INVESTIGATION OF THE GROUND WATER FLOW SYSTEM IN GEM VALLEY
by Marc A, Norton Idaho Department of Water Resources Boise, Idaho September 1981 INVESTIGATION 01<' THE GROUND WATER PLOW SYSTEM IN GEM VALLEY
Page
ACKNOWLEDGEMENTS 1
INTRODUCTION 2 Location of Gem Valley------2 Scope of the Report------2
GEOHYDROLOGIC SETTING------4 Geology------4 Hydrology------11
WELL DESIGN AND ITS AFFECT ON PUMPING LEVELS------22
CONCLUSIONS------27
RECOMMENDATIONS 28
REFERENCES------29 LIST OF FIGURES AND TABLES
Figures Page
1. Location of Gem Valley, Portneuf Valley and Gentile Valley------3 2. Geologic map of Thatcher Basin and geologic cross sections (Bright, 1963) ------5 3a-i. Development of Lake Thatcher and the present day drainage pattern (Bright, 1963) ------6-8 4. Ground water contour map showing the location of the divide and tl1e direction of flow----- 13
5. Location of observation wells------15 6. Hydrographs from several wells in Gem Valley 16 7. Hydrograph of domestic well TlOS-R40E-5CBB and precipitation data from Grace, Idaho 18
8. Hydrograph of domestic well T9S-R39E-23BAD ----- 19 9. Hydrographs showing long term ground water level fluctuations------20 10. Well designs for a shallow well------25
11. Well designs for a deep well------26
Tables
1. Specific capacity of several wells in Gem and Portneuf Valleys (Norvitch & Larson, 1970) 23 1
ACKNOWLEDGMENTS
The author would like to thank the residents of Gem Valley for their cooperation during the investigation by allowing access
to IDWR field personnel,
The assistance of John D. Carlson and Harold W. Jones, IDWR staff personnel, during the data collection phase is greatly appreciated. 2
INTRODUCTION
Location of Gem Valley
Gem Valley is located 45 miles southeast of Pocatello along the divide between the Bear and Portneuf river basins. Portneuf
Valley forms the northern boundary while the Bear River cuts through the southern end of Gem Valley (Figure 1). Mountain ranges form the east-west boundaries, with the Fish Creek Range to the east and the Soda Springs Hills and the Bear River Range to the west. The Bear River enters Gem Valley through a gap be tween the Soda Springs Hills to the north and the Bear River Range to the south. The river follows the valley edge southward before turning west, cutting the Black Canyon, then flows south through
Gentile Valley. The valley floor slopes gently away from Soda
Point at an elevation of 5700 feet above sea level towards the southwest to Turner with an elevation of 5500 feet and toward the northwest to Bancroft with an elevation of 5450 feet.
Scope of the Report
In response to inquiries from Gem Valley Water Users con cerning possible declining ground water levels and well inter ference problems, a geohydrologic study was initiated by the
Department. The specific objectives of the study were to:
1) determine if ground water levels were declining on a local or regional level; and 2) determine if well interference was affecting water user's ability to fill their water rights. 3
\ \ - 5
,1 c
Figure 1. Location of Gem Valley, Portneuf Valley and Gentile Valley. 4
-GEOHYDROLOGIC SET'rING
Geology
The drainage system of ancestral Thatcher Basin was con-
siderably different 34,000 years ago than it is today. Thatcher
Basin included all of Portneuf Valley, Gem Valley, and Gentile
Valley (Figure 2). Figures 3a-i illustrate the following
discussion. Bear River and the drainage from Gem and Gentile
Valleys flowed north, joining the Portneuf River, then leaving the Thatcher Basin through the Portneuf Gorge. Local basalt flows in the Portneuf Gorge dammed the surface drainage sys tern approximately 33,500 years ago causing Lake Thatcher to form.
