Geo 4971W/5971 Pump Test Report Analyzes Aquifer Properties
1. Geo 4971W/5971 Pump Test 7/29/16
Pumping Test Report
Produced for Geo 4971W/5971 Hydrogeology Field Camp
Sean Haugen
Geology Department, University of Minnesota Morris
600 E 4th
St. Morris, MN 56267
Updated
7/29/16
Executive summary
0.0 From July 21st
to July 23rd
2016 the University of Minnesota(UMN) Hydrology field camp class performed a multi-well pump test to study
aquifer characteristics. The test was performed at the UMN field site near Akeley Minnesota. Pumpingwas doneusing pumpingwell (PW)
2 in the surficial aquifer and HB-1 that reaches a deep confining aquifer. Monitoring wells (MW) were used for data collection. The Jacob
methodwas used for data analysis. MWnumbers6 and19 were analyzedwith this methodto evaluatethe hydrogeologicalcharacteristics
of the aquifers. PW-2 created a coneof depressionthatincreased over time with aneffective radius of over1000 feetwith steady recovery.
HB-1 caused drawdownwithin the confined deep aquifer.
1.0
2. Geo 4971W/5971 Pump Test 7/29/16
TABLE OF CONTENTS
0.0 Executive summary……………………………………………………………………………………………………………….........1
1.0 Introduction………………………………………………………………………………………………………………………………….1
2.0 Methods………………………………………………………………………………………………………………………………..........3
3.0 Results…………………………………………………………………………………………………………………………………………..4
4.0 Discussion……………………………………………………………………………………………………………………………………..5
5.0 Conclusion………………………………………………………………………………………………………………………………….…6
6.0 Appendices……………………………………………………………………………………………………………………………………7
Introduction/Background
1.0 A pumptest was performed by the University of MinnesotaHydrology field camp class of 2016. The site was locatednear Akeley in north-
central Minnesotain July 2016. Pumpingtestsare used as a methodfor studyingaquifer characteristics over an extensive area. Situated between
Crystaland Williams lakes, lakes formed by the collision and melting of Wadena andsuperior lobes. The field site is onoutwashsandfrom the two
glaciers. The sedimentis mostly fine to mediumsand.
1.1 Hydrologic map and cross sectional analysis shows flow of the upper aquifer from Crystal to Williams lake. Flow is in this site may be
considered to be generally isotropic and homogeneous(Alexendar, Sarr 2012), ideal for aquifer testing. The study was to look at how pumping will
effect a systemundermore controlled conditions.
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1.2 The first test was conductedfrom PW-2 with a depth of 105 feet. The pump test began at 12:00pmonJuly 21st
2016 in the near surficial,
unconfined aquifer with a thickness of 40 feet. A second test was performed at HB-1 and monitored from HB-2 on July 22nd
, drilled to a depth of
225.76 feet, reaching the deep confined aquifer with a thicknessof 20 feet. Each pumptest ran for 3 days. Monitoringwells (MW) 6 and 19 were
significant in the analysis and interpretation of the pump test. A multi-well pump test was used in conjuncture with the Jacob method of data
interpretation to analyze data collected. This method is used to evaluate the hydrogeological parameters for drawdown (∆s) Transmissivity (T),
Hydraulic conductivity (K), Storativity (S), andu (Appendix: figure 5)
Methods
2.0 The multi-well pumptest worksby creating a flux of water removed from a well creating drawdowncone of depressionincreasing farther
away fromthe pumpingwell with time. Assumptionsforthe testinclude the aquifer havinganinfinite areal extent, theaquifer is homogeneousand
isotropic with uniform thickness, the water table is horizontal, the pump screens the entire aquifer, flow is radial, and the aquifer is pumped at a
constantdischarge(Q) with the well being 100% efficient.
2.1 Beginning onJuly 17th
, fourdaysbefore the pumpingtest began, static water measurementswere takenusingwater level measuringtape.
