al., 2007). The transport of contamnants n aqufers s governed by groundwater velocty, and detaled knowledge of t s therefore of great advantage for remedaton desgns. Ths s partcularly true when passve n stu remedaton schemes are employed (Gavaskar, 1999; Labaky et al., 2007). Furthermore, performance assessment of remedaton systems wll also beneft from a detaled understandng of the relevant groundwater velocty feld. To facltate the drect measurement of groundwater velocty n the subsurface, a probe was developed that functons at the centmeter scale (Labaky et al., 2007). The pont velocty probe (PVP) measures the velocty of a conservatve tracer carred by water around a cylndrcal body, and relates t to the velocty of the water n the surroundng formaton. A PVP s nstalled n drect contact wth the aqufer and operates wthout a well. Drect aqufer contact results n a tool that s unaffected by well-bore effects (Labaky, 2004). At least 3 PVP desgns have been descrbed n the lterature (Labaky et al., 2009; Schllg et al., 2010; Berg et al., 2010). All have been based on a probe desgn lmted to detectng and quantfyng horzontal veloctes, and constructed

36 26 wth approxmately 5 cm dameters requrng stll larger borehole dameters durng nstallaton. Although these devces have worked qute well n ther respectve tests, there could be advantages n havng smaller dameter PVPs capable of nstallaton n small dameter boreholes and the measurement of vertcal veloctes for detaled nvestgatons of small aqufer volumes, such as flow around a well screen, or flow near dscharge ponts. The objectve of ths project was to extend the prevous work wth PVPs by developng and testng a small PVP capable of measurng vertcal and horzontal flow wthout sacrfcng measurement accuracy or precson Conventonal Estmaton of Groundwater Velocty Velocty s commonly estmated usng Darcy s law (Fetter, 2001). The method nvolves determnng the gradent at the ste by measurng the hydraulc head and combnng the gradent nformaton wth hydraulc conductvty and porosty estmates n the followng equaton [1] where! s the average lnear groundwater velocty (Length / Tme), q s the specfc dscharge (Length / Tme), n s the porosty (dmensonless), K s the hydraulc conductvty (Length / Tme), h s the hydraulc head (Length), and l s the dstance over whch the hydraulc head s observed to change (Length). A notable lmtaton of ths technque s that ts accuracy depends upon the accuracy of the aqufer K, a parameter well known to be hghly varable (Ballard, 1996; Butler, 1997). K estmates are also known to be functons of the scale over

37 27 whch the tests that generate them are conducted (Rovey and Cherkauer, 1995; Schulze-Makuch et al., 1999; Gerczak et al., 2006; Nemann and Rovey, 2009) because t can vary orders of magntude over short dstances. Ths varablty has been documented even n relatvely homogeneous aqufers (Sudcky, 1986). In areas where the hydraulc gradent s small due to short dstances between measurements or a prolfc aqufer, velocty estmates usng Darcy s law may not be relable (Devln and McElwee, 2007). Velocty can be determned through a varety of drect measurement technques. A common approach s to nject a tracer nto the subsurface and montor ts progress through the aqufer. The breakthrough of a tracer at montorng wells can be used to determne the average groundwater velocty between the njecton pont and the montorng ponts durng the tme of the test. Ths method s well establshed, but s also very tme consumng and often requres an extended samplng effort to collect the data (Sudcky, 1986; Hess et al., 2002). Furthermore, tracer tests of ths knd only provde spatally averaged veloctes wth questonable relevance to the veloctes assocated wth features smaller than the scale of the tracer test. The mportance of groundwater velocty estmates and the lmtatons assocated wth tracer tests have led to the development of several technologes to measure groundwater velocty drectly. Many of these technologes are tracer dependent. Some devces are deployed n wells, such as the collodal boroscope, borehole dluton, and the Geoflow meter, (Drost, et al., 1968; Kerfoot and Massard, 1985; Kearl, 1997; Mom et al., 1993; Labaky et al., 2009).

38 28 Installaton n wells allows for many locatons to be tested repeatedly wth lttle nstallaton cost, provded the wells are pre-exstng. However, local flow dstorton assocated wth flow through a flter pack and well screen must usually be taken nto account wth emprcal calbratons. Also, well development plays a crtcal role n the accuracy of the estmated velocty. Fnally, these technques are only capable of measurng the horzontal component of flow and therefore are not useful n three-dmensonal aqufer characterzaton (Ballard, 1996). Velocty can also be measured drectly wthout a well. The Hydrotechncs VECTOR Groundwater Flowsensor, also known as the In Stu Permeable Flow Sensor (ISPFS), operates by nstallng a dedcated probe n drect contact wth the aqufer. The velocty s determned by montorng the temperature dstrbuton around the probe, whch conssts of a heated cylnder. The technque can determne velocty n three-dmensons, however Su et al. (2006) suggested that vertcal velocty data collected wth the VECTOR Flowsensor may be ncorrectly nterpreted f the thermal conductvty of the formaton s not homogeneous. Addtonally, the VECTOR probe s 0.75 m long and therefore measures flow over a scale that may sample more than one stratum (Ballard, 1996). 3.2 Materals and Methods The verson of the PVP developed n ths work was constructed from a cylndrcal gas dffuson stone obtaned from a pet supply store. The stone was panted wth a concrete sealant leavng a small hole (~ 5 mm) uncovered to act as the njecton pont for the tracer release. Stanless steel wre pars, makng up

39 29 the conductvty detectors, were spaced 2-3 mm apart and affxed to electrcal tape, whch was placed on the probe surface n the desred locatons. Sx pars of dameter stanless steel wres were used n the current desgns (Fgure 3.1). The entre stone, wth the excepton of the njecton port and the detector wres, was then coated wth epoxy cement to ensure a well-sealed, smooth probe body and secure detector wres. The detector wres were connected to a 12- conductor cable usng heat-shrnk butt connectors to transmt the sgnal to the surface. The dffuson stone was connected to an njecton lne that carred the tracer from an njecton system consstng of a 60-mL reservor syrnge and a 1- ml njecton syrnge (Fgure 3.1). The detector system operated by measurng changes n resstance of the water as the tracer passed over the detector wres (Devln et al., 2009). Two detectors for measurng horzontal velocty were placed on each sde of the njecton port, and two more wre pars were placed above and below the njecton port to detect vertcal flow (Fgure 3.1). The breakthrough of the tracer at each detector was used to calculate an apparent velocty (! app ). These were used to determne the average lnear velocty locally n the aqufer (!! ), and the orentaton of the njecton port wth respect to that groundwater flow drecton (!) as seen below (Labaky et al., 2007). Generally, the angle! was estmated frst from the followng relaton, where! app1 and! app2 are the apparent veloctes for detectors 1 and 2, respectvely. The angle between the njecton port detector 1 s " 1, and " 2 s the [2]

40 30 angle between the njecton port and detector 2. These angles were fxed at 40 and 70, respectvely, n the current PVP desgn. After determnng #, the average lnear groundwater velocty was determned usng an apparent velocty from ether detector and the relatonshp (Labaky et al., 2007), [3] where "# s the average lnear groundwater velocty. In the case of the vertcal velocty, the apparent velocty (! app ) was assumed equal to the average lnear velocty n the vertcal drecton because the probe surface was not curved n that drecton. 3.3 Expermental Procedure The probe was tested n the laboratory usng an nexpensve flow-through tank called the Nested Storage Tank, hereafter referred to as the NeST (Fgures 2.1 and 2.3) (Chapter 2). The probe was placed n the center of the NeST, whch was then wet-packed wth sand. Ths packng procedure ensured near unform packng of the sand and elmnated measurement bases that mght have resulted from dsturbance of nstallaton n pre-packed sand. All tests were conducted n medum sand obtaned commercally. A porosty of 0.52 ± 0.13 was determned gravmetrcally. The tracer soluton conssted of a 1 g/l NaCl soluton to ensure conductvty was hgher n the tracer soluton than n the background tap water. A test began wth the njecton of a pulse of tracer (0.2 ml was typcal) usng the small syrnge n the njecton system; the larger syrnge was used to