The lake level rose and sediments from the rivers and streams we re deposited in the backwaters behind the basalt dam. Over the next thousand years, basal ts began filling the bas in and even- tually divided the lake in half, Lake levels continued to rise as no stream left the lake. Lake bed sediments and basalt flows continued to fill in the lake. Approximately 27,000 years ago,
Lake Thatcher began to overflow at its southern shore, diverting the flow south into Lake Bonneville and initiated the downcutting that formed the Oneida Narrows. By 20,000 years ago, Lake
Thatcher had drained and erosion began on the sediments that were deposited in the lake, Beat' River began cutting its present channel through the basalts to form Black Canyon. Approximately
18,000 years ago, the level of Lake Bonneville had t'isen to a level that backed its waters into southern Gem Valley and all of
Gentile Valley. Lake Bonneville overflowed its dam at Red Rock 5
Figure 2. Geologic mo cross sect i '"'p of (B,,ght,Tholcher 1963).Basin ood geol ogic
0
,·
LIOS
0 4 5mi.
CJ Volconic Pits
'l{- Cinder Cun.,s
t Springs
T.IIS
[']] Ow 0001 ~Oppl.
lilllllJ Qp Ni!er Loess EJobo
~Op1t
Og Qgvp T.12 s. o,,09vp1 i 0QVO
OTslo Figure 3C
Mountains
Drainage Divide
Basalt
Drainage
Red Rock,./ Poss
0 !Omi.
>> 34,000 YEARS AGO 33,500 YEARS AGO 32,500 YEARS AGO
Figures 3A-3C. Development of Lake Thatcher and the present day drainage pattern (Bright, 1963). "
Figure 3F
Mountains
~
Drainage Divide
Basalt
Drainage- ~
O IOmi.
YEARS AGO < 27,000 YEARS AGO 20,000! YEARS AGO
Figures 3D-3F. Development of Lake Thatcher and the present day drainage patter (Bright, 1963), '-J 'mil
Figure 3G Figure 3H Figure 3 I
Mountains ~
Drainage Divide Basalt.. Drainage ~ Terminus of Bear River Delta :-:·:·:·:-:-:·'.:·, ..
0 10 mi
1s,ooo! YEARS AGO 13,900: YEARS AGO < 11,000 YEARS AGO
Figures 3G-3I. Development of Lake Thatcher and the present day drainage pattern (Bright, 1963). 0: 9
Pass and the watet' level began dt'opping t'apidly till the channel peached bedpock (13,900 yeat's ago). Lake Bonneville continued to dt'ain at a slower' Pate. Inflow to the lake was less than outflow so the level continued to dt'op until it Peached its ppesent day size (Gt'eat Salt Lake). The supface featut'es shown in Figut'e 31 at'e similar' to ppesent day conditions.
Geblogic ct'oss sections demonstt'ate the cut'Pent geologic envit'onment (Figut'e 2). The gt'ound watet' flow system is gt'eatly affected by the geologic events that fopmed the pt'esent day topogt'aphy, The sediments that wer·e deposited in Lake Tha tchet' undet'lie the basalts in most of Gem Valley. Gt'avel and sand beds a Pe generally confined to the bas in margins and the mouths of stl:'eams. As a stpeam leaves the mountains and entet's the valley, the velocity of the stt'eam genet'ally decreases due to a change in the gcadient of the supface that the stt'eam flows over', As the stream's velocity dect'eases the ability of the stt'eam to carry sediment also decl:'eases. Ther'efol:'e, the coal:'ser, heavier', sedi ments at'e deposited fit'st. The sediments grade finer' towards the center of the valley with silt and clay beds interfinger'ing with the neat' shot'e sands and gravels. The Gem Volcanics ape dark to vel:'y dark gray porphyritic olivine basalts. PorphyPitic is a textural term desct'ibing igneous rock with lat'ge crystals, in this case - made of olivine, set in a finer mass, The basalt is fine-to-medium gpained, slightly vesicular ovel:'all, and very vesicular at the top of the flow units. Vesicular' basalts have small cavities that fot'med by the explosion of a bubble of gas or steam duping the solidification lU
of the basalt, The major source of the basal ts were the cones and fissures near Alexander and between Niter and the Grace power
plant. A second source for the basalts was the Blackfoot Lava
Field, These basalts flowed through Ten Mile Pass and past Soda
Point.
