EPA Superfund
Record of Decision:
Apache Powder Site,
St. David, AZ,
9/30/1994
PB94-964533
EPA/ROD/R09-94/120
November 1994
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SFUND RECORDS CTR
0048-00931
Apache Powder Superfund Site
Record of Decision
Apache Powder Superfund Site
St. David, Arizona
United States Environmental Protection Agency
Region 9 - San Francisco, California
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TABLE. OF CONTENTS
Record of Decision for Apache Powder Superfund Site
Part I
Declaration
1.0 Site Name and Location. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-1
2.0 Statement and Basis of Purpose. . . . . . . . . . . . . . . . . . . . . .. 1-1
3.0 Assessment of Site. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
4.0 Description of the Selected Remedy. . . . . . . . . . . . . . . . . . . .. 1-1'
5.0 Statutory Determinations. . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-2
Part II Decision Summary
1.0 Site Name, Location and Description. . . . . . . . . . . . . . . . . . . . . 2-1
2.0 Site History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
3.0 Enforcement Activities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
4.0 Summary of Site Characteristics. . . . . . . . . . . . . . . . . . . . . . . . 2-4
5,.0 Summary of Site Risks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
5.1 On-Site and Off-Site Exposure Pathways. . . . . . . . . . . .. 2-6
5.2 Average and Reasonable Maximum Cancer Risks. . . . . . . . 2-7
5.3 Noncancer Risk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
5.4 Potential Ecological Impacts. . . . . . . . . . . . . . . . . . . . . . . 2-8
6.0 Interim Cleanup Actions Conducted to Date. . . . . . . . . . . . . . . . 2-8
6.1 Alternative Water Supply. . . . . . . . . . . . . . . . . . ~'-. . . . . . 2-8
6.2 Wash 3 Soils Cleanup. . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
7.0 Highlights of Community Participation. . . . . . . . . . . . . . . . . . . . 2-9
8.0 Scope and Role of Selected Remedy. . . . . . . . . . . . . . . . . .. 2-10
9'.0 Summary of Remedial Action Alternatives - Groundwater
Cleanup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.1 No Action. . . . . . . . . . . . . . . . . . . . . .
9.2 Pumping or Well Drilling Restrictions. . . . . . . . . . . . . . .
9.3 Alternative Water Supply. . . . . . . . . . . . . . . . . . . . . . .
9.4 Pumping and Treating Groundwater. . . . . . . . . . . . . . . .
10.0 Summary of Remedial Action Alternatives - Soil Cleanup
10.1 No Action. . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .2-14
10.2 Deed Restrictions and Fencing. . . . . . . . . . . . . . . . . . . 2-14
10.3 Capping........," . . . . . . . . . .. . . . . . . . . . . . . . 2-14
10.4 Surface Controls. . . . . . . . . ',' . . . . . . . . . . . . . . . . . 2-1.5
10.5 Soil Treatment ........:....................2-15
10.6 Excavation, Treatment and Disposal Off-Site. . . . . . . . . 2-15
-10.7 Excavation, Treatment and On-Site Disposal. . . . . . . . . . 2-16
11.0 Summary of Comparative Analysis of Alternatives. . . . . . . . . . . 2-18
I
12.0 The Selected Remedy, ..................,.......... 2-26
12.1 Clean-up Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . 2-29
12.2 Pre-Remedial Design Characterization and Analysis. . . . . 2-32
12.3 Institutional Controls. . . . . . . . . . . . . . . . . . . . . . . . . . 2-34
2-11
2-11
2-11
2-12.
2-12
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Table of Contents (continued)
Record of Decision for Apache Powder Superfund Site
12.4 Annual Inspection - Capped Soils. . . . . . . . . . . . . . . . . 2-34
12.5 Monitoring - Groundwater, . . . . . . . . . . . . . . . . . . . . , 2-34
12.6 Cost. . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . 2-35
12.7 Summary of Community and State Comments. . . . . . . . 2-36
13.0 Statutory Determinations. . . . . . . . . . . . . . . . . . . . . . . . . . . 2-37
13.1 Protection of Human Health and the Environment. . . . . . 2-37
13.2 Compliance with Applicable or Relevant and
Appropriate Requirements (ARARs) . . . . . . . . . . . . . . . . 2-37
13.3 Cost Effectiveness. . . . . . . . . . . . . . . . . . . . . . . . . . . 2-38
13.4 Use of Permanent Solutions and Alternative
Treatment Technologies to the Maximum Extent
Practicable. . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . 2-38
13.5 Preference for Treatment as a Principal Element. . . . . . . 2-38
14.0 Documentation of Significant Changes. . . . . . . . . . . . . . . . . . 2-38
PART III Responsiveness Summary
1.0 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
2.0 History of Community Involvement. . . . . . . . . . . . . . . . . . . .. 3-2
3.0 Organization of Responsiveness Summary. . . . . . . . . . . . . . .. 3-2
3.1 Community Concerns on Major Issues. . . . . . . . . . . . . .. 3-2
3.2 Comment Letters Received. . . . . . . , . . . . , . . . . . . . .. 3-2
4.0 Summary of Responses to Major Issues and Concerns. . . . . . .. 3-3
4.1 Health Concerns and Site Risks. . . . . . . . . , . . . . . . . .. 3-3
4.2 Water Resources - Agricultural Irrigation. . . . . . . . . . . .. 3-4
4.3 Water Resources - Riparian Protection. . . . . . . . . . . . . .. 3-5
4.4 Water Resources - Qownstream Users. . . . . . . . . . . . . .. 3-6
4.5 Water Resources - Deep Aquifer Replacement Wells. . . .. 3-6
4.6 Effectiveness of Remedy. . . . . . . . . . . . . . . .. . . . . . .. 3-7
5.0 Detailed Response to Comments. . . . . . . . . . . . . . . . . . . . . ., 3-8
5.1 Comments from Arizona Department of Environmental
Quality (ADEQ) """""""""""""'" 3-8
5.2 Comments from Arizona Department of Water Resources
(ADWR) "'............................,. 3-11
5.3 Comments from the State of Arizona Office of Attorney
General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3-11
5.4 Comments from Kimball & Curry, on behalf of Apache
Nitrogen Products, Inc., (ANP) . . . . . . . . . . . . . . . . .. 3-12
5.5 Comments from Border Ecology Project. . . . . . . . . . . .. 3-28
5.6 Comments from Arizona State University, Center for.
Environmental Studies. . . . . . . . . . . . . . . . . . . . . . .. 3-31
5.7 Comments/Questions from Private Citizens. . . '. . . . . . .. 3-33
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Appendix
A
Figure
1
2
3
4
5A
5B
Table
1
2
3
4
5
6
7
8
9
10
1 1
12
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Table of Contents (continued)
Record" of Decision for Apache Powder Superfund Site
List of Appendices, Figures, and Tables
Page
Action-Specific and Location-Specific
Applicable or Relevant and Appropriate
Requirements (ARARs) .............,.......... 2-39
Site Location Map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-1
Facility Plan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-3
Five Remedial Action Media Areas. . . . . . . . . . . . . . . . . . . .. 2-5
What is a Brine Concentrator? . . . . . . . . . . . . . . . . . . . . . . . . 2-27
Treatment Wetlands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-28
Habitat Wetlands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-28
Perched Groundwater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
Shallow Aquifer Groundwater. . . . . . . . . . . . . . . . . . . . . . . 2-13
Inactive Pond Soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16
White Waste Materials and Drum Storage Area. . . . . . . . . . . . 2-17
Wash 3 (Excluding the Ash and Burn Area) . . . . . . . . . . . . . . . 2-17
Comparison of Alternatives
- Perched Groundwater. . . . . . . . . . . . . . . . . . . . . . . . 2-19
Comparison of Alternatives
- Shallow Groundwater. . . . . . . . . . . . . . . . . . . . . . . . 2-21
Comparison of Alternatives
- Inactive Pond Soils and Sediments. . . . . . . . . . . . . . . 2-23
Comparison of Alternatives
- White Waste Materials and Drum Storage Area. . . . . . ." 2-24
Comparison of Alternatives
- Wash 3 Area (Excluding the Ash and Burn Area) . . . . . . 2-25
EPA's Selected Cleanup Standards for Groundwater. . . .. . . . . 2-30
EPA's Selected Cleanup Standards for Soil. . . . . . . . . . . . . . . 2-31
Cost of the Selected Remedy. . . . . . . . : . . . . . . . . . . . . . . . 2-35
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PART I D~CLARATION FOR THE RECORD OF DECISION
1.0 Site Name and Location
Apache Powder Superfund Site (CERCUS ID #AZD008399263)
(7 miles south of Benson, Arizona)
2.0 Statement of Basis and Purpose
This decision document presents the remedial action selected by the U.S. .