41 31 recharge the smaller one n subsequent tests. The conductvty at the detectors was montored every 10 to 60 seconds dependng on the antcpated average lnear velocty n the test. The devce was assessed over the velocty range 12 to 625 cm/day, and wth the! angle varyng from 0 and 120. The results of the tests were compared to a calculated velocty estmated from, where Q s the dscharge of the pump (L 3 /T), A s the cross-sectonal area of the [4] saturated sand (L 2 ), and n s the porosty (dmensonless). All unts are generalzed, where L s length and T s tme. The drecton of flow was assumed to be perpendcular to the open water columns at ether end of the tank. Breakthrough curves were obtaned from each detector and were used to estmate the apparent veloctes needed for equatons 2 and 3. Ths was done by fttng the data wth a 1-D soluton to the advecton-dsperson equaton, usng smplex optmzaton algorthm coded n a vsual basc applcaton (VelprobePE) (Devln, 1994; Schllg, 2010) 3.4 Results and Dscusson The precson of PVP measurements was assessed by makng several measurements n sequence under dentcal condtons. Ths assessment was repeated at several pumpng rates wth results smlar to those reported for earler PVP desgns (Table 3.1) (Labaky et al., 2007). Also, breakthrough curves from any 2 consecutve measurements were generally found to be nearly dentcal

42 32 (Fgure 3.2). These results confrm the nherently hgh precson of the PVP nstrument. The PVP was further assessed by comparng PVP-derved veloctes to those estmated by other means, over a wde range of veloctes. In most experments, PVP veloctes could be compared wth veloctes calculated usng equaton 4. These comparsons usually showed very good agreement (Fgure 3.3). It should be noted that veloctes from equaton 4 depend upon good estmates of porosty, whch was determned emprcally to be wthn the range 0.38 to 0.65 n the NeST tests usng cores from the NeST and beakers wet packed n a fashon smlar to that employed n packng the NeST. Thus, the large uncertanty n porosty can account for much or all of the dscrepances that exsted between the PVP measurements and the equaton 4 velocty estmates. The accuracy of the PVP veloctes also appeared to be very good, wth veloctes agreeng to wthn 20% n all but one test (Table 3.2). The results of the tests at! = 60 show the hghest devatons n both magntude and drecton from Q based veloctes. The reason(s) for these dsagreements are not known for certan, but those specfc tests were conducted n a tank packed separately from the other tests, and were conducted out of sequence wth the other tests. Ths rases the possblty that the anomaly s due to dfferences n the tank condtons rather than any error nherent n the method. If ths anomalous test s excluded, the results wth the hghest error n magntude are those wth! = 90 or greater, correspondng to the 2 nd detector beng rotated nto or near a stagnaton pont on the probe surface,.e., at.! = 180 o (D Base, 1999; Labaky, 2004).

43 33 The! angle was measurable wth reasonable accuracy, ~ ± 15, over the velocty range 11 to 294 cm/day (Table 3.2). The best results n terms of accuracy and precson were obtaned for the hgher flow veloctes. Ths mght be related to dffcultes n mantanng constant flow rates from the pump at the lowest tested veloctes. Nevertheless, these data suggest that the uncertanty n PVP flow drectons s lkely less than ± 15, and the average error was ± 8, consstent wth prevous assessments for earler desgns (Labaky et al., 2007). The PVP was further evaluated by comparng ts velocty estmates to those from two tracer tests (Table 3.3). The tracers ncluded both a dye tracer and a chemcal tracer. The dye was used to conduct a test n whch the tracer could be tracked vsually. Blue food colorng was appled to the saturated sand surface near the nlet end of the tank. As water flowed through the tank, tracer was transported at the same rate and was tmed as t arrved at predetermned ponts n the tank. The chemcal tracer test was performed by addng sodum chlorde to the tank nlet water to rase ts concentraton to 1 g/l, creatng a prolonged hgh conductvty pulse that was tracked wth electrcal conductvty sensors nstalled n the tank. Both tracer tests returned velocty values that were n close agreement wth the PVP veloctes, further ndcatng the PVP probe provded accurate estmates of velocty. At the hghest veloctes (~233 cm/day), the PVPmeasured veloctes devated from the equaton 4 estmates by about 25%. However, the results from the other tracer tests were n good agreement wth the

44 34 PVP, suggestng that the error was wth the equaton 4 values rather than the measurements. Fnally, the PVP performance was drectly compared to the performance of an older desgn PVP wth a larger dameter, usng the methods prevously descrbed (Labaky et al., 2007). The two PVPs produced smlar velocty estmates, although the smaller nstrument s estmates were consstently lower n value than the larger nstrument estmates by about 20% on average (Appendx D). The reasons for the apparent bas bear further nvestgaton. For the present, t s hypotheszed that they are due to small varatons n porosty across the tank, whch would have been contnuously present throughout the tests. Alternatvely, t s possble that the smaller PVP was senstve to heterogenetes n the packng at a smaller scale than the larger PVP. As mentoned above, a goal of the PVP desgn ntroduced n ths work was to characterze flow n 3-dmensons. Ths was accomplshed by addng vertcal flow detectors to the probe. The ablty to detect vertcal flow was tested n the laboratory by orentng a PVP on ts sde and followng the same testng procedure descrbed above (Fgure 3.4). The work presented here s prelmnary and more work should be pursued n the future. However, the results suggest good accuracy and precson relatve to the horzontal flow capablty (Table 3.4). 3.5 Conclusons Laboratory testng of a new PVP desgn showed that t s capable of provdng precse and accurate estmates of velocty magntude n sandy

45 35 deposts. The velocty magntudes agreed wthn 20% of other mn-pvp measurements and wthn 25% of other velocty estmaton technques. The! drectons had an average uncertanty of 8. These uncertantes are consstent wth other PVP desgns. However, the mn-pvp measured veloctes were consstently less than the larger PVP estmates. The cause of the bas s unknown, but the accuracy and precson suggest the mn-pvp desgn s expected to perform as well as the larger desgn n sandy materal. Addtonally, the mn-pvp may be used to map complcated 3-dmensonal flow systems such as those created around a dpole well or other systems wth strong components of horzontal and vertcal flow.

46 36 Table 3.1: Indvdual PVP tests reported wth expected values for alpha and speed. These results show the reproducblty of measurements made wth a PVP. The uncertanty represents the average uncertanty for each measurement. Dscharge (ml/mn) Expected Alpha (Degrees) Measured Alpha (Degrees) Expected Speed (cm/day) Measured Speed (cm/day) 3.5 ± ± 5 79 ± 8 14 ± 3 16 ± ± ± 5 61 ± 8 9 ± 2 4 ± ± ± 5 37 ± 8 16 ± 4 13 ± ± ± 5 31 ± 8 16 ± 4 14 ± ± ± 5 68 ± 8 13 ± 3 12 ± ± ± 5 24 ± 8 44 ± ± ± ± 5 35 ± 8 48 ± ± ± ± 5 28 ± 8 43 ± ± ± ± 5 23 ± 8 42 ± ± ± ± 5 27 ± 8 68 ± ± ± ± 5 25 ± 8 72 ± ± ± ± 5 28 ± 8 73 ± ± ± ± 5 25 ± 8 72 ± ± 11 Table 3.2: Summary of PVP Assessments Usng a Laboratory Tank. The absolute error s reported. Velocty Magntude Velocty Drecton Error Alpha No. of Replcates Expected (cm/day) Measured (cm/day) Expected (deg) Measured (deg) Magntude (%) Drecton (Degrees) N/A 28.5 N/A N/A 16.0 N/A N/A 24.1 N/A

47 37 Table 3.3: Comparson of PVP veloctes wth tracer tests. The uncertanty represents the error assocated wth one standard devaton for each measurement. Approxmate Pump Rate (ml/mn) Velocty (From equaton 1) Vsual Tracer Chemcal Tracer Pont Velocty Probe (cm/day) (cm/day) (cm/day) (cm/day) 3 12 ± 4 8 ± 3 17 ± ± ± 8 40 ± 7 36 ± 7 39 ± ± ± 3 46 ± 5 68 ± ± ± ± ± 23 Table 3.4: Summary of Vertcal Velocty Data. The uncertanty represents the average uncertanty for the PVP and expected velocty. Dscharge (ml/mn) Expected Velocty (cm/day) PVP Velocty (cm/day) ± ± ± ± ± ± ± ± 26

48 Fgure 3.1: Schematc of mn-pvp showng njecton port, detector, and tracer njecton system. 38

49 Fgure 3.2: Comparson of PVP breakthrough curves from tests conducted under dentcal condtons. Symbols represent data collected from the PVP detectors and lnes represent best ft solutons to the advecton dsperson equaton (see text). In consecutve tests lke these the curves produced were nearly dentcal. 39

50 Fgure 3.3: Agreement between veloctes measured wth the PVP and the expected velocty calculated usng equaton 3. Note the slope s very near 1 ndcatng good accuracy. The horzontal error bars represent the error n expected velocty as a result of the uncertanty n the pumpng rate, porosty, and cross sectonal area. These errors combned result n an average uncertanty n the equaton 4 velocty estmates of 23%. The vertcal error bars represent 15% uncertanty, whch s the average uncertanty n magntude for the PVP. 40

51 41 Fgure 3.4: Photo depcts PVP orentaton when testng vertcal flow detecton.