Recent geophysical work in Gem Valley may have located a buried river channel along the western side of the valley (Mabey,
1971), Lake Thatcher may have overflowed the basalt dam at the
Portneuf Gap allowing a channel to form. If the buried channel exists, it may be the reason for wells penetrating more sediments along the western edge of the valley than wells further to the east. Wells completed in these sediments need to be constructed in such a way as to limit sand from entering the well,
Due to the complex geology of the interface between the lake bed sediments and the basalts, it would be difficult to identify any given well depth at which point, deepening would no longer provide an increase in well yield. Most of the wells drilled for irrigation purposes are 200-300 feet deep; only a few are deeper than 400 feet. The following wells were completed below 500 feet:
Location Depth of Well Depth to Water
1. T.8S.-R.39E,-Sec. 16 575 feet 90 feet
2. T,9S.-R,39E.-Sec. 8 585 feet 109 feet
3, T.9S.-R.40E.-Sec. 20 525 feet 140 feet
Wells #1 and #2 completely penetrated the lake bed sediments with no basalt flows before entering the sandstones, limestone, or shales of the Salt Lake formation or pre-Tertiary formations 11
(shales). Well yields from the Salt Lake Formation range from O to 1800 gallons per minute in the Bear River Valley. Well #3 did
not fully penetrate the lake bed sediments, but did penetrate
several basalt flows. No well yield information was reported for
any of the three wells. Generally, the deeper the well, the
lower the water level, but not in all cases. Continued drilling
with a~uifer tests would determine if deeper wells would be of
benefit.
Mapping of the lake bed sediment-basalt interface could only
be accomplished on a coarse scale because of the limited data
available. Because of the complex nature of interface, this
would be of little value in planning well locations and depths. More care should be taken in well design and construction the
closer the well site is to the valley margin. Also, the more
sediment encountered, the more critical the well design and con
struction.
Hydrology The ground water flow system in Gem Valley is an unconfined aquifer except where saturated porous basalts are encountered beneath clay layers of the lake bed deposits which causes arte sian pressure (confined aquifer). Wells may intercept one large producing zone or several small producing zones depending on the geology penetrated at that particular site.
Recharge to aquifer(s) occurs from precipitation both on the valley floors and as surface runoff from the mountains as there is very little surface drainage over much of the valley.
Recharge probably also occurs as ground water flows through Ten lZ
Mile Pass and through the gap at Soda Point. Seepage from irri gation canals and infiltration of excess irrigation watep, both
surface and sprinkler' applied, also recharges the aquifer.
Discharge from tl1e ground water' flow system occurs as:
1) evapotranspi ration where the potentiometric surface is neap
land surface; 2) discharge from spPings into the BeaP and
Portneuf Rivers; 3) ground water flow through the Pot'tneuf Gap;
and, 4) through it'rigation, domestic, and municipal pumpage.
Evapotranspiration takes place neap the springs and in the areas near the Pivers and streams. Several springs occur on both sides
of Black Canyon.
The direction of ground water flow in Gem Valley is uniq,rn because a ground water divide sepaPates the valley into two flow syste1ns (Figut'e 4). The ground water divide is not well defined towards Soda Point but is better' defined towards Buckskin
Mountain. The location of the divide is not stationary as changes in the flow pattern will develop in response to changes in pumpage or recharge, thus affecting the shape and position of the divide: the ground water north of the divide flows northwest discharging into the Portneuf Rivet' ot' as ground water under flow tl1rough the Portneuf Gap. South of the divide, the ground water flows south-soutln1est, discharging into the Bear Rivet' as springs in Black Canyon. Soutl1east of the Bear River, the ground water flow system is approximately 75 feet lower in elevation and the direction of flow is west towards the Bear Rivet', also discharging from sevct'al springs.
As of November 1980, there were six observation wells in the ,13 \ / • _: I / ·- . ,•. • ·~ -.-l!rr-~,~·'-"<'./--:- -- ,. •: . ------··· ...... • . .I r • r r r .• ' ' I I 1 : ·' : ( :.~· ~.:j :--~~~-~ :--rrrrr.r I~ ' ' •
,·,y·,, • 'l.~~- _.,' .... '. ' - ·r,r•r, •- •:' •' ijf![;..,c__"'=----~~~--;-,:----"---!---~ ------··,. .;,,·:. ·'
t<[f MAP
Figure 4 . Ground water contour map showing the location of the divide and the direction of flow. 14
Portneuf, Gem and Gentile Valleys monitored by the Geological
Survey. Five more wells were monitored by the Department between
July and December 1980. Continuous water level recorders were
installed on three of the wells. Figure 5 shows the location of
the observation wells.
