Ecological Research Series
IRRIGATION WASTEWATER DISPOSAL WELL
STUDIES-SNAKE PLAIN AOUIFER
Robert S. Kerr Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-77-071
June 1977
IRRIGATION WASTEWATER DISPOSAL WELL STUDIES
SNAKE PLAIN AQUIFER
by
William G. Graham
Darrel W. Clapp
Thomas A. Putkey
Idaho Department of Water Resources
Statehouse
Boise, Idaho 83720
Grant No, R802931
Project Officer
D. Craig Shew
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ADA, OKLAHOMA 74820
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DISCLAIMER
This report has been reviewed by the Robert S. Kerr Environmental
Research Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or recom-
mendation for use.
11
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FOREWORD
The Environmental Protection Agency was established to coordinate
administration of the major Federal programs designed to protect the
quality of our environment.
An important part of the Agency's effort involves the search for
information about environmental problems, management techniques, and new
technologies through which optimum use of the Nation's land and water
resources can be assured and the threat pollution poses to the welfare
of the American people can be minimized.
EPA's Office of Research and Development conducts this search through
a nationwide network of research facilities.
As one of these facilities, the Robert S. Kerr Environmental Research
Laboratory is responsible for the management of programs to: (a) investi-
gate the nature, transport, fate, and management of pollutants in ground
water; (b) develop and demonstrate methods for treating wastewaters with
soil and other natural systems; (c) develop and demonstrate pollution con-
trol technologies for irrigation return flows; (d) develop and demonstrate
pollution control technologies to prevent, control, or abate pollution from
the petroleum refining and petrochemical industries; and (f) develop and
demonstrate technologies to manage pollution resulting from combinations of
industrial wastewaters or industrial/municipal wastewaters.
This report contributes to the knowledge essential if the EPA is to
meet the requirements of environmental laws that it establish and enforce
pollution control standards which are reasonable, cost effective, and
provide adequate protection for the American public.
William C. Galegar
Director
111
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ABSTRACT
Drain wells are used to dispose of excess irrigation and surface runoff
water from approximately 320,000 a of agricultural land within the eastern
Snake River Plain area of southern Idaho. The impact of this practice on the
underlying Snake Plain aquifer, the primary source of potable water for
approximately 140,000 people, was not understood. Thus, an investigation was
initiated to evaluate the impact of irrigation disposal well practices on the
water quality of the Snake Plain aquifer.
A study site was selected where the geology was determined to be charac-
teristic of areas in the Snake River Plain where irrigation disposal wells
are extensively used. Alternating permeable and dense basalt layers underlie
the discharge site. The aquifer at the project site was defined as a leaky
artesian groundwater system.
Initial quality of the artesian groundwater was found to be within Idaho
drinking water standards. Pesticides, herbicides, and trace metal concentra-
tions in the irrigation wastewater were within drinking water standards.
Total and fecal coliform bacteria and sediment were the only contaminants
found in irrigation wastewater in excess of drinking water standards.
Wastewater discharge to the disposal well resulted in the formation of a
nonsymmetrical recharge zone. Rapid lateral movement of the discharge water
through the recharge zone indicated that flow was through fractures and chan-
nels. Bacterial levels and turbidity within the recharge zone approached
those of the discharged wastewater and were far in excess of drinking water
standards.
Deep percolation of injected wastewater resulted in bacterial contamina-
tion of both the deep perched water zone overlying the confining layer and
the artesian groundwater system. Suspended solids, as measured by turbidity,
were filtered out by the percolation process.
This report was submitted in fulfillment of Grant No. R802931 by
Idaho Department of Water Resources under the sponsorship of the U.S. Environ-
mental Protection Agency. This report covers the period November 19, 1973 to
September 22, 1976; and work was completed as of September 17, 1976.
IV
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CONTENTS
Foreword
Abstract iv
Figures vi
Tables vii
Acknowledgments ix
1. .Introduction 1
2. Conclusions 4
3. Recommendations 5
4. Description of Research Site and Construction of Facilities . . 6
Site selection , 6
Construction of facilities--1974 through 1975 6
Construction of facilities--1976 10
5. Methods 13
First discharge event 14
Second discharge event 15
Third discharge event 15
Fourth discharge event 15
Determination of geological structure 16
6. Results and Discussion 17
Geology 17
Background quality of groundwater 23
Quality of irrigation wastewater 26
Discharge events conducted during the 1975 irrigation
season 26
Discharge event conducted in 1976 42
7. References 50
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FIGURES
Number Page
1 Index map of Idaho exhibiting areas of concentrated
agricultural disposal well use 2
2 Location of disposal well project site 7
3 Site facilities—disposal well project 8
4 Locations of deep monitoring wells and shallow test wells ... 12
5 Isometric fence diagram for the disposal well project site . . 18
6 Stratigraphic cross section of the disposal well project site . 19
7 Stratigraphic cross section of initial discharge zones .... 21
8 Decrease of selected enteric bacteria in water from shallow
well, SW6 —first discharge event 41
VI
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TABLES
Numbers Page
1 Construction Features of Deep Monitoring Wells 9
2 Construction Features of Shallow Monitoring Wells 10
3 Features of Modified Deep Monitoring Wells 11
4 Construction Features of Cased Shallow Wells 11
5 Background Quality of Artesian Groundwater 24
6 Quality of Irrigation Wastewater, June 26, 1975 to
August 24, 1976 27
7 Depths to Water for Shallow Wells—First Discharge Event .... 30
8 Depths to Water for Shallow Wells—Second Discharge Event ... 31
9 Depths to Water for Shallow Wells—Third Discharge Event .... 32
10 Chemical Quality of Water in Shallow Wells and of Injected
Wastewater—First and Third Discharge Events 34
11 Chemical Quality of Artesian Groundwater During Discharge
Events 35
12 Dye Concentrations in Water from Shallow Wells 36
13 Dye Concentrations in Artesian Groundwater 37
14 Levels of Indicator Bacteria in Groundwater—First Discharge
Event 38
15 Levels of Indicator Bacteria in Water from Shallow Wells--
First Discharge Event 40
16 Levels of Indicator Bacteria in Groundwater-- Second
Discharge Event 42
17 Levels of Indicator Bacteria in Water from Shallow Wells--
Second Discharge Event 43
VII
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TABLES (contined)
Number Page
18 Levels of Indicator Bacteria in Groundwater—Third Discharge
Event 44
19 Levels of Indicator Bacteria in Water from Shallow Wells--
Third Discharge Event 45
20 Depths to Water Within Shallow and Deep Monitoring Wells-
Fourth Discharge Event 46
21 Specific Conductance and Turbidity of Wastewater and Water
from Both Shallow and Deep Monitoring Wells—Fourth
Discharge Event 47
22 Levels of Bacteria in Wastewater and Water from Both Shallow
and Deep Monitoring WeiIs--Fourth Discharge Event 48
Vlll
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ACKNOWLEDGMENTS
We gratefully acknowledge the U.S. Bureau of Reclamation for permitting
the construction of project facilities on lands administered through their
office and for water quality analyses performed in their regional laboratory.
Especial thanks are given to Everett Williams, USER, for his cooperation with
the water quality analyses.
Our appreciation is also extended to the A § B Irrigation District for
their cooperation in providing the project with a constant source of irriga-
tion wastewater, storage space for equipment, and assistance in maintaining
the project site.
IX
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SECTION 1
INTRODUCTION
Drain wells have been a common means of disposing of irrigation waste-
water and natural runoff from agricultural land within the eastern Snake
River Plain area of southern Idaho (1-2). This practice has been developed
as a result of large areas with rolling topography and internal drainage pat-
terns combined with a loess overburden of relatively low permeability. Agri-
cultural land in areas of internal drainage would have been rendered unusable
if a feasible means for disposal of wastewater had not been found.
The geology underlying the eastern Snake River Plain consists of a se-
quence of successive flows of basalt intercalated with sedimentary and uncon-
solidated pyroclastic interbeds. Many of the basaltic flows comprising this
sequence are highly fractured and readily accept large volumes of wastewater.
Where saturated, these permeable flows compose the Snake Plain aquifer,
which underlie nearly all of the eastern Snake River Plain and provide the
most prolific water-bearing sequence in Idaho (fig. 1). This aquifer is the
primary source of potable water for approximately 140,000 (3) people in addi-
tion to supporting agriculture and fish propagation.
Department records indicate that up to 1300 km2 (320,000 a) of agricul-
tural land within the eastern Snake River Plain are drained by over 2000 dis-
posal wells. Concentrated use of disposal wells occurs in Gooding, Lincoln,
Jerome, and Minidoka Counties of south-central Idaho and Jefferson, Bonne-
ville, and Bingham Counties of southeastern Idaho (fig. 1). These wells are
typically 10-30 cm in diameter, 30-50 m in depth, and are capable of accept-
ing flows up to 8 m3/min.
Studies of irrigation return flows in areas of the Snake Plain aquifer
indicate that sediment loads and bacterial concentrations in such waters
present the most obvious threat to degradation of groundwater quality (4-5).
Both Bondurant and Carter determined that the applied water in the Twin Falls
tract has low ionic concentrations and that surface runoff water exhibits only
a slight increase in nitrate ion and a decrease in orthophosphate ion as com-
pared to the applied water. No information is currently available on the
possible contamination of groundwater by the sediment and associated adsorbed
chemicals present in irrigation wastewater injected into disposal wells.
In response to public concern for the protection of groundwater quality,
the Idaho State Legislature assigned the responsibility for regulating the
use of waste disposal wells to the Department of Water Resources. The law-
makers recognized that any practice or condition which potentially limits the
usefulness of the Snake Plain aquifer has serious economic and public health
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EXPLANATION
Areas of concentrated agricultural disposal well use
—Approximate boundary of Snake River Aquifer
.....Approximate boundary of Snake River Plain
FIGURE I. Index map of Idaho exhibiting areas of concentrated agricultural disposal well use
(adapted from Moreland, Seitz and LaSala, 1976)
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implications. They also recognized that continued use of disposal wells may
be necessary to the economic survival of irrigated agriculture. Consequently,
they provided that the present or future use of any waste disposal well used
exclusively for the disposal of irrigation wastewater or surface runoff water
should not be prevented where such disposal does not adversely affect domestic
water supply. The lawmakers therefore charged the departments of Water
Resources and Health and Welfare with establishing criteria and standards for
the disposal of irrigation wastewater.
Adequate data were not available to evaluate the effect of injecting
irrigation tailwater runoff into a basalt aquifer. Thus, there was an im-
mediate need to collect this data. This study was designed to:
1) Further define the quality of irrigation wastewater.
2) Determine the areal extent of the saturated recharge zone resulting
from discharges to the disposal well.
3) Determine the ability of successive basalt flows intercalated with
unconsolidated interbeds to remove contaminants from irrigation wastewater.
4) Determine water quality changes within the groundwater system re-
sulting from the use of agricultural disposal wells.