Environmental Protection Agency (EPA) for the Apache Powder Superfund site in
St. David, Arizona, which was chosen in accordance with CERCLA, as amended by
SARA, and, to the extent practicable, the National Oil and Hazardous Substances
Pollution Contingency Plan and the Clean Water Act. This decision is based on the
Administrative Record for this site.
The State of Arizona concurs with the selected remedy.
3.0 Assessment of the Site
Actual or threatened releases of hazardous substances from the site, if not
addressed by implementing the response actions selected in this Record of .
Decision, may present an imminent and substantial endangerment to public health,
welfare, or the environment.
4.0 Description of the Remedy
This remedial action includes measures to clean up nitrate-contaminated
groundwater and contaminated soils at -the site. This action addresses the principle
threats at the site: exposure to contaminated water (through pumping and treating.
nitrate-contaminated perched and shallow aquifer groundwater and through shallow
aquifer domestic water well' replacement) and exposure to contaminated soils
(through on-site containment, off-site treatment and disposal, and institutional
controls) .
The major components of the selected remedy include: .
. Completing additional groundwater investigations to determine the extent
of nitrate contamination and to determine the appropriate rates and
locations for groundwater withdrawal and recharge;
. Extracting and treating the perched groundwater by forced evaporation
(brine concentrator), in conjunction with treatment of the company's
process wastewaters, to meet the federal and state drinking water
standard of 10 parts per million (ppm) for nitrate;
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. Extracting and treating the shallow aquifer by use of constructed
wetlands to meet the federal and state drinking water standard
of 10 parts per million (ppm) for nitrate, and recharging the
treated water through wetlands, agricultural irrigation, discharge
or some combination of these methods as determined during
Remedial Design;
. Replacement of contaminated shallow aquifer domestic wells with deep
aquifer wells;
. Implementing institutional controls so that future use of the site is
compatible with the remedial goals and maintaining the
protection provided by the clay caps;
. Groundwater monitoring;
. Clay capping of 10 Inactive Ponds with no disturbance to contaminated
soils;
. Excavating and removing nitrate-contaminated soils and drums of
vanadium pentoxide from the White Waste Material and Drum Storage
Area to an off-site facility for treatment and disposal; and
. Excavating and removing dinitrotoluene-contaminated soils, and any lead-
contaminated soils which may be discovered, from the Wash 3 Area
(excluding the Ash and Burn Area) to an off-site facility for treatment
and disposal.
5.0 Statutory Determinations
The selected remedy is protective of human health and the environment, complies
with Federal and State requirements that are legally applicable or relevant and
appropriate to the remedial action, and is cost-effective. This remedy uses
permanent solutions and alternative treatment (or resource recovery) technologies
to the maximum extent practicable for this site. This remedy satisfies the statutory
preference for treatment as a principal element. Because this remedy will result in
hazardous substances remaining in some soils on-site above background or soil
action levels, in addition to monitoring required as part of ongoing operation and
maintenance, a review will be conducted within five years after commencement of
the remedial action, in addition to annual monitoring, to ensure that the remedy
continues to provide adequate protection of human health and the environment.
~W~
Feh. Marcus Jb,
Regional Administrator
United States Environmental Protection Agency
Region IX
9.~o .qt{
Date
1-2
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PART II DECISION SUMMARY
1.0 Site Name, Location, and Description
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The Apache Powder Superfund site is located in Cochise County in southeastern
Arizona, about seven miles southeast of the incorporated town of Benson and
approximately 50 miles southeast of Tucson. The site study area includes
approximately 1,000 acres of land owned by Apache Nitrogen Products, Inc.
(ANP), formerly known as the Apache Powder Company. The site study area also
includes areas of nitrate-contaminated groundwater and surface water located
outside ANP's property boundary. The site is bordered on the east by the San
Pedro River (Figure 1).
STUDY
AREA
BOUNDARY
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Figure 1. Site Location Map
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2.0 Site History
ANP began operations in 1922 as a manufacturer of industrial chemicals and
explosives. Currently, ANP manufactures nitric acid, solid and liquid ammonium
nitrate, blasting agents, and nitrogenous fertilizer solutions. ANP also distributes
explosives materials to mining companies.
Prior to 1971, facility wastewater composed of wash-down and blow-down waters
from its power house cooling tower, nitric acid plant, and from the loading,
unloading, and storage of raw materials and products was discharged on site into
dry washes which flow to the San Pedro River. Since 1971 , wastewater has been
discharged into unlined evaporation ponds on site causing contamination of a
perched water zone, the shallow aquifer, and the surface water to the San Pedro
River (Figure 2). The site was first identified as an environmental problem in the
early 1980s, proposed by EPA for listing on the National Priorities List in 1986, and
placed on the list in 1990.
3.0 Enforcement Activities
EPA
In April 1988, EPA issued a Special Notice Letter to ANP notifying ANP of its
liability and offering the opportunity to conduct and finance a Remedial
Investigation/Feasibility Study (RI/FS). In October 1989, EPA issued ANP a
Unilateral Administrative Order (UAO) under Section 106 of CERCLA for
completion of the RI/FS. However, in a June 1993 meeting EPA verbally informed
ANP that revisions to the RI/FS reports would be necessary. By letter of October
29, 1993, ANP was informed that EPA would revise both reports. EPA completed
the revised RI and FS reports in June 1994.
EPA conducted a search for other potentially responsible parties, which included
the issuance of numerous CERCLA 104(e) letters. In May 1994, EPA sent a
general notice letter to Phelps DOdge Corporation notifying the company of
potential liability.
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ST ATE
ANP has interim status under tbe Resource Conservation and Recovery Act (RCRA)
. for treatment of explosive wastes in its Ash and Burn Area. The Ash and Burn
Area, also known as the Open Burn/Open Detonation (OB/OD) Area, is currently
undergoing closure review by the Arizona Department of Environmental Quality
(ADEQ) under its RCRA program authority. In June 1994, ANP and ADEQ signed a
State Consent Decree (CD) containing a schedule for bringing ANP into compliance
with State hazardous waste and aquifer protection regulations and permitting
requirements. As a component. of the CD, ANP currently is constructing a brine
concentrator to treat the industrial process wastewater that historically has been
the primary source of groundwater contamination at the site.
4.0 Summary of Site Characteristics
The site characteristics of the Apache Powder site are based on numerous
investigations conducted by both ANP and by EPA. A Preliminary Investigation (PI)
was completed in 1988 by EPA. ANP completed several studies (Soils .
Investigation, Source Control Plan, Study Area Survey, Hydrogeological Analysis,
and San Pedro River Supplemental Sampling) in 1990 and 1991. These studies
were summarized in ANP's 1992 Remedial Investigation (RI) Report. In 1993, ANP
completed an additional report on the Wash 3 and Drum Disposal Area
Investigation. A summary of these investigations is included in Appendix C of the
FS report. The media-specific reports (available irl the Administrative Record)
provide a detailed description and analysis of contaminants found at the site.
The contamination present on-site at the Apache Powder site exists in the soil and
groundwater. The following Chemicals of Concern (COC) and other waste
materials have been identified in the five media areas addressed by this selected
remedy (Figure 3).