Water level recot'ders designed to operate while a pump is
operating were installed in Everett Smith's irrigation well
(TlOS-R40E-Sec. 5BDD) and in Marvin Smith's irrigation well
(TlOS-R40E-Sec. 8BBA). The water level in the Everett Smith well dropped 56 feet from June 16 to June 30, 1980. Due to recorder pt'oblems, measut'ements were discontinued until October 15, 1980 when the water level was four feet above the June pre-pumping level (Figure 6). The water level Pose almost two feet during
October and November, then began a slow decline through December and January.
The Marvin Smith irrigation well, TlOS-R40E-Sec. 8BBA, had a drawdown of 62 feet, but within two days after the pump was shut off, the water' level was only two feet lower than pre-pumping levels and was higher' than pre-pumping levels within two weeks
(Figure 6). The hydrograph shows the water level recovered very rapidly when the pump was shut off. The water level fluctuated very little during the winter months.
The Russell Rich well, TlOS-R40E-Sec. 5CBB, is an unused dom estic well drilled in June 1980. The well is located approximately
1500 feet west of the E. Smith well and 2 700 feet northwest of the the M. Smith well. Monitoring of the water' level in the Rich well began the same day that both the M. Smith and E. Smith wells began ,15 .· ..
•i, r """'""-":_;",·~·.-.:- •: • ., .. ,. .. ; ' •, .• ' I r r •• r r • , ,. ' 1 : I '1 ' 'l {::.:::f-~---i • , .•. -:----·--- ... - ... • • •
-,-_,r ,, • _n - •·-..- •'
'Fq• r, <. •:' • --ry' . ' r---; ' l~(~J ,; J C~Rl80U (OUNfY J ______,, ____ l•i ~:''---·· Figure 5. Location of observation wells. Ill 5460 5456 v·· +·· ., +--~··+···-+"····"-·~· T-··+·· ··+·····.1, .. +.···-+·····+·····t---.,t..·...... _ ····+···-+ -- + - -,l.---•-1- T.95., R.39E.,23BAD - +- -+ 5452 W. Lloyd, Domestic ¥"1'-· ...... +····"'····*'' ,t·····+· 5448 Gap 5428 - 8 +- ---- . t-,t-+-+-t-t-i-t-i-... -+- -+- - ,J- i,--+--;, T.IOS., R.40E.,BBA ...... 5420 M. Smilh .,- - E Smilh ...... ___ o-o-o, __ -n- o - o - D 0 • 0-...... · -0 .... 0 ... 0 ... ·P.:::'.o:0-·::''0-- .. -·0-0-··- . <> ··•,.ow·o.--« ...... ·~"-~o-o- 0-....0 ...... o ...... -11. . • ., • . • T.!OS., R.40E.~BDD ...... ~ o--- r1..... r:r···p··--0·· 0 5412 E.Smith 0 ·c>-~· o-·-·.o···.o.. ···· T.105., R.40E.,5CBB R. Rich 5404 I I 5396 I \--<-" ..,,.__ $"({ Z.,0 -- 535:j :::;: b~ I 5388 5380 Fl GURE 6. Hydrogrophs From Several 5372 Wells In Gem Volley. 5364 .-~~~.-~-l~-J:r---:-~:.._-rJ__-;-::-::--.~--;:;::--~.-~~;---.~-;;;;;;;-~.----;;;;;;~-i-~-:;;;;;--~-.-~;;;i;---r~-;-;;-;-~r---;;:;;~--i-- 5356 Moy Jun Jul Aug Sep Ocl Nov Dec Jon Feb Mar Apr 1980 1981 ,... O' 17 pur~ping in June 1980. The water level only dropped one foot over a four week period in late June and early July. The water level rose one foot in July, 4.5 feet in August, and approximately one foot in September. The water level began fluctuating in early October with an overall rise of one foot through Octo be r-Novembe r (Figures 6 & 7). The water level declined 2.7 feet during December and January. Both an unused domestic well (T9S-R39E-Sec. 23BAD) and an irrigation well (T9S-R39E-Sec. 23AAA) of Warren Lloyd's were monitored. Spot measurements of the irrigation well were made during the summer while a water level recorder was installed on the domestic well in early July. The water level in the domestic well declined approximately one foot over' three weeks then began rising slowly for the next four months (Figures 6 & 8). The ,, water level declined approximately 0.5 feet from December to c ' 'v.