The results will be used by Idaho departments of Water Resources and
Health and Welfare to set standards regulating the use of irrigation disposal
wells. Once the standards are set, the economics of meeting these standards
can be developed.
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SECTION 2
CONCLUSIONS
Coliform bacteria and sediment were the only contaminants found in irri-
gation wastewater in excess of Idaho's drinking water standards. The chemi-
cal quality of wastewater with respect to common ions surpassed that of
groundwater. Pesticides, herbicides, and trace metal concentrations in the
irrigation wastewater were within drinking water standards.
Discharge to the disposal well generated a nonsymmetrical recharge zone.
The areal extent of the recharge zone increased during each successive dis-
charge event. This data indicated that groundwater flow in the upper receiv-
ing system was through fractures and channels in the overlying basalt after
the initial clay and rubble discharge zone had become saturated. Discharge
water moved rapidly through the upper recharge zone, having traveled beyond
120 m within 4 days during the fourth discharge event.
Purification of wastewater moving both laterally through the recharge
zone and vertically through the underlying basalt flows was limited. Bacter-
ial levels in the recharge zone approximated those in the discharged waste-
water and were far in excess of drinking water standards. Bacterial contam-
ination of both the deep perched water zone and the confined aquifer during
the discharge events was apparent. However, turbidity was reduced as the
injected wastewater percolated downward through the basalt formations.
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SECTION 3
RECOMMENDATIONS
From the results obtained in this project, it is evident that the use of
irrigation disposal wells could lead to the contamination of domestic ground-
water supplies. It is, therefore, recommended that frequent monitoring of
the Snake Plain aquifer be conducted in areas of intensive disposal well use.
It is further suggested that future studies be conducted to:
1) Determine the technical and economic feasibility of removing bacteria
and suspended solids from irrigation wastewater prior to subsurface injection.
2) Define the ability of indicator bacteria to denote the presence of
pathogenic bacteria and viruses in groundwater.
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SECTION 4
DESCRIPTION OF RESEARCH SITE AND CONSTRUCTION OF FACILITIES
Site Selection
The site selected for this project was approximately 40 km east of the
city of Twin Falls in south-central Idaho on land held by the U.S. Bureau of
Reclamation under a reclamation withdrawal (fig. 2). This site was most
suitable for the purposes of this study because:
1) Geological formations at the site were thought to be characteristic
of the basalt formations in those areas of the Snake River Plain where exten-
sive use is made of wells to dispose of irrigation wastewaters.
2) It was isolated from all other disposal wells.
3) No domestic wells were located in the immediate vicinity of the pro-
ject site.
4) A drainage ditch maintained by the A § B Irrigation District of
Rupert, Idaho, traversed the site and provided a continuous supply of waste-
water from over 12 km2 of agricultural land during the irrigation season.
5) The area was easily accessible.
Construction of Facilities—1974 through 1975
A diversion ditch (30 m long and 1.5 m deep) was excavated to deliver
wastewater to a holding pond (7.3 m wide, 8.5 m long, and 2.7 m deep) prior
to their entering the disposal well (fig. 3). A concrete diversion dam and
headgate at the diversion point allowed regulation of the rate of diverted
water, and a Parshall flume with a water level recorder was installed in the
diversion ditch to provide for continual measurement of the discharge flow
rate. The inlet pipe to the disposal well was placed in the holding pond
(1 m above bottom of the pond), and a screening structure (1.2 m square) was
erected around the inlet. A platform with a ladder leading to it was built
around the screening structure to enable water sampling at the inlet point.
A shallow disposal well, 20 cm diameter, was constructed 5.2 m from the
settling pond with a 20 cm pipe as a connector entering the well 3.0 m below
ground surface. The well was drilled to a depth of 38.1 m and terminated in
a clay and rubble interbed. It was cased into the first hard basalt zone
(8.2 m), and a surface seal was provided in accordance with Idaho minimum well
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FIGURE 2 LOCATION OF THE DISPOSAL WELL PROJECT SITE.
NI/2 SEI/4.SEC.34, TWP.9S, RGE.2IE, B.M.
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WING WALLS
Oc
,DIVERSION DITCH .SETTLING POND
rPARSHALL FLUME
3.1m
DISPOSAL WELL
SCREENING
STRUCTURE
AND RAMP
CROSS SECTION
WASTEWATER DRAINAGE DITCH
DIVERSION DITCH
- _ DIVERSION
V DAM
STILLING WELL
AND RECORDER
TOP VIEW
SCREENING
STRUCTURE
INLET TO DISPOSAL WELL
DISPOSAL WELL
FIGURES. SITE FACILITIES FOR THE DISPOSAL WELL PROJECT.
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construction standards. This construction was typical of irrigation disposal
wells.
In geological formations such as those underlying the project site, the
possibility existed that the wastewater might follow an irregular pattern of
movement for some distance through fractured basalt formations or enter the
deep aquifer in a direct path by way of interconnected fractures* thus avoid-
ing detection through a predetermined deep monitoring well network. It was
therefore decided to construct the monitoring well network in two stages.
Accordingly, two deep wells (DW1 and DW2) were constructed 15.2 m and
30.5 m distant from the disposal well along the theoretical downgradient
direction of water movement (8). These wells were drilled using air and
hydraulic rotary methods to a depth of 102.4 m, thus penetrating 6.1 m into
the aquifer, the top of which was approximately 96 m below land surface. The
wells were cased their entire length and were sealed from 1.5 m above the
bottom of the confining layer to land surface to prevent perched water from
moving through the annular space into the regional aquifer (see table 1 for
construction features). Standing water in both wells was at 82.3 m below land
surface indicating an artesian aquifer with a hydraulic head of 13.7 m. A
water level recorder was placed over well DW1 to measure changes in depth to
water in conjunction with subsequent discharge events.
TABLE 1. CONSTRUCTION FEATURES OF DEEP MONITORING WELLS
(all wells 12.7 cm ID)
Well
Number
DW1
DW2
DW3
DW4
DW5
Total
D* Depth (m)
15.2 (50) 102.4
30.5 (100) 102.4
45.7 (150) 98.5
45.7 (150) 100.9
45.7 (150) 100.9
Depth of Perforation Depth to
Casing (m) Zones (m) Packer (m)
102.4 95.4- 99.4
101.5-102.4
102.4 95.4- 99.4
101.5-102.4
96.6 89.6- 93.6
95.7- 96.6
100.9 93.9- 97.8
100.0-100.9
100.9 93.9- 97.8
100.0-100.9
90.5
92.7
85.3
85.3
85.3
* D = distance from disposal well in meters (feet).
A temporary shallow monitoring well network was then constructed. Test
holes of 10 cm diameter were drilled through the unsaturated cinder discharge
zone to a maximum depth of 42.7 m at distances of 7.6 m (SW1) and 61.0 m (SW2)
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in line with wells DW1 and DW2. Six additional test holes were placed at dis-
tances of 30.5 m and 61.0 m from the disposal well at 90° intervals around its
circumference.
Wastewater was discharged to the disposal well, and the injected water
was found to travel through the cinder and fractured basalt zones in rela-
tively short times. Injected water reached the nearest shallow well, 7.6 m
from the disposal well, in less than 20 min and was detected in the 30.5 m
distant shallow wells in less than 1 day. In view of this information, the
three additional deep wells were placed 45.7 m from the disposal well, one
each above and below and one upgradient from the disposal well (fig. 4).
Construction specifications were the same as. for the existing deep wells
(table 1).
Five of the original shallow wells (SW1-5) were maintained as part of
the permanent shallow monitoring well network and were cased through the
loess overburden to the first basalt layer. Four additional shallow wells
(SW6-9) were then constructed in like manner at intervals around the disposal
well (fig. 4). Construction features for these wells are given in table 2.
TABLE 2. CONSTRUCTION FEATURES OF SHALLOW MONITORING WELLS
(all wells 11.4 cm ID)
Well
Number
1
7
8
9
3
4
5
6
2
D*
7.6 (25)
15.2 (50)
15.2 (50)
15.2 (50)
30.5 (100)
30.5 (100)
30.5 (100)
30.5 (100)
61.0 (200)
Depth of
Well (m)
41.8
38.7
40.2
40.8
40.2
40.2
40.2
41.1
38.7
Depth of
Casing (m)
6.1
6.1
6.1
6.1
6.1
6.1
6.1
6.1
13.7
* D = distance from disposal well in meters (feet).
Construction of Facilities—1976
Appearance of bacteria and Rhodamine WT dye in the artesian aquifer fol-
lowing the discharge events conducted in 1975 and results from geophysical
logging suggested that the deep wells should be modified prior to conducting
any future discharges to the disposal well. The five deep wells were plugged,
pressure grouted with c.ement, and shot-perforated as per the specifications
given in table 3. Upon completion of the modification work, the deep wells
terminated in a saturated zone of moderately porous basalt (72.5-88.7 m below
land surface) overlying the confining layer of dense basalt.
10
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TABLE 3. FEATURES OF MODIFIED DEEP MONITORING WELLS
(all wells 12.7 cm ID)
Well
Number
DW1
DW2
DW3
DW4
DW5
D*
15.2 (50)
30.5 (100)
45.7 (150)
45.7 (150)
45.7 (150)
Original
Depth (ra)
102.4
102.4
96.6
100.9
100.9
Modified
Depth (m)
88.4
88.4
89.0
89.6
95.7
Perforated
Zone (m)
85.0-88.1
84.1-87.2
86.0-89.0
85.6-88.7
90.5-93.6
* D = distance from disposal well in meters (feet).
Five cased shallow wells (SW 10-14) were also constructed prior to the
1976 discharge event in line with DW1 and DW2 (fig. 4). These wells were
drilled by air rotary methods through the clay and rubble discharge zone and
were cased their entire length with 12.7 cm ID PVC plastic casing. Construc-
tion specifications are presented in table 4.
TABLE 4. CONSTRUCTION FEATURES OF CASED SHALLOW WELLS
Well
Number
SW10
SW11
SW12
SW13
SW14
D*
15.2 (50)
30.5 (100)
61.0 (200)
91.4 (300)
121.9 (400)
Depth of
Well (m)
38.9
37.2
36.0
36.9
40.2
Perforated
Zone (m)
25.3-38.9
28.0-37.2
26.5-36.0
25.9-36.9
29 .-6-40. 2
* D = distance from disposal well in meters (feet).
11
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N)
\"
.
ow3;
SW3 (!)
SW6 ™$ «
SW2 O OWIcw.1
O DW20 — •43<8) —
O 0 O O O Y
SWI4 3WI3 SWI2 SWII SWIO 1 ^
1
£>sw<
LEGEND
® DISPOSAL WELL
• DEEP WELLS
O SHALLOW TEST WELLS
JW9
O SW5
O —
B D|f
4
m DW4
SCALE Icm = l2m
FIGURE 4. LOCATIONS OF DEEP MONITORING, AND SHALLOW TEST WELLS.
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SECTION 5
METHODS
Wastewater samples were collected as grab samples at the inlet to the
disposal well during periods of discharge and at the diversion dam at other
times. The vast majority of samples were collected during discharge periods.