. Perched Groundwater - Arsenic, Fluoride, and Nitrate
. Shallow Aquifer - Nitrate
. Inactive Pond Soils and Sediments - Antimony, Arsenic, Barium, Beryllium,
Chromium, Lead, Manganese, and Nitrate
. . White Waste Materials and Drum Storage Area - Nitrate, Vanadium
Pentoxide '*
. Wash 3 Area (Excluding the Ash and Burn Area or OB/OD Area) -
2,4-Dinitrotoluene (DNT), 2,6-DNT, Lead, and Paraffins'* .
'* Waste Materials
2-4
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Figure 3.
Five Remedial Action Media Areas
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5.0 Summary of Site Risks
The information on site risks is taken from the Baseline Public Health Evaluation
arid Ecological Assessment completed by EPA (ICF, Inc.) in September 1992, with
additional information being provided in the revised EPA FS report of June, 1994.
The health evaluation process included: (a) identifying contaminants from historical
operations that are currently present in the groundwater, surface water, soils and
sediments; (b) characterizing the population potentially exposed to these
contaminants; and (c) evaluating the potential health effects from exposure to
contaminated groundwater, surface water, soil and sediments. EPA evaluated how
individuals might be exposed. to these contaminants under both current and future
conditions. Potential risks to natural resources also were evaluated.
5.1 On-Site and Off-Site Exposure Pathways
The site is currently zoned for industrial use. There is a possibility that the site
may be rezoned and redeveloped for residential use. Hence, exposure conditions
associated with industrial and residential use of the site were used in the
estimation of risk. In addition, risk to on-site trespassers was estimated. Because
there are occupied houses within one-half mile of the site, the potential risk .to .
occupants of the closest homes was also estimated. Those are homes located
north, northwest (NNW) and east, northeast (ENE) of the site.
Exposure of on-site workers (adults), residents (children and adults), and
trespassers (children and adults) was assumed to occur through ingestion of soil
and inhalation of airborne soil (dust) generated by wind. Exposur~ of on-site
workers to contaminated groundwater was 'considered unlikely because the water
supply for current on-site workers is the uncontaminated deep aquifer. Trespassers -
would use the same water suPP.IY. The perched and shallow aquifer groundwater
are recharged by wastewater evaporation ponds on the site. Redevelopment of the
, site for residential use would remove the evaporation. ponds and therefore the
source of the contaminated wastewater, impacting both the perched and shallow
aquifer groundwater. Consequent disappearan.ce (e.g., dewatering) of the perched
groundwater would remove the source of contamination and, over the long-term,
reduce the potential for exposure of future on-site residents to contamination in the
shallow aquifer groundwater.
To ensure a conservative, protective approach, off-site residents were assumed to
be exposed to windblown soil both by inhalation of airborne particles and ingestion
of deposited particles and assumed to be exposed to contamrnated groundwater by
ingestion of water from private wells.
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5.2 A verafJe and Reasonable Maximum Cancer Risks
Total risk estimates are the sum of the risks presented by all chemicals by
inhalation and ingestion. Each cancer risk estimate is 'an estimate of the probability
that a person will develop cancer during a lifetime if exposed to the evaluated
carcinogens under the conditions assumed in the risk assessment. For risk
assessment purposes, a cancer risk less than 1.0 x 10-6 was considered
insignificant.
For all the receptors except the on-site worker and future on-site resident, the total
average and total reasonable maximum cancer risks associated with exposure to
soil are less than one-in-one million (1.0 x 10.6). Cancer risk is highest with the
future resident, for which the average risk ranged from 6.1 x 10-6 to 2.3 x 10.5 and
reasonable maximum risk ranged from 1.1 x 10.5 to 8.9 x 10-5. The chemicals that
contributed most to the total cancer risk to the future on-site resident and the
current on-site worker are hexavalent chromium and arsenic in soil.
For the off-site resident (NNW and ENE), cancer risk asso,ciated with exposure to
soil by inhalation and ingestion is low (on the order of 1.0 x 10.8 to 1.0 x 10.9).
For the resident living ENE of the site, consumption of groundwater presents a risk
of 1.4 x 10.5 to 8.8 x 10.5 due to the presence of arsenic above background levels
in the water. Groundwater from monitoring wells NNW of the site did not contain
arsenic, which was the only carcino,gen among the chemicals evalUated.
Therefore, consumption of the groundwater does not present a cancer risk to NNW
residents.
5.3 Noncancer Risk
Each noncarcinogen'ic risk estimate is the ratio of the calculated risk to the
nontoxic dose. For individual chemicals, the ratio is called a hazard quotient. A
hazard index is the sum of the hazard quotients. When a hazard quotient or a
hazard index exceeds 1.0 (1 .OE + 00) toxic effects could occur. When these
measures of noncancer risk are less than 1.0, the occurrence of toxic effects is
unlikely.
GROUNDWATER
Noncancer risk associated with exposure to shallow aquifer groundwater is
significant for off-site residents, with a hazard index ranging from 1.7 to 39.
A primary human health risk posed by the site is the potential direct ingestion of
nitrate-contaminated shallow aquifer groundwater. Nitrate is the primary.
contaminant of concern due to the potential ingestion risk to infants that could
result in methemoglobinemia ("cyanosis"). This condition, commonly referred to as
2-7
-------
. -.....'...h_""
. .. .. .~... .' . ---.,. -. ..~- . .
. -' - .... .. -.," -...
....-.----...
......-.'" .. '.'~ .'.-
"blue baby syndrome~', occurs when "nitrate, having been converted to nitrite, is
absorbed into the bloodstream and produces methemoglobin. Methemoglobin is
not capable of carrying oxygen through the bloodstream to the same extent as
hemoglobin. The skin takes on a blue pallor due to the lack of oxygen. Infants
less than four months of age are more susceptible to this condition because of
higher levels of bacteria in their stomachs and intestines. Most cases of infant
methemoglobinemia are associated with exposure to nitrate in drinking water used
to prepare infants' formula at concentrations greater than 20 parts per million
(ppm). .
SOILS
Noncancer risk associated with average inhalation exposure to soil is significant for
the future on-site resident. For the infant, child, and adult, the hazard indices
range from 1.1 to 2.5. Under reasonable maximum exposure conditions, the
inhalation hazard indices exceed 1.0 for the on-site worker and the future on-site
resident. Noncancer risk associated with ingestion of soil is not significant. Where
noncancer risk is significant, the risk is due almost entirely to hexavalent
chromium.
5.4 Potential Ecological Impacts
EPA has coordinated, and will continue to coordinate, extensively with the U.S.
Fish & Wildlife Service (USFWS), the Bureau of Land Management (BLM), and the
Arizona Game and Fish Department, regarding any potential ecological risks"
associated with site activities.
6.0 Interim Cleanup Actions Conducted to Date
6.1 Alternative Water Supply
While investigations proceeded and alternatives were reviewed for cleanup of the
site, interim actions were taken to address potential threats to public health. In
1989, ANP began supplying bottled water to nearby residents with nitrate-
contaminated drinking water wells (wells exceeding the federal drinking water
standard for nitrate). In November 1993, EPA requested that ANP submit a revised
plan to install permanent replacement drinking water wells for those households
with nitrate contamination exceeding the maximum contamin~!1t level (MCL) of 10
. ppm. In February 1994, the contaminated shallow aquifer wells were resampled by
ANP to establish current water quality data. As of Septerrtber "1994, ANP has
installed four deep aquifer replacement wells. Four more wells are scheduled for
replacement in the fall of 1994. This selected remedy includes modification and
continued implementation of this well replacement project. (See page 2-29.)
2-8
-------
..- ... ,.-. . .-
6.2 Wash 3 Soils Cleanup
An investigation of the Wash 3 Area began in 1989. The Wash 3 Area includes
the Wash 3 channel leading to the San Pedro River, a drum disposal area, and an
area informally called the Main Accumulation Area. (The Ash and Burn or Open
Burn/Open Detonation Area is also located within the Wash 3 watershed, and
cleanup of the area will be overseen by the Arizona Department of Environmental
Quality.) The investigation included an inventory of the drums and stained soils
and a geophysical survey. A total of 127 drums were observed and inventoried,
and seven stained soil areas were identified. Excavation and removal of
deteriorated 11 O-gallon steel drums, estimated to be 30-40 years old, began in
January 1991. Approximately 230 cubic feet of oily soil were excavated and
removed from the Wash 3 area to a fenced on-site storage area;
Additional activities were conducted in May 1993, including further inventorying of
drums, sampling of stained soil areas, and excavation of 45 cubic yards of
dinitrotoluene (DNT}-contaminated soil. The final phase of the Wash 3 cleanup
(included in this selected remedy) will be to consolidate and transport the drums,
excavated soils (currently secured in the temporary on-site storage area) and
additional soils requiring excavation for off-site treatment and disposal (Figure 3).
7.0 Highlights of Community Participation
EPA has consistently kept the community surrounding ANP apprised of
developments and has solicited the community's input on site activities. Beginning
in 1990, EPA's outreach has included fact sheets, public meetings and informal
communications with community members.
On September 13, 1990, a community meeting was held in St. David, Arizona to
discuss upcoming activities related to site cleanup. This meeting was followed by
an Open House on May 30, 1991 to give community members an opportunity to
speak with EPA and state staff on the progress at the site.
In February 1994, while EPA was reviewing ANP's revised Alternative Drinking
Water Supply Plan, EPA staff met in.formally with several well owners to discuss
the deep well replacement plan. On March 22, 1994, a presentation was given by
ANP with EPA and state involvement on the hydrogeological features of the San
Pedro Basin, the nitrate-contamination in the shallow aquifer, and the details of the
proposed new wells.
2-9
-------
.... ... -'. ...-. ..._.
... .... ..~.....
EPA held two meetings in Arizona regarding the potential use of constructed
wetlands as one component of EPA's preferred remedy. On April 25, 1994, a
meeting was held in Phoenix with representatives from state and federal agencies.
A technical meeting also was conducted on June 2, 1994 with representatives
from public interest groups, university research staff, and state and federal
agencies to further discuss the constructed wetlands concept and to gather
information that EPA should consider prior to issuing the Proposed Plan.
In June 1994, EPA released the Proposed Plan for five areas with groundwater or
soils contamination due to historical practices at the facility. At the same time,
EPA gave notice that a public meeting would be held on July 6, 1994 in St. David,
Arizona, and that a public comment period would be open from June 23, 1994
through July 25, 1994. EPA also made the Administrative Record available in the
information repository maintained at the Benson Library. In addition, the Proposed
Plan was mailed to interested individuals on the mailing list. The notice of
availability of the RI reports, FS, Proposed Plan, and the rest of the administrative
record, the start of the comment period and the scheduled Public Meeting was
published in the San Pedro Valley News on June 22, 1994. On the same date,
EPA also issued a press release on the proposed cleanup plan.
At the July 6, 1994 public meeting, representatives from EPA presented the
Proposed Plan. Questions regarding the Proposed Plan and other site cleanup
activities were answered by representatives from EPA, the State, and other
\
technical experts. EPA also accepted written and verbal comments from the
public.
In light of the level of interest expressed during the public comment period, EPA
will provide additional opportunities for community input during the remedial design
(RD) process. The transcript of the July 6, 1994 meeting and the Responsiveness
Summary, Part III of this ROD, contain information on community concerns and
EPA's responses to these concerns. ...
8.0 Scope and Role of Selected Remedy
EPA's selected remedy addresses cleanup of historical contamination affecting
groundwater and soils. Concurrently, ADEQ is addressing the company's on-going
manufacturing processes to reduce or eliminate the threat of future contamination.
The EPA and the State of Arizona are coordinating their respective activities to
ensure that the cleanup qctivities performed by ANP are comprehensive and do not
duplicate company or agency effort. EPA's selected remedy addresses the
following five media areas (Figure 3):
2-10
-------
. ...".- -----" _.~.
.. .-". ---'.'"
. Perched Groundwater
. Shallow Aquifer
. Inactive Pond Soils and Sediments
. White Waste Materials and Drum Storage Area
. Wash 3 Area (Excluding the Ash and Burn Area)
9.0 Summary of Remedial Action Alternatives - Groundwater Cleanup
The alternatives summarized here were presented in the Proposed Plan. A detailed
evaluation of all the alternatives is presented in the EPA FS report, dated June
1994. Several alternatives were screened out prior to the nine-criteria analysis
used to evaluate the alternatives presented in the Proposed Plan, including
agricultural irrigation. However, due to comments received during the public
comment period which proposed the use of adjacent private properties for
irrigation, EPA will reconsider agricultural irrigation as a secondary
treatment/recharge option for the shallow aquifer groundwater during the first
phase of the RD.
9.1 No Action
The No Action alternative, required by the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP) (40 CFR 300.430(e)(6)), provides, among other
things, an analysis of the risk posed by the facility if no remedial action is
conducted. Therefore, it is used as a baseline alternative against which other
alternatives are measured. With this alternative, there would be no reduction of.
toxicity, volume or mobility of the nitrate contamination in the perched and shallow
aquifer. The contamination would be allowed to remain in the groundwater with
the potential for movement to additional private wells northwest of the site.
The only actions that would take place would be periodic groundwater monitoring -
to track the fate of the nitrate plume, and five year reviews to evaluate the overall
site conditions over time. The cost of this alternative would be approximately
$65,000 per year for additional monitoring. The No Action approach is
unacceptable to EPA because threats to human health and the environment from
groundwater contamination would continue to exist.
9.2 Pumping or Well Drilling Restrictions
Pumping or well drilling restrictions are institutional controls placed ona property to
restrict types of use. In general, institutional controls are either (1) government
controls imposed by state or local governments; or (2) proprietary controls, such as
deed restrictions, whereby a party holding an interest in property restricts the use
2-11
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'., .." -....-'-...,' ~,. .
'..- "" .-- ---.. ,.'..- ~,. _...
of that property. The purpose of institutional controls is to prevent use of the site
that could facilitate contact with contaminants. The restriction on use of the
property depends on the level of contamination that exists on the parcel and the
risks posed by that contamination. .
9.3 Alternative Water Supply
Implementation of an alternative drinking water supply is another response action that
was considered. Bottled water is currently being supplied to a number of households
located north of the ANP property, until a permanent deep aquifer replacement well
system can be installed. In addition to replacement wells, other alternatives include
installation of wellhead treatment systems or construction of a pipeline to hook up
new and existing residences impacted by the nitrate contamination to the St. David
public water supply. Wellhead treatment systems are complex and generally
unreliable for the contaminants of concern unless they are professionally maintained.
Therefore, wellhead treatment is infeasible at the site. Construction of a pipeline to
provide potable water for new residents to the affected area could be a viable
alternative to deep wells.
9.4 Pumping and Treating Groundwater
Contaminated groundwater can be treated either in the ground (in situ) or pumped out
of the aquifer and treated at the surface. The treated groundwater can then be
returned to the aquifer (by injection or infiltration), reused at the surface, evaporated,
or discharged to surface water. The following biological, physical, and chemical
treatment technologies were initially considered for treating extracted groundwater at
the Apache Powder site.
BioloQical Treatment
Phvsical Treatment
Chemical Treatment
High Rate Denitrification - ReactorsfTanks
Low Rate Denitrification - In Situ
Low Rate Denitrification - Constructed
Wetlands
Low Rate Denitrification - Land Application
Forced Evaporation (Brine Concentrator)
Reverse Osmosis (RO)
Electrodialysis Reversal (EDR)
Solar Evaporation
Distillation
Ion Exchange
Chemical Precipitation
Electrochemical Precipitation
These technologies were screened in the FS report. Five technologies were
retained for further evaluation for the perched groundwater and four were retained
for the shallow aquifer. The FS report and the glossary in the Proposed Plan
contain a brief description of these technologies. Detailed analyses of the
technologies retained for the two groundwater media areas are summarized in
Table 1 for the Perched Groundwater and in Table 2 for the Shallow Aquifer.