__(y-r "-'' January. As no well log exists for the Lloyd domestic well, well ,,- ' construction and geologic data are not available. The well is located approximately 3000 feet west of the irrigation well. Seepage from the West Branch Canal, located approximately 1000 feet west of the domestic well, probably recharges the ground water system which is indicated by W1e rise in the ground water level of the domestic well. Long term Hater level records in Gem Valley go back to 1967 and show only seasonal fluctuations. Ground water levels rise during the spring runoff and the summer irrigation season and decline during the winter months. No long term declines are indicated (Figure 9). \:;, 5418 5417 :t 5416 .··.·r- ,1' ·-i: ...... -.f ·.;{:·· ·... ··+· + ..(!.· 5415 ,.._ .. ·.. -u. ··t-. 0 Removed 5414 ..> .+ ····+-...... [ Recorder ..J .." ' 5413 en ' "<-..._ + "> ...... ,,0 t, ... '+ 5412 + Water Level Measured With Tope Or Sounder c '- .S? Water Level Token Off Recorder Charts '+, 0 + '+ > 5411 .!! R. Rich-Irrigation Well "'~ +··· " + ... 5410 3:" ~ .,, .. + +···· c :, "'0 ..._"+·t-r··· 0 5409 ~ = '---Diversions Begon .lune 18, 1980 FIGURE 7. Hydrogroph of domestic well T.IOS.,R.40E. 5 CBB and Precipitot,on Doto from Groce, Idaho. > c ~ 1 5458 ~ 5457 Recorder Removed -t Water Level Measured With Tapa Or Sounder ..:·:I':,:..,.-:,{'··: ... :.~. 5456 .. ···+ Water Level Token Off Recorder Charts -~·-'/':" · ·.. t , £ ' W. Lloyd~ Unused Domestic \A/ell ~' ' " 5455 .+ •• ' +- - "-"' .+.. : -., t• '+...._ "> 5454 '+, ...J"' .f 0 ·.· '+ U)"' ... ol' 5453 .· > "'0 f .Q 0 > + w"' 5451 ~ "' 0 ... 3' 5450 "'c -t- 5447 FIGURE 8. Hydro9roph of Domestic Well T9S., R.39E., 23 BAD 5446 Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr 1980 1981 ..... '-D ~-- Diversions Began June 18, 1980 .. OBSERVATION WELL HYDROGRAPHS, GEM VALLEY, IDAHO 9S-39E-02CBCI ( Don Rigby) 60 70 w (.) 80 ~ a:: ::::> 90 U) DRY DRY Clz 60 70 80 A A A A A - ----, ----T~~ -i-- r-----~ -- -, -1 ---- I 1-~------.------.---- 1967 68 69 70 71 72 73 74 75 76 77 78 79 80 YEAR c" Figure 9. Hydrographs showing long term ground water level fluctuations. 21 Quantification of the effects of pumping in Gem Valley on the springs in Black Canyon or on the ground water flow into the Pot'tneuf River System are beyond the scope of this study. The natural ground water flow sys tern, composed of recharge, lateral flow, and discharge, has been affected by irrigation development. Surface water irrigation added a new source of recharge to the ground water flow system. The distribution system has changed over the years as well as the timing of the discharges. Areas formerly irt'igated by surface methods have largely been conver'ted to more efficient sprinkler systems and the saved water applied to additional lands. The rnot'e efficient use of surface watet' reduces t'echarge to the ground water system and the inct'easing use of ground watet' fol' irt'igation will change tl1e natut'al discharge from A noticeable reduction 111 flow of some of the spt'ings on the c1outll side of Black Canyon resulted from the t'eplacement of the leaky wood stave pipeline which cat'ried water to the Gt'ace powet' plant. Utah Powe!' and Light Company has, in recent yeat's, found it necessat'y to pass watet' down Black Canyon at times in ordet' fot' Gentile Valley Canal to obtain an adequate supply because of an appat'ent decrease in flow of the spt'ings (,Jay Haight, Personal Comrnunic8.tion). Because t11is decrease is tI1e result of several factot's, it would be extremely difficult to segregate the effect caused by irrigation pumping. WELL DESIGN AND ITS EFFECT ON PUMPING LEVELS The specific capacity (Q/s) of a well is determined by dividing the rate of discharge from the well (Q) by the drawdown of the water level (s) within the well. Well construction, devel opment, and the amount and location of perfot'a tions affects the t'elationship between discharge (Q) and drawdown (s). The ratio between discharge and dt'awdown (Q/s) dect'eases with increasing discharge when well losses at'e high. Well loss is drawdown due to tut'bulent flow of water through tl1e perforations in the casing. Tut'bulent flow can be reduced by lowet'ing the discharge from the well until the velocity of the water passing through the perforations is between O .1 to O. 25 feet per second. A second method would be to increase the amount of open at'ea in the casing. The open area of a casing is the at'ea of open space per lineal foot. Listed in Table 1 at'e specific capacities of several wells in Gem and Portneuf valleys. The specific capacity of wells penetPating mostly basalts t'anges from 270 to 2625 gpm/ft of dpawdown while wells that penett'ate both sediments and basalts have specific capacities that t'ange ft'om appt'oximately 2 to 31.3 gpm/ft of drawdown. It should also be mentioned that fot' wells completed in unconfined aquifers, the specific capacity decreases with increased dt'awdown. Well constpuctlon plays a greater' r•ole in the pt'oductivity of v1ells completed in unconsolidated sediments than in basalts. The location, size, and amount of pet'forations must be lat'ge TABLE 1. Specific Capacity* of Several Wells i11 Geo and Portneuf Valleys ( Norvi tch & Larson, 1970) ------··----~-----·----·------·-·- Geology of Aquifer Well Deptll Discharge Drawdown Specific Static Water Qb =basalt Qal=alluvium, Location (Feet) ( GPM) (Feet) = Capacity* Level (Feet) Tsl=lake deposits 8S-39E ldad 207 1600 3, 533. 192,64 Qb 4cdc 235 200 excessive 2 75,43 Qb, Tsl? drawdown 100. 5acb 260 495 183, 2,7 48,2 Qb' Qal?, Tsl? 8bdd 293 1000 50. 20. ------Qb' Qal?, Tsl? lOada 345 1575 o.6 2625, 197,5 Qb 15cba 173 1350 5. 270. 110 .1 Qb 8S-39E 22bac 185 300 0,2 1500, 84.68 Qb 27acb 355 300 45, 6,7 107.97 Qb' Qal?, Tsl? 34add 170 1850 1, 1850. 83.39 Qb 8S-40E 16dcd 247 610 150, 4,1 63.80 Qb' Qal?, Tsl? 2ldaa 175 2288 73. 31. 3 71. 66 Qb' Qal?, Tsl? 9S-39E 2dbb 132 1350 negligible 1227, ------Qb drawdown 1.1 10S-40E 5BDD** 208 1400 56,4 24.8 88.6 Qb' Qal?, Tsl? * Discharge in gallons per minute divided by drawdown in feet, ** Data collected by IDWR personnel on E. Smith well (June 19 80) , '-""' 24 enough to allow the desired discharge to enter the well within the velocity requirements while preventing silt and sand from entering the well, Alternative well designs could include: 1) well screen alone; 2) gravel packing with well screen; or, 3) gravel packing with an increase in perforations pet' foot of casing, Thet'e at'e several kinds of screens on the mat'ket including the wire wrapped screen, the wedge shaped wire Wt'ap screen, the shutter screen, and the gravel guat'd screen. The latter' two sct'eens have a vet'tical or hot'izontal louver' designed slot pattern. Any of these screens have a greater' open area pet' foot than a slotted casing (up to 10 times as much open area pet' lineal foot [Johnson Division]), Hypothetically, compat'e the design of four wells: 1) wells "A" and "B" are 164 feet deep and are located in the same water' table aquifer (Figure 10); and, 2) wells "C'' and ''D" are 330 feet deep and penetrate two pt'oducing zones (Figure 11), Wells A and C were constructed similar to it't'igation wells in Gem Valley while wells B and D demonstrate an altet'native well design; well screen. Well screen with the same diameter as the slotted casing would allow the same amount of water to enter the well, but at a lower entrance velocity and when properly sized, prevent sand from entering the well. When the entrance velocity is maintained below 0.1 ft. per second, friction losses will be negligible and the rates of incrustation and corrosion will be minimum (Johnson Division). Wells A, B, C, and Dare only examples of possible well designs. Each well should be constructed to meet the specific geologic conditions encountered and the desired well yield. r11i;1urts 1v. vvu11 uui;;1yni;; Tor u sna11ow we11. 