Methods used for the collection, preservation, and analyses for chemical
constituents were as specified by EPA (7-8). Microbiological analyses were
carried out by the membrane filter technique according to standard methods
(9). All subsequent water-quality data presented in this report were obtained
utilizing these same methodologies.
Artesian groundwater samples for determination of background quality were
obtained from the deep wells by use of a portable groundwater sampling unit of
a design modified from that of McMillion and Keeley (10). Samples were taken
after a minimum of 30 min pumping from the 96 m depth in each well.
Three discharge events were carried out over the course of the 1975 irri-
gation season while a fourth event was conducted during the 1976 season after
modifications to the monitoring well network were completed. Groundwater,
water in the recharge zone, and injection water were monitored during the dis-
charge events and thereafter.
The total volume of wastewater injected over a given discharge period was
measured by use of a Parshall flume equipped with a Stevens A-70 water stage
recorder. The rate of diverted water was adjusted to equal the maximum inflow
to the well, and hence the flow rate through the flume was the rate of inflow
to the well. A continuous record of flow rate through the flume allowed
calculation of the total volume of discharge water.
Monitoring of groundwater focused on selected enteric bacteria (total
coliforms, fecal coliforms, and fecal streptococci) and suspended solids (as
indicated by turbidity) as these were the only contaminants found in waste-
water at levels exceeding Idaho drinking water standards. In addition,
groundwater was monitored periodically for possible degradation o.f chemical
quality. Water samples were obtained with the groundwater sampling unit at a
pumping rate of 26 1/min.
The sustained presence of indicator bacteria or high turbidity in ground-
water would be taken as adequate evidence for contamination resulting from
wastewater discharge to the disposal well. This presupposes that contamina-
tion introduced inadvertently during sampling occasions would be random which
13
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seems reasonable considering the results of monitoring for background ground-
water quality.
Depths to water in the shallow wells were measured using a Fisher M-Scope
water level indicator and water samples were taken at depths of 30.5 m when-
ever possible. Water samples for chemical analyses were taken once from the
shallow wells after termination of discharge during each of the first and
third discharge events. A Kemmerer water bottle constructed of PVC plastic
was used repetitively to obtain adequate sample volumes.
Samples for Rhodamine WT dye analyses during the first two discharge
events were taken from the upper recharge zone on the last day of the dis-
charge period and on each subsequent sampling, while samples for dye analyses
during the third discharge event were taken on each sampling occasion. The
background fluorescence of wastewater was negligible compared to fluorescence
levels from the dye and consequently was ignored.
Rhodamine WT dye was used as a tracer both to follow the movement of in-
jected wastewater and to verify infiltration of this water into the artesian
groundwater system. A Turner Model 111 fluorometer equipped with a far-
infrared source and a high sensitivity cell holder was used for dye analyses.
The limit of sensitivity was determined to be 0.005 parts per billion (ppb)
of dye.
Artesian groundwater samples were taken from each deep well for the
determination of chemical constituents at least once during each of the 1975
discharge events. Samples were obtained from depths of 96 m after pumping
each well for at least 30 min. Some wells were first purged for 30 min at the
85 m depth.
First Discharge Event
Irrigation wastewater was discharged for a period of 3.4 days between
July 27 and August 1, 1975. Initially, the well was taking water at a rate
of 1.09 m3/min. This decreased to a constant inflow of 0.48-0.51 mVmin
after approximately 6 hours. A total volume of 2360 m3 of wastewater was
discharged.
Rhodamine WT dye (4.5 kg) was added as a tracer in "slugs" over the
period of discharge. A dye concentration of 0.01 ppb or greater in artesian
groundwater would be taken as adequate evidence that discharge water had
entered the artesian system. This would allow for a 1.9 x 10s dilution of dye
in groundwater assuming an even distribution of dye in the discharged
wastewater.
Artesian groundwater, depths to water, and quality of water in the re-
charge zone were monitored during the discharge period and for 25 days
thereafter.
14
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Second Discharge Event
The second discharge event was initiated 25 days after termination of the
first discharge period. Irrigation wastewater was discharged to the disposal
well at a maximum inflow of 0.48-0.51 m3/min for a period of 8.3 days between
August 26, 1975 and September 3, 1975. The wastewater was labeled with 2.3 kg
of Rhodamine WT which was added in "slugs" over the period of the discharge.
A total volume of 4540 m3 of wastewater was injected.
Artesian groundwater was monitored during the period of discharge and at
1-week intervals thereafter, with an emphasis on analyses for indicator
bacteria and dye. Sampling techniques were modified in that the deep wells
were purged by pumping at depths of 85 m for at least 30 rain prior to sampling
at depths of 96 m. On most occasions, water samples were taken at both
depths.
Well DW1 was not sampled during the second discharge event or any of the
succeeding events because it was judged to be a dead well. This decision was
based on extreme drawdown within DW1 (13 m at a pumping rate of 26 1/min)
relative to the other deep wells (0.2 m at the same pumping rate).
Depths to water in the shallow wells and the quality of water in the
upper recharge zone were monitored in the usual manner during the discharge
period and for 27 days thereafter.
Third Discharge Event
The third discharge event was carried out over a period of 16 days from
September 30, 1975 to October 16, 1975. The volume of wastewater discharged
over the first 8 days was 4540 m3 while 2380 m3 were discharged during the
second 8 days for a total of 6920 m3. The decrease in discharge volume dur-
ing the second period was attributed to a loss in head at the point of diver-
sion resulting from a substantial decrease in the flow of wastewater in the
drainage ditch. No tracer was used in this discharge event.
Artesian groundwater was monitored during the discharge period and at
14 days thereafter. The wells were purged by pumping from depths of 85 m,
except for wells DW4 and DW5 on days 2 and 29, prior to sampling at depths of
96 m. In most cases, water samples were taken from both depths.
Depths to water in the shallow wells and water quality monitoring of the
recharge zone were carried out in the usual manner during the period of dis-
charge and for 15 days thereafter.
Fourth Discharge Event
A fourth and final discharge event was conducted in 1976 after modifica-
tion of the deep monitoring well network and addition of five cased shallow
wells (SW10-14). The special objectives of this event were:
1) To determine if prior sampling techniques used in defining the qual-
ity of water in the recharge zone were providing representative results.
15
-------
2) To confirm the premise that wastewater discharged into the shallow
recharge zone was infiltrating a saturated fractured basalt zone situated
just above the confining layer of dense basalt between 78 m and 95 tn below
land surface (hereafter referred to as the deep perched water zone).
Prior to initiation of the fourth discharge event, background quality of
water of the deep perched water zone was determined. Samples were taken from
DW3 and DW5 for this purpose after purging the wells for 30 min at the 85 m
depth. Depths to groundwater were monitored to determine drawdown.
Irrigation wastewater was discharged for a period of 11.2 days from
August 13, 1976 through August 24, 1976 at an average rate of 0.52 mS/min.
The total volume of water influent to the disposal well during this event was
estimated to be 8330 m3. Both irrigation wastewater and storm runoff water
resulting from two heavy thunderstorms were injected into the recharge zone.
During this discharge event, water samples for chemical and bacterial
analysis were taken from the cased shallow wells utilizing the mobile pump-
ing unit. Samples were taken from SW10-13 after the wells were purged for
20 min. Depths to water were determined in the same manner as previously
discussed.
Groundwater within the deep perched water zone was monitored from DW3-5
during the period of discharge with emphasis on analyses for indicator bac-
teria. Wells DW1 and DW2 were not sampled as the attempted modification of
these wells was unsuccessful.
Determination of Geological Structure
The general geological formations and the lithologic characteristics of
the upper recharge zone and underlying formations were determined from geo-
physical logs of the deep wells supplemented by driller's logs for both the
deep and shallow wells. The nature of the groundwater system was defined by
the same means..
Several geophysical functions were used to define lithologic character-
istics, including: caliper, natural gamma, gamma-gamma, neutron-epithermal
neutron, neutron-gamma, spontaneous potential, and single-point resistivity.
Hydrologic characteristics were defined by use of fluid temperature, fluid
resistivity, and neutron-epithermal neutron functions.
16
-------
SECTION 6
RESULTS AND DISCUSSION
Geology
A geologic sequence of the project site constructed from geophysical logs
is presented in figure 5. A loess overburden varying in thickness from 5.5 to
17.1 m overlies a basalt zone which extends to depths varying from 29.8 to
31.1 m. A clay and rubble zone to depths of 39.0 to 39.9 m underlies the
basalt at well DW4 while a clay and sand zone extending to a depth of 41.5 m
is found at well DW5. A second basalt layer to depths varying from 92.7 to
98.8 m overlies a saturated clay and rubble zone believed to be a principal
component of the regional aquifer.
A more detailed representation of the principal geologic formations based
on interpretations of geophysical logs is shown in figure 6. The heteroge-
neous strata of basalt underlying the recharge zone consist of several alter-
nating zones of varying permeability and of unknown continuity. One zone of
dense basalt is contiguous to the recharge zone and could impede the infiltra-
tion of discharge water into the saturated clay and rubble zone of the arte-
sian aquifer.
A stratigraphic cross section of the formations from land surface to the
upper recharge zone, compiled from both geophysical logs of the disposal well
and deep wells and driller's logs for the shallow wells, is shown in figure 7.
Here the recharge zone is seen as a clay and rubble zone with an overlying
fractured basalt layer. Both are continuous across the cross-sections but
vary considerably in depths from land surface and in formation thickness.
Considering the configurations of the clay and rubble and fractured
basalt formations in the recharge zone, it seems apparent that wastewater
discharged into these zones will not form a recharge mound in the usual
sense. Furthermore, there exists the distinct possibility of channelized flow
of injected water through any fractured basalt zones that would become
saturated.
V
The groundwater system at the project site is rather simple, the primary
aquifer being a leaky artesian system in the lower clay and rubble zone. The
dense basalt strata overlying this zone is considered to be the confining
layer for the artesian system.