52 42 Chapter 4. Velocty Characterzaton of the Dpole Flow and Reactve Tracer Test 4.1: Introducton The remedaton of contamnated groundwater s dependent upon an accurate understandng of the affected aqufer. Therefore, ste characterzaton s a crucal step n any effectve remedaton system. The need for many dfferent types of ste-specfc nformaton has led to the ntroducton of a number of characterzaton technques and tools. One of the most mportant parameters to determne s groundwater velocty (Gavaskar, 1999). The Pont Velocty Probe (PVP) was developed to address ths need. A PVP measures groundwater velocty drectly by relatng the velocty n the formaton to the velocty of a conservatve tracer on a cylndrcal probe surface (Labaky et al., 2007). PVPs are nstalled n drect contact wth the aqufer porous medum, and operate wthout a well. Ths ensures that the velocty measured s unaffected by well screens and well bore effects. The tool measures groundwater velocty at the centmeter scale, whch makes hgh-defnton characterzaton of complcated flow systems possble. In ths study, the probe s used to provde velocty nformaton around a dpole flow system. Dpole flow systems are the bass for a number of ste characterzaton and remedaton schemes. These systems, also known as groundwater crculaton wells, have been used to delver surfactants, oxdants, and nutrents for boremedaton n order to mprove remedaton performance (Phllp and Walter, 1992; Knox et al., 1997; Sabatn et al., 1997). Dpole Flow Tests can be

53 43 used to determne vertcal and horzontal K and specfc storatvty of porous meda (Kabala, 1993). Recently, the Dpole Flow Test has been combned wth a sute of tracers to determne other aqufer propertes, related to contamnant fate and transport, n a test called the Dpole Flow and Reactve Tracer Test, DFRTT (Thomson et al., 2005). The DFRTT s capable of determnng a number of physcal, chemcal, and bologcal aqufer parameters from a sngle test. The devce uses packers to solate two portons of a well screen. Water s njected nto the formaton from one screen and pumped out from the other, usng a pump located at the surface. The pressure n each chamber, and the tracer concentratons, are montored over tme and used to determne the varous aqufer parameters. It s the tracer breakthrough curves (BTCs) that were of partcular nterest n the DFRTT research because they could be used to estmate aqufer parameters such as mcrobal actvty, aqufer sorpton propertes, and contamnant degradaton rates (Roos, 2009). However, the prelmnary DFRTT modelng, whch assumed an homogeneous aqufer and no sgnfcant ambent groundwater flow, was unable to accurately reproduce the tracer breakthrough curves. It has been shown n tank experments that even small-scale heterogenetes can affect the tracer BTCs of DFRTTs (Barns et al., 2010). The possble devatons from deal BTCs nclude multple tracer peaks that are usually attrbuted to a combnaton of shortcrcutng along the well casng, and the expected BTC. Other dfferences arse n the magntudes of peak concentratons, tme-to-peak concentraton, and dfferent shapes of the BTC tals (Fgure 4.1).

54 44 In ths study, PVPs were used to evaluate the flow system surroundng an operatng dpole well n unprecedented detal. The prmary objectve of ths work was to dentfy causes of the dsagreements between modeled and measured BTCs by defnng the groundwater velocty feld at steady state near the dpole well. Attempts have been made to measure veloctes near a dpole flow system n other work (Johnson and Smon, 2007). However, those studes used VECTOR Technology nstrumentaton (Ballard, 1996) that averaged velocty measurements over a vertcal dstance of nearly a meter, and the nstrument was unable to measure vertcal veloctes nformaton crucal to properly characterzng flow around a dpole well (Johnson and Smon, 2007). That study found that horzontal velocty estmates generally agreed wth model estmates, but the agreement was not entrely satsfactory. In ths work, we extend the prevous efforts by mprovng the resoluton of the measurements and addng vertcal velocty measurements to the data collected. To accomplsh ths, PVPs were redesgned and deployed around a dpole well prevously nvestgated by Thomson et al. (2005). A secondary objectve of ths work was to evaluate the magntude of flow short-crcutng along the well casng, and to assess the effect ths mght have on the tracer BTCs. 4.2 Ste Descrpton The study ste was located 80 km northwest of Toronto, Ontaro at Canadan Forces Base (CFB) Borden. The aqufer conssted of well-sorted fne to medum sands of a glaco-lacustrne depost and was nterbedded wth peat n

55 45 some areas (Macfarlane, 1983; Brewster et al., 1995), and fne horzontal beds that were vsble n core. The aqufer was underlan by a slt and clay aqutard approxmately 9 m below ground surface (bgs) (MacFarlane et al., 1983). The ste s uncommonly well characterzed and the aqufer has been evaluated for K many tmes, usng a varety of technques. For example, constant head permeameter tests of core materal resulted n an average K of 8.0 x 10-5 m/s for homogenzed 5-cm samples of core materal (Sudcky, 1986; Woodbury et al., 1991). Intact core materal was also studed wth a mean K of 2.6 x 10-5 m/s (Tomlnson et al., 2003). Slug test estmates had a mean K of 2.5 x10-5 m/s but ndvdual measurements vared from 3.8 x10-6 to 6.1 x10-5 m/s. Pumpng tests, whch tend to sample larger volumes of aqufer than the other methods, returned K estmates that were notably greater than those from the other technques. The results ranged from 1.4 x10-4 to 2.2 x10-4 m/s (Nwankwor et al., 1984). These mxed results show that even n a relatvely homogeneous aqufer the K can vary over nearly two orders of magntude, and s scale dependent. Ths varablty can compound the uncertantes assocated wth ndrect velocty-estmaton methods, lke those based on Darcy s Law calculatons (Labaky et al., 2007). 4.3 PVP Constructon and Theory The Pont Velocty Probe operates by trackng the movement of a tracer around a cylndrcal body. The verson of the devce developed for ths project was constructed from a cylndrcal dffuson stone. In order to constran the tracer

56 46 njecton to a small area on the cylnder, the stone was panted wth a concrete sealant leavng only a small openng. Followng sealng, the detectors, consstng of 12 stanless steel wres (0.018 n dameter) n sx pars were secured to the stone wth tape (Fgure 3.1). Two detectors for measurng horzontal velocty were placed on each sde of the njecton port, and one detector was placed on each sde of the njecton port vertcally. The entre stone was then coated n epoxy cement leavng only the wres and njecton openng now the njecton port exposed. The wres were connected to a 12-conductor 20-gauge copper cable usng heat-shrnk butt connectors. The cable connected the probe to a datalogger through a half-brdge crcut that returned mllvolt sgnals proportonal to electrcal resstance of the groundwater (Devln et al., 2009). The probe was connected to an njecton lne for the delvery of tracer by a user. Tracer delvery was controlled wth a 60-mL reservor syrnge and a 1-mL njecton syrnge (Fgure 3.1). The peak ampltudes of the electrcal resstance of groundwater at each detector represented the maxmum tracer concentratons and were used to calculate the apparent velocty (" app ) of tracer movng around the probe. The procedure nvolved fttng tracer breakthrough curves at the detectors wth a soluton to the 1-D advecton-dsperson equaton. The system was automated so that sgnals from multple detectors could be processed n a sngle user step. Ths was accomplshed by codng the fttng procedure nto vsual basc, wthn Excel $, n an applcaton named VELPROBE PE (Schllg, 2010, Devln, 1994). The apparent veloctes from two detectors were used by VELPRBOBE PE to