2-12
-------
Table 1 :
Alternative
P-1A: No Action
(Continued Monitoring)
P-2: Anaerobic
Denitrification (Biological
Treatment)
P-3: Solar Evaporation
P-5A: Reverse Osmosis
(RO) (Physical
Trea1ment)
P-5B Electrodialysis
Reversal (EDR) (Physical
Trea1ment)
Table 2:
Alternative
GS-1 A: No Action
(Continued Monitoring)
G5-2A: Anaerobic
Deni1rification
(Biological Treatment)
Perched Groundwater
(Nitrate, Fluoride, and Arsenic Contamination)
AlternatIve Description
Status QUo
Extraction from 7 wells; biological
treatment In a dosed reactor vessel;
evaporation and disposal of waste sludge;
reinjection or recharge to shallow aquifer,
or discharge to the San Pedro River
Extraction from 7 wells; evaporation from
lined ponds
Extraction from 4 wells; physical treatment
with a semi-permeable membrane; reuse
of the treated water In the ANP plant,
reinjection or recharge to the shallow
aquifer, or discharge to the river
Extraction from 4 wells; physical
treatment with permeable membranes;
reuse of the treateJ water in the ANP
plant, reinjection or recharge to the
shallow aquifer, or discharge 10 the river
Ettectlveness
Not effective
Potentially capable of 97%
efficiency tor nitrate removal;
does not remove fluoride and
arsenic WIthout additional
treatment
Highly efficient for
removal of all TDS
induding nitrate,
fluoride. and arsenic
Highly efficient for removal of
all TDS Including nitrate,
fluoride, and arsenic
Shallow Aquifer Groundwater
(Nitrate Contamination)
Alternative Description
Status quo
Extraction from 4 wells; biological
treatment In a closed vessel; recharge or
reinfection to the shallow aquifer, or
discharge to the San Pedro River
Effectiveness
Not effective
Potentially capable of 97%
efficiency for nitrate removal
with 2-stage design
~,,:,.: .:.1 EPA's Preferred
. ..' ~..., Alternative
ImplementabJllty
Implementable
Implementable;
requires pilot
treatability studies
tmplementable
Cost
(million $)
$0.09
$2.96
$3.52
Implementabte
Implementable
Implementablllty
Implementable
. ImplementabJe;
requires pilot
treatability studies
$3.49
$3.72
EPA's PreferTed
Alternative
Cost
(million $)
$0.39
~17.60
Totally elimInates extracted
groundwater; leaves solid
waste matter requiring disposal
,r~~f~1 afa!;$;1~i.51ii~I~~~:~
G5-3A: Reverse
Osmosis (RO)
(PhysIcal Treatment)
G5-3B: Electrodialysis
Reversal CEDR)
(Physical Treatment)
Extraction from 4 wens; physical
treatment with a semi-permeable
membrane; recharge or reinjection to
the Shallow aquifer or discharge 10 the
San Pedro River
Extraction from 4 wells; physical
treatment with permeabte membranes;
recharge or reinjection to the shallow
aquifer, or discharge D the San Pedro
River
Highly efficient for removal of
nitrate and aD TDS
Highly efficient for removal of
nitrate and aU TOS
2-13
Implemerdable
Implemerdable
$22.65
$23.02
-------
... . ....., .... -'-. . ..' - .n
10.0 Summary of Remedial Action Alternatives - Soil Cleanup
EPA considered a number of soil alternatives to reduce the risks from potential
exposure to the contaminants and to prevent migration of contaminants to
groundwater or surface water at concentrations that would pose a threat to human
health. The Proposed Plan summarized these alternatives. The alternatives
summarized here also were evaluated in detail in EPA's FS report.
10.1 No Action
Under this alternative, contaminated soils would be left in place on-site, without
removal or treatment to diminish potential threats to human health and the
environment.. With this alternative, there would be no reduction of toxicity, volume
or mobility of the contaminants. The only actions that could be conducted under
this alternative would be re-seeding of any area.s where vegetation was disturbed
by on-site activities during the investigation, periodic monitoring required by
CERCLA (because wastes will be left on-site), and five year reviews to evaluate
site conditions over time.
10.2 Deed Restrictions and Fencing
Site access would be restricted under this alternative to prevent exposure to
contaminated soils. Measures would include placing a notice on the deed,
restricting development on parcels within the site boundary that could cause
exposure to contamination, and/or fencing selected areas of the site. While the
property owners would have the ability to propose future uses to EPA for review
and approval, the institutional controls will ensure that any future use is protective
of human health.
Because contamination would remain on-site, annual monitoring along with a series
of five-year reviews to evaluate changes in site conditions would be required for
this alternative. Annual monitoring would include soil and the underlying
groundwater.
10.3 Capping
Capping consists of placing compacted fill over the contaminated areas and
covering this fill soil with a low permeability clay. Placing a second layer of asphalt
concrete, Ponland cement concrete, or a synthetic geomembrane over the clay cap
could be used to further reduce the permeability of the cap. The goal of this
alternative is to prevent exposure to contamination, so land use decisions would
take exposure.scenarios into consideration.
2-14
-------
_..'~._. .-....
.... ...........
..-'.. ....,~...,~.... .
..' ',"n"~'_'. -"'-"'.""
... ..' ....'..., .
. ....'
.. ..~_..~ . .-... .-
Land use restrictions would be implemented to prevent activities that might breach
or damage the cap and to restrict use of properties with residual contamination so
that potential contact with contamination beneath the' properties is prevented.
Because the contamination would remain on-site for all areas under this alternative,
5-year reviews would be required. The annual monitoring strategy for all the areas
covered by this alternative would include cap stability evaluations, monitoring
groundwater over time, and other methods determined to be necessary during the
RD.
Vegetation planted on the soil and clay cap must be low-maintenance and be
drought tolerant. Also, the root systems of the selected plants will be fairly
shallow, so that the roots do not penetrate the clay layer. The plants will also be
chosen to maximize erosion protection along the slopes. At a minimum, the
vegetation should be sustainable for the climate of the Benson/St. David area
without irrigation (after initial planting).
10.4 Surface Controls
Surface control alternatives would include grading the areas surrounding the
contaminated areas to prevent surface water from flowing onto pond areas,
stabilizing the pond sediments by constructing erosion prevention structures, and
diverting and collecting water in lined ditches and canals to prevent surface runoff
from flowing into the pond areas. Because of the heavy summer rains, surface
controls will be needed.
10.5 Soil Treatment
This alternative involves treating the contaminated soils in place (in situ) or
removing and treating them physically or biologically to remove the contaminants
of concern. Physical treatment methods include physically removing (leaching) the.
contaminants from the soil, or melting soil particles and contaminants into a solid
mass (vitrification). Biological degradation consists of enhancing the breakdown of
contaminants by naturally occurring aerobic or anaerobic microorganisms in the
soil. Chemical treatment alternatives include the use of chemicals that bond the
contaminants contained within the soil mass, thereby reducing their mobility.
Examples of chemical treatment methods include fixation, polymerization,
s,olidification, and stabilization.
10.6 Excavation, Treatment and Disposal Off-Site
This alternative would excavate and remove these contaminated soils for transport
and disposal at an off-site facility permitted under RCRA to accept such wastes.
On-site or off-site treatment of the soils may be necessary prior to off-site disposal.
2-15
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_. ..
.,.- . ... --. -.-
Drums of- contaminated soil currently on the property also would be properly
disposed of off-site.
10.7 Excavation, Treatment and On-Site Disposal
Another alternative is for the contaminated soil to be excavated, treated, and then
disposed of at the Apache Powder site. The contaminated soil would be: (1)
removed and encapsulated in clean, low permeability clay; (2) disposed of in clay-
lined cells in accordance with state environmental regulations; or (3) used as fill for
existing excavations or future grading after being treated.
Detailed analyses of the retained technologies for the three soil media areas are
summarized in Table 3 for the Inactive Pond Soils, in Tobie 4 for the White Waste
Materials and Drum Storage Area, and in Table 5 for the Wash 3 Area (Excluding
the Ash and Burn Area).