Water-bearing formations were noted overlying the confining layer during
the construction of wells DW2-DW5. These may be either naturally occurring,
resulting from leakage through fractures in the confining layer, or
17
-------
DW3
DW5
Horizontal Scale- lcm=4.8m
Vertical Exogtratlon'. 1.5
Overburden
Clay and Sand
Basalt
Clay and Rubble
FIGURES. ISOMETRIC FENCE DIAGRAM FOR THE DISPOSAL WELL PROJECT SITE
-------
DW4
V—
SW4
SW8
DISPOSAL
WELL
SW7
SW3
DW3
Basalt
LEGEND
D Dense
P Porous
MP Moderate Porosity
WB Water Bearing
PWB Possible Water Bearing
V Standing Water Level
Basalt
SCALE
12
18
24
30
METERS
Cloy
and
Rubble
FIGURES. STRATIGRAPHIC . CROSS SECTION OF THE DISPOSAL WELL PROJECT SITE
19
-------
SW2
OWE
DWI
Overburden
Basalt
Clay and Rubble
Clay and Rubble
SWJ
DISPOSAL
WELL
SW9
SWS
DW3
Overburden
Baialt
Clay and Rubble
Baton
0
SCALE C
12
18 24
SO
METERS
Clay and Rubble
FIGURE 6 (CONT.). STRATIGRAPHIC CROSS SECTION OF THE DISPOSAL WELL PROJECT SITE
20
-------
N
SW4
SW8
WELL
SW7
SW3
_DW3
SCALE I
0 3 6 9 It 18
METERS
FIGURE 7. STRATIGRAPHIC CROSS SECTION OF INITIAL DISCHARGE ZONES
-------
SW2
DW2
DWI SWI
DISPOSAL
WEU
SW9
SW5
OW5
NJ
0 > » » It It
SCALC II I I I "J
METEHS
LJ Hard Basalt
FIGURE 7 (CONT.). STRATIGRAPHIC CROSS SECTION OF INITIAL DISCHARGE ZONES
-------
generated perched water zones. The source (or sources) of the latter could
have been water used in drilling operations, wastewater discharged to the
disposal well in the first year, or artesian groundwater leakage through the
annular spaces at wells DW2-5. In any event, their existence must be recog-
nized in future considerations of the quality of deep percolating discharge
water which may intersect these water-bearing formations.
Background Quality of Groundwater
Background quality of artesian groundwater at the project site was
determined from samples withdrawn from the five deep wells prior to initiation
of the discharge studies in 1975 (table 5). The chemical quality of ground-
water varied at a given well from one sampling occasion to another. In view
of this, changes of similar magnitude in the chemical quality of groundwater
during periods of wastewater discharge were not considered as evidence of
deep percolating wastewater intercepting artesian groundwater.
The rather high total coliform count found in water from well DW3 on the
first sampling event was thought to be residual bacteria introduced during
well construction. Subsequent samples from this well showed no total coli-
forms present. Water samples from two other deep wells showed low total coli-
form counts on isolated occasions and, in these cases, the bacteria may have
been introduced inadvertently during sampling. The majority of water samples
showed no total coliforms, and thus the artesian groundwater was presumed to
be free of such bacteria.
High levels of noncoliform bacteria were found in water samples from
wells DW1-3. Filtration volumes of 50 ml or more often yielded a bacterial
film on the membrane filter, and numerous colonies (up to 200) were found
for 25 ml filtration volumes. It was assumed that these noncoliform bac-
teria would not interfere with the total coliform test, and further, the
absence of total coliform colonies in a 25 ml filtration volume indicated no
such bacteria in a 100 ml sample. Water samples from wells DW4 and DW5
showed a few noncoliform bacteria on occasions, which would be expected for
groundwater. The extraneous bacteria noted in water from wells DW1-3 probably
were introduced by well construction procedures.
The specific conductance of water from well DW3 was substantially lower
than that from wells DW4 and DW5, which seemed unusual for water from wells
of such close proximity in the same artesian system. One possible explana-
tion was that water of low specific conductance entered well DW3 from a
water-bearing formation overlying the confining layer. The upper perforated
area of the well casing extended into this formation, and water withdrawn
from both the artesian system and this zone could have yielded samples of
lower specific conductance than those obtained from wells DW4 and DW5. The
source of water in the upper zone may have been relatively low specific con-
ductance wastewater injected during the preliminary discharges to the dis-
posal well.
23
-------
TABLE 5. BACKGROUND QUALITY OF ARTESIAN GROUNDWATER
(samples from 96 m after minimum of 30 min pumping)
INORGANIC CHEMICAL
a>
c
r-t
i
DWl
DW2
DW3
DW4
DW5
V
4-1
n}
•o
M
C
&
§
«
2/21/75
4/ 2/75
7/ 9/75
2/20/75
4/ 2/75
7/ 9/75
1/16/75
2/21/75
4/ 4/75
7/10/75
1/16/75
2/20/75
4/ 4/75
7/ 9/75
1/16/75
2/20/75
4/ 3/75
7/ 9/75
1
-1-4 tfl
5 *
rt *>*.
Jr£ OO
132
124
149
144
144
153
193
193
198
207
158
130
149
166
155
127
148
160
W
rH
_£
§
i
0.02
0.00
0.00
0.00
---
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
-
00
•f-l
CD
DO
0.39
0.38
0.24
0.23
0.15
0.19
...
0.13
0.10
0.06
...
0.23
0.33
0.08
...
0.16
0.29
0.05
i^
00
_£
i
3
0.07
0.18
0.18
0.04
0.09
0.14
. --
0.12
0.14
0.10
---
0.05
0.13
0.05
. --
0.04
0.09
0.12
i-H
•^
bo
J3
1
a
u
0.02
<0.01
<0.01
0.02
<0.01
<0.01
-_-
<0.01
<0.01
<0.01
0.02
<0.01
<0.01
__„
0.02
<0.01
<0.01
^.
00
£
9
u
to
73.4
70.0
62.8
73.4
66.0
74.2
41.6
38.4
38.0
36.4
78.0
77.4
73.0
84.6
76.0
75.0
71.0
82.6
1
3
o
3
61.4
68.5
61.8
59.3
60.7
60.7
26.6
27.0
28.4
29.5
73.5
72.4
72.4
78.8
68.2
67.8
69.2
68.5
oo
g
1
B
O
6
<0,02
<0.02
<0.02
<0.02
<0.02
<0.02
...
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
.--
<0.02
<0.02
<0,02
5
e
1
0.08
0.13
0.04
0.04
0.03
0.05
...
<0.01
0.02
0.04
.—
<0.01
0.02
0.02
- --
0.02
0.02
0.02
1
g
M
4.60
1.15
1.05
1.70
0.90
0.50
...
0.33
0.10
0.06
_.-
0.55
0.45
0.63
0.85
0.92
0.48
B
•o
a
3
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
..-
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
i
•H
(A
1>
&,
3
12.4
13.4
12.2
14.4
15.9
13.8
17.8
16.6
17.1
16.6
17.6
15.8
17.1
IS. 2
16.5
14.6
15.9
13.3
i
c
(Q
DO
X
0.20
0.12
0.04
0.02
<0.01
0.02
0.02
<0.01
0.01
<0.01
0.01
0.01
0.01
0.01
0.02
00 00
£* *
u ^
i %
<1.0 1.00
<1.0 0.66
<1.0 0.69
<1.0 1.45
<1.0 1.38
<1.0 1.37
0.97
<1.0 0.98
<1.0 0.94
<1.0 0.93
1.66
<1.0 1.90
<1.0 1.54
<1.0 1.52
1.72
<1.0 1.75
<1.0 1.58
<1.0 1.59
DO
s
+J
z
0.01
0.00
0.00
0.00
0.01
0.01
0.02
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.01
0.00
0.00
0.00
u
•i.
ftl
V)
o
t-
•s
s
0.01
0.03
0.03
0.01
0.05
0.03
0.02
0.02
0.02
0.03
0.01
0.01
0.02
0.02
0.01
0.00
0.01
0.02
-------
TABLE 5 (continued)
t/i
t-l
CD
XI
e
1— (
*H o e 55
"3 5 " B
in
63.4
67.2
43.2
63.4
67.2
65.3
45.6
46.6
37.4
37.4
72.5
69.1
69.6
73.9
64.3
63.4
64.3
63.4
M
0.06
0.02
0.04
0.03
0.01
0.02
0.02
<0.01
0.01
0.03
<0.01
0.03
0.02
<0.01
0.04
u -a
30
18
15
25
16
14
__
13
8
6
23
15
13
-_
22
16
14
X
a.
7.94
7.89
7.57
7.17
7.54
7.63
7.80
7.57
7.45
7.46
7.81
7.64
7.49
7.55
7.72
7.65
7.29
7.65
pecific conductance
v mhos/ cm)
C/J ^-J
550
580
580
570
600
610
520
510
520
520
645
650
670
680
650
640
630
650
otal dissolved
olids (mg/1)
H Vi
352
370
346
438
415
PHYSICAL
f — *
<3
O H
I *
2 -3
-H / — >
r^ ,-H O f-4
€ £ u £
l/) t/l O
go £ o u o
^ o Co o o
O •"•< O r-t 4-1 r-*
• H tfl *rH t/> 0) (A
•-« B rH fi HE
O tf) O « 4-> W
O -H O -H t/l -H
s s s
<— 1 EO »— < OS •— * TO
ol oa ol 00 d oa
4-1 h U H U H
o o o o o o
H v-f
0
8
0
0
0
0
20
0
0
0
0
4
0
0
0
0
0
4
U. ^-^
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
u, <-*
0
0
0
0
0 "
0
0
0
0
0
0
0
0 *
0
0
0
0
0
-------
Quality of Irrigation Wastewater
Data for the quality of irrigation wastewater is presented in table 6.
For purposes of comparison, Idaho drinking water standards (11), the proposed
drinking water standards of the EPA (12), and the recommended water-quality
criteria for public water supplies (13) are given for parameters included
therein.
Data in table 6 substantiated our belief that bacteria and sediment would
be the only contaminants in the wastewater at the site that could cause de-
gradation of groundwater below drinking water standards. Removal of these
contaminants from the discharge water prior to their intersecting ground-
water would result in recharge with comparatively high quality water.
Discharge Events Conducted During the 1975 Irrigation Season
Depths to water in shallow monitoring wells, SW1-9, during the first
discharge event and in the 25-day interval thereafter demonstrated that a
normal cone-shaped recharge mound was not formed (table 7). To illustrate,
depths to water in well SW4, 30.5 m from the disposal well, were substantially
less than those in SW8, 15.2 m from the disposal well, throughout the dis-
charge period. Furthermore, discharge water did not appear in well SW3,
30.5 m from the disposal well, although water reached wells SW7, SW4, and SW5,
all 30.5 m within 1.3 days.
Dewatering of the upper recharge zone after termination of discharge also
indicated the formation of an unsymmetrical recharge zone. Wells SW4 and SW5
were dry shortly after termination in contrast to a steady decline in depths
to water in wells SW1, 5, 6, 7, 9, and the disposal well. Water in the latter
wells may have been "ponded water" in a wetted recharge zone rather than water
in a saturated perched zone.
Monitoring of the upper recharge zone during the second discharge event
also indicated the formation of a nonsymmetrical recharge mound. Data for the
depths to water in the shallow wells given in table 8 again show water levels
in well SW8 to be greater than in well SW4, with no water in well SW3 as con-
trasted to wells SW9, 7, and 4. Water appeared in wells SW4 and SW8 sooner
than during the first discharge event. This was attributed to the receiving
formations having been wetted previously. The presence of water in well SW2
indicated that discharge water had traveled beyond 61 m in that direction.
Dewatering of .the upper recharge zone, after termination of the second
discharge, again appeared to be unusual. Wells SW2, 4, and 8 were dry within
a short time; whereas water levels in wells SW1, 5, 6, 7, 9, and the disposal
well gradually declined.