57 47 determne the orentaton of the njecton port wth respect to the groundwater flow drecton (!) as seen below (Labaky et al., 2007): [1] where " app1 and " app2 are the apparent veloctes for detectors 1 and 2, respectvely. The angle between the njecton port and detector 1 s % 1, and % 2 s the angle between the njecton port and detector 2. For the PVPs used n ths study, these angles were fxed at 40 and 70 respectvely. After determnng!, the average lnear groundwater velocty was calculated by VELPROBE PE from (Labaky et al., 2007): [2] where " # s the average lnear groundwater velocty. In the case of detectors orented to measure vertcal veloctes, the apparent velocty (! app ) was assumed equal to average lnear velocty because the tracer path was straght (no cylnder curvature) between those detectors and the njecton port. 4.4 PVP and Well Installaton The well used to create the dpole flow system (MW-3) was a 5.1 cm nsde dameter (ID) PVC well nstalled to a depth of 5.5 m bgs and completed wth a 3 m long slot screen. The well was nstalled by drvng a 7 cm ID hollow steel casng nto the aqufer and then flushng the casng wth water to remove the sand. After flushng, the PVC well was placed nsde the casng, whch was subsequently removed allowng the aqufer materal to collapse

58 48 around the well screen and rser ppe. Ths method of nstallaton s known as jettng and has the advantage of creatng a well bore wth the least possble dsturbance of the surroundng aqufer materal (Labaky, 2009). Addtonal wells were nstalled wth the purpose of permttng an evaluaton of short-crcutng along the well casng durng pumpng. In these cases, the rser ppes located between the two screens were ftted wth PVP-type detectors to measure vertcal tracer veloctes along the well body (Fgure 4.2). In order to evaluate the effect of a flter pack on short crcutng, one well, MW-A, was constructed wth a 1.5 m screen and nstalled to a depth of 5.5 m, as descrbed above. A second well, MW-B, smlarly constructed, was nstalled wth a flter pack. The flter pack was created by jettng a larger steel casng (13 cm ID) and fllng the annulus around the well wth the pack materal. The PVPs were constructed as descrbed above n the secton ttled PVP Constructon and Theory. They were mounted onto 1 PVC rser ppes and nstalled by jettng usng a 3.8 cm ID hollow steel casng wth no flter pack. Altogether, 18 probes were deployed at 3 dfferent dstances and depths surroundng MW-3 (Fgure 4.3). The horzontal dstances were chosen to fully characterze the flow system n an effort to explan the BTC devatons from the DFRTT model (Fgure 4.1). Prelmnary modelng usng MODFLOW was used to decde placement of the PVPs so the nnermost PVPs would record flow wthn the 70% cumulatve flow boundary.

59 49 The depths of montorng were chosen to provde a detaled threedmensonal mage of the dpole flow system n the vcnty of the pumpng and extracton screens, whch were centered at 4.9 m bgs. 4.5 Dpole system A downhole devce, hereafter referred to as the dpole packer assembly (DPA), developed at the Unversty of Waterloo, was used to create the dpole flow system n ths nvestgaton (Fgure 4.2) (Roos, 2009). It conssted of 3 nflatable rubber packers that were used to solate the njecton and extracton chambers. The DPA had the characterstc dmensons L = 0.22 m and & = m (Fgure 4.2). These measurements are mportant when dscussng the area of nfluence of the dpole well, where 70% of flow occurs wthn the regon bounded by 3L (Kabala, 1993; Zlotnk and Zurbuchen, 1998). The DPA also contaned two pressure transducers (Huba Control, Type 680) that were mounted n the upper and lower packers, and connected to the chambers wth stanless steel tubng. The pressure transducers were montored wth a data logger and used to determne steady state flow condtons. A perstaltc pump (Cole Parmer, K ) was located at the surface and used to nduce flow. The surface mounted pump resulted n a smaller DPA desgn as well as ease n plumbng the other surface equpment (Roos, 2009).

60 Feld Methodology Dpole operaton The dpole flow system was created by nsertng the DPA nto MW-3 such that the md pont between the screens was at a depth of 4.9 m bgs. Ths depth was chosen because prevous dpole experments returned reproducble results at ths well/depth combnaton (Roos, 2009). After nsertng the dpole, the packers were nflated to a pressure of approxmately 30 pounds per square nch (PSI). Ths pressure was suffcent to ensure no short-crcutng of flow through the well bore, nsde the well screen. Followng packer nflaton, the dpole unt was connected to a perstaltc pump at the surface. In these experments, the pumpng rates chosen were ~700 ml/mnute and ~1150 ml/mnute. The pump was operated from 0.5 (June, 2009 experment) to 14 hours (September, 2009) before measurements were made to allow the system to reach steady state. In both cases, head measurements made wth pressure transducers n the DPA ndcated that steady state flow was establshed wthn the screen Velocty feld characterzaton In order to characterze the flow system surroundng the dpole well, 18 Pont Velocty Probes were nstalled around t at varous depths. Followng nstallaton of the PVPs, or after long perods of non-use (>7 days), the PVP lnes were flushed wth fresh tracer soluton. In the frst set of experments, a tracer soluton of 1 g/l of NaCl was utlzed wth success, but sgnal ampltude was less than desred. To mprove detecton, the later experments were conducted wth 3

61 51 g/l NaCl, whch had proven satsfactory n prevous feld tests (Labaky et al., 2009). After flushng, the resstance measured at the PVP detectors was montored untl t returned to background levels before begnnng subsequent tests. Tests were begun by smultaneously njectng a known volume of tracer at each probe. The volumes chosen were between 0.3 ml and 0.7 ml. The resstvty was montored for a perod of at least 10 hours to ensure that breakthrough n the slowest velocty zones was complete. The datalogger was programmed to record resstvty measurements at 30-second ntervals. In experments utlzng the detectors on the dpole well tself, data were collected at one-second ntervals. 4.7 Results and Dscusson In all tests, the feld data were marked by a small peak n tracer concentraton at early tmes. Ths peak has been observed n prevous tests and attrbuted to tracer short-crcutng along the well casng and reachng the extracton chamber earler than expected (Roos, 2009). Testng was completed to specfcally examne ths phenomenon (at MW-B), and tracer movement along the casng was confrmed, presumably through a skn of dsturbed porous medum at the casng-aqufer contact (Appendx A). The tests showed that the tracer that short-crcuted the flow system traveled at unusually hgh veloctes (>8500 cm/day). If correct, the early tme peaks effectvely mark the start tmes of the njectons,.e., the tmes when the tracer entered the formaton after the

62 52 pump was started. Takng nto account the tme for the tracer to return to the surface detector through the DPA tubng and ntake screen, a conservatve delay of 6 mnutes was estmated. Wth ths adjustment to the tme axs, the small short-crcut peak can be used as a tme-zero marker. Data from the varous tests were tme corrected as descrbed above to permt the BTCs from the June and September tests, and model smulatons, to be drectly compared. In addton, all data were normalzed to the peak maxma C max, agan to facltate comparsons. These measures had the advantage of enhancng the vsual dfferences n the fallng lmbs of the tracer BTCs, referred to as the tals (Fgure 4.4). The extreme rght ends of the tals are assocated wth the longest flowpaths. Tals can also be extended due to nondeal transport caused by heterogenetes n the aqufer. Sutton et al. (2000) suggested that only 10% of the flow from the njecton chamber of a dpole well s responsble for the BTC peaks, whereas the remanng 90% of flow controls the shape of the tal. The DFRTT model assumed an homogenous aqufer, and because heterogenety was lkely to be a prmary cause of the dsagreement, another model was created, usng Vsual MODFLOW Pro, that could ntroduce heterogenety as requred (Appendx B). In addton, the MT3DMS (Zheng and Wang, 1998) engne was used to model tracer breakthrough. Ths model was used to smulate all flow and transport n the experments. The breakthrough-curve peaks from the frst data set (June 2009) arrved earler than predcted by the Vsual MODFLOW Pro model and earler than observed n the prevous tests (Fgure 4.4). In all cases, the tals of BTCs from

63 53 the experment declned more quckly than observed n earler tests (Fgure 4.4). Ths suggested that the tracer mass was returnng to the ntake screen along shorter and/or faster flowpaths than would be present n an homogeneous aqufer. The PVP velocty data were used to evaluate the lkelhood of ths nterpretaton. A projected cross secton of the PVP results was compared to the homogeneous model created n Vsual MODFLOW Pro (Fgures 4.5). The results show good qualtatve agreement n velocty magntude and drecton. Generally, water was flowng away from the well near the njecton screen (measured wth the shallow PVPs) and toward the well near the extracton screen (measured wth the deep PVPs). Furthermore, flow was downward at the mddepth PVPs (4.9 m bgs), as expected n a dpole system. Despte the generally good agreement between the modeled and expermental data sets, some locaton-specfc dsagreements were observed. Ths was partcularly evdent at the shallowest PVPs, where some of the measurements ndcated a notable upward component of flow nstead of domnantly horzontal flow, as predcted by the model. The magntudes of the measured veloctes also showed some devatons from the MODFLOW modeled veloctes. Expermental veloctes were hgher near the well than those predcted by the model (Fgures 4.5 and 4.6). Outsde the regon of fast flow some of the veloctes were lower than model predctons. These results suggest that the area of nfluence of the well may have been smaller than predcted and that local heterogenetes may have contrbuted to these dfferences. Hydraulc conductvty proflng wth the dpole

