United States
Environmental Protection
Agency
Office of
Emergency and
Remedial Response
EPA/ROD/R09-91/065
September 1991
Superfund
Record of Decision:
Indian Bend Wash Area
(Operable Units 1,4, 5, 6), AZ
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,-~
,50272-101
REPORT DOCUMENTATION 1'. REPORTNO.
PAGE EPA/ROD/R09-91/065
I ~
3. RecIpient's ACC888Ion No.
4. 11tI8 IIId SubtItle
SUPERFUND RECORD OF DECISION
Indian Bend Wash Area (Operable
Second Remedial Action
7. Aulhor(s)
5. Report Date
09/12/91
Units"l, 4, 5, 6), AZ'
6.
8. ~ Organization Rept. No.
8. PWfotmIng Orgllnlzation Name IIId Add-
10. ProjectlTulllWork Unh No.
..
11. Contnct(C) or Grant(G) No.
(C)
..
(0)
13. Type of Report & Period Coftnld
1~ ~ng Org8lllDllon Name IIId Addr888
U.S. Environmental Protection
401 M Street, S.W.
Washington, D.C. 20460
Agency
800/000
14.
-.
15. Supplement8l}' No....
16. Abatract (Umlt: 200 _rds)
The Indian Bend Wash Area site is an active electronics manufacturing and metal
plating facility located in the cities of Scottsdale and Tempe, Maricopa County,
Arizona. The site consists of two study areas, the North Indian Bend Wash (NIBW) and
South Indian Bend Wash (SIBW), both of which contain portions that lie in the
100-year floodplain of the IBW. TheNIBW area is the focus of this Record of
Decision (ROD) and consists of four operable units; 1, 4, 5, and 6. Land use within
the 10-square mile NIBW study area is mainly residential, commercial/industrial, and
developed open space (parks and golf 'courses). In addition, the Salt River
Pima-Maricopa Indian Community maintains a portion of NIBW as Cropland. The Indian
Bend Wash provides the major surface water drainage for the.NIBW area. Since 1950,
various electronics manufacturing and metal plating facilities, as well as other
industries,- have been. active at NIBW. Onsite operations have included the use and
disposal of organic solvents. During operations, waste solvents and wastewater
containing solvents were released from solvent storage..tanks and pipes directly to
dry wells, surface pits, ponds, lagoons, and the ground surface. In 1981, the State
conducted well sampling and identified VOC contamination in several municipal supply
(See Attached Page)
17. Document An8/y8Is L De8crlpto..
Record of Decision - Indian Bend Wash Area (Operable Units 1, 4, 5, 6), AZ
Second Remedial Action
Contaminated Media: soil, gw
Key Contaminants: VOCs (benzene, PCE, TCE, toluene), other organics,
b. Idenllller8/00000EncIedTenna metals (arsenic, chromium, lead)
c. COSA TI FIeIdIGrlq)
16. AveiIabIIty Statement
18. SecurI1y CIu8 (Tills Report)
None
20. SecurI1y Cts.. (TIlle Page)
Non~
21. No. 01 Pagea
100
n Price
See ANSl-De.1.
See /Mtructi- on Re-
(4-77)
(Formerty NTI~)
Depertment 01 Commerce
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EPA/ROD/R09-91/065
Indian Bend Wash Area (Operable Units 1, 4, 5, 6), AZ
Second Remedial Action
Abstract (Continued)
wells. EPA investigations have concluded that the methods used for solvent disposal
led to soil contamination, which in turn acted as a source o~ contamination for.
underlying alluvial units. A 1988 ROD provided for remediation of the middle and deep
alluvial units at NIBW. This ROD addresses contamination in the vadose zone and in the
upper alluvial unit within the NIBW area: However, because the vadose zqne overlies
the upper alluvial unit, which overlies the middle and deep alluvial units, remedial
actions documented in this ROD are ~ependent upon successful c9mpletion of the 1988
ROD. The primary contaminants of concern affecting the soil and shallow ground water
are VOCs including benzene, PCE, TCE, and toluene; other organics; and metals including
arsenic, chromium, and lead. EPA has designated 13 areas at NIBW for potential
contamination in the vadose zone, Twelve of these Areas are designated by number. The
13th area is in the vicinity of several city of Scottsdale ground water supply wells.
The selected remedial action for this site includes installing a soil vapor extraction
system for Areas 7 and 8 consisting of soil vapor extraction wells, a manifold
collection system, a vacuum pump, and a .vapor-phase carbon adsorption system;
installing additional soil vapor monitoring wel~s to continue investigations in Areas
3, 5, 6, 9, 11, and 12 with either soil vapor extraction or no further action ~emedies
as. needed; conducting no further action for Areas 1, 2, 4, 10, and the .City of
Scottsdale wells; and ground water monitoring in the upper alluvial unit. The
estimated present worth cost for this remedial action is a minimum of $21,576,000,
depending. upon the need for soil vapor extraction in Areas 3,5, 6, 9, 11, and 12,
which includes an annual O&M cost of at least $935,000 for 30 years.
PERFORMANCE STANDARDS OR GOALS: Chemical-specific soil and ground water criteria are
based on the more stringent of State water quality standards, Federal MCLs, or non-zero
MCLGs. These criteria include PCE 5 ug/l (MCL), TCE 5 ug/l (MCL), toluene 1000 ug/l
(MCL), arsenic 50 ug/1 (MCL),. chromium 50 ug/l (State), .and lead 50 ug/l (MCL).
,/ .
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RECORD OF DECISION
NORTH INDIAN BEND WASH O.U. J, X y
SUPERFUND SITE
Volume 1 of 3:
Declaration, Decision Summary, and
Appendix A«ARARs and Other Criteria for NIBW
September 1991
PHX69014.PS.RD
EPA Work Assignment No. 31-01-966G6-P20
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. CONTENTS
"
Volume 1
I
Declaration
'A. Site Name and Location.
B. Statement of Basis and Purpose
, C. Assessment of the Site
D. D~scription of the Selected Remedie~
E. Statutory Determinations
II Decision Summary
A. Site Name, Location and 'Description
B. Site History and Enforcement Activities
C. Highlights of Community Participation
D. Scope and Role of this Decision Docume.nt within the Site Strategy ,
E. Summary of Site Characteristics
F. Summary of Site Risks
G. Description of Alternatives' ,
H. Summary of the Comparative Analysis Alternatives
I. The Selected Remedies
J. Statutory Determinations
~. Significant Changes,
Appendix A--ARARs and Other Criteria for NIBW
Chemical-Specific ARARs and TBCs
Location-Specific ARARs and TBCs
Action-Specific ARARs and TBCs
Figures
1 Site Location Map
2 Site Map
3 Surface Water Features
4 Typical Geologic Cross Section
5 Potential Contaminant Source Areas ,
6 April 1991 Contours for UAU TCE Greater than 5 J.Lg/I
7 April 1991 Contours for MAU TCE Greater than 5 J.Lg/I
8 April 1991 Contours for LAU TCE Greater than 5 J.Lg/I
9 Potential Contaminant Source Areas
10 Decision Tree for Operation of Soil Vapor Extraction Systems
11 Schematic of Typical Soil Vapor Extraction System
12 Area 7 Soil Vapor Monitoring and Extraction Well Locations
. ,
RDD\R40S\OS6.51
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1
1
1
1
11
III
1
1
8
22
24
29
36
41
50
61
85
87
A-I
A-5
A-5
2
3
6
7
9
26
27
28
43
44 '
46
62
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CONTENTS (Continued)
'. ,
-' Volume 1 (Continued)
Figures (Continued)
13 Area 8 Soil Vapor Monitoring and Extraction Well Locations
14 Area 3 Soil Vapor Monitoring Well- Locations
15 Area 5"C" Soil Vapor Monitoring Well Location
16 Area 6 Soil Vapor Monitoring Well Locations
17 Area 9 S.oil Vap<;>r Monitoring Well.Location .
18 Area 11 Soil Vapor Monitoring Well Locations
19 Area 12 Soil Vapor Monitoring Well Locations .
20 Areas in the UAU with a Saturated Thickness ~5 Feet and
Contaminated above. VOC MCLs
Tables
1 NIBW Potential Source Areas
2 Chronology of Events at North Indian Bend Wash
3 Summary of Contaminant Concentration by Media
4 NIBW VOCs of Concern Cancer Potency Slope Factors and'
N oncancer Reference Doses ..
5 Future Use Scenario--Esti~ated Excess Lifetime Cancer Risk and
. N oncancer Hazard Quotient for Ingestion of Chemicals in Drinking'
Water ..
6 Summary of Estimated Excess Lifetime Cancer Risks and
Nonacarcinogenic Health Effects; Potential from Deep Soil
Ingestion Based on Maximum Reported Concentrations
7 Components of Ground-Water Remedial Action Alternatives
8 Ground-Water Remedial Action Alternatives Remaining after
Screening. .
9 Estimated Costs for Soil Vapor Extraction Systems.
10 Estimatled Costs for Further Vadose Zone Investigations
11 Estimated Costs for Ground-Water Alternatives Undergoing
Detailed. Analysis
12 Soil Gas Results for Area 8
13 Soil Gas Results foer Area 3
14 Soil Gas Results for Area 12
A-1
A-2
A-3
Chemical-Specific ARARs and Other Criteria for NIBW
Location-Specific ARARs and Other Criteria for NffiW
Action-Specific ARARs and Other. Criteria for NIBW
RDD\R40S\OS6.51
. Page
64
70
73
78
80
81
82
84
11
18
30
: 36
39
40
47
48
54
54
60
65
71
74
A-2
A-6
A-8
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CONTENTS. (Continued)
Located in Other Volumes
Volume
Appendix B--Administrative Record File Index
2
Appendix C--Response Summary
3
RDD\R40S\OS6.S1
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I. DECLARATION
A. SITE NAME AND LOCATION
This' Recard af Decisian (ROD) is far North Indian Bend Wash, the narth~rn partion
af the Indian Bend Wash Superfund site. The Iridian Bend Wash site is lacated in the
. cities af Scattsdale and Tempe, Maricapa CauntY, Arizana. The site includes a partian
af the Salt River Pima-Maricapa Indian Cammunity.
B. STATEMENT OF. BASIS AND PURPOSE
In September 1988, EP A selected a remedy far deep and middle-depth graund water at
Narth Indian Bend Wash (NIBW). Building upan that 1988 remedy, this decisian
dacument selects additianal remedial actians for the vadase zaneand shallaw graund
. water~ This dacument also. identifies applicable or relevant and'. appropriate
. requirements (ARARs) and ather criteria with which the 1988 remedy and the
remedies selected in this dacument shall camply. EP A has chasen these remedial
actians far NIBW in accardance with the 'Camprehen~ive Enviranmental Respanse,
Campensatian and Liability Act, 42 U~S.c. Sectian 9601 et seq., as amended by the
Superfund Amendments and Reautharizatian Act af 1986, Pub. L. No.. 99-499, 100 Stat.
1613 (1986) (CERCLA), and, to. the extent practicable, the Natianal Oil and Hazardaus
Substances Pallutian Cantingency Plan, 40 C.F.R. Part 300 (NCP). Da~a callected at
NIBW have been callected and analyzed in accardance with EP A-approved sampling
and. quality assurance plans. EP A cansiders site data to. be af adequate quality to.
suppart the selectian af reme~ies presented in this dacument. Appendix B af this
. ROD cantains the index far the Administrative Recprd File upc:>n which this decisian is
based.' .
The State af Arizana cancurs with the selected remedies.
. C. ASSESSMENT OF THE SITE
Releases af valatile arganic campaunds (VOCs) such as trichlaroethene (TCE) have
canta~inated the vadase zane and. ground water at NIBW. Actual aJ.: threatened
releases 'af hazardaus substances from this site, if nat addressed by implementing the'
respanse actians selected in this ROD, may present an imminent and substantial
endangerment to. public health,. welfare, or the environment. .
RDDIR40S,1)SO.Sl
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D. DESCRIPTION OF THE SELECTED REMEDIES
In September 1988, EPA selected a ground-water remedy for the Middle Alluvial Unit
(MAU) and the Lower Alluvial Unit (LAU) at NIBW. That remeqy, commonly
ref~rred to as the Scottsdale Operable Unit remedy, consists of groUlld-water extraction
using four City of Scottsdale wells" treatment at a central facility with air stripping and
vapor-phase carbon adsorption, and placement of treated water into Scottsdale's muni-
cipal water supply system. Although the initial configuration of the extraction well field
is limited to the four Scottsdale wells designated in the 1988 ROD, the remedy requires
containment and capture of all ground water in the MAD and LAU with VOC levels
that exceed federal drinking water standards (and certain other levels, as discussed in
this document). To achieve full containment and capture, the Scottsdale Operable Unit
remedy requires extensive ground-water monitoring and a supplemental analysis to
determine appropriate additional response actions to ensure full' capture in the MAU
and LAU. "
This document selects additional response actions to address the vadose zone and the
Upper Alluvial Unit (UAU) at NIBW. However, because the vadose zone overlies the
UAU, and the UAU in turn overlies the MAD and LAD, the success and appropri-
ateness of the remedial actions described in this ROD are dependent upon successful
, implementation of the 1988 ROD. .
EP A has investigated 13 areas' at NIBW for potential contamination in the vadose
zone. EP A has designated twelve of these areas by number; the thirteenth area is the
vicinity of several City of Scottsdale ground-water qsupply wells. In five of the areas
EP A has studied, Areas 1, 2, 4, 10 and the City of Scottsdale wells, data indicate that
the amount of VOCs present is not sufficient to warrant further action. At Areas 7
and 8, analyses indicate the mass of VOCs present could continue to contaminate
underlying ground water for hundreds of years. Therefore, for Areas 7 and 8, EP A has
chosen Soil Vapor Extraction, including
.
Additional soil vapor monitoring ~ells,
Soil vapor extraction wells, .
Piping to a vacuum extraction system, and
Vapor-phase carbon adsorption.
.
.
.
The vadose zone remedies for Areas 7 and 8 include periodic evaluation of the poten-
tial ground~water quality impacts from the residual mass and distribution of VOCs in
, the vadose zone.
For Areas 3, 5, 6, 9, 11 and 12, EP A data indicate that vadose zone contamination may
threaten ground-water quality. However, at this time, EP A does not have sufficient
information to determine if Soil Vapor Extraction is warranted in these areas. There-
fore, EP A is selecting additional response actions to further characterize the extent of
RDDIR40SIOS0.51
11
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VOC contamination iri tQese areas.,' The response actions vary from area to area, but
include"""
.
Shallow soil gas sampling, ,
.
P~pth-specific soil vapor monitoring; and
Estimating potential ground-water impacts due t6 migration of VOC
mass from the vadose zone.
. ,
, .
Based' on the further characterization of Areas 3, -5, 6, 9, 11 and 12, EP A will require
Soil Vapor Extraction for those areas that threaten to contaminate ground water at
levels above federal. drinking water standards. For areas. that do not present this
. ' threat, EP A believes no further action 'will be necessi;lry.
. ,
Under existing conditions, there appears to be significant migration of VOCs out. of the
UAU (1) through ground-water flow down wells that provide a conduit between the
UAU and the lower units and (2) through vertical ground-watei'flow across large areas
of the contact between the UAU and the MAU; Available data also indicate contami-
nated areas of the UAU generally overlie areas of the MAU and/or LAU that are also
,already contaminated. Analyses by the Arizona Department of Water Resources indi-
cate that, with the Scottsdale Operable Unit remedy in place to address contamination
in the MAU ,and LAU, the estimated time required to achieve acceptable levels of
VOCs in the UAU and in the overall ground-water system is not likely to change signi-
ficantly whether or not ground-water extraction from the U AU. is included as part o~
the ~emedy. In addition, the limited and variable saturated thickness of the, UAU could
make it difficu1t to operate and maintain an effective UAU ground-water extraction
system. Therefore, EPA has determined that ground-water extraction from the UAU is
not warranted at this time. However, in order to ensure (1) that the mass of VOCs in.
'the UAU, is significantly and' continuously decreasing due to migration to the MAU
and/or LAU and (2) that VOCs are not migrating to uncontaminated areas in the
UAU, MAU or LAU, EP A is selecting an expanded ground-water monitoring program,
including additional ground-water monitoring wells in the l!AU and MAU. If analyses
indicate the mass of VOCs in the UAU is migrating into the MAU and/or LAU too
slowly or that formerly uncontaminated areas of the UAU, MAU or LAU are
becoming contaminated by migration of VOCs within or from the UAU, EPA will
, reassess the appropriateness of additional ground-water extraction and, treatment at
NIBW. .
E. STATUTORY DETERMINATIONS
The selected remedies for NIBW, including the Scottsdale Operable Unit remedy, are
protective of human health and the environment, comply with Federal and State
requirements that are legally applicable or relevant and appropriate to the remedial
RDDIR40SIOSO.Sl
11~
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actions, and are cost-effective. The NIBW remedies utilize permanent solutions and
alternative treatment or resource recovery technologies to the maximum extent practi-
cable and satisfy the statutory preference for remedies that employ treatment that
reduces toxicity, mobility or volume as a principal element.
Because the NIBW remedial actions will result in hazardous substances remaining on-
site above health-based levels while ground-water extraction continues, a review will be
conducted within five years after commencement of the remedial actions to ensure the
remedies continue to provide adequate protection of human health and the
environment. -
. ~. ~
~ anJ 4tlln~~
Daniel W. McGovern .
Regional Administratoi~ EP A Region IX .
RDDIR40SIOS0.51
iv
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q . ) ~ . Cf ,-
Date
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ll. DECISION SUMMARY
A. SITE NAME, LOCATION AND DESCRIPTION
The' Indian Bend Wash Superfund site. consj~ts of two study areas--North Indian Bend
Wash (NIBW) and South Indian Bend Wash (SIBW)--primarily in Scottsdale and
Tempe, Maricopa Comity, Arizona (See Figure 1). This Record of Decision addresses
remedial actions 'forNIBW. SIBW is the subject of a~ ongoing Remedial Investigation.
1. LOCATION'
The NIBW study area encompasses the ten square miles bounded on the north. by
Chaparral Road, on the ,east by PimalPrice Road, on the west by ScottsdalelRural
Road and on the south by the southern edges of Sections 11 and 12, Township 1 North,
,.Range 4 East. Approximately eight square miles of NIBW are within the City of
Scottsdale, while approximately one square mile, is within the City of Tempe and
. another square mile is part of the Salt River Pima-Maricopa Indian Community (See
Figure 2). '.
2. LAND USE
Irrigation activities began in the late 1800s with the completion of the Arizona Canal
and were consolidated with the formation of the Salt River Valley Water Users
Association (SRVWUA) in the early 1900s.', By 1943, most of the study area was irri-
gated using surface water provided by the Salt River Project (SRP) for the SRVWUA
members, supplemented by ground-water pumpage. Urbanization has gradually
decreased the area under'irrigation. . At present, approximately 70 percent of NIBW is
residential, 23 percent is commercial/industrial and 7 percent is developed open space
(parks, golf courses, etc.). Current land use patterns ate not likely to change signifi-
cantly in the near future because the area is nearly completely developed. The Salt
River, Pima-Maricopa Indian Community maintains the area along the east and south-
east of NffiW as. irrigated cropland. '
3. POPULATION
The 1990 resident population within NIBW was approximately 42,810. Due to tourism
and winter residency, the population in the area increases during the winter and
decreases in the summer. Although the City of Scottsdale predicts continued
population growth through the year 2000, the population increase within the study'area
is likely to be limited by the existing high degree of development.
RDDIR40SIOSl.51
1
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NOT TO SCALE
FIGURE 1
SITE LOCATION MAP
NORTH INDIAN BEND WASH ROD
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BEND WASH
B01.INDARY
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2000
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4000 FEET
.......----.q
FIGURE 2
SITE MAP
NORTH INDIAN BEND WASH ROD
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4.. CUMA TE
The climate in the study area is semiarid. The average daily maximum temperature is
85°F, and the average daily minimum temperature is 55°F. ,As a long-term average,
winds are from the west at 6 miles per hour. Precipitation averages 7 inches of rain
per year. More than two-thirds of the annual precipitation occurs in summer and
winter. Winter rains are more gentle and of longer duration than the summer rains,
which occur as short, intense, localized thunderstorms. Pan evaporation, measured at
the nearby Mesa Experimental Farm, averaged 108.66 inches per year between 1972
and 1986. '.
5. TOPOGRAPHY
The surface topography of NIBW is relatively flat. The surface ranges from 1290 feet
above mean sea level at the corner of Chaparral and Scottsdale Roads down to approx-
imately 1160 feet above mean sea level in the bottom of the Salt River bed. Slopes of
the overall land surface range between 0.2 percent to 3 percent. Slopes of more than
100 percent are present locally on bank protection for the Indian Bend Wash and the
Salt River.. . .
6. SURFACE WATER
The Indian Bend Wash (the "Wash") provides the major surface water drainage for the
NIBWarea. Historically, the Wash was a natural desert wash emptying southward into
the Salt River. During the 1970s, the U.S. Army Corps of Engineers, Maricopa County
and the. City of Scottsdale developed the Wash as a "green belt" within NIBW. It now
consists of a series of linked ponds surrounded by irrigated recreational areas such as
parks and golf courses. The Wash is lined, with concrete south of the southernmost
pond. SRP canals or wells and City of Scottsdale wells provide water to fill the ponds.
and for irrigating the green belt. During periods. of flooding, the ponds in the Wash
may overflow and discharge water to the Salt River. A second major wash, the Granite
Reef Wash, drains water along the eastern side of NIBW down to the Salt River. .
. "
Swimming and wading historically have been restricted in the ponds a~d connector
streams in the Wash. However, fishing is permitted in several of the ponds. Fishing.
restrictions were issued in 1984"when VOCs were detected in ground water used to fill
the ponds. Wafer, sediment and fish tissue samples confirmed the presence of VOCs
in the ponds. By 1988, after discharge from contaminated wells had been halted,
analyses of water, sediment and fish tissue samples indicated the ponds had returned to
an uncontaminated state. Fishing is still prohibited in some of the ponds for reasons
other than the presence of contaminants associated with the Superfund site.
The Salt River channel overlies the southern boundary of NIBW. Flow in the river
near NIBW is a rare event because of the impoundment of runoff in SRP's reservoirs
on the Salt and Verde Rivers. Normally, all water in the Salt River is diverted
upstream from NIBW at Granite Reef Diversion Dam into the Arizona and South"
RDDIR405t051.S1
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"-- I .
...,;
. ,
. Canals for irrigation and municipal use in the Phoenix area. Significant spills of water
a~ Granite Reef Dam leading to flow by NIBW have occurred in the Salt River since
1964, although these spills had relatively short duration (usually less than 5 days).
Recharge of ground water occurs during such flood events on the Salt River.
The ,~QO-year floodplains of the Wash and the Salt River have been channelized by
man-made "improvements". The 100-year floodplain for the Granite Reef Wash varies
from approximately, 1800 feet wide at Thomas and ,Pima Roads to approximately 400
feet wide at McKellips ~oad. Figure 3 shows the relationship of the NIBW surface
water features to the 100-year floodplains and the Standard Project. Floodplains (as
defined by the U .5. Army Corps of Engineers). ..
7. GROUND WATER
Ground water in NIBW occurs principally in four, alluvial, units bounded' below by
. relatively impermeable basement rocks (See Figure 4). The amount of storage and
flow within the alluvial units varies ,considerably wit~: area a,nd depth. The shallowest
occurrence of ground water is 'currently in the Upper Alluvial Unit (UAU) at approxi-
mately 100 feet below land surface. The Middle Alluvial Unit (MAU) and the Lower
Alluvial Unit, (LAU) underlie the UAU. The UAU is composed primarily of sand,
gravel, cobbles and boulders, the MAU is composed primarily of sandy silts and clays,
and the LAU is cOJDPosed primarily of variably-cemented sands and gravels; The
fourth alluvial unit, the Red Unit, is expected to occur between the LAU and the
basement rocks, but the Red Unit has not been identified conclusively in NIBW drilling
data. . . .