Depths to water in the shallow wells during and after the third dis-
charge are given in table 9. These data affirm the generation of a non-
symmetrical recharge zone which extended an undefined distance beyond 61 m
in the direction of well SW2. The increase in depths to water on days 7.2
and 8.0 is attributed to a lower wastewater inflow to the disposal well over
the weekend.
26
-------
TABLE 6. QUALITY OF IRRIGATION WASTEWATER, JUNE 26, 1975 to AUGUST 24, 1976
N)
PESTICIDES
•§ w1
^ -H p, C
^ »J X •-* Pi O
*J ^ ?-\ P, O «J ^ -rl
&4J 4-» P, p. ^ P« -C
p>| Pj ,*^ \_> gj 4J pt H 4^
+J ^-^ pi, p| 4J ^, \—s O rt
O. U^-, r-, ^ ^^aOO •S'C 3g
"— ' C3+J4J *J CS^-^^^ ° OP,
(tiP«Q. P**H° X.C 4>'H >\
c -oSS 5 hgcoo cjs 5T*
• H JH^—' >_< --^ TS'HiHrtrt^^«4J O X^^
ti O ^N(H*->*J*->TJrt J3^5«J
•O ^HQ UJ H ti 'OTJP.CUOtC'^ *-»*-»p«
-H XQ a Q •H'rtct>4)O«T!'S Ji^o<
< (JQ a • Q QOwx x ^^ J z z z ^
Nuwber of
determinations 9 99 99-99999 99 99
High <10 <10 <10 10.6 14.9 37.3 <10 <10 <10 <10 <10 <10 <10 <10
Idaho Drinking
Public Water
Supply Criteria 1,000 3,000 --- 50,000 — - 1,000 — 500 100 100 5,000 — - 1,000
E.P.A. Proposed
Drinking Water
Standards — - 3,000 --- 200 100 100 4,000 --- 100,000
Parathion Cppt)
Toxaphene (ppt)
9 9
<10 <10
5,000
5,000
HERBICIDES
4-»
P.
s ^
> ' A
O
1M (N
9 9
<10 <10
20,000 2,000
100,00 10,000
-------
TABLE 6 (continued)
go Number of
determinations
Low
Mean
High
Idaho Drinking
Water Standards
Public Water
Supply Criteria
E.P.A. Proposed
Drinking Water
Standards
in i~*
a z
rH (fl
"M *
-5 C
if £
:-•
10
0.05
0.11
0.22
—
...
—
-------
TABLE 6 (continued)
Number of
determinations
Low
Mean
High
Idaho Drinking
Water Standards
Public Water
Supply Criteria
E.P.A. Proposed
Drinking Water
1
•H
Potass
10
3.91
5.90
11.3
---
r-1
DO
a
§
Seleni
4
0.9
1.2
1.8
10
10
-^
M
^B
1
•H
05
5
...
...
<0.01
0.05
0.05
INORGANIC CHEMICAL
r7 ~^
— bfl r—*
ME r-l
B
Sodium
10
15.9
17.,6
22.8
---
---
01
a
1-1
"3
CO
10
30.7
33.2
37.4
250
250
"M
u
•H
M
5
0.01
0.02
0.02
5.0
5.0
IL
O M
B
i-H *—*
a
Chemic
demand
10
13
24
37
--
--
8
§
+•>
3 "S
•a > ,--
§r-l .H m
0 -~~
O ^-x i/> bO D
B in B
(J u .H ^-* tj
•H V. -O '—'
t« m vt
•HO -H TJ K
o ,c rt -H o
US 4J iH r-4
X P, 3. 00 0
p4 CO t~~/ HI/1 CJ
14 49 9 9
7.94 350 197 <5
382 225 43
8.94 445 290 >70
- 500 15
500 75
PHYSICAL MICROBIOLOGICAL
« -a ^ ^ .H ^,
^ X C? r-l O r-l
G 1 3 S . e «E S B
S|? Br7 .P .3 • |§ |§ 0§
d> S .'H'SO J^bfl .nflj *w--, IH-^ p*1^^
h <«£ ^ ,8, grl |H g ^H g g g
2 i* 5 QJ 4)4) OW Ol/) +JW
rt -H C 1> *J o *J r-i o -H o -H in -H
H T3 3 rH3 r^-H/-~, C ^S _.S
0) -H fH'O -HT3 .H+Jr-l r-lrt ^S. *2S,
S. J3 «.H iHTi «««»-. rtM rtM rtoo
F t< 4->« e« C-IM *Jrl Orl OH
a) -j oa> oa> OOB oo a>o a>o
27 48 35 33 33 45 45 38
5.6 7.7 9.3 0.6 4.1 580 65 900
17.2 86 237.1 151.8 33.2 29,000 850 7,400
35.0 320 1652 731.2 108.1 96,000 13,000 16/000
5 — - — - — 2(MPN)
29.0 5 — -
10
o.c
-------
TABLE 7. DEPTHS TO WATER FOR SHALLOW WELLS--FIRST DISCHARGE EVENT (measurements in meters
from reference elevation of 1263.7 m; discharge terminated after 3.4 days)
Days from Inception
Well
Number
SW1
SW7
SW8
SW9
SW3
SW4
SW5
SW6
SW2
Disposal
well
D*
7.6
15.2
15.2
15.2
30.5
30.5
30.5
30.5
61.0
0
0
DRY
DRY
DRY
DRY
DRY
DRY
DRY
DRY
DRY
DRY
0.3
26.76
DRY
DRY
26.95
DRY
DRY
27.77
27.98
DRY
0.9
26.09
25.82
DRY
25.73
DRY
DRY
26.24
27.07
DRY
1.3
26.15
25.82
34.47
25.42
DRY
26.95
26.24
26.76
DRY
1.9
26.15
25.82
34.47
25.42
DRY
26.03
26.24
26.76
DRY
2.3
25.85
25.51
34.47
25.42
DRY
26.34
26.24
26.58
DRY
of Discharge
2.9
25.85
25.51
34.17
25.42
DRY
26.03
25.94
26.58
DRY
3.2
25.54
25.21
28.68
25.42
DRY
DRY
25.94
26.46
DRY
9.3
27.77
27.74
DRY
27.77
DRY
DRY
27.71
27.71
DRY
27.77
14.3
28.10
28.10
DRY
28.13
DRY
DRY
28.04
28.10
DRY
28.10
28.3
28.56
28.53
DRY
28.83
DRY
DRY
28.41
28.47
DRY
28.50
D = distance from disposal well in meters.
-------
TABLE 8. DEPTHS TO WATER FOR SHALLOW WELLS--SECOND DISCHARGE EVENT (measurements in meters
from reference elevation of 1263.7 m; discharge-terminated after 8.0 days)
Days from Inception of Discharge
Well
Number
SW1
SW7
SW8
SW9
SW3
SW4
SW5
SW6
SW2
Disposal
well
D*
7.6
15.2
15.2
15.2
30.5
30.5
30.5
30.5
61.0
0
0
28.50
28.44
DRY
28.65
DRY
DRY
28.13
28.41
DRY
28.29
0.9
25.88
25.79
34.35
25.48
DRY
26.18
26.37
26.98
DRY
1.1
25.82
25.63
33.01
25.48
DRY
26.31
24.99
26.82
DRY
1.9
25.70
25.70
32.22
25.48
DRY
26.24
26.49
26.64
DRY
2.9
25.54
25.45
29.44
25.18
DRY
25.97
26.09
26.00
DRY
8.
26.
25.
27.
25.
0
09
21
22
48
DRY
26.
26.
26.
29.
--
18
09
46
63
-
8.9
26.76
26.15
33.01
26.34
DRY
DRY
26.82
25.73
DRY
26.46
15.0
27.68
27.65
DRY
27.62
DRY
DRY
27.83
27.68
DRY
27.62
35
28.44
28.41
DRY
28.53
DRY
DRY
28.26
28.44
DRY
28.29
•
* D = distance from disposal well in meters,
-------
TABLE 9. DEPTHS TO WATER FOR SHALLOW WELLS—THIRD DISCHARGE EVENT (measurement in meters
from reference elevation of 1263.7 m; discharge terminated after 16.0 days)
CM
to
Well
Number
SW1
SW7
SW8
SW9
SW3
SW4
SW5
SW6
SW2
Disposal
well
D*
7.6
15.2
15.2
15.2
30.5
30.5
30.5
30.5
61.0
0
0
28.44
28.41
DRY
28.53
DRY
DRY
92.6
28.44
DRY
28.29
0.1
26.70
27.01
DRY
26.85
DRY
DRY
27.49
27.77
DRY
0,9
25.94
25.85
34.44
25.63
DRY
27.49
26.49
26.98
DRY
Days
1.2
25.82
25.70
32.89
25.48
DRY
26.61
26.49
26.82
DRY
from Inception of Discharge
1.9
25.66
25.54
29.41
25.36
DRY
26.12
26.00
26.58
DRY
2.2
25.54
25.45
27.95
25.21
DRY
25.88
25.94
26.49
DRY
3.0
25.51
25.27
27.04
25.05
DRY
25.66
25.88
26.43
27.74
7.2
26.46
26.27
27.52
25.79
DRY
26.24
26.24
26.46
27.37
8.0
26.85
31.18
26.88
DRY
26.91
26.79
26.82
28.32
15.0
25.97
25.85
29.78
25.70
DRY
26.03
26.03
26.58
27.62
28.3
27.95
27.95
DRY
27.92
DRY
DRY
27.83
27.92
DRY
* D = distance from disposal well in meters.
-------
Dewatering of the upper recharge zone paralleled that for the first two
discharge events; i.e., wells SW2, 4, and 8 were dry shortly after termina-
tion of discharge. Depths to water in all other wells (excluding SW3) was
approximately 30.0 m 15 days after termination of discharge.
Chemical quality of water from the shallow wells was determined after
completion of the first and third discharge events (table 10). A comparison
of these values with the corresponding constituents in the wastewater over a
given discharge event indicated an overall deterioration in the chemical
quality of discharge water in the upper recharge zone.
The chemical quality of groundwater was monitored both during and after
the three wastewater discharge events conducted in 1975 (table 11). No degra-
dation in the chemical quality of the regional groundwater system was
observed.
Dye concentrations of water from the shallow wells for the three dis-
charge events indicated that considerable adsorption of the dye had taken
place (table 12). A homogeneous solution of the dye in the wastewater dis-
charged during the first event would have yielded a dye concentration of
1930 ppb: An even greater dye concentration would have been expected on the
last day of discharge as 10% of the dye was added to the last 5% of the dis-
charged wastewater. However, the maximum dye concentration in well SW1 on the
last day of discharge (8/1/75) was determined to be 64% of the value calcu-
lated for a homogeneous solution. Furthermore, considerable decreases in dye
concentrations occurred after termination of the first and second discharge
events. These data could be taken as evidence of adsorption of the dye both
on the sediment in the wastewater and on the clays in the upper recharge zone.