64 54 assembly, usng the equatons of Zlotnk and Zurbuchen (1998), showed varatons n K wth depth that support ths possblty but fall short of defnng a K feld that could explan the BTC dscrepances (Fgure 9). However, the velocty dfferences detected by the PVPs were suffcent to begn alterng the model to match the feld data. To mprove the agreement between modeled and measured veloctes, the aqufer was treated as a layered system n MODFLOW. Smulatons were conducted n whch the K profle from Fgure 4.7 was used to defne a contnuous zone extendng across the entre doman wth a K of 3.87 x 10-5 m/s near the njecton screen and 5.8 x 10-5 m/s above and below the stratum (based on an average K from the dpole tests) (Fgure 4.8 A). In another smulaton, a hgh-k stratum (K = 5.8 x 10-5 m/s) between the njecton and extracton chambers was assumed, whle the surroundng formaton had a lower K (K=3.87 x 10-5 m/s) (Fgure 4.8 B), and n yet another smulaton a contnuous low-k layer (K = 3.87 x 10-5 m/s) at the depth of the extracton chamber was smulated whle the surroundng formaton had a K of 5.8 x 10-5 m/s (Fgure 4.8 C). In all cases, these smulatons tended to cause only small changes n arrval tmes and peak concentratons of the tracer at the extracton chamber compared to the homogeneous aqufer smulatons (Fgure 4.8). The nature of the trends agreed wth expectatons from tank experments (Barns et al., 2010), but the magntudes of the changes were too small to explan the experment-model dfferences. It was concluded that only heterogenetes n the mmedate vcnty of the dpole

65 55 well were lkely to nfluence calculated breakthrough curves enough to force a match between the modeled and measured data sets. The PVP veloctes were hgher than predcted near the well, suggestng that aqufer was generally more permeable there than further away. Therefore, smulatons were performed based on the assumpton that K wthn 0.4 m from the well was relatvely hgher than elsewhere (Fgure 4.9). Ths smulaton dd not acheve the desred convergence n measured and modeled BTCs (Fgure 4.8D). However, the presence of a hypothetcal zone wth hgher K even nearer (0.1 m radal) to the dpole well (K = 8.7 x 10-5 m/s near the well and K=5.8 x 10-5 m/s at dstance) resulted n changes n the smulated BTCs n the drecton of the feld data (Fgure 4.10A). Proxmal zones of lower K were also consdered (K = 1.93 x 10-5 m/s near the well and K=5.8 x 10-5 m/s at dstance) and found to result n smulated BTCs wth broader, lower peaks, and longer tals than the prevous homogeneous aqufer smulatons (Fgure 4.10B). Ths seres of smulatons showed that ndeed heterogenetes mmedately next to the dpole well were lkely domnatng the expermental BTCs. Fnally, an attempt was made to quanttatvely reduce the dscrepancy between smulated and expermental BTCs. A small proxmal zone of aqufer wth a K of 6.5 x 10-5 m/s was placed near the well (0.1 m) and the rest of the aqufer was assgned a K of 5.8 x 10-5 m/s. Ths scenaro resulted n an mproved match between the modeled and measured BTCs, as desred (Fgure 4.11). The match could be further mproved, but for the smulatons to best

66 56 represent realty, addtonal feld data defnng the velocty feld wthn 0.4 m of the dpole well would be requred. 4.8 Conclusons The dffcultes n modelng a dpole flow system led to usng PVPs to map groundwater veloctes n the aqufer at an unprecedented level of detal. The feld measured veloctes were found to be hgher proxmal to the dpole well than predcted usng an homogenous, sotropc aqufer model, and average feldmeasured K estmates. Addtonal smulatons usng Vsual MODFLOW Pro, assumng steady-state flow, showed that the measured breakthrough curves could be better descrbed by assumng materal proxmal to the dpole well that was more permeable than the surroundng aqufer, and less permeable materal further away, consstent wth the PVP velocty data. A permeablty ncrease of as lttle as 12% was suffcent to mprove the model-experment BTC match. It was further shown that the BTCs were nsenstve to contnuous horzontal layerng of the aqufer between the dpole screen ntervals, partally because the BTCs were mnmally affected by changes to the aqufer propertes affectng the more dstal flowpaths. Under the condtons of these tests, the dpole well BTCs were only senstve to aqufer propertes less than 0.4 meters radal dstance from the well.

67 Fgure 4.1: Comparson of DFRTT data collected at ~700 ml/mn and the model predcton. Adapted from Roos,

68 58 Fgure 4.2: Schematc of devce to test well skn veloctes. PVP Style detectors were placed between the two sectons of screen on the dpole well. The detectors and screen between the njecton and extracton chamber were sealed and secured wth epoxy. The characterstc dmensons 2& and L determne the dmensons of the flow system

69 Fgure 4.3: Expermental Desgn depctng orentaton of well MW-3 (Center) and the 18 PVPs surroundng t n 3 dmensons. 59

70 Fgure 4.4: Comparson of model and tracer test data. The curves are normalzed by the peak concentraton to show the dfferences n the fallng lmbs. The shaded secton shows the devaton from prelmnary modeled behavor that led to ths work. 60

71 Fgure 4.5: Projected cross secton of PVP Results (Bottom) as contrasted wth the Vsual MODFLOW Model (Top). Veloctes are reported n cm/day. 61

72 Fgure 4.6: Plan Vew of PVP Results (Bottom) as contrasted wth the Vsual MODFLOW Model (Top). North s toward the top of the dagrams. The drecton markers ndcate the domnant flow drecton at each locaton. Veloctes are reported n cm/day. It should be noted that the upper row of PVPs are nstalled at 4.5m BGS, the mddle row s 4.9 m BGS, and the bottom row s 5.3 m BGS. 62

73 Fgure 4.7: Hydraulc conductvty profle of Well MW-3. The lower hydraulc conductvty area near 4.5 m BGS s near the depth of the shallow PVPs. 63

74 Fgure 4.8: Tracer breakthrough curves as estmated usng Vsual MODFLOW. Curve A smulates a layer of lower hydraulc conductvty (K = 3.87 x 10-5 m/s) s placed near the njecton porton of the dpole. Curve B smulates a layer of hgher hydraulc conductvty (K = 5.8 x 10-5 m/s) placed between the screens of the well. Curve C (K = 3.87 x 10-5 m/s) smulates tracer breakthrough when an area of lower hydraulc conductvty s placed near the extracton screen. Curve D shows the BTC assocated wth a small zone of hgh hydraulc conductvty (K = 8.7 x 10-5 m/s) near the well. The results suggest the BTC behavor s nsenstve to heterogenety at dstance from the well. 64

75 65 Fgure 4.9: Projected cross secton of PVP Results (Bottom) as contrasted wth the Vsual MODFLOW Model (Top). In ths model, a layer of hgh hydraulc conductvty surroundng the well s smulated. Veloctes are reported n cm/day.

76 Fgure 4.10: Tracer BTCs as estmated by Vsual MODFLOW. Curve A smulates a hghly conductve area proxmal to the well usng a zone of hgh hydraulc conductvty near the well. Curve B smulates a less conductve zone proxmal to the well usng a lower hydraulc conductvty zone. These results suggest that tracer BTC behavor s very senstve to heterogenety very near the well. 66

77 Fgure 4.11 Comparson of breakthrough curves for the homogeneous case (A) and the best fttng heterogeneous case (B). The curves are normalzed by the peak concentraton to show the dfferences n the fallng lmbs. The shaded secton shows the devaton from modeled behavor. 67

78 68 Chapter 5. Parameter Optmzaton Usng Velocty Data 5.1 Introducton Drect velocty measurements are useful for determnng contamnant transport pathways and other hydrogeologc nformaton. These measurements are related to the K of a formaton, but are not subject to the hgh uncertanty assocated wth measurng K or, n some cases, the hydraulc gradent (Devln and McElwee, 2007). Ths ndependence may prove useful for helpng to determne model nput parameters for complex hydrogeologc systems such as the flow surroundng a dpole well. Aqufer parameter estmaton and optmzaton features have been avalable n commercal groundwater models for several years. Usually, the software optmzed the K feld to provde a best ft for smulated tracer breakthrough data or hydraulc head measurements to measured data. However, there are no commercal or publshed models capable of performng parameter estmaton based on velocty data known to the author at ths tme. In ths work, a smple 2D model s developed to optmze K estmates based on drect velocty measurements to demonstrate how velocty data mght be used n conjuncton wth modern numercal models. 5.2 Model Development The model to be used n ths demonstraton s based on the heterogeneous 2D general flow equaton at steady state (1):

79 69 " "x K x "h "x # $ % & ' ( + " "y K y "h "y # $ % & ' ( # $ % & ' ( = 0 where K x and K y are the hydraulc conductvtes n the x and y drectons, respectvely, and h s the hydraulc head. The equaton can be approxmated usng fnte dfferences (Equaton 2): 0 1,,, 1,, 1, 1,, 1,,, 1,, 1, 1,, =! " # $ % & ' ( ( ) * + +, -!.. ( ( ) * + +, -!. +! " # $ % & ' ( ( ) * + +, -!.. ( ( ) * + +, -! y y h h K y h h K x x h h K x h h K j j j j j j j j j j j j j j j j where K s the effectve hydraulc conductvty between the nodes referred to by the superscrpts and subscrpts, h s the hydraulc head at the node referred to by the subscrpts, and $x and $y are the dstances between nodes n the x and y drectons. The hydraulc head at the central locaton s h j. The subscrpt gves the poston n the x drecton and j denotes ts poston n the y drecton. The effectve hydraulc conductvty between two nodes s calculated from the harmonc mean of the hydraulc conductvtes on the nodes of nterest (Equaton 3) !!! + = K K K K K Equaton 3 s substtuted for the effectve hydraulc conductvtes n equaton 2, and t s assumed that $x and $y are equal. After these steps, the equaton can be solved for the head at each node as seen n Equaton 4: (1) (2) (3)

80 70!! " # $ $ % & + +!! " # $ $ % & + +!! " # $ $ % & + +!! " # $ $ % & +!! " # $ $ % & + +!! " # $ $ % & + +!! " # $ $ % & + +!! " # $ $ % & + = ' ' + + ' ' + + ' ' ' ' + ' ,, 1,, 1,, 1,, 1,, 1,, 1,, 1,, 1,, 1,, 1, 1,, 1,, 1, 1,, 1,, 1, 1,, 1,, 1,, j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j K K K K K K K K K K K K K K K K K K K K h K K K K h K K K K h K K K K h h These equatons form the bass for estmatng the hydraulc head at any pont n the model doman. The system to be modeled s a projected cross secton of the dpole system dscussed prevously (Chapter 4). The physcal system s actually radal n geometry, but for the purposes of ths demonstraton the 2D formulaton s a reasonable approxmaton. To represent the njecton and extracton nodes n the dpole, a modfcaton s made to equaton 4 so the pumpng rate (Q) can be used nstead of fxng head values (equaton 5): h, j = h +1, j 2K, j K +1, j K, j + K +1, j " # $ % & ' + h (1, j 2K, j K +1, j K, j + K (1, j " # $ % & ' + h, j +1 2K, j K, j +1 K, j + K, j +1 " # $ % & ' + h, j (1 2K, j K, j (1 K, j + K, j (1 " # $ % & ' Q + 2K, j K +1, j K, j + K +1, j " # $ % & ' + 2K, j K (1, j K, j + K (1, j " # $ % & ' + 2K, j K, j +1 K, j + K, j +1 " # $ % & ' + 2K, j K, j (1 K, j + K, j (1 " # $ % & ' The equatons were used n a spreadsheet model wth constant-head boundares at the left and rght sdes of the doman and no-flow boundares at the top and bottom. Followng the defnton of the boundary condtons, equaton 4 was coped nto each cell and equaton 5 was placed where the njecton and extracton ponts of the dpole were located. The model calculated hydraulc heads teratvely, based on the neghborng hydraulc head values, hydraulc conductvty, and the dstances between the nodes. The hydraulc head values were used to determne groundwater veloctes n the horzontal and vertcal drectons usng Darcy s Law. These vector values were used to determne the total veloctes at each node, whch were compared to the measured veloctes. (4) (5)

81 71 The resdual sum of squares (RSS) between the measured and modeled veloctes were used to optmze the model. Ths was accomplshed usng the solver tool n Mcrosoft Excel $ to vary the hydraulc conductvtes of selected zones wthn the doman to mnmze the RSS. 5.3 Results The model was desgned wth the hydraulc conductvty at each node specfed. Whle ths flexblty could result n a perfectly optmzed velocty feld, the results would not necessarly be geologcally meanngful. Therefore, zones of varyng K were nferred n the doman on the bass of the PVP velocty measurements, and the results of Chapter 4 (Fgure 5.1). Ths analyss consdered 3 hydraulc conductvty zones where groups of PVPs had sgnfcantly dfferent speeds (Fgures 5.1 and 5.2). The ntal guesses for the hydraulc conductvtes were selected to gve reasonable fts to the velocty data (Table 5.1). Once the prelmnary velocty comparsons were satsfactory, the solver tool was used to optmze the hydraulc conductvtes to obtan a best ft. Before optmzaton, many of the veloctes modeled for large dstances from the well were hgher than the measured veloctes. These dscrepances are seen n the lower-left regon of Fgure 5.3A. Also, the model veloctes near the well (wth hgher magntudes) were slower than measured (Fgure 5.3A). The solver-optmzed soluton provded an mproved match between the expermental and modeled veloctes compared to a smulaton assumng an homogeneous aqufer (Fgure 5.3). Apart from one outlyng pont where a good ft could not be

82 72 obtaned, the measurements generally fell near the lne of perfect agreement between modeled velocty and measured velocty. The optmzed velocty soluton resulted n a zone wth 35% hgher hydraulc conductvty near the well than the background estmates. Ths result was smlar n magntude to the 12% conductvty dfference seen n the best breakthrough-curve match seen n Chapter 4, and demonstrated the senstvty of the flow system to heterogenety close to the well. 5.4 Conclusons Drect velocty measurements can be used as an optmzaton tool for groundwater modelng. However, no off-the-shelf tools yet exst to use ths type of data for optmzaton. In ths work, a smple model was used to optmze hydraulc conductvty estmates usng velocty. The results show marked mprovement n the match between modeled and expermentally determned velocty estmates, and demonstrated the utlty of the technque. The optmzed velocty model used a hydraulc conductvty near the well that was 35% hgher than the background value. Ths small change further demonstrated the senstvty of the flow system to the area proxmal to the well and was smlar n magntude to the best match breakthrough curve soluton seen n Chapter 4. In the future, ths model could be adapted to three-dmensons, and smlar technques could be adapted to commercal modelng software.

83 73 Table 5.1: Hydraulc conductvty values used n velocty optmzaton. Zone Hydraulc Conductvty Intal Tral (m/s) Hydraulc conductvty Tral 2 (m/s) Measured Veloctes Faster than Modeled Veloctes (Yellow Zone) Measured Veloctes Slower than Modeled Veloctes (Blue Zone) Optmzed Hydraulc conductvty (m/s) 1.74 x x x x x x 10-6 Background (Whte Zone) 1.16 x x x 10-5

84 Fgure 5.1: The locaton of PVPs n cross secton. The PVP measured veloctes are projected nto the same plane n the model. The yellow regon corresponds wth the PVP measured veloctes that were hgher than expected. The blue regon corresponds wth PVP measured veloctes that were lower than expected. 74

85 Fgure 5.2: The hydraulc conductvty feld of the model. The yellow regon corresponds wth the PVP measured veloctes that were hgher than expected. The blue regon corresponds wth PVP measured veloctes that were lower than expected. 75

86 76 Fgure 5.3: Measured and modeled velocty comparson for the homogeneous (A) and optmzed (B) velocty models. The lne represents the best case where both veloctes are equal.