25 WELL A WELL B Typi ca I Construction Alternative Construction Pump Pads Ground Surface Surface Seal Surface Sea I Broken Lava Static Water ----~Silty Sand ----~ Level Solid Lava 14" Casing---, Silty Clay -14"Casing Yo llow Clay a I a B B 1 14"Slotted Sandy Grovel 1 8 I DI I I I I I Cosing Gray Clay 14"Slotted Gravel Pack Casing Sandy Cloy -14" Well Screen I 1111 20 Slot I I I Sandy Gravel r1gure 11. we11 oes1gns for a shallow well. WELL C WELL D Pump Pads Typical Construction A I tornative Construction Ground Surface Top Soil Surface Seal ----- Surface Seal -----Yellow Clay----- 20" Casing 20" Casing Solid Lava Static Water Level 20" Slotted B I I I I --f-- Broken Lava I Casing B I I I U I 2 o" s I otted -Casing Solid Lava Yellow Clay Gray Silty Clay Brown Silty Clay Soma Gravel 14"Casing- Hard So Ii d Lava -14" Casing 14" Slotted Broken Lava 14" SI otted Casing Casing 14" Wei I Screen 20 Slot ~-!..14" Slotted Hard Sol id Lava Casing ii 27 Conclusions 1, Wells penetrating the basalt aquifers in Gem Valley are good to excellent producers (1350 GPM with 5 ft. of drawdown) while wells completed in the lake bed sedi- ments and basalts interfingered are poor to good produ- cers ( 610 GPM with 150 ft. of drawdown) . 2. USGS observation wells in Gem Valley do not indicate any long term decline of grou11d water levels, 3. An irrigation well, TlOS-R40E-Sec. 8886," re cove red rapidly from pLimping for' tne 1980 irrigation season. 4. Two unused domestic wells showed very little response to nearby irrigation pumping. 5, Wells that encounter heaving sand zones in the lake bed sediments could show a decrease in the well yield and/or excessive wear on the pump bowls if the well construe- tion does not prevent the movement of sand into the well. 6. Ground water fluctuations do not indicate that the cones of depression caused by production pumping are of great areal extent, therefore, well interference does not play a significant role in well yield problems at this time. 7. Pumping levels in Gem Valley are a result of aquifer chan1cteristics and well construction, not major well interference or large scale depletion of the ground water resource, 28 Recommendations 1. Wells penetrating the lake bed sediments that are experiencing yield problems should either be pumped at a lower rate so that the pump does not ''suck air" or be deepened, either encountering more pt'oduction zones or ppoviding stot'age and the ability to pump fpom a lower depth. 2, New wells or reconstructed wells to be completed in sand zones should consider alternatives to slotted casing: 1) well scpeen, 2) well screen and gravel packing, or 3) gravel packing with slotted casing. z ') REFEHl,NCES Bright, Robert C., 1963, Pleistocene Lakes Thatcher and Bonneville, Soutl1eastern Idaho, PHd. Thesis, University of Minnesota. Dion, N.P., 1969, Hydrologic Reconnaissance of the Bear River Basin in Southeastern Idaho, Water Information Bulletin No. 13, Haight, Jay, 1980, Utah Power and Light Company, Personal Communication to A, Robertson. Mabey, Don R., 1971, Geophysical Data Relating to a Possible Pleistocene Overflow of Lake Bonneville at Gem Valley, South eastern Idaho, U.S. Geological Survey Prof. Paper 7508, Norvitch, R.F., and Lar'son, A.L., 1970, A Reconnaissance of the Water Resources in the Portneuf River' Basin, Idaho, Water' Information Bulletin No. 16, U.S. Geological Survey - Water Resources Division, 1980, Ground water Levels in Caribou County, Idaho. Mabey, Don R., 1975, Gr'ound Water and Wells, Johnson Division, UOP Inc., Saint Paul, Minnesota.