Several municipalities and wate~ purveyors pump water from within, or adjacent to,
NIB:W, in~luding . '.,' . '
.
Arcadia Water Company,' .
Paradise Valley 'Water Company, , .
Salt River Pima-Maricopa Indian Community,
Salt River Project,
City of Scottsdale, and"
. City of Tempe.
.,.'
.
.
.
.
.
'.
Most production wells in NIBW produce water froIn the MAU and LAU. Few, '.if any,
wells pump'water dire'cdy from the UAU. . .
,Scottsdale obtains much of its drinking water from surface water 'supplied by SRP arid
the Central Arizona Project (CAP), and the remaining portion from ground water. The
ratio of ground water to surface' water is dependent lipon available' surface water
, supplies. In drought periods, the ground-water consumption increases. Approximately
. 24 existing production wells and 36 unused wells (abandonment procedures typically
have not been dO,cumented), including the known municipal, ,industrial, domestic and
irrigation wells, are located within NIBW.. ' ,
, ,
5
RDDIR40SIOSl.Sl
-------
CHAPARRAL ROAD
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, COS .,. COS TT COS 11
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~=--....
COS 78 WELL IDENTIFICATION NUMBER
. AGRICULTURAL PRODUCTION WELL
. MUNICIPAL PRODUCTION WELL
. MONITORING WELL/S). TEST HOLES OR DESTROYED
WELLS WITH LITHOLOGIC INFORMATION
DOMESTIC PRODUCTION WELL
INDUSTRIAL SUPPLY WELL
AREA COVERED BY 100 YEAR FLOODS
AREA COVERED BY STANDARD PROJECT FLOODS
I. cos,
.~M.11..
l'-.
"-.
.03
OOS 73.-
_:.B~Q..,,-
2000
4000 ~E E-
----------
~
FIGURE 3
SURFACE WATER FEATURES
NORTH INDIAN BEND WASH ROO
-------
MONITORING WELLS
0- 0 ,Q'~' ~,- 0" ~<:~ - ~ ~ ------,
, 0 : _Water Table 0 ,0: e::, " ~ ' 0" 0 ,0 ~ ";-0 <::> ~ """----0 ' 0 e::,
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Red Unit
o
FEET
BELOW
GROUND
SURFACE
FIGURE 4
TYPICAL GEOLOGIC
CROSS SECTION
NORTH INDIAN BEND WASH ROD
-------
B. SITE HISTORY AND ENFORCEMENT ACTMTIES
, 1. HISTORIC INDUSTRIAL ACTMTIES
Various electronics manufacturing and metal plating facilities, as well as other indus-
tries, have been active at NIBW since at least the 19505. Operations at many of these
facilities have included the use and disposal of organic solvents. Several means of
solvent disposal, including
'.
Release of waste solvents or wastewater containing solvents to dry wells, .
.
Release of wastewater containing solvents to surface pits, ponds and,
" lagoons, , . .
.
. Release from solvent storage tanks and pipes, and
.
Release of solvents and other waste directly to the ground surface
,have had the potentiat' to contaminate soils and ground water in the' study area.
EP A has grouped possible source facilities by location into "potential source areas" (See
Figure 5). Table 1 presents a summary of information pertaining to each of the poten-
tial source areas. In many of the potential source areas, buildIngs and other structures
covering large portions of the areas continue to be used for industrial'and commercial
operations.
2. SITE DISCOVERY
In October 1981, the City of Phoenix detected volatile organic compounds (VOCs) in
two of its wells in Scottsdaleffempe area. The State of Arizona, SRP and the cities of
Phoenix, Scottsdale and Tempe conducted additional sampling that identified VOCs--
primarily trichloroethene (TCE}.-in several other municipal supply wells in the Indian
Bend Wash area. Based on these initial indications of contamination and further sam-
pling, EPA proposed the.Indian Bend Wash for inclusion on the National Priorities List
(NPL) in September 1982. The Indian Bend Wash Superfund site achieved final NPL
status on September 1, 1983. .
3. SITE INVESTIGATIONS
The earliest hydrological studies in NIBW and adjoining areas were conducted by Davis
(1897), Lee (1905), and Meinzer and Ellis (1915). Later studies by Arteaga et al.
'. (1968), Halpenny et al. (1967) and Laney and Hahn (1986) contained additional
detailed work on the hydrogeology of the Paradise and Salt River Valleys in the vicinity
of NIBW. These studies emphasized the regional hydrogeology and water supplies of
the area.
RDDIR40SIOSl.Sl
8
-------
, .
D:;. ROAD
~"-~""-""~'-'
FIGURE 5
POTENTIAL CONTAMINANT
SOURCE AREAS
NORTH INDIAN BEND WASH ROD
:]2
.':
2000
'.~"
~ooo FEET
-~...... ,"-
P""'"""""'"
ROAD
>
,
.
.
. ".)..
'-.
-......" ~"
19
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-------
......
o
Table 1
N1BW Potential Source Anas
Sheet I 01 7
Occupant From To Land Use or Activities Types 01 Materlab1 Used Methods 01 Release Comments
Anal, Maricopa County Parcel No. 131-17-OOS0 .
City of Scottsdale --- Early 1Wo sewage polishing ponds Sewage eenuent Release of liquid eenuent to ponds. Ponds were removed and/or filled in
Sewage Treatment 19605 totaling 11.1 acres Nature of pond lining is unknown. 1980 as part of the Army Corps of
Facility Engineers' Indian Bend Wash Chan-
South of Cuny Road nelization Program.
and West of ~yden
Road
Ana%, Maricopa County Parcel No. 131-7-OO1C
City of Scottsdale 1959 1966 Pri!DaJY treatment facility Unknown Release of liquid eenuent to ponds. Oxidation in ponds was preceded by
Sewage Treatment with 13.4 acres of oxidation Nature of pond lining is unknown. primaJY treatment.
Plant ponds
City of Scottsdale ; .1966 Present Equipment Unknown Unknown
Maintenance Yard maintenance/storage
Area 3, Maricopa County Parcel Nos. 131-15-013B,C; 131.IS.I09A, 131.15-OIIN, and 131.IS-011A
Marro Plating! 06nt 7186 Metal finishing operations 1,I,I-TCA, metal hydroxide Waste hauler, recycling.
Technical Metal sludge
Finishing
Corporation
7811 E. Pierce Street
Marro Plating! 7186 Present Metal finishing 1,I,I-TCA . Waste hauler.
Plainville West
7811 E. Pierce Street '
Genesis II 1976 P.resent Isopropanol, oil, Freon-TMS Wastes stored.onsite. An underground gasoline storage
Electronics, Inc. tank may be located on the property.
7901 E. Pierce Street
-
Beckman Instruments 12173 03/82 Gas discharge display TCE, chloroethene, Freon- Direct release onto the ground,
350 N. Hayden Road assembly, etching, washing, TF -TMS, -TWD602, discharge to drains, waste haulers.
screen printing, soldering toluene, isopropanol,
methanol, acetone, hydro-
fluoric acid
Com tech 04/82 11184 Manufacture and testing of TCE, isopropanol, Freon, Recycling, release to city sewer.
350 N. Hayden Road eleclrical components I,I,I-TCA
Fairchild Dala 12/84 Present Circuil board assembly, l.l,I-TCA, TCE, ferric Waste hauler, release to city sewer.
350 N. Ilayden Road wave soldering and cleaning, chloride solution, Freon-
melal immersion coating TMS, oakitc L-25 and L-33,
ammonium persulfale
solution, isuprop.mol
RDD!l{4
-------
~
......
I Table I I
NIBW Potential Source Anas
Sheet 2 of 7
Occupant From To Land Use or Activities Types of Materials Used Methods of Release (:omments
Ana .3 (ContJnued)
Sperry Infortniition omo 12173 Degreasing Freon-TA, hydrofluoric acid, 'Recycling, release to city sewer.
methanol, isopropanol
Hainey's Machine 12170 Unknown Machining of metal parts CUlling oils and solvents
Tool Co., Inc.
- ~ .
Ana 4, Maricopa County Parcel No. 131-lZ-142
Ames Meat Pre- 1957 ('1) CatfISh ponds, livestock Unknown Unknown
Southeast comer of 1949 pens, meat processing
intersection of Miller
and McDowell Roads .,
Golf Driving Range '1964 ('1) Recreational N/A N/A
Gas Station 1970 ('1) Commercial Unknown Unknown
'.
Race Track 1970 (1) Recreational Unknown Unknown
~
Multifamily I'lousing 1979 (1) Residential N/A N/A
Display Division
Area S. Maricopa County Parcel No. Not Identmeet
Salt River Project -- -- Water supply well Solvents (Shell 360, Unknown Pump equipmenl was reportedly
Granite Reef Well Mirachem 100) cleaned al a mainlenance yard wilh
(A-I-4) lABAI solvenl degreascr. At various limes,
(SRP 23.6E, 6N) pump lubricalion oil has been found
, floating on Ihe ground water in' Ihe
. well. Analysis of the floaling oil has
indicaled Ihat TCE concenlralions
in the oil may have ranged from less
Ihan 100 j1g!110 more than
30,000 j1g!1 (Monlgomery & Asso-
ciates, Inc., 04/0 1188). SRP person-
nel mainlain thai TCE has mowd
preferentially from solulion in Ihe
ground waler \0 solution in Ihe
floaling oil.
K-Man -- -- Shopping Cenler -- Unknown Organic solvent use is nor known for
Ihis sile.
RDDIR4'J!004.51-2
-------
.....
"->
Table I
NIBW Potential Source Areas
Shff. 3 or 7
. Occupan' From To Land Use or Adlvllles Types or Materials Used Me'hods or Release Commenls
Area 5 (Continued)
Granite Reef Wash .. .- Drainage channel -- Unknown VOCS detected in soils and soil gas.
Dniinage or Area 6 facilities may be
related.
Area 6, Maricopa Coun'y Parcel No. UO-39.ooIa,b,d
Siemens 1974 05182 Manufacture of zener Hydronuoric acid, Freon, Recycled, waste hauler, release to ADEQ RCRA inspection identified
Components, Inc. diodes methanol, ethanol, MEK, sewer. waste solvent storage area with
8700 E. Thomas Road manganese nitrate, TCE, unsealed drums and evidence or
chloroethene, phenol, spillage, November 1981.
sodium hydroxide, ammonia, '
potassium ferricyanide,
potassium silver cyanide
Dickson Electronics 6/67 1974 Manufacture of electrical Etching acid, TCE. Organic solvents and neutralized acid
8700 E. Thomas Road components discharged to city sewer, recycling of
solvents and cyanide.
Micro Semiconductor 05182 . Present Manufacture or electrical 1,I,t-TCA, chloroethene, Recycled, waste hauler, neutralized
8700 East 'll1omas '. components isopropanol, etching acid, compounds released to city sewer.
Road cyanide
Area 7, Maricopa Coun.y Parcel Nos. 13O-24.oo5OD, J; 13O-24.ooSG
Rolamech 1974 Present Manufacture or pens and 1,I,I-TCA, cutting oil Waste hauler Filed notification or storage tank.
3719 N. 75th Street metal machining buried sinCe approximately 1940 or
unknown size or contents.
Dickson Electronics 1961 1967 Manufacture of electrical Solvents Unknown
components
City of Scottsdale Present Police Impound Yard' -- Unknown
Area .. Maricopa Coun.y Parcel No.(s) No' Iden'lOed
Dickson Electronics 05160 Manufacture of silicon TCE, PCE Unknown
(248 South Wells wafers
Fargo; later designated
300, 308, and 310 South
Wells Fargo)
IWDIR491OO4.51-3
-------
.-.
w
I Table t I
NIBW Potential Source Areas
Sheet 4 0(7
Occupant From To Land Use or Adlvlties Types or Materials Used Methods or Release comments
. Area 8 (Continued)
Dickson Electronics Manufacture of solid-state Solvents Unknown
(Southwest comer of circuit breakers
2nd Street and Wells
. Fargo)
Dickson Electronics Manufacture and assembly Unknown Unknown
(310 S. Wells Fargo)a of tantalum capacitors
Dickson ElectroniCs 1964 1967 Assembly of zener diodes, Solvents Release to dry wells and/or Maricopa County Health Deparl-
(425 E. 2nd Street) product testing cesspool/septic system. ment approved conslruction of a
waste disposal pit, April 1%2.
. .
Dickson Electronics Present Field effect transistor Unknown Unknown
(Ball Park Plaza/Civic - operations
Center Plaza)a .
"The Strip JOynt 0ln2 09/86 Furniture stripping Methylene chloride; Waste sludge spread on the ground
2940'N. 73rd Street I,I,I-TCA onsile
Bells of the West 04187 Present Manufacture of wind bells Unknown Unknown
2'140 N. 73rd Street
City o[ Sco!tsdale. pre- Pre.1972 Sign painting Unknown Unknown ,
1%1 .,
Arizona Public Service pre- 1%5 Vehicle storage Unknown Unknown
1961 .-
Frontier Motors .. .- -- Auto repair Unknown' Unknown
.
Unidentified 10/84 09187 Storage of tile, stone, Unknown Unknown
decorative metalwork; paint
~praying
Marro Plating 1962 1966 Metal finishing TCE Discharge of industrial wastcwiner to
22 E. 4th Street septic syslem and/or vacant lot
(address since changed)
IWD/IH9/004.51-4
-------
~
.c::.
I Table 1 _IS 0,,1
NIBW PoleoUai Source Areas
Occupant From To Land Use or Activities Types or Malerlals Used Methods or Release Comments
Area 9, Maricopa Couoty Parcel No. Not IdenWied
Sail River Project Well -- b -- Water supply well Organic solvents (Shell 360, Unknown Pump L'quipment was reportedly
(A-I-4) 2DBB Mirachem 1(0) cleaned at a maintenance yard with
(SRP 22.SE, S.SN) solvent.degreaser. At various times,
pump lubrication oil has been found
Dooting on the ground water in the
well. Analysis of the Doating oil has
indicated that TCE concentralions
in the oil may have ranged from
21,000 I1g/1to more Ihan 100,000
. 11g/1 (Monlgomel)' & Associales, .
Inc., 04/(1188). SRP personnel
maintain Ihat TCE has moved pref-
erentially from solution in the
ground water to solution in the'
Dooling oil.
Area 10, Maricopa County Parcel No. Not IdentIred
Advance Auto Supply " Aulomotive component CUlling oils, solvents Discharge to city sewer system
machining -
Area II, Maricopa County Parcel No. Not IdenUDed
Dickson Electronics 1964 . . 1966 Tantalum capacitor Unknown Unknown
(Southeast corner assembly
. Hayden and Roosevell)
Union 76
1965 1979 .Auto repair Unknown Unknown
Motorola
1968 1969 Office Unknown Unknown
RDD/l{49/004.S I-S
-------
Occupant
From
To
Land Use .or Actlvilies
Area 12, Maricopa County Parcel No. 131-09..oo2C
Motorola
Government.
Electronics Group
8201 E. McDowell
Road
'.
.....
U1.
1{[)I)/R491OO4.51-6
1957
Present
Manufacture of electrical
componenls
Table 1
NIBW Pokntlal Source Areas
Types or Makrlals Used
TCE (1957-1976), rCE,
I,I,I-TCA, MEK, toluene,
methylene chloride, Freon,
isopropyl alcohol, metal plat-
ing waste, beryllium oxide,
gasoline'
Methods or Rekase
Small quantities may have joined
waslewater which went 10 dry wells
from 1957 to 1959; dry wells were 20
to 200 feet deep.
Small quantities may have joined
wastewater which went 10
infiltration/evaporation lagoons {rom
1959 to 1980.
Tank and pipeline leakage.
Release directly to ground.
Recycling, waste hauler.
Two 5-fooHliameter dry wells
approxiniately 25 feet deep
occasionally received cooling. tower
discharge or soap solutions resulting
from was~ing and rinsing of tools.
Sheet 6 or 7
Comments
In Deccmber of 1986, a release of
approximalely 5 to IO gallons of
I,I,I-TCA occurred at the corner of
Building 6 at the Hayden Road site
of Motorola GRG. Two sampling
efforts were compleled subsequenl
10 Ihis release 10 del ermine Ihe
vertical and hori:mntal extent of
conlaminalion. l11e dat.i derived
from these sampling efforls did nol
determine the vertical exlent of .
I,I,I-TCA since samples collecled al
the deepest depths slill contained
I,I,I-TCA atlhree 10 five times Ihe .
analytical detection limil.ADEQ
files did not have any type of follow-
up reporl as 10 whelher any cfforls
were made to dean up Ihis release.
On Oclober 10, 1981, MOlorola
personnel reporled to Ihc EI'A a
release from a 5OO-gallon waste'
solvenl tank. Approximalely 10 feet
of soil was removed from heneath
the lank when Ihe lank was
removL'd. Aller removal of the tank,
the area lleneath the tank was
apparently excavated to a depth of
approximately 60 feel. 'll1e rL'Sults
from the anal~is of samples collec-
ted during .Ihe deep excavation indi-
cated Ihat contaminanls had not
been released to the vadose zone.
June 1981, soils wilh preeipilaled
metals l>enealh Ihe retired surface
impoundments were excavated and.
shipped 10 a smeller.
Septemhcr .1982, an induslrial waste-
water Irealmenl planl pipeline leak
was delecled. Six cubic yards of soil
were removed and soil samples were
collected 10 a depth of 24 feel.
-------
1 Table 1 ...." 01 ,I
NIBW Pokntlal Source Areas
Occupant From To Land Use or AdlvlUes Types 01 Makrlals Used Methods 01 Release Comments
Area COS Wells, Maricopa County Parcel No. Not IdenliOed
City of Scousdale Well -- C -- Water supply well Solvents (Shell 360, Pump equipmenl owned by SRI-' was
No.6, SRP 23.3E, 7.SN Mirachem 100) reportedly cleaned at a maintenance
(A-2-4) 2SBCD, Nos. yard wilh solvent degreaser. At
2S, 71, 72, 73, 7S,and various times, pump lubrication oil
76 has been found noating on the
ground water in the well. Analysis
of the noaling oil has indicated thai
TCE concentrations in the oil may
have ranged from less than 10 jiglto
2,000 jigll.(Montgomery &
Associates., Inc., 04101188). SRP
personnel maintain that TCE has
moved preferentially from solution
in the ground water to solution in
the noating oil.
aThis facility may be outside "designated" boundary of Area 8. .
bWell constructed November 1948.
cWell c
-------
Numerous studies related to contamination have been performed at NIBW since 1980.
Table 2 is a chronology of important studies and related events at NIBW since 1980.
EP A began the Remedial Investigation for the Indian Bend Wash site in June 1984.
EP A released its Phase I ,Remedial Investigation Report in August 1986.' In April'1988,
as the overall Remedial InvestigationfFeasibility Study (RIfFS) continued, the City of
Scottsdale completeci the Operable Unit' Feasibility Study for Remediation of
Groundwater in the Southern Scottsdale Area (Scottsdale OUFS). The Scottsdale
OUFS focused on development and analysis of remedial action alternatives for contam-
ination in the MAU and LAU. EPA released the overall North Indian Bend Wash
RIfFS, which focuse~ on contamination in the UAU and in the vadose zone, in April '
1991. The relationship between the Scottsdale Operable Unit and the overall RIfFS is
discussed in greater detail in Section. n.D of this Record of Decision. .
As indicated i;ll Table 2, the study of contamination at NIBW has included many types
of activities conducted by various entities. The Arizona Department of Health Services
first coordinated these numerous activities through the Indian Bend Wash TCE Task
Force, which met between March ~982 and September 1984. A Project Committee
formed by EP A in October 1984 superseded the Task Force. During the RIfFS, the
Project Committee has ,been an information-dissemination body through which EP A
maintains communication with state and local agencies, potentially responsible parties
(PRPs) and their, contractors, and v¥.irious other interested parties.
4. ENFORCEMENT ACTIVITIES
EPA has sent RCRA 3007/CERCLA 104(e) 'information request letters regarding
NIBW to eighteen parties. EP A also has conducted interviews, title searches and finan-
. cial assessments at the' site. Table 1 includes information regarding many of the poten-
tial PRPs for NIBW. There are also a few property owners in the' study area who are
not listed. in Table 1 but who could be potentially lia~le.
Eleven parties' received Special N'otice Letters notifying them of their potential liability
: for the. Scottsdale Operable Unit remedy. Following issuance of this ROD, EPA
expects to, send Special Notice Letters for the re~ainder of the work ~nd for past
response costs.
During the RIfFS, ¥otorola Government EI~cironics Group (Motorola) entered into
three Administrative Orders on Consent (Consent Orders) with EPA over the period
from February 1985 through July 1987. Under these Consent Orders, Motorola has
installed 21 ground-water monitoring wells, measured .water levels, sampled
groundwater, tested production wells and performed shallow soil gas sampling. Outside
any EP A enforcement mechanism, Motorola also has installed at least 19 additional
ground-water monitoring wells and performed soil borings.
p'"
RDDIR40SIOSl.S1
17
-------
Table 2
Chronology of Events at North. Indian Bend Wash
Sheet 1 of 4
Date Activity
6180 Investigation of Motorola Government Electronics Group was conducted.
12180 Motorola conducted a soil boring/sampling program of trace metals in former waste
impoundments (Higgens and Hansen, 1981).
IOl8r TCE was detected in Phoenix water supply wells COP 35 and COP 36.
11/81-12181 . Additional well sampling conducted by ADHS, Salt River Project, City of Phoenix,
City of Scottsdale and City of Tempe, found TCE in eight wells, including cas 6,
cas 31, cas 75 (formerly COP 34), cas 72 (formerly COP 35), and cas 71
(formerly COP 36) as well as three others.
12181 Soil sampling for VOCS began at Motorola and in Indian Bend Wash by ADHS
(ADHS, 1982). "
3182 ADHS established IBW TCE Task Force.
5182 U of A collected soil gas samples adjacent to Well SRP 23.6E,6N and COP 35.
5/2182 SRP sampled soil in boring a~ Well SRP 23.6E,6N.
6182 ADWR inventoried wells and conducted aquifer test of COP 35,
6182 EP A-FIT (Ecology and Environment) collected data from the Indian Bend Wash site
for use in the EP A's hazard ranking system.
9182 EPA--FIT sampled'20 wells.
9182 Indian Bend Wash site was nominated for inclusion on EP A's National Priorities List
(NPL).
10182 Six soil borings advanced by Dames & Moore in Area 1 for City of Scottsdale.
, ADHS took soil samples and sampled cas 69. Dames & Moore sa,mpled soil gas for
methane.
2183 EPA-FIT conducted sampling at Comtech Data Corporation (formerly Beckman).
4183 SRP sampled storm event on Granite Reef Wash at McDowell.
7183-8183 SRP conducted aquifer test of Well SRP 23.6E,6N and collected VOC samples.
8183 Motorola advanced three soii borings: ST-l, ST-2, and ST-3, analyzed selected soil
samples'from them for VOCS, completed them as Upper Alluvial Unit monitoring
wells, and collected VOC and inorganic water quality samples. Water-level
monitoring began with these wells.
9/1183 Indian Bend Wash site appeared on NPL in Federal Register.
9183 EPA developed Remedial Action Master Plan to guide site investigation activities.
1-6184 City of Scottsdale sampled water and fish in ponds in Indian Bend Wash.
6/1184 ' Remedial Investigation of the Indian Bend Wash site officially began.
RDD/R40SIOS2.S1-1
18 "
-------
. Tab~e 2
Chronology of Events at North Indian Bend Wash
Sheet 2'of 4
Date Activity
Summer Motorola insta~led, conducted aquifer tests,. and collected VOC and inorganic water
1984 quality samples from 13 moriitoring wells:
Upper Alluvial Unit Wells: M-ZUA. M-3UA. M-4UA. M-5UA. M-6UA. and
M-7UA .