Table 3:
Inactive Pond Soils
(Metals and Nitrate Contamination)
~£~~iJ;~~ ;::::,=~rred
Alternative
Alternative Description
Effectiveness
Implementabliity
Cost
(million $)
5-1A: No Action
Status quo ,
Not Effective
Itnplememable
$0.00
5-2: OIl-Site Disposal of
Contaminated Soils from
Pond 7 and the Dynagel
Pond; On-Site Disposal
of Remaining Soils In
Inactive Ponds
Excavation. backfill and day capping 01
all 1 0 inactive ponds; off-site disposal 01
waste materials from Pond 7 and the
Dynage1 Pond at a RCRA pennitted
treatment, storage and disposal tadllty .
Effective; partial deanup, but
pennanent; some corrtamlnated
solis remain on site; however,
excavation 01 solis for removal
may pose risk to wor1ters
Implementable
$4.68
5-3: On-Site Disposal 01
All Soi1s In Inactive Ponds
or CeDs (Excavation 01
contaminated solis from
PontI 7 and the Dynagel
Pond)
'E:.:~#i\'I~~a,...
Excavation, backfill and day capping 01
all 1 0 Inactive ponds; disposal of waste
materials from Pond 7 and the Dynagel
Pond In a,new, on-slte,llned, day
capped cell
Effective; partial deanup, but
pennanent; all contaminated
solis remain on site; however,
relocation of solis may pose
risktoworkers .
Implememable, but
dlffiaJlt to meet state
technical
requirements
$2.59
2-16
-------
~Q?2~~::i ::;~~~~~~H:~r:';
';;iCNI -:ccintamlnated~QII~)ieilcl~sPo
F;aRCRA peirriitteil,~atnieirt:atOia'
"~.cfisposal1.&i:DltY<
Excavation and bac/dill of contaminated
soils; on-site treatment (fixation) and
disposal 01 lead-contamlnated solis in a
new,lined, clay capped cell; off-site
transport, treatment (Incineration) 01
DNT-contamlnated solis, and disposal at
a RCRA permmed facility
Table 4:
Alternative
W5-1A: No Action
iL~~~~~"1
W5-3: Excavation,
On-site Disposal 01 Solis
Table 5:
Alternative
W3-1A: No Action
~3:Excavation, ,
On-Site and Off-Site
Treatment and
Disposal (3O-Year Life
Cycle 10 MaIntain Cell
Cap)
o
White Waste Material and Drum Storage Area F:' "<1 EPA's Preferred
(Nitrate Contamination and Drummed Vanadium Pent oxide): ' ",,':: Alternative
Alternative Description
Cost
(million $)
Effectiveness
Implementabllity
Status quo
Not effective
$0.00
Implementable
~~Jt~~~~~~=~~~i;:i~~~'~'"
":~dlsposBlata ;RCRApenn.'tted ~ ft;,
, ;i8tOr:agearic(dlspos8lfaclJlty/:~'~!;
Remove drums; excavation and backfill of
all drummed wastes and contaminated
solis; treatment (fixation) and disposal In
an on-site, unlined, clay-capped cell
containing Inactive pond sediments, or In
a lined, clay-capped cell containing Wash
3 solis
Effective; effected area
cleaned up permanenlly, but
contaminated soUs remain on
site
$0.02
Implementable, but
difficult to meet
state technical
requirements
Wash 3 Area (Excluding the Ash and Burn [OB/OD) Area)
(Lead and DNT Con~mination)
j':" \;"""::Y"l EPA's Preferred
::::}~~\;8\ Alternative
Alternative Description
Cost
(million $)
$0.00
Effectiveness
Implementabllity
Status quo
Not effective
Implementable
Effective; affected area cleaned
up permanently, but $()me
materials remain on site
Implementable, but
difficult to meet state
technical
requirements
$0.71
2-17
-------
[
. .-:.. ..,..,_....> ,
11.0 Summary of Comparative Analysis of Alternatives
The NCP sets forth nine criteria to be used for a detailed, comparative analysis of
alternatives that have been retained after the screening portion of the Feasibility
Study. The nine criteria are as follows:
. Compliance with applicable or relevant and appropriate requirements
(ARARs)
. Overall protection of human health and the environment
. Long-term effectiveness and permanence
. Reduction of toxicity, mobility, or volume through treatment
. Short-term effectiveness
. Implementability
. Cost
. State acceptance
. Community acceptance
A detailed analysis was presented in EPA's FS report, while a summary analyzing
effectiveness, implementability, and cost was in the Proposed Plan. An analysis of
the nine criteria for each of the retained alternatives is contained in Tables 6
through 10. Please refer to Section 6 of EPA's FS report, dated June 17, 1994,
for additional details on the alternatives 'and the nine criteria, with the exception of
state and community acceptance.
2-18
-------
Criteria
Overall
Protectiveness
ARM
Compliance
Long-term
Effectiveness
Implementability
Short-term
Effectiveness
.~. - .. ..._~....
Table 6 - Comparison of"Altematives - Perched Groundwater
. . ...
. . :A't P-1A.
No Action>.
(Continued ... .
Monitoring) ....;.
...... . ......
No, existing
risk remains
Not applicable
to No Action
alternative
No, only
natural
degradation
and attenuation
Yes
No increased
short-term risks
.-.-
. AttP-2 ...Att P-3 .
.. . Anaerobic:. .. . ....Solar .
Denitrification. .. : Evaporation .
(Biological.
Treatment)
Yes, reduces
nitrate
concentrations
Yes
Yes, effective
in the long-
term;
groundwater
quality would
be restored
and perched
groundwater
would no
longer
threaten the
shallow aquifer
Yes; requires
pilot studies
Increased
short-term risk
from fugitive
dust and
transport and
handling 'of
methanol
.....
Yes, reduces
nitrate
concentrations
May not meet
State aquifer
protection
requirements
Yes, effective
in the long-
term;
groundwater
quality would
be restored and
perched
groundwater
would no
longer threaten
the shallow
aquifer
Yes, a simple
technology that
does not
require pilot
studies;
construction of
ponds may be
subject to
complex state
technical
requirements
Increased
short-term risk
from fugitive
dust
2-19
...Att P-4
::.:~orced
: Evaporation
.... . (Brine :.
(;:oneentrator) :
.i;:;.........:.'.... :.
Yes, would
reduce nitrate
concentrations
Yes
Yes, effective
in the long-
term;
groundwater
quality would
be restored
and perched
groundwater
would no
longer threaten
the shallow
aquifer
Yes, could be
implemented
as part of
installation of
brine
concentrator
by ANP for
treating
process
wastewaters
Increased
short-term risk
from fugitive
dust and from
transport and
handling of
acid
.
Att P-5A
..Reverse
...Osmosls
..(RO)
. . (Physical
Treatment)
Yes, w.0uld
reduce nitrate
concentrations
Yes
Yes, effective
in the long-
term;
groundwater
quality would
be restored
and perched
groundwater
would no
longer
threaten the
shallow
aquifer
Yes, proven
technology for
TDS removal,
including
nitrate; pilot
studies
needed to set
final design
parameters;
multiple
vendors with
pre-designed
modules
Increaesd
short-term risk
from fugitive
dust and from
transport and
handling of
acid
,"... '..... ---. -._. ...
AIt P-5B
..Electro-
dialysis (EDR)
. . (Physical
Treatment)
Yes, would
reduce nitrate
concentrations
Yes
Yes, effective
in the long-
term;
groundwater
quality would
be restored
and perched
groundwatr:r
would no
longer
threaten the
shallow aquifer
Yes, proven
technology for
TDS removal,
including
nitrate but not
to the extent
of RO; rT)ore
extensive pilot
studies than
RO; limited
number of
vendors
Increased
short-term risk
from fugitive
dust and from
transport and
handling of
acid
-------
Criteria.
Reduction of
Toxicity, Mobility
or Volume
through
Treatment
Cost
State
Acceptance
Community
Acceptance
. -~....~.. '.'" ".~' ~.
Table 6 ':'Comparison of.Alternatives -Perched Groundwater
. .. .
An P-1A .i
No Action .,;,'...'."
(Continued .
Monitoring)
No
$ 91,000
(Monitoring
Cost for 30
Years)
The State
indicated that it
would not
support a
decision of No
Action.
The community
expressed no
interest in a
No-Action
remedy
selection.
~
... ... .
n;Art~-2' . . .'
Anaerobic '.
Denitrification
(Biological ':
:!~nt)... .
Yes, reduces
toxicity and
volume of the
nitrate plume;
this option
converts
nitrate to
molecular
nitrogen gas,
the major
component of
air
$ 2,963,000
The State did
not indicate
support for this
option
The
community did
not indicate
support for this
option;
however, the
community
expressed
strong support
for immediate
action to clean
up the
perched
groundwater to
implement
source control
. n
:.Alt P-3 .
.. .;.Solar
i:vCiporat1()n
"""....} .
Yes, reduces
toxicity and
volume of the
nitrate plume:
under this
option the
nitrate will
ultimately be
part of a waste
solid (a waste
brine that will
need to be
dewatered and
landfilled)
$ 3,516,000
The State did
not iridicate
support for this
option
The community
did not Indicate
support for this
option
2-20
AltP~ "..
forced n..
Evaporation
. .:.(8rine. .
.' Concentrator) ...
Yes, reduces
toxicity and
volume of the
nitrate plume;
under this
option the
nitrate will
ultimately be
part of a waste
solid (a waste
brine that will
need to be
dewatered and
landfilled)
$ 2,352,000
The State
expressed
support for this
option, since
the perched
groundwater
could be
treated simul-
taneously with
the treatment
of the process
waste~ters
The
community
supported the
use of the
brine
concentrator to
clean up both
the process
wastewaters '-
and the
perched
groundwater
.: AlfP-5A
. Reverse
Osmosis
(RO)
(Physical
. Treatment)
Yes, reduces
toxicity and
volume of the
nitrate plume;
under this
option the
nitrate will
ultimately be
part of a
waste solid (a
waste brine
that will need
to be
dewatered
and landfilled)
$ 3,492,000
The State did
not indicate
support for
this option
The
community did
not indicate
support for
this option
AItP-5B
. . £Iectro- .
dialysis (EDR)
(Physical
Treatment)
Yes, reduces
toxicity and
volume of the
nitrate plume:
under this
option the
nitrate will
ultimately be
part of a waste
solid (a waste
brine that will
need to be
dewatered and
landfilled)
$ 3,724,000
The State did
not indicate
support for this
option'
The
community did
not indicate
support for this
option
.'
~
-------
- _..< -_..- _.~. . ..
Table 7 - Comparison of Alternatives - Shallow Aquifer Grouncwater
Criteria AIt GS-1A Ait GS-2A GS-2B Alt GS...JA Ait GS...JB
No Action . Anaeorbic Constructed Reverse Electrodialysis
. . (Continued Denitrification (I;) . Wet'ands Osmosis (RO) Reversal (EDR)
Monitoring) Reactor Tanks)
Overall No, existing risk Yes, reduces Yes, reduces Yes, reduces Yes, reduces
Protectiveness remains nitrate nitrate nitrate nitrate
concentrations concentrations concentrations concentrations
ARAR Not applicable to No Yes Yes Yes Yes
Compliance Action altemative
Long-term No long-term Yes, effective in Yes, effective in Yes, effective in Yes, effective in
Effectiveness effectiveness or the long-term; the long-term; the long-term; the long-term;
permanence other. residual waste waste bacterial however, however,
than natural brine or sludge will sludge will be concentrated concentrated
degradation and contain less incorporated into waste brine waste brine
attenuation metals than RO or the wetlands containing a high containing a high
EDR system concentration of concentration of
metals will require metals will require
removal from the removal from the
system, system;
evaporation, and evaporation, and
disposal disposal
Implementability Yes Yes; proven Yes; would Yes: proven Yes, proven
technology for require long-term technology for technology for
nitrate conversion (1-2) years start- TDS removal TDS removal
to nitrogen: pilot up time to including nitrate; including nitrate,
studies needed to establish plant pilot studies but not to the
set design species and to needed to set extent of RO;
parameters, monitor efficiency final design pilot studies
including of nitrate parameters; needed; limited
determining the conversion and multiple vendors vendors avaUable,
viability of various uptake; may be with pre-designed so less design
bacterial strains subject to modules flexibility; siting of
and determining complex State available; siting of evaporation
the form and technical evaporation ponds for waste
quantity of carbon; requirements for ponds for waste brine may be
o. -. multiple vendors construction and brine may be subject to
are available for siting of wetlands subject to complex State
detailed cells complex State technical
equipment design technical requirements
and procurement requirements .
Short-term No increased s~ort- Potentially Provides ancillary Increased short- Increased short-
Effectiveness term risks; avoids effective in benefits (wildlife term risks from term risks from
any evaporation loss achieving 97% habitat, potential transport and transport and
resulting from the nitrate destruction; recreational use, handling of acid handling of acid
extraction and potential risks green space, used as an anti- used an an anti-
treatment of shallow from transport and protection of scalant during scalant during
aquifer groundwater handling of >riparian pilot testing and . pilot testing and
methanol, if used ecosystem); takes operations (risks operations (risks
as a carbon the longest to are lower than are lower than
source; potential start up (2-3 those posed by < those posed by
risks from fugitive growing seasons) methanol in methanol in
dust when compared to other > option GS-2A) option GS-2A)
excavating options; estimated and from fugitive and from fugitive
evaporation ponds 10% evaporation dust when dust when
for drying bacterial loss; potential risk excavating excavating
waste sludge from fugitive dust evaporation evaporation
when excavating ponds for waste ponds for waste
wetland cells brine brine .
2-21
-------
.-.- ....- -~...._... .,. .'. ~. ..,...'
: '.
Table 7 .,~ Comparison of Alternatives -Shallow Aquifer Groundwater
..{;riteria
.' ".< ,::,<:.. "..:
". .'.":"':"'.".:::. ':"."'."
.... ',,,,::"":.:" .,
..'''' ,.
Reduction of
Toxicity,
Mobility or
Volume through
Treatment
Cost
State
Acceptance
Community
~ptance
: AJt GS~1A
...' No Actlon/.
(Continued,
"Monitoring) . .
No
$ 390,000
(Monitoring)
The State indicated
that it would not
support a decision of
No Action.
Some community
members expressed
support for no action,
because of concern
for too much water
loss or evaporation
during the extraction
and treatment
process; individuals
wanted continued
monitoring and study
of the shallow aquifer
to determine if
nat1.lral biological
degradation and
attenuation would
reduce nitrate levels
..M GS~2A '.
: .,..' Anaeorblc...:.. :...
Denitrification (In .'
ReactofTanks) ...'
Yes, reduces the
toxicity and
volume of the
nitrate-
contaminated
plume; converts
the nitrate to
molecular nitrogen
gas, the major
component of air
$ 17,595,000
The State did not
indicate support
for this option
The community
expressed some
interest in this
option, if it would
result in less
evaporation loss
of the shallow
aquifer
groundwater than
other altematives
., 'GS-28
.,.Constructed
. " ":"""Wetlands
',....''': .
.'
Yes, reduces the
toxicity and
volume of the
nitrate-
contaminated
plume; converts
nitrate to
molecular nitrogen
gas, the major
component of air
$ 16,194,000
The State
expressed support
for constructed
wetlands and
additional
evaluation of
agricuttural
irrigation as a .
form of secondary
treatment or as an
end-use option
The community
expressed some
interest in this
option, if the
evaporation
losses were not
too great and if
the wetlands
could be made
available to the
public for
recreational use
2-22
Alt GS-3A .
, Reverse
'Osmo.sis (R()J "
:'., .'"
