30 April 1978
DRAFT FOR INTERNAL USE ONLY
Department of Civil Engineering
Stanford University
Stanford, CA 94305
GROUNDWATER RECHARGE
BY INJECTION OF RECLAIMED WATER IN PALO ALTO
Interim Progress Report
1 August 1977 to 28 February 1978
Supported by
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
Project Officer: Marion R. Scalf
and
Department of Water Resources, State of California
Sacramento, CA 95814
Conducted in cooperation with
Santa Clara Valley Water District
San Jose, CA 95118
-------
TABLE OF CONTENTS
I. OBJECTIVES OF THE PROJECT 1
II. BACKGROUND INFORMATION 2
Need for the Study 2
Reclamation and Recharge Facilities 3
Reclamation Plant 3
Injection-Extraction Facility 6
Construction Progress 8
III. PROJECT PLANT 10
Phases of the Study 10
Schedule 11
IV. PROGRESS SUMMARY 14
V. DETAILED PROGRESS REPORT 18
Phase One - Preproject Monitoring and Testing 18
Phase Two - Water-Quality Monitoring Field Study 18
Introduction 18
Pilot Injection Study Objectives 19
Injection Site 19
Injection Rate and Pressure 23
Monitoring Program 25
Reclamation Plant Operation 27
Water-Quality Changes 28
Redevelopment of the Injection Well 83
Phase Three - Hydraulics of Recharge 85
Phase Four - Water and Aquifer Quality Changes 90
Potential for Microbial and Organic Chemical Changes .... 90
Chemical and Geochemical Changes 94
Cation-Exchange Capacity and Selectivity 104
Phase Five - Treatment Plant Optimization 108
Phase Six - Hydraulics and Water-Quality Monitoring 108
VI. FUTURE PLANS 113
VII. PROJECT PUBLICATIONS 118
VIII. PROJECT PERSONNEL 119
IX. REFERENCES 121
ii
-------
LIST OF FIGURES
FIGURE Page
1 Location map of the wastewater reclamation study area 4
2 Plan of facilities in the Palo Alto Baylands 4
3 Basic process flow diagram of reclamation plant 5
4 Diagrammatic geologic profile of Palo Alto-Mountain View
area near proposed injection-extraction site 7
5 Interactions between tasks 12
6 Project schedule 13
7 Layout of observation wells at pilot injection site 21
8 Schematic section showing permeable strata 22
9 Injection rate and pressure as function of cumulative
injection volume 24
10 Potential surfaces 26
11 Conductance response curves for well samples versus time 40
12 Breakthrough of injected water at P4 43
13 Relative concentration of major cations 43
14 Sodium adsorption ratio 44
15 Concentrations of major cations at Well P4 as a function of
time after injection initiated 45
16 Breakthrough curves for trace organic compounds at Well P4 — 53
17 Expected responses to a step change in concentration 55
18 Breakthrough of naphthalene at Well P4 57
19 Estimation of the chlorobenzene removal capacity of the
aquifer 59
20 Probability distribution for concentrations of trace organic
substances in injection water and well samples 61
21 Gas chromatographic analyses of injection water and ground-
water at Well P4 before and after injection 63
22 Concentration responses of trace metals at Well P4 76
23 Breakthrough of ammonia at Well P4 78
24 Concentration response of phosphate at Well P4 79
25 Bacteria counts in injection water and observation well
samples 81
26 Geological sections through Well 12 87
27 Distribution of depths of sand and gravel units 88
28 Distribution of thicknesses of sand and gravel units 89
iii
-------
FIGURE Page
29 Concentration of chlorinated benzene during incubation with
primary-effluent inoculum 93
30 Rate of pyrite oxidation 99
31 Effect of pyrite concentrations on the rate of oxidation 101
32 Effect of pH on the rate of oxidation 102
33 Effect of pyrite surface and pH on the pseudo-first order
rate 103
34 Layout of wells for proposed study at Il/El 116
iv
-------
LIST OF TABLES
TABLE Page
1 Characterization of the Lower Aquifer at Injection and
Observation Wells 20
2 Composition of Formation Groundwater Compared to Estimated
Injection Water Quality 27
3 Reclamation Plant Effluent Quality Data, 19 August to
15 September 1977 28
4A General Chemical Analysis—Background Samples of Formation
Groundwater at Well I2-Lower 29
4B General Chemical Analysis—Injection Water. Period 24 August
1977 to 18 November 1977, Prior to Operation of Activated
Carbon Treatment in Reclamation Plant and Period Following
13 December 1977; full treatment in the Reclamation Plant,
including activated carbon 30
4C General Chemical Analysis—Well PI 32
4D General Chemical Analysis—Well P2 33
4E General Chemical Analysis—Well P3 34
4F General Chemical Analysis—Well P4. Period 20 August 1977 to
18 November 1977, Prior to Operation of Activated-Carbon
Treatment in the Reclamation Plant and Period Following
13 December 1977, After Beginning Injection with Fully
Treated Reclaimed Water, Including Activated-Carbon Treatment 35
4G General Chemical Analysis—Well S3-Lower 37
4H General Chemical Analysis—Wells I2-Upper, S3-Upper, and 38
Mi-Lower
5 Approximate Time Required for Breakthrough of Injection
Water 41
6A CLSA Organic Characterization of Injection Water During
Period 12 September through 18 November 1977 Prior to
Activated-Carbon Treatment . 48
6B CLSA Organic Characterization of Injection Water, Period
Following 13 December 1977 After Beginning of Activated-
Carbon Treatment 49
7A CLSA Organic Characterization of Samples from Well P4,
Period 24 August 1977 to 18 November 1977 Prior to Opera-
tion of Activated-Carbon Treatment in Reclamation Plant 50
v
-------
TABLE Page
7B CLSA Organic Characterization of Samples from Well P4,
Period Following 13 December 1977; Full Treatment in the
Reclamation Plant, Including Activated Carbon 51
8A VOA Organic Characterization of Injection Water, Period
24 August to 18 November 1977 Prior to Activated-Carbon
Treatment 64
8B VOA Characterization of Injection Water, After Beginning
of Activated-Carbon Treatment 13 December 1977 65
9A VOA Characterization of Samples from Well P4, Period
24 August to 18 November 1977 Prior to Activated-Carbon
Treatment 66
9B VOA Characterization of Samples from Well P4, After
Beginning of Activated-Carbon Treatment 13 December 1977 67
10 Coliform, Bacteriophage, and Animal Virus Isolation from
Palo Alto Well Water, Injection Water (Tertiary Effluent),
and Secondary Effluent 69
11 Supplemental Information, Virus Monitoring at the Palo Alto
Facility 70
12 Removal of Bacteria and Viruses by Secondary Treatment and
Chlorination 72
13 Trace Metal Analyses—Injection Water 73
14 Trace Metal Analyses—Well P4 74
15 Trace Metal Analysis—Formation Groundwater Before Injection 75
16 Coliform Counts 82
17 Redevelopment Test at Well 12 84
18 Exchange Coefficients and Cation-Exchange Capacity 106
19 Estimated Surface Concentrations of Exchangeable Cations
Before and After Injection 107
20 Estimated Travel Times from II to Nearby Observation Wells— 115
vi
-------
GROUNDWATER INJECTION OF RECLAIMED WATER
IN PALO ALTO
I. OBJECTIVES OF THE PROJECT
The Santa Clara Valley Water District has proposed to carry out advanced
waste treatment and injection of two million gallons per day of municipal
wastewater into an aquifer in the Palo Alto Bayfront area to serve as a bar-
rier against seawater intrusion into the groundwater. As a long-term goal,
this facility will be used for research to determine the feasibility of such
a system for reclaiming water for potable uses. To answer questions relevant
to this long-term goal, Stanford University proposed a three-year program de-
signed to acquire fundamental knowledge concerning the transformations of con-
taminants and aquifer material resulting from the injection of treated waste-
water. This research was funded by the U.S. Environmental Protection Agency
under Grant EPA-R-804431, beginning May 1, 1976. The questions to be addressed
are specifically those related to the injection and resulting changes in the
aquifer character and permeability, and movement of and resulting changes in
the quality of injected and aquifer waters.
The major objectives of this proposed research study are as follows:
1. To determine the changes in the quality of the injected water during
passage through the aquifer and to identify the chemical, physical, and
biological processes that cause these changes.
2. To determine the effect that the injected wastewater will have on the
hydrologic and mineralogic characteristics of the aquifer.
3. To seek the optimum quality for injected water which will result in a
high-quality groundwater and minimum damage to the hydrologic charac-
teristics of the aquifer.
4. To develop generalized mathematical models for describing the movement of
water, the changes in hydrologic characteristics, and resulting changes
in water quality from wastewater injection in order to make the results
of most value for application in other similar projects.
1
-------
II. BACKGROUND INFORMATION
NEED FOR THE STUDY
The necessity of obtaining fundamental knowledge regarding the feasibil-
ity of wastewater reclamation by means of advanced waste treatment and direct
injection to recharge a groundwater resource was documented in Stanford Uni-
versity's original proposal for the full, three-year project.
Both the Federal Water Pollution Control Act Amendments of 1972 and the
Safe Drinking Water Act of 1974 indicate the importance of renovation and re-
cycling of wastewaters as alternative means of meeting future water demands.
Section 105(d) of the Water Pollution Control Act Amendments of 1972 requires
that the Administrator of EPA conduct on a priority basis an accelerated ef-
fort to develop, refine, and achieve practical application of advanced waste-
treatment methods for reclaiming and recycling water and confining pollutants.
Section 1444 of the Safe Drinking Water Act authorized a development and demon-
stration program to: (1) investigate and demonstrate health implications in-
volved in the reclamation, recycling, and reuse of wastewaters for drinking;
and (2) demonstrate processes and methods for the preparation of safe and
acceptable drinking water from wastewaters.
Nevertheless, it would be premature to enter into wastewater reclamation
for potable use on a large scale before certain fundamental questions have
been clarified. This can be achieved only by a program of fundamental research
carried out in conjunction with a field study conducted under controlled con-
ditions.
The advanced wastewater treatment and injection-extraction system built
by the Santa Clara Valley Water District (SCVWD) offers an unparalleled oppor-
tunity to conduct the research necessary to evaluate one of the most promis-
ing systems for reuse of reclaimed wastewater to augment potable water supplies.
The Santa Clara Valley Water District (SCVWD) has the responsibility for the
surface and groundwater resources of Santa Clara County, California, supplying
a population of approximately one million. Groundwater supplies approximately
60 percent of the municipal and industrial water needs of the area. However,
demand has exceeded the natural recharge rate for decades. The heavy demand
for groundwater has resulted in land subsidence, and in some areas, intru-
sion of saline water from San Francisco Bay to such an extent that it has
2
-------
been necessary since the 1950s to import fresh water for recharge of the
groundwater supply. The supply problem will worsen with continued growth
and, because of the shortage of additional water for importation, the District
is looking toward wastewater reclamation to supplement its water supply [1].
RECLAMATION AND RECHARGE FACILITIES
A 1. 5 m 3/s (35 mgd) regional activated-sludge wastewater-treatment plant
was recently completed in the Baylands in Palo Alto, which is situated at the
northern end of Santa Clara County. The SCVWD has constructed an advanced
wastewater treatment plant with a capacity of 8.8 x 10-^ m-Vs (2 mgd) for re-
charge to preserve and restore the groundwater resource in the Palo Alto-
Mountain View bayfront area which has suffered degradation through salinity
intrusion. This project has been approved by the California Water Resources
Control Board and Region IX of the U.S. Environmental Protection Agency. Con-
struction of this facility began in 1975 and should be completed in 1978. The
SCVWD contemplates operating the facility for a minimum period of ten years,
during which the feasibility of reclamation by this method will be decided
upon.
While the initial goal of the water-reclamation facility is to prevent
local salinity intrusion, the long-range objective is to determine the opti-
mum combination of treatment processes and injection system required to achieve
the most cost-effective and safe system of supplemental water supply using
reclaimed water [1], Thus, the facility offers opportunities for evaluating
on a small scale potential technology for larger reclamation efforts. The
advanced waste-treatment plant will be operated at a constant hydraulic load-
ing, but otherwise will be subject to the full spectrum of stochastic varia-
bility to be anticipated in a plant treating secondary effluent.
Figure 1 contains a map showing the location of the study area. Figure
2 shows the layout of the project facilities. The SCVWD Reclamation Facility
is located adjacent to the Palo Alto Regional Water Quality Control Plant.
Figure 3 shows the basic processes to be incorporated in the Reclamation Fa-
cility. The influent is chlorinated secondary effluent from the Palo Alto
Plant.
Reclamation Plant
The reclamation plant includes the following: high-lime treatment, an
aerator-fountain spray for ammonia removal, single-stage recarbonation,
3
-------
SAN
FRANCISCO
STUDY1
AREA
NOi
SAN FRANCISQUITO
SU0AREA
Figure 1. Location map of the waste-
water reclamation study area
SAN
FRANCISCO
BAY
0 500
1 _i i _i j L_i_.
SCALE
SCVWD WATER'RECLAMATION FACILITY--
WATER QUALITY
control! PLANT
INJECT WELL (TYP)/
E3
\ EXTRACT
\ WELL(TYP)
E4-
Os
M
E5 j
.19
PALO
or
ALTO
LEGEND
O EX TRACTION WELL
-»0- INJECTION WELL
9 M0'>iiT03 WELL
Figure 2. Plan of facilities in the Palo Alto Baylands
-------
r—— — *4>——
" LIME
BIOL
SECOND
¦o
® CHLORINE s-*.
CONTACT TANK
(EXISTING
SECONDARY
EFFLUENT
' . SE<
u
PUMPING
PALO ALTO
SECONDARY
TREATMENT
PLANT
WASTE
POLYMER "8* WATER
@ Q
PLASH w v'
MIXING FLCCCULATCR/
CLAHlr iER
© ©
rOZON
ifKTT1rta5:T£[
•CHLORINE"^*
AWMONiA /
SI RIPPING ^/R
SCVWD FACILITY
SALINITY
INTRUSION
BARRIER
ELL
INJECTION SYSTEM
2 M.G.O
PUMPING
INJECTION
WELLS
FILTERS
2 M.G.O.^
/pumping
RECARBONATION
& OZONATION
STORAGE &
CHLORINE CONTACT
EXTRACTION
WELLS
rO'OH
J. ~ jr
UMPING ©
chlorine
CARBON
ADSORBERS
^ CARBON FILL
SPENT
CARBON
i
1
FRESH
CARBON
SPENT REGENERATION
CARBON FURNACE
STORAGE
CARBON REGENERATION
SYSTEM
FLOW DIAGRAM
SCVWD AWT FACILITY
SCVWD WATER RECLAMATION & INJECTION/EXTRACTION WELL FACILITY A
AT PALO ALTO, CALIFORNIA Santo Clara Volley Water District f)
Figure 3. Basic process flow diagram of reclamation plant.
-------
breakpoint chlorination for further nitrogen removal, ozonation, mixed-media
filtration, activated-carbon adsorption with thermal regeneration, chlorina-
tion, and storage. The design is sufficiently flexible to allow for alterna-
tive treatment sequences. For instance, the water can be filtered after
activated-carbon treatment as well as before if removal of carbon fines be-
comes necessary. The design specifications for the reclamation plant are
summarized elsewhere [ 1, 2].
Injection-Extraction Facility
The stored reclaimed water will be injected into and withdrawn from the
groundwater aquifer through use of pairs of injection-extraction wells, known
as doublets, as indicated in Figure 2. A total of nine injection-extraction
doublet well systems have been constructed. Each injection well is designed
for a maximum injection gauge pressure of 138 kPa (20 psig) and a pumping rate
of 9.5 x 10"^ m^/s (150 gpm). Each extraction well will be located approxi-
mately 300 meters from its injection well counterpart, and the doublet systems
will be approximately 300 meters apart. This arrangement is intended to allow
injection of reclaimed water into the injection wells and the complete removal
of this water through the extraction wells. In addition, there is a network of
62 monitoring wells.
Hydrogeologic characteristics of the groundwater basin are illustrated
in Figure 4. The basin is divided into an upper zone, which is less than 30
meters (100 feet) deep, and a lower zone, which contains a fresh-water aquifer
at a depth of about 60 meters (185 feet). The two zones are separated by an
impermeable aquiclude. Salt water has intruded into the upper zone. At the
proposed site of injection, the upper zone has an aquifer at about the 6-meter
(20-foot) level and another at the 15-meter (45-foot) level, which are hydrau-
lically connected. The aquifers in the upper zone at depths of approximately
6 meters and 15 meters are referred to in this report as the "upper" and
"lower" aquifers, respectively, while that at 60 meters is designated the
"deep" aquifer. Under the present proposal, reclaimed water will be both
injected and extracted from the lower aquifer.
The injection-extraction system will permit the establishment of a
"mound" of fresh water in the seawater-intruded portion of the groundwater
sub-basin. Most, of the injected water will be utilized initially to displace
the saline, formation groundwater and maintain a freshwater mound in the
6
-------
FV»bcr Zw _ . _ Confined ft;ibaf Zont
r.vrfinad Area Lt*e1
owd S*t»-P*tEw< Zow«« V#a>g* Ltwl
Up>)tf Z*y* Co«ifiord G'Qw*i«o_*f' Lt¦ ;l
Stmi -tnfch»< Go*jrxlwjttf
Upptf ?0"ji Lfne«flM»d
Cr»jfidwot«r Lt«fir «tl~iC"il 'C^ord to qva^i j
Figure 4. Diagrammatic geologic profile of Palo Alto-Mountain View
area near proposed injection-extraction site.
-------
lower aquifer. This flushing will be effected and maintained on the bay side
by establishing a positive gradient toward San Francisco Bay to sweep out and
prevent the return of sea water. On the landward side, the extraction wells
will pump out the mix of brackish formation groundwater and injection water
until fresh water has replaced the saline water throughout the sub-basin.
Owing to the well configuration, the flow field can be expected to exhibit
several convenient, properties that make this installation ideal for research,
so long as the aquifer characteristics do not deviate too far from ideality.
The flow field is expected to be well defined and amenable to several hydraulic-
modeling approaches. The flow field may also be isolated, so that at some time
after steady-state conditions are reached, virtually all injected water even-
tually reaches the extraction well and all extracted water is predominantly
of injection origin.
The extracted water is expected to be suitable in quality for potable
reuse after the freshwater mound is sufficiently well established. The
validity of this assumption is reasonably assured by the high quality of the
reclaimed water to be injected and the additional security provided by a long
distance of travel and residence time in the aquifer.
Construction Progress
Construction of the reclamation plant was substantially completed in
April 1977 and production of reclaimed water began in July 1977. All liquid
processing units have been in continuous operation since March 1978. The
construction of the nine pairs of injection-extraction wells as well as the
associated monitoring wells was tentatively completed in January 1977, pend-
ing final evaluation of the test data. It is anticipated that the contract
will be let in Spring 1978 for construction of the pipeline connecting the
injection and extraction wells to the treatment plant. In the interim, the
Stanford project group has been injecting reclaimed water into Well 12 using
temporary facilities.
Preliminary interpretation of the test data indicate that, while substan-
tial deviations from design capacity occur at some individual wells, there is
good connection between wells through much of the aquifer. It appears certain
that, for the purposes of this project, sections of the well field can be
chosen for detailed analysis that are sufficiently easy to characterize, moni-
tor, and model.
8
-------
Full-scale operation of the first injection-extraction well pair Il/El
is scheduled to begin in June 1978. Construction of the necessary facilities
will be carried out in May 1978. The SCVWD has agreed to make this well pair
available to the Stanford University project group for water quality studies.
According to the test data the aquifer is reasonably continuous and homo-
geneous in the region of Il/El. This site will provide an excellent field
laboratory for water-quality monitoring, interpretation and modeling.
9
-------
III. PROJECT PLAN
PHASES OF THE STUDY
Phase One, a preliminary effort of preproject monitoring and testing
supported by the Santa Clara Valley Water District (SCVWD), was concluded
in 1976. Needed information on quality of the present secondary effluent,
quality changes to be expected from the proposed treatment system, quality
of the present basin waters, and mineralogic and hydrologic characteristics
of the basin was obtained.
Phase Two consists of water-quality monitoring for microbiological, in-
organic, and organic chemical and physical characteristics of wastewater and
groundwater. In some respects it is a continuation of the preproject moni-
toring activities of Phase One. More importantly, the state-of-the-art is
being extended by developing sensitive analytical methods for quantitative
determination of specific organic compounds and viruses at the very low con-
centrations at which they occur in reclaimed water and groundwater. These
methods as well as conventional techniques will be applied to characterize
the water-quality changes that occur during treatment and passage through the
aquifer after injection. Emphasis is placed on determining virus counts and
the concentrations of specific organic compounds that are of potential public
health significance.
Phase Three entails characterizing hydraulic characteristics of the
injection-extraction system. Mathematical models describing the flow of in-
jected water through the aquifer are formulated and calibrated with field
test data. Observations of the flow and the head distributions after injec-
tion begins will be used to calibrate and verify the flow models. The veri-
fied models can be applied to estimate travel times of injected water.
Phase Four pursues the central objective of providing explanations for
the changes in water quality and aquifer characteristics as injected water
passes through the aquifer material. It will be through the understanding
obtained from this phase that effects from injection in other basins can be
predicted and a knowledge of desirable modifications in quality of treated
water can be obtained in order to enhance extracted water quality and main-
tain desirable aquifer characteristics.
10
-------
Phase Five deals with the performance of the treatment plant and is con-
cerned with determining and improving plant reliability, determining best
treatment procedures for changing water quality as dictated by the results
of the Phase Four studies, and minimizing treatment costs.
Phase Six is concerned with integrating models for simulating water-
quality changes with those for simulating flow in the aquifer so that changes
in water quality can be predicted as a function of time and space. The water-
quality models used in Phase Six will incorporate modified versions of those
developed in Phase Four, adapted to enhance computational efficiency.
There is overlap between the various phases, and success of one phase
frequently will depend on obtaining the correct information from another
phase. Thus, close coordination between phases is required. The interrela-
tion between phases is illustrated in Figure 5.
SCHEDULE
During the current budget period we are emphasizing field work at the well
field in the Palo Alto Baylands. The major objectives are: to obtain field
data that will provide insight into the phenomena that occur when reclaimed
water is injected into an aquifer; to observe water-quality changes during
passage through the aquifer and to evaluate them from the viewpoint of potable
reuse; to gain understanding of the phenomena and quality transformations ob-
served in the field through fundamental laboratory research; and to develop
computer models capable of explaining the field data and predicting behavior,
if conditions of recharge were to be changed. The revised project schedule is
shown in Figure 6.
11
-------
CONSTRUCTION AND
OPERATIONS
(Responsibility
of SCVWD)
WELL FIELD
CONSTRUCTION,
TESTING, AND OPERATION
Field Data
(Hydraulics)
TREATMENT PLANT
CONSTRUCTION, OPERATION,
AND MONITORING
Field Data
(Quality)
Operating
Recommendations
RESEARCH
(Responsibility of Stanford University)
WATER-QUALITY
MONITORING
Phase Two
Field Data
Monitoring"
I
Recommendations
WATER-QUALITY
CHANGES
Phase Four
I
Transfor-
mation
Models
HYDRAULICS
OF RECHARGE
Phase Three
_ _Ef_fects_o_f _
Nonidealities
Interpretation of^
Field Data
Consequences
of Models in
Field
Situation
FLOW AND WATER-
QUALITY MODELING
Phase Six
~t
Monitoring Data
Predicted
Effects of
Operating
Policies
Effluent
Quality
Predictions
Operating Recommendations
_3L
TREATMENT PLANT
OPTIMIZATION
Phase Five
Figure 5. Interactions between tasks.
-------
1976
1977
1978
19 79
RECLAMATION FACILITIES
Well Field
Treatment Plant
RESEARCH PROGRAM
Phase One - Preproject
Work
Phase Two - Water-
Quality Monitoring
Phase Three -
Hydraulic Modeling
Phase Four - Water-
Quality Changes
Phase Five - Treatment
Plant Optimization
Phase Six - Water-
Quality Modeling
{
/
I
Well Construction
and Tests
Construction
I r.
Pipeline i
:ns truction'
Startup
Reclamation System |
1 in Full Operation '
(until 1986 or beyond)
Production of Reclaimed Water .
^ Period Covered by This Report
|Background Monitoring Completed
Development of Methods for
Chemical and Biological Monitoring
Trace Organic & Virus Analyses'
iObservation Well Construction
Doublet Modeling
Finite-Element Model Development
ijicticjir
Field Testing
Chemical and Biological Method Development
Process Evaluation
Interpretation of Changes in Water Quality
and Aquifer Properties
Treatment Performance Evaluation & Modification
Finite-Element Model Development | Definition of
Combined Modeling of
Parameters
Figure 6. Project schedule
Flow and Quality
-------
IV. PROGRESS SUMMARY
Funding for the first budget period commenced on 1 May 1976 and continued
until 30 July 1977, including a 90-day extension granted by the funding agency.