A look at the data for the third discharge event (no dye was added)
shows the expected decrease in dye concentrations from 10/1/75 (or 10/2/75)
to 10/15/75. However, there was an increase in dye concentration 14 days
after termination of discharge, which indicates that an equilibrium had been
reached for dye adsorption-desorption. An equilibrium dye concentration of
45 bbp (mean value for 10/5/75) was attained.
Further adsorption of dye was possible as discharge water percolated
down through lower geological formations. The dye concentration could have
been reduced to a level such that subsequent dilution in groundwater would
have resulted in a concentration below the limit of detection a short dis-
tance from the point of entry. Thus, it appeared that adsorption limited the
value of Rhodamine WT dye as a tracer for wastewater discharges.
Significant dye concentrations in the regional groundwater table were
detected on days 15, 16, and 17 after initiation of the first discharge event
and on days 1, 2, 8, 9, and 15 after initiation of the second discharge event
(table 13). A failure in the groundwater sampling unit prevented earlier de-
tection of the dye during the initial discharge in 1975. However, presence of
the dye within the regional aquifer indicated that discharge water had infil-
trated the groundwater.
33
-------
TABLE 10. CHEMICAL QUALITY OF WATER IN. SHALLOW WELLS AND OF INJECTED WASTEWATER
FIRST AND THIRD DISCHARGE EVENTS
H
B
rH
rH
Disposal well
SW1
SW5
SW6
SW7
SW9
Wastewater*
Disposal well
SW1
SW5
SW6
SW7
SW9
Wastewater *
M
B
.i-t
r-l
!
o
^
Q
8/13/75
8/13/75
8/13/75
8/13/75
8/13/7S
8/13/75
7/28-8/1/75
10/30/75
10/30/75
10/30/75
10/30/75
10/30/75
10/30/75
9/30-10/16/75
Z
^ S3
K)
O fH
>-,U £
'H en
B ctf ctf
•rl 'H
"3^ §
•* °° 1
-IB 1
< v_, 3
183
160
156
144
171
179
176
180 0.26
230 0.01
245 0.01
189 0.02
202 0.01
180 0.01
169 0.00
«— 1
M
|
0.16
0.19
0.16
0.19
0.19
0.18
0.09
0.13
0.11
0.12
0.08
0.12
0.07
O.OS
fl
3
1
'o
rH
3
36.6
33.2
30.2
30.0
27.0
26.8
42.2
48.4
43.2
34.2
42.6
29.8
35.0
44.8
•^
oc
&
«I
•H
rH
6
24.8
26.3
24.5
25.6
23.1
23.4
16.0
21.6
20.9
20.6
20.9
19.9
20.6
19.2
!
• H
tf>
!
17.4
22.4
25.1
21.8
26.1
29.3
11.2
21.0
21.2
25.3
19.0
25.4
27.3
17.0
z
1
»
H
• H
Z
FIRST
2.45
3.15
1.80
1.45
1.15
2.15
0.19
THIRD
0.48
1.60
0.88
1.48
0.80
1.38
0.08
Z
3
a>
+j
•H
n
f*
•r»
Z
a
1
Ul
O
§*»-<
h in
S a
T-4
~%
i
•H
VI
Z
o.
f \
p- 1
m^
a
o
•H
r-4
•H
in
l~~\
&
§
o
%
S
DISCHARGE EVENT
0.01
0.03
0.01
0.00
0.10
0.00
O.OS
0.14
0.16
0.07
0.12
0.10
0.10
0.12
7.43
7.43
7.82
7.43
7.82
9.00
5.71
31.0
31.7
40.8
31.6
36.5
37.5
14.1
19.8
19.6
20.9
17.7
20.9
22.1
16.3
31.7
31.7
32.6
30.7
31.7
32.6
30.9
28
32
35
32
26
20
27
470 276
460 289
425 277
430 259
430 263
480 288
365 205
DISCHARGE EVENT
0.00
0.00
0.00
0.01
0.00
0.00
0.01
0.33
0.26
0.13
0.26
0.13
0.15
0.05
5.87
6.26
7.04
5.47
7.04
7.43
4.30
27.0
28.5
31.7
24.9
34.9
35.6
19.1
23.0
22.5
22.5
21.1
22.1
23.9
19.3
41.8
40.3
43.7
40.8
40.3
44.2
37.4
24
47
18
13
14
12
13
470 287
460 259
460 252
450 239
440 241
480 269
417 252
•Wastewater: Mean values for first and third discharge events.
-------
TABLE 11. CHEMICAL QUALITY OF ARTESIAN GROUNDWATER DURING DISCHARGE EVENTS
(samples from 96 ra after minimum of 30 min pumping)
tn
t*
0>
e
l-H
I-H
eu
DW1
DW2
DW3
DW4
DW5
ampling date
t/>
7/29/75
8/12/75
7/29/75
8/12/75
8/28/75
9/10/75
10/ 3/75
7/29/75
8/12/75
9/10/75
10/ 3/75
7/29/75
8/12/75
9/10/75
10/ 2/75
7/29/75
8/12/75
8/28/75
9/10/75
10/ 2/75
To
c
y
0
V)
CO
1-4
E
X
>H
C
• H
i— 1
i—l
<
142
146
153
141
154
152
151
204
191
202
205
166
153
166
166
158
150
147,
157
161
/— N
8
1-4
00
cd
•H
B
<
...
...
0.00
0.00
---
0.00
0.00
0.00
0.00
...
0.00
0.00
f— t
I
o
CO
0.05
0.16
0.07
0.16
0.11
0.06
0.04
0.14
0.22
0.13
0.09
0.07
0.15
0.02
0.04
0.08
0.16
0.12
0.02
0.02
/— *
r-4
00
•H
U
i-l
a
u
56.6
62.0
71.0
69.0
71.2
72.4
71.8
41.0
40.8
42.4
40.8
76.6
74.8
79.0
79.0
77.0
76.6
78.2
75.8
76.6
*-"•!
1— 1
DO
4)
•O
•a
o
rH
-C
O
64.3
60.7
62.1
62.5
62.1
61.8
63.2
29.5
29.5
29.1
30.8
80.2
86.3
73.5
88.7
69.6
84.1
68.9
69.9
71.0
agnesium (mg/1)
s
12.9
15.0
14.5
15.9
16.0
14.4
15.6
18.1
18.9
18.7
20.3
17.9
19.2
19.6
17.0
13.7
16.3
16.9
15.4
16.7
z
cd
i— t
00
6
374
389
397
403
393
397
380
335
339
398
420
430
* —
410
402
403
399
404
emperature (°C)
H
16.5
16.5
16.5
16.5
16.0
16.5
16.0
17.0
16.5
16.5
16.5
16.5
16. S
16. S
17.0
16.5
16.5
16.8
16.5
16.5
D
f-'
X
.H
•o
-H
3
t"
34
38
1.1
6.0
1.3
3.8
2.9
0.9
3.6
6.7
1.0
1.9
6.0
1.2
1.5
1.0
3.5
2.0
4.2
0.67
-------
TABLE 12. DYE CONCENTRATIONS IN WATER FROM SHALLOW WELLS (ppb)
in
Well
number
SW1
SW2
SW4
SW5
SW6
SW7
SW8
SW9
Disposal
well
First discharge event
8/1 8/6 8/13 8/26
1240 514 524 380
720
616 406 402 288
696 518 524 370
640 378 366 336
572
972 432 330 336
508 526 325
Second discharge event
9/3 9/10 9/30
343 254 270
132
378
132 204 150
570 310 200
301 260 180
186
380 177 171
322 150
10/1
4.00
43.5
87.0
27.3
51.0
40.5
34.8
Third discharge event
10/2 10/3 10/7 10/15
5.19
43.5
51.0
22.8
46.5
43.5
25.8
9.70
34.8
36.2
43.5
14.5
39.0
36.2
11.6
10.4
13.7
22.8
24.2
8.45
34.0
30.2
21.2
0.91
9.90
22.8
27.2
3.75
30.2
27.2
4.00
10/30
49.5
37.8
45.0
48.0
45.0
45.0
-------
TABLE 13. DYE CONCENTRATIONS IN
ARTESIAN GROUNDWATER (ppb)
First Discharge Event
Well
Number
DW2
DW3
DW4
DW5
0
0
Days from Inception of Discharge
15*
4.5
1.4
0
0
16#
17#
6.0 1.0
1.4 0.01
0.5 0
0.5 0
25#
0
0
Second Discharge Event
Well
Number
DW2
DW3
DW4
DW5
0
0
1*
0.14
0.01
Days from Inception of Discharge
1.1 0
-- 0
0.1 0
0.0 0
0.45 0
0.08 0
15#
0.01 0
0.01 0
-- 0
-- 0
Third Discharge Event
Well
Number
DW2
DW3
DW4
DW5
1#
0.12 0
0 0
0 0
0 0
0
0
Days from Inception of Discharge
3#
0 0
0 0
7#
0.01 0
0 0
0 0
0 0
29*
0
0
0
30#
0.01 0
* Samples from depth of 96 m after minimum of 30 min pumping.
# Samples from two depths: 85 m (1st column) after 5 min pumping and 96 m
(2nd column) after minimum of 30 min pumping.
37
-------
The absence of dye in the groundwater during the third discharge event
except for samples from DW2 at the 85 m depth appeared unusual. One would
have anticipated the presence of dye in samples which showed high total coli-
form counts. However, no dye was added in the third discharge event; and the
adsorption of dye previously added coupled with dilution of dye in receiving
water could have been responsible for dye concentrations below interpretative
significance.
Bacterial samples collected from the deep monitoring wells (DW1-5) were
analyzed for total coliforms, fecal coliforms, and fecal streptoccoci
(table 14). Though not shown in table 14, water from wells DW1-3 gave high
counts of noncoliform bacteria (150-300 colonies for 25 ml filtration volumes)
on each sampling occasion, as did water from wells DW4 and DW5 on day 4 and
thereafter (50-200 colonies for 40 ml filtration volumes). It was assumed
the extraneous bacteria did not interfere with the test for total coliforms.
TABLE 14. LEVELS OF INDICATOR BACTERIA
GROUNDWATER--FIRST DISCHARGE EVENT
(organisms/100 ml)
IN
Days from Inception of Discharge
Well
Number
DW1
DW2
DW3
DW4
DW5
Organism* 1# 2*
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
0
0
0
0
0
4
0
0
3
1
0
0
0
0
2
4
0
8
8
0
12
3
0
0
8
0
2
0
0
2
4#
0
0
4
--
4
0
0
15#
2
2
0
8
6
1
66
32
0
16
4
0
8
0
1
16t
20
0
0
28
8
0
4
0
0
2
0
0
17t 25#
0
0
40 —
00 —
00 —
00--
00 —
— — 0
-- — 0
— — 0
— — 0
-- — 0
0
* TC = total coliforms; FC = fecal coliforms; FS = fecal streptococci.
# Samples from depths of 96 m after 30 min pumping.
t Samples from two depths: 85 m (1st column) after 5 min pumping and 96 m
(2nd column) after minimum of 30 min pumping.