Initial measurementswere done to assessthe average water level in each well which could thenbe usedas a reference to find drawdown. Multiple
water level measurementswere takenfor each well to within 0.01ftin order to minimize humanerror. During pumpingwater measurementswere
also taken from monitoring wells in the surrounding area each day using water level tape or monitored electronically using data loggers installed
inside someof the well.
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2.2 Pumps were attached to PW-2 and HB-1. Each pumped water into a 120-gallon metal basin which drained into PVC pipe. PW2 used 33
lengths of 10-foot pipe and some amount of white piping (conversation with Scott), draining the water over 330 feet away into a topographic
depression known as lake Randolph. Pumping for PW2 started at 12:00pm on July 21st
and ran for 3 days before unexpected factors caused the
pumpto shutoff around7:00amonJuly 24th
. PW2 was notturned back on as sufficient data hadbeen collected. HB2 started pumpingonJuly 22nd
at 1:20pmand was deliberately stoppedon July 24th
at 12:20pm. Finalwater levels were collected after pumpingended to assess recharge of the
system.
2.2 The data was compiled and analyzed using the Jacob method to determine the hydrologic conditions of the aquifers. Graphical
representations of the data were created in association with the Jacob method. The Jacob method for drawdown is based on Taylor series
approximations. Assumingasmalluvalue, as pumpingtime(t) increases andradial distance(r) of the monitoringwellsfrom the pumpwell decrease,
u will become small. This then simplifies the
equation and the Jacob equation can then be
converted into logarithmic base 10 form
(Alexander and Sarr, 2011). From the simplified Jacob equation, and graphs based on
the collected data, Transmisivity, storativity, and hydraulic conductivity can be found. Transmissivity was calculated differently for distance
drawdownand time drawdown(appendix: figure 1)
DistanceDrawdown for T
𝑇 =
2.3𝑄
2𝜋∆𝑆
Time–Drawdown for T
𝑇 =
2.3𝑄
4𝜋∆𝑆
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Results
3.0 Pumpinginthe surficial aquifer from PW-2 discharged140 gallonsperminute. The analysisfromthe Jacobmethodfordrawdownwith time
show’san initial spike in drawdown early during the pumptest for bothMW-19 andMW-6. MW-19 islocated at a radius closer to PW2 thanMW-
6. Time drawdownfor MW-6 (Graph 1) showsa spike in drawdown starting at 40 minuteswith a steady increase in drawdownoccurring until 300
minutes. MW-19(Graph 2) however shows a significant increase occurring at around 10 minutes and achieves a steady state at 350 minutes.
drawdownis larger at MW-19 thanit is at MW-6. T andS are bothlarger at MW-19 thanatMW-6 (appendix:table 1).
3.1 Distance drawdown (graph 3) shows the radius in feet of the monitoring wells away from PW-2. Drawdown was monitored for each well
andrecorded attimes 180, 1320,and2050minutes(appendix:table2)duringthepumptest. The first day of pumpingshowswellsthathada radius
of over 100 feet away from PW-2 having very little or no drawdown. Average drawdown for each well during the first day is 0.3 feet. The T value
showsarate of 22.84 squarefeetperminute. Thesecondday showsasignificant increase indrawdownfor all monitoringwellswith a large decrease
in T and a slight decrease in K. The point of zero drawdown was at a radius of 575 feet. There was however an increase in S and the subsequentu
value. The thirdday yielded only a slight increase of 0.10 inthe hydraulic head. There was a 125-footincreasein the value where where drawdown
equalszero. T decreased only slightly by about.2 squarefeet per minuteandK decreased by less than.1 footper minute. Theaverage S onthe third
day varied slightly by .02. The u value also fell on the final test day by .05. MW-15, locatedclosest to PW2 with a radiusof 11.5 feet and did show
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significantly more drawdown than all the other wells throughout all three days the pump test was performed. It can thus be disregarded when
plottingthe line of best fit for each series in this analysis. (see appendix: graph3, table 2)
3.2 HB-2 is located at a radius552 feet away from HB-1. HB-1 was pumpingat a rate of 40 gallons per minute. Significant Drawdownstarted to
occur at 4.5 minutesfrom the start of pumpingandremained relatively linear from 9 minutes to 200 minutes(appendix:figure 4). The data shows
a high rate of T, low hydraulicconductivity, anextremely low S, anda relatively low u value.