Middle Alluvial Unit Wells: M-IMA. M-ZMA. M-3MA, M-4MA. M-5MA. M-6MA.
and M-7MA
10184 Proj~t Committee formulated by EP A with ADHS, ADWR; USGS, City of Phoenix,
City of Scottsdale,City of Tempe; Motorola GEG, Beckman Instruments, and others.
10184 ADWR contaminant transport modeling study began. ADWR installed a water-level
recorder OU ST-Z, and began monitoring.
11184 Beckman conducted onsite soil sampling in .seven boreholes and ~pleted two of
these as soil vapor monitoring wells.
11-1ZI84 Beckman conducted onsite shallow soil gas sampling and sampled two soil vapor
monitoring wells. , . .
3185 Fish sampling was conducted by Arizona Game and Fish in some Indian Bend Wash
ponds.
3185 Administrative consent orders were signed by EP A and Motorola, and EP A and
Beckman.
Spring 1985 Motoro~a installed, conducted aquifer tests, and collected VOC and inorganic water
quality samples from 10 monitoring wells including:
Upper Alluvial Wells: M-8UA. M-9UA. M.-lOUA. M-llUA. and M-IZUA
. .
Middle Alluvial Wells: M-9MA. M-lOMA. M-UMA. and M-IZMA
Lower Alluvial Well: M-lOLA. ..
7185 .'
City of Tempe collected depth-sp~ific samples from Well COT 6 ~th packers.
RDDIR40SIOS2.S 1-2
19
-------
..
Table 2
Chronology of Events at North Indian Bend Wash
Sheet 3 of 4
Date Activity
Summer Beckman installed, conducted aquifer tests, and collected VOC and inorganic water
1985 quality samples from four monitoring wells:
Upper Alluvial Wells: B-J, B-UA-l, and B-UA-3
Middle Alluvial Well: B~MA-l
EP A installed, conducted aquifer tests, and collected VOC and inorganic water
quality samples from seven monitoring wells and one piezometer: .
. .
Upper Alluvial Wells: ~ E-IUA, E-2UA, E-3UA, E-4UA, and E-5UA
Middle Alluvial Well: E-IMA
.
Middle Alluvial Piezometer: E-IMP
Lower Alluvial Well: E-ILA
1985 City of Scottsdale installed an air stripper on COS 6.
11185 Forty-two wells were sampled as part of community well sampling program.
6186 Nine areas were identified north of the Salt River by the EP A for source
investigations.
8186 Motor~la signed an Administrative Order: on Consent to conduct shallow soil gas
testing and spinner lOgging.
. .
8186 Phase I RI report was. written by Ecology and Environment for the EP A
9186 Motorola conducted soil gas survey adjacent to existing UAU monitoring wells.
10186 Dames & Moore conducted soil sampling from five auger borings and four backhoe
pits near a storage tank and chemical storage area at Motorola.
10186-1188 Motorola conducted spinner logging on SRP 23.6E,6N~ SRP 22.5E,5.5N, SRP 23.3E,
'.5N, SRP 23.3E,7.3N, SRP 22.5E,6N, COS 25, COS 71, COS 72, COS 75, and
COT 6.
2187 The EPA conducted a shallow soil gas survey in Ar~ 1,2,3,4,5,6, 7, and 8.
2187,3187 Motorola and EPA conducted a 10000y aquifer test With Well SRP 236E..6N.
6187 The EPA conducted additional shallow soil gas sampling in Areas 3, 5, 6,7,8, and 9.
RDDIR40SIOS2.S1-3 .
20
-------
Date
8/87-2/88
",
9187-12/87
12187
1188-3/89
2188
.Summer
1988
4188
9/21188
11188
2/89-3/89
6189
6189-8/89
9189
Table.2
,Chronology of Events at North Indian Bend Wash
Sheet 4 of 4
Activity
"
Motorola installed. conducted aquifer tests, and collected VOG and inorganic water
quality sam~les ~om 11 monitorin~ wells:
Upper Alluvial Wells: M-13UA. M-15UA, and M-16UA
"
Middle Alluvial Wells: M-14MA, M-15MA, and M-16MA
Lower Alluvial Wells: M-2LA"M-5LA, M-9LA, M-14LA, and M-16LA
Motorola decommissioned three onsite wells.
The EPAconducted additional shallow soil gas sa,mpling in Areas 3 and 8.
EPA sampled soils at Areas 2. 3. 4. 5. 6. 7, 8. and 9.
The EP A collected sediment. fish. and water samples from Indian Bend Wash ponds.
Beckman installed, conducted aquifer tests. and collected YOC and inorganic water
quality samples from UAU Well E-12UA The EPA installed. conducted aquifer
tests. and collected VOC and inorganic water quality, samples from six monitoring
wells:
"
..
Upper Alluvial Wells: E.6UA, E-7UA, and E-9UA
"
"
Middle Alluvial Wells: E-5MA and E-8MA"
Lower Alluvial Well: E-7LA
Scottsdale OUFS, Public Comment Draft.
Scottsdale OU ROD signed.
. .
SRP and Gradient sampled soils and soil gas at 23.6E.6N and. 22.5E.5N for VOCS
EPA installed soil vapor wells at Areas 3. 6. 7, 8, 10, and 11 and UAU Well E-13UA
at Area 11.
Administrative consent order signed by EP A arid Siemens.
Siemens installed, conducted aquifer tests. and collected YOCand'inorganic water
q~lity samples from four monitoring we!ls: ,
" Middle Alluvial Wells: S-lMA, S-2MA
..
Lower Alluvial Wells: S-ILA,S-2LA
~P A shallow soil gas sampling at Motorola.
-
11189-12189 EP A shallow soil gas sampling at COS wells.
RDDIR40SIOS2.51-4
21
-------
EPA issued a Unilateral Administrative Order (Unilateral.Order) to Beckman Instru-
ments (Beckman) in July 1984. After challenging the Unilateral Order, Beckman
agreed to install and monitor four ground-water monitoring wells and to perform soil
borings. Beckman has installed and monitored an additional ground-water monitoring
well under a December 1988" Consent Order.
. . , .
The Siemens Corporation (Siemens), as a suc~essor to Dickson Electronics, entered
into a Consent Order with EPA in July 1989. Under the Consent Order, Siemens has
installed and sampled four ground-water monitoring wells. Motorola and Siemens also.
recently installed additional ground-water monitoring wells outside the scope of their
Consent Orders with EP A
In July 1989, EPA issued a Unilateral Order to Advanced Auto Supply, Beckman,
Dickson Electronics, Marro Plating, Motorola,PlainVille West, Salt River Project,
Siemens and the Strip Joynt. The Unilateral Order required the recipierits to imple-
ment the remedy for the MAU and LAU. After amending the Unilateral Order in
December 1989, EPA agreed to negotiate a Consent Decree with Beckman, Motorola,
Salt River Project and Siemens on the condition that they comply with the Unilateral
Order until the Consent Decree became effective. The Department of Justice expects
to lodge the Consent Decree with the Federal District Court in Phoenix in the fall of
1991. ... .
In the near f~ture, EP A will commence enforcement. activities to implement the
response actions selected in this ROD and to recover EP A's past response costs.
C. HIGHLIGHTS OF COMMUNITY PARTICIPATION
EP A currently maintains NIBW information repositories at the EPA Region 9 office in
San Francisco and at the Scottsdale, Tempe and. Phoenix Public Libraries. The EP A
Region 9 office and the Scottsdale and Tempe Public Libraries maintain copies of the
entire Administrative Record File on microfilm, while the Phoenix Public Library main-
tains a collection of selected key site documents, including the RIIFS. In addition, the
Arizona Department of Environmental Quality maintains an information repository in
its Phoenix office. .
EP A also mamtainsa computerized Indian Bend Wash mailing list, currently with over
1,000 addr~sses. In addition to continually updating the mailing list, EP A sent a fact
sheet in December 1990 to approximately 35,000 addresses in the area of the Indian
Bend Wash Superfund site in an effort to expand the list.
EP A also operates and publicizes a toll-free information message line to enable inter-
ested community members to call EPA with questions or concerns about Indian Bend
Wash Superfund site activities. Beginning in the fall of 1990, EPA has been responding
. . - .
RDDIR40SIOS1.S1
22
-------
to numerous inquiries about effects of potential Superfund liability upon residential and
small business property located within or near the site boundaries.
Belpw is a chronological list of other community relations activities EP A has conducted
for NIBW in order to comply With the public participation requirements of CERCLA
Section 113(k)(2)(B) and 117. .
RDDIR40SIOSl.Sl
. .
.
July 1984--Distriquted a letter arid fact sheet announcing the start-up of
RIIFS activities.. .
.
August 1984--Held a public meeting to provide a summary of the
Superfund process and to inform interested parties of upcoming RIIFS
activities. . .
.
September 1984--Released a Community Relations Plan based upon
interviews With Phoenix, Scottsdale and Tempe. residents and State and
local offici~lls. .
.
February 1985--Distributed a fact sheet updating the community on
RI/FS and enforcement activities.
.
July 1986--Distributed a fact sheet informing the community about the
completion of the Phase I Remedial Investigation Report and other activ-
ities, including the community well sampling program and the lake and
. fish sampling program; .' . -
.
August 1986--Held a public meeting to update the community on site ac-
tivities, to present the re'sults of the Phase I Remedial Investigation and
to discuss future RIIFS activitIes. .
.
April 1988--Published a public notice in the Arizona Republic announcing
the start of the public review and comment period and the scheduled
public meeting for the. Scottsdale OUFS.
April 1988--Mailed the Proposed Plan fact sheet for the Scottsdale OU
remedy to the site mailing list.
.
. .
May 1988--Held a.public meeting to present ,the EPA's preferred alterna-
tive for the Scottsdale OU, answer questions, hear concerns and receive.
formal public comments. .
October 1988--Mailed a fact sheet 'announcing the remedy selected for
the Scottsdale 0 U. .
.
.
.. ,
March 19, 1991--MaiIed AdministrativeOI~ecord File to Scottsdale and
Tempe Public Libraries. .
23
-------
. .
.
April 10, 1991--Mailed .the RIIFS and the Proposed Plan factsheet for the
UAU and vadose zone remedies to the Scottsdale, Tempe, and Phoenix
Public Libraries and the NIBW Project Committee. Mailed Proposed
Plan factsheets to the site mailing list.
, .
.
April 15, 1991--Started a 3D-day public review and comment period for
the overall RIIFS and the Proposed Plan. for the UAU and vadose zone.
remedies. Appendix C of this ROD presents' the public comments
received and EP A's responses. .
May 1, 1991--Published public notices in the Arizona Republic and the
Scottsdale Arizona Progress announcing a 3D-day extension (through June
13, 1991) to the public review and comment period.
.
May 3; 1991--Mailed a flyer announcing the comment period extension to
the site mailing list. . . . .
.
May 7, 1991--Mailed an Administrative Record supplement to the
Scottsdale and Tempe Public Libraries.
.
May 8, 1991--Held a public meeting to present the EPA's preferred alter-
natives for the UAU and soils, answer questions, hear concerns and
receive formal public comments.
.
May 31, 1991--Mailed fact sheets announcing the availability of the
Administrative Record supplement to the site mailing list. Published a
public notice in the Arizona Republic announcing the availability of the
Administrative Record supplement.
.
June 6, 1991--Published public notices in the Arizona. Republic and the
Scottsdale Arizona Progress. announcing the availability of the
Administrative Record Supplement: .
Do. SCOPE AND ROLE OF THIS DECISION DOCUMENT
WITHIN THE SITE STRATEGY
This ROD focuses on remedial measures for soils and the UAU, which are not specifi- '
. cally addressed by the Scottsdale Operable Unit remedy. In addition, Appendix A of
this ROD identifies the applicable or relevant and appropriate requirements (ARARs)
~d other criteria to be considered (TBCs) for both the Scottsdale Operable Unit.
remedy and the remedies selected in this ROD. .
Ground-water contamination is an area-wide problem at NIBW, extending vertically
through the UAU, MAD and LAU and currently spreaq ,across approximately 6 square
RDDIR40SIOS1.51
24
-------
miles (S~e Figure~ 6, 7 & 8). EP A has- studied 'soil contamination in more limited
areas, 'in association with historical practices that- may have led to releases of VOCs at
particular facilities. Soil areas studied ~s potential continuing source areas generally'
overlie contaminated groundwater. As shown on Figures 6 through 8, contaminated
areas in the UAU also generally overlie contaminated areas of the MAU and/or LAU,
although in some areas the UAU 'and LAU are contaminated whil~ the intervening
MAU is not. .
As' previously discussed, the UAU .directly overlies the MAU; the saturated UAU is
itself overlain by unsaturated soils. It is likely that VOCs have migrated, and .continue
to migrate, downward through. the soil profile, laterally in the' saturated UAU, down-
ward into the MAU and LAU, and laterally in the MAU and LAU. Contaminants in
t~e UAU are likely to enter the .MAU arid.LAU both through leakage at the
UAU/MAU contact and through water-supply wells with openings across large vertical
intervals. Therefore, contaminated ~oils ~re effectively a source of contamination to
the saturated UAU (or the MAU where the UAU .is not saturated), and the saturated
UAU in.turn acts as a source to the underlying alluvial uIiits. Because of this relation-
'ship between the unsaturated soils,and the saturated UAU, MAU and LAU, remedial
actions selected in this Record of Decision are tied closely to the Scottsdale Operable
Unit remedy and will rely upon full compliance with the terms of the proposed Consent
Decree negotiated for that remedy. . . '. .
. . As shown in Table 2, EP A . signed the Record of Decision selecting the Scottsdale
Operable Unit remedy in September 1988. The 1988 ROD requires ground-water
extraction from the MAD and LAU using four existing City C?f Scottsdale production
wells, treatment with air str~pping and vapor-phase carbon adsorption-to remove VOCs,
and placement of the treated water into Scottsdale's municipal distribution system. The
proposed ConsentDecree, which is.expected to replace the Unilateral Order, requires
Motorola, Siemens, Beckman and SRP to (1 )6perate and maintain a groundwater
monitoring program, including the installation of 23 additional groundwater monitoring
wells; (2) fund treatment system design costs above $500,000; (3) construct the
treatment plant and pipelines leading from the extraction wells to' the plant;
(4) reimburse the City of Scottsdale for the costs of operating the treatment plant; and
(5) reimburse EPA and the State of Arizona for oversight costs. The City of Scottsdale
is designing the treatment plant and the pipelines. Scottsdale is .providing $250,000 for
the design and the State of Arizona is providing a grant for an additional $250,000.
Scottsdale also has agreed to operate the extraction and' treatmerit' system and to
accept the treated water into its distribution system. '
. ,
Although EPA expects the four wells specified in the 1988 ROD to remove a large
portion of the mass of VOCs in the MAU and LAD, additional extraction at other
locations is likely to be necessary to achieve full capture in the MAU and LAU.
Additional ground-water extraction also may be appropriate in order to address areas
of high contaminant concentrations or to reduce the time for achieving in-situ ARARs;
RDDIR40StOS1.S1 .
. 25
"
. '
-------
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.
.
.
.
.
WELL IDENTIFICATION NUMBER
AGRICULTURAL PRODUCTION WELL
MUNICIPAL PRODUCTION WELL
MONITORING WELL(S), TEST HOLES OR DESTROYED
WELLS WITH LITHOLOGIC INFORMATION
DOMESTIC PRODUCTION WELL
INDUSTRIAL SUPPLY WELL
.
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,
~
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2000
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FIGURE 6
APRIL 1991 CONTOURS FOR
UAU TCE GREATER THAN 5 ug/l
NORTH INDIAN BEND WASH ROD
-------
CHAPARRAL ROAD
12 II ~
':"i
';- .,::a":
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LEGEND
COS 78
.
.
.
.
.
WELL IDENTIFICATION NUMBER
AGRICULTURAL PRODUCTION WELL
MUNICIPAL PRODUCTION WELL
MONITORING WELL(S), TEST HOLES OR DESTROYED
WELLS WITH LITHOLOGIC INFORMATION
DOMESTIC PRODUCTION WELL
INDUSTRIAL SUPPLY WELL
FIGURE 7
APRIL 1991 CONTOURS FOR
MAU TCE GREATER THAN 5 ug/l
NORTH INDIAN BEND WASH ROD
.
$M't. KC
Q
2000
4000 FE ET
.... . .
ROAD
. MCDOWELL
r (. r-
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.
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-------
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;J
-------
Therefore, the proposed Consent Decree requires the settling- PRPs to evaluate the
Scottsdale Operable Un~t extraction and treatment system and to propose measures to
ensure the success of theMAU/LAU cleanup. EPA and the settling PRPs then will
negotiate the implementation of any such additional.measures.
E. SUMMARY OF SITE CHARACTERISTICS
1. CONTAMINANTS OF CONCERN
Industrial facilities at NIBW have used the VOCs T~E, tetrachloroethene (PCE) and
1"I,I-trichloroethane (1,1,I-TCA), typically as solvents. These compounds, along with
chloroJorm, 1,I-dichloroethen~ (DCE), and to some extent 1,2-dichloroethene (1,2-
DCE: cis- and trans-), have been detected in deep and shallow soil, deep and shallow
soil gas, and groundwater from monitoring wells and supply wells. Trace metals do not
appear t
-------
Table 3
Summary or Contaminant Concentrations by Media
. Sheet 1 or 2
'. Number or
Concentrations Number or Detec:tlonsl
Sample No. or
Maximum Minimum Median Mean Locations Samples
Ground.Water Samples
-------
Table 3
.. Summary or Contaminant Concentrations by Media
Sheet 2 or 2
Sumber or
Concentrations Number or DetectlonsJ
Sample, No. or
Maximum Minimum Mean " Locations . Samples
Median
Soli Gas Samples, Deep (1&W1 or 5011 gas) .'
TCA 6,770 0 29 680,12 7 W(25
PCE 238' 0 6.9 33,45 7 W(25
DCE 88 0 0 9,08 7 6(25
TCA 74 0 0 7,7 7 10(25
CFM 43 0 0 2.63 7 8(25
Surface. Water Samples JNI/l or water ~Iutlon)
,-
TCE 76 0 0 22.51 15 7115
PCE 3 0 0 0.52 15 5115
DCE 0 0 0 0 15 0115
TCA 0 0 0 0 15 0115
CFM 1 '0 0 .0.17 15 3115
aChlorofonn was not analyzed for in all of these'tests.
.,
Note: ND indicates less than the detection limit.
Means and medians were calculated by setting NO, 10 zero.
RDD1R491OO9.51
31
',\.
-------
, .
Because TCE is the most widespread contaminant at NIBW, its fate is discussed
below. The other VOCs identified at NIBW have similar fate characteristics.
, , ,
With TCE's relatively high vapor pressure, volatilization is the most significant removal
mechanism when TCE is released onto surface soils. Once TCE is released into the
atmosphere, it is readily photo-oxidized, ultimately to hydrochloric acid (HCl), carbon
monoxide (CO) and carbon dioxide (C02). While these breakdown products are
undesirable as components of photochemical smog, the long-distance transport and
accumulation of TCE itself in the atmosphere generally has' not been a concern
because its half-life in )air is approximately 3.7 days.
Soil' properties and conditions governing the movement of air through soils and
subsequent volatilization of TCE from unsaturated soils include soil porosity,
temperature, convective currents and barometric changes. TCE sorption to soils
increases most significantly with high organic content in soils. Sorption also increases
with clay content, increases slightly with decreasing temperature, increases moderately
with increasing salinity of soil wat'er and decreases moderately as dissolved organic
content increases.
Reported soil adsorption 'coefficients forTCE indicate high mobility in soils and low
potential adsorption. Therefore, TCE leaches readily to groundwater. Once TCE
reaches ground water, volatilization ceases to be a significant process. Biodegradation
takes over but is relatively slow. Therefore, with minimal volatilization and slow
biodegradation, TCE is expected to persist for months to years.
Estimates from soil and soil gas concentrations indicate TCE is present in the vadose
zone at some of the potential source areas in quantities from tens to hundreds of
pounds. The Arizona Department of Water Resources has estimated that, as of 1988,
approximately 313 gallons of TCE were present in 'UAU ground water, and approxi-
, mately 5900 gallons of TCE were present in the overall ground-water system. Although
EP A has not estimated the total quantity of other VOCs in the vadose and saturated
zones, in some areas VOCs other than TCE are expected to represent a significant
proportion of the total quantity of VOCs present. . Future monitoring and analyses will
take into account all VOCs identified at NIBW. '
2. POTENTIAL SOURCE AREAS
As previously stated, Figure 5 and Table 1 provide information regarding 13 areas EP A
has studied as potential sources of contamination at NIBW~ Some of these areas are
associated with only one suspected source activity or facility, while others may have had
several operations that could have contributed to the contamination. The 12 areas
shown on Figure 5 and the Scottsdale wells are discussed further in Section 11.1 (THE.
SELECfED REMEDIES) of this ~OD.
EPA also studied the Indian Bend Wash ponds. The Indian l3end Wash ponds were
designed to be constructed of compacted natural materials. Based on seepage tests
RDDIR40SIOSl.Sl
32
-------
. conducted in 1979 and 1980 at two of the ponds, the Salt Riv.er Project estimated
average seepage rates ~t 0.003 to 0.029 feet per day. - For several years, water pumped
from nearby Salt River Project and municipal wells was used to maintain the level of
the ponds. - Some of these wells are now known to have been contaminated. Water
quality sampling in 1984 indicated that several of the ponds were contaminated with
VOCs, but historic water quality data are not available to 'estimate the mass of VOCs
that could have seeped through the bottom of the ponds. EP A conducted additional
water quality sampling at the Indian Bend Wash ponds in 1988, by which time the use
of contaminated wells to fill the ponds had been discontinued. One water sample con-
tained VOCs at a level just above the detection limit; all o~her results were below the
de~ectionlimit. - -
3. RECHARGE SOURCES/SURFACE WATER
. . -
The dominant source of recharge at NIBW appears to be irrigation by' the' Salt River
Pima-Maricopa Indian Community.. The heavy agricultural irrigation occurs to the east
of NIBW; hydrographs. indicate water then flows laterally under NIBW within the
. UAU. DAU modeling in the RIIFS assumed recharge from the source ranging froni
, 1,0'00 to 1,600 acre-feet per year. Additional irrigated binds just. to the east of the
model boundary may add substantially to this estimate. .
, Recharge at NIBW also may come from residential irrigation (estimated at approxi-
, mately 270 acre-feet per year) and flood irrigation of parks, schools and cemeteries'
(estimated-at 300 to 400 acre-feet per year). Seepage also occurs from the laterals that
make up SRP's surface water d~livery system.
As discussed previously in Section II.A.7" three prominent surface water features are
present at NIBW: the Indian Bend Wash pond system, the Granite Reef Wash and the
Salt River. Assuming a seepage rate of 0.01 feet per day and an approximate total
. pond surface area of 20 acres, the Indian Bend Wash ponds may provide approximately
70 acre-feet of recharge per year. The Salt River appears to be an important source of
recharge at NIBW when the river is flowing. The Salt River does not flow frequently,
principally because of the Granite Reef Dam. ,However, hydrographs indicate that
winter releases from Granite Reef Dam add to summer peaks in DAU water levels
frqm irrigation. Noticeable recharge'impacts due to the intermittent flow in the Indian
Bend Wash and the Granite Reef Wash are not evident. ' .
Infiltration from precipitation seems insignificant in the hydraulic analysis for NIBW '
. ground-water flow because of low amounts of.precipitation, lack of catchments resulting
in ponding. and high evapotranspiration. .
"
'.
RDDIR40SIOS1.S1
33
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4. GROUND WATER
8. UAU
The UAU consists of unconsolidated sand, gravel, cobbles and boulders, with local thin
interbeds of silt and clay. The combined thickness of the saturated and unsaturated
zones of the UAU ranges between 110 and 170 feet. The elevation of the base of the
UAU lies between 1,030 and 1,126 feet above sea level within NIBW.
The saturated UAU appears to be an unconfined aquifer. Water levels measured
during July 1989 were between 1,085 and 1,115 feet iri elevation and were roughly 90 to
140 feet below land surface. The saturated thickness at monitoring well locations
ranged from 0 to approximately 34 feet based on July 1989 measurements. This satu-
rated thickness generally decreases to the north. -
, The horizontal gradient in the UAU during July 1989 ranged from approximately
0.0023 to 0.0046 towards the west-northwest over the majority of the area. The
gradient fluctuates seasonally, becoming steeper in the summer and flatter in the
winter. The horizontal hydraulic conductivity ranges from 370 to 4,200 gallons per day
per square foot (gpd/ft2). No systematic zonation of hydraulic conductivity estimates is
apparent from available information. Average porosity has been estimated to be
approximately 0.30 to 0.35 based on lithologic and geophysical logs, and the specific
- yield has been estimated to range from 0.15 to 0.20 based on comparisons with pub-
lished values fot similar materials.
b. MAU
The MAU consists of weakly cemented, interbedded clay, silt, sand and gravel. The
MAU ranges in thickness from approximately 250 to 800 feet at NIBW. The base of
the MAU lies between 300 and 800 feet in elevation. The base of the unit appears to
dip to the east in the study area. Individual aquifers in the MAU are expected to be
confined where there is a saturated thickness in the UAU. Individual aquifers in the,
MAU may also be confined where there is not a saturated thickness in the UAU.
Water levels (based on wells screened between 250 and 300 feet below land surface)
measured during July 1989 ranged from 1025"to 1050 feet above sea level, or approxi-
mately 155 to 202 feet below land surface. Horizontal gradients in the MAU change
significantly in magIiitude and direction during the year in response to groundwater
pumping. The most recent water level measurements suggest that a "trough" occurs
across the site- such that water tends to flow to the south-southeast in the northern
portion of the site and to the north-northwest in the southern portion of the site.
Horizontal hydraulic conductivity estimates for the MAU range from 7 to 690 gpd/ft2.
Co LAU
The LAU consists of weakly to strongly cemented gravel, boulders, sand, sandy clay,
silty sand and interbedde,d clay. The portion of the LAU penetrated by monitoring
RDDIR40S,1)Sl.S1
34
-------
, wells has generally coarser-grained materials than the MAU. The thickness of the
LAU in the study area is not well known. A few water supply wells in the northern
portion of NIBW may have reached the contact between the LAU and the Red Unit.
~owever, drillers' lithology descriptions of these wells are imprecise and therefore do
not identify the LAUlRed Unit contacts with certainty.
. ,
At NIBW, the LAU is confined by aquitards in the MAU. Water levels measured in
February 1989 ranged from 1015 to 1031 feet in elevation or 166 to 212 feet below land
surface. Flow within the ',LAU appears to be generally to the north. Horizontal
hydraulic conductivity estimates for the LAU range from 80 to 3,000 gpd/ft2.
. d. Red Unit
. The Red Unit underlies the LAO and overlies the bedrock complex in much of the
NIBW area. The Red Unit consists of debris flow materials comprised of reddish-
colored, well-cemented breccia, conglomerate, sandstone and siltstone. Water is most
. likely produced from fractures and faults within the Red Unit. As previously stated, ,
data are not sufficient to characterize the Red Unit in significant detail. '
e. Vertical Communication Between Units
There is an average downward vertical gradient of approximately OA between the UAU
and the MAU in the study area. Therefore, ground water flows downward from the
, UAU to the MAU, probably over a large area. Near the western boundary of the
saturated UAU, ground water appears to flow laterally into the MAU. Vertical flow
also appears likely between the MAU and LAU, betwee'n which there is an average
downward vertical, gradient of approximately 0.1. However, because the vertical
hydraulic conductivities are not known, it is difficult to estimate the' rate of vertical
flow. . .
Fluid movement investigations in the study area indicate that ground water' from the
UAU and the upper, portion of the MAU enters several wat~r supply wells and travels
downward into the lower units. There are at least 26 supply wells at NIBW that could
serve as conduits because they cross the saturated UAD and the lower units, but the,
total discharge fr
-------
F. SUMMARY OF SITE RISKS
1. HUMAN HEALTH RISKS.
8. Toxicity Assessment
, EP A has classified TCE as a probable human carcinogen based upon laboratory experi-
ments indicating excess liver tumors' in mice exposed to TCE through ingestion.
. Chlorofc:>rm is classified as a probable human carcinogen based upon experiments that
produced liver cysts in dogs and kidney tumors in mice' through ingestion exposures.
EPA considers l,l-DCE a possible human carcinogen because of kidney tumors that
developed in mice that were exposed through inhalation. PCE is either a possible or
probable human carcinogen; EP A currently is assessing PCE's carcinogenic classifica-
tion. The other VOCs of concern at NIBW have not been classified or have not been
assessed for carcinogenicity.
In terms of non-cancer risks, the general class of VOCs found at NIBW can cause
depression of the central nervous system, kidney and liver disorders, nausea, headaches,
dizziness and respiratory irritation.
. ,
Table 4 includes the cancer potency slope factors and the non-cancer reference doses
(RIDs) for the VOCS of concern at NIBW. Other compounds detected less frequently
may contribute to the cancer and non-cancer risks posed by the site.
Table 4
NIBW VOCs of Concern
Cancer. Potency Slope Factors
and Noncancer Reference Doses
Noncancer
Cancer Potency Reference
Slope Factor , Dose (RID)
Compound (mg/kg/day)"l (mg/kg/day)
Trichloroethene .. 0.011 0.00735
Tettachloroethene 0.051 0.01
1,1-Dichloroethene 0.6 0.009
1,1,1- Trichloroethane 0.09
, "
Chloroform 0.061 0.01
RDDIR40SIOS1.S1
36
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b. Exposure Assessment.
i. Ground Water.. The City of Scottsdale relies upon ground water for approximately
70 percent of its drinking water supply, with the remainder of its water coming from
surface water supplies such as the. Central Arizona Project.. Beginning in 1981,
Scottsdale began tomonitbr closely the level of VOCs in its'NIBW ground water supply
wells, discontinuing use of those with contamination above drinking water standards.
One exception is ~cottsdale's well #6, which is owned by SRP and leased by
Scottsdale. Water from this well is pumped and treated by air stripping at the wellhead
to meet drinking water standards before being placed into the distribution system.
The City of Tempe does not use any. of the contaminated wells at the site to provide
water for its distribution system. ,SRP supplies the bulk of Tempe's water from uncon-
taminated surface and ground-water supplies.
Based on the above discussion, no one receiving water from the local municipal distri-
bution systems currently should be exposed to VOCs in their drinking water at levels
above federal. Maximum Contaminant Levels (MCLs).
Although inhalation and dermal exposures due to activities such as showering, cooking
and domestic irrigation. may introduce VOC exposures that are significant relative to
exposure through ingestion, the careful management of the local distribution system
. should be minimizing the potential exposures from these routes.
SRP also supplies ground, water for urban irrigation. However, the ground water
supplied by SRP is not from contaminated wells at the site.
Some residents may operate small private ground-water wells within the contaminated
. area. Small private wells. are not normally subject to the monitoring requirements
applicable to the larger water supply systems. Although at this time EP A is not aware,
of the use of small private wells at NIBW, any such use could increase the potential for
exposure to VOCs.. . .
, .
ii. Surface Water. The surface water provided for the NIBW area by SRP is not from.
the site and therefore should not increase potential exposures to VOCs unless the
water is contaminated from other sources before reaching the site.
Sampling in the Indian Bend Wash ponds in 1988 failed to reveal the VOC contam-
ination indicated by similar sampling in 1984. Furthermore, swimming is not allowed in
any of the ponds, while fishing is prohibited in several of the ponds. Based on low to
undetectable contaminant ~evels and restricted access, therefore, the IBW ponds do not
appear to present significant potential exposures to VOCs.
.. .
iii. Soil and Soil Gas. .Workers at facilities with VOCs in shallow soil gas may have
low levels of exposure through inhalation. Otherwise, direct exposure to soil and soil
gas contamination at land surface is expected to be minimal.
RDDIR40SIOS1.S1
37
'-,
-------
, '
VOC contamination has been detected (at low levels) in only five surface soil samples.
Based upon available data, therefore, EP A considers transport of contaminants via
wind, surface water, and erosion an unlikely exposure p~thway and did not quantita-
tively evaluate this pathway in the risk assessment. Workers could be exposed to con-
taminated soil and soil gas during excavation activities., Residents liVing near areas of
high soil-gas concentrations could have additional VOC 'exposures if the gas were to
migrate to homes through conduits such as sewer lines and collects in crawl spaces or
basement. Although these possible residential exposures cannot be quantified using
available data, EP A believes they are minimal. '
iv. Fish. Analyses of fish tissue samples in' 1984 indicated VOC contamination was
present in some fish taken from the IBW ponds. Sampling was repeated in 1988 after
the City of Scottsdale had stopped using contaminated wells to fill the ponds. With the
exception of one anomolous result for chloroform, the 1988 sampling indicated that the
fish that were sampled were free of VOCs. Therefore, EP A considers the potential
exposure to VOCs through ingesting fish from' the IBW ponds to be minimal. Fishing
in some of the ponds is currently restricted for reasons unrelated to EP A's Superfund
activities.
Co Risk Characterization
EP A has estimated cancer and non-cancer human health risks due to potential
exposures to VOCs at NIBW. EP A estimates cancer using assumptions EP A believes
tend to favor health protectiveness. The risk estimates presented in this section are
intended to be conservative but not unrealistic. Actual risks are unlikely to exceed, and
may be less than, these estimates.
Site risks are discussed in the following sections by environmental medium. Tables 5
,and 6 summarize the risk characterization for the exposure pathways at NIBW for
which EP A was able to quantify the risk.
i.Ground Water. Using assumptions of 2 liters of water per day every day for 30
years by a 70 kilogram person, EP A has estimated an upper bound excess cancer risk
due to reasonable maximum drinking water exposures at NmW. In order to provide a
baseline for comparison, EP A has estimated the excess cancer risk assuming the use of
contaminated supply wells (which are actually currently closed) to supply drinking
water, primarily from the MAU and LAU. Under this scenario, the excess cancer risk
is estimated at approximately 10-4, or one in ten. thousand, from exposure to VOCs.
The non-cancer hazard index for exposure to VOCs in water from these wells would be
0.95. If water from only the UAU were consumed, the cancer risk from VOCs is
estimated at approximately 10-5, and the non-cancer hazard index would be 0.11. As
previously stated, inhalation and dermal exposures could increase these baseline risks
. .
RDDIR40SIOS1.S1
38
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~
\0
TableS
. . FutUR U5e Scenario
Estimated E1u:as Uletlme Cancer Risk and No~cer Hazard Quotient lor Ingestion 01 Chemicals In Drinking Water
Water Carcinogenic Noncarcinogenic
eooc:eatratlon Effects Chronic Effects Chronic
(GeoaIe8rlc MeaD) DaUy Intake Slope Factor Excess Uletlme ~11y Intake RID
(IIWI) (mWII&-clay) (kg-clay/mg) Cancer RIsk . (mWIIg-clay) (~-clay) .NIIQ
ExlsUna Supply WeD
TeE- 199.709 2.4 x 10-3 0.011 2.7 x 10-5 5.7 x 10-3 0.00735 .7.8 x 10-1
PCE 49.94 6.1 x 10-4 0.051 3.1 x 10-5 1.4 x 10-3 0.01 1.4 x 10-1
1,I-DeE 4.971 6.1 x 10-5 0.6 3.7 x 10-5 1.4 x 10-4 0.009 1.6x 10-2
I,I,I-TCA 1.252 1.5 x 10-5 3.6 x 10~5 Q.09- 4.0 x 10-4
Chloroform 4.134 5.1 x 10-5 . 0.0061 3.1 x 10-7 1.2x 10-4 0.01 1.2 x 10-2
Sum 9.5 x 10.5 . - 9.5 x 10.1
.
Upper Alluvial Unit Only
TCE 22.748 2.8 x 10-4 0.011 3.1 x 10-6 6.5 x 10-4 0.00735 8.8 x 1O~2
PCE 5.259 6.4 x 10-5 0.051 3.3 x 10-6 1.5 x 10-4 0.01 -U x 10-2
. I,I-DCE 3.078 3.8 x 10-5 0.6 2.3 x 10-5 8.8 x 10-5 0.009 9.8 x 10-3
1,I,I-TeA . 0.688 8.4 x 10-6 2.0 x 10-5 0.09 2.2x 10-4
Chloroform 1.348 1.7 x 10-5 0.0061 1.0 x 10-7 3.9 x 10-5 0.01 3.8 x 10-3
Sum 3 x 10.5 0;)
Exposure Assumptions:
Daily Intake = 2 liters/day - Exposure Frequency = 365 daysiyear
. Body Weighl = 70 kg Exposure Duration =.30 years
RDD1R49/012.51
-------
~
o
Table 6
S~ry or Estimated Excess LIfetime
Cancer Rlsils and Noncarcinogenic Health Efreds
- Potential rrom Deep SOU Ingestion Based on Maximum Repo~ Concentrations
Detected Detected
Compouud Compound
F..xhJbIUna EsUmated Excris Exhibiting
Carelllogenk Slope Factor UftIme Cauc:er Noncarcinogenic RID Dally Intake Dally I nlake
Site Elreets (~day).1 Risk Effeets (mglkflday) (mglkWday) Exceeds RID
Area' 5 Chloroform 0.0061 1 x 10-11 Chlorororm 0.01 8.6 x 10-5 No
Area 7 Trichloroethene 0.011 '3x 10-10 NA NA NA
Area 8 Trichloroethene 0.011 7x 10-12 NA NA NA
Area 9 Chlorororm 0.0061 2 x 10-12 Ctilorororm 0.01 1.4 x 10-7 No
Area 10 Trichlorethene 0.011 .1 x 10-12 NA NA NA
1 x 10-12 .
Area 11 Trichlorothene 0.011 NA NA NA
NA = Not applicable.
Exposure Assumptions:
Daily Soillntake..l00 mg/day
Body Weight--70 kg
Number or dayslweek exposed:-5 days '.
Number or weekslyear exposed--12 weeks
Number of years exposed--O.16 year
RDD/R49/013.51
-------
by increasing the overall exposu.fe to.VOCs. Steps taken by local water providers often
help to reduce these baseline risks.
ii. Surface Water. With little or no VOCs detected and limited access, surface water
does not appear to present an increase. in excess ca~cer or non-cancer risk from VOCs.
'iii. Soil and Soil Gas. Direct exposure to VOC.contaminated soil and soil gas in shal-
low soil does not appear to pose significant cancer or non-cancer risks. However, EPA
expects transport of VOCs to the ground water from the vadose zone could contribute
to the ground-water risks described previously. .
. Under a potential deep excavation scenario, the ex<;ess cancer risk to workers from
exposure to VOCs would be approximately one-in-ten billion, assuming 100 milligrams
of soil ingested five days a week over a' twelve week period (excavation is. considered a
one-time event). None of the estima~ed potential dailyintakes exceedxeference doses.
EP A can notqua~tify risks' due to other potential exposures to contaminated soils and
so.il gas with the available data. .
iv. Fish. Based on the 1988 tissuesamples from fish from the IBW ponds, ingestion of
fish would not present. an increase in either cancer or non-cancer risk from VOC
exposure. . . '.
.2. ENVIRONMENTAL EVALUATION
No endangered species or critical habitats have been identified at NIBW. Contamina-.
tion at the site does not appear to threaten wetlands. .' .
As previously stated, the condition of the IBW ponds was assessed in 1984 and again in
1988 through water and . fish sampling. EP A also collecte4 sediment samples. Although
the 1984 sampling indicated that the water, sediI11ent and fish contained VOCs, the
1988 sampling indicated that the use of uncontaminated ground water to fill the ponds
apparently had flushed YOCs from the ponds. With the continued use of uncontami-
nated water to fill th~ponds, fish and waterfowl do not appear- at further risk.
"
G. DESCRIPTION OF ALTERNATIVES
As discussed in Section II.!) of this Record of Decision, although. this document focuses
primarily on the vadose zone and the UAU, the success of the overall. remedy for
" NIBW will. be highly dependent upon the effectiveness of the remedy being imple- .
mented for the MAU and. LAU, including any modifications. SomC! of the significant
MARs. for NIBW are discussed in the following. sections; Appendix A of this ROD
identifies all of the ARARs for NIBW. Capital, annual operations and maintenance,
RDD/R40S,uSl.51
41
-------
and ti>tal present worth cost estimates for vadose zone and UAU remedial ~ction
alternatives that underwent detailed ~nalysis are presented in Section II.H.
1. VADOSE ZONE
, .
a.Development and Screening of Alternatives
EPA has considered vadose zone (soilrrtatrix, soil gas and liquid adhering to the soil
matrix) remedial action for the 12 numbered areas .shown on Figure 9 as well as for the
area around several City of Scottsdale wells investigated at the site. Although EP A
initially considered a wide range of technologies and other remedial measures, including
excavation, soil washing and capping, the types of contaminants and the considerable
depth of vadose zone contamination quickly reduced the number of possible options.
As discussed in Section II.F.1.c.iii, vadose zone contamination does not appear to
present significant risks through direct exposure. Therefore, analyses to date for NIBW
indicate that the reason for remedial action for the vadose zone in any particular area
of the site will be the potential impact upon ground water. The va"Qose zone alterna-
tives considered in the detailed analysis were No Action and Soil Vapor Extraction.
: b. Description of Remaining Alternatives
i. No Action. As required, the No Action alternative was developed for comparative
purposes, but also may be appropriate for areas where the mass of VOCs in the vadose
zone do not pose a threat to the underlying ground water. . Under the no-action
scenario, any VOC mass in the vadose zone would be allowed to migrate towards the
ground-water table. No remedial measures would be implemented to speed or limit
the rate of contaminant migration..
EPA has not been abie to identify ARARs that pertain directly to soil. However, the
Arizona Department of Environmental Quality's. Health-Based Guidance. Levels
(HBGu) for Contaminants in Drinking Water and Soil are other criteria that pertain
to soil. Available data indicate the No Action alternative will comply with. HBGLs for
soil. . But with continued contaminant migration to the water table, depending upon the
distribution and mass of vadose zone contaminants, the No Action alternative may not
comply with ground-water ARARs.
n. Soil Vapor Extraction (SVE). For NIBW,' the remedial action objective for SVE
would be to remove the potential for continued ground-water contamination due to
migration of contamination from the vadose. zone; the. criteria for the extent of an
action would be achieving a residual distribution and mass of VOCs in the vadose zone
. that does not threaten. to contaminate underlying ground water at levels exceedi~g'
federal drinking water standards (Maximum Contaminant Levels, or MCLs) and the
other ground-water criteria selected in this ROD. The distribution and mass of residual
VOCs would be evaluated at. regular intervals throughout operation and/or monitoring
of the SVE alternative. Figure 10 presents a flowchart of SVE operation based on the
objective of protecting ground water.
RDDIR40S~S1.S1
42
-------
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FIGURE 9
POTENTIAL CONTAMINANT
SOURCE AREAS
NORTH INDIAN BEND WASH ROD
P"""""""
-------
RESTART
SVE' SYSTEM
YES
. j
EVALUA TE NEED
FOR SVE
IMPLEMENT SVE AT
LOCATIONS OF HIGHEST VOC's
IN THE VADOSE ZONE
PREPARE AN ESTIMATE OF
THE DISTRIBUTION OF, '
CONTAMINANT MASS
NO
MONITOR'SOll VAPOR
FOR REBOUND IN
, CONCENTRATIONS
PREPARE AND ESTIMATE OF
THE DISTRIBUTION OF
CONTAMINANT MASS
MOVE SVE SYSTEM TO NEXT
HIGH CONCENTRATION AREA
YES
MAKE ADJUSTMENTS TO SVE
SYSTEM IF NECESSARY
REEVALUATE DATA, WEll
lOCATIONS AND OPERATIONS
. '
FIGURE 10
DECISION TREE FOR
OPERATION OF SOIL VAPOR
EXTRACTION SYSTEMS
NORTH INDIAN BEND WASH ROD
-------
SVE consists of a network of extraction wells installed in the vadose zone, connected to
the suction end of a vacuum unit through a collection manifold system. Injection of
ambient air into the vadose zone may be necessary to enhance recovery. The vacuum
. extraction unit produces a vapor/air flow through the unsaturated zone into the .extrac-
tion wells. The extracted gas flows through the collection system to the extraction unit
where, at NIBW, it would be collected using a vapor-phase carbon adsorption system.
Figure 11 is a diagram of a typical SVE system.
A network of multi-port soil vapor monitoring wells would be used to monitor the
effectiveness of the SVE system. Data from the soil vapor monitoring wells would be
used to revise the estimate of residu~l mass in the. vadose zone. The mass estimate
would then be used to estimate the remaining potential for contamination of underlying
ground water.' .
. .
One key ARAR for an SVE system would be the federal Clean Air Act. Specifically,
an SVE system would have to comply with any regulations that are part of the State of
Arizona's EP A-approv~d State Implementation Plan (SIP). In addition, VOC regula-
tions adopted by Maricopa County but not in the SIP would be other criteria to be
considered. .
The feder~l Resource Conservation and Recovery Act (RCRA) would be an ARAR in'
several respects. Subpart X of RCRA, which addresses miscellaneous units, including
arty closure and post-closure care, would be applicable or relevant and appropriate to
an SVE treatment system. The requirements of 40 CFR Parts AA and BB would be
relevant and appropriate for' air emissions from the SVE system. Under the "contained
in" principle, the RCRA regulations would be applicable or relevant and appropriate
for spent activated carbon~ \vhich would have to be managed as a hazardous waste.
. Subpart S, although not an ARAR, includes additional criteria to be considered.
2. GROUND WATER
, .
a. Dev~lopmentand S~reening of Alternatives,.
The ground-water remedial action components that, remained after technology screen- :
ing are listed j.rf Tabl~.-7' . " .
. With the exception of the first two ground-water extraction components listed in the
. first coluI.IID of Table 7, which do not 'require treatment ,or end use (beyond that
included as part of the Scottsdale Operable Unit remedy),EPA combined each of the
ground-water extractiort components with each of the treatment components and in
turn with each of the end use components. EP A initially formed a total of 50 ground-
water alternatives and evaluated them based on effectivenes~, implementability and
'cost. This screening process is summ,,:rized below; the. full discussion is provided in
Ch~pter 10 of the RI/FS. . .
RDDIR40S,uS1.S1
. 45
-------
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CAPABLII OF 110 TO 300
SCFM AT \','CUUM
OFOTOt..N,
MERCURY AT
THIS POINT
FIGURE 11
SCHEMATIC OF TYPICAL SOIL
V APOR EXTRACTION SYSTEM
NORTH INDIAN BEND WASH ROD
-------
Table 7
Components of Ground-Water -,
Remedial Action Alternatives
Ground-Water Ground-Water Treated Water
Extraction -. Treatment End Use
No Action in ~AU; Scottsdale Liquid-Phase Carbon Municipal Distribution System
Operable Unit Remedy in Adsorption (COS)
Place to Address the MAU &
LAU Photochemical Oxidation Recharge
Monitoring of the Fate of the ;.\ir Stripping w/o Vapor-Phase Mixed Use wlRecharge
VOCs in the UAU w/o UAU Carbon Adsorption
Pumping'l Mixed Use w/o Recharge
UAU Pumping at 900 gl?ma,b Air Stripping wNapor-Phase
Carbon Adsorption
~AU Pumping at 750 gp~a,b
UAU Pumping at 400 gpma,b -
aScottsdale Operable Unit remedy in place to address ,the MAU and LAU.
bIncludes the monitoring required in the Monitoring w/o UAU Pumping option.
. EPA eliminated the "No Action in the UAU" alternative, which would allow unmoni-
tored migration of VOCs, because EP A do~snot consider this alternative protective.
The "Monitoring of the Fate of VOCs in the UAU without Pumping from the UAU"
alternative was retained because the monitoring would . provide information to deter-
mine if adequate protection of human' health and the environment is attained without
pumping from the UAU. '. '
- - ,
EP A removed from consideration all the alternatives that included air stripping without
vapor-phase carbon adsorption as the treatment component (12 alternatives) because
air stripping by itself does not reduce the toxicity, mobility or volume of VOCs. Air,
stripping without emission controls also would not be likely to meet Maricopa County-'
air emission guidelines for VOCs. EPA screened outaltematives with liquid-phase
carbon adsorption as the treatment component (12 alternatives) because a similar
technology, vapor-phase carbon adsorption (in conjunction with air stripping), promises
similar results at lower cost. . ' ,
Of the remaining alternatives, EP A eliminatecl'those'\Vith end uses other than recharge'
, alone (18 alternatives). TheUAU is saturated over only a thin interval. Therefore, the'
maximum available recharge would be needed to increase the feasibility of extraction
from the DAU.' . In addition, EPArecently' has encoi.mtered significant difficulties
implementing remedies where specific water systems are designated as part of the end
use for tre'ated' ground water. Therefore, because the objectives and constraints of a
Superfund response action and of a particular supply system may not be reconcilable,
EP A has screened out those alternatives that rely on a water distribution system as part
RDDIR40SIOSl.Sl
47
-------
of the end use. Were water purveyors to express a greater interest in receiving treated
water, a water ~i~tribution end use might be significantly more practicable.
b. Description of ~emaining Alternatives
Table 8 lists the ground:'water remedial action alternatives that remained for detailed
evaluation. In Table 8, the different rates of extraction evaluated in the FS have been
consolidated to form a single component. The 'rationale for consolidating the relevant
alternatives is- as follows: '
.
If an alternative that included ground-water extraction from the UAU
were selected, the actual number, placement and pumping rate ot extrac-
. tion wells likely would be determined according to incremental design
and implementation decisions, which would be based upon well and aqui-
fer testing.'
.
Because of the pot~ntial difficulty of extracting water from the thin satu-
rated thickness of the UAU, EPA expects that any alternative. that
includes ground-water ,extraction from the UAU would begin with the
placement and operation of extraction wells in the area of the greatest
saturated thickness. The 400 gpm rate is the estimated feasible extrac-
tion rate for two ~ells in the area of the greatest saturated thickness and
contaminant concentrations. .
.
, Depending on the degree of success obtained with initial wells, other
extraction wells 'would be added incremen-tally in areas of more limited
saturated thickness and/or lower contamination concentration. The 750
gpm and 900 gpm rates represent the estimated sustainable rates 'for two
conceivable "final" configurations that were eval~ated in the FS.
Table 8
Ground.Water Remedial Action Alternatives
Remaining After Screening'
1. Monitoring of the Fate of voes in the UAU without Pumping from the
UAU
2 UA~ Pumping; Photochemical Oxidation; Recharge8
3. UAU Pumping; Ai~ Stripping with Vapor-Phase Carbon Adsorption;
Recharg~8
a Alternatives 2 and 3 include the additional monitoring required by Alternative 1 a~d.
assume the"Scottsdale Operable Unit remedy is in place to address the MAU and
LAU. Note that t~e numbers designating the alternatives do not conform to those
used in the RIIFS and Proposed Plan.
, RDDIR40SIOSl.Sl
48'
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, ,
1. Monitoring the Fate of VOCsin the UAU without Pumping from the UAU
As previously stated,' this alternative does not include additional ground-water extrac-
tion or treatment beyond, that required for the Scottsdale Operable Unit remedy.
Monitoring wells would be installed in the UAU and MAU to track the fate of VOCs
currently present in the UAU. The, monitoring well network would be designed to
allow evaluation of the tate of migration of VOCs from the UAU and of the locations
within the UAD, MAU,. and LAU to which the VOCs are migrating. If VOC mass
reduction in the UAU were occurring too slowly (i.e., at a rate slower than indicated by
ADWR's modeling analysis), or if formerly uncontaminated portions of the UAU,
MAU or LAU were becoming contaminated, extraction from the UAU would be reas-
, sessed. .
2.
UAU Pumping; Photochemical Oxidation; Recharge
In addition to the monitoring network described above, this alternative would include
extraction from the UAU, piping to a treatment facility and upgradient recharge of the
, treated water. As previously discussed; implementation likely would, begin with extrac-
tion wells in the areas of greatest saturated thickness, with wells be~ng added incremen-
tally based upon the performance of previously installed wells. In the photochemical
oxidation treatment, contaminated water would be injected with ozone and/or hydrogen
perQxide before ,entering a reaction vessel. Ultraviolet lamps with~n the vessel would
destroy the VOCs present in the water, creating ,carbon dioxide .and halide ions.
Recharge of the treated water would help to maintain a more stable saturated
thickness.' .
,3. UAU Pumping; Air Stripping with Vapor-Phase Carbon Adsorption; Recharge
, .
, '
This alternative is identical to Alternative 2, except that ground-water would be tre;ated
by air stripping with vapor phase carbon adsorp~ion. In an air stripping tower, a high
volume 9f air is forced upward past a lower volum~ of. contaminated water trickling
down through packing materi~l. Because VOCs have a greater affinity for the vapor
phase, the air would "strip" the VOCs from the water., The' now-contaminated air
would th~n pass through carbon filter units~ VOCs in the air would adsorb, or cling, to
the specially prepared carbon. ' , . '
KeyARARs for ground-water rem,edial actions include the federal Safe Drinking
Water Act Maximum 'Contaminant Levels (MCLs) and non-zero Maximum Contami-
nant Level Goals (MCLGs). MCLs are applicable to the quality of drinking water at
the tap and therefore would be considered relevant and appropriate for the quality of
treated water being discharged to any water supply system that includes potential drink-
ing water uses. Pursuant to 40 CFR Section 300.430(e)(2)(i)(B), MCLs and non-zero
MCLGs are relevant and appropriate as in-situ aquifer water quality standards for
ground water that is or may be used as drinking water. The state of Arizona interprets
all aquifers of the state to be potential drinking water aquifers.
RDDIR40SIOSl.Sl
49
"
, ,
-------
Both the Federal Water Quality Criteria arid the State Water Quality Standards for
Navigable Waters (A.R.S. Section 49-221 and implementing regulations) will be appli-
cable or relevant and appropriate for surface-water discharges.
The RCRA "contained in" principle will apply to materials produced during the installa-
tion and sampling from monitoring wells.
As with the vadose zone. alternatives, 40 CFR Subparts AAand BS will apply to air
emissions from a ground-water treatment facility. Maricopa County Regulations 210,
320 and 330 are criteria to be considered in setting air emission requirements.
H. SUMMARY OF THE COMPARATIVE
ANALYSIS OF ALTERNATIVES
In this section, the remedial action alternatives are compared in detail in terms of the
nine criteria set forth in th~ National Contingency Plan: ' ,
1.'
2.
3.
4.
5.
6.
7.
8.
9.
Overall Protection of Human Health and the Environment
Compliance with ARARs ,
Long Term Effectiveness and Permanence
Short Term Effectiveness '
Reduction of Toxicity, Mobility or Volume through Treatment,
Implementability ,":, "
Cost
State Acceptance
Community Acceptance
Comprehensive remedial action for NIBW will include vadose zone components in
addition to ground-water components: EP A has not eXplicitly combined vadose zone
alt~rnatives and ground-water alternatives for detailed evaluation because ground-water
alternatives have been designed to address an area-wide problem, while contamination
in the. vadose zone has been identified' to date only within relatively limited areas.,
Nonetheless, analyses of vadose zone and ground-water alternatives are highly depen-
dent upon one another. For example, analyses of ground-water pumping scenarios
performed by ADWR as part of the RI/FS assumed that the potential for further
. releases of contaminants to the grourid water would be addressed by vadose zone
remedial actions at the potential source areas.. '
" ,
RDDIR40SIOS1.51
'50
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1. ,VADOSE ZONE .'
Because historic operations and resulting contaminant concentrations vary significantly
across NIBW, EP A has evaluated the necessity for vadose zone cleanup on . an area-
specific basis. Based on the results of the RI' and contaminant transport modeling
presented, in Appendix K 'of the FS, the vadose zone in both Area 7 and Area 8 has
sufficient mass of TCE to pose a continued threat to the groun'd water. Other'VOCs
that add 'to the threat to ground water also are present in Areas 7 and 8. As a result,
the comparative analysis summarized in this section focuses on Areas 7 and 8. For
Areas 1, 2, 4, 10, and the Scottsdale wells, where there does not appear to be a
significant threat to ground water, the No Action alternative is already protective and
cost-effective and complies with ARARs. For Areas 3,'5, 6, 9, 11, and'12, if further
study reveals a significant ground-water threat, the comparative analysis' will essentially'
parallel the analysis for Areas 7 and 8. If these areas do not significantly threaten
ground water, the No Action Alternative will be adequately protective, cost-effective,
. and will comply with ARARs.
a. Overall Protection of Human Health and, the Environment
The No Action alternative would be protective of human health and the environment
in the short term in that no significant exposure to soil or soil gas contamination is
" expected. However, because contaminated soil and soil vapor would be left in place,
the chance for future exposure,during potential deep excavation would remain. In the
vicinity of Areas 7 and 8, the No Action alternative for the vadose zone is expected to
resuit in VOC contamination of ground water above drinking water standards for hun-
dreds of years. ' ,
The Soil Vapor Extraction alternative would offer greater overall protection in that the
uncertainty regarding the fate of vadose zone contamination would be reduced. The
, expected long-term adverse impact on the ground water expected under'the No Action
alternative would be averted. However, an SVE alternative with carbon adsorption
would produce a spent activated carbon residual and possibly low-level VOC air
emissions.
b. Compliance with ARARS
The ARARS and other criteria for NIBW are presented in Appendix A. - The SVE
alternative should meet chemical-specific, location-specific and action-specific ARARs.
The No Action alternative may not meet ARARs such as the ground-water protection
provisions of the Arizona Environmental Quality Act (1986), because VOCs would
continue to represent a continuing source of contamination to, the underlying ground
water.' - ' ' ,
RDDIR40SIOSl.Sl
51
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c. Long- Term Effectiveness
Both alternatives would be expected to remain effective once a level. of acceptable
residual mass has been achieved in the vadose zone. Assuming no influx of additional
contaminants to the vadose zone,. most of the VOCs currently existing in the vadose
, zone are expected eventually to be leached or volatilized out of the vadose zone if SVE
is not implemented. Although sorpt,ion to the soil is expected to be minor, some parti-
tioning into the vapor phase (rebound) may occur after apparent equilibrium has been,
reached. This potential highlights the necessity for continued monitoring to assess the
:need for further response.
Some transition of VOCs into and out of the vapor phase and the aqueous phase is
expected immediately above the contaminateq water table. However, based upon con-
taminant transport modeling as presented in Appendix K of the FS, the principal driv-
ing force is expected to be infiltration of water through the vadose zone toward the
ground-water table. Therefore, no significant net impact on the long-term effectiveness
of either vadose zone alternative would be expected from vapor,phaselliquid phase
transitioning.
d. Reduction of Toxicity, Mobility or Volume through Treatment
The No Action altern~tive does not include any treatment to reduce toxicity, mobility
or volume. As a result, it is expected that contaminants would continue to leach
through the vadose zone to the underlying ground water and, to a lesser extent, would
continue to be released by volatilization to the atmosphere. Biodegradation activity has
not been characterized at NffiW, but if biodegradation is occurring at significant levels,
it wo~ld be expected to decrease concentrations of VOCS.
The SVE alternative could reduce the mobility of most of the contaminant mass by
sorbing it onto activated carbon. The volume of VOCs also may be reduced, depend-
ing upon the final disposition of the spent carbon. Low-level air emissions may result
in increased mobility for a small portion of the contaminant mass that escapes the
activated carbon. If the SVE system did not include activated carbon, neither toxicity,
mobility or volume would be reduced until the VOCs were broken down, principally
photochemically, in ambient air. Breakdown products would contribute to photo-
chemical smog.
e. Short-Term Effectiveness
The No Action alternative would not present appreciable short-term direct contact or
inhalation human health risks. Under the No Action scenario, however, the bulk of the
contaminant mass is expected to migrate from the vadose zone over possibly hundreds
of years. This contaminant mass would, therefore, continue to threaten the quality of
underlying ground-wate.r. '
RDDIR40SIOSla.Sl
52
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It is difficult to estimate 'accurately the time required to meet remedial action objectives
with the SVE alternative. The rate of extraction is a function of site-specific character-
istics, such as quantity and nature of VOC contaminations and depth to ground water.
Based upon extraction rates cited by Malot (1985), Argelot, et aI., (1985), and Wood-
ward-Clyde (1984), the SVE alternative would be expected to remove the bulk of the
vadose zone contaminant mass within several years. As a result; the. threat to ground-
water quality would be reduced significantly faster than under the No Action scenario.
. .
Implementation of the SVE alternative would entail construction-related risks during
drilling of vapor extraction .and monitoring wells. However, with appropriate, readily
available monitoring and protective equipment, safety risks associated with installation
and operation of SVE systems at NIBW can be mitigated. . .
There could be low-level emissions of VOCs not. captured by the activated carbon.
Regeneration, treatment or disposal (most likely off-site) of spent carbon also would
entail some handling and transportation risks.
f. Implementability
The No Action alternative would not have implementation obstacles. In addition, there
are no operation and maintenance requirements for the No Action alternative.
. '.
Soil vacuum extraction has been used successfully to remove VOCs from soils. As an
example, in Puerto Rico, the technique extracted about 250 pounds. per day of carbon
tetrachloride from unsaturated soil below an underground storage tank (Malot, 1985;
Argelot, et al., 1985). ' .
. .
Soil vapor extraction appears to be effective even in relatively tight clayey silt and silty
clay soil. It also appears to be applicable to the removal of contamination beneath
buildings. The performance of similar systems in the. past indicates that the use of an
SVE system would result in a significant reduction of VOC contaminants present in
unsaturated soils during the useful life of the equipment and wells. The vacuum pump
and carbon recovery system could be temporary, skid-mounted equipment, and the
w,ells and manifold could be removed or abandoned once remedial action objectives are
achieved. .. . .
The most-desired locations for the SVE wells may be inaccessible. Nonetheless, EP A
believes adequately effective locations could be found.
Spent carbon would require treatment, regeneration or disposal. Options for ultiniate
disposition would be expected to become increasingly limited over the course of the
remedial action as nationwide restrictions. on land disposal become more stringent.
Otherwise, equipment and personnel should be readily. accessible for the actions
included in the SVE alternative. .
RDDIR40SIOSla.Sl
53
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g. Cost
. The costs estimated in the FS for SVE systems at Areas 7 and 8, assuming 2 years of
operation, are presented in Table 9. .
. Table 9
Estimated Costs for Soil Vapor Extraction Systems
Average Annual
Operations and Total Present
Capital Maintenance Worth
Area 7 $482.000 $74.000 $619.000
Area 8 $278.000 $60.000 $387.000
Although it is difficult at this time to estimate costs associated with the No Action alter-
native for the vadose zone, they would be expected to include expenses for many
decad~s of additional ground-water pump-and-treat activities in the MAU and LAU.
No Action in the vadose zone may necessitate ground-water extraction directly from the
UAU. ~able.lO.presents estimated costs for further characterization for Areas 3, 5, 6,
9, 11, and 12. If SVE is shown to be necessary for these areas, estimated remedial
action costs will be similar to those shown in Table 9 with adjustments for area-specific
. requirements--the number of wells, their depths, etc. .
Table 10
Estimated Costs for Further
Vadose Zone Investigations ($)
. Soil Vapor Monitoring Well Data
. Costs Reporting!
Shallow SOU Interpretation
Area Gas Cost Installation Analytical Costs Total
3 . 0 18.700.. 6.400 8.250 33,350
SA 3,000 9,350 3.200 4,125 19,675
58 0 9,350 3,200 4,125 16.675
5C 0 9,350 3,200 4,125 16,675
6 0 18,700 6,400 .8,250 . 33,350
9. 0 9,350 3,200 4,125 16,675
11 0 18.700 6,400 8,250 33,350
12 0 43,000 16.000 20,625 79.625
RDDIR40S,uSla.51
54
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h. State Acceptance
, .
Because the State of Arizona has the statutory r.esponsibility to, protect ground-water
quality for all present and, reasonably foreseeable future uses, the State supports the,
Soil Vapor Extraction alternative over the No Action alternative for those vadose zone
areas that present a potential threat to ground-water quality. The Arizona Department
of Environmental Quality, encourages EP A to pursue an aggressive schedule for
defining the potential threat to ground-water quality at Areas 3, 5, 6, 9, 11, and 12.
APEQ concurs with the requirement for implementation of the SVE alternative as
soon as possible in those areas where a threat to ground water is determined to exist.
i. Community Acceptance
Community members strongly prefer alternatives that maximize the removal of hazard-
oussubstances from near their residences. Commentors at the RIIFS public m~eting
expressed a strong preference that potential threats from all possible source areas
should be cleaned up. ;: "
2. GROUND WATER
a. Overall Protection of Human Health and the Environment
, .
All three of the alte'rnatives listed in Table 8' will. provide signifiCant overall protection'
, of human health and the environment.
, Alten1ative 1 would provide warning regarding potential human exposure to contami-
nated ground water through extensive sampling and analysis of the UAU, MAU and
LAU in the North Indian Bend \yash. The ground-water monitoring also ~hould indi-
cate the rate and direction of con'taminant mass flow within and out of the UAU. All
of the alternatives, rely heavily upon the Scottsdale Operable Unit rerpedy to contain
and remove contaminants from the aquifer system. Therefore, the overall protective-
ness of any of the ground-water alternatives will likely be highly dependent upon the
Scottsdale Operable Unit remedy, including any modifications to th~t remedy.
. ."
In addition to the monitoring provided in Alternative 1, Alternatives 2 and 3 include
ground-water extraCtion and treatment ,~easures beyond the . Scottsdale Operable UIiit
. remedial, action. By including ground-water extraction and treatment in areas of the
UAU that have high contaminant levels, Alternative 2 and 3 could provide, at least in
the short term(a reduction in uncertainty regarding the fate of some of the contamina-
, . tion. Modeling by ADWR suggests tQat the 750gpm configuration evaluated in the FS
would go furth~r toward this end than the 400 gpm and 900 gpm configurations.
ADWR's modeling can be used as one measu're of the p~tential reduction, with UAD.
extraction, in the uncertainty about the fate of VOCs currently present in the' UAU.
o ADWR's work suggests that, for periods on the order of tens of years, the rate for
. reduction of contaminant mass, both within the' UAU and within the entire
RDDIR40SIOSla.51
55
-------
UAU/MAU/LAU system, may rely more heavily upon (1) natural and conduit-aided
flow of contaminant mass from the UAU into the MAU and LAU and (2) Scottsdale
Operable Unit r~medial pumping, than upon ground-w~ter pumping from the UAU.
Alternative 2 would be protective because its treatment component offers nearly com-
plete on-site destruction of the contaminants of concern. By comparison, the overall
protectiveness of Alternative 3 would be reduced' slightly by (1) low-level air emissions
from the air stripper( s j and (2) production of a treatment residual in the form of spent
activated carbon. The spent carbon would require regeneration or treatment and even-
tual disposal off-site. .
There is some risk that a lapse in the effectiveness of Scottsdale Operable Unit treat-
ment facility could result in human exposure to untreated drinking water, although
some dilution within the distribution system would be expected to reduce the levels of
exposure. A similar problem with a UAU ground-water treatment system would not
pose the same threat because an end use other than discharge to the distribution
system is contemplated for the remaining UAU alternatives. Because the end use
would be recharge, there should not be direct human contact.
b. Compliance with ARARs
Alternatives 1, 2 and 3 all likely would' attain the ARARs and other criteria for in-situ
ground water. Although Alternatives 2 and 3 initially would be expected to remove
more VOC mass from the UAU than Alternative 1, ADWR's modeling suggests the
time necessary to attain acceptable levels throughout the UAU will not differ substan-
tially whether or not the UAU is pumped. ADWR's modeling also suggests the 'time
required to attainARARs throughout the'MAU and LAU would not be altered signifi-
cantly by pumping from the UAU. . ,
Alternatives.2 and 3 would be able to meet the water qualityARARs that would be
applicable to treated water intended for recharge. Alternatives 2 and 3 should also be
able to attain ARARs 'for VOC air emissions. '. ."
ADWR's modeling suggests the initial configuration of the Scottsdale Operable Unit is
insufficient to contain and capture the MAU and LAU ground water for which the
., contaminantJevels currently, exceed ARARs. Recent monitoring data from the site
appears to support. this interpretation. Therefore, the ability of the overall remedy for
NIBW to attain ARARs for in-situ ground water, particularly within an acceptable time
frame, likely will be highly reliant upon continuing evaluations of~ and modifications t
-------
c.
Long-Term Effective'ness and Permanence
All of the alternatives are expected' to provide essentially equivalent on-site long-term
protection once acceptable levels have been met. Residual risks at the end of imple-
mentation should be at or below approximately one in one million. It may be difficult
to identify satisfactorily when, a~ceptable levels have been met, however, due to poten-
tial rebound of contaminant levels within the aquifer. Long-term monitoring would
offer the ability to watch for. potential rebound and the 'presence of extraction wells
would make it easier to address concentration increases should they arise.
Alternative 3 potentially would result in some off-site risks after implementation is
complete," depending upon the disposition of the spent activated carbon.
"d. Short-Term . Effectiveness
Alternative 1 wquld rely solely :upon the Scottsdale Operable Unit to remove contami-
nant mass from the ground-water system. With respect to the UAl)', therefore, Alter-
native 1 would rely upon existing flow of contamination from the UAU into the lower
units via conduit wells and flow across the contact between the UAU and the MAU. '
Alternatives 2 and 3 offer some measure of greater short-term effectiyeness through"
,the direct removal of contaminant mass from the UAU. Recharge of treated water
would minimize the, chance for direct human contact to residual VOCs in the treated
water. '
,
The total clean-up time' frame for, the entir"e UAU/MAU/LAU system can not be
, reliably estimated at this tim~. As stated above, Alternatives 2 and 3 initially should
accelerate reduction of contaminant mass within the' UAU. ADWR's modeling
suggests, however, that the additional direct mass removal provided by UAU ground-
water extraction may' not have a significant impact on the overall time to meeting
acceptable levels in the MAU and LAU when compared to the Scottsdale Operable
Unit remedy alone. "" '.
ADWR's modeling suggests that the original configuration of the Scottsdale Operable
Unit remedy will allow some migration of contamination beyond the hydraulic influence
: o. of the extraction system. The rate and extent of this migration cannot be accurately
estimated at thistime. Nonetheless, ADWR's work suggests implementation of addi-
tional measures for the MAU and LAU will be necessary.
: None of the UAU alternatives would be expected to introduce significant additional
adverse impacts due to ground-water'treatment activities. Alternatives 2 and 3 both
would be expected to result in some low-level VOC air emissions. Alternative 3 would
produce spent activated carbon that would require additional handling.
The Scottsdale Operable Unit"remedy will "have low-level VOCair emissions as a by-
product of ground-water treatment. The emissions should" not result in excess risk
" above one in one million., The Scottsdale Operable" Unit will also 'include .use of
RDDIR40SIOSla.Sl
57
-------
treated water in the public supply syste'm. As. a' ~result, people. drinking the treated
water would have at most an excess risk between one in one hundred thousand and
one in one million due to residual VOCs. This risk likely would be reduced by some
level of dilution within the supply system.
The installation of additional monito~ing wells under Alternatives 1, 2 and 3 entails
construction-related risks. However, potential accidents and exposures to contaminants
could be reduced substantially through careful planning.and appropriate precautions.
The collection of samples would increase the likelihood of low-level (particularly
worker) eXposures. Experience at this site and others indicates this risk can be mini-
mized through adherence to standard health and safety procedures. The additional
activities included in Alternatives 2 and 3 would include some additional construction-
related risks due to extraction and recharge well installation, pipeline installation and
treatment facility construction. With appropriate mitigative measures, the additional
construction-related risks associated with Alternatives 2 and 3 could be minimized. The
Scottsdale Operable Unit remedy presents similar risks of accidents and eXposures
during construction. '
. There is some risk during implemeniationthat supply wells could be placed in areas
where the ground water is contaminated, but this risk probably is not substantial.
e. Reduction of Toxicity, Mobility or Volume through Treatment
All three remaining alternatives would rely heavily upon the Scottsdale Operable Unit
remedy for reducing the mobility of contaminants through treatment. Whether or not
, the UAU is pumped, significant VOC mass is eXpected to travel from the UAU into
,the MAU and LAU. The Scottsdale Operable Unit remedy is designed to capture the
bulk of the contaminant mass from the MAU' and LAU on activated carbon, which
itself would have to be regenerated or disposed of once spent. Some mobilization 'of
the VOCs will occur during implementation of the Scottsdale Operable Unit remedy
because of low level air emissions of VOCs not captured by the carbon. No reduction,
in toxicity or volume of contaminants would be eXpected unless the spent activated
carbon is treated to destroy contaminants adsorbed to the carbon.
. .
Over approximately the first ten years of operation, Alternatives 2 and 3 would offer
reduction of mobility or volume of VOCs beyond the reductions offered by the
Scottsdale Operable Unit remedy over the same period of time. Alternative 2 wo~ld
reduce contaminant volume through on-site destruction of the contaminants removed
from UAU ground water, while Alternative 3, employing the same treatment as the
Scottsdale Operable Unit, would reduce the mobility of VOCs. '
Over the longer term, however, the distinction between the alternatives with UAU
pumping and Alternative 1 would be eXpected to diminish. This is principally due to
the significant communication, between> the UAl]. and the lower units. Over its
eXpected operating life, the Scottsdale Operable Unit remedy would be eXpec.ted to
capture. and immobilize the VOCs that would otherwise be captured and immobilized
RDDIR40SIOSla.51
58
-------
.'
through UAU ground~water pumping and treatment. In fact,. as ,discussed above; the
Scottsdale Operable Unit remedy will be relied upon to capture significant amounts of
VOCs migrating out of the UAU whether or not the uAu is pumped. The Scottsdale
Operable Unit remedy is designed . for continued evaluation to ensure full capture of
VOCs in the MAU and LAU. .. '
f. Implementability
"
All of the alterna,tives would require coordination and land availability for the installa-
tion of monitoring wells.' Access agreements would also be required to provic;le fot
long-term monitoring at. the well sites. The availability of materials, e,quipment ,and
personnel to carry out the wO,rk should not: be a significant issue. Appropriate well .
installation may be difficult because of lithologic changes. ' .
, '
Alternatives 2 and 3 would be more diffiCult to implement than Alt~rnative 1 because
. of land requirements for piping and treatment equipment. .Some necessary construc-
tion activity, particularly pipe installation, would be expected to disrupt traffic flow on
, major streets. Although sufficient land and easements are available in the North Indian
Bend Wash to implement all of these alternatives, more difficulty would be expected as
the size of the alternative increased. . .
Alternatives ~and 3 would be, difficult to implement because of the, limited and
variable saturated, thickness of tq~ UAU. Even with recharge, at least localized
dewatering of the UAU would be expected to affect significantly the ability of the
,extraction wells to remain productive. . . .
There are fewer uncertai~ties with Alternative 3 than Alternative 2 because air strip-
'ping and granular activa~ed carbon technologies are used more commonly than photo-
chemical oxida~ion. To compensate for its .'lessercertainty, Alternative 2 may require
more extensive operations and maintenance requirements to monitor the adequacy of
perfonnance. On the other hand, Alternative 3 would have t!J be designed with careful
consideration of the' disposition of .sp~nt carbon, as options (such as land disposal)
become more restrictive.. . '
All alternatives likely would require replacem~nt of some or all physical components
(pipelines, treatment equipment, monitor wells, extraction wells, well pumps; etc.)
b~~ore the remedial action objectives have been attained. Therefore, additional con-
struction, with all the accompanying difficulties and risks, likely would be necessary in
'the future. .
. . .
Extensive coordination may be necessary to most appropriately and expeditiously dis-
pose of water produced during drilling 'and sampling eyents.
RDDIR40SIOSla.51
, 59
-------
g. Cost
The estimated capital, annual operating and total present worth costs of the alterna-
tives are sumn.tarized in Table 11. . In this table, capital costs include only the initial
outlays for each alternative. Replacement costs and salvage values are not reflected
under Capital Costs but are reflected in the Total Present Worth Cost. The Total
. Present Worth Cost is based on 30 years at a. discount rate of 6%. Capital and
operating costs for the Scottsdale Operable Unit remedy are included. Costs are
summarized by remedy component in Chapters 7, 8 and 9 of the RIIFS.
Table 11 "
Estimated Costs for Ground.Water Alte~atives Undergoing Detailed Analysis
(in thousands of dollars)
Capital. . Annual Operating Total Present
Alternative Costs Costs Worth Costs
. 1 8,580 801 20.570
2 .10.764 - 12,962 1.014 - 1,144 25,846 - 29,584
3 10,714 .~ 12,515 964 - 1,078. 25,102 - 28,142
I
h. State Acceptance
The State of Arizona has expressed a preference that as. much contamination as
possible be removed from the ground water as soon as possible. The Arizona
Department of Environmental Quality is concerned with the continued migration of
. contaminants. from the UAU into the underlying sources of drinking water and the
efficacy of allowing these contaminants to further migrate to the Scottsdale Operable
Unit for .ultimate removal. ADEO prefers active remedial alternatives for ground-
water contamination, especially those alternatives which remove highly contaminated
ground water from source or "hot spot" areas. ADEQ concurs with the selected
monitoring alternative but expects that UAU.extractioitwill be required if the mass of
co~taminants does not decrease as predicted. Furthermore, ADEQ expects that if
UAD extraction beco~es necessary, EP A will require its implementation at t~e earliest
possible time. The State is concerned about the effectiveness of the Scottsdale.
Operable Unit remedy, especially in light of ADWR's modeling results and the most
recent monitoring data. There is discomfort with the idea that overall effectiveness.
may rely very. heavily upon the ability to incorporate changes into the Scottsdale
Operable Unit remedial action~ With or without extraction, both ADWR and ADEQ
put a high value on the ability to monitor comprehensively the flow of contamination at
the NIBW site. .
[
I
I .
i. Comm,unity Accep~nce
. .. .
Alternative 1 is looked upon somewhat negatively by. some in the community because
of the lack of pumping froin the DAD. Assurance~ of monitoring safeguards help
address some of this concern. Alternatives 2 and 3 would have increased acceptance
due to additional short-term actions to control contamination in ground water.
RDDIR40SIOSla.Sl
60 .
-------
I. THE SEtECTED REMEDIES
. . , ,
Based upon comparative analyses: of th~ alternatives with' respe~t' t~ the nine e~al~ation
criteria, EP A is. selecting' for NIBW the vadose. zone and ground-water remedies
described below. This section jnclud~s a discussion of some of the specific standards
that shall be achieved by the selected alternatives for NIBW. ,Appendix A 'presel1ts the
complete list of ARARs a'nd 'other ctiteria that shall be'compl~ed wi,th/attained by the,
selected 'remedial actions.' . ,
1. VADOSE ZONE
"
. ..
EP A has 'Sroupedthe vadose ~one areas that h~ve been studIed tntothree categories:
(a) those that do not' appear ,to significantly threaten ground water, (b) those, that
continue to significantly threaten ground: water and (c) those that may significantly
threaten ground water, but that require further' characterization and analysis to evaluate
the degree of threat. , '. .
a.', Areas 1,2, 4, 10 and the City of Scottsdale' Wells
...
, .
. . .
, "
Based on avaihibleinformation, the vadose zone'in Areas 1, :2, 4 and 10 and the City of
Scottsdale Wells do not appear to present a continued threat to ground water from
VOC contamination in the vadose zone. Data indicate that VOCs are not present at
significant levels in these areas., Therefore, EPA iS,selecting No Further Action for the
vadose zone in Areas 1, 2, '4'and 10 and af the COS Wells..
,..'t<
. b. Areas 7 and 8
;.\
, . . .
Because the vadose zone in Areas. 7 and 8 present unacceptable threats to ground
water, EP A is selecting Soil Vapor Extraction for, Areas 7 and 8. The purpose of the
, SVE systems will be to reduce VOC mass in the vadose zone to a level that no longer
threatens to contaminate groundwater at levels above MCLs and other ground;.water
criteria selected in this ROD. TheSVE system for Area 7 will consist of soil vapor
extraction wells,' a manifold collection system, a vacuum pump, and a vapor-phase
carbon adsorptiqn system., The extent of the area requiring remedial action at Area 7
can not be defined at this time. Therefore, the approach for implementation at Area 7
will ~e as foll9WS:
.
Install additional soil vapor monitoring well clusters with co~pletion
intervals. similar to well 7-209. At least three additional monitoring
points, at the approximat~ locations shown in Figure 12, will, 'be required.
Install a soil vapor extraction well near well 7-209 and a. second soil
vapor extraction well near 7-207. Construct ,the 'appropriate soil vapor
treatment facilities with capacity to add additional soil vapor extraction.
.
RDDIR40SIOSla.51
61, .
-------
SAMPLING
LOCATION
001
002
003
004
005
101
102
103
104
105
106
107
108
109
110
111
112
11?
11«
111
116
117
118
119
120
TCE
27.0
25. 0
41.0
35.0
24.0
6.80
9.70
7.70
NO
3.60
0.30
14.0
23.0
31.0
18.0
15.0
24.0
30.0
17.0
1.40
9.60
9.10
5.60
18.0
21 .0
1,1,1-TCA '
5.00
12.0
0.56
ND
ND
ND
0.06
0.05
ND
ND
ND
ND
ND
ND
0.03
ND
ND
ND
ND
ND
1.90
0.60
0.01
0.01
0.02
PCE
2.30
3.60
6.60
0.88
0.68
0.10
1.00
0.84
0.01
0.51
0.12
1.40
1.40
3.30
2.00
1.80
3.20
3.60
1.90
5.20
4.20
4.60
1.30
2.30
3.00
1.1-DCE
47.0
59.0
ND
5.30
ND
1.90
ND
0.14
0.60
0.97
ND
0.98
ND
ND
1 .70
ND
0.60
1 .60
0.30
0.28
45.0
11.0
0.96
0.59
1.20
ND
NOT DETECTED
too
100
200 FEET
LEGEND
(t) APPROXIMATE ADDITIONAL SOIL VAPOR
T MONITORING WELL LOCATION
• SOIL GAS SAM PLING LOCATION
A EXISTING SOIL VAPOR MONITORING WELL
© PROPOSED SOIL VAPOR EXTRACTION WELL
FIGURE 12
AREA 7 SOIL VAPOR MONITORING AND
EXTRACTION WELL LOCATIONS
NORTH INDIAN BEND WASH ROD
-------
" ,
.
.' ,
Based on the results from the additional soil vapor monitoring wells, EP A
may require additional eXtraction wells, or if the extent of ,contamination
is still too unce'rtain, additional soil vapor monitoring wells will be
required. '
J.
, '
, '
For Area 7, a single soil vapor extraction. well should be capable of, drawing 200
standard c,ubic feet per,minute (scfm) of soil vapor. Based On the average TCE con- '
cent ration in, soil vapor monitoring point 7-~096f 2,945 micrograms per liter, at startup
the SVE system may remove approximately 50 pounds of TCE per day. Therefore, in
order to comply with air emission standards and to reduce, ~he mobility and volume of
hazardous substances, vappr-phase carbon emission, controls Will be included in the
Area 7 SVE system.' " ,
The Area 8 SVE system will consist of soil vapor extraction:wells, piping from the wells
, .to the treatm~nt system, a vacuum pump 'and a vapor-phase carbon adsorption system.
As' with Area' 7, the total area of Area 8 -requiring remedial action can not be deter-
,mined with available'information, so the approach for implementing SVE at Area 8 will
, be as follows:
."
Install additiqnal soil vapor' monitoring wells with completion intervals
similar to ;8-211." At least three ,additional monitoring points, at the
approximate locations shown on Figure 13, will be req~ired. (Data,
values for soil gas sampling points shown on ~igure 13 are provided in
Table 12.) " ' ",
.
, Install a soil vapor extraction well near 8-211. Construct the appropriate,
soil vapor ,treatment facilities with 'the capacity to add additional soil
vapor extraction. '
,.
, Based on the results from, the additional soil vapor monitoring wells, EPA
may require. additional soil vapor extraction wells, or if the extent of the
, conta~ination is still too uncertain, EP A 'may require additional soil
. vapor monitoring wells.
At Area, 8, a single' vapor extraction weil should be capable of drawing 200 scfm of soil '
vapor. Based on the average TCE concentration of 277 micrograms per liter at point
8-211, at startup the SVE system should remove approximately 5 pounds of TCE per
day. Vapor-phase carbon air emission controls will be necessary as part of the Area 8
. SVE system in order toconiply with air emission standards 'and to reduce the mobility
and volume of hazardous substances.
For both Areas 7 and 8, the VLEACH model, or, a similar an~lytical tool determined
acceptable by EP A, shall be used to evaluate the continued threat to ground water and,
therefore, the need to continue operation of the SVE system and/or to install additional
soil vapor monitoring wells (See Figure 10). Values. for soil, contaminant, and
underlying saturated zone parameters to be used in the application of VLEACH and
RDDIR40S~Sla.sl
63
-------
APPROXIMATE ADDITIONAL SOIL VAPOR
MONITORING WELL LOCATION
• SOIL GAS SAMPLING LOCATION
A EXISTING SOIL VAPOR MONfTORING WELL
© PROPOSED SOIL VAPOR EXTRACTION WELL
FOR SOIL GAS SAMPLE
CONCENTRATION DATA
SEE TABLE 12
100
100
200 FiET
FIGURE 13
AREA 8 SOIL VAPOR MONITORING AND
EXTRACTION WELL LOCATIONS
NORTH INDIAN BEND WASH ROD
-------
•;• . ,*['•* * f " v • .
Table 12
Soil Gas Results for Area 8
Oig/i)
Sheet 1 of 4
Location
001
002
003
004
005
006
007
008
101
102
103
104
105
106
107
108
109.
110
111
112
113
114
115
116
117
118
119
Soil Gas Sample Concentrations
CFM
NA
;NA
NA"
NA
NA
NA
NA
NA
NA .
NA
NA
NA
NA
NA
. NA
' NA
:NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
TCE
3.52
2.93
2.69
1.88
14.00
3.01
14.10
5.35
3.28
1.35
0.20
ND
0.66
8.22
" ND
6.12
ND
12.69
0.55
13.60
42.54
32.93
32.10
9.76
12.00
11.68
ND
1,1,1-TCA
ND
ND"
. 0.147
ND
ND
ND
..ND
,ND'
•ND
ND
ND
ND
0.02
3.98
0.01
0.04
0.01
0.04
0.06
0.16
ND
0.17
0.02
0.02
0.02
0.%
ND
PCE
0.225
0.113
0.154
0.172
0.485
0.847
0.815
0.513
1.16
1.22 '
0.45
1.46
1.75 .
6.06
2.77
2.48
3.54
3.07
1.41
2.42
5.57
2.48
4.44
1.23
1.27
1.64
0.03
U-DCE
9.210
ND
. 0.729
•ND
ND
ND
6.43 '
ND
1.43
1.75
0.60
0.67
0.28
3.55
0.28
3.96
0.40.
3.78
1.33
0.50
0.56
3.28
22.00
2.12
4.33
4.54
0.90
RDD\R405\053.51
65
-------
Table 12
Soil Gas Results for Area 8
(j1g/1)
Sheet 2 of 4
Soil Gas Sample Concentrations
"
Location CFM TCE 1,1,1- TCA PCE 1,I-DCE
120 NA 0.54 ND 2.21 NA
121 'NA 16.32 . 0.03 8.76 37.44
122 NA . 2.53 0.29 6.15 2.54
123 ' NA 4.32 0.02 2.38 9.54
JODI NA 0.99 0.46 11.72 0.03
JOO2 NA 11.02 0.17 3.30 0.03
J003 NA 0.89 0.02 2.64 0.06
JOO4 NA 2,.12 0.03 1.64 0.00
J005 NA 2.15 0.16 0.26 0.01
JOO6 NA .3.12 0.22 1.32 0.14
J007 NA 5.99 0.08 1.46 0.29
J0070 NA 7.80 0.11 1.86 1.05
, .
JOO8 NA 0.00 0.00 4.05 8.85
JOO9 NA 8.41 2.24 5.92 0.22
"
JOlO NA 10.12 0.10 5.06 1.04
J011 NA 2.72 0.32 1.16 0.13
J012 NA 3.83 0.07 0.91 0.31
J013 NA 0.00 0.15 0.89 0.27
J014 NA 2.20 0.00 0.65 0.46
J015 NA 2.07 0.00 0.45 0.16
009 NA 0.27 NO 0.04 NO
010 NA 2.20 0.05 0.16 NO
011 NA 0.03 ND 0.04 NO
012 NA 0.74 NO 0.05 NO
124 NA 1.40 . 5.60 0.97 NO
125 NA 5.90 66.0 2.60 1.70
126 NA ' 4.70 0.04 1.50 2.00
" 'RDD\R40S\OS3.51
66
-------
~
Table. 12
.soil Gas Results for Area 8
(~g/I)
Sheet 3 of 4
. . . Soil Gas Sample Concentrations
Location CFM TCE 1,1,I.TCA PCE 1,I.DCE
127 NA 6.00 0.32 .4.20 0.57
128 NA 20.0 0.34 3.70 7.00
129 NA 7.40 13.0 ' 2.40 5.20
130 NA .'. 0.61 0.08 '0.29 2.20
131 NA 0.08 0.07 0.99, 3.00
132 NA . . 0.73 0.02 0.67 0.84
133 NA 0.06 0.02 O.ll 0.46
134 NA 0.04 0.04 0.05 1.60
135 NA NO 0.05 0.38 0.94
136 NA NO 0.01 0.39 0.58
137 NA NO 0.01 3.50 2.40
138 NA NO 0.05 1.00 6.40
8-301 1.65 4.48 1.27 7.48 1.11
8-302 2.00 5.97 1.42 . 9.40 1.60
8-303 NO 10.50 NO 16.90 .1.14
8-304 NO 0.27 NO 0.79 NO
. .
8-305 NO. 0.15 NO. 0.60 NO
8-307 0.94 .8:97 NO 12.10 6.71
8-308 0.62 17.60 0.37 23.30 4.16
8-309 0.55 28.80 0.31 52.90 1.09
. 8-310 1.07 2.50 0.83 4.88 0.66
8-3ll NO 34.10 NO 40.40 45.90
'.
8-312 0.1'7 40.00 NO 62.30 8.77
8-313 0.06 1.18 NO 0.12 2.72
8-314 NO 2.97 O.ll 1.20 12.70
8-315 0.08 20.80 NO. 22.60 19.90
8-316. 0.13 18.40 0.18 18.70 23.40
RDD\R40S\OS3.S1 .
, 67.
-------
Table 12
. Soil Gas Results for Area 8
( ~gtl)
Sheet 4 of.4
Soil Gas Sample Concentrations
Location CFM TCE 1,1,1-TCA PCE 1,1-DCE
8-317 Np 13.40 ND 10.90 3.09'
8-318 ND 4.00 ND 4.17 2.66
8-319 ND ND ND ND ND
8-320 NO 0.57 '0.05 0.02 3.63
8-321 ND 1.53 0.13 2.15 9.89
8-322 0.18, 3.81 ND 2.44 19.80
8-323 ND NO ND NO NO'
8-324 ND 3.23 ND 2.42 6.35
8-325 ND 1.36 ND 0.28 0.99
8-326 ND ND ND NO ND
8-327 0.02 0.07 0.02 NO 3.48'
8-328 0.10 2.86 0.06 2.37 17.30
8-329 ND ND NO, ND NO
8-330 NO 0.12 0.02 0.05' . 0.46
8-331 ND 0.31 ND 0.19 ND
Notes: ND = not detected. . .
NA = not analyzed. . ,
RDD\R40S\OS3.51
68
'"
-------
. :.J.
','
, '
mixing zone calC~l~tions shall be those selected by EP A and presented in Appendix K
, ,of the RIIFS, or other values approved by EP A based on additional field data or other,
information. '.' ' ' ,,' ' " '
, c. Areas 3, S, 6, 9, 11 and 12
,',
The amount, and tYPes of data for Areas 3, 5, 6, 9, 11 and tz are not uniform.
'Available information suggests there may be a continued threat to "ground water froIP
, VOC ,contamination .in the vadose zone in these areas. However; data were not suffi-
cient to estimate the mass ,of VOCs in the vadose ione. Therefore, evaluation of the
, need for remedial action at Areas '3, 5, 6, 9, 11 and 12 will be made after additional
investigations, as discussed below.' " ,
, '
i. Area 3. At least tWo 'additional soil vapor monitoring wells, at the approximate
locations shown on' Figure 14, shall be installed. (Data values for Figure 14 are
, provided in Table 13.) Construction shall be similar to that of well 3-213. The purpose
'of these wells will be to estimate the extent, areallyand vertically" of vadose zone' VOC
contamination and to estimate its mass. Depth-specific soil gas samples from these soil
,vapor monitoring wells" shall' be collecteg and analyzed. Additional soil vapor
monitoring wells may be required based on informati9n from the. first tWo wells.
"ii. Area S. In Area 5A, further s~allow s'oil gas sampling shall be performed in the
, Granite Reef Wash, in the vicinity of sample point 5-102. 8ased on the results of shal-
lq,w soil gas sampling, at least ,one soil vaI:'0r monitoring well similar to well 3-213 shall
be installed to estimate the eXtent" areally and' vertically,' vadose zone VOC "
contamination and to estimate its m~ss. Depth-specific soil, gas samples from the soil
,vapor monitoring" well shall, be collected and analyzed., Additional soil vapor
, ,monitoring wells maybe, required based on information from' the'first well. ' '
In Area 58, at least one soil vapor monitoring well similar to well 3-213 shall be
installed to estimate the extent, areally and vertically, of vadose zone: VOC
contamination and, to estimate its mass. Depth-specific soil gas samples from this soil
, vapor monitoring well shall be collected and analyzed. Additional soil. vapor
monitoring wells may be required based on information from the first well.
A soil vapor monitoring well shall be installed in Area 5C at the approximate location
shown on Figure 15 in order to estimate the extent, areally and vertically" of vadose
zone VOC cont~mination and to estimate its mass. Depth-specific soil gas samples
from this soil vapor monitoring' well' shall be collected and analyzed. Additional soil
vapor moni~oring wells may be required ~ased on information from the first well.
iii. Area' 6. Two soil vapor monitoring wells shall be installed, at the approximate loca-
tions shown on Figure 16 in order to estimate the extent, areally and vertically, of
vadose zone VOC contamination and to estimate its 'mass. Depth-specific soil gas
samples from ~hese soil vapor monitoring wells shall be collected and analyzed.
RDDIR40SIOSla.Sl
69
-------
LEGEND
100
too
200 FEET
NOTE
FOR SOIL GAS SAMPLE
CONCENTRATION DATA
SEE TABLE 13
APPROXIMATE ADDITIONAL SOIL VAPOR
MONITORING WIILL LOCATION
SOIL GAS SAMf'UNG LOCATION
EXISTING SOIL VAPOR MONfTORING WELL
FIGURE 14
AREA 3 SOIL VAPOR
MONITORING WELL LOCATIONS
NORTH INDIAN BEND WASH ROD
-------
Table 13
Soil Gas Results for Area 3
(Hg/D ' ' ' ' •
Sampling
Location
001
002
003
004
005
006
007
008
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
G001
G002
G003
G004
G004D
TCE
20.0
10.0 ,
4.40
19.0
.ND
4.40
2,00
0.22
14.0
15.0
17.0
ND
2.80
6.60
11.0
ND
3.70
ND
18.0
13.0
7.60.
14.0
7.60
4.79
0.61
. 3.75
0.70
0.85
1,1,1-TCA .
2.60
3.40
2.30
2.10
ND
1.60
0.82
0.093
4.30
6.50
3.70 '
0.02
3.80
ND
ND
0.09
0.23
0.12
11.0
5.40
1.10
5.60
1.10
0.16
ND
0.22
0.09
0.14
PCE
0.64.
0.31
0.32
0.46
0.03
0.73
0.35
0.17
2.20
2.90
2.00
0.04
3.40
2.70
4.10
0.03
2.60
0.14
1.80
2.70
0.77
2.0
0.77
0.31
0.47
0.60
0.35
0.42
1,1-DCE
' 5.50
19.0
ND
5.0
ND
ND
5.30
ND
7.20
5.70
3.50
0.46
5.0
32.0
35.0
0.75
4.1
0.24
2.60
0.14
1.20
6.80
1.20
ND
0.28
ND
0.13
0.13
1,2-trans-DCE
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
ND
ND
ND
ND
ND
RDD\R405\054.51
71
-------
Table 13
Soil Gas Results for Area J
(~g/I)
Sampling .
Location TCE 1, 1, 1-TCA PCE 1,1-DCE 1,2-trans-DCE
0005 6.67 0.34. 0.37 0.87 NO
"
0006 33.4 8.55 1.98 14.0 NO
0007 .
2.22 0..08 0.31 0.13 "'iO
POOl 0.14 10.0 0.03 0.10 0.01
P002 20.68 137.0 0.46 20.4 0.31
P003 26.6 24.3 0.52 27.9 0.99
I NOle, NO = not detected. I
NA = not analyzed.
" .
RDD\R40S\OS4.51
72
-------
---~*:
s^e|pw:ifV r;t
3pf^Wf^'"l
,-J*,.- •Sf.'i'fcM&iw1!,, ,.,s / i *»*
nrft^^t*^^
GROUNDWATER
MONITORING WELLS
'
•*
SOIL GAS SAMPLE CONCENTRATIONS (uq/ll
TOT 1,1,1-TCA PCE 1,1-DCE
APPROXIMATE AODmONAL SOIL VAPOR
I MONrrORING WELL LOCATION
SOIL GAS SAMPLING LOCATION
ir--- ^.^ i.
2000 FEET
r^ *'
FIGURE 15
AREA 5 'C* SOIL VAPOR
MONITORING WELL LOCATION
NORTH INDIAN SEND WASH ROD
-------
001 0.30 NO 0.01 NO +
002 0.31 0.20 0.01 NO APPROXIMATE ADOmONAL SOIL VAPOR
003 4.50 0.28 0.60 NO MONITORING WELL LOCATION
004 1.10 10.0 0.06 NO
005 2.40 1.30 NO NO . SOIL GAS SAMPUNG LOCATION
006 19.0 1.80 0.22 NO
007 15.0 0.09 0.31 NO A EXISTING SOIL VAPOR MONITORING WELL
008 45.0 0.17 0.42 NO
101 3.30 0.02 1.90 180.0
102 4.40 1.90 1.80 170.0
103 8.20 0.10 1.00 NO
104 0.23 4.30 2.40 89.0
105 8.80 0.38 1.50 84.0
106 9.90 NO 0.89 130.0
107 12.0 28.0 1. 40 170.0
108 7.50 3.10 1.30 160.0
109 13.0 NO 0.79 220.0
110 10.0 16.0 1. 30 120.0
111 8.90 1.40 1. 20 140.0 Q
112 6.60 4.60 0.85 67.0
113 NO NO NO NO
114 ND NO NO 0.60
115 NO 0.03 NO 3.80
116 5.60 9.50 0.83 120.0
117 NO 1.90 0.70 97.0 '00 0 100 200 FEET
118 NO 5.40 0.42 150.0 ~-
119 0.07 3.60 NO 17.0
120 0.47 3.40 0.23 110.0
121 0.60 10.0 2.40 150.0
122 NO 1. 70 NO 280.0
123 NO 0.58 1. 10 130.0
124 6.00 0.22 0.32 130.0
125 1.90 NO 0.59 31.0
126 1.60 0.02 0.21 81.0 FIGURE 16
127 1.50 0.01 0.61 39.0
128 0.03 NO 0.44 NO AREA 6 SOIL VAPOR
NO . NOT DETECTED MONITORING WELL LOCATIONS
NORTH INDIAN BEND WASH ROD
,...,tJ
1-
-------
. o,~ ror. - ~~~~~~~':~;~~i~F
.. ."t~::~~:;.;J;;':t,~:~",~ ",...
, '
Additional soil vapor monitoring wells may be required based on information from the
first two wells." .. .
.'. . ,
iv. ' A~a 9. A soil vapor monitoring well shall be installed at the approximate locations
, shown on Figure 17 in order to estimate the extent, are ally and - vertiCally, of vadose
zone VOC contamination, and to estimate its mass. Depth-specific' soil gas samples
from this soil vapor monitoring well shall be collected and analyzed. Additional soil
vapor monitoring wells,m~y be required based on info~~atlon from the first well.
..'
v. Area 11. Two soil vapor monitoring well shall be instaIled at the approximate loca- ;'
tions shown on Figure 18 in order to estimate the extent, are ally and vertic~lly, of.
vadose zone VOCcontamination and to estimate its mass. Depth-specific ~oil gas
samples from these soil vapor monitoring wells shall be < collected and analyzed.
: Additional soil vapor monitoring wells may be required based on information from the
first two wells. ' '
vi. ,Area 12. . Fi~~ soil vapor monit9r:ing wells shall be installed - at the approximate'
locations indicated on FigUre 19 (data values for FigUre 19 are presented in Table 14)
in order to - estimate the extent, are ally and vertically, of, yadose zone VOC
~ontamination ~nd to estimate its mass. Depth-specific soil gas samples from these soil
vapor monitoring wells shall be collected and analyzed. 'Based on data from these five
wells~ addi~ion~l soil vapor. monitoring' wells shall be ..installed and, sampled, as
necessary. ' .
, For each of these areas, data from the add,itional 'investigations described above shall
be used in conjunction with existing information to develop vot mass estimates as
inp,ut for analyses with the VLEACH model, or a similar analytical tool determined
- acceptable by EP A. Mixing-zone calculatio'ns shall then be performed to estimate
potential impacts on the underlying saturated zone. Values for soil, contaminant, and
. underlying saturated zone parameters to be used in the application of VLEACH and
'. mixing-zone calculations shall be selected and approved by EP A based on field data
from each area.
" .
For areas that demonstrate a threat to ground water based on the VLEACH (or
VLEACH equivalent) analysis, the detailed analysis applied to Areas 7 and 8 will be
applicable. Therefore, the Soil Vapor Extraction ~lternative shall be implemented in
areas where the vadose zone represents a threat to ground water quality at levels above
the in-situ ground-water standards listed in Appendix A. The design of the SVE system
for each such area - will. be . designed based upon area-specific conditions. During
implementation, samples from soil vapor monitoring wells and the application of
VLEACH (or VLEACH equivalent) shall be used to continue to evaluate the necessary
scope and duration of the vadose zone remedial action.
Consistent with the decision for Areas 1, 2, 4, 10 and the Scottsdale wells, the No
Action alternative shall be selected for areas where the vadose zone does not threaten
ground water ,quality at levels above the standards listed in Appendix A.
RDDIR40S,uSla.51
75
-------
w»*«o
. • »«ji-iTj Aci »; (a
SAMPLING
LOCATION
101
102
103
SOIL GAS SAMPLE CONCENTRATIONS (ug/1)
TCE1,1.1-TCAPCE1,1-DCE
3.00
2.80
0.64
ND
KO
ND
0.49
0.52
0.07
1.20
2.40
0.53
ND - NOT DETECTED
LEGEND
APPROXIMATE ADDITIONAL SOIL VAPOR
MONITORING WELL LOCATION
;>OIL GAS SAMPLING LOCATION
EXISTING SOIL VAPOR MONITORING WELL
100
100
ZOO FEET
FIGURE 17
AREA 9 SOIL VAPOR
MONITORING WELL LOCATION
NORTH INDIAN BEND WASH ROD
-------
LOCATION .~ l,l-DeE £!!£!d l,l,1-TeA ~ PCE Q
11-01 ND 0.49 0.14 ND 21. 90 0.40
11-02 ND 0.14 0.07 ND 11. 80 0.18
11-03 ND 0.06 0.13 ND 1.08 0.08
11-04 ND ND ND ND ND NO '00 0 100 200 FEET
11-05 NO 0.71 0.12 NO 23.30 0.53 P""""'Io...---
11-06 NO 1. 08 0.35 NO 37 .20 1.54
11-07 NO NO ND NO 2.04 4.55
11-08 NO 1.36 0.54 NO 29.00 0.97
11-09 NO 3.19 1. 37 NO 181. 00 2.40
11-10 NO 0.20 0.04 NO 4.66 0.19
11-11 NO 1.79 0.34 ND 73.00 1. 20 LEGEND
11-12 NO 1. 26 0.79 NO 33.20 1.44
11-13 ND 0.13. 0.08 ND 6.10 0.17 +
11-15 ND 1.04 0.29 ND 34.20 1. 32 APPROXIMATE ADDITIONAL SOIL VAPOR
11-16 NO 0.06 0.20 0.02 9.27 0.17 MONITORING WELL LOCATION
11-17 NI) ND 0.08 ND 10.00 0.15
GEG-03 ND 0.31 0.02 ND 6.73 0.17 . SOIL GAS SAMP.l,ING LOCATION
GEG-06 ND 0.39 ND ND 4.43 0.11
GEG-09 ND 0.62 ND ND 8.43 0.31
GEG-12 ND 1.18 ND ND 17.60 0.52
GEG-IS ND 0.62 ND ND 11. 90 0.32
CONCENTRATIONS IN uq/l
Note: 11-14 not sampled. Too many buried utilities. FIGURE 18
AREA 11 SOIL VAPOR
MONITORING WELL LOCATIONS
NORTH INDIAN BEND WASH ROD
,..,,.,,
-------
LEGEND
APPROXIMATE ADDfTIONAL SCHL VAPOR
MONITORING WELL LOCATION
SOIL GAS SAMPLING LOCATION WITH
RESULTS FOR DCE. TCE, AND PCE
NOTE
FOR SOIL GAS SAMPLE
CONCENTRATION DATA
SEE TABLE 14
FIGURE 19
AREA 12 SOIL VAPOR
MONITORING WELL LOCATIONS
NORTH INDIAN BEND WASH ROD
-------
Table 14
Soil Gas Results for Area 12
(Hg/0 '
Sheet I of 4
Point
F01
F02A
F02B
F03
F03B
F04
F05
F06
F07
F08
N01A
N01B
N02
N03
N04 , ':
N05
N06
N07
N08A
N08B
N09
N10
N11A
NUB
N12
N13
N14
N15
VCL
<0.01
. <0.01
<0.01
<6.oi
, <0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
.
<0.01
<0.01
<0.01
18.00
29.00
77.00
160.00
170.00
50.00
8.60
14.00
2.00
3.40
16.00
42.00
58.00
75.00
8.10
0.05
<0.01
<0.01
TCA
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
. <0.01
<0.01
<0.01
<0.01
1.60
3.00
3.40
2.80
0.82
0.08
<0.01
0.09
0.07
0.18
0.20
0.15
1.30
2.20
1.10
0.57
0.17
<0.01
TCE
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
'18.00
24.00
. 39.00
62.00
76.00
29.00
1.80
28.00
13.00
24.00
42.00
32.00
34.00
38.00 J
21.00
8.20
0.51
0.61
PCE
-------
Table 14
Soil Gas Results 'for Area 12
(~Wl)
Sheet 2 of 4
Point' VCL DCE TCA TCE PCE
N16 <0.01 6.50 0.62 11.00 2.30
N17 <0.01 28.00 45.00 21.00 ' 57.00
N18 ' <0.01 '0.09 0.48 0.36.. 0.08
~19 <0.01 ' , 0.35 0.02 0.04 2.50
N20 <0.01 2.30 <0.01 <0.01 <0.01
N21 <0.01 '3.60 0.90 2.90 4.10
N22A ,,<0.01 32.00 62.00 0.34 12.00
N22B <0.01 25.00 53.00 0.16 6.30
N23 <0.01 17.00 <0.01 12.00' 49.00
N24 <0.01 ' 1.10 0.05 0.04 0.14
N25 <0.01 7.70 <0.01 5.70 12.00
N26 <0.01 1.40 <0.01 4.20 4.70
N27 <0.01 <0.01 <0.01 <0.01 <0.01
N28 <0.01 1.00 51.00 <0.01 <0.01
SOL '<0.01 <0.01 0.23 <0.01 <0.01
S02 '<0.01 <0.01 0.22 <0.01 <0.01
S03A <0.01 <0.01 0.02 <0.01 0.03
S03B <0.01 <0.01 <0.01 ' <0.01 <0.01
S04A <0.01 <0.01 0.02 <0.01
-------
Table 14
Soil Gas Resu~ts for Area 12
( ~g/I)
Sheet 3 of 4
Point VCL DCE TCA TCE PCE
513A <0.01 0.05 0.08 6.20 0.15
513B <0.01 <0.01 0.10 6.90 0.13
514 <0.01 0.47 0.09 3.70 0.15
515 : <0.01 5.50 0.05 . 13.00 0.89
,516 <0.01 6.40 1.30 ,32.00 3.30
"
517 <0.01 0.82 0.27 29.00 2.60
518 <0.01 <0.01 <0.01 14.00 0.19
519A <0.01 <0.01 0.03 2.10 0.06
519B <0.01 <0.01 0.03 0.94 0.15
520A <0.01 <0.01 " , 0.02 <0.01 0.Q1
520B <0.01 <0.01 <0.01 <0.01 <0.01
521 <0.01 <0.01 <0.01 .' <0.01 <0.01
.522 <0.01 ' <0.01 <0.01 0.14 0.28
523 <0.01 <0.01 <0;01 1.30 0.01
524 <0.01 2.80 0.82 ' . 38.00 21.00
525 <0.01 26.00 3.60 61.00 15.00
526 <0.01 0.79 0.15 1.60 0.32
527 '<0.01 '0.32 0.11 0.06 ,0.12
528 <0.01 0.21 0.05 0.16 0.30
529A <0.01 <0.01 <0.01 <0.01 <0.01
,529B <0.01 <0.01 <0.01 <0.01 <0.01
530A <0.01 3.30 0.29 16.00 11.00
530B <0.01 3.10 0.20 14.00 9.70
531 <0.01 <0.01 0.09 1.40 1.40
532 <0.01 <0.01 <0.01 <0.01 <0.01
533, <0.01 <0.01 0.02 0.02 0.33
534 <0.01 <0.01 :,,<0.01 <0.01 0.12
535 <0.01 . <0.01 <0.01 ' <0.01 <0.01
RDD\R40S\OSS.SI
81
-------
Table 14
Soil Gas R.esults for Area 12
(loLgll)
Sheet 4 of 4,
Point VCL DCE TCA TCE PCE
536 <0.01 <0.01 <0.01 1.40 0.54
537 <0:01 7.00 0.07 7.20 12.00
538A <0.01 25.00 0.11 9.00 12.00
538B <0.01 18.00 0.06 4.20 .7.60.
539 <0.01 16.00 0.01 7.50 8.40
S40 <0.01 1.90 o.n 0.94 0.87
541 <0.01 . 0.39 0.02 0.08 ,0.13
542 <0.01 0.73 <0.01 0.04 0.24
543 <0.01 35.00 0.11 25.00 25.00
S44 <0.01 110.00 1.20 38.00 40.00
545 <0.01 99.00 0.38 31.00 37.00
546 <0.01 <0.01 <0.01 0.03 0.49
547 <0.01 <0.01 <0.01 0.13 14.00
548A <0.01 0.49 0.26 6.80 7.30
S48B <0.01 0.49 0.95 5.00 5.60
549 <0.01 <0.01 <0.01 <0.01 <0.01
550 <0.01 " <0.01 0.02 <0.01 0.01
551 <0.01 0.04 0.17 .0.49 3.40
".
RDD\R405\055.51
82
-------
2. GROUND WATER
Because current analyses. indicate UAU alternatives that include pumping would not
~ignificantly reduce the overall ground-water clean-up time when compared with not
pumping from the UAU and do not otherwise offer significantly greater protection of
human health or the environment, the pumping alternatives appear costly in proportion
to thei,r estimated effectiveness. However, in order for a remedy without{)AU
pumping to be protective, it will be necessary to ensure thanhe fate of VOCs from the
U AU has' been characterized accurately. Therefore, EP A is selecting Monitoring the
Fate ofVOCs in the UAU without Pumping from the UAU. This alternative relies
, upon (1) leakage through the contact of the ~AU and the MAU/LAU and (2) flow
through wells .perforated through the UAU and the MAU and/or LAU to move VOCs
in the UAU into the lower units. VOCs then will be captured by the Scottsdale
Oper~ble Unit remedy. '
¥onitoring wells shall be installed in the' UAU and MAU to track the fate of VOCs
currently present in the DAU. The monitorin'g well network shall be designed to allow
(1) evaluation of the rate of VOC mass reduction.in the UAU due to migration of
VOCs out of the UAU and (2) evaluation of the locations within the UAU, MAU and
LAU to which VOCs presently in the UAU are migrating. If VOC mass in the UAU
decreases significantly and continuously, or if uncontaminated areas of the UAU, MAU
or LAU become contaminated because of migration of VOCs from the UAU, EP A
shall re-evaluate ground:'water pumping' . . " .
from the UAU. ' '. ' ,
Initially, monitoring wells shall be installed in the UAU and MAU in the three general
areas shown on Figure 20 where a contaminated saturated thickness has been identified
in the UAU. The monitoring wells shall be installed to attain a density of at least one
well in the UAU and'MAU for each 40 acres. The exact numbers and locations of
wells for each area shall be based upon the most recent indications of the extent of
UAU contamination. As necessary, additional wells ~ll be installed to monitor
adequately the presence and migration of VOCs.
The 1988 Record of Decision for NIBW selected specific clean-up levels for water
treated by the Scottsdale Operable Unit remedy but did not specify requirements for
water remaining in place at the completion of remedial action. In this Record of
Decision, EP A is selecting, and in some cases revising, standards for water treatment
. and for ground water left in place.
In the 1988 ROD, EPA.selected a water treatment level for PCE corresponding to a
orie-in-one million (1 x 10-0) excess cancer risk level because no federal drinking water
standard for PCE existed at that, time. EP A has now established a 5 micrograms per
liter (or 5 parts per billion) MCL for PCE. This level corresponds to an excess cancer
risk closer to one-in-one hundred thousand (1 x lO-s). Because this risk is still low and
the total risk will be within the ,acceptable risk range defined by EP A, EP A is now
ROOiR40SIOSla.51
83
-------
CHAPARRAL~OAD
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.m"'-'.' .o"
J ,
t ......2.3 .
COS2~~~::.~'1 ~~ ::::::' ..'
-- - !' .~.:::~~~
I ~,-""
".
~~ ' I
. ... .23 / "'..c. I 1'4
. ~,~:W~M (.sQ~-T\:" ,- I.' . .'. ROAD
~"rr." '.~.~'-~ ~ .",~ """"-"':-'r - -. .,..
~ ,:'~~~;:::.~:::::::'::~; , I'. - C~lI CCln.'. cos"
'''""-"~~,~:f 01
::~I:' .
-------
selecting thC? 5 micrograms per liter 'MCL for PCE as the required clean-up standard
for treated water as well as fo~ ground' water left in place at NIBW. '
, ,
EP A also selected a treated water standard of 0.5 micrograms per liter for chloroform
in the 1988 ROD. This standard corresponded to a one-in-onemillion excess cancer
, risk level. A federal: drinking water standard exists for chloroform, but the standard
specifically accounts for cases where chloroform is present as a by-product of chlorina-
tion, a process used to kill bacteria that could o,therwise cause widespread illness and
death. EPA has reassessed the potency of chloroform as a potential cause of cancer in
humans. As a result, 6 micrograms per liter of chloroform now corresponds to the one-
in-one million excess cancer risk level. Therefore, EP A is selecting 6 micrograms per
liter as the required clean-up standard for both treated water and for ground water left
in place at NIBW. .
. .'
, .
For most other VOCs at NIBW, EP A is selecting the MCLs as the required clean-up
standards for both' treated water and ground water left in place: Proposed MCLs and
ADEQ Human Health-Based Guidance Levels will be the treated water and ground-
water standards for certain other substances. As a result, the overall excess cancer risk
'from NIBW will be at most on the order of one-in~one hundred thousand, which is '
within EP A's acceptable risk range of 10-4 - 10-0. Because some blending of water is
likely within the municipal supply systt::m and most VOCs will be w~ll below their
maximum allowable levels, the actual risk IS expected to be even lower. '
J. STATUTORY DETERMINATIONS
1. ' PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
EP A believes the combination of SVE, ground-water monitoring and the previously
selected Scottsdale Operable Unit remedy (including, modifications, as necessary) is
protective of human he'alth and the environment. . '. .
Based on sampling performed at the site~ EP A considers potential direct human expo-
, sures to VOCs in the vadose zone and surface water at NIBW to be minimal. There':
fore, no measures are being :requir~d' specifically to further reduce potential direct
exposures, although the Soil Vapor Extraction designed for ground-water protection
will, in fact, reduce the amount. of VOCs available for potential direct exposures from
the vadose zone. ' , .
At NIBW, the principal risk to human health is through contact with and ingestion. of
contaminated ground water. By removing from the vadose zone VOCs that could
threaten ground-water quality and by carefully monitoring the fate of VOCs currently
present in the UAU; the selected alternatives will help to ensure that the ground water
underlying NIBW is returned ~o levels acceptable for drinking water use in a
reasonable timeframe. In addition, water extracted from the MAU andLAU as part of
, RDDIR40SIOSla.51
85
-------
the site remedy shall be treated to meet all state ~nd federal drinking water standards.
The remedy shall attain an exce,ss cancer risk level within'the 10-4 ~ 10-6 risk range, and
the Hazard Index for all non-cancer endpoints shall be less than 1.
During implementation, careful installation of the s9il vapor monitoring and extraction
wells and of the additional ground-water- 'monitoring wells will prevent any unacceptable
short-term risks. " , , '
2. COMPLIANCE WITH ARARS
, '
Appendix A identifies the ARAR~ and other criteria for NIBW. The selected alter-
natives shall comply with all ARARs and other critieria identified in Appendix A.
3. COST-EFFECTIVENESS
The remedial actions selected by EPA for NIBW'are cost-effective in that their costs
are proportionate to their effectiveness. '
, ,
EP A considers the costs for the seiected vadose zone alternatives to be proportionate
to their effectiveness in removing the potential for hundreds of years of ground-water
contamination and avoidance of the sl.lbstantial monitoring and' clean-up costs that such
contamination would entail." ,
Additional monitoring with no ground-water extraction from the UAU is cost-effective,
in that it will maximize the use of the investment in pumping from the MAU and LAU
. 'without sacrificing assurances about the fate of VOCs from the UAU.
, ,
4. UtilizatioDof Permanent Solutions and Alternative Treatment Technologies or
.' Resource RK9very Technologies to the MaXimum Extent Practicable
EP A believes the alternatives selected for NIBW utilize permanent solutions and alter-
native treatment technologies orres
-------
implementation, less short-term risk, and at less cost, than alternatives that include
UAU ground-water extraction. In addition, the required monitoring will provide data
to evaluate whether or not the selected UAU alternative is actually effective and
protective. .
5. Preference for Trel:\tment as a Principal' Element
Although EPA is not selecting pumping and treatment of ground water from the UAU,
the SVE systems and the Scottsdale Operable Unit air stripping facility (including vapor' ,
phase carbon adsorption) satisfy the statutory preference for the use of remedies that
include treatment as a principal element~ .