87 77 Chapter 6: Conclusons and Recommendatons 6.1 Conclusons The objectves of ths thess were: Desgn, construct, and test a smple, nexpensve, and leak resstant apparatus sutable for creatng a controlled flow system n porous meda at the benchtop scale; desgn, construct, laboratory test, and feld-test a prototype PVP capable of measurng horzontal and vertcal flow; desgn, construct, and feld-test a devce capable of measurng groundwater velocty n the well skn of an operatng dpole well; and characterze the flow system around a dpole well to assst n the smulaton of tracer movement n the aqufer durng a Dpole Flow and Reactve Tracer Test wth a numercal model. The need for an nexpensve flow-through tank desgn resulted n the desgn and constructon of the Nested Storage Tank system, NeST. Ths system was desgned as an easy-to-construct apparatus for laboratory testng where a well-controlled flow system was requred. The flow was unform n the tank ~10 cm and beyond from the upgradent boundary, whch was non-unform because of the rrgaton fttngs. There were no observable boundary effects n the center of the porous medum where most tests were conducted. Furthermore, the velocty was predctable and several dfferent velocty estmates agreed wthn 25%. Much of the uncertanty n velocty was attrbutable to the porosty, whch was dffcult to measure precsely. The NeST s sutable for many applcatons where a flow-through tank s desred ncludng teachng and research. The PVP presented n ths work s a novel desgn, whch s smaller than the prevously avalable PVPs and constructed usng a dfferent technque. The

88 78 PVP s capable of measurng horzontal and vertcal flow wth an average uncertanty n magntude of 15% and an average uncertanty n drecton of ± 8. These results agree well wth prevous PVP desgns n sandy materal, but showed a small negatve bas (Labaky et al., 2007). The veloctes determned usng the PVP was also compared to veloctes calculated for the NeST usng flow and tracer tests. The complete sute of veloctes agreed to wthn 25% n velocty magntude, despte operatng on dfferent prncples and scales. These results suggest the PVP can successfully characterze flow n a 3-dmensonal flow system n sandy materal. After testng the Pont Velocty Probe n the laboratory usng the NeST, an array of probes was deployed surroundng an operatng dpole well n the feld. The PVP results ndcate veloctes were faster near the well than predcted by a model. Furthermore, the areal extent of the test was smaller than an homogeneous-aqufer model predcted. These results helped explan some of the dfferences observed n breakthrough curve behavor n a Vsual MODFLOW Pro model usng the MT3DMS transport engne (Zheng and Wang, 1999). The model results show that many dfferent types of dstal heterogenety can result n smlar breakthrough curve behavor. However, the area wthn 0.4 m of the well s crtcal to the shape of the BTC. A devce to determne velocty n the well skn of an operatng dpole well was also desgned and used. Ths devce showed that velocty n the zone mmedately next to the outsde of the casng was very fast. In the case of the flter packed well, the average velocty was ~8500 cm/day for a pumpng rate of

89 ml/mn. The results at the non-flter packed well and at hgher flow rates were dffcult to nterpret because the resoluton of the datalogger was nsuffcent to dscern arrval tmes of the tracer at the detectors. Despte ths dffculty, the velocty appears to be much faster than n the non-flter packed well and suggests a near-nstantaneous transmttal of tracer from the njecton screen to the extracton screen. Fnally, a smple model was developed to optmze hydraulc conductvty values usng measured veloctes. Ths model demonstrated that twodmensonal model velocty estmates could be mproved usng the technque. A 2D model s lmted, but t was beyond the scope of ths work to develop a threedmensonal model wth a connected nonlnear optmzer Recommendatons Ths research focused on the development of a small PVP capable of measurng flow n 3-dmensons. Ths type of data s desrable for characterzng complex flow found n remedaton systems. Development of the PVP should be furthered to provde hgh-qualty velocty data for many projects. The manufacturng process currently lmts the speed of PVP desgn evoluton. Automatng the constructon of PVPs wth a rapd prototypng machne could overcome ths lmtaton, and should be pursued. Another area that requres further nvestgaton s the affect of PVP sze on velocty. Prelmnary results presented n Appendx D ndcate a possble sze

90 80 bas, but ths s not supported theoretcally. Therefore, a systematc nvestgaton of ths effect s recommended. In the case of the Dpole Flow and Reactve Tracer Test, the area very close to the well appears to be crucal to the breakthrough curve results. The PVPs were placed at dstances of 0.4 m and greater from the well. PVPs placed even closer to the well may be able to provde more nformaton nsde ths crtcal zone. The model results suggest that heterogenety at greater dstances has less affect on the BTC behavor, but a heterogeneous model may be necessary to accurately estmate aqufer parameters usng the DFRTT. Further work could be done to characterze the velocty n the well skn of a DFRTT by ncreasng datalogger resoluton, or ncreasng the separaton of the detectors. The utlty of drect velocty measurements n modelng was demonstrated n Chapter 5. However, the work was lmted to the 2D case. Developng a 2D radal flow model, or a 3D model would make ths optmzaton more valuable. Addng parameter estmaton and optmzaton usng velocty data to an off-theshelf model would enhance the utlty of drect velocty measurements and allow wder access to the optmzaton tools.

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95 85 Reha, B A Numercal Interpretaton Model for the Dpole Flow and Reactve Tracer Test. M. Sc. thess, Department of Earth Scences, Unversty of Waterloo, Waterloo, Ontaro, Canada. Roos, G.N Development of the Dpole Flow and Reactve Tracer Test for Aqufer Parameter Estmaton. M. Sc. thess, Department of Earth Scences, Unversty of Waterloo, Waterloo, Ontaro, Canada. Rovey, C.W., and D.S. Cherkauer Scale Dependency of Hydraulc Conductvty Measurements. Ground Water vol. 33, no. 5: Sabatn, D.A., Knox, R.C., J.H. Harwell, T. Soerens, L. Chen, R.E. Brown, C.C. West Desgn of a Surfactant Remedaton Feld Demonstraton Based on Laboratory and Modelng Studes. Ground Water vol. 35, ssue 6: Schllg, P.C., J.F. Devln, J.A. Roberts, G.P. Tsoflas, and M.A. McGlashan Transent Heterogenety n an Aqufer Undergong Boremedaton of Hydrocarbons. Ground Water. Do: /j x Schllg, P.C VelProbePE: An Automated Spreadsheet Program for Interpretng Pont Velocty Probe Breakthrough Curves. In Preparaton. Schulze-Makuch, D., D.A. Carlson, D.S. Cherkauer, and P. Malk Scale dependency of hydraulc conductvty n heterogeneous meda. Ground Water vol. 37, no. 6: Sllman, S.E., Zheng, L., and Conwell, P The Use of Laboratory Experments for the Study of Conservatve Solute Transport n Heterogeneous Porous Meda. Hydrogeology Journal vol. 6: no. 1: Smpson, M.J., Clement, T.P., and Gallop, T.A Laboratory and Numercal Investgaton of Flow and Transport Near a Seepage-Face Boundary. Ground Water vol. 41, no. 5: Sternberg, S.P.K., Cushman, J.H., and Greenkorn, R.A Laboratory Observaton of Non-local Dsperson. Transport n Porous Meda vol. 23: Su, G.W. B.M. Frefeld, C.M. Oldenburg, P.D. Jordan, and P.F. Daley Interpretng veloctes from heat-based flow sensors by numercal smulaton. Ground Water 44, no. 3: Sudcky, E.A A natural gradent experment on solute transport n a sand aqufer: Spatal varablty of hydraulc conductvty and ts role n the

96 86 dsperson process. Water Resources Research vol. 22, no. 13: Thomson, N.R., Reha, B., McKnght, D., Smalley, A.L., and Banwart, S.A An overvew of the dpole flow n stu reactor. In Proceedngs, 33rd Annual Conference of the Canadan Socety for Cvl Engneerng. Toronto, Ontaro. June 2-4, Tomlnson, D.W., Thomson, N.R., Johnson, R.L., and Redman, J.D Ar dstrbuton n the Borden aqufer durng I n stu ar spargng. Journal of Contamnant Hydrology vol. 67, no. 1-4: U.S. EPA Roy F. Weston, Inc. and IEG Technologes Corporaton Unterdruck-Verdampfer-Brunnen (UVB) Technology. EPA/540/R-95/500. March. U.S. EPA Technology Evaluaton Report for the NoVOCS TM Technology. EPA/540/R-00/502a. Watson, S.J., Barry, D.A., Schottng, R.J., and Hassanzadeh, S.M On the Valdty of Darcy s Law for Stable Hgh-concentraton Dsplacements n Granular Porous Meda. Transport n Porous Meda vol. 47, no. 2: Woodbury, A.D., and Sudcky, E.A The geostatstcal characterstcs of the Borden aqufer. Water Resources Research vol. 27, no. 4: Zheng, C., and P.P. Wang MT3DMS, A Modular Three-Dmensonal Multspeces Transport Model for Smulaton of Advecton, Dsperson, and Chemcal Reactons of Contamnants n Groundwater Systems. Documentaton and User Gude. Contract Report SERDP-99-1, U.S. Army Engneer Research and Development Center, Vcksburg, MS. Zlotnk, V.A., and Zurbuchen, B.R Dpole probe: Desgn and feld applcatons of a sngle- borehole devce for measurements of vertcal varatons of hydraulc conductvty. Ground Water vol. 36, no.6:

97 87 Appendx A: Well Skn Velocty Determnaton The formaton-well casng nterface s an area of nterest n many pumpng wells. Ths area, known as the well skn, can have a great effect on the results of aqufer tests. These effects are only sparsely reported n the groundwater lterature. The avalable studes show that skns are lkely caused by compacton of the formaton durng well constructon, nvason of drllng mud and fnes nto the aqufer, or cloggng of the well screen tself (Barrash et al., 2006, Novakowsk, 1989). Much of the avalable research has been theoretcal and resulted n models that show well-skn effects may lead to naccurate aqufer characterzaton (Barrash et al., 2006, Ramey and Agarwal, 1972). Some have suggested that hydraulc conductvty has been naccurately estmated by 1-2 orders of magntude n sngle-well aqufer tests due to the presence of well skns (Hyder and Butler, 1995, Faust and Mercer, 1985, Moench and Hseh, 1985). The skn effect fnds relevance n ths study because of prelmnary results of the Dpole Flow and Reactve Tracer Tests suggest an early breakthrough of tracer that may be related to the well skn. In order to nvestgate ths phenomenon, wells were constructed wth PVP style detectors on the outsde of the casng (Chapter 3). These wells, one wth flter pack and one wthout, were used to montor the breakthrough of salne tracer along the well skn of an operatng well. Two detectors were placed approxmately 15 cm apart on the well casng and the arrval of tracer at each detector was used to determne the velocty.

98 88 Results The velocty n the skn zone s very fast. In the case of the flter packed well, the average velocty s ~8500 cm/day (Table 1). These veloctes were determned at a pumpng rate of 300 ml/mn, whch s slower than used n most DFRTTs. Tests conducted at hgher pumpng rates had results that were hard to nterpret because the peaks arrved too close together. Ths was also a problem for the tests conducted n the well wthout a flter pack. The resoluton of the datalogger was not suffcent to dscern the dfference n arrval tme precsely. However, the velocty appears to be greater than 100,000 cm/day. Ths results n a nearly nstantaneous transmttal of tracer from the njecton screen to the extracton screen. Ths nstantaneous response s useful because t allows for the start tme of DFRTT results to be more precsely determned for the purpose of modelng and aqufer characterzaton.

99 89 Table 1: Well skn velocty data from well MWB. Ths well has no flter pack and the detectors are 15.8 cm apart. The velocty data here s dffcult to nterpret because the datalogger resoluton was not hgh enough. Month Test Peak Detector Tme 1 Tme 2 Average Velocty June June June June June June June June Sept Sept Sept Sept Sept Sept Sept Sept Sept Sept Sept Sept

100 Table 2: Well skn velocty data from well MWA. Ths well s completed wth a flter pack and the detectors are 14.7 cm apart. The average velocty s 8510 cm/day. Month Test Peak Detector Tme 1 Tme 2 Average Velocty June June June June June June June June June June June June June June June June June June Sept Sept Sept Sept Sept Sept Sept Sept Sept Sept Sept Sept

101 91 Appendx B: Vsual MODFLOW Model In order to evaluate feld velocty data, a model was created to smulate the effect of heterogenety on the velocty and breakthrough curves. The model conssts of a 10 x 10 x 10 m (x, y, z; wdth/length/depth) doman wth the dpole devce centrally located. The dpole was represented by two pumpng wells, one extracton well and one njecton well placed at dfferent depths. The cells between the wells were nactve and represented the porton of the well bore closed by a packer. The doman was hghly dscretzed n the regon near the pumpng well. The water table was represented 0.5m below ground surface (bgs) by constant-head boundares. A small gradent (0.007) was mposed n some cases usng slghtly dfferent constant-head boundares. The tracer was modeled usng the MT3DMS engne wth a conservatve tracer at a pumpng rate of 700 ml/mn. The system was generally modeled for 4 hours, but some longer runs were used to evaluate dfferent hydraulc conductvty regons. When veloctes were compared, the pumpng rate was 1100 ml/mn. Other general model nput data can be found n Table B.1. A lst of dfferent cases presented n Chapter 4 can be seen n table B.2.

102 92 Table B.1: Vsual MODFLOW model parameters. Parameter Specfc Storage Value Source 1.00E-05 MODFLOW Default Specfc Yeld 0.3 Nwankwor 1984 Porosty 0.4 Brewster et al Longtudnal Dspersvty 0.01 Sudcky et al Injecton well screen dmensons Extracton well screen dmensons 5.24m to 5.4 m 4.8m to 4.96 m Tracer njecton tme 10 mn Feld Condtons Dpole prototype dmensons measured from bottom up Dpole prototype dmensons measured from bottom up Table B.2: Vsual MODFLOW nput parameters used to smulate breakthrough curve behavor at a flow rate of 700 ml/mn. Tral Breakthrough Curve Results Overall Hydraulc Conductvty (m/s) Secondary Hydraulc Conductvty (m/s) Model Doman Fgure Homogeneous Fgure 4.8 Homogeneous 5.80E-05 N/A Fgure B.1 Homogeneous wth Gradent Identcal to Homogeneous 5.80E-05 N/A Fgure B.1 Shallow Lower K zone Fgure 4.8 A 5.80E E-05 Fgure B.2 Central Hgh K zone Fgure 4.8 B 3.87E E-05 Fgure B.3 Deep Lower K zone Fgure 4.8 C 5.80E E-05 Fgure B.4 Hgh Conductvty zone near well Fgure 4.8 D 3.87E E-5 Fgure B.5 Hgh Conductvty zone proxmal to well Fgure 4.10 A 5.80E E-05 Fgure B.6 Low conductvty zone proxmal to well Fgure 4.10 B 5.80E E-05 Fgure B.6 Hgh Conductvty zone proxmal to well 2 Fgure 4.11 B 5.80E E-05 Fgure B.6

103 Fgure B.1: A cross secton of the hydraulc conductvty doman used for the homogeneous and homogeneous wth gradent modelng cases. The dmensons are 10m by 10m. 93

104 94 Fgure B.2: A cross secton of the hydraulc conductvty doman used to smulate a low hydraulc conductvty zone near the njecton porton of the dpole well. The whte zone has a hydraulc conductvty of 5.8 x 10-5 m/s and the blue zone has a hydraulc conductvty of 3.87 x 10-5 m/s. The dmensons are 10m by 10m.

105 95 Fgure B.3: A cross secton of the hydraulc conductvty doman used to smulate a hgh hydraulc conductvty zone between the screen of the dpole well. The whte zone has a hydraulc conductvty of 3.87 x 10-5 m/s and the blue zone has a hydraulc conductvty of 5.8 x 10-5 m/s. The dmensons are 10m by 10m.

106 Fgure B.4: A cross secton of the hydraulc conductvty doman used to smulate a low hydraulc conductvty zone near the extracton screen of the dpole well. The whte zone has a hydraulc conductvty of 5.8 x 10-5 m/s and the blue zone has a hydraulc conductvty of 3.87 x 10-5 m/s. The dmensons are 10m by 10m. 96

107 Fgure B.5: A cross secton of the hydraulc conductvty doman used to smulate a dscontnuous hgh hydraulc conductvty zone near the dpole well. The whte zone has a hydraulc conductvty of 3.87 x 10-5 m/s and the blue zone has a hydraulc conductvty of 5.80 x 10-5 m/s. The dmensons are 10m by 10m. 97

108 Fgure B.6: A cross secton of the hydraulc conductvty doman used to smulate a hgh hydraulc conductvty zone proxmal to the screen of the dpole well. The whte zone has a hydraulc conductvty of 5.8 x 10-5 m/s and the blue zone has the hydraulc conductvtes reported n Table B.2. The scale here s smaller than the other fgures (B.1-B.5) to capture the detal near the well. The dmensons show the regon from 2.9 to 6.8 m (n x) and 3.9 to 6.1 m (n z). 98