Accomplishments during that period are described in Technical Report No. 225
[2], The achievements can be summarized as follows:
(a) Acquiring background information regarding the geology and chemistry
of the aquifer at the injection site.
(b) Obtaining estimates of the effectiveness of the treatment processes
to be used at the reclamation plant and predicting the expected
quality of the injection water.
(c) Developing specialized analytical procedures to be used in the
monitoring study, particularly for virus assays and detailed organic
characterization of water samples.
(d) Surveying the well field to characterize the composition of the
formation water before injection.
(e) Identifying the minerals which may tend to dissolve or precipitate
after injection begins.
(f) Formulating models for adsorption and biodegradation of trace organic
substances in an aquifer environment,
(g) Adapting both analytical and finite-element models to permit com-
puter simulation of the flow in the region of a single injection-
extraction doublet and in the well field as a whole.
The preliminary results of work during the second budget period since
31 July 1977 are described in Section V. These can be stated briefly as
follows:
(a) A pilot injection field study was conducted at Well 12 to test the
methodology developed in the first budget period and to gain ex-
perience for the full-scale injection-extraction field work proposed
for the third budget period.
(b) Based on the experience gained from the field work, the analytical
methods are being refined to permit more rapid and accurate deter-
minations of a wide variety of trace organic compounds.
(c) The insights from the field observations have provided new directions
for laboratory studies of adsorption, ion exchange, biodegradation,
14
-------
and oxidation/reduction processes. Evidence for the significance of
these processes was obtained.
(d) Substantial advances were made in the application of biofilm theory,
ion exchange and adsorption concepts, and chemical equilibrium model-
ing to explain water-quality phenomena observed in the field and in
the laboratory.
(e) The finite-element model for flow and contaminant transport in a two-
dimensional aquifer was developed to an operational state and used
to interpret injection rate and potential distribution data.
Experimental work is continuing in the field and in the laboratory.
Preparations are being made to begin the next phase of field work at the de-
monstration scale before the end of the second budget period.
The major objectives of the field work at the injection-extraction facil-
ity in the Palo Alto Baylands are: to obtain field data that will provide in-
sight into the phenomena that occur when reclaimed water is injected into an
aquifer; to observe water-quality changes during passage through the aquifer
and to evaluate them from the viewpoint of potable reuse; to gain understand-
ing of the phenomena and quality transformations observed in the field through
fundamental laboratory research; and to develop computer models capable of ex-
plaining the field data and predicting behavior if the conditions of recharge
were to be changed.
The injection pilot study has resulted in major achievements in method-
ology development for groundwater recharge field work. It also has yielded
data on water-quality changes that confirm many of our expectations regarding
the important phenomena affecting water quality in an aquifer.
Breakthrough curves for conservative inorganic constituents, other
major ions, nutrients, trace organic compounds and trace metals were measured
at observation wells near the injection well. From these data the travel
time and dispersion of the injected water and contaminants can be estimated.
The movement of trace organic contaminants and trace metals was strongly
attenuated during the passage through the aquifer. Adsorption is believed to
be the principal mechanism. The aquifer passage also greatly reduced the co-
efficient of variability of concentration of a trace organic compound selected
for detailed study, chlorobenzene. In this respect, the adsorption and disper-
sive properties of an aquifer greatly improve reliability even after the net
removal capacity is exhausted.
15
-------
Biological activity in the aquifer was observed, as reflected in reduc-
tion of COD and DO concentrations between the injection and observation wells
and by high bacterial plate counts. However, there is evidence that the
types of nonpolar compounds monitored using gas chromatographic methods (VOA
and CLSA) for the most part are not degraded in the aquifer at the concentra-
tions presently being injected.
Substantial advances were made in theoretical development and experi-
mental confirmation of a model for biological activity in thick films under
conditions applicable to groundwater recharge. A quasi-linear model has been
formulated that is computationally amenable to integration into the combined
model for finite-element simulation of water-quality transformation and
flow.
Strong evidence of ion exchange was inferred from the concentration re-
-l_ 2+ 2+ +
sponses of the ions Na , Mg , Ca , and NH^. The retention capacity of the
aquifer for ammonium ion was estimated from the field data and confirmed
with acceptable accuracy in laboratory determinations of ion exchange capacity
and selectivity conducted with core samples.
Confirmatory evidence was found for phosphorus precipitation, as pre-
dicted by computer models of chemical equilibrium.
Clogging of the aquifer was observed while partially treated reclaimed
water was being injected during the first half of the pilot study. This was
shown by a decline in both the injection rate and the field pressures at con-
stant injection pressure. Pumping the injection well from the surface was only
partially successful in restoring the original aquifer capacity. Analyses
of the water pumped to the surface during redevelopment showed very high
concentrations of bacteria as well as contaminants present in the injection
water. These findings indicate that the clogging was caused by a combination
of biological growth and filtration of particulates present in the reclaimed
water. Most importantly, the clogging has not progressed since the quality
of the reclaimed water improved at the midpoint of the pilot study, when the
activated-carbon and mixed-media-filter treatment units were brought into
operation.
The injection rate and field pressure observations were used as input to
calibrate parameters in the finite-element computer model of flow in the
aquifer. The results show unequivocally that the injection horizon 12 is
discontinuous to such a degree that the situation can only be described as
injection into a sand lens embedded in less porous aquitard material.
16
-------
Geological evidence and well test data suggest that conditions at the
next field study site, Il/El, will be more favorable for the interpretation
of the field data and their application to computer modeling. It has been
concluded that the subregion Il/El is the only area in the well field suit-
able for field work in this research project. This collapsing of alterna-
tives greatly simplifies the task of choice, and helps us to focus efforts
on a limited area with maximum promise of conclusive results.
17
-------
V. DETAILED PROGRESS REPORT
PHASE ONE - PREPROJECT MONITORING AND TESTING
The first phase of preproject monitoring and testing was concluded in
1976, supported by the Santa Clara Valley Water District (SCVWD) and needed
information was obtained on quality of the present secondary effluent,
quality changes to be expected from the proposed treatment system, quality of
the present basin waters, and mineralogic and hydrologic characteristics of
the basin. The progress in Phase One was described in more detail in Tech-
nical Reports 206 and 225 [3,2].
PHASE TWO - WATER-QUALITY MONITORING FIELD STUDY
Introduction
In this section the methodology and results of a pilot field study of in-
jection of reclaimed water are described. Reclaimed water produced at the
Palo Alto Water Reclamation Plant was injected into the lower (15-meter) aqui-
fer at Injection Well 12 beginning in August 1977. This injection study was
intended primarily to investigate water quality and hydraulic behavior in the
immediate vicinity of the injection well. Therefore, it was not necessary
to pump \7ater simultaneously from the nearby extraction well.
The preliminary phase of injection was carried out over a period of 86
days, from 2k August 1977 until 18 November 1977. During that period, a total
of 4,500 m^ (3.66 acre-feet) of reclaimed water was injected. Treatment in
the reclamation plant consisted of lime treatment at pH 9, air stripping,
chlorination, recarbonation, and ozonation. The injection water was filtered
through an 18-inch deep sand filter at a rate of 15 m/hr (6 gpm/ft^) to remove
particulates that might clog the injection well. After a 25-day interlude for
reclamation plant maintenance and injection well redevelopment, injection was
resumed on 13 December 1977. Since then, the reclaimed water has received
full treatment, including activated-carbon and mixed-media filtration in addi-
tion to the processes listed above. From 13 December 1977 until 1 March 1978,
3,030 m of reclaimed water were injected.
Concentrations of major cations and anions, inorganic nitrogen species,
trace metals, individual trace organic compounds, total organic carbon (TOC),
chemical oxidation demand (COD), phosphate, dissolved oxygen, total bacterial
plate counts, and coliform counts were determined in samples of injection
water and groundwater. Virus assay procedures developed during this research
were applied in the field.
18
-------
Pilot Injection Study Objectives
The goals of the pilot injection study at Well 12 are as follows:
(a) To obtain quantitative data regarding the water-quality changes that
occur during passage through the aquifer;
(b) to obtain evidence that transformation processes such as adsorption,
biodegradation, ion exchange, and oxidation/reduction and precipita-
tion/dissolution reactions occur in the aquifer;
(c) to estimate the rate of movement of pollutants relative to the rate
of movement of the injected water through the aquifer;
(d) to estimate from water-quality data the field capacity of the aqui-
fer for retaining specific pollutants as well as to obtain estimates
of parameters such as dispersion coefficients;
(e) to utilize the injection rate and pressure distribution data to re-
fine the flow field simulation model;
(f) to measure the rate of loss of permeability in the aquifer, to ascer-
tain the causes and to evaluate alternative methods of prevention
and redevelopment.
This pilot study focused on the short-term behavior in the immediate vicinity
of the injection well, in order to obtain data that otherwise could be ac-
quired only in long-term studies during full-scale field operation over large
distances. Furthermore, such a preliminary study is valuable in gaining ex-
perience prior to operating the full injection/extraction program, in identi-
fying potential problems, and in designing the monitoring program for the
full-scale operation.
Injection Site
The location of the injection site at Well 12 is shown in Figure 2 in
the main body of the proposal. Well 12 was chosen by reason of the proximity
to the main pipeline constructed in Summer 1976 to supply reclaimed water to
the City of Palo Alto for landscape irrigation. The properties of the lower
aquifer at 12 were estimated by analysis of step-drawdown tests conducted by
the Santa Clara Valley Water District's contractor, with S3 as the monitoring
well. The results are as follows:
Maximum Drawdown 13 m (42.9 ft)
Maximum Pumping Rate 1.4xl0~^m3/s (22 gpm)
Maximum Injection Rate at 172 kPa (25 psig) 2.0 x10~3m3/s (31 gpm)
Transmissivity 7.0 x10~^m^m~^s-^(519
gal-day~^-f t--'-)
-3
Storativity 2.0x10 (dimensionless)
19
-------
It is apparent from these results that the injection capacity of the well is
considerably smaller than the design rate of 10 liters/sec (150 gpm) per in-
jection well used by the SCVWD's consulting geologist as a basis for the proj-
ect. Nonetheless, the relatively low injection capacity was not a serious
impediment to fulfilling the principal objectives of the pilot study, since
these were related primarily to behavior in the immediate vicinity of the
injection well.
Four additional observation piezometers were constructed at a distance
of approximately 8 m (26 feet) from 12 to provide more detailed spatial
coverage around the injection well. The new piezometers were perforated
through the entire thickness of the lower aqifer, which in the vicinity of
12 is encountered at a depth of approximately 12 to 14 m (40 to 46 feet).
The depth and thickness of the lower aquifer varies appreciably, as shown in
Table 1. The layout of the observation wells, including shallow monitoring
TABLE 1
Characterization of the Lower Aquifer at Injection and Observation Wells
Distance
Depth
Thickness
from
to Lower
of Lower
Injection
Aquifer,
Aquifer,
Well
Well, m
m
m
Type of Material
12
0
14.0
1.5
Fine to medium sand, some gravel
PI
7.6
13.3
0.3
Silty sand
P2
9.1
12.8
0.3
Silty sand
P3
7.6
12.8
0.3
Silty sand
P4
7.6
13.7
2.1
Medium to coarse sand, gravel
S3
16.8
12.2
1.0
Sand, fine to medium
Ml
150
11.2
2.4
Silty to coarse sand
well S3 constructed by the SCVWD, with respect to the injection well 12, is
shown in Figure 7. The well log data show evidence of significant hetero-
geneity of the lower aquifer in the vicinity of 12. This is illustrated by
the geological section from P2 through 12 and P4 to S3, constructed from the
well logs as shown in Figure 8. While there appears to be good conformance
among the permeable strata at 12, P4, and S3, there is no obvious connection
from 12 co P2 in the vicinity of 15 meters depth. Similarly, PI and P3 show
no good connection to 12 in the depth range of the lower aquifer.
20
-------
PI
P4
P2.
r\
12
\
\
::i
\
\
\P3
7
5'
12
:: l'
S3
Figure 7. Layout of observation wells at pilot injection site
21
-------
P2
12
P4
S3
urrrrri
IT
22
-o'o •0
¦ . • • • . 0 . ' e . o ' n ' " ¦ • 1?
• »-'c ¦ O. ¦ ¦ »' . " o ¦ ¦ ¦
' - ° . " . •*> 0 *«?* '°
..00-
c[ ' <> ' '• ° ° ' ' :
' a -o.' o ' .o' ° >0 'o °
\ •0 ¦ o #'o, ;o'o . 0,'. » V, :
* :/ 'o 'c°.
0 ' ' , • . o o . o
\ \ ...
" tp'"' ¦ 'q' ' a' o
¦0. 0 • b ¦ ' ® . ' •>* /
: * o ." • 0 0 '
. V y/
/
/
" 0:
f. e>'
V;
z
' ' : s
' • i \ t
• ' v •
». *
i l l 1 II
cd cji ^ oj ro o
o o o o o _
Feet Below Ground Surface
Figure
8.
Schematic -section, showing permeable strata
-------
A drawdown test was conducted by pumping from 12 and observing changes in
water levels at the observation wells. This test confirmed that the connec-
tion from 12 to P4 was quite direct, whereas the responses at PI, P2, and P3
were much slower. The drawdown at S3 agreed with the previous test conducted
by the SCVWD's contractor.
Injection Rate and Pressure
Injection at 12 has been carried out at a constant well-head pressure of
approximately 100 kPa (15 psig).
During the first four weeks of operation, the initial injection rate
into a relaxed field was approximately 1.25 liter/sec (20 gpm) at an injec-
tion pressure of 100 kPa (15 psig). As the pressure in the aquifer rose in
response to pressurizing the injection well, the flow rate tended to decrease
asymptotically toward a steady state, reaching a value of approximately 1 li-
ter/sec (15.8 gpm) within a few days after the well was pressurized. This
phenomenon was observed repeatedly over the first four weeks of injection.
The injection rate and pressure are shown as a function of cumulative injec-
tion water volume in Figure 9. The data shown correspond to the period
from 24 August 1977 to 1 March 1978.
The steady-state injection rate began to decline following a 7-day
shutdown at the reclamation plant (22 to 29 September 1977), as is evident
from Figure 9. The steady-state injection rate had fallen from 1 liter/
sec (15 gpm) to approximately 0.5 liter/sec (8 gpm) by the end of the first
phase of injection, in mid-November 1977.
The decline in injection rate was paralleled by decreasing pressures
measured at the observation wells around 12. During the first four weeks of
injection, the pressure at Observation Well P4 was approximately 100 kPa (15
psig) and the differential between the injection well head and Observation
Well P4 was 3.5 kPa (0.5 psig) or less. The initial pressures at PI, P2, P3,
and S3 were much lower, approximately 7 to 15 kPa (1 to 2 psig), but all of
the wells were under sufficient pressure to permit bleeding a continuous flow
of approximately 1 liter per minute to purge the piezometer tube.
After the shutdown in September, however, the pressures at all observa-
tion wells decreased markedly. The pressure at P4 fell to approximately
35 kPa (5 psig), corresponding to a pressure differential between 12 and P4
of approximately 80 kPa (12 psig). The gauge pressures at PI, P2, P3, and
23
-------
ho
.0-
V)
S
U~j
cu
LU
cr
£ 0.6
o
1—
o
LiJ
~D
LJ
<
CC
LU
§
1.2
1.0
0.8
0.4
0.2
0
1—i—i—i—|—i—i—i—i—[-
RATE
t i—i—[ i—I—i—1—|—i—i—i—i—|—i—i—i—i—|—r
i—|—i—i—i—r
PRESSURE
MAX
_ ~L
MIN
I
Injecllon of
actk'oied ccrbon-treoled water
C
J
o
Xi
"to
a.
LU
or
ZD
V)
in
LJ
cr
o_
0 12 3 4 5 6 7
CUMULATIVE INJECTED VOLUME, lO'm3
Figure 9. Injection rate and pressure as function of cumulative injection volume
8
-------
S3 decreased to less than 3.5 kPa (0.5 psig), and the wells were no longer
artesian. The isopotential surfaces at the beginning and end of the first
phase of injection are compared in Figure 10.
The decline in flow rate as well as the decrease in pressures at the
observation wells are evidence of clogging of the aquifer. The significant
clogging apparently was occurring neither in the gravel pack nor on the well
screen. The pressure measured at the gravel addition pipe, 15 centimeters
distant from the well screen, was essentially equal to the injection well
head pressure.
The subsequent effort to redevelop the clogged aquifer is described
elsewhere in this report. Pumping from the surface was insufficient to re-
gain the original injection rate, as seen in Figure 9. Nonetheless, when
injection was recommenced the rate did stabilize, showing no decline as 3000
O
mJ were injected from 13 December 1977 to 1 March 1978. The improved quality
of reclaimed water brought about by activated-carbon treatment and filtration
is believed responsible for the mitigation of the clogging problem.
Monitoring Program
The design of the monitoring program was predicated on the assumption
that there would be substantial differences between the composition of the
injection water and that of the formation groundwater into which it was to
be injected. The chemical quality of the formation groundwater was characte-
rized in the first year's work and was summarized in Technical Report 225 [2].
In the vicinity of 12, as elsewhere in the well field, the groundwater was
highly brackish prior to injection. The mineral composition in the lower
aquifer approximated that of sea water. The composition of the groundwater
in the lower aquifer is compared with the anticipated quality of injection
water in Table 2. This indicates a substantial change in mineral quality
could be expected at the observation wells as the injected water displaced
the formation water. The concentrations of all major ions are lower by a
factor of ten or more in the injection water, with the exception of bicarbo-
nate (alkalinity).
Hence, it was planned to monitor conductivity at the observation wells
after injection had begun. The conductivity response was taken as the field
criterion for the arrival of the front of injection water. Samples were
taken at intervals along the conductivity response curve for determination
25
-------
14.5
P4
PRESSURE, psig
EARLY PERIOD
Aug-midSept.
— — LATE PERIOD
(mid Nov.)
14.5
Figure 10. Potential surfaces
26
-------
TABLE 2
Composition of Formation Groundwater Compared to Estimated Injection Water Quality
Formation
Groundwater3
Injection
Std.
Water^
Msfln
Dev.
Calcium, mg/1
1,920
23
117
Magnesium, mg/1
1,210
27
2
Sodium, mg/1
6,600
200
162
Potassium, mg/1
103
1.0
11
Chloride, mg/i
15,500
610
262
Sulfate, mg/1
1,090
51
85
Alkalinity, mg/1 as CaC03
253
49
177
Total Dissolved Solids, mg/1
29,700
297
860
Specific Conductance, pS/cm
1,250
Ammonium-N, mg/1
1.98
0.1
39
Phosphate, mg/1 as PO4
0.64
0.13
2
Total Organic Carbon, mg/1
T C
approx. 7
approx. 8e
Iron, yg/1
5
Copper, yg/1
2i
17
Cadmium jJg/1
2.f
1
aMean and standard deviation of five samples taken
c0ne sample from S3-lower.
from I2-lower during drawdown test, 18 Aug. 1977
•
^One sample from I2-lower.
,
eEstimated
from
COD values.
"Mean of effluent quality after lime treatment,
ammonia stripping, recarbonation, ozonation,
and filtration of secondary effluent. See
Technical Report 206.
of major cations and anions, individual trace organic compounds, trace metals,
bacterial counts, nitrogen species, fluoride, phosphate, TOC, COD, iron, sul-
fide, and total dissolved solids. The monitoring and sampling activities
centered on observation well P4, where the most rapid and complete breakthrough
of injection water was anticipated owing to the relatively favorable hydraulic
connection to the injection well.
Reclamation Plant Operation
During the first phase of injection (August to November 1977), the Palo
Alto Reclamation Plant operated intermittently at a loading of approximately
22 liter/sec (0.5 mgd), compared to the design rate of 88 liter/sec (2 mgd).
The plant was being run on manual control in a startup mode. The
plant treated chlorinated Palo Alto secondary effluent under the following
27
-------
conditions:
Lime Treatment pH 9.5
Air Stripping One surface aerator operating intermittently
Recarbonation To pH 7.5
Ozonation Dose approximately 50 mg/1 O3
Chlorination Dose approximately 2 to 5 mg/1 CI2 following
ozonation
A preliminary summary of effluent quality data reported by the NASA monitor-
ing facility operating at the Palo Alto plant for the period 19 August to 15
September is given in Table T-3.
TABLE 3
Reclamation Plant Effluent Quality Data
19 August to 15 September 1977
n
Mean
Standard
Deviation
PH
24a
7.2
0.47
Conductivity, mS/cm
203
1.44
0.055
Ammonium-N, mg/1
17a
18.2
3.8
Alkalinity, mg/1 as CaCO^
20a
280
37
Combined Chlorine Residual, mg'l
14a
5.4
1.6
Coliforms, MPN/100 ml
30b
3.0
5.5
3
These data are compiled from daily averages provided by the NASA
Computer Plotting Routine.
^Multiple tube determinations carried out by the laboratory of the
Palo Alto Water Quality Control Plant. Of the 30 samples, 20
indicated the absence of coliform bacteria.
Water-Quality Changes
The water quality changes after injection are summarized in the follow-
ing:
Table 4 Major Ions, TDS, Conductivity, D.O., Nitrogen Species,
Phosphate, TOC, COD, and Total Plate Counts
Tables 6-9: Trace Organic Substances
Tables 10^12: Bacteria and Viruses
Tables 13-15 Trace Elements.
28
-------
TABLE 4A
General Chemical Analysis
Background Samples of Formation Groundwater at Well 12-Lower
Dace Tine
Total
Elapsed
Time
(lirs)
Cumul
Inj.
Volume
Con-
duc-
tivity
pS/cm
pH
Dis-
solved
Oxygen
mg/1
Sample
No.
Concentrations
¦ rag/1
TDS
Ca
Mg
Na
K
CI
S04
\\ k as
CqCO -j
P04
F
B
NH.-N
4
no2-h
NO-j-N
TOC
COD
27/4/77
Before 1
nj.
49,800
6.9
<0.5
131
2B.760
1,450
1,240
6,610
91
16,000
1,650
324
26/7 20
inin. Drawdown
36,500
6.9
<0.5
142
25,000
1,720
1,010
3,980
20
13,500
965
242
SO
tain.
"
38,000
7.0
<0.5
143
27,600
1,670
1,050
4,240
70
14,000
1,140
265
120
min.
ii
40,000
6.9
<0.5
144
29,400
1,630
1,120
5,420
100
14,800
1,170
280
160
rain.
"
41,000
6.9
<0.5
145
30,300
1,590
1,180
5,670
130
15,600
1,460
300
to
£»
O
min.
"
42,000
6.9
< 0.5
146
28,200
1,570
1,180
5,750
140
15,900
1,530
300
10/8
Before InJ.
34,000
7.6
<0.5
165A
29,700
1,880
1,200
6,400
104
15,500
1,050
166
0,7
18/0
*¦
32,100
7.0
< 0.5
165B
26,600
1,930
1,200
6,400
102
15,700
1,090
278
0,7
2.0
18/8
"
31,BOO
6.8
< 0.5
165C
26,100
1,920
1,200
6,600
103
15,100
1,040
286
0.8
1.4
2.1
18/8
"
"
29,700
7.0
< 0.5
165D
26,200
1,920
1,200
6,800
102
14,800
1.160
265
0.5
1.95
18/8
"
"
29,400
7.2
< 0.5
165E
27,800
1,940
1,260
6,800
104
16,400
1,110
271
0.5
1 .9
1.85
-------
TABLE 4B
Period 24 Aug. 1977 to 18
General Chemical Analysis—Injection Water
Nov. 1977, Prior to Operation of Activated-Carbon
Treatm. in Reclamation Plant
Total
Elapued
T line
Oirs)
CumuL.
Inj.
Vol UIDC
Con-
due-
11v1ty
US/cm
Ms-
no.! ved
Oxygen
ma/.I
Concentrations.
mg/.l
Du ce
Time
pll
Samp]e
No.
TDS
Cn
Mr
Na
K
CI
SO4
AIk.au
CaC03
F
B
NH. -N
4
no2-n
no3-n
TOT
COO
24/8/77
8
27
1 ,fi00
7.6
194
920
70
21 .6
190
13.8
272
77
308
4 .4
2.9
0.73
26
0.065
0. 58
19.6
2rs/a
11
49
1,800
7.7
L95
910
87
26.3
1.80
14.3
328
77
314
4.4
27
0.066
0.41
25/8
07:50
20
62
1,800
7.5
196
860
70
20.5
180
13.1
273
80
302
4.3
29
0.065
0.43
22.3
25/a
16:00
28
91
1,700
7.6
L97
850
70
20.4
150
13.6
273
82
319
2.8
4.2
0.82
36
0.024
0. 28
21.5
25/8
23:40
36
1J2
1,800
7.4
198
876
80
22.3
160
L5
259
82
314
3.6
32
0.056
0.39
19.7
26/8
08:00
44
158
1.800
7.4
L99
936
80
22.9
L70
15.2
289
80
319
2.8
29
0.05
0.40
26/8
13:50
52
180
L, 700
7 . 1
200
960
70
22.7
170
14.8
273
82
279
3.1
3.7
0.77
• 29. 5
0.054
0.36
30.2
31/8
15:30
172
384
1,350
7.8
214
886
44
16
177
15.6
273
83
353
0.8
0.73
h/9
09:30
262
696
L.600
7.0
215
931
54
22.8
176
14.8
300
100
30H
1 .6
3.3
25
13.7
8/9
10:00
358
1,060
1,400
7.2
242
827
61
16.5
194
14.8
248
91
245
1 .1
3.0
25
0.017
1 .98
12/9
11:50
456
1,440
1.500
7.5
246
863
68
J 9.1
172
14.3
273
105
285
2.3
3.4
23
0.033
0.97
15/9
09:40
526
1,590
1.700
7.15
248
897
62
21.9
187
14.2
328
96
268
3.0
10
21/9
11:00
667
2.160
1,500
7.9
251
850
48
21
186
14.4
300
11 L
205
5.4
30
3/10
12:30
957
2,430
850
8.0
258
451
30
11.2
89
8.4
155
54
118
2.8
4.0
17.2
0.10
0.74
12/10
11:00
1174
2,860
1,340
7.3
262
695
61
7.2
152
10.7
247
79
165
1.1
4.5
0.63
23.6
18/10
10:30
1318
3,160
1 ,800
7.8
265
908
110
11.0
208
13.6
317
90
142
0.5
1 .6
28
15.2
27.6
21/10
10:30
1463
3,450
1,200
7.5
269
880
108
13.4
178
12.6
277
77
318
2.9
3.0
28.3
16.7
29.2
2/11
1679
3,860
1,150
7.3
277
791
75
10.6
165
16
290
88
164
1.1
2.7
32.5
17.9
16.1
7/11
9.6
280
26.3
18.8
8/11
9.2
283
20.0
9/11
1868
4,140
1,580
7.9
9.2
286
83L
71
9.6
170
17
260
103
249
0.6
3.2
34.3
20.5
14.4
10/11
9.7
290
21.2
18/11
2062
4,510
1,150
7.65
300
831
70
13
165
17.4
270
99
243
1.9
3.2
34.5
17.0
15.6
TABLE 4B cont.
-------
TABLE 4B cont.
Period Following 13 Dec. 1977; full treatment in the Reclamation Plant, incl. activated carbon
To ta.l
Elapsed
Time
(hrg)
Ciwiul.
Tn,1 •
Volume
Con-
duc-
tivity
pS/cm
Dls-
so]ved
Oxygen
mg/1
Sample
No.
Concentrations, mj;/l
Dat*>
Time
pll
TDS
Ca
Mg
Na
K
CI
SO,
Co CO ^
P04
F
B
NH.-N
4
COD
UT>f
13/12
10i65
1.-5
0
7,900
7.7
309
790
68.8
15.6
196
13.2
266
86.6
245
1.5
3.2
32
14/12
L97&:
6/1
09:00
23
4 6
7.5
314
790
68.8
14.6
195
12.4
262
84.7
255
1.3
3. 2
32
09i03
573
980
1,500
6.0
2.8
335
750
71. 2
13. 2
197
12.6
275
84.4
156
1.1
9/1
11:20
6S0
1,100
5.8
1.7
337
740
72.4
13.4
194
12.6
277
80. 5
155
1.1
3.2
28
4/2
11:05
1389
2, 280
1,730
1.2
350
770
52.5
17.1
194
14.2
253
106
165
11.3
5.4
lfi/2
1557
2,540
1.680
6.6
0.3
352
750
89.8
16. 3
188
14.1
24 3
106
152
10
19.6
22/2
13:00
1703
2,770
3,520
6.7
0.7
355
790
90.6
17.2
187
15.0
263
120
159
11
28.7
1/3
10:05
1868
3,020
1,880
6.6
4.1
361
188
14.2
2 51
128
142
7.5
28.1
-------
TABLE AC
General Chemical Analysis—Well PI
Total
Elapsed
Time
(hrs)
Cunm.
Inj.
Volume
ID '
Con-
duc-
tivity
IjS/cq
Dis-
solved
Oxygen
mg/l
Concentrations, mg/l
Date Time
PH
Sample
No.
TDS
Ca
Mg
Na
K
CI
so4
Mk .as
CaCOj
P04
F
B
NH^-N
N02-N
no3-n
T0C
COD
. 20/8/77
Before
Inj.
57,000
7.2
170
46,700
792
1,800
14,000
'4 35
25,200
3,480
581
1.37
24/8 12:10
0
0
56,000
6.7
210
46,800
381
1,420
16,300
209
24,000
3,600
581
2.43
<0.01
0.001
24/8 15:00
3
14
7.2
201
45,567
530
2,270
15,000
290
24,000
3,280
270
9.1
26/8 01:30
38
120
25,000
7.0
202
22,400
480
580
5,080
LOO
11,200
1,740
524
1.25
0.068
0.23
15.1
26/8 09:15
45
1S8
15,000
7.6
204
19,800
190
700
5,750
L20
10,100
1,620
513
1.16
0.077
0.27
31/8 14:50
170
407
7,000
7.7
216
4,553
166
139
1,880
26
2,620
280
380
0.72
0.183
0.15
2/9/78
216
570
9,600
7.7
217
6,900
280
198
1,990
27
3,820
366
353
16.0
2/11
1679
3,860
5,000
7.6
275
4,780
146
180
1,380
69
2,410
368
329
16.75
18/11
2062
4,510
5,100
7.8
299
3,460
96
100
1,100
46
1,650
267
299
1.2
12.3
-------
TABLE 4D
General Chemical Analysis--Well P2
Total
Slapsec
Time
(hrs)
Cumul.
Inj.
/olvuoe
Con-
Dis-
solved
Oxygen
nig/1
Conccncrat Lens, mg/1
Date
Time
tivity
MS/cm
P«
Sample
No.
IDS
Ca
Mg
Na
K
CI
SO^
A1K. as
CaCO}
P04
F
R
NH.-N
4
j
1 *5
;
z 1
O
1 |
T0C
COD
1977:
20/8
Before
Inj.
>8,500
6.85
169
49,300
936
2,100
14,700
475
26,890
3,830
608
24/8
12:40
1
2
53,000
6.65
209
49,574
950
2,070
14,800
340
25,06t
2.03C
576
2.66
<0.01
0.14
9.9
25/8
o
CM
24
83
32,000
6.9
227
4,400
0.057
0.16
13.2
26/8
OA : 10
40
132
13,300
7.3
203
10,600
1 B0
200
2 ,560
78
4.91C
8)0
547
< 0.1
<0.1
16.9
28/8
10:00
94
254
9,000
7.9
205
6,520
150
130
1,800
42
3,0CC
400
456
30/8
13:40
145
308
7,aoo
7.7
246A
138
39
2,75:
381
587
3L/8
15:10
171
407
8,500
7.6
21 a
6,590
297
184
2,029
33,5
3,439
35*
410
2/9
11:00
216
555
7,700
7.6
226
6,000
275
174
1,780
25
3,124
384
370
0.65
0.34
0.373
L6.G
3/10
10:00
957
2,430
12,000
7.2
256
11,400
642
435
2,925
40
6,483
693
288
18/10
11:00
1319
3,200
LJ , 700
7.5
267
9. 347
543
336
2,362
31
5,294
596
279
4.15
0.013
0.087
11.2
J1.6
18/11
2062
4,510
8,000
7.5
301
7.040
331
195
1.880
43
3,940
447
307
-------
TABLE 4E
General Chemical Analysis—Well P3
Total
Elapsed
Tine
(hrs)
Cujnul.
Inj
Volume
*3
Con-
duc-
tlvIty
MS / cm
Dis-
solved
Oxygen
mg/l
Concentrations, mg/l
Date
Time
PH
Sample
No.
TDS
Ca
Hg
Na
K
CI
S04
Alk. as
CaC03
P04
F
B
JH, -N
4
no2-n
NO^-N
TOC
COD
1977:
20/8
Before 1
nj.
30,000
6.95
168
44 ,000
669
1,520
12,900
480
22,700
2.88C
655
3.0
24/8
12:40
1.0
2
>1,000
6.6
211
45,200
801
1,940
14,100
475
24,000
3,640
621
3. 5
<0.01
0.0075
9.6
25/8
00:30
12.5
37
31,000
7.0
183
29,500
770
700
6,090
168
10,900
2,190
553
34
25/8
07:30
19.5
62
12,000
7.15
184
15,300
240
350
3,500
91
7,700
1,2 70
530
25/8
12:30
24.5
83
L6.000
7. 3
185
12,600
260
380
3,160
60
5,720
530
467
1.0
0.11
0.036
17
26/8
00:45
37
116
14,000
7.8
186
9,660
420
230
2,500
75
6,000
80C
490
31/8
15:30
171
407
7,700
7.7
187
5,070
80
70
1,350
30
2,730
400
460
0.013
0.007
24/10
1461
3,440
6,200
7.25
271
8,160
339
346
2,150
29
4,740
447
141
12.1
<0.01
0.08 .
10.7
.8.8
18/11
2062
4,510
5,500
7.6
302
6,850
308
190
1,280
40
4,520
336
288
1.1
16.7
'
-------
TABLE 4F
General Chemical Analysis—Well P4
Period 20 Aug. 1977 to 18 Nov. 1977, Prior to Operation of Activated-Carbon Treattn. in the Reclamation Plant
Date
Time
Total
Elapsed
Ti me
(hrs)
Curaul.
In J.
Volume
m3
Con-
due-
tlvlty
MS/cm
pH
Dis-
solved
Oxygen
mg/l
Sample
No.
ConcentraLIons
. rag/1
TDS
Ca
Mg
Na
K
CI
S04
A1 k. as
CaC03
P04
F
B
NH. -N
4
N02-N
i°3-N
TOC
COD
20/8/77
Prior to Inj.
37,000
7.4
<0.5
167
35,700
1,580
1,520
9,300
246
20,900
1,910
336
<0.2
0.2
2.7
24/a
12:30
0.5
3
42,000
6.8
<0.5
212
28,700
1, 700
1,250
7,500
142
16,300
1,60
336
<0.2
2.30
1.92
<0.01
:0 .001
4.4
24/8
14:15
2.25
9
34,000
6.85
<0.5
171
29,600
1,990
930
5,320
75
13,900
1,260
296
0.3
1.67
24/8
18:10
6.1
17
27,000
7.0
<0.5
172
26,200
1,670
860
5,240
58
13,100
1,100
274
<0.2
1.9
0.006
0.024
5.1
24/8
23:05
11
34
23,500
7.9
< 0.5
173
12,300
940
510
3,750
40
8,730
810
308
< 0.2
1 .40
1.9
<0.01
<0.001
24/8
23:55
12
37
13,000
7.5
< 0.5
174
13,600
1,140
410
2 ,830
37
7,640
820
331
<0.2
1 .45
7.6
25/8
00:55
13
39
11,000
7.4
<0.5
177
13,500
690
500
2,950
34
6,550
640
331
0.1
0.4
I .05
0.056
0.16
9.1
25/8
02:30
14.5
42
12,000
7.35
<0.5
176
12,200
620
370
2,880
41
6,000
560
331
0. 1
1.30
1.0
25/8
04: 20
16. 3
49
8,000
7.6
<0.5
178
8,660
330
330
2,160
21 .5
5,190
420
336
0.4
0.24
25/8
11:20
23. 3
80
7,000
7.6
<0.5
175
3,750
170
90
1,070
21.5
1,640
190
342
0.4
0.625
0.124
0. 35
10.4
26/8
04 :00
40
133
3,800
7.8
< 0.5
179
1,980
80
24
570
6.2
7 30
105
365
1. 1
0.025
0.31
0.07
25 J.
26/8
10:15
46
163
2,900
7.8
<0.5
180
1,460
50
17
500
4.6
600
146
35 3
1.2
1.45
26/8
13:39
49
179
2,600
7.9
< 0.5
181
1,620
70
14. L
450
4.2
530
96
348
1.0
2.3
0.90
0.85
18 A
27/8
10:00
70
210
2,500
8.1
< 0.5
182
1,500
45
15. 1
4 70
4.8
545
130
422
0.9
2.1
1.75
0.036
0.001
28/8
09:40
94
253
2,500
7.9
<0.5
206
1,560
27
14.1
440
4.5
491
100
342
0.8
0.98
0.65
30/8
13:00
145
308
2,000
7.8
<0.5
219
1,300
13
9. 1
430
4.3
491
129
353
0.7
3.3
1.00
0.4 '
0.038
0.085
17 3
31/8
14 :25
170
407
1,800
7.65
<0.5
220
1,120
14
9.2
328
3.4
328
124
274
0.9
0.8
0.004
0.046
4/9
10:00
262
690
1,450
7.65
<0.5
221
1,040
50
30.2
275
8.2
328
124
331
0.7
0.92
9.1
0.017
1.723
15 JO
8/9
10: 30
356
J ,060
1,400
7.15
0.7
243
080
53
27.4
222
11.6
300
76
262
0. 7
1.9
13.8
0.027
1.653
18.7
12/9
12:00
456
1,440
1,500
7.8
0.8
247
830
57
3L
203
13.6
294
81
291
1.1
2.9
18.6
0.020
0.92
21 9
15/9
10:00
526
1,580
1,600
7.2
0.5
249
780
48
24.4
183
12.5
273
95
194
0.9
3.5
0.81
17.8
0.045
0.28
21/9
10:45
670
2,070
1,500
7.4
0.8
252
860
47
19.6
189
13.4
328
107
200
20.8
15 0
3/10
10:45
957
2,4 30
900
7.75
0.5
255
16.4
13 J
12/10
10: 30
1174
2,860
1,200
6.9
0.5
264
685
54
16.8
147
10.4
216
82
203
1 .4
2.8
0.6
23.8
0.01
<0.1
18/10
11: 30
1320
3, 160
1,500
7.85
266
840
60
22.2
192
11.5
313
65
269
1.2
2.3
25.5
0.01
<0.1
14 O
14.0
24/10
10:30
1463
3,440
1,400
7.5
1.25
274
830
64
24
180
16
269
99
287
0.6
2.3
29.5
<0.01
<0.01
14 2
12.4
2/11
10:45
1679
3,860
1,420
7.45
0. 75
276
870
63
23
180
15.8
280
95
285
0.9
2.8
31.6
10.7
19.6
7/11
10: 0C
1822
4,050
0.2*
279
12.8
8/11
08: 5(
1845
4,100
<0.1*
285
14.0
9/11
08:1!
1868
4,140
1,400
7.3
0.8,0.3*
287
810
59
21
150
16.f
265
io;
249
0.9
2.9
30.8
<0.01
<0.05
26 j6
8.4
10/11
07:2!
1892
4,190
<0.1*
292
8.4
11/11
07: 5(
1916
4,240
295
18/11
J 0:00
2062
4,520
1,550
7.5
0.9
298
900
"1
21
210
13. i
320
87
255
0.8
3.2
0. 76
32.5
<0.01
<0.05
19.6
14.
Analysis by lodoraetric method, otherwise with D.O. electrode.
TABLE 4F cont.
-------
TABLE 4F cont.
Period Following 13 December 1977, After Beginning Injection with
Fully Treated Reclaimed Water, Including Activated-Carbon Treatment
Total
Elapsed
Time
(hrs)
Cumul.
Inj.
Volume
m3
Con-
duc-
tivity
WS/cm
Dis-
solved
Oxygen
mg/1
Sample
No.
Concentrations, mg/1
Dace
Time
pH
TDS
Ca
Mg
Na
K
CI
SO.
4
:aco3
P04
F
B
NH^-N
COD
1977:
13/12
10:20
0.5
0
2,160
7.3
310
L.110
38.8
28.8
314
13.4
412
95.3
263
0.85
2.9
34
14/12
1978:
6/1
08:50
23
46
7.2
311
890
S9.6
22.4
220
12.4
314
92.5
264
0.85
2.9
33
09:15
575
980
1,600
6.3
0.2
336
740
S3.2
16.0
202
12.2
266
80.5
173
0.4
7.7
9/1
11:30
650
1,101
6.3
0.2
338
730
f>2.0
15.4
197
11.2
262
77.3
169
0.4
3.0
30
3/2
13:15
1247
2,050
0.2
348
4.6
9/2
11:15
1389
2,280
1,880
7.2
0.2
351
830
86.6
16.8
200
15.5
275
109
212
21
1.9
16/2
1557
2,540
1,780
7.2
0.4
353
790
B2.4
15.8
194
13.7
258
111
191
18
25.6
22/2
1703
2,770
7.3
0.4
359
800
35.4
15.8
195
14.2
248
120
197
17
6.5
1/3
10:15
1868
3,020
1,860
7.0
0.7
360
195
13.4
256
124
188
1.2
16.9
-------
General
—Well S3-Lower
Toi a 1
KliijijJud
I I mi:
(lira)
(!i trim 1 .
Con-
din:-
livlty
ItS/cta
J)Ih-
KI>1 Vl!l
oxygm
mi;/1
Conceit t rn t Ions
. ui«/l
l)/i u
T1 me
Inj .
Vti 1 umu
.n'»
s.irapl e
No.
TOS
C;i
mr
Nil
K
CI
S,)4
A Ik. 'iM
CiiCO-
''°4
K
B
NH.-N
4
*0 -N
w3-n
.TOC
COD
I 9? 7:
2 7/4
Hl-Iuiu 1
n|.
71.100
6.8
127
44 ,900
5 70
1 ,790
1 J,800
557
23,2oo
3,350
654
0. 1
20/8
"
M
48,000
/.6
1 76
41,800
492
1,600
12,600
495
21,700
2,990
606
4.9
24/8
1A : SO
3
10
45,000
6.y
1 HB
16,900
8 70
1,570
7,98*)
3 30
19,700
2,24 5
4 79
<0.2
4 . 10
35
2^/ti
OH 50
21
6 7
30.000
7.6
ias
"J 1,400
2, 1 10
1 ,060
6,030
113
17.500
1,420
35 3
<0.2
2.74
!). 010
1.009
14.3
25/8
10:25
22
76
27,000
6 . 8
190
28.900
1. 580
1.080
6,140
112
15,300
J, 580
36 5
0. 1
2S/H
M:h
2?
Hh
21,000
7.0
191
24, J0/>
],«50
890
5. 120
110
12,600
1,310
36 5
<0. 1
2.36
0,021
).13
9.9
26/H
07:45
44
150
15,000
7.1
192
10,500
270
270
2,550
70
5,460
600
410
0.3
26/8
12 : 30
h H. 5
1 70
10,900
7.3
I M 3
8,880
2 30
220
2,200
13. H
3,820
535
39 3
<0.2
1 .!&
0.235
[>. 1 I
13.0
28/8
10:00
y4
250
fl, 100
7 . 5
222
4,600
127
95.5
1.500
22. 7
2,320
301
376
0.5
* j /a
16:00
172
400
7,200
7.6
223
5, 3(10
130
1 36
1 .660
35. 7
2, 700
39 3
36 5
1 .0
0.86
ll. U
3.047
25.1
4/y
1 1 :40
2 6 J
690
3,200
B. 2
224
2, J00
5.3
40.2
750
12.6
1 ,040
225
353
0.7
B/9
10:45
'358
l ,060
Z.BOO
7.8
245
47
44
300
10.7
98'J
1 12
296
1 .0
0.42
0.16
2.30
15/y
11:13
52 7
1 ,590
3,200
7. 7
250
J .950
44
36.9
666
1 1 . 1
90!
9 1
302
0.6
0. 72
0.042
0. 178
21/y
10:50
667
2, IhO
7.6
25 J
1 , 380
49
40.6
454
13. 1
573
99
217
0.8
7. 1 7
i d
957
2,4 JO
1 , 800
8.0
25 7
1 ,100
24.1
22.7
34 7
11.2
443
108
199
0.4
6.7
0.032
0.13
12/ 10
'
1 174
2 , Hhfl
1 ,500
7.6
26)
87
25
15.2
275
7.4
371
6 1
160
0.5
6. 1
<0.01
<0.1
18/10
I 319
.3, 160
3, BOO
fl.O
260
2.390
9 3
81
650
I ft
I , 180
L 88
259
I .4
9.4
0.012
<0. 1.
U .0
16.4
2/i / 10
1463
J.450
2. BOO
7.9
272
J ,960
87
78
505
16
880
200
273
1 .9
13.6
0.01
0.051
18.2
15.6
2/11
lb 79
1,860
J, 200
7. 7
2 78
1 14
90
700
21
I ,210
209
300
2.1
14. 1
9.7
1«.4
9/11
1H6B
4, 140
J ,750
7 .y
289
1 , 240
58
44
300
20.4
488
126
290
0.7
18.0
IB. 1
27.6
18/11
2062
4.520
3,250
B.O
29b
2, 340
116
87
650
27
1 , 1 70
BB
27 7
0,9
17.4
-------
TABLE 4H
General Chemical Analysis—Wells I2-Upper, S3-Upper, and Mi-Lower
Total
Elapset
Time
(hrs)
Curaul.
Inj.
Volume
m-*
Con-
duc-
tivity
US/cm
Dis-
solved
Oxygen
mg/l
Concentrations
mg/1
Dace Time
pH
Sample
No.
TDS
Ca
Mg
Na
K
CI
S°4
A lk. as
CaC03
P0«
F
B
NH.-N
4
jo2-n
io3-n
TOC
COD
12 upper
Before
Inject.
6.1
29 Apr. 77
"
"
8.1
140
8,570
50
90
2,340
110
3,770
860
606
1.4
29 July 77
360
L2.90O
8.0
141
6, 730
110
100
2,190
80
3,500
750
595
3.5
8 Sept. 77
1,460
8.0
244
10,263
234
195
3,200
102
5,598
780
228
23.8
24 Oct. 77
8.6
270
1,731
37
45
545
12.6
756
16:
222
S3 upper
27 Apr. 77
before ^
nject.
L7,300
7.6
126
9, 260
40
170
2,820
92
4,642
1,125
64 8
0.2
(7.4)
8 Sept. 77
360
7.A
241
10,735
138
314
3,188
120
5,720
895
570
1.7
24 Oct. 77
1,460
7.6
273
8,811
122
294
3,125
83
4,130
719
534
2.50
ML lower
3 Sept. 76
Before I
nject.
!4,400
7.7
10
L8.224
1,160
650
4,200
83
9, 320
735
209
<0.1
4 Sept. 77
260
7.45
225
17,725
1,220
70O
4,700
74
9,910
944
273
0.45
12 Oct. 77
1,170
6.7
261
19.057
1,572
888
4,370
46
11.000
991
248
0.60
18 Nov. 77
2,060
7.2
297
12,937
810
500
3,300
52
7,290
751
364
0.59
-------
Mineral Quality and Fractional Breakthrough
A decrease in the concentrations of the major ions, total dissolved solids,
and conductivity was observed at all of the observation wells after injection
began. This decrease was interpreted as evidence of the arrival of water of
injection origin. The fraction of water of injection origin in a given sample
was calculated as
f^ = fraction of water of injection origin at well i and time t
K. - K.
= (1)
K. - K.
1,0 1W
where K is the conductivity in msiemens/cm and the subscripts have the follow-
ing meaning:
i,o = formation groundwater at well i and time 0 ,
i,t = groundwater at well i and time t ,
iw = injection water, average for the period August to November 1977
= 1.45 mS/cm.
The conductivity was used as a surrogate for a conservative tracer such as
chloride, because the conductivity was measured more frequently than samples
were taken for chemical analysis. The correlation coefficient between con-
ductivity and chloride concentration is r = 0.967 for 17 paired values at
Well P4, during the breakthrough period. The regression equation is
CC1 = -194 + 0.461K (2)
where K is the conductivity in usiemens/cm and is the concentration
of chloride in milligrams per liter. Similarly, the relation between TDS and
conductivity is
CTDS = -131 + 0.86K (3)
where C^DS is the total dissolved solids concentration in milligrams per
liter, and r = 0.951 for 14 paired values.
The conductivity response is shown in Figure 11 for three observation
wells: P4, PI, and S3. The response curves show a broad, s-shaped form when
plotted logarithmically as in Figure 11, in contrast to the sharp edge that
would be expected if the flow were ideal plug or piston flow. This is indica-
tive of a wide spread of travel times between the injection well and a particu-
lar observation well. Possible reasons for this behavior are: hydromechanic
39
-------
INJECTION WATER OBSERVATION WELLS
4^
O
Mean ± Std. Dev.
o
A
P 50
©
©
10 20
50 100 200 500 1000 2000
TIME, hours
Figure 11. Conductance response curves for well samples versus time
-------
dispersion; aquifer heterogeneity, particularly dead spaces of low permeabil-
ity; and formation of a current of light fresh water that passes over a "wedge"
of the denser formation water, only gradually displacing it. The interpreta-
tion of the conductivity response curves is further complicated by irregulari-
ties in injection rate during the first hours of operation. Nonetheless, it
is clear that the Well P4 responded most rapidly of the observation wells, as
is consistent with the information from drillers' logs and drawdown testing.
Only at Well P4 was a smooth, monotonic approach observed all the way
into the range of conductivity values characteristic of the injection water.
At the other observation wells, PI, P2, P3, and S3, large fluctuations in con-
ductivity were observed after the midpoint of the breakthrough curve. Complete
breakthrough, in the sense that conductivity measurements fell within the
confidence limits for the injection water, occurred only at P4.
At Ml, 160 meters (500 feet) distant from 12 in the direction of E2,
there was no evidence of the arrival of fresh injection water during the first
1000 hours. The salinity of the last sample, taken after 2000 hours, was
approximately one-third lower than that of the formation water, perhaps indi-
cating influence from prolonged injection. This will be pursued further in
future work.
The fractional breakthrough values calculated from conductivity data are
summarized in Table 5. The breakthrough curve for injected water at Well P4
is shown in Figure 12.
TABLE 5
Approximate Time Required for Breakthrough of Injection Water
Percent of
Time Required, hours
Water of
Well
Injection Origin
PI
P2
P3
P4
S3
Ml
50
35
30
18
11
30
*
90
500 (?)
200(?)
200 (?)
30
150
*
95
*
A
*
40
-500
*
99
*
*
*
100
*
*
*
Not reached within
2000 hours.
^The mean and standard deviations for the injection water over the period from
24 August to 18 November 1977 was 1530 + 280 yS/cm for 20 determinations.
41
-------
The relative proportions of cations changed dramatically during and
shortly after the freshwater breakthrough, as is evident in Figure 13.
After the midpoint of the conductivity response curve at 11 hours, the ratio
of [Na~*"] to ([Ca^+] + [Mg^+]) rose from approximately 1.5, which was charac-
teristic of the formation water, and reached a peak value of approximately 10
to 12 at a time of 150 hours. Thereafter the ratio of sodium to calcium plus
magnesium declined, after 500 hours reaching nearly the original value of 1.5.
The corresponding ratio for the injection water was 1.56 + 0.33 for the entire
operation period.
The strong displacement in ion ratios suggests that a process such as ion
exchange, precipitation, or dissolution may have occurred. Such a phenomenon
might be masked by the mixture of fresh and brackish water during the early
stages of breakthrough, and become apparent only after breakthrough was essen-
tially complete.
The sodium, calcium, and magnesium data are plotted in terms of the so-
called "Sodium Adsorption Ratio" (SAR) in Figure 14. The SAR decreases from
a value of 25, characteristic of the injection water, and reaches a value of
approximately 5 after 500 hours, which is within the range of values for the
injection water, 4.87 ± 0.58. Between 50 and 200 hours, there is a sharp
positive deviation from the otherwise smoothly declining curve. This peak
corresponds to the time between completion of freshwater breakthrough and the
onset of ammonia breakthrough, which is discussed in a later section. In view
of the relation of the SAR to ion exchange equilibrium, this phenomenon appears
related to the exchange of ammonium, calcium and magnesium ions for sodium.
The concentrations of individual cations are plotted on a milliequivalent
basis as a function of elapsed injection time in Figure 15. During the early
stages of freshwater breakthrough, the concentrations of the three major cat-
ions decreased from the high values characteristic of the formation groundwater
and approached the values typical of the injection water as a lower limit.
The conductivity closely paralleled the concentrations of the major cation,
sodium. After approximately 50 hours, the concentrations of both calcium and
magnesium dipped below the range characteristic of the injection water, and
rose again into the injection water range only after 200 hours. The minima
for Ca and Mg occurred at approximately 150 hours, the same time at which the
SAR and the ratio of sodium to calcium plus magnesium reached their peaks.
The maximum deficits of calcium and magnesium were approximately 4 meq/1 and
42
-------
1.0
-J
<
~ y 0.5 r
O
h-
<
cr
LL.
x
o
3
O
tr
<
UJ
K
m
F it'/jre 12.
10 20 50 100 200
TIME, hours
Breakthrough of injected water at P4
500 1000
INJECTION
WATER ^
qOLL-C
200
500 1000
TIME, hours
Figure 13. Relative concentration of major cations
43
-------
25
P4
SAR =
0.5 | [ca2+] +[Mg2+] |°'5
INJECTION WATER, T± S
CO
1000 2000
20
100
200
500
50
TIME, hours
Figure 14. Sodium adsorption ratio
-------
cr
o
2:
O
£
q:
i—
2!
LlI
O
o
o
200
J00 -
-Ck_
WELL P4
0 Na
A Ca
O Mg
INJECTION WATER
Mean ± Std. Dev.
50
20
i 0
0.5
A
~
Na
h Ca
Mg,
00
o
o
o
A
o o o
A
-0-0 =OOC1=
o Q
"tr
_A.
A
u „ A
~ D ~
XL
—A
AAa
-a—^
¦~cfq5
TJ
$
!
10 20
50 100 200
500 1000 2000
TIME, hours
Figure 15. Concentrations of major cations at Well P4 as a function
of time after injection initiated
45
-------
1 meq/1, respectively. During the same period between 50 and 200 hours, the
steady decline in sodium concentration terminated temporarily at a constant
level of approximately 20 meq/l3 i.e., 12 meq/1 above the injection water
average.
The major anions behaved in a more conventional manner. The sulfate con-
centration at PA declined smoothly, reaching the injection water range within
50 hours. The chloride concentration at P4 also declined smoothly without
passing through a minimum, but there was a plateau significantly above the
injection water range during the period from 50 to 150 hours. During that
time the excess over the mean injection water concentration amounted to
6 meq/1 CI. There was no significant difference in alkalinity between the
injection water and P4.
In summary, the relationships among major ions followed the pattern to be
expected when brackish water is displaced by injected fresh water, except for
the anomalous behavior at the end of and shortly after passage of the fresh
water breakthrough front. During that time there was an excess of 12 meq/1
i o j 2+
Na and 6 meq/1 Cl~, balanced by deficits of 4 meq/1 Ca , 1 meq/1 Mg , and
2 meq/1 NH*, comparing Observation Well P4 to the injection water. These
apparent discrepancies may be explained by (1) ion exchange of calcium,
magnesium, and ammonium for sodium, and (2) gradual displacement of sodium
and chloride ions from portions of the aquifer that have very low permeability.
Trace Organic Substances
Characterization of individual trace organic substances was achieved by
three methods based on gas chromatographic analysis of concentrates: (1) the
volatile organic analysis (VOA) procedure of Bellar and Lichtenberg for
components such as trihalomethanes, (2) the closed-loop stripping (CLSA) pro-
cedure of Grob for determination of moderately volatile substances such as
benzene; toluene; xylenes, mono-, di-, and trichlorinated benzene isomers;
and naphthalene, and (3) solvent extract analyses (SEA) in which samples were
concentrated by hexane extraction prior to gas chromatographic analysis for
less volatile substances such as pesticides, polynuclear aromatic hydrocar-
bons, and polychlorinated biphenyls. The cone en tr'at ions of substances re-
covered by the latter solvent extraction analysis (SEA) from injection and
well-water samples were in the range of background concentrations (low ng/1
level) and hence the results are not reported here.
46
-------
The analytical techniques used extensively in the current project year can
be described briefly as follows:
Volatiles_(VOA): The following modified process will be used in the second-
year study. 50-mI samples will be extracted with 1 ml of pentane. The extracts
will be analyzed on a packed column (10% W/W squalane on 80/100 mesh Chromosorb
W/AW) using an electron capture detector. The procedure has been outlined by
J. E. Henderson et al. in "Identification and Analysis of Organic Pollutants in
Water," L. H. Keith (ed.), Ann Arbor, Michigan, Ann Arbor Science Publishers,
Inc. (1976), p. 105. This procedure which is now in use in many water quality
laboratories requires the same sample size and method of collection as the
previous procedure.
Closed-Loog_Strigging_Anal^ses_^CLSA): 200 to 500 ml of a sample (usually
taken from a 1-liter sampleT will be extracted by air recirculation. The purg-
able substances are trapped by a 1-mg activated-carbon filter, from which they
are eluted with carbon disulfide. The extracts obtained in this way are chro-
matographed on a 25m Ucon HB 5100 glass capillary column. For quantitation an
internal standard is added. The extracts are investigated as needed by GC/MS.
The closed-loop stripping procedure has been used for the analysis of a variety
of water samples for more than one year. It is specially effective for the
analysis of clean waters. A detailed description has been given by K. Grob
and F. Zuercher in Journal of Chromatography, 117, 285 (1976).
The following types of SEA characterization are used in our laboratory
on a routine basis and are used in this project occasionally:
Hexane-Extraction Analysis_(HEA): The portion of the sample purged by
the CLSA procedure is combined with the remainder of the 1-liter sample and
extracted with hexane (2 times with 15 ml). The pH is in the range of 6 to 7.
The extract is cleaned on a microflorisil column and concentrated to 0.5 ml.
The concentrated extract is then analyzed by gas chromatography using a 20m
SE 54 glass capillary column. An electron capture detector will be used for
the analysis of halogenated compounds and a flame ionization detector for the
detection of hydrocarbons.
Acidic_Methylene Chloride Extraction (AMEA): This procedure will be used
only for detailed characterizations. After the neutral hexane extraction, the
1-liter sample is acidified (pH 2) and extracted two times with methylene
chloride. The extract is concentrated and separated on a reversed phase
column by HPLC. The various fractions are investigated by solid-probe mass
spectrometry and/or after derivatization by GC/MS. This method can be used
to analyze polar chlorination products.
The results of CLSA analysis of samples of the injection water and Ob-
servation Well P4 are summarized in Tables 6 and 7.
The CLSA characterization shows that a few compounds, notably chloro-
benzene, three dichlorobenzene isomers, trichlorobenzene, naphthalene and
several alkylated naphthalenes, styrene and heptaldehyde, dominate in the in-
jection water (Table 6A). The concentrations of the above-mentioned compounds
47
-------
TABLE 6A
CLSA Organic Characterization of Injection Water
During Period 12 September through 18 November 19 77 Prior to Activated-Carbon Treatment
Total
Elapsec
Time
(hrs)
Cumul.
Inj.
Volume
ni^
Concentrations
* ng/l
DaCe
Chloro-
benzene
1,3-di-
chloro-
benzene
1,4-di-
chloro-
benzene
1, 2-di-
chloro-
benzene
1,2,4-
trichloro-
benzene
Naph Lha-
lene
2-methy 1
naphtha-
lene
1-metliyl
naphtha-
lene
Styrene
Unknown
y
Unknown
z
Hept-
aldehyde
Unknown
A
Unknown
B
12/9
456
1,440
34,000
920
960
2,000
690
2,200
<15
<15
15/9
526
1,580
12,500
1,300
980
2,231
551
470
-
-
5,000
1,150
<15
-
420
-
5/10
1005
2,570
614
89
110
621
172
72
104
36
190
-
-
-
-
-
12/10
1174
2,860
5,400
950
1,030
4 ,400
379
1,100
346
65
950
610
220
3,310
635
240
10/10
1318
3,160
1,700
310
270
1,600
<15
960
200
110
1,100
290
210
2,400
440
-
24/10
1463
3,440
750
1,200
860
1,700
260
6,500
540
230
1,100
400
390
1,700
750
270
2/11
1679
3,860
2,800
4,400
1,000 •
5,300
230
3,400
-
-
1,200
550
650
2,200
990
860
9/11
1847
4,140
10,500
180
140
950
<15
340
-
-
8 B0
350
100
1,800
120
-
18/11
2063
4,520
6,700
5 20
850
2,300
605
710
not able|
to quantiJ
y
J75
1,100
190
215
3,000
270
<15
*
An identifiable peak too small to be Interpreted
corresponding peak was riot discerned.
quantitatively Is
denoted as < (detection limit), e.g.
<15 ng/l. A (-) signifies
that the
-------
TABLE 6b
CLSA Organic Characterization of Injection Water
Period Following 13 December 1977 After Beginning of Activated-Carbon Treatment
-p-
VO
Total
Elapsed
Time ^
(hrs)
Cumul.
Inj.
Volume
ra3 0
Concentrations ,* ng/1
Date
Ethyl-
benzene
Chloro-
benzene
1,3-di-
chloro-
benzene
1,4-di-
chloro-
benzene
1,2-di-
chloro-
benzene
1,2,4-
trichloro-
benzene
Naphtha-
lene
2-me thyl
naph tha-
lene
1-rae thyl
naphtha-
lene
Styrene
Unknown
y
Hept-
aldehyde
^3/12-18/lf
0-120
0-20
45
5,710
60
40
215
<15
100
<15
<15
275
_
<15
19/12-23/12^
120-240
25-43
45
5,990
-
-
-
-
50
<15
<15
45
15
305
27/12-9/lf
330-650
48-89
• <15
1,880
15
<15
25
-
<15
-
-
-
-
-
26/1
1056
1, 380
-
110
<15
720
75
-
<15
-
-
<15
-
-
9/2
1389
1,770
15
750
<15
35
15
-
<15
-
-
75
<15
20
16/2
1557
1,960
<15
1,480
-
75
<15
-
<15
-
-
40
<15
-
16/2
1557
1,960
<15
1, 350
<15
60
<15
-
<15
-
-
40
<15
-
22/2
1703
2,130
<15
1,530
-
30
<15
-
<15
-
-
40
<15
-
1/3
1868
2,320
-
540
-
<15
-
-
30
-
-
<15
<15
-
An identifiable peak too small to be interpreted quantitatively is denoted as < (detection limit), e.g. < 15 ng/1. A^-ysignifies that the
corresponding peak was not discerned.
'Time and injection volume after beginning injection of reclaimed water that had received activated-carbon treatment.
^Composite of five grab samples.
aThis sample analyzed on older column which had a different response to styrene, unknown y, and heptaldehyde.
-------
TABLE 7A
CLSA Organic Characterization of Samples^ from Well P4
Period 24 August 1977 to 18 November, 1977,
Prior to Operation of Activated-Carbon Treatment in Reclamation Plant
Total
Elapsed
Time
(hrs)
Cumul.
Inj.
Volume
m3
*
Concentrations,
ng/1
Date Time
Chloro-
benzene
1,3-di-
chloro-
benzene
1,4-dl-
chloro-
benzene
1,2-dl-
chloro-
benzene
Naphtha-
lene
Styrene
Unknown
y
Unknown
z
Benzo-
nitrile
24/8 12:30
0
i
49
-
-
-
<15
24/8 18:10
6.1
17
85
-
<15
190
<15
24/8 23:55
12
37
390
<15
<15
220
350
25/8 11:20
23
80
99
<15
86
<15
100
-
-
-
-
26/8 13:40
49
179
480
-
-
-
240
<15
160
-
-
4/9 10:00
262
690
1,450
150
90
160
900
210
400
-
-
8/9 10:30
355
1,060
1,400
<15
<15
110
170
1,000
210
-
150
12/9 12:00
456
1,440
3,200
<15
<15
<15
500
880
500
-
<15
15/9 10:00
526
1,580
2,600
<15
<15
70
69
560
1,360
-
430
5/10
1005
2,570
3,000
59
86
220
54
324
<15
-
<15
12/10
1174
2,860
2,600
26
52
170
33
460
88
<15
30
18/10
1320
3,160
3,400
72
69
305
65
1,400
4 30
50
110
24/10
1463
3,440
3,200
110
110
440
70
2,700
490
90
180
2/11
1679
3,860
5,300
150
200
790
55
3,600
500
130
260
9/11
1847
4,140
3,200
85
85
490
100
2,200
400
60
170
18/11
2063
4,520
2,400
40
75
380
35
2,100
2 30
50
130
A
An Identifiable peak too small to be Interpreted quantitatively Is denotec
<15 ng/1. A (-) signifies that the corresponding peak was not discerned.
as < (detection limit), e.
g-
^All samples
were analyzed on UCON 20M
column.
-------
TABLE 7B
CLSA Organic Characterization of Samples from Well PA
Period Following 13 December 1977;
Full Treatment in the Reclamation Plant, including Activated Carbon
Total
Elapsed
Time
(hrs)
Cumul.
InJ.
Volume
m3
*
Concentrations, ng/1
Date
Ethyl-
benzene
Chloro-
benzene
1,3-di-
chloro-
benzene
1,4-di-
chloro-
benzene
1,2-di-
chloro-
benzene
1,2,4-
trichloro-
benzene
Naphtha-
lene
2-methyl
naphtha-
lene
1-methyl
naphtha-
lene
Sty-
0
rene"
Unknown
y#
13/12
0
0
55
1,650
20
40
180
_
50
_
_
155
1,130
14/12
23
37
55
1,420
35
45
220
40
85
65
60
190
900
16/12
71
140
60
1,700
60
30
260
<15
140
<15
<15
200
700
19/12
143
255
40
2,540
60
60
410
<15
120
-
-
210
250
21/12
190
345
50
1,330
35
40
230
25
20
-
-
95
250
23/12
240
389
50
1,320
35
55
220
<15
15
-
-
95
190
27/12
333
592
40
980
30
35
210
-
15
-
-
75
60
30/12
405
707
50
1,530
45
100
240
0
65
70
45
110
100
3/1
500
859
45
1, 390
40
40
250
<15
40
-
-
85
170
6/1
575
980
45
1,670
40
65
310
-
35
-
-
100
160
9/1
650
1,010
65
2,900
75
75
450
-
60
-
-
180
320
13/1
745
1,250
40
1,080
35
45
200
-
20
-
-
75
110
26/1
1,060
1,740
25
1,050
20
130
170
-
<15
-
-
120
55
9/2
1,390
2,280
40
1,470
30
75
230
-
<15
-
-
85
65
16/2
16/2 +
1,560
2,540
35
1,340
15
35
200
-
<15
-
-
90
70
1,560
2,540
30
970
35
45
180
-
<15
-
-
70
50
22/2
1,700
2,770
25
1,090
20
30
180
-
<15
-
-
75
60
1/3
1,870
3,020
20
870
30
30
180
-
-
-
-
50
30
l/3+
1,870
3,020
35
1,250
15
35
210
-
<15
-
-
60
75
An identifiable peak too sma-JLl to be interpreted quantitatively is denoted as < (detection limit), e.g. < 15 ng/1.
A (-) signifies that the corresponding peak was not discerned.
^All samples were analyzed on new UCON 50M column. Response factors for styrene and unknown "y" differ from previous
analyses with UCON 20M column (Table A-7A).
^Duplicate.
-------
were in the range of 500 to 10,000 ng/1 during the first three months of in-
jection (Table 6A). The concentrations of components determined by CLSA were
reduced by 90 percent or more when activated-carbon treatment was begun in
the reclamation plant (Table 6B) with the exception of chlorobenzene.
Among these compounds, chlorobenzene alone was present in concentrations con-
sistently above 1 yg/l during the period after 13 December 1978.
The concentrations of compounds identified by CLSA in samples of forma-
tion groundwater were generally near or below the detection limits. As the
injection water moved past Well P4 a general rise in the concentrations of
organic compounds did occur (Table 7A). Compounds such as chlorobenzene,
the dichlorobenzene isomers, styrene, and heptaldehyde rose from background
levels to concentrations approaching that of the injection water. This con-
centration rise began shortly after the midpoint of freshwater breakthrough,
i.e. 11 hours, in the case of chlorobenzene, but not until 200 to 300 hours
for styrene and heptaldehyde, and approximately 1000 hours for the dichloro-
benzene isomers. The alkylated naphthalenes and unknowns B and W, all present
in the injection water in concentrations of 100 to 1000 ng/1, had yet to ap-
pear at Well P4 after 2000 hours of operation. The behavior of naphthalene is
anomalous; its concentration rose to a broad peak well above 100 ng/1 in the
initial period and decreased to between 50 and 100 ng/1 after 500 to 2000 hours.
The "breakthrough" curves for some representative compounds at Well P4
are shown in Figure 16. The concentrations in samples taken during the first
ten hours of operation were for the most part less than the background level,
i.e. 50 ng/1. The concentration of chlorobenzene rose after 10 hours and ap-
proached a plateau during the period between 450 and 2000 hours of operation.
The logarithmic mean concentration from 9 chlorobenzene determinations during
that period, i.e. 12 September to 18 November 1977, is 3100 ng/1 with 95 per-
cent confidence limits on the mean of 2600 ng/1 to 3700 ng/1. Thus, the con-
centration of chlorobenzene at PA after breakthrough is not significantly
different than that in the injection water, for which the mean is 4,100 ng/1
and the 95 percent confidence limits are 1,500 to 12,000 ng/1. The dichloro-
benzene isomers did not appear consistently at P4 until after 1000 hours had
passed. Even after 2000 hours of operation, the concentration of dichloro-
benzene isomers was significantly below their respective concentrations in the
52
-------
COMPOUND
CONC.
CONC. IN
INJ. WATER
AT P4
LOG MEAN
95% C.L.
CHLOROBENZENE
o
4120
1480 TO 11500
STYRENE
~
1020
490 TO 2120
1,3-DICHLOROBENZ
A
630
255 TO 1550
1,4-DICHLOROBENZ
V
530
265 TO 1060
10,000
o _
5,000
2,000
cn 1,000
r- '
~/
500
200
v -
o
100
50
20
100 200
500 1000 2000
50
ELAPSED TIME, hr
Figure 16. Breakthrough curves for trace organic compounds at Well P4
53"
-------
injection water. Styrene exhibited still a different behavior. Its concen-
tration rose from the background level after 20 hours to greater than 2,000
ng/1 in the four samples taken after 24 October. These values are signifi-
cantly above the concentration of styrene in the injection water, for which the
95 percent confidence limits are 500 to 2,000 ng/1.
The form of the concentration response expected when a step change in
concentration is made in the input to an aquifer is shown schematically in
Figure 17. This concept, valid in principle for any reactor vessel, can be
adapted to the situation at an observation well after beginning continuous
injection of a water different in composition from that of the formation
groundwater. The concentration relative to the concentration Co in the injec-
tion water is plotted versus the elapsed time relative to the average travel
time from injection to observation point. The average travel time t can be
estimated from the concentration response of a conservative tracer at the
observation well. For ideal plug or piston flow without dispersion a sharp
wave front is expected. Dispersion acts to smear the sharp front, resulting
in an s-shaped wave with mean arrival time equal to t . Adsorption of a
contaminant causes a delay in the mean arrival time and, coupled with disper-
sion, a further flattening and spreading of the curve. Eventually the limit-
ing value of C/Co equals unity and is reached when the aquifer's adsorption
capacity is exhausted. If biodegradation is responsible for removal, the
concentration should at first rise as if only dispersion were operative, un-
til a concentration is reached that is sufficient to support growth. There-
after, the concentration might decline to a low value that is needed to support
growth. Assuming significant biodegradation, C/Co would not reach unity.
Other concentration responses are conceivable, for example if a compound is
produced during travel through the aquifer by biological or other processes.
The data suggest strongly that chlorobenzene is retained by adsorption
during passage through the aquifer. The time required for its concentration
at Well PA to reach one-half the concentration in the injection water is
300 hours, compared to a half time of only 11 hours for arrival of a conserva-
tive tracer. The smooth rise of chlorobenzene concentration at P4 to values
approximating those in the injection water supports the adsorption hypothesis.
It is also reasonable to assume that adsorption would be effective for removing
54
-------
1.0
ideal
Plug Flow
0
Dispersion
Adsorption
and Dispersion
J3iodegradation
and Dispersion"
0
TIME RELATIVE TO AVERAGE
TRAVEL TIME, t/t
Figure 17. Expected responses to a step change in concentration
-------
the more highly chlorinated aromatic substances such as di- and trichloro-
benzenes. These compounds are more strongly adsorbed and are less readily
biodegradable than chlorobenzene. The tendency to be very strongly adsorbed
would explain the incomplete breakthrough of dichlorobenzene isomers and the
total absence of trichlorobenzene observed at PA.
The broad concentration peak observed at PA for naphthalene between 10
and 500 hours (Table 7A and Figure . 18) supports the hypothesis that it is
removed by biodegradation, as well as by adsorption. The concentrations during
that period lie between 100 ng/1 and 500 ng/1. After 500 hours, the concen-
tration is consistently lower than 100 ng/1. The high values of naphthalene
concentration first appear at times corresponding to the latter half of the
injection water breakthrough front which also is consistent with the expecta-
tion for "dispersion and biodegradation" in Figure 17.
The concentration behavior of styrene is anomalous. Styrene may be pro-
duced by biological activity in the aquifer. Otherwise it is difficult to
explain the observation that its concentration at PA exceeds that in the injec-
tion water during the last quarter of the field experiment.
For substances such as chlorobenzene that show a complete breakthrough,
the retention capacity of the aquifer can be estimated from the concentration
response at an observation well. The total amount of compound i that
is removed is given by
(i = i
J (1 - £.) dVIW - / (1 - fIW) dV
IW
¦ (C°'i J (f™ - fi> dviw (4)
where = g of compound i removed; (C0) = average concentration of com-
pound i in the injection water; f = fractional breakthrough of compound i
at the observation well (dimensionless); V = volume of water injected; and
f is the fractional breakthrough of injected water at the observation well.
The specific retention capacity of the aquifer is given by
R.
r. = i
1 -J 3 (5)
e J (1 " V dvIW
aq 0
56
-------
INJECTED WATER
Ui
--0
*4*
CL
_J
U
$
5
X
(S>
ZD
o
a:
X
h-
<
UJ
en
QD
_J
<
I—
Si
(Z
Li_
— NAPHTHALENE
irCr
/
\
/
/
/
/
100 200
500 1000 2000
TIME, hours
Figure 18. Breakthrough of naphthalene at Well P4. The response suggests that adsorption, dispersion and
biodegradation play significant roles, with biodegradation predominating after 1000 hours
-------
where r. is the specific retention capacity, g of compound i removed per
m of aquifer; and £ is the effective porosity of the aquifer. The de-
nominator in Eq. (5) represents the total aquifer volume effectively permeated
by injected water. The specific retention capacity can be converted to a
weight basis if the bulk density of the aquifer material is known;
*
= i .. ..
1 aq
where
r. = r./p (6)
i l aq
r^ = specific aquifer retention capacity, g of component i removed/g
aquifer material;
p = average bulk density of aquifer material under field conditions,
a" g/m3.
The breakthrough curves for chlorobenzene and injected water are plotted
in Figure 19 in a manner suitable for estimating the value of the specific
retention capacity r . The value of R is calculated by graphically inte-
grating the area between the two breakthrough curves, according to Eq.(5).
The result is
R. = C x [(area above fTTT curve) - (area above chlorobenzene f-curve)]
i o IW
= 4.1 x (1627 - 43)
R. = 6.5 g chlorobenzene removed
i °
Assuming a porosity of e = 0.3 , the specific retention capacity is:
r^ = q_/0^3) y 43 ^ ^ mS chlorobenzene removed per m^ aquifer
6 3
Assuming a bulk density of p = 2 x 10 g/m ,
aq
&
r^ = 22 ng chlorobenzene removed per g aquifer material
The specific retention capacity is dependent on conditions such as the
type of aquifer material; the nature and concentration of the compound being
considered as well as other organic compounds present; and other physical and
chemical properties of the groundwater such as pH, surface tension and ionic
58
-------
Ui
VO
O
Z)
O
en
JZ
I—
<
Ixl
cr
CQ
o
I—
o
<
cr
u_
1.0
0.8
0.6
0.4
02
7^
i I i—i—i—r~i—i—r~r
i i i 11 1 r i i | i i i i | ) i i i |—i i—Piiii—r
/
/
°/
/ O
Q
k
°/
/
°/
i i i 1 i i i i 1 i i i i
injection Water
—° Chlorobenzene
i i i i I i i i i I i i i i i i i i i i i i i i i i i i
0 1000 2000 3000 4000
CUMULATIVE INJECTION VOLUME, m3
Figure 19. Estimation of the chlorobenzene removal capacity of the aquifer. The area between the
f curves for injected water and for chlorobenzene gives a value for the total amount
of chlorobenzene removed
-------
strength. Laboratory studies are being conducted to relate the field estimates
of specific retention capacity to adsorption equilibrium data.
There is considerable variability in the concentrations of individual
organic compounds determined by CLSA of injection water samples. The typical
range of values for an individual substance in the nine samples analyzed
stretches over one to two orders of magnitude. It is felt that the concen-
tration variability is a measure of real fluctuations in injection water
quality. This fluctuation is greatly attenuated as the water moves through
the ground. For example, the coefficient of variation of the chlorobenzene
concentrations for samples from Well P4 after complete breakthrough is only
1.25 compared to 3.80 for the injection water over the same period. The
spread factor (SF), which is calculated as the antiolog of the ratio of the
logarithmic standard deviation to the geometric mean, is a convenient meas-
ure of the degree of variability. If the concentrations are distributed
logarithmically, then 68 percent of the values lie between the limits given
by log 1(log x) x SF and [log "*"(log x)]/SF , where log x is the logarith-
mic mean.
The distributions of observed concentrations of some individual organic
compounds are shown graphically in Figure 20. The data in general are
well fitted by straight lines on logarithmic probability paper, indicating
that they conform t^o a log-normal rather than a normal distribution. This
is to be expected when dealing with values showing a large variance relative
to the mean. A comparison of the slopes of the lines drawn through the
chlorobenzene data for Well PA and the injection water shows very well that
passage through an aquifer over even a short distance and period of time,
i.e., in this case 8 meters and approximately 10 hours, suffices to dampen
out sizable concentration fluctuations. The spread of data is reduced by an
amount approximately proportional to the square of the ratio of the spread
factors, i.e. (3.8/1.25)^ = 9 .
The great attenuation of concentration variability can contribute sig-
nificantly to overall system reliability and is an important factor in
evaluating the feasibility of water reclamation incorporating direct re-
charge. If confirmed in further tests and with additional organic compounds,
it could mean that analysis of samples after only a short distance and time
60
-------
CTn
M
® CHLOROBENZENE
^ I, 3-DICHL0R0BENZENE
O I, 2, 4-TRICHL0R0BENZENE
~ NAPHTHALENE
INJECTION
WATER
o CHLOROBENZENE, OBSERV. WELL P4
t ^ Z)
jpz
CL < 1JJ
GEOMETRIC
STD. DEV
i i i i i 11
50 100 500 1,000 5,00010,000
CONCENTRATION (ng/£)
5xl04
Figure 20. Probability distribution for concentrations of trace organic substances in injection
water and well samples
-------
of travel in the ground would be sufficient to insure a desired level of reli-
ability was being met. Furthermore, this finding implies that continuous,
real-time monitoring of trace organic contaminants in the injection water or
in reclamation plant effluents is unnecessary. If short-term fluctuations
are dampened out effectively in the overall system, a monitoring system
based on careful, quantitative characterization of organic contaminants in
daily or even weekly composite samples could be more meaningful as well as
less costly and troublesome than a continuous monitoring system.
The qualitative similarities and differences in the CLSA complexion of
trace organic substances in samples of injection water and groundwater are
evident in Figure 21. Figure 21A . (top) shows the typical range of sub-
stances found in the reclaimed water used for injection, compared to internal
standards of 2000 ng/1. The groundwater at Observation Well P4 500 hours after
the start of injection (Figure 21C) . contains many of the same substances at
approximately the same concentration as in the injection water. The substances
are identified as follows:
1.
Toluene/tetrachloroethylene
9.
1,3-dichlorobenzene
2.
Ethylbenzene
10.
1,4-dichlorobenzene
3.
p-xylene
11.
1,2-dichlorobenzene
4.
m-xylene
12.
Benzonitrile
5.
Chlorobenzene with trace of
13.
1,2,4-trichlorobenzene
o-xylene
6. Heptaldehyde 14. Naphthalene
7. Styrene 15. Cl-C^ (Internal Standard)
8. CICg (Internal Standard) 16. Cl-C^g (Internal Standard)
This spectrum of substances is virtually absent from the formation groundwater
(Figure 21B), where identifiable substances were present in concentrations
substantially lower than the internal standard of 200 ng/1.
The compounds detected by VOA show evidence of early breakthrough (Tables
8 and 9). These compounds include the trihalomethane group, tri- and tetra-
chloroethylene, and trichloroethane. The concentrations of the VOA components
for Well P4 for the early period of injection (Table 9) were substantially
lower than in the injection water (Table 8A). During the first 50 hours of
injection, corresponding to the period of freshwater breakthrough, the mean
concentrations of chloroform (CHCl^), trichloroethane (Cl^CCH^), trichloro-
ethylene (C^C^HCl), chlorodibromomethane (CHCIB^), and bromoform (CHBr^)
62
-------
12 9/15/77
2000 NG/L I S.
16
15 II o
I 'f1?..? I"?i 1.
P4 INITIAL
B 200 NG/L IS
16 I
J>_A . iA
15
14
P4 9/15/77
1000 NG/L I S.
15
16
* l*i
14
12
i6,bu
-90
-80
-70
-60
-50
-40
p30
r 20
-10
-0
u
-60 ^
-50 &
-40 _j
-30
-20
-30 p
Ll
-^L
50
40
30
20 10
-10
-0
•60
¦50
-40
-30
-20
-10
o
IxJ
Q
ZD
L-0
TIME (rnin)
170°
150°
130°
110°
90°
70°
*50°
TEMP (°C)
Figure 21. Comparison of gas chromatographic analyses of injection
water and groundwater at Well PA before and after injection.
(A) Injection water; (B) Well P4 prior to injection;
(C) Well P4 after 500 hours of injection.
The concentrations are calculated from the peak areas
relative to those of the Internal Standards, peaks 8, 15
and 16
63
-------
TABLE 8A
VOA Organic Characterization of Injection Water
Period 24 August to 18 November 1977 Prior to Activated-Carbon Treatment
c*
-c-
Total
Elapsed
Time
(hrs)
Cumul.
Inj.
Volume
J
A
Concentrations, ug/1
Date
chci3
C CI.
4
ci3c ch3
ci2c=chci
CHCl^Br
ci2c=cci2
CHClBr2
CHBr3
24/8
8
27
2.7
ND
3.6
5.5
6.0
<0.1
2.5
3.0
25/8
28
91
12
ND
15
46
-
<0.1
40
31
26/8
52
180
2.4
ND
3.5
16
ND
<0.1
6.5
25
8/9
356
1,050
1.5
ND
1.7
1.7
0.7
2.7
1.3
-
12/9
356
1,440
3.9
ND
-
16.4
2.8
4.0
2.6
58.7
15/9
526
1,570
2.9
ND
12. 7
8.5
1.6
0.8
8.1
-
2/10
2,380
1.2
-
2.1
2.4
0.1
3.0
—
0.3
3/10
957
2,450
0.2
-
-
<0.1
-
0.2
-
-
18/10
1320
3,160
0.3
-
-
0.4
-
0.3
-
0.2
2/11
1679
3,860
7.1
0.1
12.8
20.8
0.7
9.0
-
0.2
9/11
1868
4,150
1.5
0.6
2.8
4.0
0.1
2.9
-
-
24/8-26/8
n = 3
Log. Mean
Spread Factor
4.3
2.4
ND
5.7
2.3
16
2.9
e
<0.1
8.6
4.0
13
3.6
8/9-18/11
n = 8
Log. Mean
Spread Factor
1.37
3.4
<0.1
0.82
1.0
2.35
7.5
0.29
5.0
1.58
3.8
<0.1
0. 2
Analyses of samples before 1 October 1977 by head space VOA method; thereafter by liquid-liquid extrac-
tion VOA. An Identifiable peak too small to be interpreted quantitatively is denoted as < (detection
limit), e.g. < 0.1 vig/1. A (-) signifies that the corresponding peak was not discernible. ND means
that the compound could not be detected with the method used because of peak overlap.
^Distribution too irregular to permit calculation of a mean value.
-------
TABLE 8B
VOA Characterization of Injection Water
After Beginning of Activated-Carbon Treatment 13 December, 1977
o->
On
Total
Elapsed
Time
(hra)
Cumul.
Inj.
Volume
J
*
Concentrations, yg/1
Date
chci3
c ci4
CljC CH3
C12C=CHC1
CHCljBr
C12C=CC12
CHClBr2
CHBr3
13/12
0
0
0.2
-
0.4
0.4
-
1.6
-
-
14/12
23
46
0.2
-
0.4
0.7
0
3.6
-
-
16/12
70
140
0.4
-
0.5
0.8
-
1.1
-
-
19/12
143
255
2.8
0.1
1.8
2.0
0.1
3.2
-
0.1
21/12
190
345
0.4
-
2.2
1.3
-
5.6
-
0.1
2 3/12
240
4 34
0.1
-
0.2
0.2
-
2.2
-
-
27/12
330
592
0.1
-
0.5
0.2
-
6.4
-
-
30/12
405
707
0.1
-
0.5
0.2
-
6.3
-
-
3/1
503
859
0.1
0.1
0.6 .
0.2
-
8.5
-
-
6/1
575
980
0.1
-
0.2
0.1
-
1.2
-
-
9/1
650
1,101
0.2
-
0.4
0.2
-
2.7
-
0.1
13/1
745
1,250
4.2
-
0.2
0.2
0.2
3.5
<0.1
0.2
26/1
1056
1,7 40
0.2
-
<0.1
<0.1
-
1.8
-
-
3/2
1247
2,050
0.1
-
2.8
<0.1
-
1.5
-
-
9/2
1389
2,280
0.2
<0.1
3.5
0.2
-
1.8
-
<0.1
9/2
1389
2,280
0.2
<0.1
3.4
0.1
-
1.7
-
<0.1
16/2
1557
2,540
0.3
-
4.7
0.6
<0.1
3.0
<0.1
<0.1
22/2
1703
2,770
1.7
-
<0.1
<0.1
-
0.6
-
-
1/3
1868
3,020
0.8
-
<0.1
<0.1
-
0.3
-
-
13/12/77
n -
-1/3/78
18
Log. Mean
Spread Factor
0.25
3.1
<0.1
0.46
4.1
0.23
3.1
<0.1
0.35
2.3
<0.1
<0.1
All analyses by liquid-liquid extraction VOA method. An identifiable peak coo small to be inter-
preted quantitatively Is denoted as < (detection limit), e.g. < 0.1 Pg/1. A (-) signifies that the
corresponding peak was not discernible.
-------
TABLE 9A
VOA Characterization of Samples from Well P4
Period 24 August to 18 November 1977 Prior to Activated-Carbon Treatment
Total
Elapsed
Time
(hrs)
Cumul.
Inj.
Volume
n,^
•k
Concentrations, yg/1
Date
chci3
c ci4
ci3c ch3
C12C=CHC1
CHCl2Br
ci2c=cci2
CHClBr2
CHBr3
24/8
0.5
3
0.1
ND
-
-
-
-
0.6
-
24/8
6
17
-
ND
-
-
-
-
<0.1
-
25/8
13
40
-
ND
-
-
-
-
-
-
26/8
40
130
2.1
ND
ND
13
-
2. 7
4.5
-
26/8
50
150
1.5
ND
-
1.0
-
-
-
-
27/8
70
170
1.6
ND
0.7
2.0
<0.1
<0.1
2.4
-
30/8
145
250
2.0
ND
<0.1
2.0
-
-
1.5
-
4/9
260
690
1.3
ND
0.7
0.8
-
0.8
-
-
8/9
356
1,050
4.4
ND
5.6
3.6
1.4
<0.1
-
-
12/9
456
1,440
4.0
ND
9.3
7.1
2.0
-
2.7
3.4
15/9
526
1,570
4.6
ND
6.8
6.3
1.3
1.1
-
1.3
3/10
957
2,450
31.9
-
11.3
19.0
1.2
2.5
0.2
0.4
2/11
1679
3,860
1.7
-
6.5
3.5
0.1
0.3
0.1
0.1
9/11
1868
4,150
0.9
-
2.2
2.6
-
1.5
-
-
: 18/11
2062
4,520
2.4
-
2.3
3.3
-
1.8
-
-
24/8-26/8
n = 6
Log. Mean
Spread Factor
0.33
6.2
ND
<0.1
0.38
11
<0.1
<0.1
0.3
8.0
<0.1
-8/9-18/11
n = 7
Log. Mean
Spread Factor
3.7
3.1
<0.1
0.73
1.9
5.1
0. 31
5.0
0.48
5.4
<0.1
0. 22
2.1
Analyses of samples before 1 October 1977 by head space VOA method; thereafter by liquid-liquid extrac-
tion VOA. An identifiable peak too small to be interpreted quantitatively is denoted as < (detection
limit), e.g. < 0.1 Mg/1. A (-) signifies that the corresponding peak was not discernible.
-------
TABLE 9B
VOA Characterization of Samples from Well P4
After Beginning of Activated-Carbon Treatment 13 December,1977
Total
Elapsed
Time
(hrs)
Cumul.
Inj.
Volumt
m^
A
Concentrations, Ug/1
Date
chci3
C CI.
4
C13C CH3
ci2c=chci
CHCl2Br
CI
2c=cci2
CHClBr2
CHBr3
13/12
0
0
2.7
-
2.2
3.1
-
1.1
—
0.1
14/12
23
46
3.5
-
4.6
5.8
-
2.0
-
0.2
9/1
650
1,100
0.9
-
6.3
3.5
-
1. 6
-
-
26/1
1056
1,740
¦ 1.1
-
3.2
6.3
<0.1
1.4
<0.1
-
3/2
1247
2,050
1.5
-
6.7
10.4
<0.1
2.1
<0.1
0.1
9/2
1389
2,280
0.8
-
2.8
5.3
<0.1
1.0
<0.1
<0.1
16/2
1557
2,540
1.2
-
6.5
9.8
<0.1
2.2
<0.1
<0.1
16/2
1557
,2540
1.4
-
7.7
10.4
<0.1
2.2
<0.1
<0.1
22/2
1703
2,770
0.3
-
2.1
3.7
-
1.1
<0.1
-
1/3
1868
3,020
0.3
-
2.2
3.7
-
1.1
<0.1
-
13/12/77-1/3/78
n = 9
Log. Mean
Spread Factor
1.05
1.4
<0.1
3.9
1.7
5.6
1.6
<0.1
1.5
1.4
<0.1
<0.1
*
All analyses by liquid-liquid extraction VOA method. An identifiable peak
preted quantitatively is denoted as < (detection limit), e.g., < 0.1 yg/1.
corresponding peak was not discernible.
too small to be inter-
A (-) signifies that the
-------
are in the range of 4 yg/1 to 16 yg/1 in the injection water and less than
0.5 yg/1 in samples from Well P4. The breakthrough of these compounds begins
after 40 to 50 hours, i.e., at the tail of the injected water breakthrough
curve (Figure 6).
After breakthrough of the VOA compounds, their concentrations at the ob-
servation well reached levels approximately equal to those in the injection
water. The values at Well P4 were not significantly different from those
for the injection water samples. The variability of the data is such that
breakthrough curves cannot be plotted as for the compounds analyzed by CLSA.
The concentrations of trace organic compounds found using VOA on injec-
tion water samples decreased markedly when activated carbon treatment began
in the reclamation plant (Table SB). The concentrations are two to ten times
lower after activated-carbon treatment was applied. During this later period
following 13 December 1977, the concentrations at Well P4 are higher than in
the injection water, as seen by comparing the mean concentrations given in
Tables 8B and 9B. Chloroform, trichloroethane, trichloroethylene, and
tetrachloroethylene are present in concentrations sufficient for quantitation.
Their mean concentrations are four to twenty times higher at Well P4 than in
the injection water. This may be explained by desorption of organic compounds
previously adsorbed in the aquifer during the previous period when the concen-
trations of trace organic substances were higher. A laboratory investigation
of the adsorption capacity and equilibria is in progress. A spike-response
study will be carried out in the field to determine how rapidly the aquifer
equilibrates with the composition of the injection water.
Virus Monitoring
Eight samples have been analyzed for virus at the Palo Alto facility: a
background sample, a virus-seeded recovery efficiency sample, a P4 well-water
sample, and two samples of the injection water. The results are presented in
Tables 10 and 11.
For virus analyses, water is filtered on a batch basis using a manifold-
type filtration apparatus designed for this study. The apparatus holds four
0.45 ym porosity cartridge filters connected in such a way that both parallel
(filtering of water) and series (eluting) flow through the filters can take
place. Water to be filtered is collected in 50-gallon drums, pH is lowered
to 3.5 with 4N HC1, AlCl^*61^0 is added to give 0.0005M Al, and the water is
68
-------
TABLE 10
Coliform, Bacteriophage, and Animal Virus Isolation from Palo Alto Well
Water, Injection Water (Tertiary Effluent), and Secondary Effluent
Confirmed
Fecal
Bacteriophage
Animal virus
Field
Water
Conforms
Conforms
(MPN per 100 ml)
Exp. No
per 100 ml
per 100 mj
1
UC1 Well
<2
<2
Water I 2
C2 Hell
4
—
<20*
ND5
Water I 2
2
C Well
—
—
12Z Recovery
12X Recovery
Water I 2
(Cqliphage No.3)
(Polio type 1)
3
UC Injection
<2
<2
<1
Waters
C Injection
—
—
<20
ND
Water
4
UC Injection
220
<2
<1
Water
UC Well
23
2
<1
—
Water P4
C Well Water P4
—
—
<20
ND
5
UC Injection
<2
<2
<1
Water
C Injection
—
—
<20
ND
Water
6
UC Injection
14
<2
<1
Water
UC Well
34
<2
—
—
Water P4
C Injection
—
—
2.7Z Recovery
33X Recovery
Water
(Coliphage No.3)
(Polio type 1)
7
UC Post
7,000
2
<1
—
Injection Well
Water I 2
C Post Inj.
<20
ND
Well Water I 2
8
UC Chlorinated
490
22
3,500
Secondary
Effluent
C Chi. Secondary
—
0.04X+
12 PFU per
Effluent
recovery
100 gal.
1
UC, Unconcentrated
2
C, Concentrated
3
Injection Water is
Palo Alto tertiary effluent
4
, not measured
5
ND, None detected.
Assuming 33£ recovery and isolation of 1
PFU,
ND means less than
approx. 5-£
PFU
*
<20 per 100ml of concentrated
eluant. All
other KPN's represent counts
per 100ml of water
+
0.04Z, a poor recovery of the natural phage population was achieved.
69
-------
TABLE 11.
Supplemental Information, Virus Monitoring at the Palo Alto Facility
Water Characteristics
Field
Exp. No.
Date
Water
Gallons of
Water Filtered
Filter Time,
Hours
pH
Specific Conductance
(Micro mhos/cm at 25°C)
Chlorine
Residual
1
7/26/77
Well Water
I 2 (Loner)
720
3.5
7.2
51,000
1
2
8/18/77
Well Water
I 2 (lower)
1,000
3.8
7.2
50,000
3
9/15/77
Injection
Water
1,008
A. 1
6.8
1,620
Present
(.>_ 1 ppm)
A
10/3/77
Well Water
PA
1,000
5.1
7.6
1,120
Absent
(<¦1 ppm)
5
10/24/77
Injection
Water
1,000
3.6
7.2
1,710
Present
(il ppm)
6
11/7/77
Injection
Water
1,040
3.6
7.5
1,650
Present
(approx.
.5ppm)
7
8
11/30/77
2/21/78
Post injection
Well Water I 2
(Collected dur-
ing Well Rede-
velopment .
Chlorinated
Secondary
Ef fluent
1,000
501
2.9
3.75
6.85
7.01
1,970
1,920
Absent
(<.1 ppm)
Present
(7.3 ppm)
^ , Not measured.
2
Presence or Absence o£ a chlorine residual
Field Exp. No. B In which a portable Iodine
was determined using a simple 0-colidine chlorine residual test kit,
method field kit was used.
except for
-------
then pumped through the filter apparatus at a flow rate between 3 and 6 gal-
lons per minute. Three 50-gallon drums are used; while the pH is adjusted in
one, the others are being filled or used for filtering. After filtration the
filters are switched to series flow, washed with 17 liters of pH 3.5 saline
(0.85% NaCl) and then eluted with 3 liters of 3% Bacto-Beef Extract previously
adjusted to pH 9.0. The pH of the eluant is then adjusted to neutrality and
transported to the laboratory on ice. The eluted material is further concen-
trated to 50 to 70 ml using a Millipore Pellicon Casette System (an organic
flocculation technique was used with Sample 1, but the casette system is now
being used since it appears that better recoveries are achieved). A major
portion (25-35 ml) of the concentrated material is assayed for animal virus
by plaque assaying on BGM cells. A portion is also removed and assayed for
bacteriophage using both the MPN (5-tube at 1, 0.1, 0.01) and plaque assay
techniques (JE. coli li host) . An unconcentrated sample is also assayed for
coliforms (5-tube MPN at 10, 1, 0.1) and bacteriophage (5-tube MPN at 50, 10, 1).
No animal viruses or bacteriophage were detected in any of the samples
and coliform bacteria were detected on only one occasion (Sample 4). The
presence of a significant chlorine residual is likely a major factor contrib-
uting to the absence of viruses and coliforms (sodium thiosulfate was added
to samples to neutralize chlorine residual). In Sample 4 where coliforms were
detected, no chlorine residual was found. The virus recovery efficiency study
with Sample 2 showed a 12 percent recovery for both poliovirus and phage No. 3
seeded into well water from 12 (bacteriophage Nos. 1, 2, and 3 were added but
only No. 3 was recovered; this agrees with previous laboratory observations).
Although a 12 percent recovery seems rather low, it is acceptable if the high
degree of concentration (1,000 gallons to 69 ml) and low level of seeding
(polio, 8.5 PFU/gal; phage No. 3, 5,162 PFU-gal) are considered.
In view of these findings and the fact that both bacteriophage and animal
viruses have been routinely isolated in Palo Alto's primary effluent, Field
Experiment No. 8 was conducted to determine the extent of removal through the
chlorinated secondary effluent stage of the treatment train. The results for
this experiment are found in Tables 10 and 11 and are summarized in Table 12.
The results from Field Experiment 8 help substantiate the often observed
phenomenon of greater virus resistance to chlorination. In this case coli-
forms declined five orders of magnitude compared to two and three orders of
magnitude for phage and animal virus, respectively. Information provided by
71
-------
TABLE 12
Removal of Bacteria and Viruses by Secondary Treatment and Chlorination
Results of Field Experiment No. 8 (21 February 1978)
Confirmed
Coliforms
per gallon
Fecal
Coliforms .
per gallon
Coliphage
per gallon
(E.coli B host)
Animal virus
per gallon
Primary Effluent
Chlorinated Sec-
ondary Effluent
1.7 x 109
1.9 x 104
2.6 x io8
8.3 x 102
3.0 x io7
1.3 x io5
1.61 x io2
1.2 x io-1
treatment plant personnel indicated that the secondary effluent was probably
exposed for 30 to 60 minutes at chlorine residuals ranging from 14 to 17.3
ppm. The low animal virus levels in the chlorinated secondary effluent helps
explain why none have been detected in the more highly treated reclaimed
water used for injection.
Trace Elements
Trace metals were determined by flameless atomic absorption spectro-
photometry following APDC chelation and methyl isobutyl ketone extraction of
acid-preserved, unfiltered grab samples. As and Se were analyzed by hydrogen-
argon flame atomic absorption spectrophotometry using a hydride gas generator.
Analyses for Ag, As, Cd, Cr, Cu, Fe, Pb, and Zn have been conducted on samples
of injection water (Table 13) and Well PA (Table 14). The results for
the formation groundwater before injection are given in Table 15. Only Fe
was present in excess of 1 mg/1 in the formation water. The concentration
of Cu was significantly higher in the injection water than in the formation
groundwater, the concentrations of As, Cr, of iron were significantly lower,
the concentration of Cd was slightly lower, and the concentrations of Ag, Pb,
and Zn were approximately the same in the injection water compared to the
formation water.
The initial concentrations of all metals except Fe and Zn were near the
respective detection limits in samples taken at Well P4 shortly after injection
began (Table 14). The responses of the Cu and Cd concentrations as a
function of elapsed time after the beginning of injection are shown in
Figure 22. After 2000 hours of injection, the concentration of Cd had
72
-------
TABLE 13
Trace Metal Analyses—Injection Water
total
Elapsed
Time*
(hrs)
Cumul.
Inj .
Volume
m3 *
Sample
ID
Concentrations, yg/1
Date
Ag
As
Cd
Cr
Cu
Fe
Pb
Se
Zn
24/8/77
8
27
194
2
1.6
2.5
<1
60
51
2.5
60
25/8
18
91
197
3
2.2
2.5
<1
85
45
1.0
64
26/8
52
180
200
2.5
2.2
2.0
<1
104
77
0.5
21
4/9
262
696
215
4
1.9
1.5
<1
110
15
0.6
<1
8/9
358
1,060
242
1.5
1.3
1.5
<1
120
22
0.6
11
12/9
456
1,440
246
3
1.7
2.5
<1
140
58
1.8
23
3/10
957
2,430
258
5.9
0.9
1.8
<1
85
270
4.0
22
12/10
1170
2,860
262
1.4
<0.5
1.6
<1
120
340
1.1
130
18/10
1320
3,160
265
<0.5
<0.5
0.7
<1
71
41
0.6
9
24/10
1460
3,450
269
1.6
0.7
1.5
<1
100
140
2.0
8
2/11
1680
3,860
277
1.9
<0.5
1.1
<1
93
160
0.9
17
9/11
1870
4,140
286
<0.5
2.0
2.1
<1
80
140
<0.5
9
18/11
2060
4,510
300
1.2
1.1
3.8
<1
140
180
2.1
16
18/Ilt
2060
4,510
300 #
<0.5
1.1
3.0
<1
120
46
1.0
38
13/12f
1.5
2
309
<0.5
3.9
1.0
<1
81
140
0.9
32
14/12
23
46
314
<0.5
3.4
<0.5
<1
31
180
1.6
27
20/12
170
300
321
<0.5
2.0
<0.5
<1
14
160
<0.5
38
9/1/78
650
1,100
337
<0.5
3.4
0.9
<1
14
140
0.2
18
16/2
1560
2,540
352
<0.5
3.6
0.5
<1
12
85
1.4
18
22/2
1700
2,770
355
<0.5
4.3
0.6
<1
6.0
50
0.8
4
1/3
1870
3,020
361
<0.5
2.8
<0.5
<1
13
96
1.4
5
24/8-18/11
n = 14
Mean
Std. Dev.
2.05
1.57
1.25
0.71
2.01
0.81
<1
102
24
113
98
1.33
1.04
30.6
34.2
13/12-1/3
n = 7
Mean
Std. Dev.
c0.5
3.34
0.75
0.54
0.31
<1
24.4
26.0
121
46
0.94
0.56
20.2
12.9
*
Time and cumulative injection volume counted anew beginning with operation
of the full treatment sequence on 13 December 1977.
^Injection terminated 18 November 1977 and resumed 13 December 1977.
^Filtered, 0.45 ym membrane filter, before acidification and extraction.
73
-------
TABLE 14
Trace Metal Analyses—Well P4
Total
Elapsed
Time*
(hrs)
Cumul.
Inj .
Volume
m^ *
Concentrations, yg/1
Date
o3ITlp-L6
ID
Ag
As
Cd
Cr
Cu
Fe
Pb .
Se
Zn
24/8/77
0
3
212
<0.5
8
2.5
<1
<1
<0.5
<0.5
25
25/8
13
39
177
<0.5
13
<0.5
<1
1
460
<0.5
6
26/8
49
179
181
<0.5
21
<0.5
<1
10
26
<0.5
2
27/8
70
210
182
<0.5
20
1.0
<1
5
710
0.8
<1
30/8
145
308
219
<0.5
14
0.5
<1
5
22
0.8
<1
8/9
358
1,060
243
<0.5
9
0.5
<1
18
45
12
<1
12/9
456
1,440
247
<0.5
9
<0.5
<1
12
59
1.2
<1
15/9
526
1,580
249
<0.5
11
1
<1
14
52
1.5
<1
3/10
957
2,430
255
<0.5
13
4.4
<1
14
400
0.7
10
12/10
1170
2,860
264
<0.5
9
1.4
<1
31
150
0.6
97
18/10
1320
3,160
266
<0.5
13
0.5
<1
21
110
1.9
<1
24/10
1460
3,440
274
<0.5
9
<0.5
<1
25
170
2.3
<1
2/11
1680
3,860
276
<0.5
10
1.9
<1
31
270
2.1
<1
9/11
1870
4,140
287
<0.5
13
0.5
<1
31
270
<0.5
<1
18/11+
2060
4,520
298
<0.5
15
4.4
<1
24
320
1.2
2
13/12+
1.5
2
310
<0.5
16
1.1
<1
1.9
370
0.7
28
14/12
23
46
311
<0.5
16
6.4
<1
11.9
335
1.4
5
9/1/78
650
1,100
338
<0.5
3
2.4
<1
3.5
5.0
1.0
2
16/2
1560
2,540
353
<0.5
3
3.9
<1
6.5
28
2.1
<1
22/2
1700
2,770
359
<0.5
7
0.6
<1
6.0
<1
2.3
-------
TABLE 15
Trace Metal Analysis—-Formation Groundwater Before Injection
Concentrations, yg/1
Well
Ag
As
Cd
Cr
Cu
Fe
Pb
Zn
12-lower
1
13
2.5
<60
20
1,450
<5
<5
S3-lower
<1
6
33
190
40
2,200
<5
160
reached and indeed exceeded the range of Cd concentrations in the injection
water. The concentration of Cu had reached 25 to 30 percent of the mean
injection water concentration, and the concentration of Ag had yet to rise
above the detection limit at P4 (Table 14).
From these data it is estimated that the half-time for response of Cd
was approximately 50 times the half-time for the arrival of injection water,
and that for Cu and Ag were in excess of 100 times that for the arrival of
injection water. The field capacity (as previously calculated for chloro-
benzene) for the retention of Cd is on the order of 100 mg per nr and for
3
copper is in excess of 10 g per m of aquifer material.
Nitrogen Species
The concentrations of ammonium, nitrite and nitrate nitrogen are
given in Table 4A through 4H. The removal of ammonium during aqui-
fer passage in the early stages of injection is evident when data for the
injection water in Table 4B are compared with those for Well P4 in
Table 4F. The mean concentration of ammonia nitrogen in the injection
water over the full period was 27.4 mg/1 N, with a standard deviation of
6.2 mg/1. The 95 percent confidence limits on the mean are 24 and 30 mg/1
N. The concentration of ammonium in the formation groundwater at 12-lower
was 1.98 ± 0.10 mg/1 N. For the first eleven hours after injection, the
ammonium concentration in samples from Well P4 was 1.85 ± 0.12 mg/1 N,
then decreased below 1 mg/1 N until after 250 hours had passed, and there-
after rose to values in excess of 10 mg/1 N. Within 1000 hours, ammonium
rose to concentrations typical of the injection water. The mean and
standard deviation of six samples taken after 12 October 1977 was 29.0 + 3.5
mg/1 N, compared to 30.2+4.3 for six samples of injection water from the
75
-------
INJECTION WATER WELL P4
Mean ± Std Dev.
-------
same period. Thus, there was no significant decrease in ammonium concentra-
tion once breakthrough was complete. The fractional breakthrough of ammonia
at Well P4 is shown as a function of the cumulative injection volume in
Figure 23.
The removal of ammonia nitrogen during the early stages of operation
was probably caused by ion exchange, since once the aquifer material be-
came saturated, complete breakthrough occurred. Biological nitrification
and denitrification reasonably can be rejected as possible removal mecha-
nisms. Neither nitrate nor nitrite was found at the observation well in
concentrations above those in the injection water. In samples of injection
water taken on September 8 and 12, the concentration of nitrate rose above
the normal range. On those days, the nitrate concentration was abnormally
high at P4 as well, indicating that denitrification did not occur to a
significant extent.
The removal of ammonium ion between the injection well and P4 equals
2.1 meq/1 during the first 200 hours of operation. This can be accounted
for within the increase of 12 meq/1 Na which occurred between the period
after completion of freshwater breakthrough and prior to the beginning of
ammonium breakthrough at P4. The increase in sodium supports the hypo-
thesis that exchange of ammonium ion for sodium on clays could have
occurred.
The half-time for ammonium response was approximately 400 hours, or
forty times the half-time for freshwater breakthrough. The ammonium re-
tention capacity of the aquifer can be calculated as for chlorobenzene,
integrating the area above the breakthrough curve as in Figure 23. A
total of 1315 meq was removed by the aquifer. The specific retention
capacity is 57 meq/m assuming a value for e equal to 30 percent.
Laboratory studies are being conducted with core samples to ascertain
more directly the capacity of the aquifer material to remove ammonia by
ion exchange.
Phosphorus
Phosphorus was removed during passage through the aquifer (Figure 24) .
The concentration of phosphate was less than 0.2 mg/1 PO^ in samples from
P4 during the first 12 hours of operation. Thereafter, the concentration
rose, reaching a plateau of 0.83 + 0.12 mg/1 at times in excess of 50 hours.
77
-------
0.8
0.6
0.4
0.2
1000 2000 3000 4000 5000
CUMULATIVE INJECTION VOLUME, m3
Figure 23. Breakthrough of ammonia at Well PA
-------
vo
d
Q_
o
CP
E
£
a:
I—
Z
LU
O
o
o
OBSERVATION
0 P4
INJECTION WATER
—— Dato Points ond
C" "O Mean ± Std. Dev.
for t = 0 to 1000 hours ^
100 200
500 1000 2000
TIME, hours
Figure 24. Concentration response of phosphate at Well P4
-------
Thus, the time required for completion of the concentration response of
phosphate was approximately equal to the time required for complete dis-
placement of formation water by injected water, i.e. 50 hours. The 95 per-
cent confidence limits on the mean are 0.71 to 0.95 mg/1 PO^ for P4 after
the breakthrough was complete. This is significantly less than the mean
concentration of 2.8 mg/1 PO^ in the injection water, which had 95 percent
confidence limits of 1.5 to 4.1 mg/1.
The observed decrease in phosphate concentration from the injection
well to P4 is consistent with our previous calculations showing that the
injection water is oversaturated with respect to phosphate and that pre-
cipitation of minerals such as apatite can be expected [ 2].
Bacteria
Standard fclate Count determinations of bacteria were conducted on
samples of injection water and groundwater from observation wells (Tables
4A through 4H and Figure A-25).
Observation well samples typically gave plate counts in the range of
9 fi
10 to 10 , compared to background values of less than 10 per ml in the
formation groundwater prior to injection. The number of bacteria was
consistently higher at the observation wells than in the injection water
(_< 10^/ml) . These findings can be interpreted as evidence of growth of
aerobic and facultative bacteria in the aquifer or wells after injection.
Further interpretation of these data is not warranted, owing to the in-
herently empirical nature of the method and the variability of the data.
Determinations of total and fecal coliforms were made in five paired
samples from injection water and Well P4 (Table 16). Coliform bacteria
were found at both the injection point and Well P4. Because of the small
number of samples and the variability of results, a quantitative inter-
pretation is not justified. The high coliform count in the water pumped
from the injection well during redevelopment may be indicative of accumula-
tion in or near the well bore caused by either filtration or growth.
Dissolved Oxygen, COD, and TOC
There was a consistent and significant reduction in dissolved oxygen
(DO) concentration during passage through the aquifer, as seen by comparing
80
-------
INJECTION WATER
00
I—
o
o
LU
£
Q
01
<
Q
t
CO
OBSERVATION WELLS
+ PI ~ P3
O P2 —O— P4
O S3- L
©
I—A A'
500
1500
2000
TIME, hours
Figure 25. Bacteria counts in injection water and observation well samples
-------
TABLE 16
Coliform Counts
MPN/100 ml
Sampl
e
Injection Well
Well P4
Date
Time
Total
Fecal.
. Total
Fecal
During injection of
reclaimed water of
intermediate quality
18/10/773
24/10a
2/llb
<2
<2
2.3
<2
<2
<0.2
<2
*
24
<2
*
0.2
9/llb
13
<0.2
2.3
<0.2
18/llb
<0.2
<0.2
4.9
<0.2
Samples of water
pumped from 12-lower
during redevelopment
attempt
30/llb
30/llb
11:30
13:30
>240
>240
0.8
0.5
*
*
*
A
During injection of
high-quality
reclaimed water
13/12b
16/2/78c
22/2°
<0.2
1
64
<0.2
1
0
<0.2
0
1
<0.2
0
1
Coliform Determination Method:
a. MPN, 10-ml sample.
b. MPN, 100-ml sample.
c. Membrane filter method.
Not determined.
the values in Tables 4B and 4F. The concentration in the injection water
near saturation, 7 to 9 mg/1 DO, whereas at P4 it was consistently below 1 mj
Possible explanations are: aerobic metabolism of organic substrate by micro-
organisms, biological nitrification, and chemical or biological oxidation of
aquifer material. It appears that biological oxidation of organic substrate
introduced with the injected water is the most plausible explanation for the
reduction in DO.
Determination of COD and TOC in paired samples from the injection
water and Well P4 were made weekly over the period from 12 September to
18 November. The reduction between the two points was 8.8 ± 5.5 mg/1 COD
for 16 sample pairs and 3.4 ± 2.1 mg/1 TOC for 13 sample pairs. A meas-
ured increase occurred between P4 and S3-lower of 4.8 ± 7.1 mg/1 COD for
7 sample pairs and 1.72 ± 2.3 mg/1 TOC for 8 sample pairs.
82
-------
The reduction in both COD and TOC between the injection point and Well
P4 is significant at the 95 percent confidence level, while that between P4
and S3-lower is not. The reduction in COD agrees well with the decrease in
DO concentration between the same two points. Thus, it appears that the dis-
appearance of dissolved oxygen can be accounted for by the aerobic biodegrada-
tion of organic substrate, as measured by both COD and TOC. The slight in-
crease in TOC and COD between P4 and S3-lower is not significant at the 95
percent level.
Redevelopment of the Injection Well
The clogging behavior of the aquifer is being investigated further. The
3
well was redeveloped by withdrawing 9.4m of water from the well over 6 hours
at a pumping rate of 0.5 liters per second, the steady-state rate at a maximum
drawdown of 6 meters. The volume withdrawn is equal to the void volume of the
well bore plus aquifer out to a radius of 2.5 meters.
Ten samples of the withdrawn water were analyzed for total and volatile
suspended solids (TSS and VSS), chemical oxygen demand (COD), total plate
count, trace metals, and particle count (Table 17). The first three samples
essentially represent water drawn from the well casing, gravel pack, and
from the aquifer near the bore hole interface. These samples contained con-
centrations of TSS, VSS, COD, bacteria, and particulates that are considerably
higher than are typical for the injection water. Based upon the ratio of VSS
to TSS, the suspended solids were approximately 50 percent organic, as con-
firmed by the high COD and high plate counts. The total count of particles
greater than 2.5 Um in size was two to three times higher in the first sam-
ples from redevelopment, compared to the injection water. Samples of these
solids are being investigated by x-ray diffraction to identify any clays or
other crystalline minerals.
The quality of withdrawn water improved rapidly after the first hour.
After four hours of pumping, it was equal to or superior to that of typical
injection water in terms of suspended solids, with the exception of bacterial
counts, which were still more than an order of magnitude higher. It was
concluded that at the end of six hours the fullest extent of redevelopment by
this method had been reached.
Following resumption of injection in mid-December, the rate was essen-
tially the same as before the redevelopment attempt (Figure 9). Thereafter
83
-------
TABLE 17
Redevelopment Test at Well 12
Water Quality Analyses
Date
and
Average
Cumul.
With-
drawal
Elapsed
Total
Suspended
Volatile
Suspended
Total
Plate
Particle Count
N per liter
Trace Metal Concentrations, yg/1
Pumping
Time
Volume
m
Solids
Solids
COD
Count
Rate
Time
(hrs)
mg/1
mg/1
mg/1
N/ml
> 2.5 ym
> 20 ym
Ag
Cd
Cr
Cu
Fe
Pb
Zn
21/11/77
09:55
0
0
-
-
-
-
-
-
-
-
-
-
-
-
-
Q =
0.47 1/s
10:05
10:25
0.17
0.5
0.19
0.70
106
64
58
36
300
130
2.3 x107
2 x io7
2.7 x106
4 x io6
1.7 xio6
1.4 xio6
30
8.8
11
11
< 1
1
>500
480
13,300
4,800
17
10
480
260
10:55
1.0
1.63
32
14
46
106
3.5 x10°
7.2 x io
4.0
7.2
1.3
350
900
4
110
11:25
1.5
2.57
2
16
31
> 3 x io5
4.1xio6
1.04x 105
1.4
5.3
< 1
280
490
2.0
41
12:00
2.0
3.48
2.2
1.4
25
6 x io4
4 x io6
7.2 xio3
< 1
5.6
< 1
270
470
2.1
21
30/11/77
09:30
2.0
3.48
18.6
4.2
19
8 x 105
5.3 x106
8.4 x103
< 1
10
< 1
210
1,900
1.9
>500
Q =
0.44 1/s
10:30
11:30
12:30
3
4
5
5.03
6.51
7.99
3
< 1
1
3
< 1
1
46
28
26
6 x 104
A
3 x i(T
4
1 x HP
1.7 xio6
1.0 xio6
3.2 xio5
2.8 x103
2.4 xio3
1.64x 103
1.3
< 1
< 1
17
6
6
< 1
< 1
< 1
120
65
5
1,300
1,300
700
2.2
<0.5
1.9
29
9
11
13:30
6
9.39
< 1
< 1
23
8 x 103
< 1
5
< 1
55
600
0.7
7
< 103
5 x io3
Injection Water (Typical)
1 to 5
< 5
-25
1.5 x 5
to 2 xio4
2
2
< 1
100
150
1
20
-------
the flow rate stabilized rather than continuing to decline, presumably as a
result of the improved injection water quality. It was concluded that more
drastic alternatives, such as dosing of high concentrations of chlorine or
acid treatment, will be needed to restore the injection well's original
capacity.
PHASE THREE - HYDRAULICS OF RECHARGE
Objective
The objective in this second year was to utilize available models and
field data to interpret measurements and to build a useful understanding of
field conditions.
Progress
The predesign phase of the project suggested that modeling of groundwater
flow within the shallow aquifers of the area would be a straightforward task.
Accordingly, as reported last year [2], a series of idealized models were
constructed and used to gain an early insight into the system performance.
Initially, wells had been drilled in the northwestern edge of the study
area (near II). Logs and well tests showed that there were two shallow zone
aquifers (at depths of 6 meters (20 feet) and 15 meters (45 feet)) separated
by a leaky aquitard. A third, thicker aquifer was found in the deeper zone,
at a depth of 60 meters (185 feet). The deeper aquifer was hydraulically
separate from the shallow-zone aquifers. Design of the injection-extraction
system was carried out on the basis of the predesign tests. Subsequent devel-
opment of injection, extraction, and observation wells showed that the results
of the predesign tests were not representative of the entire field.
A review of the geologic history, geomorphology and stratigraphy of the
area has yielded a comprehensive picture of the hydrogeologic environment of
the injection-extraction site. The aquitard which separates the shallow-zone
aquifers from the deep aquifer (60 meters (185 feet)) is composed of estuarine
silts and clays which were deposited during the Sangamon interglacial high
stand of the seas. During the subsequent Wisconsin ice age the sea level fell
and these estuarine deposits were partly eroded and covered with alluvium de-
rived from the foothills and mountains bordering the Santa Clara Valley. In
particular, the alluvial piedmont slope deposits underlying Palo Alto baylands
85
-------
are the suspended and bed load of San Francisquito Creek. The upper reach of
the creek has remained in approximately its present position since the Late
Pleistocene. The lower reach has migrated back and forth across the face of
the San Francisquito Creek Alluvial Fan, leaving channel and overbank depo-
sits in its wake. Near the northwestern edge of the study area the coarse-
grained deposits are continuous and form the 6- and 15-meter aquifers found
in the predesign tests. But as one moves to the southeast the deposits are
continuous over much shorter distances. Here, a more apt description is
probably that of a collection of individual sand and gravel lenses embedded in
a silt and clay matrix.
The potential distribution data from the pilot study of injection at Well
12 confirm that the lower aquifer is not continuous. With an injection pres-
sure of 103 kPa (15 psi), a steady-state discharge into the lower aquifer of
about 9.5 x 10 ^m^/s (15 gpm) was originally attained. The steady-state hy-
draulic head distribution (pressure distribution) was shown in Figure 10.
Based on that distribution and on well logs from 12 and the five neighboring
observation wells the configuration shown in Figure 26 was inferred. Note
the complete absence of an aquifer at PI, P2, and P3 in the 15-meter (45-feet)
depth region. To gain further information as to the distribution of sand and
gravel units with depth, the profile derived from plotting
D(z) - ± I f„Cz)
n=l
is shown in Figure 27. Here N is the total number of well logs over the
field (injection, extraction, and observation wells) and ^n(2) i-s a func-
tion which equals 1 if the n1-*1 log shows a sand or gravel unit at depth z
and equals 0 otherwise. As such, D(z) represents the density or percentage
of sand and gravel units with depth averaged over the injection-extraction
field. Figure 28 shows the percent of sand and gravel units greater than a
particular thickness. The nonuniform thickness of deposits is apparent.
This lack of continuity between lenses suggests a very complex flow pat-
tern, one that is virtually impossible to model with sufficient accuracy for
use in contaminant transport investigations.
Thus, for successful completion of the contaminant transport modeling
phase we must focus our investigation on the Il/El doublet pair. This is the
only area in which one is likely to find continuous deposits between the
86
-------
00
Figure 26. Geological sections through Well 12
-------
00
00
CO
r>
_i
LU
> I
< )_
cc a
uj
0 Q
1 °
o
q:
ui
CL
DEPTH, meters
Figure 27. Distribution of depths of sand and gravel units
-------
PERCENT GREATER THAN GIVEN THICKNESS
25 50 75 100
w
v_
0)
CD
cr
LJ
_J
LlI
_J
C3
<
'jlI
s
q:
ijj
CL
o
cn
CO
LsJ
2:
o
X
I-
30 40 50
NUMBER OF LAYERS
Figure 28. Distribution of thicknesses of sand and gravel units
89
-------
injection and extraction wells. While even here there is a great deal of
variability in thickness of the deposits, this type of nonhomogeneity is
easily handled by the finite-element method of numerical analysis
(Phase Six).
PHASE FOUR - WATER AND AQUIFER QUALITY CHANGES
Potential for Microbial and Organic Chemical Changes
The pilot injection study conducted during the past year in the Palo
Alto Baylands have raised certain biological questions which are currently
under study. Biological activity in the aquifer has been indicated by a con-
current and equivalent reduction in soluble COD and dissolved oxygen as the
injected water passes through the aquifer. This is an indication of aerobic
biological activity. There are no indications of anaerobic nor autotrophic
activity. During the past year, we have constructed a model for biological
degradation in an aquifer based upon kinetics wich includes simultaneous mass
transport and degradation within a biofilm. This model is being tested in
laboratory columns and will be used in an attempt to simulate transforma-
tions noted to occur in the field.
The field studies have also indicated that chlorinated benzenes are
prevalent in the reclaimed water and that chlorobenzene and probably methylene
chloride pass through the aquifer without biodegradation. The laboratory
studies currently being conducted and described below indicate that these
two materials are biodegradable. The question arises about why decomposition
does not occur in the aquifer. Several hypotheses to explain this are out-
lined in the proposal. In the following, the preliminary studies which ad-
dress this question are described.
Methylene Chloride Degradation
Recent work has been performed to determine if methylene chloride can
serve as a metabolite by supporting bacterial growth as the sole energy and
reduced-carbon source. The alternative condition is that methylene chloride
is degraded but cannot support growth; in this case, methylene chloride is a
co-metabolite, and another compound must be available to serve as the metabolite.
Two special techniques were used to test if methylene chloride supports
growth. In the first case, bacteria that had been enriched from an inoculum
90
-------
of primary sewage effluent by feeding methylene chloride were inoculated into
closed systems containing liquid media with methylene chloride and sodium ace-
tate. The following results were obtained: (1) Aerobic growth on sodium ace-
tate was rapid and complete whether 1 g/1 of methylene chloride was present
or absent. (2) No significant growth on or utilization of methylene chloride
alone occurred in about two weeks of incubation. This may indicate that dur-
ing culturing on acetate, enzymes for methylene chloride degradation are
repressed or not induced. It may also mean that bacteria which cannot uti-
lize methylene chloride predominate when acetate is the energy source.
Finally, high levels of methylene chloride may be inhibitory to its metabolism.
A second experiment was instigated to avoid the complications of high
concentration inhibition and acetate selection or repression. An inoculum
was placed in 60-ml hypovials which contained media and approximately 1 mg/1
of methylene chloride. The bottles were sealed with serum caps. Methylene
chloride was measured weekly by removing 1 ml of liquid with a syringe and
extracting the sample with 0.1 ml of octane, followed by GC analysis. With
sewage seed methylene chloride was reduced to less than 10 Ug/1 within 12
days, while this required 19 days with an inoculum grown on acetate.
Semi-continuous cultures, which involved daily feeding of methylene chlo-
ride to bottles prepared as in the batch studies, were also employed to test
if growth occurred. One ml/day of dilute methylene chloride was fed to 60-ml
bottles, and 1 ml/day of media was removed before feeding. The feed concen-
tration of methylene chloride was successfully increased from 1 mg/1 to 10
mg/1 to 100 mg/1 and finally to 1330 mg/1. Analysis indicated the methylene
chloride was rapidly consumed. Because of this and the formation of visible
bacterial floes, it is believed that methylene chloride can support aerobic
bacterial growth when it is the sole energy source.
Future research goals are to ascertain if methylene chloride degradation
is enhanced or repressed by the presence of other organics and to determine
the minimum concentration that will support growth and/or induce degradative
enzymes. The evidence to date suggests that the presence of an easily de-
graded, exogenous energy source may repress utilization of a synthetic com-
pound, such as methylene chloride.
91
-------
Chlorinated Benzene Degradation
Preliminary results on the degradation of volatile organics in lime-
treated secondary effluent [ 2 ] suggested that chlorobenzene, 1,3-dichloro-
benzene, and 1,4-dichlorobenzene may be biologically degraded. More detailed
studies were performed to find the degradability of these compounds at dif-
ferent concentrations.
A stock solution of chlorobenzenes was prepared in methanol. Dilution
of this stock solution in defined aqueous media gave nominal concentrations
of 1 mg/1 chlorobenzene, 0.74 mg/1 1,4-dichlorobenzene, 0.13 mg/1 1,3-di-
chlorobenzene, and 3.8 mg/1 methanol. The aqueous media was transferred to
60-ml hypovials inoculated with primary effluent (2 ml/1) and sealed with
teflon caps. Non-seeded controls were also used. Weekly, control and inocu-
lated samples were extracted with hexane and analyzed by GC.
Figure 29 . shows that chlorobenzene was completely degraded after a
one-week lag period. The dichlorobenzenes showed little and inconclusive
degradation.
The experiment was repeated with the initial concentration of chlorinated
benzenes in the same order of magnitude as in lime-treated effluent: 8 yg/1
chlorobenzene, 6 yg/1 1,4-dichlorobenzene, and 1.1 yg/1 1,3-dichlorobenzene.
From 0.1 to 10 ml/1 of primary effluent was used for a seed. After three
weeks of incubation, no degradation was observed in any culture. These re-
sults suggest that very low levels of chlorinated benzenes may not be de-
graded because they cannot induce enzymes or support growth of bacteria, even
though higher concentrations (i.e., 100 to 1000 yg/1) may be degraded. This
hypothesis may explain why no degradation of chlorobenzene was seen during re-
charge experiments. These experiments are continuing.
Experimental Verification of Biofilm Model
Biofilm models have been developed for application to recharge conditions.
The critical developments that have been formulated are:
1. The variable-order model [2], which gives the substrate flux into
a biofilm as an explicit function of the liquid concentration.
This model is restricted to biofilms which are "deep" and for which
one substrate is limiting.
2. A modification of the variable-order model which allows calculation
of the substrate flux into a "shallow" biofilm. In addition, this
92
-------
chlorobenzene
1.3-dichlorobenzene
1.4-dichlorobenzene
1000
800
600;
400
200
100
40
10
Detection Limit
14 21
Time of Incubation, days
Figure 29. Concentration of chlorinated benzene during incubation
with primary-effluent inoculum. Closed symbols are
inoculated and open symbols are non-seeded controls
93
-------
modification determines from the liquid concentration when a biofilm
can be "deep" and when it must be "shallow." This feature is espe-
cially important in recharge because low organic concentrations can
support only thin films.
3. A tabulation of methods for calculating the depth of the "effective"
diffusion layer, which represents mass transport to the biofilm.
4. A method for relaxing the requirement that only one substrate limits
the reaction.
Experimental verification of the model is being carried out with a spe-
cially designed glass column, 3 cm in diameter by 12 cm in length. It has
sampling ports along the depth, and the media are 3-mm diameter glass beads.
The column is seeded with bacteria cultured on acetate and methylene chloride,
which are the metabolites to be studied. The kinetic parameters of these
bacteria growing on acetate have been determined by suspended-growth experi-
ments. They are: Kg = 5.4 mg/1 as sodium acetate, k = 28 mg sodium acetate/
mgC-day, Y = 0.12 mgC/mg sodium acetate, and b = 0.27 day-^". These experi-
ments will be continued to determine suitability of the model to describe or-
ganic degradation in submerged aquifer systems.
Chemical and Geochemical Changes
Objectives
1. To design and test an experimental approach for detecting, inter-
preting, and forecasting changes in water quality and chemically-
induced changes in aquifer characteristics which may occur as injected
water moves through the aquifer.
2. To identify processes responsible for expected or observed changes
as well as to begin developing thermodynamic and kinetic models of
each significant process to incorporate in hydrologic water-quality
models.
3. To describe in a similar fashion those reactions that appear to pro-
duce significant changes in the mineralogic or hydrologic charac-
teristics of the aquifer.
Progress
Progress to date has covered four major areas: thermodynamic equilib-
rium modeling of native and injected waters; a pilot study of injection of re-
claimed water; a laboratory study of the kinetics of oxidative dissolution of
94
-------
pyrite with hypochlorous acid; and determination of ion exchange selectivity
coefficients for the clays present in the groundwater formation.
Modeling of native and injected waters: Thermodynamic equilibrium models
have been used in the identification of possible chemical reactions, and to
provide boundary conditions toward which the system will tend as equilibrium
is approached. Several equilibrium models were collected and evaluated to
assess which ones were appropriate for the conditions of the project. The
computer programs SOLMNEQ and MINEQL were chosen for continued use because
their capabilities complement each other. The programs have been used to
model the native waters, reclaimed waters, and a mixture of these two. The
range of native water compositions is large, samples vary in Total Dissolved
Solids from around 5,000 mg/1 to greater than 80,000 mg/1. Individual wells
representative of this range in concentrations have been modeled and analyzed
to check for consistency in thermodynamic data and individual chemical reac-
tions considered, as well as possible under- or over-saturation with respect
to the mineral constituents of the aquifer.
In addition to the above-mentioned wells, modeling efforts have concen-
trated upon the I2/E2 doublet, where the pilot injection study took place.
Water compositions for the observation well, S3; the expected quality of the
tertiary treated effluent; and an equal mix of the native and injected waters
have been modeled. The results of these models have been included in previous
progress reports; therefore only a summary of the results will be given here.
The model of the native water (Well S3) shows a relatively high level of ac-
tivities for the major cations (Ca^+, Mg+^, Na+, K+). The major complexes
formed occur between these cations and the sulfate and carbonate ligands. The
water also shows slight supersaturation with respect to calcite (CaCO^) and
gypsum (CaSO^), and a much higher degree of supersaturation with respect to
the phosphate minerals, ferric oxides, and all heavy metal sulfides. It is
near saturation with respect to fluorite (CaF2)• An indication of supersatu-
ration means only that the system should be precipitating a solid if it is
reacting towards equilibrium. Supersaturation, however, gives no indication
of how fast equilibrium is approached.
The reclaimed water is of high quality with respect to the native water.
The former has Total Dissolved Solids of 765 mg/1 compared to around 35,000
mg/1 for the native water. The activities of the major free cations are
95
-------
accordingly lower. The major complexes are again formed by the cations and
the sulfate and carbonate ligands. The water is supersaturated with respect
to the phosphate minerals and near saturation with respect to calcite and
fluorite. It is undersaturated with respect to most of the remaining minerals
considered.
The mix of reclaimed and native waters shows a similar pattern in the
sense that cations show the highest activities. Over 90 percent of all major
cations exist as free metals. Sulfate forms the strongest complexes with
cations, with about 60 percent of the total in ionic form. The only precipi-
tated solid is hydroxyapatite. The phosphate minerals are oversaturated in
the three cases presented, and therefore should precipitate under the condi-
tions considered. It must be pointed out that the phosphate concentration
used (0.5 mg/1) was chosen as a reasonable guess for tertiary effluents since
no analytical data were available at the time. The mean concentration of
phosphate in the reclaimed water during the period from 24 August to 18 No-
vember 1977 was 2.8 mg/1, owing to the fact that lime treatment in the recla-
mation plant was carried out at pH 9. The models show that even low concen-
trations of phosphate in the injected waters will tend to precipitate in the
aquifer.
Another important task carried out has been a critical interpretation
of the equilibrium models, since they are idealized abstractions, and real
systems may or may not be approximated by them. Among the limitations of the
equilibrium models under consideration are: (1) Pertinent chemical equilibria
may have been ignored or important species may not be considered. (2) Thermo-
dynamic data on assumed species may be incorrect or inadequate. (3) Analyti-
cal data on certain chemical species may be lacking or inadequate. (4) Tem-
perature, pressure, and activity-concentration corrections may require
refinement. Efforts have been made to minimize these limitations by checking
the important chemical species and thermodynamic data; and by gathering anal-
ytical data on those species considered relevant to our objectives. There
are, however, other limitations that are also important. (5) The rates of
certain chemical reactions may be so slow that equilibrium is not achieved in
the real system. (6) Problems associated with the conceptualization or com-
putation of equilibria in the model itself. The concept of equilibrium in-
herently limits the incorporation of potentially oxidizing chemical species
96
-------
such as ozone, chlorine, and dissolved oxygen. Since these species are highly
reactive and do not form stable complexes, the present models are not well
suited to incorporate them.
Field measurement of oxidation-reduction state: During the pilot injec-
tion study described under Phase Two, pH, eh/pe, dissolved oxygen, and some of
the electroactive chemical species such as iron and sulfide were measured.
Conductivity measurements were used because its instantaneous response pro-
vided a good indication of the breakthrough of reclaimed water. Attempts
were made to characterize the oxidation-reduction state of reclaimed and
native waters by electrode potential measurements before, during, and after
injection. The native waters averaged electrode potentials of 150-200 milli-
volts, while the average for the reclaimed water is approximately 450 milli-
volts with large fluctuations towards higher potentials when the water was
chlorinated. As the reclaimed water moved through the aquifer, there was
a general trend for the electrode potential levels to rise towards those of
the reclaimed water but they did not reach these levels. Iron analyses were
performed to calculate the redox potential by applying Nernst's equation in
reverse. The calculated potentials did not agree well with the electrode
potentials measured. This can be attributed to the error that arises from
calculating ferric iron concentrations as a difference between total and
ferrous iron, necessitated by the lack of an analytical technique for direct
measurement of ferric iron.
Kinetics of oxidative dissolution of pyrite by hypochlorous acid: Ter-
tiary treated effluents contain significant concentrations of oxidizing
chemical species such as chlorine compounds and dissolved oxygen. On the
other hand, reduced mineral species are common to groundwater aquifers. As
the injected waters react with the reduced minerals in the geologic formation,
oxidation-reduction reactions are likely to take place, with consequent changes
in water quality and aquifer characteristics.
As discussed in previous reports, a laboratory study was conducted to
study the kinetics of the reaction between hypochlorite species and the iron
disulfide mineral pyrite, one of the most common sulfide minerals which is
found under a wide variety of geologic conditions. The objective of this re-
search was to establish the rate expression for the oxidative dissolution of
pyrite by hypochlorous acid.
97
i
-------
The work encompassed a parametric study including the major variables
that determine the rate of reaction under the conditions likely to prevail
during injection of reclaimed wastewater. The temperature range was that
between 15-25°C, except as dictated by the conditions necessary to study the
activation energy of the reaction. The neutral pH range of 5-9 was considered,
and the ionic strength varied from 0.05-1.0M. The range of concentrations of
total hypochlorous acid varied from 2 x 10"^ to 4 x 10"^M. The concentrations
of the solid FeS2 varied from 5 x 10"^ to 1 x 10"%.
Reactants and reaction products: Hypochlorous acid reacts with pyrite
in aqueous solution to form a ferric oxyhydroxide phase and sulfate ion as
primary reaction products. In addition, variable amounts of hydrogen ions
are released depending on the degree of dissociation of the hypochlorous acid
(pK = 7.6) at the pH of the experiment. The stoichiometry of the reactions
are:
1. Hypochlorous acid
FeS2 + 15,/2 H0C1+ 7^2 H20 ^ Fe (OH) 3 + 2S0^ + 15^2 CI" + 23/2 H+ (7)
2. Hypochlorite ion:
FeS2+ 15/2 0C1" + 111 H20 * Fe (OH) 3 + 2S0^ + 15?2 CI" + 4H+ (8)
Free energy computations for the reaction show that the forward reaction is
strongly favored, with a log k = 22 per electron transferred.
The experiments were carried at constant temperature and pH. Known
concentrations of pyrite and total hypochlorite were added to a light-
shielded water-jacketed reactor and the decrease in hypochlorite concentration
was monitored as a function of time. Both reactants and reaction products
could be monitored throughout the experiments. The hypochlorite concentra-
tion was measured by the standard iodometric titration. The oxidation products
ferric iron and sulfate were analyzed colorometrically. In addition, an in-
dependent check on the reaction was provided by the pH stat, which recorded
the amount of base added to the system. X-ray diffraction techniques were
used for the identification of the solid FeS2 and the ferric oxyhydroxide
formed.
Figure 30 depicts the results of a typical experiment. The upper por-
tion shows the decrease in H0C1 as a function of time. The reaction shows a
first-order dependence with respect to the concentration of hypochlorous acid
in solution over the range of 0.1-3.0 x 10 H0C1. The rapid initial rate
98
-------
200
0
*
100
JE
,—,
80
CJ
O
60
X
0
50
0
-J
40
30
20
PYRITE OXIDATION EXPERIMENT
[FeSg] 200 mg //
[HOCl] 150 mg/J>
pH 7.0, I 0.1 M NaCI, 25°C
8 12 16
TIME (HOURS)
20
24
A. Disappearance of HOCl
100
80
PYRITE OXIDATION PRODUCTS
[FSS2] 200 mg/jP
[HOCl] 150 mg//
pH 70, I 0.1 M NaCI,
O 30
6 ,
X
5 +
4 x
3
O
1
w
- 2
TIME (HOURS) .
Rise in concentrations of oxidation products in the same experiment
Figure 30. Rate of pyrite oxidation
99
-------
observed is believed to be the product of the grinding process of Fe$2 which
tends to energize the outer layers of the particles. The lower portion of
the figure shows the two soluble oxidation products formed during the reac-
tion. A ferric oxyhydroxide precipitate is also formed. The stoichiometry
of the reaction has been confirmed by these experimental results.
Figure 31 presents the effect of pyrite surface area on the rate of
reaction. The experiments shown cover FeS2 concentrations in the range of
50-800 mg FeS2/l. There is a general trend to higher oxidation rates as
more pyrite is added to the system. The response, however, is not first
order.
Figure 32 depicts the effect of hydrogen ion activity on the rate of
oxidation. The trend here is toward higher rates of oxidation as the pH is
lowered.
Since the experimental set-up does not allow for chemostating of the
hypochlorous acid concentration, the effect of surface area and pH is inves-
tigated by comparing the pseudo-first order constants. It is known that both
pyrite surface area and pH have an effect on the rate of oxidation. There-
fore, if we compare the pseudo-first order constants as either FeS2 or pH are
varied, it is possible to gain some insight into their effect. The pseudo-
first order rate constant is written
-d[H0Cl]/dt = k[H0Cl]
where k is actually a function of FeS2 and pH.
The effect of pH and surface area on the pseudo-first order rate constant
obtained from the experiments in Figures 31 and 32 are plotted in Figure
33. The upper portion shows the effect of pyrite concentration, and conse-
quently surface area, on the rate constant. If this pseudo-first order con-
1/2
stant is divided by [FeS2] , a second constant, independent of surface area,
is obtained. Therefore one can write the expression:
i /?
-d[H0C1]/dt = k'(FeS2) ' [H0C1]
where k' = k/(FeS2)"'"^ .
A similar approach can be undertaken with respect to pH, except that
the increase in the rate as the pH decreases can be the product of changes in
the reactivity of the chlorine species as the pH changes. At pH 4 a small but
100
-------
200
e> 50
o
40
30
PYRITE OXIDATION EXPERIMENTS--
EFFECT OF SOLID CONCENTRATION
? 100
[HOCl] 125 mg/S
pH 7.0, I 0.1 M NaCI, 25°C
FeS2 50 mg/4
o
FeS2 100 mg/S
FeSg 200 mg/,/
20
4 6 8 10
TIME (HOURS)
12
A. Range of pyrite concentrations from 50-200 mg/1
200 j- PYRITE OXIDATION EXPERIMENTS'
! EFFECT OF SOLID CONCENTRATION
*
I* 100,
rX 80
o
Jl 60
CD 50
o
-J 40
30
O —^(~V/eS2 800mg/J?
0-.Q^FeS2 400 mg/^7 .
FeS2 200 mg//~"
_
^ ^
"O-c
[HOCl] 90-150 mg//
pH 7.0, I 0.1 M NaCI, 25°C
4 6 8
TIME (HOURS)
10
B. Range of pyrite concentrations from 2U0-800 rag/1
Figure 31. Effect of pyrite concentrations on the rate of oxidation
101
-------
200Q
20
[FeS2] 200 mg/J
- [HOCl] 100-200 mg/J
l r
PYRITE OXIDATION EXPERIMENTS'
EFFECT OF pH
o-
pH 8
I 0.1 M NaCI, 25°C
pH7
pH 6
J L
8 12 16 20
TIME (HOURS)
A. pH 6-8 range
•O
24
200 -
/
cn
100
80
o
o
60
X
o
50
o
_j
40
30
T
PYRITE OXIDATION EXPERIMENTS'
EFFECT OF pH
N)»!
p'H 5
CK
- [FeS2] 200 mg/J
[HOCl] 100-200 mg/J
I 0.1 M NaCI, 25°C
20
JL
10
2 4 6 8
TIME (HOURS)
B. pH 4, 5
Figure 32. Effect of pH on the rate of oxidation
102
12
-------
A
2.4
g 2.0
V)
1.6
m
¦
O
x |.2
0.8
0.4
o^-°'
JL
0 200 400 600 800
FeS2 mgMl
A« Effect of pyrite concentration
A
o
o
w
in
'o
x
5
4
3
2
-o-
-o
6 7
pH
B. Effect of pH
8
Figure 33. Effect of pyrite surface and pH on the
pseudo-first order rate
103
-------
significant amount of CI2 is present. Aqueous chlorine is believed much
more reactive than H0C1. Hence, the pH effect may be due to a larger frac-
tion of aqueous CI2 present at low pH values. However, at the present time
the reactive species has not been identified.
Cation-Exchange Capacity and Selectivity
Field monitoring of the concentrations of major ions following injec-
tion into Well 12 revealed evidence of ion exchange (Phase Two). Based on
the concentration responses at Observation Well PA, it appeared that sodium
was replaced on clays by ammonium, calcium, and magnesium ions. Preliminary
work indicated that the clay fraction of aquifer material from the Palo Alto
Baylands has a cation-exchange capacity of approximately 0.10 milllequiva-
lents per gram [2].
Experiments were undertaken to investigate ion-exchange selectivity and
capacity of core samples taken from the lower aquifer in the immediate study
area of the injection experiments. Cores of aquifer material acquired during
the drilling of Wells 12 and P4 were used. The objectives were to determine
the cation-exchange capacity of the bulk mineral assemblage of the lower aqui-
2+
fer as well as the selectivity coefficients for exchange reactions among Ca ,
Mg^+, Na+, K+ and NH^ for these minerals.
The CEC and effective selectivity coefficients were determined over the
range of ion strengths from 0.01 to 0.5, corresponding to the conditions of
the injection water at the lower extreme to the formation groundwater at the
upper extreme.
To obtain selectivity coefficients, the surface concentrations (or
quantity adsorbed per weight of solid) and solution concentrations at equi-
librium must be known. These can then be used to define selectivity coeffi-
cients applicable to the specific conditions under which they are measured.
Thus, for the reaction
Na(on clay) + NH^(aq) £ NH^(on clay) + Na+(aq)
The selectivity coefficient can be written
rNn,[Na+1
Ksel
WV
104
-------
in which the bracketed quantities are the measured solution concentrations and
the r are concentrations of ion i in or on the solid phase expressed as
milliequivalents per gram of dry solid. Because the main adsorbing solids
are clays it was expected that the measured CEC would be independent of solu-
tion conditions over the range of interest. Because of the large amount of
data required, and the practical nature of these objectives, no attempt will
be made to obtain true thermodynamic quantities for the exchange reactions.
A new technique for simultaneous CEC and exchangeable cation determina-
tions was adapted to wet cores of poorly sorted aquifer materials. This method
is based on the very high affinity of the Ag-thiourea complex ion for soil col-
loids, which allows complete displacement of exchangeable ions at low (0.005M)
silver concentrations. The total uptake of silver determined by difference is
used to calculate the CEC. The concentrations of exchangeable cations re-
leased are determined in the same solution. Flame atomic absorption is used
for the Ag, Na, K, Mg, and Ca measurements.
The procedure is attractive for several reasons. It is direct and rapid
and the reproducibility is good. The use of a displacing cation unlikely to
be present in the soil samples permits direct analysis for all major cations
of interest, except ammonia which must be measured in an independent experi-
ment.
By combining a measurement of surface concentrations with known solution
compositions at equilibrium, effective selectivity coefficients can be deter-
mined. A series of measurements was made over a variety of solution composi-
tions. Sieved aquifer materials (usually still wet) are shaken for 24 hours
with electrolyte, filtered through a 0.05 um membrane, and then shaken for
12 hours in 0.01M AgNO^ with 0.1M thiourea (100 ml). After centrifugation an
aliquot of centrate is removed, combined with the filtrate from the previous
step, and analyzed for Na, K, Mg, Ca, and Ag. Surface concentrations (T-values)
are expressed as milliequivalents per gram of dry solids. Experiments were
carried out on 12 and P4 cores, at low and high ionic strength, and with and
without ammonia. The results are summarized in Table 18.