Discussion
4.0 Time drawdown analysis in the surficial aquifer shows that PW-2 created a cone of depression that increased over time with an effective
radius of over 1000 feet. Drawdown between MW-19 andMW-6 differ by 0.16 feet. There also seem to be discrepanciesof K andT between MW-
19 and MW-6. Thelow K andT valuesin MW-19 seemto indicate thatwater is unable tomove aseasily throughthe aquifer even thoughMW-19 is
closer to PW-2. However, this is due to MW-19’s well being deeper, with a depth of 77 feet. The screened section of MW-19 is also accessing a
portionlesspermeable fine sandlayeralongwith a portionof coarserpermeable sediment. MW-6 islocatedat a shallowerdepthof 68 feet, located
in theeasily permeable sedimentlayer(appendix:table 5). MW-6 isalsolocatedcloser tolake Randolphwhichismostlikely providingsomemeasure
of seepage intoMW-6, effecting drawdownandfacilitating recovery.
4.1 Distance drawdown analysis shows that the radial distance away from PW-2 has a significant impact on the hydrologic properties of the
aquifer. Graph2 in the appendicesclearly indicates thatwells located closer in radiusto PW-2 havehigheramountsofdrawdownin each measured
time. The drastic changein water flowing with respect to T, fromday 1 to day 2 showsthatthe environmentin which flow is occurringhas changed
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from broadandextensive drawdown, to a more concentrated flow, getting water from deeper within the aquifer. This illustrates the idea of a cone
of depression. The low storativity values in the initial and late stages of pumping show that volume of water being drawn down is lowest during
initial and final stagesof pumping. However, day 2 showed a large increase in storativity whichshowsthat thesurficial aquifer is actively recovering
with recharge occurring at fairly high rates. This higher recharge is most likely due toleakage from lake Randolph.
4.2 HB-2 shows that pumping has substantial effects in a confined aquifer. The effects can bee seen by lookingat the much lower discharge of
40 gallons per minute thatis yielding a larger drawdownvalue than either of the surficial monitoringwells. Other significant effects can be seen by
looking at the large T value and extremely small S (appendix: table 3) in the deep aquifer. These values show that water is moving at a high rate
throughtheaquifer at 1.35 squarefeet per minute. There is noindication of any inflow of water tooffset discharge duringthetest period indicating
thatrecovery is restricted. From thesediment analysiswe knowthatthere is a fine sandlayer with low permeability thatis limiting recovery butnot
inhibitingit. Thus doesnot confirm a completely confined deep aquifer and may suggestrecharge occurring elsewhere in the aquifer.
4.3 Alexander and Sarr (2011) suggest a umax of 0.2 to fit within the regression. In order to produce a sufficiently low u using the Jacob time-
drawdownanalysis, alow u mustbe extrapolatedfrom time basedthegraph’sdisplayedinthe appendices, ufor time-drawdownislow with a value
of u=.19 at480 minutes. ufordistance-drawdownissufficiently low when calculated, andu for the deepaquifer is sufficiently low with u= 0.19 after
13 minutes.
Conclusion
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5.0 Pumpingtest can providevaluable insight into the hydrogeologic setting of aquifers. This pumptest shows that recovery can be a limiting
factor as seen with lake Randolph having effected the recovery rate of MW-6 without any effect on MW-19. This must be considered when
interpreting recovery rates. However, Lake Randolph cannot explain all of the recovery occurring in the surficial aquifer. Results from the pool
drainage would providea goodindication for recovery rates in the surficial aquifer if performed in multiple areas.
5.1 There is also a limitation for measurementsof HB-2, as HB-1 is the only monitoringwell for the deep aquifer. In order to fully understand
hydrologicsetting in the deep, confined aquifer, more wells mustbe drilled and monitored.
Appendices:
