United States
Environmental Protection
Agency
Office of
Emergency and
Remedial Response
EPA/ROD/R09-88/019
September 1988
&EPA Superfund
Record of Decision:
Indian Bend, AZ
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50272 ., ,
REPORT DOCUMENTATION
. PAGE
1. REPORT NO.
EPA/ROD/R09-88/0l9
2..
3. Recipient's AccesSion No.
4. Title and Subtitle
SUPERFUND RECORD OF DECISION
I
~I~dian Bend~ AZ .
F1rst Remed1al Act10n
50 Re,~ ?~I; 8 8 .
6.
7. Author(s)
8. Performing Oraanizatlon Rept. No.
9. Performing O,.anizatlon Name and Address
10. Project/Task/Work Unit No.
._,. -- ~--
11. Contract(C) or Grant(G) No.
(C)
(G)
'-'--' ------------.--
12. SpOnsoring Organization Name and Address
U.S. Environmental Protection
401 M street, S.W. .
Washington, D.C. 20460
13. Type of RepOrt & Period Covered
Agency
800/000
14.
15. Supplementary Notes
16. AbstraCt (Limit: 200 words)
The Indian Bend site (IBW) encompasses 13 square miles in Scottsdale and Tempe,
Arizona. The portion of the site addressed in this remedial action, t.he scot.t.sdale
Ground Water Operable Unit, covers approximately eight square miles wi~hin the -
Scottsdale city limits. The Indian Bend Wash runs north - south through the site and
supports recreational uses. Ponds in the wash were used as a water qollection system;
however, ground water was no longer discharged to the wash when-contamination was
detected in the ponds. The land use of this area is primarily residential with
approximately 30 percent used for commercial,' light industrial and. developed
recreational purposes. The resident population of Scottsdale- was 115,500 in 1986, and
is expected to reach 129,500 by 1990. Approximately 70 percent of the City of
Scott.sdale's municipal water current-ly, is supplied by ground water. -Future populat.ion
growth will' requir:e great.er use of ground water resources, part-icularly from t,he
contaminated areas. In 1981, TCE was discovered in the ground water from_several City
of Scottsdale and City of Phoenix municipal wells at concentrations exceeding the
Arizona Department of Health Services action levels. Several facilities within the site
boundaries have records of past use of TCE.in their. manufacturing process. Seven of the
12-city wells within the boundaries of this op~rable unit have levels of VOCs exceeding
(See Attached Sheet) .
17. Document Analysis a. Descrtpto....
Record of Decision
Indian Bend, AZ
First Remedial Action
Contaminated Media: gw
Key Contaminants: VOCs
b, Identifiers/Open.Ended Terms
(TCE, PC E)
c. C05ATI Field/Group
~ Availability Statement
19. Security Class (This RepOrt)
None
21. No. of Pages
54
20. S8Cu~8I!SS (ThIs Pap)
22. Price
(5.. AN51-Z39.18) .
5ee InstructIons on Reve,.e
OPTIONAL FORM 272 (4-77)
(Formerly NTI5-3S)
Department of Commerce
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~PA/ROD/R09-88/019
Indian Bend, AZ
First Remedial Action
16.
ABSTRACT (continued)
primary. drinking water standards. One of the seven is equipped with a VOC treatment
facility and is used as a potable water supply source. The other six wells are
currently offline. The site was placed on the NPL in 1982. The primary contaminants of
concern affecting the ground water are VOCs including TCE and PCE.
The selected remedial action for this operable unit of the site includes: extraction
of ground water by pumping City of Scottsdale Wells No. 31, 71, 72 and 75 at a minimum
of 75 percent. of ~heir histotical capacities; treatment of ground water using.packed
column aeration to transfer ~he VOCs from the water to air, with vapor phase GAC
adsorption to remove VOCs from the air waste stream; and distribution of the treated
water to the City of scottsdale municipal water system. This remedial action addresses
ground water contamination only in the Middle and Lower Alluvium Units beneath the north
portion of IBW within the Scottsdale City limits. Contamination beyond these limits in
the ground water of the Upper Alluvium limit and in the soil will be addressed in .
subsequent remedial actions for the IBW site. The estimated total capital cost for this
operable uriit is $4,008,000 wit.h an est.imat.ed annual O&M cost of $520,000.
~.: ':~3J:::")'~~-:,:,;"~:;>":"~:'~ ';":-:/~:<":r:.:~;".~,;t{ ?:;"':T: :c<:.~.:..~.{':::'.: :':."'~;';'" . . '." ." ~::. :::' '.:,: '':::<;'.~:::~'~..''::,:~-':::.' ,~. .-:.~,:, t':.'
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-------
FINAL
RECORD OF DECISION
SCOTTSDALE GROUND WATER OPERABLE UNIT
INDIAN BEND WASH
. SUPERFUND SITE
SCOTTSDALE, ARIZONA
September 1988
RDD63592.RA
Work Assignment 029-9L20.0
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(.
CONTENTS
I
II'
III
IV
v
VI
VII
paqe
Declaration for the Record of Decision
Site
Purpose
Basis
Description
Declaration
Record of Decision Concurrence Page
I-I
I';'l
I-l
I-I
I-I
I-3
I-4
Site Description
II-l
Site History and Background
Site History
Site Characterization
Receptors .
Toxicity
III-l
III-I
III-l
III-2
III-3
Enforcement History
IV-l
Community Relations History
Alternatives Evaluation
Listing of Alternatives
Screening 9f Alternatives
Evaluation of Alternatives
V-I
VI-l
VI..;l
VI-2
VI-6
Selected Remedy
Description
St~tutory Determinations
VII-I
VII-l
VII-2
VIII References
'VIII-I
AppendixA. . Index of Administrative Record
Appendix B.
TABLES
III-l
VI-l
VI-2.
VI-3
VII-l
VII-2
Response. Summary'
Summary of Exposure Routes and Risks
Percent TCE Removed
III-S
VI-3
Screening of Vo,C Removal Technologies
VI-4
. .
Water Quality Design Criteria for Evaluation
of Treatment Technologies'
Preliminary Cost Estimates
. VI-7
VII-2
State and Federal ARARs and Other Cri,teria'
VII-3
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-------
I .
CONTENTS
(continued)
FIGURES
I-l
I-2
. III';"I
III-2
Follows
Page
Project Location Map
I-l
City of Scottsdale Well Locations
VOC Contaminated City of Scottsdale Wells
I-2
'III-2
Potential Future Exposure Pathway and
Receptor Summary
III-3
RDDlR741002'
I '
I
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I.
DECLARATION FOR THE RECO,D OF DECISION
SITE
Indian Bend Wash (IBW) Superfund site, Scottsdale Ground
Water Operable Unit, Scottsdale, Arizona. .
PURPOSE
In accordance with the National Contingency Plan; the Com-
prehensive Environmental Response, Compensation, and Liabil-
ity Act of 1980 (CERCLA); and the Superfund Amendment and
Reauthorization Act of 1986 (SARA), potential remedial.
actions have been developed for the Scottsdale Ground Water
Operable. Unit. This decision document represents the
selected remedial action. The Operable qnit has been devel-
oped to provide potable water for the City of Scottsdale and
addresses ground water contamination only in the Middle and
Lower Alluvium Units beneath the north portion of IBW within
the Scottsdale city limits (see Figure I-I). Contamination
beyond these limits in the ground water of the Upper
Alluvium Unit and in the' soils will be addressed' separately .
in subsequent operable units for the IBW site. The Arizona
Department of Water. Resources and the- Arizona Department of
Environmental Quality concur with the selected remedy.
BASIS
This decision is based on the administrative record for the
IBW site, which includes the results of the: Remedial ,Inves-
tigation and the Scottsdale Ground. Water Operable Unit Feasi-
bility Study. Appendix A identifies the items contained in
the Administrative Record upon which the selection of the
remedial. action is based.
DESCRIPTION
The IBW study. area lies in the southwestern Paradise Valley
encompassing approximately 13 square miles in Scottsdale and'
Tempe, "rizona. The study area is bounded on the,north by
Chaparral Road, on the east by Pima/Price Road, on the south
by Apache Boulevard, ,and.on.the; west by Scottsdale/Rural
Road. . The Salt River, flows thr,ough the study area from east
to west, physically separating the site into north and south
areas. . The area. south of the river is' suspected to have
other so~rce areas than those suspected in the north, and is
being considered for a separate operable unit by the U.S..
Environmental Protection Agency (EPA). .
An Operable Unit is a discrete part of an overall site and
, can be examined separately if the remedial action fo~ the
RDD/R91/001
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SHEA BLVD.
SCOTTSDALE WATER RESOURCES
PLANNING BOUNDARY',
.1::::;::::::::::::::::::::1 INDIAN BEND WASH SUPERFUND
STUDY AREA
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SUPERSTITION FREEWAY
, RDD6,3592.RA AUGUST 1988
FIGURE 1-1 -:. .
PROJECT LOCATION MAP .."
INDIAN BEND WASH SCOTTSDALE ROD
-------
, 0
Operable Unit can be done expeditiously, is cost-effective,
controls contaminant sources o.r migration, and is consistent
with the final site remedy. The Scottsdale Ground Water
Operable Unit is the portion of the study area within the
Scottsdale city limits. There are 12 city wells within the,
Operable Unit, 7 of which ~ave level~ of volatil~ organic,
compounds (VOCs) exceeding primary drinking water standards.
FigureI-2 shows the locations of the 12 wells. Presently,
one of the seven contaminated wells is equipped with a VOC'
treatment facility and used as a potable water supply
source. The remaining six are 'currently offline. Wells
No. 31, 71, 72, and 75 are being ,considered 'for treatment'
under this Operable Unit. 'In addition, several monitor
wells screened in the'Middle and Lower Alluvium Units have
higher concentrations of VOCs than the city wells.
The Scottsdale Ground Water Operable Unit'has been developed
to address the following objectives: '
o
Protect public health and the' environment by
protecting una'ffected wells from VOCs.
Provide a mechanism for the long-term management
of' the VOC-affected gro.und water in order to
improve the regional aquifer's suitability for
potable use by the City of Scottsdale.
o
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, '
Provide a potable water source for the City within'
the constraints. of projected water demands while,
utilizing existing facilities to the maximum
extent f~asible.'" ,
One of the remedial actions developed to meet these objec-
tives involves ext~acting ground. water from the Lower and
Middle Alluvium Units by pumping existing municipal wells'
that are currently not in ~se and are screen~d in these
units. .' "
The selected remedial action meets' the abov:e objectives.
The major' components of the remedy involve pumping'
Scottsdale Wells No. 31, 71, 72, and 75 at 75 percent of
their historical capacities. Preliminary analysis indicates,
this pumping regimen will reduce the mass of contaminants '
and volume of contaminated ground water in the Lower and
Middle Alluvium Units. Once the system is operating and.:the
effectiveness of removing VOCs ,from the Lower and Middle
Alluvium' Units is evaluated,. additional ,pumping of these
wells and the installation and pumping of additional extrac;-
tion wells will be considered. Levels,of, contaminants in ,
the extracted ground water will be reduced to meet drinking
water standards. Air stripping is the preferred treatment
alternative to meet these criteria, and will include air
emission controls. The treated water will be delivered, to
the City of Scottsdale municipal water system. '
RDD/R91/001
I-2
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PARADI'SE" VAL EY
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LEGEND
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CITY WELL OR SR
WELL USED BY CI.
CITY WELL WITH VOC
TREATMENT.
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. AFFECTED CITY WEL1.S
~ - -' SCOTTSDALE CITY
< LIMITS
:IE """ SUPERFUND STUDY
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CITY OF SCOTTSDALE
WELL LOCATIONS
INDIAN BE~D WASH SCOTTSDALE ROD
RDD63592.RA AUGUST 1988
:.0>. ....~ . '-;.'" :
-------
DECLARATION.
The selected remedy for this Operable Unit is protective of human
health and the environment, mee~sFederal and State requirements
that are applicable or relevant and appropriate, and is cost-
effective. This remedy satisfies the preference for treatment
that reduces toxicity; mobility,'or volume as a principal ele-
ment. .AII sUbstantive permit requirements 'will be met during im-
plementation of this remedial action. . It is determine that the
rem~dy for this Operable Unit uses permanent, solutions and alter-
native treatment'technologies to the maximum extent practicable.
The Arizona Department of Environmental Quality and the Arizona
Department of Water Resources have concurred with the remedy
presented in this document.
q,;",9~
Date
q . 2.0. e'~ .
Date
:;:-7- ',:;>::,7~ :.\'" e",":';:' ":.;~'?'~ .' ~,~.!" --:.:r:.C_:"': ;,~<.'--;' .,' ::';.:::::':~~. : .:,:~~;,::~-~' ~::;'.. ':':.;':'.'~; c""":.~"o.; :'-.:":. ",
'Daniel'W. McGovern
Regional Administrator
Region IX .
d~w~
John W., Wise
Deputy Regional
R~9ion IX,
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-------
RECORD OF DECISION
CONCURRENCE PAGE
Site: Indian Bend Wash Superfund Site, Operable Unit,
Scottsdale, Arizona
The attached Record of Decision package for the Indian Bend
Wash Superfund Site, Operable Unit, Scottsdale, Arizona, has
been reviewed, and I concur with the contents.
Date Nancy Marvel
Regional Counsel
Office of Regional Counsel
U.S. Environmental Protection
Agency, Region IX
Date ..,' JeffZelikson
Director
Toxics & Waste Management Division
U.S. Environmental Protection
Agency, Region IX
Date Harry Seraydarian
Director
Water Management Division
U.S. Environmental Protection
Agency, Region IX
Date David P. Howe k amp
Director
Air Management Division
U.S. Environmental Protection
Agency, Region IX
Date' Norfa McGee
Acting Assistant Regional Administrator
Office of Policy and Management
U.S. Environmental Protection
Agency, Region IX
RDD/R91/001 1-4
-------
RECORD OF DECISION
CONCURRENCE PAGE
Site: Indian Bend Wash Super fund Site, Operable Unit,
Scottsdale, Arizona
The attached Record of Decision package for the Indian Bend
Wash Super fund Site, Operable Unit, Scottsdale, Arizona, has
been reviewed, and I concur with the contents.
?/ l-\ %% _ A x*~o^ J •
^ Nanc Marve
Date Nancy Marvel
Regional Counsel
Office of Regional Counsel
U.S. Environmental Protection
Agency, Region IX
Date Jd-ff <-2eli*-ron
Director
Toxics & Waste Management Division
U.S. Environmental Protection
Agency, Region IX
Date Harry Seraydanan
Director
Water Management Division
U.S. Environmental Protection
Agency, Region IX
Date David P. Howekamp
Director
Air Management Division
U.S. Environmental Protection
Agency, Region IX
Date Nora McGee
Acting Assistant Regional Administrator
Office of Policy and Management
U.S. Environmental Protection
Agency, Region IX
RDD/R91/001 1-4
-------
RECORD OF DECISION
CONCURRENCE PAGE
Indian Bend Wash Superfund Site, Operable Unit,
Scottsdale, Arizona'
The- attached Record of Decision packaqe for the Indian Bend
Wash Superfund Site, Operable Unit, Scottsdale, Arizona, has
been reviewed, and I concur w:ith the contents.
Site:
Date
Nancy Marvel
Reqional Counsel
Office of Reqional
U.S. Environmental
Aqency, Reqion IX
Counsel
Protection
Date.
Je.ff Zelikson
Director
Toxics , Waste Manaqement Division
U.S. Environmental Protection'
Aqency, Reqion IX
~J4;.1~ ~- -ra~ ~.
Harry Seraydar1an .'
. ~_p~rector .
~ater ManaqementDivision
U.S. Environmental Protection
Aqency, Reqion IX .
Date
David P. Howekamp
Director
Air Manaqement Division'
U.S. Environmental Protection
Aqency, Reqion IX
Date
Nora McGee, .' .
Actinq Assistant.Reqional Administrator.
Office of Policy and Manaqement
u.S. Environmental Protection
Aqency, Reqion IX
RDD/~9i"oOl
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1-4
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-------
RECORD OF DECISION
CONCURRENCE PAGE
Indian Bend Wash Superfund Site, Operable Unit,
Scottsdale, Arizona
The attached Record of Decision package for the Indian Bend
Wash Superfund Site, Operable Unit, Scottsdale, Arizona, has
been reviewed, and I concur with the contents.
S1 te.:
Date
Date
Date
gp?'/89
Date '
Date
"1\
....~
~'.
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. RDD/R91/001
Nancy Marvel
Regional Counsel
Office of Regional
U.S. Environmental
Agency, Region IX
Counsel
Protection
Jeff Zelikson
Director
Toxics , Waste Management Division
U.S. Environmental Protection
Agency, Region IX
Harry Seraydarian
Director
Water Management Division'
U.S. Environmental Protection
Agency, Region IX
~~..~
Director .
Air Management Division
U.S. Environmental Protection
/ Agency, Region IX
Nora McGee
Acting Assistant Regional Administrator
Office of Policy and Management
U.S. Environmental Protection
Agency, Region IX
I-4
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II.
SITE DESCRIPTION
The Indian Bend Wash site encompassE!s' approximately
13 square miles in Scottsdale and Tempe, Arizona (see
Figure I-1). The Scottsdale Ground Water Operable Unit area
covers approximately 8 square miles in the southeast portion
of the Scottsdale city limits. Approximately 70 percent of
the area is classified as residential. Approximately
23 percent is used 'for commercial and light industrial pur-
poses, with the remaining 7 percent as developed open spac~.
Land use patterns in the area are not expected to change.
The Indian Bend Wash itself runs north/south through the
site and supports recreational uses. In the past, the ponds
in the Wash were used as a water collection system. The'
water would eventually discharge to the G~and Canal. After
contamination was detected in the surface water of some of
the ponds, ground water was no longer discharged to the
Wash. Currently, the City of Scottsdale pumps water into
the ponds as needed to maintain the surface water for fish-
ing, where allowed, and for the aesthetic qualities it pro-
vides to the Wash. .
Scottsdale provides water. and sewer for most of its resi-
dents. The City relies on ground water for approximately
70 percent of its municipal supply, with the additional
30 perce~t supplied by surface water from the Central
Arizona Project. .
. .
RDD/R9l/002
\.
.RDD/R91/002
II-1
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. . ", "..:;. '. t. ..'. \:.'., ..., : ~... :.
-------
III.
SITE HISTORY AND BACKGROUND
SITE HISTORY
In 1981, trichloroethene (TCE) was discovered in the
ground water from several City of Scottsdale and City of
Phoenix municipal wells at concentrations exceeding Arizona
Department of Health Services action levels in effect at
that time. The contaminated wells included City of
Scottsdale Wells No.6 and 31,'and City of Phoenix Wells
No. 34, 35, and 36 (currently Scottsdale Wells No. 75, 72,
and 71, respectively). These, wells were removed from
potable use. Well No.6 was equipped by the city with a VOC
treatment system and returned to potable use in,1985.
IBW was added to the National Priorities List in 1982, and a
Remedial Investigation began in July 1984. . The Remedial
Investigation is being conducted by EPAin cooperation with
private companies and State and local agencies. EPA has
identified several facilities within the site boundaries
that have records of past use of TCE in their manufacturing
processes. Two of these facilities, Motorola and Beckman
Instruments, have been identified as Potentially Responsible
Parties and are participating in the RI/FS. .
The Remedial Investigation has focused on collecting ground
water, soil, and soil gas samples for chemical analyses, and
defining ground water flow in the study area. '
SITE CHARACTERIZATION
The climate of the Scottsdale area is characterized by long
hot summers and short mild winters. Climate information for
Phpenix, Arizona, indicates the annual average daily temper-
ature is 85°F for the high and 5soF for the low. Precipita-
tion is in the form'of rain and averages 7 inches per year.
Winds are predominantly f,romthe west at, 6 miles per hour
(Climates of the States, 1980). '
The IBW study area is underlain by alluvial sediments which
can be divided into three hydro stratigraphic units. Thes~
units consist of the Upper Alluvium Unit (UAU), the Middle
Alluvium Unit (MAU),and the Lower Alluvium Unit (LAU). The
UAU varies. in thickness: however, in the vicinity of the
study area, the thickness of the UAU is approximately 120 to
160 feet. The UAU consis~s primarily of sand, coarse gravel,
cobbles, and boulders in this area. Ground water occurs at
depths ranging from approximately 90 feet to,approximate1y
130 feet, with up to 40 feet of saturated thickness. The
saturated thickness of the unit changes with the time of
. year, but generally decreases to the north. Ground water in
the UAU appears to be flowing in a west-northwest 'direction.
'ROD/R8S/002
I I I-I .
.":.: :~:,' \'':'-,;-::'''i'~':;:' 7t-'-:': ,-::,~~:::.-.;.-.~,'- :;."";~;,'/7,..-:;:~'.:~..':.:.:~, ~"C'.~"F:,':'i:::r.:,(::'. ..:>~::t7:-"', ':.:' ':;.,~-;::: :::;:.:- . '!::-',;','~ .,-'-;'''':'-'';'.)',:~: :r" .<':;' ".'
:n.",- ':','''' ",'''', "'-;'","';:,':
...-.,. '~-;"';'- ~.'" ~~:
"; ....~~';':':'- 5' .:
'. '.~ ~". .
," ,,",.'
,'..",.:.
-------
I '
The MAU primarily consists of silt, clay, and interbedded
fine sands. Relatively thin la~ers of coarser deposits are
scattered throughout the unit. Ground water flow in the MAU
appears to be toward the north-northwest in the study area.
The thickness of the MAU ranges from approximately 360 to
660 feet. Water levels in wells perforated in the MAU occur
at'depths of 140 to 180 feet.
The LAU is less well' defined. Samples collected during moni-
toring well installation indicate the unit consists of moder-
ately to well-cemented sands and gravel. The depth of the
unit is not well defined: however, it is known that the LAU
is underlain by the Red Unit which consists primarily of
fanglomerate, conglomerate, and sandstone. The direction'of
ground water flow in the LAU is thought to be similar to that
of the HAU.
Water level data indicate that there is a downward~directed
vertical hydraulic gradient between the UAU and the MAU and
between the MAU and the LAU.
Ground water quality data indicate contamination at IBW from
various organic solvents, particularly TCE, tetrachloro-
ethene (PCE), l,l-dichloroethene (l,l-DCE), and 1,1,1-
trichloroethane (l,l,l-TCA). All of these chemicals have
been found in monitoring wells at concentrations exceeding
State' action levels. TCE is the most widespread contaminant
with a maximum reported concentration of 2,500 ppb from a
UAU monitoring well. The maximum concentration reported
from a Middle or Lower Alluvium monitoring well is 700 ppb.
TCE has been detected in several municipal wells at concen-
trations up to 390 ppb and from depths as great as 1,100
feet below land surface. "
Six City of. Scottsdale we.lls are affected by VOC contamina-
tion including TCE and lower levels of PCE, l,l-DCE and
chloroform. TCE is the only VOC quantified in samples'from
these wells at, levels- that exceed prim~ry drinking water
. standards. As mentioned earlier, six of the seven affected
wells are not currently ~perating and the seventh (City of
Scottsdale No.6) is equ~pped with a VOC treatment system.
Figure III-l shows the location of the contaminated City
, wells. .
"
RECEPTORS
ENVIRONMENT
The environment of the Scottsdale area encompassed by the
IBW site is primarily residential, commercial, and indus-
trial. There are no unique habitats or threatened or
endangered species. Vegetation of the area is ,typical of
residential and industrial areas for that geographic area.
RDD/R85/002
III-2
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-------
The Indian Bend Wash, which traverses through Scottsdale,
supports some wildlife, primarily fish and waterfowl. Some
native fish, such as the Gila sucker (Catostomas insignis)
and the roundtail chub (Gila robusta) live in the ponds
located along the Wash. . These ponds also supportpopula-
tions of largemouth bass (Micropterus salmoides) and carp
.(Cyprinus carpio)..
POPULATION
The resident population o£ Scottsdale was approximately
115,500 in 1986 according to the population projections
issued by the City of Scottsdale (1986). By 1990~ the resi-
dent population is expected to reach an estimated 129,500,
and 180,800 by. the year 2000 (City of Scottsdale, 1986).
Scottsdale also supports a sea~onal increase in population;
however, this transient population varies from year to year.
All City of Scottsdale drinking water wells currently' in use
for municipal supply meet applicable Federal and State
health standards. However, future population growth wili
result in greater usage of ground water resources,particu-
larly in the contaminated areas. If no action is taken at
this site and contamination migrates to areas that contri-
bute to municipal ground water supplies, use of the ground
water will result in a potential exposure to contaminants
through the means illustrated in Figure III-2.
TOXICITY
ORGANIC COMPOUNDS
This group of compounds includes most of the contaminants
identified at the IBW site. Several of these compounds--
carbon tetrachloride, chloroform, 1,1,1-TCA, PCE, and TCE--
may produce liver injury. Carbon tetrachloride and chloro-
form have more serious effects on the liver than TCE and PCE
(Doull et al., 1980). Carbon tetrachloride, chloroform, .
PCE, and TCE have been classified by the U.s. EPA Carcinogen
Assessment Group as probable human carcinogens (Group B2)
via ingestion (U.S. EPA, 1986).
Exposures to the above compounds through inhalation may
result in central nervous system depression, including anes- .
thesia. TCE has been used as an anesthetic (NRC"l977).
Other effects may include irritation of the mucous membranes
of the nose and throat and irritation to the eyes (NRC, 1980).
TCE and PCE are also classified 4S probable human carcinogens
(Group B2) by the Carcinogen Assessment Group via the inhala-
tion-route (U.S. EPA, 1986).
RDDlR8 5 / 00 2
III-3
:-: ';-:':;':::';'~::'.\>~~t':~': ..~. :.:'~",'~' .:.'~:-: :'.~' ~ '. ': ':~:-':.' ":. ~): -.:~':'~ ,:..
. :., ""'.'':.~'
-------
MEDIA
GROUNDWATER
DIRECT EXPOSURE PATHWAY" RECEPTOR
INGESTION BY RESIDENTS WHO USE
MUNICIPAL WATER FOR THEIR POTABLE
WATER SUPPLY
, ,
RDD63592.RA AUGUST 1988
. .'; '.':,~-~'!~\'.:;7:. '5'.:::~':~~" "i'- <. '';-'::' ':..-;-: ".- '.', ~..':'" ."~'~ '::. ::;:':;',:. ',:,:;,: -.'~ 1'~.-;~ :~....~. ;.~';'_:~. :'~"'~'~~"'.:':"_.~:.':'-.. >:
I NHALA TION OF VOLA TI LES STRI PPED FROM
. THE DRINKING WATER DURING IN~HOME
. USES SUCH AS BATHING AND COOKING
DERMAL CONTACT WITH CONTAMINATED
DRINKING WATER'
FIGURE 111-2 '
POTENTIAL FUTURE EXPOSURE
'PATHWAY AND RECEPTOR SUMMARY
. 'INDIAN BEND WASH SCOTTSDALE ROD
,"".,", '."'
":.' "c'.:
.._<:! ~s;~':.:. :;' ;:'-."":':>
-,- ','''.
: ...~;,:::.-~':..""" ~:.>:.'::~ ',': ~'~'. . .~ .~:!.\' ,:,;:~.< >~':.' :.> :'.-:,::"':
.~. ::::>?;':." ..:.';.~::...
.-:.,'
-------
Similar toxic effects to humans through inhalation and inges-
tion exposures are exhibited by l,l-DCE. This compound has
anesthetic properties~ and exposures to high concentrations
may cause nausea and vomiting (U.S. EPA, 1985).
RISK
Risk is a function of toxicity and exposure, both in terms
of the dose received and the duration of exposure. At pre-'
sent, there is no exposure to contaminated ground water above
Federal Primary Drinking Water Standards. However, future
use of the City of Scottsdale wells currently not used due
to contamination and future migration of the contaminants
could affect plant and animal life, and human exposure to
the contaminated ground water may result in excess lifetime
cancer risks as shown in Table III-I.
The risk associated with exposures to contaminated ground
water, particularly for future use scenarios, is a~4excess
lifetims cancer risk that may be as high as 3 x 10 to
1 x 10- due primarily to the pres~nce of PCE and TCE. This
assumes that an individual ingests 2 liters of water daily
for 3 months each year over the course of a 70-year life-
time. It is assumed that the 3 months constitute the peak
demand months of summer when surface-water supplies may' be
limited and ground water resources would be necessary.
Noncarcinogenic effects resulting from ingestion exposure to
l,l-DCE, PCE, zinc, and lead are of concern.
RDD/R85/002
RDD/R85/002
III-4
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. /:.-:".'::.::' ,::>~:7~.:~;"
..' "',"',
." '"
-------
Table III-l
SUMMARY OF EXPOSURE ROUTES AND RISKS
Medium
Ground water
Exposure Setting .
Residential—Potential Future
Exposure
Route
Ingestion
I
01
Results
The estimated excess lifetime cancer risk
from ingestion of ground water from the
Beckman monitor wells presents a 1 x 10
to 7 x 10 range of additive risk for
organic contaminants. A 1 x 10 excess
lifetime cancer risk was calculated for
arsenic; the MCL of 50 \iq/\ for arsenic
was not exceeded in this well. The daily
intake of lead resulted in a daily intake
that exceeded the AIC for the 18- to
70-age category. At this time, the lead
found in the ground water sample is not
believed to be the result of disposal
activities in the area. The concentration
of lead did not exceed the MCL of 50 iig/1.
For other noncarcinogens evaluated, there
does not appear to be an ingestion risk
based on the limited available data.
For the various municipal wells evaluated,
an estimated excess lifetime cancer risk
from ingestion presents a 1 x 10 to 6 x
10 range based on the organic contami-
nants with cancer potency factors. A 1 x
10 excess lifetime cancer risk was cal-
culated for arsenic; however, the MCL of
50 pg/1 was not • xceeded for any of the
wells.
There is no known ingestion risk due to non-
carcinogens from these wells based on the
limited available data.
The estimated excess lifetime cancer risk
from ingestion of ground water from the I:IJA
-------
-".}
',,".
'"
. .
,,':
-;:,
'~"J
.:.
";',::
'..<
,,'-::
, .
. ~.
.,',
I?:
\]
. ,
. .
. .
Table 111-1
. (continued)
Medium
Exposure Setting
Exposure
Route
Results
-5
mo~itor wells presents a 7 x 10 to 2 x
10 range of additive risks for organic
contaminants. For noncarcinogens, the
acceptable intake or the hazard index were
exceeded for the following contaminants
and wells:
o
E-1MA: . zinc; 0 to 6 years, AIS; 6 to
11 years, AIS; 18 to 70 years, AIC.
o
E-2UA: lead, chromium; 18 to 70 years,
hazard index.
~
H
I
0\
For other noncarcinogens evaluated, there
does not appear .to be an ingestion risk,
based on the limited available data.
The estimated excess lifetime cancer risk
from ingestion of ground water from the -4
Motorola ~nitor wells presents a 3 x 10
to 2 x 10 range of additive r!]ks for
organic contaminants. A 3 x 10 excess
lifetime cancer risk was calculated for
arsenic; however, the MCL was not exceeded.
For noncarcinogens, the acceptable intake
or the hazard index were exceeded for the
following contaminants and wells:
o
M-4UA: l,l-dichloroethene, per-
chloroethene; 18 to 70 years,
hazard index.
o
M-SUA: 1,1-dichloroethene, pcrchloro-
cthene; 18 to 70 years, hazard ind~x.
c~ .' ,',' -; ""T,
-------
I';
I)
"1
~
I":
:';/~
'..
~':
-:;,~
.j~
'~':i
;~~
..',
,.'.
'.,-
. /~
::;i
'",'.
.',
!:'~
[..',
ii::
;~ ;
:)
'.~ :i
,<.
. .
i..':
",)
'..
, ".'-
, '
.:;.'
,.
.}
.>:'}
. .
:~ :.{
'..
...'
'..\
Medium
H
H
H
I
-:-J
. Ground water
Exposure Setting
Residential--Potential Future
. Table 111-1
(continued)
Exposure
Route
Inhalation
Results
o
M-7MA:chromium~ nickel, cadmium; 18 to
70 years; .hazard index.
o
M-lOUA: 1,l-dich10roethene, perc~loro-
ethene; 18 to 70 years, hazard index.
o
ST-1: 1,1-dichloroethene, perchloro-
ethene; 18 to 70 years, hazard index.
o
ST-2: 1,1-dichloroethene; 18 to
70 years, AIC (based on maximu~ con-
centration~. 1,1-dichloroethene,
perchloroethene; 18 to 70 years,
hazard index (average concentrations).
"
o
ST-3: copper, zinc; 0 to 6 years, haz-
ard index. 1,I-dichloroethene,per-
chloroethene, chloroform, copper;
18 to 70 years, hazard index.
For other noncarcinogens evaluated, there
does not appear to be an ingestion risk,
based on the limited available data.
The estimated excess lifeti~e cancer risk'
~ro~ in?estion of ground water fro~4sRP
. 1rr12gt10n wells presents a 2 x 10 to 3
x 10 range of additive risks for organic
contaminants. There is no known ingestion
risk due to noncarcinogens from these
wells based on the limited available data.
The risk from inhaltttion of volatiles
released from the ground water in the
cou rse of h)-home uses such as cook i nl) ,
-------
"
.,
}~
,';
.,:;
.~,
,'~
i~
~1
-,.1
'1
:,}
:j
d
~. ~
.:!
:.i
;
:~
'.
..'
:"1
::~
:.:
.',
';'
.{;
1'1
i,j
..
.;
(,
I:;
I:.;
'.;!
::, ~
': ~
.j
.:)
Table 111-1
. (continued)
Medium
Exposure Setting
Exposure
Risk
Dermal
Contact
~
H
I
CD
. RDD/R16/017
; ~.
Results
bathing, etc., cannot be quantified.
However, it should be recognized that this
exposure could contribute to the overall
risk from the use of contaminated
ground water.
The risk from dermal cpntact with contam-
inated ground water and. subsequent exposure
to organic contaminants cannot be quanti-
fied. ~t should be recognized that this
exposure has been demonstrated to be sig-
nificant (Brown et al., 1984) and there-
fore could contribute to the overall risk
from the use of contaminated ground water.
~.t I
"
-------
IV. ENFORCEMENT HISTORY
In the Indian Bend Wash area, Motorola, Government Electron-
ics Group (Motorola) and Beckman Instruments, Inc.
(Beckman), have received general notice letters compelling
their involvement in the Remedial Investigation/Feasibility
Study (RIfFS). .
The efforts expended by both companies have beeninvestiga-
tory in nature and include such activities as source inves-
tigation and ground water monitoring. A history of the
administrative orders follow:
Docket Number Company Authority
84-01 Motorola RCRA-3013
84-04 Beckman RCRA-3013
86-06 Motorola CERCLA-106
87-05 Motorola CERCLA-106
Both companies are continuing to participate in the RI/FS.
These specific activities include conducting monthly water
level measurements, sampling ground water wells quarterly,
installing ground wa~er monitoring. wells, and.conducting
other field activities to determine the extent of soils and
ground water contamination.
RDD/R85/018
. .
RDD/R85/0l8
IV-1
I II.
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-c, -. .n, ,"'~." .~.~
. ".; c':
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-------
v~
COMMUNITY RELATIONS HISTORY
, .
The following is a list of community relations ac~ivities
conducted by the U.S. Environmental Protection Agency at the
Indian Bend Wash Superfund site:
RDD/R4/019
.' "'i '~';':j -.::' '",' :
".,~ .
o
Conducted interviews with Phoenix, Tempe, and
Scottsdale residents and State and local officials
to improve the Agency's understanding of community
concerns~ These interviews provided the basis for
the Indian Bend Wash Community Relations Plan
released in September 1984.
o
Established information r~positories at the
Arizona Department of Health Services, Phoenix
Public Library, Scottsdale Public Library, and
Tempe Public Library. Updated repositories per-
iodically with factsheets and other relevant
documents.
o
Publicized and maintained a toll-free information
message line to enable interested residents to
call EPA with questions and comments on the Indian
Bend Wash Superfund site activity.
Established and maintained a computerized mailing
list with more than 200. names and addresses of
interested individuals.
o
o
In July 1984, distributed a letter and fact sheet
announcing startup of RI/FS activities. A public
meeting was held in August 1984 to provide an
overview of the Superfund process 'and to inform
interested community members of upcoming RI/FS
activities. '
o
Sent out a factshe~t in February 1985 to update
, the community on RI/FS and enforcement activities.
o
In July 1986, distributed a factsheet informing
the community about the completion of the Phase I
Remedial Investigation Report and other site- .
related activities including the community well
sampling program and the lake and fish sampling
program.
Held a community meeting in August 1986 to update
the community on site activities, present the.
results of the Remedial Investigation Phase I
Report, and discuss future RI/FS activities.
Approximately 30 people attended this meeting.
o
V-I
',: :"'-"":';.,,'~
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,.:, \~.~;" .\~:......:::":':i.;:'.. .'" . ..
(',"'. -,-
c': ~:r:. ? ,~~.: ;[=: -(:;';:.~<::: ,: ::':" >;..: ", .'../.:'. ~'. ~:: '~_-:-'\' .
-------
t
I '
I
RDD/R4/019
I '
FDD/R4/019
o
o
o
'0
In April 1988, distributed a factsheet informing
the community about the cleanup alternatives
described in the Operable Unit Feasibility Study
(OUFS) and EPA's proposed partial cleanup remedy
for Scottsdale's drinking water aquifer.
Placed public notice advertisements in the
Scottsdale pr09ress and the Phoenix Gazette news-
papers announc1ng the proposed plan and the May 5,
1988, community meeting. ' Advanced notice flyers
were mailed to the site mailing list 2 weeks
before the start of the comment period.
Held a public comment period on the cleanup alter-
natives evaluated ,in the pUFS. The comment period
extended from Apri~ 19 through May 18, 1988.
Held a community meeting on May 5, 1988, to dis-
cuss the OUFS report and EPA's proposed cleanup
solution and to accept public comments 9n the
proposed plan. The meeting was attended by ,
approximately 25 persons. -
',V-2
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-------
. 'I"
VI.
ALTERNATIVES EVALUATION
LISTING OF ALTERNATIVES
The alternatives identified for the Scottsdale Ground Water
Operable Unit are broken into two categories: containment
alternatives and treatment alternatives.,
Containment alternatives were selected to prevent migration
6f contamination in the aquifers and to mitigate present and
future environmental damage. Treatment alternatives were
selected based on their ability to remove VOCs from water.
Since a major objective of the Scottsdale OUFS is to provide
potable water for use by the City of Scottsdale, the water
end use is fixed. '
CONTAINMENT ALTERNATIVES
The Middle and Lower Alluvium Units have been chosen for
remedial action as part of this Operable Unit. These'are
the units, in which the affected wells are screened' and serve
as a source of potable water to the City of Scottsdale. The
Upper Alluvial Unit remedy will be decided in, a subsequent
Operable Unit. The following containment alternatives were
developed for the Scottsdale Ground Water Operable Unit.
o
P.O";-No action altern~tive
-
o
P.1--Pumping of existing city wells at their his-
tarical capacities
P.2--Pumping of existing city wells' at 75 percent
~their historical capacities
o
o
P.3--Pumping of some city wells and addition of
three new wells to, optimize the aquifer area
affected ','
o
P.4--Pumpinq of city wells for 10 years and
subsequent addition of three new wells to optimize
the aquifer area affected
, ,"
, . . .
Construction of a containment barrier is inappropriate in
this ,case due to the, depth of alluvial units, and it does
,not satisfy the preference under SARA' ~o permanently and
significantly reduce the volume of hazardous substances.
TREATMENT ALTERNATIVES
The following options were considered for removal of low
concentrations of VOCs from aqueous solutions:
~
,
~
.;.,
RDD/R48/011
'VI-l
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- - '.. '-". --,'" '''''. ..
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o
o
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o
o
o
Stripping (air and steam)
Activated carbon adsorption
Reverse osmosis
Aerobic biological treatment
Anaerobic biological treatment
Chemical oxidation
SCREENING OF' ALTERNATIVES
As promulgated under CERCLA and SARA, remedial actions are
those responses to releases that are consistent with a '
permanent remedy to prevent or minimize the release of haz-
ardous substances, pollutants, or contaminants so they do
'not migrate to cause substantial danger ,to present or future
public health or welfare or the environment. SARA, Sec-
tion 121, states further, "Remedial actions...shall attain a
degree of cleanup of hazardous substances, pollutants, and
contaminants released to the environment and of control of
further release at a minimum which assures protection of'
human health and the environment. Such remedial actions
shall be relevant and appropriate under the circumstances
presented by the release or threatened release bf such sub-
stanc~, pollutant, or contaminant." SA,RA also states that
remedial actions should be favored ~hat permanently and sig-
nificantly =educe the volume, toxicity, or mobility of haz-
ardous substances, pollutants, and contaminants. The ,offsite
transport and disposal of hazardous substances or contami-
nated materials without such treatment should be the least
,favored alternative remedial action where practicable treat-
ment technologies are available.
The OUFS must also be consistent with the overall site
remedia tion strategy. In keeping with, this, 'the following
objectives have been defined for the Scottsdale OUFS.
o
Protect public health and the environment by pro-'
tecting unaffected wells from VOCs.
o
Provide a mechanism for the long-term management
of the VOC-affected ground water in order to improve
the regional aquifer's suitability'for potable use
and potential recharge/recovery activities by the
city." '
o
Provide a potable'water so~rce'for the City of,'
Scottsdale, wi thin" the constraInts, of projected
water demands, while utilizing existing facilities
to the maximum extent feasible. .
CONTAINMENT ALTERNATIVES
The no-action alternative must be evaluated as dictated by
law and is retained for further analysis.
RDD/R48/011
~
<'
~
.,'"
VI-2
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~-_._--- -.-..--
, .
The four remaining'pumping alternatives were evaluated by
modeling ground water and transport flow within the affected
alluvium units. Table VI-l summarizes the percentage of TCE
estimated to be removed from the aquifer followirig pumping'
for various periods. The percentage removed is based on
in~tial ma~sestimates of TCE and results of the transport
flow model presented in the OUFS.
Table VI-l
PERCENT TCE REMOVED
5 Years
25 Years
SO Years
P.O
P.l
P.2
P.3
P.4
6
7
9
6
7
25
45
42
40
41
44
85
79
83
90
The results indicate that Alternatives P.I and P.4 are the
most effective at reducing amounts of TCE over a SO-year
period. However, Alternative P.2 is more effective over a
period of 5 to 25 years. It is ex~e~te4 that during opera-
tion of the extraction system,. changes would be required to
optimize the system. These changes are impossible to define
at this time. ' .
In' addition to.being compatible with all the tr3atment ,
options, P.I uses only existing wells an~ appears to be as
effective as the remaining options. Therefore, it was
chosen for developing system capacities and water quality
design, criteria to evaluate the tre~tment options,.
TREATMENT ALTERNATIVES
Table VI-2 presents. an evaluation of the technologies for
VOC removal and screens out those not considered applicable.
The water quality design criteria are based on TCE, chloro-
form, l,l-DCE, PCE, and l,l,l-TCA. Air stripping and acti-
vated carbon adsorption were retained for the detailed
evaluation. The other technologies were dropped from fur- ,
ther consideration for a'variety of reasons including poor,' .
variable, or unproven performance,' ,iristitutional and manage-
ment constraints, or inappropriateness for expected
contaminant concentrations.
,RDD/R48/0ll
VI-3
1\
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Table VI-2
SCREmlNG OF VOC 1U1t0VAL TiX:HNOLOGIES
Process State of Treatment Performance Relative Costs Retained for
Description Development CapabUity Record Capital Operation Waste Streams Additional Comments Further Analysis
Air Stripping COlllllercial Capable of Excellent 1.0", (.0'" Air exhaust (can Commonly used for Yes
achievi~g high VOC to be treated) removal of VOCs al 10'"
rHoval Hoderate concentrations.
Steam Stripping COIIIIIercial. Capable of Excellent Moderate High Small air Not typically used for No--Not ",ell demon-
achieving high VOC exhaust, this type of strated for cost
re80val condensate ",ith application. removal of low con-
organics central Ions of VOCs.
Huch higher energy
requirements than
air stripping wilh-
out any signlf icant
< advantages.
H
I
~ Activated COIIIIIerc1al Capable of Excellent. 1.0", Moderate Carbon ",ith Cost-effectiveness is Yes--Useful for
Carbon achieving high VOC to to adsorbed organics sensitive to carbon vapor and aqueous-
Adsorption reaoval Moderate High requires periodic usage rate. phase VOC removal.
regeneration or
replacement
Reverse Commercial Relative poor per- Poor for High High Produces a con- Generally used for No--Poor performanc~
Osmosis formanee for VOCs VOC removal cent rate stream removal of dissolved for VOC removal.
that requires inorganics and high
additional molecular ",eight
treatment organics~
I: Aerobic COIIIIIIercial Some compounds not. Variable High High' Sludge requires Hay not be stable, No--Varlablt!
Biological readily performance disposal susceptible to shock, performance.
biodegradable for VOCs temperature-dependent;
10: accl1mation is
" : important.
'u
I . ~
Anaerobic Commercial Hay not con- Variable High High. Sludge produced Hay not he stable, No--Var lab Ie:
" Biological slstently meet performance suscepll~le lo shock, performance.
standards for VOCs lemperalure-dependenl;
acclimaUun Is
important.
:.~J.
i:'~
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I:~~
I!;
"
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,.:
"
1,:\
c'
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.,
"
:.,~
-..I
g
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ij
iJ
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"
:::~
r~1
i~~
>~;
~.~
.,
"'i
.:'1
IS
H
~~~:
>'
.,1
<:
H
I
U'I
."
.'
:
"
.'.:J
i\
1"<
I:
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I:'::
.'
(::
H
~: "'1
,"
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-',:
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.'.
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)
;',j
:,j
:-,{
I\'t
Process
Description
Chemical
Oxidation
/
..t.
:;,. t
State of
Development
COllllerc1al
Treatment
Capability
Capable of
. achieving high VOC
relloval
Source:
Performance
Record
Applic~le
. to lov con-
centrations
Table VI-2
(continued)
Relative Costs
.
Capital Operation
High
Higb
City of ~ottsdale,'Operable Unit Feasibility Study for Remediation of
Groundwater in the Southern Scottsdale Area. Prepared by Malcolm Pirnie.
April 1988.
p'nfj /~,} \7i f~ /:'"'('i~" 1)
Waste Streams
CO plus
2
byproducts
Additional Comments
High power require-
ments, oxidants may be
toxic. Potential (or
toxic brea~dovn pro-
ducts to be formed. .
o
Retained (or
. .
Further Analysis
Ho--Hot demonstrated
for large-scale
application. Fur-
ther analysis is
requi~ed regarding
the potential forma-
tion of general oxi-
dation products
prior to application
in large drinking
vater systems. The
process maybe fea-
sible for smaller
capacity systems,
particularlyvhere
VOC concentrations
are relatively hiqh
and a nonpotable
vater use is
specified.
-------
, .
I
Chapter 3 of the Scottsdale OU of Ground Water Treatment
Remedial Tec~nologies for Indian Bend Wash, prepared in
September 1987, provides more detail on the screening
process.
EVALUATION OF ALTERNATIVES
GROUND WATER ALTERNATIVES
P.O No-Action Alternative
o
The no action alternative would allow contaminated ground
water to spread over a widening area and, ~n light of the
proposed increased usage of ground water in the area, cause
adverse environmental and health consequences.
Pumping of Ground Water
Each pumping alternative (P.l through P.4) is potentially
feasible and satisfies the objectives of CERCLA and SARA by
reducing the amount of contamination in the Middle and Lower
, Alluvium Units. They also satisfy the objectives of the
OUFS in stopping contaminant migration and supplying a
. source of water for the City of Scottsdale. '
TREATMENT ALTERNATIVES
Both air stripping and activated carbon adsorption achieve
the desired goal of reducing volume and toxicity of the
ground water sufficiently to meet the applicable and appro-
priate requirements and will likely exceed these require-
ments. 'Table VI-3 presents the treatment goals and water
quality design criteria. Treatment of contaminated ground
water, either by air stripping or the use of granular acti-
vated carbon, has. been shown to be very effective, with
removals of organics often exceeding 99.9 percent. These
processes are relatively predictable, and they have been
used successfully at a number of CERCLA sites.
The air stripping and adsorption facilities will require
operator attention for periodic monitoring, maintenance
inspections, and water sampling. With industrial grade
components and regular preventive maintenance, process
integrity should be 25 years or'more. If periodic cleaning
of.the packing and internals due .to scaling becomes neces-
sary, provisions for adding antiscalant will be made during
the pre,lim~nary and final design phases. '
Neither of the treatment alternatives
construction materials or practices.
either facility could be designed arid
24 months. '
will require unusual
It is estimated that
constructed in 18 to
~
<
. ~,
-.'"
RDD/R48l0ll
VI-6,
, :";'5~:-:!r,'-~~',-';~:o
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;'~-:"','.~~:"I",~i'.:';"~"';',.:::;./.; C;::.-:". ':-J~~::~-:; \:. :""~": :;,"'
-------
The City of Scottsdale has requested that vapor phase GAC
adsorption be included to remove VOCs from the packed column
emissions., '
VOCs other than TCE, chloroform, PCE, l,l-DCE, and l,l,l-TCA
have been detected in some monitoring wells. The most pre-
valent of these other VOCs are toluene and methylene chlor-
ide. Given the design criteria developed for treatment of
the most commonly detected VOCs at IBW, toluene would be
effectively removed by either air stripping or GAC adsorp-
tion. Methylene chloride would be removed by air stripping
at 95 percent efficiency.
Since the treated water will be for municipal use rather
than reinjection, both air stripping and carbon adsorption
were evaluated based on the criteria of treating the water
to meet ARARs.The alternatives were' considered further for
treatment below the ARAR levels.
Table VI-3
WATER QUALITY DESIGN CRITERIA
FOR EVALUATION OF TREATMENT TEDiNOLOGIES
Treatment to Meet ARARs:
Treatment
Goal C~q/l)
Average
Water Quality
Influent' Percent
C~q/l) RelllOval
, Chloroform
l,l-dichloroethylene (DCE)
Tetrachloroethylene (PCE)
l,l,l-trichloroethane CTCA)
TrichloroethyleneCTCE)
, 0.5
" 7
0.67
200
5
95.00
,10
, 5
20
NO
300
96.65
98.33
Treatment to Exceed ARAb:
Treatment
Goal (Uq/l)
Average
Water Quality
Influent Percent
(uq/l) Removal
, Chlorofom' .
. l,l-dichloroetbylene (DCE)
, Tetrachloroethylene (PCE) ,
'l,l,l-trichloroethane (TCA)
Trichloroethylene (TeE)
95.00
30.00
97.50
10
5
20
NO
300
0.5
,3.5
0.'5
: 100,
3
99.00
Note: NO denotes nondetectable.
"Worst Case"'
Water Quality
Influent Percent
CUg/l) Removal
50
20
100
10
1,500
99.00
65.00
99.33
99.67
"Worst case"
Water Quality
Influent Percent
(uq/l) 'Removal
. 50
. 20
100
10
1,500
99.00
82.50
99.50
99.80
RDD/R48/.011
VI-7
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-,".:-".j.,
-------
VII.
SELECTED REMEDY
DESCRIPTION
Presently, the preferred alternatives for the Scottsdale
Ground Water Operable Unit are:
Containment Alternative-~Ground water will be extracted
from the Middle and Lower Alluvium Units by pumping
City of Scottsdale Wells No. 31, 71, 72, and 75 at a
minimum of 75 percent of their historical capacities
(P.2). This alternative is chosen.because it utilizes
existing wells and appears to be the most effe,ctive for
reducing the amount of TCE during the first years of
operation (See Table VI-I). Once the system is operat-.
ing and the effectiveness of removing VOCs from. the
Middle and Lower Alluvium Units can be further evalu-
ated, additional pumping of these wells (up to
100 percent of their original capacities) and the use
of additional extraction wells will be considered. . The
pumped water will be sent to the City of Scottsdale
water system for potable use after contaminant levels
are reduced to meet primary drinking water standards.
Treatment Alternative-Air Stripp'ing with Air Emission
Controls-~The extracted ground water will be sent
through a collection system to a centralized ~reatment
facility. Air stripping will be used since all of the
contaminant levels can be lowered to me~t drinking
water sta~dards at a lower cost than by using granular
activated carbon. Specifically, packed column aeration
will be used in which the wate~ passes over the packing
material. by.gravity. Air is forced upwards through the
column to provide a counter-current flow. The VOCs are
transferred from the water to the air and exhausted at
the top of the columns. Vapor phase GAC adsorption
will be used to remove VOCs from the air waste stream
from the treatment plant. . .
End.Use--Tocompletely satisfy the objectives of the
Operable Unit, the end use will be distribution to the
City .of Scottsdale water system. Any recharge project
proposed by the City of Scottsdale will be evaluated
fo~ any adverse impact on the Operable, Unit.
. . . .
After 50 years of operation, the' chosen alternative is esti-
mated to remove between 79 and 85 percent of the present.
mass of TCE in the Lower and Middle Alluvium Units. . This
remedy will provide potable water to the city while utiliz-
ing existing facilities, improve the regional aquifer's
suitability for potable use by removing contaminants, and
protect public health and the environment by protecting. .
unaffected wells from VOCs~ It also fulfills the statutory
preference for permanent solutions at Superfund .sites.
. . .
RDD/R32/020
VII.;.l
~.:, -,:,.,.-,<~,.'7';~i:2,~;,'~':.7<>~~": .. .~' ;'.~C '~r~:'7' c:' :r;,-~~:; '::"'~::-,>"i',:..::::,:-:::';;,.:':' ': ',;:t :":;:...' '~.:'~~':' . :;.: ~:,::~.::::;, :',', ':.!:~. .:' :;-;.: '.
. .,.'":.
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'.~ : . "~" " '.:' .. ;~-- :'.'~',' :~:' '. ;-:- ::::: ".'-.:'. ~'r :~. "". :.~:. :- .:~. . ", .>:' C;"'.:. ~,. ~. ;:.~'~.:':' ,:"; '~:'--:."::: ~.: ;;~~ :::, :;"':',~ :':;~::';'
-------
1---
I
Present worth cost estim~tes for the pumping and air strip-
'ping treatment 'alternative are presented in Table VII-I.
Costs include piping and treatment equipment, maintenance,
regeneration of vapor phase GAC, and engineering and design.
The estimates are based on a system capacity equal to the
historic pumping capacities of Wells 31, 71, 72, and 75
(8,400 gpm) and the treatment goals in Table VII-2. If the
MCLs for the VOCs or other constituents such as heavy metals
are changed, the remedy will be reevaluated to determine if
a design modification is necessary. Cost estimates were
initially developed for two alternatives within the air
stripping alternative. One considered stainless steel
columns with circular cross sections, and the other con-
sidered concrete columns with rectangular cross sections.
The estimates presented in Table VII-l are based on the
concrete columns, which is the preferred design. .
STATUTORY DETERMINATIONS
CERCLA, and its reauthorization, SARA, requires that perma-
nent reductions of contaminants through treatment be pre- .
ferred over containment alternatives. It also requires that
Applicable or Relevant and Appropriate Requirements (ARARs)
be used to determine the treatment levels. By achieving
these requirements, the selected remedy for the Scottsdale
Ground Water Operable Unit reduces the pre sept and future
risks associated with use of the ground water in the
Scottsdale area. ' By reducing the contaminant levels and
restricting their mobility, this remedy protects both human
health and environmental quality.
Table VII-2 shows the ARARs identified for the ground water
and the proposed treatmen~ goals. Contaminant'levels found
in the IBW wells are greater than the Safe Drinking Water
Act maximum contaminant levels and the Arizona Department of
Health Services action levels.
Table VII-1
PRELIMINARY COST ESTIMATES--PRESENT WORTH
PACKED COLUMN AERATION WITH VAPOR-PHASE
PUMPING OF EXISTING WELLS
ANALYSIS
GAC AND
I,
Total Capital Cost
/ Annual Operating Cost
Present Worth of Operating Costs at
Total Present Worth at 10 percent'
10 percent
$4,008,000
520,000
4,720,000
8,728,000
Notes:
System capacity = 8,400 gpm.
Present worth factor is based on an annual interest
rate and 25 years of operation.
RDD/R32/020
VII-2
-------
/:., .
; r .'",' -1 ~ ":'! ;. -'. ,1::1
The selected remedy satisfies the requirements for treatment
and risk reduction, and does ~o economically. Initial anal-
ysisof the pumping regimen indicates the volume of contami-
nated ground water and mass of VOCs will be reduced.
Of the proven technologies, air stripping proved to be the
most economical treatment method available, both for capital
and operating costs. It will also reduce residual wastes to
a minimUm.. ..
Distributiori of the treated water to the City of Scottsdale
water system is the only end use that will satisfy the
objective of providing a potable water source to the City.
The selected remedy satisfies the requirement of reducing
the mobility, toxicity, and volume of contaminated water.
It does so by using treatment technology to the maximum
extent practicable and does so in a cost-effective manner.
APPLICABLE OR
Table VII-2
STATE AND FEDERAL.
RELEVANT AND APPROPRIATE
AND OTHER. CRITERIA
(concentrations in ppb)
REQU I REMEmSa
ADHS
SDWA. SDWA Action Treatment
.Compound MCL MCLG Level Goal
Trichloroethene 5 0 5 5
1,1,1-Trichloroethane 200 200 200 200
1,1-Dichloroethene 7 7 7 7
perchlol'oeShene 1 0.67
Chloroform 3 0.5
aCleanWater Act requirement~.will be determined during NPDES review..
bsource is not a byproduct of municipal water supply chlorination.
Notes:
ADHS--Arizona Department of Health Services
AWQC--Ambient Water Quality Criteria
MCL---Maximum Contaminant Level
MCLG--Maximum Contaminant Level Goal
SDWA--Safe Drinking Water Act
Sources:
U.S. EPA 1986. Public Health Assessment Manual
ADHS 1987. S. Eberhart
RDD/R32/020
VII-3
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VIII.
REFERENCES
City of Scottsdale, Arizona. August 1986. Population Pro-
, jections, 1986-2010. Growth and Development Report, Planning
and Economic Development.
Climates of the States. 1980. Second Edition, Vol. I,
Detroit, Michigan: Gale Research Company.
Doull, J., C.D. Klaassen, and M. D. Amdur.
MacMillan.
1980.
Toxicology.
NRC (National Research Council). 1980.
Health. Vol. III. Washington, D.C.
NRC (National ReE!earch Council).' 1977.' Drinking Water and
Health., vol. I. Washington, D.C.
Drinking Water and
U.S EPA. 1986. Superfund Public Health Evaluation Manual~
Washington, D.C.: Office of Emergency and Remedial
Response, Office of Solid Waste and Emergency Response.
U.S. EPA. 1985. Chemical, Physical, and Biological Pro~- ,
erties of Compounds Present at Hazardous Waste Sites. F1nal
Report. Washington, D.C.: ,Office of Waste Programs, Enforce-
ment, Office of Solid Waste and Emergency Response.
P.DD/R48/012
RDD/R48/0l2
VIII-l
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Appendix A
INDEX OF ADMINISTRATIVE RECORD
-------
Appendix B
RESPONSE SUMMARY
-------
Appendix B
RESPONSE SUMMARY
OPERABLE UNIT FEASIBILITY STUDY (OUFS)
FOR REMEDIATION OF GROUNDWATER
IN THE SOUTHERN SCOTTSDALE AREA
OVERVIEW
During the public comment period for the April 1988 OUFS
(Draft for Public Comment) from April 19 through May 18,
1988, EPA received comments on the recommended partial rem-
edy for ground water at the Indian Bend Wash (IBW) area.
Comments were received from State regulatory agencies and
from'businesses presently or previously located in the IBW
area. EPA also received comments from the general public 'at
its Public Me~ting held May 5, 1988, at Scottsdale City Hall.
Most of the comments received were of a technical nature.
Substantial'technical comments are responded to herein.
None of the comments raised issues that would affect EPA's
selection of a partial remedy or require reissuance of a
revised 'OUFS. Therefore, the April 1988 Public Comment OUFS,
along with clarification provided by this Response Summary,
shall constitute the Final OUFS for this project. .
.
SUMMARY OF PUBLIC COMMENTS
. AND AGENCY RESPONSES
GENERAL COMMENTS
Fr()m Arizona [)epartment of Water Reso\1rc.es:
Arizona Department of' Environmental Quality
Concerns were expressed regarding the level of detail
in discussions of ground water pumping alternatives, new
water quality data obtained for Scottsdale Well No. 76,
and the limitations of analysis results obtained from
the two-dimensional ground water model utilized.
RESPONSE: . The purpose of the two-dimensional model is to
evaluate the feasibility of various pumping regimens to
achieve the. remedial action objectives for ground water stated
in the OUFS: (1) to protect unaffected wells fromVOCs, .and
(2) to improve the regional aquifer's suitability for potable
use. Although the two-dimensional model is more simplistic
than a properly constructed and operated three-dimensional
model, the two-dimensional model adequately considers the
hydrogeologic conditions, and the projections are suitable
to evaluate the feasibility of pumpinq to achieve the
1.
J'
RDD/R4/0l9
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ground water remediation objectives of the OUFS. Additional
detailed modeling may refine the understanding of the com-
plex hydrogeologic system: however, a higher degree of
detailed modeling is not required for the purposes of the
OUFS. It should be noted that the Operable Unit remedy is
designed to be a partial remedy, and additional mod~ling and
consideration of other potentially feasible pumping alterna-
tives will be considered in the overall FS for the IBW area.
Acquisition of new water quality data and further work with
ADWR's three-dimensional model is encouraged, and new avail-
able data should be used, when appropriate, to propose modi-
fications to the remedial action program to more effectively
achieve the objectives of the remedy.
Results of computer modeling cannot be regarded as absolute
and must' be considered using professional discretio~. For
practical purposes, Scottsdale Well No. 76 was s~mulated as
an extraction well in two pumping regimens and is located on
the 5 ~g/l TCE contour for initial modeling conditions." The
model results predict that Well No. 76 could soon be affected
with low concentrations of VOCs: and this has been verified
by recent sampling, after which the well was removed from
potable service. The model results do not indicate that
there will be no further migration of the zone of contamina-
" tion. , The results do suggest that under the' pumping regi-
mens used for modeling operations, migration should not be
substantial and the areal extent of affected ground water
should beredaced. Pumping regimens used for modeling opera-
tions were based on the assumption that pumping patterns in
the model area would 'remain unchanged. Attempting to predict
future pumping patterns throughout the model area based on
historic pumping data is at best an approximation, but a
necessary one for this mOdeling application. In no way do
the model's limitations indicate that the proposed partial
remedy may not achieve the remedial action objectives stated
in the OUFS.
SPECIFIC QUESTIONS AND COMMENTS
From EPA Reqion IX, Quality Assurance Manaqement Section
1.
The OUFS report mentions sampling programs and water
quality in the Background and Site History Section, but
the actual quality of the data is not, mentioned. The
author should discuss whether the quality of the data
, was determined, and whether the data quality was consid-
ered in developing potential remedial actions at the
IBW site. ' .
RESPONSE: The presentations of water quality data in the
OUFS are brief summaries of extensive available data from
monitor wells and affected City wells. These data were sum-
marized in order to provide a manageable database from which
RDD/R4/019
B-2
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: c'>,~'-:."::~~-'::;'~':;:'.: ""..:_c<'.~/.~:::' ::.O:"~"",
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, ,
, ,
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to estimate potential water quality from extraction wells
for use in treatment analyses. All monitor well sampling
and analyses were performed in accordance with EPA Contract
Laboratory Program (CLP) procedures for Quality Assurance/
Quality Control. QA/QC results were accounted for during
compilation of the water quality data summaries ,in the OUFS
and were a major factor in limiting the list of VOCs of con-
cern to five compounds. In addition, potential impacts on
the treatment alternatives by two other compounds (toluene
and methylene chloride) are evaluated in Section 5 of the
OUFS because, although very, limited in occurrence, some of
the analyses that indicated detectable results of these com-
pounds in monitor wells appeared to pass QA/QC criteria. As
stated on page 1-6, paragraph 2 of the OUFS, more extensive
presentations of water quality data can be found in the
Remedial Investigation and related reports, although the
cited references should be 1, 3, 4, 5, and 6, not 4 through
8 as shown. ' ,
From Beckman Instruments, Inc.
The OUFS should include additional consideration of
whether the proposed remedy is consistent with the cur-
rent state of knowledge of the Upper Alluvium Unit and
any ultimate remedial program for the unit. TheUpper
Alluvium Unit in the southerly portions of the North "
IBW site contains significant quantities of water and
VOCs, and we believe the distribution of chemicals of
concern in the unit should be considered and discussed
further in the OUFS. ' '
RESPONSE:' The current understanding of the 'hydrogeology of
the Upper Alluvium Unit is summarized in Section 1 of the
OUFS, and more detailed ,discussions are available in the
Remedial Investigation, and other related reports included in
the administrative record. Potential impacts of Upper Allu-
vium Unit groundwater on the remedial action alternatives
are examined thoroughly in Sections 4 and 5 of the OUFS, and
will also b~ considered during final design of the partial
remedy. The proposed partial remedy of pumping contaminated
wells and subsequent treatment for potable use will not be
inconsistent with the final remedy for the IBWsite, and the
current migration of VOCs from the Upper to the Middle and
Lower Alluvium Units through short-circuiting in wells and
, low-rate percolation willcontin~ewhether or not the pro- '
,posed remedy is implemented'. As stated in the OUFS, sealing
of well casings in the Upper Alluvium Unit would not elimi-
nate the downward migration of VOCs, and, .is not necessary,
because the proposed partial remedy will accommodate impacts
from Upper Alluvium ,Unit contamination and. provide for some
level of cleanup .for Upper Alluvium Unit water. The OUFS is
not intended. to provide a final remedy for the entire IBW
'1.
RDD/R4/019
B-3
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site. EPA will address the Upper Alluvium Unit further in
the overall Feasibility Study.' .
2. Why was the 1 x 10-6 level used in establishing several
, "Other Criteria" and_sTreatment g~als to Meet ARARs"
rather than a 1 x 10 or 1 x 10 level? Why wer~ the
"Treatment Goals to Exceed ARARs" for some chemicals
fixed at one-half the MCLs rather than at other levels
closer to the ,MCLs? ' '
RESPONSE: ARARs and Other Criteria were established for the
, OUFS in accordance with "~PA Interim Guidance on Compliance
With Other Applicable or Relevant and Appropriate Require-
ments" (52 FR 32496 et seq) and in conference between the
City of Scottsdale and EPA Region IX, Toxics and Waste Man-
agement Division Officials. For chemicals that have not
been assigned Safe Drinking Water Act Maximum Contaminant
Levels MCLs), it is EPA's,policy to set cleanup levels (for
potable end use) such that the total additive excess life-
time cancer :is~ of all chemicals-iresent_~n the treated
water fall w~th~n the range of 10 to 10 . As a general
mat6er, EPA recommends consi,deration of a risk level of
10- , since this level is effective in protecting human
health and the environment and can be reasonably
implemented.
The National Contingency Plan (NCP) requires the evaluation
. of alternative remedial actions that will achieve and exceed
ARARs. EPA has not established guidelines for quantita-
tively determining cleanup levels that "exceed ARARs."
However, the identified "Other Criteria" were chosen for
'carcinogens, and one-half of the MCLs were chosen for non-
carcin~gens as treated water levels which would illustrate
. the differences, in cost-effectiveness for the treatment
alternatives based on achieving ~ significantiy higher,
public health risk reduction than would be achieved when
"meeting ARARso" This is the intent of the dual~analyses
provision of the NCP. It should be noted that analyses in
Section 5 of the OUFS indicated that no practical differ-
, ences in the design criteria, capital, costs, and operating
and maintenance costs occ~r between the two sets of treat-
ment goals due to the nature of the treatment processes,
evaluated. Also, neither of the VOCs that had treatment
goals set at one-half of the MCL were determined to be
controlling constituents in the,treatm~nt analyses.
From Arizona Department of Environmental Quality.
1.
The 5 ~g/l TCE' contour surrounding the zone of ground
water contamination is identified on Figure 6, Appen-
dix A. Data defining the occurrence and concentrations
of contaminants in some of the study area are incomplete
RDD/R4/019
B-4
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-------
or lacking. What specific data in these areas were
used to establish the 5 ~g/l boundaries?
RESPONSE: All available ground water chemistry data were
used to construct water quality data matrices, and the con-
centrations of TCE.were ~ontoured as accurately as possible
using these data. The zone of contamination was defined and
the model was ~onstructed using the best available data.
Although the e...tent of contamination is not, and may never
be,' precisely defined, the effectiveness of pumping and
treatment of. contaminated ground water can be evaluated using
available data. Future work may provide data that would
more accurately delineate the zone of. contamination: however,
those data are not available at this time. It is premature
to .draw a final conclusion regarding the extent of contami-.
nation, but it is not premature to make qualitative conclu-
sions about the effectiveness of pumping as a ground water
control for the OUFS. .
Ground water inflow via leakage from ~he Upper Alluvium
Unit was not included in the model recharge because it
is not believed to be substantial relative to other
recharge sources. It should be noted that contaminant
movement from the Upper to the Middle and Lower Allu-
vium Units is believed to be the primary mechanism for
the occurrence of deeper contamination. What data,
calculations, and assumptions were used to determine
the recharge volume of the Upper Alluvium Unit? How do
these calculated volumes specifically compare to the
other recharg~ sources?
RESPONSE: Results of recently completed fluid-movement inves-
tigations in t~e Indian ~end Wash area production water wells
indicate that water from the Upper Alluvium Unit migrates to
the Middle Alluvium.Unit and Lower Alluvium Unit via exist-
ing wells which serve as conduits for ground water transport.
Water from the Upper Alluvium Unit moves down the well cas-
ing to the underlying aquifer units where water moves into
the lower part of the Middle Alluvium Unit and into the
Lower Alluvium Unit through perforations at that level.
Ground water is also believed to migrate from the Upper
Alluvium Unit to the underlying units via movement in the
annular space between the casing and the borehole wall.
Leakage from the' Upper Alluvium Unit is believed to be sub-
stantially less than migration.via these methods. The vol-
ume of water contributed to the Middle Alluvium Unit via
leakage from the Upper Alluvium Unit is believed to be small
relative to underflow, and leakage was not considered for
this modeling investigation. ADWR has conducted a detailed
study of the water budget for the IBW area and has .calcula-
ted recharge to the Middle Alluvium Unit via leakage.
Because ADWR leakage values were based on an.unreliable flow
net analysis., a low level. of confidence was assigned to the
2.
RDD/R4/019
B-S
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,::;";- ;'~;~~'. ,~;.." ,::'-.. ,'"'.
.~~ '.:~: ',.', "..,:'-<.~..:::':':~"...'.~':':'.:- ". .
:',.' ":' ~;::;"_:':'-::<~:"'.~"'~.. :.": - ./':":'":', ;".-. :".< '.
-------
ADWR values for leakage, and leakage was not used for the
model. (See response to ADWR Comment No. 20.)
3.
The TCE is assumed to be in a dissolved phase and
modeled as a nonreactive tracer. Should TCE more
ately be modeled as a nonreactive tracer with the
priate retardation coefficient? .
was
accur-
appro-
RESPONSE: TCE tends to adsorb onto organic carbon, and the
migration ofTCE in contaminated water is thereby retarded.
A retardation coefficient could be used in the solute trans-
port model to simulate this adsorption. The results would
-indicate zones of contamination of smaller areal extent than
results obtained.by assuming no retardation. VOC-affected
ground water migrates fastest in the coarse gravel zones in
which there is less organic carbon and retardation would not
be expecte~ to be substantial. .
From Arizona Department of Water Resources
1.
Paragraph 4 on page ES-S seems unclear. Are P.2, P.3,
and P.4 no more effective than P.O, or P.l?
RESPONSE: There is an error in this paragraph. Page ES-S,
paragraph 4, sentence 2 should read: "Modeling results indi-'
cated that all of these other alternatives were significantly
more effectIVe in managing the affected ground water zone
than pumping Alternative P.o (no-action)."
2.
On Table 3-1, injection should be addressed because it
appears to be a viable ground water control for this
area. .
RESPONSE: Injection is not addressed because it. is not com-'
patible with the fundamental remedial, action objective of
potable end use for the City of Scottsdale.
3.
The effects of Upper Alluvium Unit contamination' and
its impacts on this OUFS should be more fully addressed.
RESPONSE: Based on the best available data, the potential
impacts of the Upper Alluvium Unit on the remedial action,
alternatives are thoroughly discussed and evaluated in Sec-
tions 4 and 5 of the OUFS. As additional data become avail-
able, they will be examined with respect to potential impacts
on the selected partial remedy during final design and will
be addressed' in the overall FS for the IBW site.
4.
Do the proposed pumping alternatives exclude the Upper,
Alluvium Unit?
. RESPONSE: None of the extraction wells for VOC-affected
ground water in Pumping Regimens P..l through P.4 will pump
RDD/R4/0l9
B-6
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.'." :,~"',~.~ '~.';':.V"'.': .;"'-:"'7'-"":,--:
:'.-.'.""'1';'~ ",:..,:.. -~ .- .
:~'.' :< . . . : ;~~":. .:;" . . ':' ~-'
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~,', ..!, , ~--;-;-;-;. '-,:,,;'. ,T ;~,
primarily Upper Alluvium Unit water. However, short-
circuiting .is oc;:curring in some of the wells, and Upper Allu-
vium Unit water which migrates down the well, whether inside
or buts ide of the casing, will be pumped. As stated in Sec~
tions 4 and 5 of the OUFS report, the potential impacts of
this water have been .accommodated in treatment facility analy-
ses~ The Upper Alluvium Unit will be addressed fu~ther in
the overall FS for the IBW site.
-5 .
Was the City of Scottsdale's CAP allotment. and conserva-
tion measures called for in the Second Management Plan
taken into acco~nt in the modeling of the various pump-
ing regimens? .
RESPONSE: Pumping regimen analyses are compatible with the
demand proje~tions of the City of Scottsdale's Water'
Resources Management Plan, June 1987. As stated in the Insti~
tutional Analysis portion of SectionS, Scottsdale has service
area rights to pump the ground water within the limitations
of its Active Management Area targeted per capita usage goals
for the entire service area. .
Regarding the Ground Water Management Act of 1980, the
applicability of the Act is that it requires remedial
ac.tions to be consistent with the Act and are subject
to management goals established by the AMA in which
remedial actions are located~ All of the alternatives
of the remedial' action are' affected as they are under
the jur~sdiction of and require the approval of the
Department of Water Resources.
RESPONSE': The Arizona Department of Water Resources, as
well as Environment Quality, will be asked to concur with
EPA',s Record of Decision.
6.
7.
DWR is concerned with the justification and effect of
constant head cells at most of the ground water model's
boundaries, the effect bf not inputting recharge into.
the model, the effect of not utilizing the Upper Alluv-
ium Unit as a source of contaminants, and the effect of
not knowing the western edge of the zones of contamina-
tion in the Middle and Lower Alluvium Units.
RESPONSE: No-flow cells are used to represent Camelback
Mountain and Mummy Mountain, where the geologic formations
are believed to have very low permeability. . The remaining.
boundary cells are designated as constant head cells to sim-
.ulate' ground water underflow into the model area. The effect
of constant head boundary cells is that.drawdown will not
occur within these cells. Because these boundaries are sub-
stantial distances from pumping centers used in the modeling
operations,' this approximation does not have a s~bstantial
effect on migration of the zone of contamination.
RDD/R4/019
B-7
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'.> . :,,' ..::<~:.":~~ :':""~~'~'.: ::'~.. ".:.;' ~~':.:::.;.:,:~'~~ :;~:. ~:": ~., ",:" ':~,~:-." ~~.-: :".~ ..~;:~';::~:~':'.'
-------
Recharge into the combined Middle and Lower Alluvium Units
aauifer"in the model area is believed to be small in. rela-
tion to underflow into the model area. Analysis of water
level hydrographs for the Upper, Middle, and Lower Alluvium
Units indicates that recharge into the Upper Al:uvium Unit
has little effect on the pattern of ground water flow in the
lower units, and recharge was not considered in the two-
dimensional model.
The effect of not considering the Upper Alluvium Unit as a
source of contamination in the model is that the contamina-
tion problem could coritinue for a longer period of time than
if it were considered. To disregard the Upper Alluvium Unit
as a source of contamination does not affect the areal extent
of contamination in the combined Middle and Lower Alluvium
Unit, but it may result in an underestimation of the length
of time -that contaminated ground water will occur in .the
aquifer system. .
The zone of contamlnation was estimated for the model using
the best available data.. The feasibility of pumping and
treatment of ground water was evaluated based on available
data. If additional water quality data become available for
the western part of the study area, the zone of contamina-
tion could be delineated more precisely, and pumping regi-
mens might be refined to more effectively remove contamination.
At this time ther~'are no monitor wells or production water
wells in the western part of the study area~ therefore, pre-
cise definition of the western boundary of the zone. of con-
tamination is problematic. However, available data are.
adequate to conclude that pumping and treatment is a viable
remedial action, and the requirements for the OUFS are met.
8.
The number and complexities of the proposed remedial
actions are limited and should be expanded to explore
ways of minimizing cleanup time and enhancing
containment.
RESPONSE: There are a number of potential scenarios for
remedial action. The alternatives in the OUFS covered a
broad spectrum while trying to identify reasonable actions
that could be easily implemented. .
The following comments were directed to specific sections of
Appendix A--Ground Water Modeling:
9.
Page 3, paragraph 2: The saturated thickness of the
Upper Alluvium Unit reaches a maximum of 60 feet or
more in the southern part. of the model area.
I
RESPONSE:
Comment noted.
RDD!R4/019
B-8
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-------
Page 4, paragraph 1: Ground water flow directions are
quite different than north and northwest in the central
and north parts of the model area, where localized cones
of depression ~xert influence.
RESPONSE: Ground water flow directions discussed in Appendix
A are general flow directions for ground water in the allu-
vium units. This particular paragraph indicated the direc-
tion of ground water movement ~n the Middle Alluvium Unit in
areas where water level measurements in monitor wells have
been made. .
10.
11.
Page 4, paragraph 2: . The thickness of the Lower Allu-
vium Unit in the IBW area is probably greater than "200
to 600 feet." According to Oppenheimer .and Summer. (1980) ,
total thickness of s~diments below the Middle Alluvium :
Unit is on the order of 4,000 feet in the northeast
part of the model area. Much of this thickness is com-
posed of the Red Unit, but the thickness of the Lower
t.1nit is really unknown in most of the study area. .
RESPONSE:. Thickness for the Lower Alluvium Unit given in
.thereport was derived from analysis of drillers logs on
file withADWR. . ..
12.
Page 5, paragraph 2': It should be stated that the Lower
Alluvium Unit is probably a much. more important aquifer
than the Red Unit in the south part of the Paradise
Valley basin. .
RESPONSE:
Gomment noted.
13.
Page 7, paragraph 2: Under "model input," more data
are needed to adequately evaluate the model. Can you
please provideADWRwith the data matrices input into
. the model? Also, we would like copies of MODFLOW and
MOC model runs in order to review the models' assump-
tions and limitations in an effective manner.. Addi-
tionally, the uncertainty associated with most
assumptions should be stated, and a range of possible
values discussed.. . .
RESPONSE: . Errol L. Montgomery 'Associates, the developer
of the model and author of Appendix A to the OUFS, will con-
.tinue to. be available to discuss the ground water model in
detail .with representatives from ADWR. .
14.'
Page 8, paragraph.1: . Along .the north, south, and east
boundaries, constant head nodes are employed. Compari-
son of 1982 with 1988 water level measurements from
wells located within one-half mile of those boundaries
shows that, in the last 6 years, water levels have risen
from 23 to 161 feet in the north, and have dropped
49 feet in the east.. This suggests that the north and
RDD/R4/019
B-9
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. east boundaries. are not actually constant head areas,
as the model assumes.. Input of variable head bound-
aries would greatly affect the model's results, and the
effect of such variation in heads should be explored
during the sensitivity analysis process to see if the
proposed remedial actions are affected. ..
RESPONSE: If sufficient data were. available to accurately
calculate flux along the boundary, then a head dependent
prescribed flux boundary condition would be more accurate
than a constant head boundary condition. However, data are
limited and an algorithm for head dependent flux would be .
very approximate. The model boundaries are located at sub-
stantial distances from the zone of contamination (the area
of concern for the modeling investigation) and do not sub-
stantially affect water levels in that area. ..Bec~use1of the
location of the area of concern and the limited data avail-
able, the constant head boundary cells are believed to ade-
quately approximate the hydrologic conditions and are
suitable to evaluate the proposed partial remedy.,
15.
Page 8, paragraph 1: The use of con$tant head nodes at
the western model boundary appears to be unjustified,
unless transmissivity values are so low as to effect-
ively simulate no-flow cells. Constant head cells may
provide considerable underflow into the model area, and
this underflow may not be. actually occurring between
Papago Buttes and Camelback Mountain, where depth to
bedrock is probably less than 100 feet, and on the east
side of the Papago Buttes.. How much inflow is simulated
along the western boundary? The effect of inappropri-
ately large inflow values from the west. (and north) may
be to disallow contaminant transport to the west land
north). Migration of the contaminant zone along its
western and northern margin in all pumping scenarios is
minimal, even in contaminated areas inside or adjacent
to cones of depression of extraction wells. Histori-
cally the zone of c:ontamination has most likely,
migrated a considerable distance to the west and north,
a situation not simulated by model results. ~he lack
of contaminant migration along the western margin of
the zone of contamination may be an effect of assuming
unrealistically high ground water inflow values from
the western boundary.
,
RESPONSE: The hydraulic head. west .of Papago Buttes, Camel-
back, and Mummy Mountains is substantially higher than the
hydraulic .head in'the Paradise Valley basin. The steep
hydraulic gradient and the coarse';'grained lithology of the
sediments allow large amounts of ground water to enter the
Paradise Valley basin as underflow, even though saturated
thickness between Papago Buttes and Camelback Mountain and
between Camelback Mountain and Mummy Mountain may be rela-
tively small.
RDD/R4/019
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16.
Page 8, paragraph 2: Uncertainties of the flow net
analysis should be stated (for example, the lack of
detailed wat~r levels and gradients~ unknown leakage
from the Upper, Alluvium Unit, and unknown recharge from
land surface to the Middle Alluvium Unit where the Upper
unit is not saturated). . .
RESPONSE:
Comment noted.
17.
Page 8, paragraph 3: Could you provide a reference for
the reported values of storage coefficient?
RESPONSE: Sev.eral references are given at the end of.Append-,
ix A. In additibnto references cited in the report, studies
by the U..S. Geological Survey and Arizona Depa'rtment o.f Water
Resources, which include data for the Indian Bend Wash area,
were used to provide estimates for storage coefficient.
Page 9, paragraph '9: How sensitive is the model to the
assumption that the Lower Alluvium Unit maintains a
constant thickness? .
RESPONSE: Pumping is 'the most sensitive stress' on the. .
ground water system. In the' Lower Alluvium Unit, thealti-
tude of the bottom of the. perforations is substantially
higher than the base of the Lower' Alluvium Unit. Therefore,
the. sensitivity of the model to the thickness of the Lower
Alluvium Unit is small. In effect, to estimate the thick-
lies's of th Lower Alluvium Unit is to ,estimate the' transmis- .
,sivity~ so the sensitivity of the thickness of the Lower
Alluvium Unit is less than the, sensitivity of transmissivity.
18.
19.
Page 9, paragraph 1: Ground ~ater recharge is usually
considered to be a separate component from ground water
underflow. Ground water recharge is here defined as
deep percolation from the land surface to the aquifer,
which is a different form of inflow than ground water
underflow. A separate section on ground water recharge
(as here defined) should be included in the report for
completeness. "
RESPONSE: For purposes of the modeling investigation, which
deals only with the Middle and Lower Alluvium Units, ground
water recharg~ is considered to be negligible.
20.
Page 1,0, paragraph 1: In the ADWR IBW water budget
memo dated 9/9/87, ground water' recharge via leakage
from the Upper Alluvium Unit and via direct recharge
. into the Middle Alluvium Unit was estimated to be equal
to about 150 percent of total pumpage,and about 200
. percent of ground water underflow. Not taking recharge
into the Middle Alluvium Unit into account is a limit-
ing assumption of the model and should be discussed
. more fully.
RDD/R41019
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RESPONSE: Additional evaluation of the estimates of under-
flow and recharge in the ADWR water budget is required. The
ADWR flownet shows converging streamlines which imply infin-
ite' transmissivity. The Operable Unit model assumes that
recharge is small relative to underflow, and therefore,
recharge is disregarded in the two-dimensional model,
although additional discussions with ADWR concerning this
a~alysis are warranted.
21.
Page 11, paragraph 2: Better water level data now avail-
able indicate head differences between composite wells
and Middle Alluvium Unit-only or Lower Alluvium Unit-
only wells range from as low as 10 feet where little
pumping occurs to as much as 70 feet in areas where
heavy pumping occurs. .
22.
RESPONSE:
Comment noted.
Page 12, paragraph 1: Effective porosity is'reported
to be 25 percent, but on page 8 the specific yield is
reported to be 10 percent. Which value was used in the
model? This is particularly important because the model
is reported to be sensitive to variations in effective
porosity (page 13). .
RESPONSE: Effective porosity was used for MOC,and specific
yield was used for MODFLOW.
23.
Page 12, paragraph 2: Can you please provide a refer-
ence for the reported values of dispersivity?
RESPONSE: Appropriate references can be found in: Hargis &
Montgomery, 1982. Digital Simulation of Contaminant Trans-
port in the Regional Aquifer System, U.S. Air Force Plant
No. 44, Tucson, Arizona: Interim Report, October 11, 1982.
Page 12, paragraph 3: How sensitive is the mode.l to
variations in initial TCE concentration, pa~ticularly
along the western margin of the zone of contamination
which is basically undefined? Given the lack of TCE
data in the west, what would be the effect of a "worst-
case" scenario of contaminated ground water extending to
the western boundary? .
RESPONSE: If contaminated ground water extended to the.west-
ern boundary of the model area, projections for the areal
extent of contamination for the different pumping regimens
would be larger. If water quality da~a become available to
document. this hypothetical zone of contamination, a new
pumping regimen could be investigated to more effectively
remove the contaminated ground water from the west.
24.
RDD/R4/019
B-12
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Page 12, paragraph 3: The MOC model does not allow for
introduction of additional contaminants into the system.
Vadose 'zones in the Middle Alluvium Unit may contain
sufficient TCE to provide a new source area not taken
into account by the model. Additional sources not taken
into account by. the model include leakage-contaminated
water from the Upper Alluvium Unit through cascading
wells, as well as areawide vertical leakage .from the
Upper Unit. The effects of this model limitation are
important and should be stated and discussed.
RESPONSE: Comment noted. The potential impacts of the Up-
per Alluvium Unit on the remedial action alternatives are
thoroughly discussed and evaluated in Sections 4 and 5 of
the OUFS..
25.
Page 13, paragraph 3: The sensitivity analysis would
be much more useful if provided in greater detail. Why
were sensitivity runs for the flow model stopped after
S years, but were run for 25 years' for the transport -
model? What ranges of values were explored?
RESPONSE: The ground water flow system in the model
approaches steady-state conditions after about 5 years after
pumping starts. Therefore, the sensitivity analysis con-
ducted on MODFLOW stopped after 5 years. The contamination
distribution does not reach steady state, and 25 years was
chosen as sufficient time for sensitivity analysis using
MOC. Transmissivity, coefficient of storage, and hydraulic
-conductivity were varied by +20 percent. Effective porosity
was varied by t60 percent, and longitudinal dispersivity was
varied by +400perc.nt~ . .
26.
The pumping values assigned to the different scenarios
need justification by comparing them with future use
projections for this area from the City of Scottsdale,
the Phoenix Active Management Area, Paradise Valley
- Water Company, and/or Arcadia Water Company.
RESPONSE: .For the purposes of the two-dimensional model,
pumping patterns for wells other than the extraction wells
for VOC-affected water were assumed to remain unchanged from
1986 pumping rates. As pumping in the future is documented,
the model can be appropriately updated. (Also see response
to ADWR Comment No.5.)
. .
27..
RDD/R4/019
B-13
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,---
SUMMARY OF PUBLIC COMMENTS AT
MAY 5, 1988 COMMUNITY MEETING
ON INDIAN BEND WASH SUPERFUND SITE
From Pamela Swift, Toxic Waste Investigative Group
EPA should study health impacts of past exposure to
contaminated drinking water.
RESPONSE: It is the responsibility of the Agency for Toxic
Substance and Disease Registry (ATSDR) to conduct a health
assessment at each Superfund site.
1.
.'
'2.
EPA.should put more effort into cost recovery.
RESPONSE: EPA will pursue co~t recovery actions at Superfund
sites in an appropriate manner.
3 .
DEQ should set up air toxics standards before the air
stripper is built.
RESPONSE:
No EPA comment.
4.
City of Scottsdale should become more involved in this
process--Mayor Drinkwater should hold a meeting with
citizens.
RESPONSE:
No EPA comment.
5.
City. of Scottsdale should consider impacts' on EPA's
projects when planning and zoning large projects that
will need large amounts of water.
RESPONSE:
No EPA comment.
From Carolina Butler, Scottsdale Resident
1. : EPA should look.at cancer rates among 40- to 50-year-old
women who lived in the Indian Bend Wash area. Government
should focus more on health problems.
RESPONSE:
See No.1 from above.
RDD/R4/019
B~14
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