38
-------
From the data in table 14, it is obvious that bacterial contamination of
artesian groundwater had occurred during the first discharge event. An analy-
sis of the data indicates that the bacteria could have been introduced from
contaminants adhering to the submersible pump on day 15. However, it seems
highly improbable that the bacteria found on other sampling occasions were
introduced by sampling techniques.
Levels of indicator bacteria were determined for water in the shallow
wells during and after the discharge period (table 15). The variations in
bacterial levels in the upper recharge zone reflected the wide variations for
bacteria in the wastewater. In some wells, the levels of indicator bacteria
approached those of the wastewater. This indicated that discharge water
pursued a relatively direct path to those wells.
A rather rapid decrease in levels of indicator bacteria were found after
termination of discharge (fig. 8). However, after 25 days, levels of total
coliform bacteria remained high relative to drinking water standards.
Results of monitoring artesian groundwater for indicator bacteria during
the second discharge event are given in table 16. As in the previous dis-
charge event, high counts of noncoliform bacteria were found in samples from
all deep wells. Data in table 16 show bacterial contamination of artesian
groundwater from wells DW2 and DW3 on days 8, 9, and 15 and no contamination
in water from wells DW4 and DW5.
Levels of indicator bacteria in the shallow wells are presented in
table 17. Variations in the level of indicator bacteria were expected in view
of pronounced variations found for these bacteria in wastewater. As in the
first discharge event, levels of indicator bacteria decreased considerably
with time.
Data obtained from the monitoring of artesian groundwater for indicator
bacteria during the third discharge event are given in table 18. Again, high
levels of noncoliform bacteria were found in water from all wells which limi-
ted filtration volumes to 25 ml or less.
The rather high levels of indicator bacteria found in water from wells
DW2 and DW3 on days 2, 7, and 8 offer evidence that wastewater discharged to
the disposal well led to contamination of artesian groundwater at these wells.
Furthermore, the repeated presence of noncoliform bacteria noted in water from
wells DW4 and DW5 indicates that discharged wastewater entered the artesian
system. Prior to the discharge of wastewater, few, if any, noncoliform bac-
teria were found.
The levels of indicator bacteria in water from the shallow wells are
given in table 19. Here it can be seen that levels of total coliform bac-
teria increased during the first days of discharge and then decreased notice-
ably on days 7.2 and 8.0 even though the levels of bacteria in the waste-
water were found to remain relatively constant. This could indicate prefer-
red movement of wastewater through the fractured basalt layer once the under-
lying clay and rubble zone was saturated. Water within the latter zone, from
which we were sampling, would not be continually intermixed with recently
39
-------
TABLE 15. LEVELS OF INDICATOR BACTERIA IN WATER FROM SHALLOW WELLS
FIRST DISCHARGE EVENT (organisms/100 ml; discharge terminated at 3.4 days)
Days from inception of discharge -V
Well
number D*
SW1 7.6
SW7 15.2
SW8 15.2
SW9 IS. 2
SW4 30.5
SW5 30.5
SW6 30.5
Disposal well 0
Organism* 0
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
1.4
63,000
1,300
6,300
29,000
350
5,400
47,000
1,000
6,500
27,000
500
6,800
9,800
150
5,500
14,000
130
6,200
2.4
24,000
50
5,200
23,000
200
3,100
22,000
<50
2,000
23,000
550
5,500
40,000
350
2,300
10,000
200
6,600
33,000
300
3,800
3.0
68,000
600
5,000
14,000
<4
2,800
10,000
100
2,400
15,000
100
4,200
18,000
200
4,400
10,000
200
2,400
25,000
200
4,200
8.0
20,000
<100
200
500
<100
100
___
1,000
<100
<100
_ .—
<100
<100
100
800
<50
<100
40,000
<100
200
14.4
1,000
35
600
580
<5
10
260
10
40
___
130
<5
<5
660
10
40
25,000
35
440
28.3
580
<5
10
40
<5
20
...
---
40
<2
4
___
20
<5
15
70
<5
5
670
<5
25
* D = distance from disposal well in meters.
# TC = total coliforms; FC = fecal coliforms; FS - fecal streptococci.
-------
TOTAL COLIFORMS
FECAL COLIFORMS
FECAL STREPTOCOCCI
5 10 15 30 ZS
NUMBER OF DAYS FROM TERMINATION OF DISCHARGE -
30
FIGURE 8. DECREASE OF SELECTED ENTERIC BACTERIA IN WATER
FROM SHALLOW WELL 6 DURING THE FIRST DISCHARGE EVENT.
41
-------
TABLE 16. LEVELS OF INDICATOR BACTERIA. IN GROUNDWATER—
SECOND DISCHARGE EVENT (organism/100 ml)
Well
Number
DW2
DW3
DW4
DW5
Organism*
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
0#
-_
—
_ _
—
—
0
0
0
0
0
0
Days
It
0 0
0 0
0 0
0
0
0
— _ «._
—
—
__ __
—
-- --
from
2#
0
0
0
_ _
--
—
_ _
--
--
0
0
0
Initiation of
8t
„
—
—
800
0
—
0
0
0
0
0
0
..
--
—
76
0
0
0
0
0
0
0
0
Discharge
9t
8 0
0 0
0 0
__ _ _
—
—
__ __
__
—
__ __
__
— — — —
15t
8
0
0
12
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
* TC = total coliforms; FC = fecal coliforms; FS = fecal streptococci.
# Samples from depths of 96 m after minimum of 30 rain pumping.
t Samples from two depths: 85 m (1st column) after 5 min pumping and 96 m
(2nd column) after minimum of 30 min pumping.
discharged wastewater. In this event, a decrease in levels of total coliforms
would be expected in the clay and rubble zone from both die-off and
adsorption.
Geophysical logs showed that the packers on wells DW2-5 were placed above
the suspected confining layer. Consequently, deep percolating wastewater
could have entered the artesian system by traveling through the annular space
below the packers. In order for this to have occurred, the wastewater would
have had to penetrate five additional layers of dense basalt (fig. 6) situated
below the recharge zone but above the confining layer. Furthermore, an arte-
sian head of approximately 14 m would need to have been overcome.
Discharge Event Conducted in 1976
Water levels within the five cased shallow wells are presented in
table 20. Depths to water in wells SW10 and SW11 decreased within hours
(0.2 days) after commencement of discharge to the disposal well. Wells SW12
and SW13 responded within 4 days; and water was detected in the bottom of
SW14, 122 m distant from the disposal well, on day 5. Depths to water in-
creased with increasing distance from the disposal well from day 4 through
42
-------
TABLE 17. LEVELS OF INDICATOR BACTERIA IN WATER FROM SHALLOW WELLS
SECOND DISCHARGE EVENT (organisms/100 ml; discharge terminated at 8.0 days)
t/4
Days from inception
Well
number
SW1
SW7
SW8
SW9
SW4
SW5
SW6
SW2
Disposal
well
D* Organism*
7.6 TC
FC
FS
15.2 TC
FC
FS
15.2 TC
FC
FS
15.2 TC
FC
FS
30.5 TC
FC
FS
30.5 TC
FC
FS
30.5 TC
FC
FS
61.0 TC
FC
FS
0 TC
FC
FS
0
580
<5
10
40
<5
20
40
<2
4
20
<5
15
70
<5
5
670
<5
25
1.0
5,500
600
3,200
8,200
80
4,700
2,600
260
2,400
6,200
460
3,700
\
1,100
410
750
4,200
240
4,000
2.0
11,000
400
2,400
8,400
130
1,100
1,600
50
1,300
3,400
75
1,300
4,200
50
1,700
1,200
100
700
2,600
50
1,600
2.9
11,000
100
2,300
6,500
50
2,600
3,800
<50
2,400
10,000
50
4,200
4,800
100
2,300
2,800
50
1,000
2,000
SO
5,800
_.-
—
—
of discharge
8.0
5,500
50
1,600
750
25
700
500
<25
500
3,300
50
2,100
1,800
25
1,300
500
25
350
4,000
50
1,300
4,000
25
1,800
6,300
75
5,000
8.9
300
<20
75
500
17
280
400
17
350
700
<20
300
500
<20
300
2,500
17
350
...
1,000
<25
130
15.0
150
<10
80
120
<10
55
80
<10
20
45
<5
35
90
<3
35
...
400
<10
290
35.0
25
<3
780
<5
---
520
<5
5
<3
35
<5
...
320
<2
* D = Distance from disposal well in meters.
It TC = total coliforms; FC = fecal coliforms; FS = fecal streptococci.
-------
TABLE 18. LEVELS OF INDICATOR BACTERIA IN GROUND-
WATER—THIRD DISCHARGE EVENT (organisms/100 ml)
Days from Inception of Discharge
Well
Number Organism* It 2£ 5t 7t 8t 29# 50t
DW2 TC 00 — TNTC6 560 0§ 10 50 5 50
FC 00— 0 00000— 00
DW3 TC 0 0 — 56 20 — — 44 0 — —
FC 0 0 — 0 o — — 0 0 0 — —
DW4 TC 000 ————000— —
FC 000 _______ 0 0 0 — —
DW5
TC
FC
0
0
0
0
8
0
__ __ — 0
_. __• __ o
0
0
4
0
__
* TC = total coliform; FC = fecal coliform.
# Samples from depths of 96 m after minimum of 30 min pumping.
t Samples from two depths: 85 m (1st column) after 5 min pumping and 96 m
(2nd column) after minimum of 30 min pumping.
6 TNTC = Too numerous to count for a filtration volume of 2 ml.
§ 150 distinct deep red colonies plus numerous other noncoliform colonies for
a filtration volume of 1 ml.
termination of the discharge event. Water levels in all the cased shallow
wells declined after day 4 because of reduced inflows to the disposal well.
The above data indicate that recharge during the fourth discharge event
was of a regular pattern along the axis of the cased shallow wells (fig. 4).
This may indicate that the injected wastewater moved uniformly through the
clay and rubble zone rather than assuming a more channelized path as was
apparent with the 1975 discharge events.
Depths to water within the modified deep wells were between 81.3 m and
81.9 m below land surface prior to initiation of the fourth discharge event
(table 20). These levels were approximately 1 m above the level of the
artesian aquifer (82.3m below land surface) which indicate that the modifi-
cation procedures effectively isolated the deep perched water zone from the
artesian aquifer.
Water levels within wells DW3 and DW5 increased after 4 days of dis-
charge to the disposal well and appeared to be directly influenced by the
volume of injected wastewater. Reduced inflows to the disposal well not only
44
-------
TABLE 19. LEVELS OF INDICATOR BACTERIA IN WATER FROM SHALLOW WELLS
THIRD DISCHARGE EVENT (organisms/100 ml; discharge terminated at 16.0 days)
Days from inception of
Well
number
SW1
SW7
SW8
SW9
SW4
SW5
SW6
SW2
Disposal
well
D* Organism*
7.6 TC
FC
FS
15.2 TC
FC
FS
15.2 TC
FC
FS
IS. 2 TC
FC
FS
30.5 TC
FC
FS
30.5 TC
FC
FS
30.5 TC
FC
FS
61.0 TC
FC
FS
0 TC
FC
FS
0
25
<3
780
<5
—
—
—
520
<5
•
5
<3
35
<5
.