The values of the total bulk cation-exchange capacity range from 0.04 to
0.06 meq/g, slightly less than half of the value found for the -200 mesh
fraction of an aquifer core obtained near Well II. The selectivity coeffi-
cients for the exchange of calcium and magnesium are:
105
-------
TABLE 18
Exchange Coefficients and Cation-Exchange Capacity
Selectivity Coefficients
Exper-
. //
iment'
Description
(< 0.02 meq/1
nh4-n
unless noted)
^ore
Na ->
< 2 mm
frac-
tion
Mg
bulk
Na -*
< 2 mm
frac-
tion
Ca
bulk
Mg ¦+ Ca
Cation-
Exchange
Capacity
meq/g
Low Ionic
Strength
4.7
P4
125
160
184
236
.462
5.91x10"2
4.8
124
159
183
235
.459
5.86 "
4.9
2 meq/1 NH^-N
P4
132
169
201
257
.431
5.83 "
4.10
132
169
201
257
.431
5.76 "
5.4
P4
140
179
219
280
.409
5.90 "
5.5
139
176
212
271
.430
5.81 "
5.1
12
135
203
200
302
.456
3.92 "
5.2
133
201
198
298
.451
4.06 "
High Ionic
Strength
5.3
12
136
204
216
326
.396
4.19 "
4.5
P4
120
153
183
234
.430
5.96
4.6
P4
123
157
185
237
.442
6.05 "
Kinetic
Experi-
ments
Equilibrated
with electrolyte
for 24 hours
5.4
P4
140
179
219
280
.409
5.9
5.5
P4
139
176
212
271
.430
5.81 "
5.6
Equilibrated for
9 hours
P4
135
173
204
261
.438
5.65 "
5.8
Equilibrated for
2 hours
P4
127
162
191
244
.442
5.62 "
Sulfate &
Ca dissolu-
tion exper-
iments
5.7a
P4
141
180
211
270
.447
5.78 "
5.7b
P4
140
181
217
278
.416
[6.29] "
*
x ¦+ y means replacement of x by y.
'iow Ionic Strength = 0.015; High Ionic Strength = 0.5.
106
-------
r 1/2, +1
2+ + fa ^Na J
2Na(clay) + Ca ^ Ca(clay) + 2Na ; K - —-7— = 200
sel r [Ca ]
Na
r 1/2 r + ,
2+ . 4- Mg
2Na(clay) + Mg £ Mg(clay) + 2Na ; K = —= = 140
sei rNa[Mg ] 7
The selectivity coefficient for the exchange of ammonium with sodium was found
to be
V[Na+]
— = 3.83
rNa [NV
The selectivity coefficients imply that Na and Mg on clays will be re-
2+ +
placed by Ca and NH^ as the injection front passes through the aquifer
(Table 19) . The percentage of the total CEC accounted for by Ca rises from
33 to 78 percent, while that of ammonium ion rises from less than one to nine
percent.
TABLE 19
Estimated Surface Concentrations of Exchangeable Cations
Before and After Injection
Fluid
Composition
Surface Concentration
£
Initial
Final^
meq/g
Percent
I = 0.5
I = 0.02
Initial
Final
Initial
Final
Na
339
7.1
0.026
0.0031
43
5
Mg
100
0.88
0.014
0.0048
23
8
Ca
62.9
3.6
0.020
0.046
33
78
NH.
4
< 0.1
2.3
<0.001
0.0055
< 1
9
Total
0.061
0.059
100
100
Assuming that the aquifer material was in equilibrium with the formation
groundwater before injection began.
[
Assuming equilibrium with the injection water.
107
-------
The experimentally determined values for CEC and ammonia exchange selec-
tivity can be applied to the observed ammonia breakthrough curve obtained from
field data (Figure 23). It was estimated that 3.9 x 10^ equivalents of am-
monium ion were removed by the aquifer between 12 and P4.
According to the estimates of surface coverage and CEC this would require
6.7 x 10^ kg of aquifer solids. Finally, using the density of sample solids
in the P4 core, and an estimated effective pore volume of 43 m^ obtained from
the conductivity curve, a porosity estimate of 19 percent is obtained for the
reinjection zone between 12 and P4. In other words, the estimates of ammonia
exchange based on laboratory work agree with aquifer capacity estimates based
on field work, if it is assumed that the effective porosity of the aquifer is
19 percent. This value for the porosity seems reasonable, although it is some-
what lower than had been assumed previously [3,2]. An accurate, independent
estimate of porosity has not been possible. Estimates of porosity based on
the pore water content of core samples are of doubtful accuracy because the
pressure gradients during sampling may cause differential movement of pore
fluid into the tube.
PHASE FIVE - TREATMENT PLANT OPTIMIZATION
During the current project year the studies of treatment plant effective-
ness commenced as an integral part of the monitoring effort. The objective
is to obtain background information on the full-scale reclamation plant for
comparison with the predictions based on our pilot plant studies [3]. The
results are summarized under Phase Two. Optimization studies on treatment
plant reliability are being undertaken in the second half of the current
project year, as the reclamation plant is brought into continuous operation.
PHASE SIX - HYDRAULICS AND WATER-QUALITY MODELING
General Objectives
(a) To develop generalized mathematical/numerical models for describing
the movement of water and changes in water quality resulting from wastewater
injection. The models should be able to handle nonhomogeneities in the aqui-
fer characteristics, connectivity between aquifers and transient phenomena,
(b) To lay the groundwork for modeling a myriad of chemical and biological
reactions and processes, several water types, dispersion phenomena, and
108
-------
possible coupling between chemical and biological processes and the aquifer
characteristics, e.g. precipitation reactions and changes in permeability,
and coupling simplified forms of these quality models to the flow model.
Progress
We have focused on the development of numerical, finite-element
computer models because they can handle the real non-ideal flow patterns
found in the field aquifers [2,4].
Hydraulics
One of the goals of Phase Six was the development of state-of-the-art
contaminant transport models. Implicit in this goal is the assumption that
one can adequately model the flow of groundwater within the aquifers of the
Bay Area. If the flow is not modeled adequately then anticipated reactions can
only serve to compound the error and make quantitative interpretation of field
results impossible.
Here the past year's progress in modeling of porous media hydraulics is
reviewed. This phase of the work has reached its completion and with the
achievements to be mentioned we feel we have a sound base for quantitatively
investigating contaminant transport over part of the injection-extraction well
field. In the subsection about Hydraulics of Recharge in Phase Three above,
the hydrogeology of the area was reviewed. A great deal has been learned
since the predesign phase of the project, and this additional information
plays a decisive role in the question of whether or not we will be able to
successfully complete the contaminant transport modeling phase.
In attempting groundwater flow simulation of injection-extraction well
systems there are certain minimum requirements which a model must possess.
First, the model must be able to address nonhomogeneous fields. For practical
purposes this requirement eliminates analytical methods. A second require-
ment, for the particular site of interest, is the ability to include the ef-
fects of vertical leakage between adjacent aquifers. This requirement has
not turned out to be as important as originally thought. Finally, and this
is the biggest obstacle to be overcome, a method must be devised for handling
the singular nature of flow in the immediate vicinity of wells.
The following is a list of the major accomplishments over the past
year:
109
-------
1. We obtained a standard finite-element code from George Pinder at
Princeton University. This code had within it the ability to in-
clude leakage from an adjacent aquifer.
2. Functional coefficients, as described by Pinder, Frind and Papadopulos,
were incorporated into the code. This allowed the continuous per-
scription of nonhomogeneous parameters, such as transmissivity, over
the simulation area.
3. A technique was developed for modeling groundwater flowfields con-
taining point singularities (wells in a two-dimensional flowfield).
The technique consists of embedding a Green's function, which
exactly describes the flow in the vicinity of the well, within the
finite-element method. The Green's function cancels the effects of
the well and leaves a "regular" (Cq) problem for solution by the
finite-element method. Then, the finite-element solution and
Green's function are superposed to describe the potential and
velocity fields. This technique yields excellent accuracy through-
out the field.
4. A technique was devised for aiodeling multiaquifer systems whereby
the aquifers were coupled through their leakage terms. This quasi
three-dimensional model yielded very little to the present effort
and was disbanded.
5. A method was devised whereby the continuous basis function expansion
of the finite-element solution was used to generate on-line contour
plots of the output. This greatly simplified interpretation of the
finite-element solution.
6. The continuous basis function expansion of the potential (hydraulic
head) was used to generate a continuous velocity field through
differentiation and averaging over adjacent elements. This velocity
field, when combined with that obtained from the Green's function,
was used in the contaminant transport model. Convergence in magni-
tude to the exact velocity field is very rapid, though convergence
to the exact direction of the velocity vector lags behind.
7. From the derived continuous velocity field a system of streamlines
were generated. Integration along the streamlines gave times of
travel to any point in the domain for a non-dispersive fluid. In
particular, by finding the times of travel along various streamlines
110
-------
between the injection and extraction wells, a graph of concentration
of injected water in the extraction fluid could be derived. While
dispersion will have a large effect on the initial breakthrough time,
the results are still of great interest.
These achievements provide a sound base for contaminant transport model-
ing of the Il-El doublet pair. The description of the flowfield is very ac-
curate, notably in the immediate vicinity of wells. The framework is general
enough for analysis of confined, nonhomogeneous (even anisotropic) leak
aquifer systems with wells.
Water-Quality
The original numerical, finite-element contaminant transport model, which
was implemented during the first year of the project, has been successfully
modified to account for first-order decay and cation exchange. There are
currently two versions of the contaminant transport model:
a) Single species undergoing first-order decay.
b) Ttoo-species ion exchange with the possibility of first-order decay.
Here,
1. the ion-exchange reactioif is assumed to be governed locally by
equilibrium chemistry;
2. each species exists in both a mobile (aqueous) and immobile
(exchanger) phase; either phase may undergo first-order decay;
3. the equilibrium coefficient is assumed independent of species
concentration;
4. there are no activity corrections due to ionic strength variation.
The two versions of the transport model have been tested and verified for
certain simplified flow regimes which possess analytical solutions.
The nonlinear terms in the ion-exchange transport model have been sub-
jected to a preliminary study. A simple predictor-corrector scheme seems to
be a satisfactory method of dealing with the nonlinear differential equations.
Finally, the finite-element methodology was modified to account for the mass-
flow type of boundary conditions which are appropriate at an injection well
location.
Between the present (April 1978) and the end of this second year of work,
we anticipate doing the following:
a) A study to identify field-site dispersion coefficients, will be con-
ducted. This will include:
111
-------
1. Review of the literature pertinent to both the physical signifi-
cance of hydrodynamic dispersion and the optimal determination of
field parameter values, which are crucial elements of the trans-
port model.
2. A radioactive tracer study at the 12 injection site in April.
The data from this experiment will be utilized to identify dis-
persion coefficients according to the optimal methods determined
above. Our new understanding of the hydraulics at 12 (see the
section on Hydraulics of Recharge under Phase Three) will be a
key factor here.
b) The cation-exchange model will be modified to incorporate an array of
exchanging species and ligand complexation. Equilibrium coefficient
variations and ionic strength corrections will be incorporated if
deemed necessary by Phase Four investigators. We will then run our
computer model and compare its output with the results of the 12
pilot injection operation.
c) The equilibrium-modeling methodology of the cation-exchange model will
be extended in a straightforward fashion to the case of trace metal
and trace organic adsorption.
112
-------
VI. FUTURE PLANS
The injection pilot study begun in the first half of the second budget
period is continuing. We are emphasizing studies on the transport, biode-
gradation, and adsorption of those organic substances that appear to move
most rapidly through the aquifer. These include the trihalomethanes, tri-
chloroethylene, tetrachloroethylene, and carbon tetrachloride, as well as
chlorobenzene, styrene, and naphthalene.
Tracer Studies
Field studies of the travel times of injected water to the observation
wells surrounding Well 12 are being conducted using radioactive tracers to
confirm the earlier estimates based on conductivity measurements. The
qq q 9
tracers being used are Te , Br and tritium.
Transport of Organic Contaminants
In conjunction with the tracer tests, slugs of trace organic contaminants
and of virus are being injected. Samples for organic characterization will
be taken at Observation Well P4 at frequent intervals during several days,
while the monitoring for the radioactive tracer is in progress.
In the first experiment we will inject a conservative radioactive tracer
followed by an organic "spike" containing 4 g each of chloroform, carbon
tetrachloride, trichloroethane, trichloroethylene, dichlorobromomethane,
tetrachloroethylene, dibromo chloromethane, and bromoform. The organic
solutes will be dissolved in 500 ml methanol to increase the miscibility in
water. We expect the peak concentration of 10 yg/1 to 100 pg/1 to be ob-
served at Well P4 within fifty hours after injection. The concentration
responses will be compared to that of the conservative, radioactive tracer.
From the delay and attenuation of the peaks, we can estimate the capacity of
the aquifer to smooth fluctuations in the concentrations of these contami-
nants, as well as the approximate field capacity for adsorption.
Transport of Viruses
Concurrent with the injection of radioactive tracer and organic trace
contaminants, we plan to introduce a spike of viruses into the injection water.
The spike will include sufficiently large quantities of bacteriophage, polio
113
-------
virus, and ECHO virus so that these viruses can be detected at Well P4 if the
attenuation is a factor of ten or less. Three sample volumes of 1000 gallons
from Well P4 will be taken one, two, and five days after the spike injection
and will be analyzed for these viruses.
Laboratory Studies of Adsorption and Biodegradation
Laboratory studies of the adsorption equilibria of organic trace con-
taminants on aquifer materials have been undertaken. We are studying the
adsorption of CLSA components such as chlorobenzene, dichlorobenzene, and
trichlorobenzene isomers and naphthalene on bulk samples of cores obtained
at Well El in the Palo Alto Baylands. Adsorption isotherms are being deter-
mined for the above compounds in the range of concentrations from 1 to 100
yg/1. These results will add to our understanding of retention capacity and
transport dynamics in the aquifer.
Laboratory studies of biodegradation in the yg/l-concentration range are
continuing. Special attention is being devoted to the degradation of naph-
thalene to confirm the hypothesis based on field observations that naphthalene
is degraded to a limiting concentration of approximately 0.1 yg/1 in the
aquifer environment.
Full-Scale Demonstration of Injection-Extraction
Preparations are being made for the research to be conducted in the field
in connection with the full-scale demonstration of injection-extraction. This
program is scheduled to begin in the latter half of the current budget period,
in June 1978.
The injection-extraction well pair Il/El has been chosen for this demon-
stration. The location of the wells is shown in Figure 2. The principal
reason for the choice of Il/El is the relative homogeneity of the aquifer in
that subregion compared to the rest of the well field.
Reclaimed water will be injected into and extracted from the lower (15-m)
aquifer. Water also will be from the upper (8-m) aquifer at II at a rate
equal to 10 percent of the injection rate to avoid surface flooding. The
steady-state injection rate at a well head gauge pressure of 103 kPa (15 psig)
is predicted to be 9.5 x 10~^ m^/s (150 gpm). Assuming ideal, homogeneous
aquifer properties and no clogging, it will take approximately two months for
the first injected water to appear at the extraction well El. It is estimated
that after six months, approximately half of the water being extracted will be
of injection origin.
114
-------
The proposed observation network is shown in Figure 34. There are exist-
ing observation wells completed in the lower aquifer at distances of 15 m,
40 m, and 150 m from II, shown in Figure 2 as Wells S23, S24, and 522, respec-
tively. This is the most detailed coverage in the SCVWD's monitoring network.
However, it is not deemed sufficiently dense for the purposes of Stanford Uni-
versity's monitoring program. Therefore, it is proposed to install three
additional piezometers at distances of 10 m, 20m, and 40 m from II. These
piezometers, designated P5, P6, and P7 in Figure 6, will lie approximately on a
line from II to S22. Observation piezometers on the direct line Il/El are not
feasible because a golf-driving range is being constructed that would hinder
access and endanger project personnel.
The estimated travel times from the injection point to the observation
wells are summarized in Table 20. Thanks to the higher rate of injection, as
compared to 12, it will be possible to sample groundwater corresponding to a
time of travel of as little as 3 hours.
TABLE 20
Estimated Travel Times from II to Nearby Observation Wells
Distance
m
Travel Time*
SCVWD Wells
S23
16
7 hours
S24
43
51 hours
S22
163
30 days
Proposed Piezometers
P5
10
2.8 hours
P6
20
11 hours
P7
40
45 hours
Extraction Well
El
300
A
Calculated assuming injection rate = 9.5 x 10
2 m; porosity = 0.3.
nrVs; aquifer thickness =
The monitoring work will encompass the full range of water-quality param-
eters that can be determined quantitatively, including trace contaminant anal-
ysis and virus assays.
115
-------
X
X INJECTION/EXTRACTION WELL /
© MONITORING WELL (SCVWD) f
O SAMPLING PIEZOMETER
SCALE:
0
1 ¦ 1 ¦ ¦ * 1 ¦ ¦ 1
meters
/
100 200
' .1 I In. I I I I I li.l
CITY OF PALO ALTO GOLF COURSE
P5 S23
P7 —I^oOXll
FENCE
9
S24
EMBARCADERO ROAD
Figure 34. Layout of wells for proposed study at Il/El
116
-------
The principal objectives will be: to obtain quantitative data regarding
water-quality changes that occur during passage through the aquifer; to gather
evidence that transformation processes such as adsorption, biodegradation, ion
exchange, oxidation/reduction, and precipitation/dissolution reactions occur
in the aquifer; to estimate the rate of movement of contaminants through the
aquifer relative to the velocity of the injected water; and to estimate the
field capacity of Che aquifer for retaining specific contaminants. These ob-
jectives will be fulfilled by comparing the concentrations of selected contami-
nants in the injection water and in groundwater samples from observation wells,
emphasizing trace organic contaminants and viruses.
117
-------
VII. PROJECT PUBLICATIONS
McCarty, P. L., R. Schertenleib, and S. Niku, Preproject Water Quality Evalu-
ation for the Palo Alto Water Reclamation Facility, Technical Report No.
206, Civil Engineering Department, Stanford University (April 1976).
Niku, S., Laboratory Studies for Evaluation of Palo Alto Water Reclamation
Plant, Thesis for Engineer Degree, Civil Engineering Department, Stanford
University (June 1976).
Pinkos, T., Seawater Intrusion at the Proposed Palo Alto Reclamation Site,
Thesis for Engineer Degree, Civil Engineering Department, Stanford Uni-
versity (August 1976).
Schertenleib, R., Laboratory Investigations for the Palo Alto Water Reclama-
tion Plant, Thesis for Engineer Degree, Civil Engineering Department,
Stanford University (November 1976).
Zaghi, N., Effect of Injection-Production Doublets in Shielding Coastal
Aquifers from Brine Intrusion, Ph.D. Dissertation, Department of Petro-
leum Engineering, May 1977.
Zaghi, N., M. Tariq, F. G. Miller, and H. J. Ramey, Jr., "Shielding Charac-
teristics of Injection-Production Doublets in Steady Flow Fields,"
ASCE Hydraulics Specialty Conference, Texas A&M University, August
10-12, 1977.
Charbeneau, R. C., and R. L. Street, "Modelling Groundwater Flowfields Con-
taining Point Singularities," submitted to Water Resources Research, 1977.
Roberts, P. V., P. L. McCarty, and W. M. Roman, "Direct Injection of Reclaimed
Water into an Aquifer," accepted for publication, J. Env. Eng. Div.,
ASCE, 1978.
Roberts, P. V., J. 0. Leckie, P. L. McCarty, F. G. Miller, G. A. Parks,
H. J. Ramey, Jr., R. L. Street, L. Y. Young, and M. Reinhard, Ground
Water Recharge by Direct Injection of Reclaimed Water in Palo Alto;
First-Year Summary Report, Technical Report No. 225, Civil Engineering
Department, Stanford University (February 1978).
Rittman, B. E., and P. L. McCarty, "Variable-Order Model of Bacterial,
Fixed-Film Kinetics: A Practical Solution for Deep Biofilms," submitted
to J. Env. Eng. Div., ASCE, 1978.
118
-------
VIII. PROJECT PERSONNEL
STANFORD UNIVERSITY, STANFORD, CALIFORNIA 94305
Dyche, Janis
Leckie, James 0.
Umana, Alvaro
Kruger, Paul
McCarty, Perry L.
Rittmann, Bruce
Urbassik, Mark
Naylor, Anthony
Parks, George A.
Marshall, Steve
Trepathy, Vijay
Reinhard, Martin
Nguyen, Huong
Schreiner, Joan
Roberts, Paul
Jones, David
Hopkins, Gary
Street, Robert
Charbeneau, Randy
Valocchi, A1
Civil Engineering Dept.
(415-497-3504)
Civil Engineering Dept.
(415-497-2524)
Civil Engineering Dept.
(415-497-0315)
Civil Engineering Dept.
(415-497-4123)
Civil Engineering Dept.
(415-497-3504)
Civil Engineering Dept.
(415-497-0315)
Civil Engineering Dept.
(415-497-0315)
Civil Engineering Dept.
(415-497-0308)
Applied Earth Sci. Dept.
(415-497-3768 or 2747)
Applied Earth Sci. Dept.
(415-497-2747
Applied Earth Sci. Dept.
(415-497-2747)
Civil Engineering Dept.
(415-497-0308)
Civil Engineering Dept.
(415-497-0308)
Civil Engineering Dept.
(415-497-0308)
Civil Engineering Dept.
(415-497-1073)
Civil Engineering Dept.
(415-497-0315)
Civil Engineering Dept.
(415-497-0315)
Civil Engineering Dept.
(415-497-3921)
Civil Engineering Dept.
(415-497-1478)
Civil Engineering Dept.
(415-497-1478)
Project Secretary
Water Chemistry and Geochem.
Transport Tracing
Principal Investigator
Biological Processes Treatment
Water Quality Analysis
Geochemistry and Water Chem.
Organic Characterization
Project Manager, Process Eng.
Field Monitoring
Modeling of Transport
119
-------
Young, Lily Y.
Dickson, David
Civil Engineering Dept.
(415-497-3505)
Civil Engineering Dept.
(415-497-1478)
Biological Interactions
SCHOOL OF PUBLIC HEALTH, UNIVERSITY OF CALIFORNIA, BERKELEY, CA 94720
Cooper, Robert 57-642-1136 Virus Analysis
(415-642-1136)
Brown, Larry
Straube, David
Lysmer, Delores
57-231-9531
57-231-9531
57-642-0761
SPONSORING ORGANIZATIONS
ROBERT KERR ENVIRONMENTAL RESEARCH LABORATORY, ENVIRONMENTAL PROTECTION
AGENCY, ADA, OKLAHOMA 14820
Scalf, Marion R. (405-332-8800) Project Officer
DEPARTMENT OF WATER RESOURCES, STATE OF CALIFORNIA, SACRAMENTO, CA 95814
Kleine, Charles
(916-445-0831/322-1571) Project Officer
COOPERATING ORGANIZATIONS
SANTA CLARA VALLEY WATER DISTRICT, 5750 Almaden Expressway, San Jose, CA 95118
Fowler, Lloyd
Beaudet, John
Roman, William
Johnson, Ron
(415-265-2600) Chief Engineer
(415-265-2600) Project Coordinator
(415-265-2600/322-9506) Project Manager
(415-265-2600) Data Reporting Coordinator
PALO ALTO WATER QUALITY CONTROL PLANT, 250 Hamilton Ave., Palo Alto, CA 94301
Remmel, Ray
Miks, William
Nice, Ralph
Facilities Design
Jenks, John H.
Sheahan, Tom
(415-329-2598)
(415-322-9506)
(415-329-2598)
Jenks & Adamson, Engrs.
543 Byron Street
Palo Alto, CA 94301
(415-326-2570)
Superintendent
Reclamation Plant Chief Oper.
Chief Chemist
Reclamation Plant Design. Eng.
c/o Brown & Caldwell Geologist, Well Field Design
P. 0. Box 83 Arroyo Annex
Pasadena, CA 91101
120
-------
IX. REFERENCES
1. Jenks, J. J., A Program for Water Reclamation and Groundwater Recharge
Serving the Palo Alto Bayfront Area, Report to the Santa Clara Valley
Water District, October 1974.
2. Roberts, P. V., J. 0. Leckie, P. L. McCarty, F. G. Miller, G. A. Parks,
H. J. Ramey, Jr., R. L. Street, and L. Y. Young, Groundwater Recharge
by Injection of Reclaimed Water in Palo Alto, Department of Civil Engi-
neering Technical Report No. 225, Stanford University, February 1978.
3. McCarty, P. L., R. Schertenleib, and S. Niku, Preproject Water Quality
Evaluation for the Palo Alto Water Reclamation Facility, Technical
Report No. 206, Civil Engineering Department, Stanford University,
April 1976.
4. Charbeneau, R. C., and R. L. Street, "Modelling Groundwater Flowfields
Containing Point Singularities," submitted to Water Res. Res., 1977.
121
------- |