K. SIGNIFICANT CHANGES
1. UAU AREAS REQUIRING MONITORING: '
Since the release of the RIIFS and Proposed Plan for public co~ment, recent data
indicate additional areas of the UAU have sufficient saturated. thickness and ground-
water contaminant concentrations to warrant monitoring as part of the selected UAU
ground-water alternative. Figure 20 indic~tes the UAU areas requiring monitoring
based on recent information.
2. ARARs
Based on comments received during the public comment period, some ARARs or other
criteria not included in the RIIFS are identified in this ROD. For example, the
Arizona Aquifer Water Quality Standard of 50j.1g!l is the most stringent ARAR for
chromium. In addition, the vinyl chloride MCL of 2 j.1gl shall be an ARAR. ADEQ
Human Health~Based Guidance Levels also have been, considered in the selection of
. .
final clean':up requirements. All ARARs and other criteria with which the Scottsdale
Operable Unit remedy and the remedies selected in this ROD shall comply are
identified in Appendix A
RDDIR40SIOSla.51 '
87
, .
-------
. Appendix A .
ARARs AND OTHER CRITERIA FOR NIBW
-------
, . Appendix A . . . '
ARARs AND OTHER CRITERIA FOR NIBW
This appendix identifies ARARs and other criteria to be. considered (TBCs) for the
selected remedial actions for NIBW. . ' .
CHEMICAL-SPECIFIC ARARs'AND TBCs
Table A-I presents chemical-specific ARARs and other criteria for water arranged by
chemical compound. The major regulations which contribute, to the list of potential
chemical-specific ARARs are the Clean Water Act (CW A), the. Safe Drinking Water
Act (SDWA), and Arizona Water Quality Standards for Na~gable Waters. The chem-
ical-specific TBCs for the NIBW site include (1) Arizona Department of Environmental
Quality (ADEQ) Human Health-aased Guidance Levels for Contaminants in Drinking
Water anq Soil (HBGLs), (2) Federal Health Advisories, ancJ (3) proposed ADEQ
Water Quality Standards. . .' . .
The SDWA Maximum Contaminant Level (MCL) standards are based on human con-
sumption of water for drinking, cooking; bathing, etc. Economic considerations and
technical feasibility of treatment processes are included in the justific~tion for these
levels. MCLs are applicable to the quality of drinking water at the tap pursuant to the
Safe Drinking Water Act ~nd are ARAR for treated ground water when the end use is
, drinking water. " .
, .
Pursuant to 40 C.F.R. Section 300.430(e)(2)(i)(B), MCLs and non-zero Maximum
Copt~minant Level Goals are relevant and appropriate as in-situ aquifer standards for
ground water that is or may be used for drinking water. .
ADEQ Aquifer Water Quality Standards [AR.S. Section 49-223 and implementing
regulations] genera.lly ate identical to SDW A MCLs at this time, and therefore are not
referenced in Table A:-l. One notable exception is the. 50 J1g/l chromium Aquifer
Water Quality Standard, which is more stringent than the current MCL and therefore
is an ARAR and the selected water treatment standard for chromium for NIBW.
The CWA Water QualitY Criteria are designed to protect aquatic life (b9th marine and
freshwater). These standards are expressed on the .bases of acute and chronic toxicity
levels. Both the Federal Water Quality Criteria and the State Water Quality Standards
for Navigable Waters [AR.S. Section.49~221 and implementing regulations] are ARAR
fo~ surface-water discharg~s. .'
RDDIR3101020.S1
A-I
-------
~
N
ToIIIeA.1
CbolDkaJ..lipcdllc AILUIa .... Otbor Crttoot.;... NIBW
1<--10 JII/I)
Sbool I' 01 J
~.. ....-.... Appnoprt8Ie OIbor Crttorla 10 ... 1:0001""'"
AWQC U.s. .:rA 11..1... Alhbort...
S...<:I... NIBW n..n..p
SDWA SOWA I...... Term AIII-.:Q Slaodllnl rvl' 'I'ft.acd
SOW A SOWA 10-6 C......r ~ --.. . I"", 10-4aJ IJkIlme 1l1IG~"" Wak.. .oct IQ SUa
eoa.,o.... MCL MCW Toa1dIJ IIIdI MCL MCW ' 10" 10" 10" 70" 70" W..n G.........sW.kr
1,I,I.Tricbloroclbaae 200 200 19,000 200 140,000 3S,OOO 3S,OOO 12S,ooo 1.000 200 200'
1,1-()idI1orodba...
1,1.DicbJorocIbeae 7 7 0.033 1,000 1,000 1,000 3,500 3SO 7 7
1,I,2-TricbIoro-2,2,I.TriOuorodbaae
I ,2.Did.toroeaba... S 0.94 S 740 740 740 2,600 N/A 0.311 5
1,J.Dic1IlurubetIuoe 8,930 8,930 8,930 31,2S0 3,I2S 620 620
1,2-DidIJoropopane S 6 90 O.S<> 5
M,thyl Ethyl Kdoar: . 7S,OOO . 7,SOO 1,500 8,600 \!tAl \10 \10
H'.DDT >.0012 0.10
Aa:toar: 7011
Be- S 0.67 S 233 233 N/A N/i\ N/A 1.3 S
BiI(2-ctbylbelyl)pblbalal<. 21,000 4 0 .1 4
~ba... 100 0.19 100
'.
BnxDororm 100 0.19 IIMI.
Carbon Tetrachloride S 0.42 4,000 100 7\ 2SO N/A 0.27 5
('blorubeDlOllO 100 100 00 I,I!OO I,I!OO 9,000 3,000 :1,150 100 lUll
(.bloro(orm 100 . 6 b 6
Di_ba.... '. 0.19
Di.n.burylphlbalal. 44,000 ' 4 4
1>;..<><1,1 ph'balol.
Mdbykn< cbk>ridc 5 0 47 S
IUJI)/lOIO/021.S ...
-------
>
I
~
T_A.I
Cboadcal-Spcclllc AIIAIIa .... 01lIo. crUorta lor NIBW
(-_.. I'WI'
Shull .1 J
AppUuIIIo - lie....... .... AppRprtate Otbo. crUorta .. 100 ('0"'''''''''
AWQC V.s. t:PA "raUb.w.borIro
~lKkd NIHW (:It.,u.p
SDWA SDWA l..oapr 1'~rm Am:Q Sl8ndan1101' l'r~.1t1I
SDWA SDWA 10-6 C--. """" """-' 1""1 10-<181. IJlrIImr IlliG I.. 10.. W...-.. andIlo SII.
~ MCL M(:W .TexldlJ - MCL MCW 10" 10" 10" 10" 10" Wa"'.. Grvaod Wain
Slyrme 100 100 , 140 21,000 2tI.000 2tI,000 10,000 1,000 ~ 100
TetrKlllorocl- S 0.118 U Nil' 34,000 1,940 0,IlOO NIA 0.01 ~
Toluene 1,000 1,000 1S.000 2,UUU 18.000 0,000 NIA NIA 10.100 2,000 1,000
T",..-I,2-dichlorucl- 100 100 10 2,120 1,000 1,000 J,500 .l5U 10() 100
-rrichloroet- S 2.8 5 3.2 5
Trid>IoroIIuoruaoetbaoc: 2.100 1,100
Vinyl Chloride 2 0 2 U.Ol 2
Aluminum 20 1:1 20
Anlimony J 146 5nO 15 :1 5
AncDic .SO O.oolS SO 50 5U 50 50 50 ~O SO
Barium 2,000 .2.000 1.IlOO S,UUU 2.000
lIcryIIium O.ooJY 1 0 0.0(11 1
Boroo
Calmium S 5 IU 4J M 5 1M 1M ~ .\
(''bromium 100 100 SO 1.400 1,400 24U H4U 11U 10(' ~U
('.opper 1.000 1,]00 1,]00 1,.100 1.0(111
lad SO 50 2tI 20 ~&ld.y 2U ~&lday lO ~&lday 20 ~U
Mercury 2 2 IU 3 5.~ 1 1
Nickd 15.4 IOU IOU 1.000 100 100
Selenium SO SO 10 45 ~~ ~U
Silver SO 5U ~O ~U
KI>L>/lOIO.Q2I.SI-2
-------
~
~
T_".I
CbomJcal.8pcdllc .u.u. - OIbor CrIIorta lor NIBW
(--....-.,
Sb«1 J of J
A,.uc8k .. ...- - AppnprtaIo OtIwr (:rt..rIa ... be (:0"0111.."
"WQC II.S. .;p" 1I.8Itb -!>colin
s......... NIBW U....op
SOW" SOW" I..,..; Tum Aln:Q S""""'d 101 'I'n_kd
SOW" SOW" 104 c.-r ""-' ....... I..., '1_, IJ'....... l18Ca~ 10, W.'n .nd ID Sliu
C8mpoooM MCI. MCLG TaIdIJ - MC!. MCIJ.; 10" .0" 10" 70" 70" Wain (;I'oood W.kr
StronlWm
V8lllldium 7
7.iDe S,OOO S,OOO S,OOO ~,OUo
Nola: ADEQ - ArizoIIII Depart....... 01 EIMIoomctII.1 Quolily.
AWQC - Ambical WOIU QIWiIy Crilaio; 1IIj_1.. OOIIIIImpboo 01 drinkinl _I" DIlly; fllb in",I;DII """ponen. rcmow:d (U.S. IiPA, 1'JII6).
AWQC (IO~ - The Ambieal W.I.r QIWiI, CriIeN raulliAc in . 10-6...... iiI...... I>IIUIU,v2151.3
-------
Federal Health Advisories are criteria developed by either EP A's Office of Drinking
Water Health Advisory Program or the National Academy of Sciences (NAS). The
Federal Health Advisories are based on NAS-Suggested Non-Adverse Response Levels
(SNARLS) at which no known or anticipated adverse human health effects would
occur, given an adequate margin of safety.ADEQ HBGLs have been selected as water
treatment standards for 1,3-dichlorobenzene, methyl ethyl ketone, and trichloro-
fluoromethane. ADEQ HBGts are aiso to be considered for direct exposure threats
from potential soil ingestion.
. LOCATION-SPECIFIC ARARs AND TBCs
Table A-2 identifies the loc~tion-~pe~ific ARARs' and. other criteria' for NIBW.
Location-specific ARARs differ from chemical-specific or action-specific ARARs in that
they are not as clos~ly related to the characteristics of the wastes at the site, or to the
specific remedial alternative under consideration. Location-specific ARARs are con-
cerned with the area in which the site is located. . Actions may be required to preserve
or protect aspects of the environment or' cultural resources of the area that may be
threatened by the existence of the site, or by the remedial actions to be undertaken at
. the site. . .
ACTION-SPECIJ4'IC ARARs AND TBCs
. .
, , ,
Table A-3 identifies 'action-specific ARARs and other for NIBW. The actions included
m Table A-3 are components of remedial actions selected' in this ROD and the
remedial action selected in the 1~88 ROD (the Scottsdale. Operable Unit remedy).
Further identificatio~ and discussion of OSHA requirements" air emissions
requirements, and additional State ARARs and other cnteria are provided following
Table A-3.' ,
RDD1R310mo.51
A-5
-------
>
I
01
T"'" A.1
Loc8Uoo-SpecUk' AIIAIb ..... OIbrr (:rtkrta for NIBW
Sbtoll of 1
.- a..pIft_aa PrenqllbJk(a) CIIaIJoa AILU (7011U1Wnb
J. wiIIIiD 100.,- IIoodpIoiD FI..II<'lcd
",lItr fIuod.prooc an:as. facilitD an 10 be Iocalc:d in 8 OtJCJdpl3in, Bf..'(:cpb."tJ ':IuudpJUu.ing
aod u.bet Rood QXllml mc:uura .11 he uodcrtakcn 10 ilc:hlCYC
fIuod proIcc'ina. Wlltncvcr pIlIC.ical, llruc\ura shall be d....,.01
lbove ,he base fIDpcd.
Cluae irrr:pInIbJc bum, ..... or artifaas. IhrcalclllligniHcanl JCieolific, .nd Ilistnrical
dcIIInI
-------
~
...J
T_A-2
Loc8IJoa.sp.cUlr AILUb - 0IIwr Crtlo.. .... NIBW
Shoo. 1 of 1
-- D . ' -_14 """"_'") (;Ua"'D AILUI (:.........ab
5. Wdlud AaiallIO miIIimizc die "'rue. w..1and .. ddiocd ." El
-------
""lIDo
Air SiriJ11>ia8
Coal~ SIcnce
(OoIile) .
~
00
-.
RDDIR3Io,Q23.SI-1
.................
RCRA 1Ia-.. for COIluul or cmiuioaI or wUlile
orpaIca.
Coalrol or lir cmiuioaa or wUliIe orpnica IIId
p8COUI ooawnlaaalL
CoaI8iacn or Iw8rdouo - ..;... be:
-.
. MaiDIIiDcd iD ....... oondilioa
. Compaliblc wllb IwanIoua _e 10 be .1ORd
. com durin. "..... (CllCtplIO add or mDIM:
......)
.-
Inspca ooawacr "..... IRII wcctJy for
dctcrioralioa.
Place COIlbiacro OIl I 1Iopcd. cract-frcc base. Iud
proIcc:t from conlICI witb aa:umulalcd liquid.
PnMdc ooaWnlllClll optcm wilb I capacity or
10 pm:cIIl or lbe volume or ooabiDcd or fROC
liquids. .
Rcmavc .pilled or leaked _I. in I limely IIUIn-
10 ....-01 ooa1Iow or lbe ooal8iomcol optcm.
Keep ooalliacro or ipibble or raclivc Will. IIIcIII
SO fccl from lbe fadlily'. pcupcny lioc.
Keep iDmIDpalibic malerials ocparal.. Separale
iDcompalible malerials lIorcd ocar caeb other ~ I
dike or other barria. .
AI ckaurc. n:1JIOVC "I hazardous ...... IDd rcoiduca
from lbe roolaiomen. iystem. and dc:c:ootaminate or
I"CIDO¥e all wolaincn. linen.
T_A,3
""IIoa,Spodllc ARAIb - OIbor Crtlorta lor NIBW
Pro....""''''
RCRA Iwardoua Will..
nla- AIIAII
40 CFR Subpal1l AA "1111 ARAR
Maricopa Counly Rules 210, 'mc
320, 3JO.
40 CI'R 264-111 (11.111-18- ARAR
264.110, el ""'I.)
40 CFR 264.172 ARAR
40 CFR 264.113 ARAR
:
40 CI-R 264.114 ARAR.
.
40 CI-R 264.17S ARAR
Emisoioa or VUe. or ......... lir ronllmi-
DlDIa.
RCRA bazardouo will. (tilled or ARAR
40 CFR 264.177 ARAR .
40 CFR 264.178 ARAR
-------
~
\0
T_A.J
AdJoo..SpecIIk ARARa - OCbor (:rIIorta Cor NIBW
< Sb... J uI J
- ".~- 'Ie",- . (:b8IIoa - (~oma:wDbi
DiIed DiIdwJe of ApplIcable FcdcnI WIler quality crileria lor lbe SutIaoe disdw"p: utlraled efnucal. SO FR Ju7114 (JUly 2'J, I9!lS) AKAK See the inilial Krecoin. laNe for dlemic4tI.~pC(:ilic
TrauDau ............ of 8IpII1ic Ute - be """'plied wilb ARAK..
s,ucm EIIIucDI wIIc8."""""'" f8cIon... beiDa COIIIidcraI.
AriIIoa8 SIIIc Wiler QuaIiJy SIaDdordI I... ru.;pble Oilcbarp: 10 oavipble WIlen. AKS 49.221 'AKAK
Wilen
T~ SIaDdordI Cor M;....I'._- uaill (1ooa-IenD re. Treatment 01 bazardoua .uta ill unill DOl '40 CI-R 2M (Subpan X) AKAK '.be: subr..anIWe poniuns ullhac= U.-qulI-cmcnl5 will be
IrieoabIe ....., 1bcnuI1~ OIbcr IbaD iodJI. reaullied - uoder RCRA (c. I., 8ir , applicahk O( rdevana and appwPfialc lu the:
cnIOn, opal ......... opal dcIoDaIioII, cbcmIcaJ. IlrippcnJ: construction. upc=ralion, mainlcrulm;c, and chll:!l.urc (at
pbysIc8I. aDd IIioqic8J IIaUIICIII uaiII uoia8 oIbcr -any miKdlancous (raIment unil (a Irealment uoil
Ibao ...... ........ -1"''''''-''. ... IIod _I . 1ru.1 D 001 cbcwbcn= regulalcd) COfUlruclcd un the:
uaiIa) require - miacdlaocoua uaill 10 aalisfy : NIUW lite ft.. Ircalmrol andJl:..- dbpU~.a1 ur baurdoua
....uoaaimtaI perf- - .., proIectioD lite wasla,
of puuod _cr, aurf- WIler, - air qll8lily, 80d
.., IiIDiIiq IUIface - 8IIIIourfacc ...,....ioG.
TrcaI_1 of -.. IUbjecllO baa 011 lIod dil",-, TrallDCal of WR _c. 40 CFR 2b8 (Subpan I» ARAK 'Ibe sumaanlive poniuM. ur .hac: rc.."'Iuircmcnls arc
mUll 8118ia Ic¥dI acbicvable .., .beII *",,-raIcd applil'able 10 the dispoul ~,. any NIIIW ~iic Wa~IQ
ovaiJat.Ic I....IIDCIII IcduIoIo8ioa (BOA 1') Cor acb ahat can be defined u ralrH:It.-d ha/.arduus wallo.
. .....- aalilUCIII iD acb IiIIcd WIlle.
,. .. The ,ut.lanINe poniuns 0'- Ihac rcquircmenls ilrC
BOAT ILUIdarda 8ft baaed 011 OIIC of lour lecb. n:banl and appmprwlc Iu Ihe IrcalRK."f11 I)riur 10 and
........ ... a>mbiDalioaa: Cor_en (I) lI..m '. du.po.al ur .ny NIHW Wlc w~o 1h4tll:uillain '
IlrippiaI; (l) IIioqic8J IRaIIDCllt; ... (3)"'- .' (:umponeDls 01 ralnelcd wi!Wa in o)nl'Cnlnuions lbal
8doorpIioD (u-... iD _iOD witb (I)'" (l); . make the lilc WDIQ .uUkieRIIy similar In lbe
- Cor aU oilier - (4) iDciacnliOll.. IIlry : .. rCluialcd ."0. 'Ibe rcquircmcnls spt.'t'iay kvcb of
ICdudot.Y III8J be 1aaI. -, if II will acIIinc IfeaUDCollbat mUll be allaiDed prior 141 land du.ptIYI.
Ibc CIIIII:ICIIU1II ..... apa:;rlcd.
..
R"UlllioDa ,... 1Iod.1>ucd a>rrecIM aclioDa 81 laod.1>ucd lCIDcdiaillClioD. 40 CI.R s~bpan S (Reviled) TIIC
RCRA lacilila.
Grouod,W8Ier Well IIlry ......... material (c.i., pouod _Ier or 1Oi1) NOIIWIIIc ....erial ooOwa"l Iilled R('RA "WIIlinoed in" AKAK .
IDll8l\aliOII, lbal CXIOI8iaa 8 liIIed I>azanIOID ....c mull be I>azanIOID _c pO""iplc
DcvcIos-m. TCllq; .......... II if iI wen: . bazardoua ""c.
aod SampIiD&
Orouod.Wllcr Orouod- IDOIIiIoriJo& II - ... CIiIIiDa RCRA CrcalioD 018 DCW dispuoal uail. ",malial 40 CFR, Subpan F AltAK
MoaiIoriaa ~uai... Kliuoa II ao c:liatina RCNA uoit ur
di>pt.uI of KCRA bazanloua....c .
'-
ROO/R3I1Wl3.Sl.l
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THE OCCUPATIONAL SAFETY AND HEALTH ACT (29 CFR 1910.120)
, ' '
The Occupatienal Safety and Health Act (OSHA) requirements fer werker protectien,
training, and menitering are applicable to. remedial actiens at the NIBW site, and will
also. be applicable to. the eperatien and maintenance ef any treatment facilities, cen-
tainment structur~s, er dispesal facilities remaining ensite after the remedial actien is
cempleted.
OSHA regulates expesure ef werkers to. a variety ef chemicals in the werkplace, and
specifies training pregrams, health and environmental menitering, and emergency pro-
cedures to. be implemented at facilities dealing with hazardeus waste and hazardeus
substances. ' '
AIR EMISSIONS REQUIREMENTS
The 'Clean Air Act (CAA) has been implemented threugh a series ef regulatiens
(40 CFR 50-99) that define, the air quality management pregrams used to. achieve the
CAA geals. The State ef Arizena is respensible fer preparatien ef a State Implemen-
tatien Plan (SIP), which describes hew the air quality programs will be, implemented to.
achieve cempliance ,with primary standards. Upen meeting the primary standards, an
area is classified as "in attainment." The SIP must also. identify hew the programs ,will
maintain attainment status fer each ef the primary pellutants. NIBW remedial actiens
must cemply with the substantive requirements ef the' CAA and its related pregrams,
including the EP A-appreved Arizena SIP. '
RCRA standards fer centrol ef VOC air emissiens frem units such as air strippers are
feund at 40 CFR Subparts AA and BB. These standards require reductiens, but de not
include specific numeric standards.
, . ,
Recent guidance en centrel ef. air emissiens frem air strippers used at Superfund sites
fer greund.:.water treatment is' to. be. censidered fer air stripper emissiens at NIBW.
Centrels are mest needed en seurces with an actual emissiens rate ef 3 lb/hr er
15 lb/day er a petential rate ef 10 tens per year ef tetal VOCs because VOCs are
ezene precursors (EPA OSWER Directive 9355.0-2.8, June 1989). The basis ef the
need fer contrel indicates this guidance to. be censidered fer SVE emissiens at NIBW
as well. . .
Maricepa County Rules 210, 320, and 330 are criteria to. be censidered fer air emis-
siens at NIBW. Maricepa Ceunty's January 1991 guidelines fer implementing Rule 210
require VOC air emissien centrels fer remediatien sites where tetal uncentrelled VOC
air emissiens weuld exceed 3 peunds per day. The air emission centrels must have an
everall efficiency ef at least 90 percent. These criteria are selected as the air emissien
standards fer NIBW based en a consideratien ef the petential aggregate impacts ef the
numereus air stripping and soil vapor extractien systems that likely will be in eperatien
at the site.
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ADDmONAL STATE ARARs AND TBCs
Portions of the Arizona statutory code for cleanup of hazardous substances related to
contaminated ground water ("Arizona superfund", Ariz. Rev. Statute Section 49-282, et
seq.) and implementing regulations (Ariz. Ad. Code R18-7-109, et seq.) are applicable
or relevant and appropriate to the NIBW site. . The implementing regulations incorpo-
rate by reference state law provisions that (1) establish that all definable aquifers are
drinking water aquifers unless' they qualify for an aquifer exemption and (2) establish
water. quality standards for these aquifers. Finally, the Arizona Superfund statute and
regulations require that, to'the extent practicable, NIBW remedial actions provide for
the control, management, or cleanup of hazardous substances so. as to allow the
maximum beneficial use of the waters of the state.
Section 45-454.01 of the Arizona Groundwater Management Act (GMA) [A.R.S.
Sections 45-454.01] is applicable or 'relevant and appropriate to the NffiW site. The
remedial action selected in the 1988 ROD (Scottsdale Operable Unit remedy) requires
an offsite use of the treated ground water. All offsite uses are subject to state law
outside the context of the Superfund action.. However, for activities conducted onsite,
the substantive portions of the provisions referenced within Section 45-454.01 of the
GMA shall be applicable or relevant and a~propriate. .
The Arizona Department of Water Resources well spacing guidelines are TBC.
RDD1R3101020.51
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