320
<2
1.2
250
180
600
70
300
85
300
60
300
100
350
95
200
110
—
.. .
—
2.2
1,500
260
2,200
60
1,200
130
1,200
140
1,400
120
1,100
80
1,500
190
—
—
—
.
—
3.0
2,600
200
2,300
130
2,200
80
2,750
230
1,800
260
950
100
2,500
230
2,000
270
...
discharge
7.2
270
55
730
180
40
200
20
5
120
450
160
460
200
10
190
25
10
140
280
110
480
200
55
...
15.0
1,200
43
2,200
450
20
120
100
10
100
750
100
1,000
320
25
220
70
3
65
650
90
1,140
450
60
480
...
30.0
5
<5
40
10
<5
35
. ..
<5
<5
55
<5
<5
15
15
<5
15
15
5
55
* D = distance from disposal well in meters.
# TC = total coliforms; FC = fecal coliforms; PS = fecal streptococci,
-------
TABLE 20. DEPTHS TO WATER WITHIN SHALLOW AND DEEP MONITORING
WELLS—FOURTH DISCHARGE EVENT (measurement in
meters from reference elevation of 1263.7 m)
Days from Inception of Discharge
Well
Number D* 0.0
0.2 0.4 4.4 5.1 6.0 11.3 12.0
SHALLOW WELLS
SW10
SW11
SW12
SW13
SW14
15
31
61
91
122
DRY
34.32
DRY
33.99
DRY
24.87
27.19
DRY
34.29
DRY
24.41
26.49
DRY
34.29
DRY
23.74
24.41
25.12
26.58
DRY
23,77
24.48
25.18
26.58
39.41
23.77
24.48
25.15
26.58
39.41
24.11
24.69
25.24
26.58
DRY
24.99
24.99
25.57
26.82
DRY
DEEP WELLS
DW3
DW4
DW5
46 81.32
46 — 81.38
46 81.90
81.20
81.38
81.47
81.23
81.41
81.50
81.26
81.47
81.50
81.23
81.41
81.50
D = distance to disposal well in meters.
led to decreased water levels within the recharge zone but also resulted in
lower water levels within the deep perched water zone.
Specific conductance and turbidity of wastewater and water withdrawn
from the shallow and deep monitoring wells are presented in table 21. Speci-
fic conductance of the wastewater ranged from 325-400 vmhos/cm, while values
of turbidity varied from 18 to 120 NTU. Values of both specific conductance
and turbidity for samples withdrawn from the shallow wells approached those
of the injected wastewater.
Specific conductance and turbidity of water withdrawn from the modified
deep wells were similar to values obtained for the artesian aquifer
(table 21). However, specific conductance of the deep perched water zone was
observed to decrease after 5 days of discharge to the disposal well, thus
indicating that this zone was influenced by injected wastewater. Levels of
turbidity did not appear to be affected by deep-percolating wastewater.
Levels of indicator bacteria were determined for the injected wastewater
and water from both shallow and deep monitoring wells (table 22). Variations
in the bacterial levels of the wastewater were attributed to a diversity of
sources of wastewater. Two heavy thunderstorms occurred during the discharge
event, and storm runoff water comprised a large portion of the irrigation re-
turn flows shortly thereafter. Storm runoff was followed by a period of low
irrigation demand during which the return flows decreased and were principally
comprised of bypass water of relatively low bacterial levels.
46
-------
TABLE 21. SPECIFIC CONDUCTANCE AND TURBIDITY OF WASTEWATER,
AND WATER FROM BOTH SHALLOW AND DEEP MONITORING
WELLS—FOURTH DISCHARGE EVENT
Well
Number
Days from Inception of Discharge
Parameter''
0
1
11
Disposal well
inlet
KS
Turb.
400
120
349
28
325
18
SW10
SW11
SW12
SW13
KS
Turb.
Ks
Turb.
KS
Turb.
KS
Turb.
SHALLOW WELLS
350
30
350
25
350
20
350
35
DEEP WELLS
DW3
DW4
DW5
KS
Turb.
Ks
Turb.
KS
Turb.
520
0.4
— — —
645
1.5
520
4.1
650
2.0
600
17
450
0.4
549
0.8
550
1.8
* Ks = specific conductance (ymhos/cm); Turb. = turbidity (NTU).
47
-------
TABLE 22. LEVELS OF BACTERIA IN WASTEWATER AND WATER
FROM BOTH SHALLOW AND DEEP MONITORING WELLS-
FOURTH DISCHARGE EVENT (organisms/100 ml)
Well
Number
Disposal well
SW10
SW11
SW12
SW13
DW3
DW4
DW5
Organisms*
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
TC
FC
FS
Days from Inception of Discharge
0.0 0.2 0.4 5.2 5.6 11.2
1660 5600 3222 3518 1900
100 2560 2200 120
— 4620 5200 1950 3050 4200
SHALLOW WELLS
2480
300
— 2050
- 680
110
__. 310o
- 1500
60
___ 4850
___ 112Q
330
___ 2100
DEEP WELLS*
0 — — -— 15 22
0 — — — o 0
0 — — — - 510 200
0
o
380
4 — o --- — —
0 — - 0
2 — 360
11.4
. .»
---
• •» M
___
---
__ _
___
— — —
.» _ _
24
0
1000
76
0
1920
* TC = total coliform; FC = fecal coliform; FS = fecal streptococcus.
# Samples from depths of 96 m after minimum of 30 min pumping.
48
-------
Bacterial levels of the recharge zone, as monitored through the cased
shallow wells, approached those levels determined for the wastewater. Dif-
ferences found between samples withdrawn from the cased shallow wells were
indicative of integration of different sources of wastewater and bacterial
movement and die-off rates. There were no apparent differences in bacterial
levels between samples withdrawn from the cased shallow wells during the 1976
discharge event and samples collected from the uncased shallow wells during
the three discharge events conducted in 1975.
Prior to initiation of the fourth discharge event, bacterial levels in
the deep wells were found to approach those of Idaho drinking water stand-
ards. However, within 5.6 days after inception of discharge, increases in
levels of total coliforms and fecal streptococci were observed. These in-
creased bacterial levels clearly indicate that wastewater was infiltrating the
deep perched water zone situated some 42 m below the recharge zone.
49
-------
SECTION 7
REFERENCES
1. Moreland, J. A., H.R. Seitz, and A. M. LaSala, Jr. Effects of Drain
Wells on the Ground-Water Quality of the Western Snake Plain Aquifer,
Idaho. U.S. Geological Survey, draft copy, 1976.
2. Whitehead, R. L. Chemical and Physical Data for Disposal Wells, Eastern
Snake River Plain, Idaho. Idaho Department of Water Resources, Water
Inf. Bull. No. 39, 1974.
3. Young, H. W., and W. A. Harenberg. Ground-Water Pumpage from the Snake
Plain Aquifer, Southeastern Idaho. Idaho Department of Water Administra-
tion, Bull. No. 23, 1971.
4. Bondurant, J. A. Quality of Surface Irrigation Runoff Water. Annual
Meeting of American Society of Agricultural Engineers, Paper No. 71-247,
1971.
5. Carter, D. L. Irrigation Return Flows in Southern Idaho. Proceedings of
National Conference on Managing Irrigated Agriculture to Improve Water
Quality, 1972. p. 47.
6. Mundorff, M. J., E. C. Crosthwaite, and C. Kilburn. Ground-Water for
Irrigation in the Snake River Basin in Idaho. U.S. Geological Survey,
Water Supply Paper No. 1654, 1964.
7. Environmental Protection Agency. Methods for Chemical Analyses of Water
and Wastes, 1971.
8. Environmental Protection Agency. Methods for Organic Pesticides in
Water and Wastewater, 1971.
9. American Public Health Association. Standard Methods for the Examination
of Water and Wastewater, 13th ed., 1971.
10. McMillion, T. G., and J. W. Keeley. Sampling Equipment for Groundwater
Investigations. Ground Water, 6(9), 1968.
11. Idaho Department of Health. Idaho Drinking Water Standards, 1964.
12. Federal Register, vol. 40, No. 51, Part II, Friday, March 14, 1975.
50
-------
13. Federal Water Pollution Control Administration. Water Quality Criteria,
1968. p. 20.
51
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-77-071
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Irrigation Wastewater Disposal Well Studies--Snake
Plain Aquifer
5. REPORT DATE
June 1977 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
William G. Graham, Darrel W. Clapp, and Thomas A.
Putkey
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Idaho Department of Water Resources
Statehouse
Boise, ID 83720
10. PROGRAM ELEMENT NO.
1BA609
11. CONTRACT/GRANT NO.
R-802931
12. SPONSORING AGENCY NAME AND ADDRESS
Robert S. Kerr Environmental Research Lab.
Office of Research and Development
U.S. Environmental Protection Agency
Ada. Oklahoma 74820
- Ada, OK
13. TYPE OF REPORT AND PERIOD COVERED
Final 11/73 - Q/76
14. SPONSORING AGENCY CODE
EPA/600/15
15. SUPPLEMENTARY NOTES
16. ABSTRACT
An investigation was conducted to evaluate the impact of irrigation disposal well
practices on the water quality of the Snake Plain aquifer. A study site was selected
where the geology was determined to be characteristic of areas in the Snake River Plain
where irrigation disposal wells are extensively used. Alternating permeable and dense
basalt layers underlie the discharge site. The aquifer at the project site was definec
as a leaky artesian groundwater system.
Initial quality of the artesian groundwater was found to be within Idaho drinking
water standards. Pesticides, herbicides, and trace metal concentrations in the irriga-
tion wastewater were within drinking water standards. Total and fecal coliform bac-
teria and sediment were the only contaminants found in irrigation wastewater in excess
of drinking water standards.
Wastewater discharge to the disposal well resulted in the formation of a nonsym-
metrical recharge zone. Rapid lateral movement of the discharge water through the re-
charge zone indicated that flow was through fractures and channels. Bacterial levels
and turbidity within the recharge zone approached those of the discharged wastewater
and were far in excess of drinking water standards.
Deep percolation of injected wastewater resulted in bacterial contamination of
both the deep perched water zone overlying the confining layer and the artesian ground-
water system. Suspended solids were filtered out by the percolation process.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Irrigation, Drainage, Recharge wells,
Drainage wells, Surface water runoff,
Waste water, Pollution, Ground water
Recharge, Hydrogeology
Snake River Plain,
Snake Plain Aquifer,
Idaho, Ground Water
Bacterial Contamination
13 B
18. DISTRIBUTION STATEMENT
Release to public.
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
62
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
52
GOVERNMENT «INTI«G OFFICE: 1977*757"056/6
------- |