Yes, reduces the
toxicity and
volume of the
nitrate-
contaminated
plume; nitrate will
be ultimately be
part of a waste
solid (a'waste
brine that will
need to be
dewatered and
landfilled)
$ 22,654,000
The State did not
indicate support
for this option
The community
did not indicate
support for this
option
..Alt GS-3B
Electrodialysis
. ,Reversal (EDR) .
.. '''C':'' ..
Yes, reduces the
toxicity and
volume of the
nitrate-
contaminated
plume; nitrate
ultimately will be
part of a waste
solid (a waste
brine that will
need to be
dewatered and
landfilled)
$ 23,022,000
The State did not
indicate support
for this option
The community
did not indicate
support for this
option
-
-------
Tables
=;
Criteria
Overall
Protectiveness
ARAR Compliance
Long-term Effectiveness
Implementability
Short-term Effectiveness
Reduction of Toxicity,
Mobility or Volume
through Treatment
Cost
State Acceptance
Community Acceptance
- Comparison o1
Alt S-1A
No Action
Existing risks remain;
infiltration of rain
continues; may impact
groundwatcr
Not applicable to No
Action alternative
Since wastes will be left
on-site, there will not
be effective control to
prevent contact with
contamination or rain
infiltration
Yes
No increased short-term
risks
No
$0
The State indicated that
h would not support a
decision of No Action.
The community has
expressed no interest ID
a No-Action remedy
selection.
: Alternatives - Inactiv
Alt S-2
Excavation and Off-Site
Disposal
Yes. removes contaminated pond
soils to a regulated off-she
facility; potential exposure risks
during excavation and transport
Yes
Yes, since affected area would be
cleaned up permanently
Yes
Moderate increase in short-term
risk due to fugitive dust during
excavation and potential exposure
risk during transport
Yes, reduces mobility, volume and
toxicity by removing contaminants
to an off-she regulated facility for
treatment and disposal
$ 4,678,000
The State has expressed hs
support for off-she treatment and
disposal, but also considers
options S-3 and S-4 to be
protective and not as costly
The fianijfunjfy wants the ponds
closed and cleaned op, but did not
state a specific opinion on whether
the ponds soils needed to be
removed off-site for treatment and
disposal
e Pond Soils and Se
-— •" ••-— — - - --^— -
Alt S-3
Excavation, Treatment,
Containment, and On-
Site Disposal
Yes, controls risk of direct
exposure and rainwater
infiltration if cap integrity is
maintained; no transport off-
she; lined, on-site landfill she
would be more protective than
capping in-place
Yes
Yes, if cap integrity is
maintained to prevent
exposure to contaminated
materials left on-she; liner
provides additional long-term
effectiveness over capping in-
place
Yes, however may be difficult
to meet state technical on-she
landfill disposal requirements,
since contaminated materials
would be excavated and
moved to another location on-
she
Moderate increase in short-
term risk due to fugitive dust
and potential exposure risk
during on-she transport to
disposal cell; no off-she
transport risks
Reduces mobility since
capping will reduce rainwater
infiltration and liner will
prevent further contaminant
migration; no reduction of
volume or toxichy of
contaminated soils
$2^90,000
The State has expressed
certain reservations about
excavation and redisposal of
the contaminants on-she
because of the Stale landfill
leqniiciuents
The community wants the
ponds closed and cleaned up,
but did not state a specific
opinion on the method; one
general comment was that they
did not want the contamination
just moved from one place to
another without sufficient
monitoring
diments
^ :-^——^-— -- ~~~ ' —
Alt S^t
:-: Containment
(Capping in Place)
Yes, controls risk of direct
exposure and rainwater
infiltration if cap is
maintained; no transport
off-she or within site
Yes
Yes, if cap integrity is
maintained to prevent
exposure to contaminated
matrrinls left on-she;
long-term effectiveness
considered adequate
Yes, however will need to
meet state aquifer
protection requirements for
on-she containment
Slight increase in short-
term risk due to some
earthwork required while
capping ponds; no major
excavation or transport
risks
Reduces mobility since
capping will reduce
rainwater infiltration; no
reduction of volume or
toxichy of contaminated
soils
$ 1,926,000
The State has expressed hs
support for this option,
assuming that the capping
is consistent with State
aquifer protection
requirements
The community seemed to
••support this option; the
community's primary •
concern is that the ponds
are closed and 'cleaned up;
no one opposed capping
the contaminated soils in-
place
2-23
-------
'.-"" - "'"'.
Table 9 - Comparison of Alternatives -White Waste Materials and Drum Storage Area
Criteria . ..:. .AJt wS-1A . ... ... .Alt WS-2 Alt WS-3
;:: No Action ... .....:.... Excavation and Off-Site Excavation and On-Site
. Disposal. Disposal . .
Overall Protectiveness No, existing risks remain; Yes, removes all Yes, existing risk due to
infiltration of rainwater contaminated soils from the direct exposure is
continues and may impact area to a regulated off~site controlled, if integrity of cap
groundwater facility; potential moderate is maintained; rainwater
risks during excavation and infiltration is controlled; no
off-site transport off-site transport risks
ARAR Compliance Not applicable to No Action Yes Yes
altemative
Long-term Effectiveness Since wastes will be left on- Yes, since affected area Yes, if cap integrity is
site, there will not be would be cleaned up maintained to prevent
effective control to prevent permanently exposure to contamination;
contact with contamination however will require
continual monitoring
Implementability Yes Yes Yes, but requires more
effort to meet state
technical requirements for
. on-site landfill than WS-2
Short-term Effectiveness No increase in short-term Potential exposure to Potential exposure to
risks fugitive dusts during fugitive dusts, but no off-
excavation; also potential site transport risks
exposure risks during off-
site transport
Reduction of Toxicity, Mobility or No Reduces mobility, volume Reduces mobility, and
Volume through Treatment and toxicity in the affected could reduce some volume
area by removal of the and toxicity if during
contaminants to an off-site excavation, hot spots are
regulated facility for discovered and treated on-
treatment and disposal site
Cost $0 $ 51,000 $ 19,000
State Acceptance The State indicated that it The State supports WS-2, The State would support
would not support a since this option provides a this option, but has
decision of No Action. permanent remedy without concems about option
substantial cost meeting state technical
requirements for an on-site
landfill
Community A~ptance The community has The community wants the . The ~ommunity wants the
expressed no interest in a contamination removed and contamination removed and
No-Action remedy cleaned up cleaned up, but has not
selection. expressed specific
requirements on whether
they want off-site versus
off-site disposal
2-24
-------
-.- - . ~-. . .'
...--....-,p ".~..
. '," --"-"
-'p'''' " "'".p '.- ..:.- ..,.~_.", -".,.,"~.",~ -..~.
-- '-'.".._n-'-
. .
Criteria ..
Table 10 - Comparison of Alternatives.';: Wash 3 Area (Excluding the Ash and Bum Area)
Overall Protectiveness
AAAR Compliance
Long-term Effectiveness
Implementability
Short-term Effectiveness
Reduction of Toxicity, Mobility or
Volume through Treatment
Cost
State Acceptance
Community Acceptance
:...
. ..>H
... ..
...Alt W3-1A
.No Action
No, exising risks remain;
infiltration of rain continues
and may impact
groundwater
Not applicable to No Action
altemative
No long term effectiveness
or permanence, since
contaminants will be left on-
site with no effective control
to prevent contact
Yes
No increased short-term
risks
No
$0
The State indicated that it
would not support a
decision of No Action
The community has
"expressed no interest in a
No-Action remedy selection
. Alt W3-2
. Excavation and Off-Site
. "" ". Disposal
Yes, removes all
contaminated soils from
area to a regulated off-site
facility for treatment and
disposal; potential risks
during transport
Yes, would meet action-
specific and location-specific
ARARs; however, no
chemical-specific AAARs for
soils were identified
Yes, since affected area will
be cleaned up permanently
Yes
Potential exposure to
fugitive dust and community
exposure to transport risks
Reduces mobility; reduces
volume and potential toxicity
by removing the
contaminants to an off-site
regulated facility for
treatment and disposal
$ 591,000
The State supports W3-3,
since this option provides a
permanent remedy
The community wants the
contamination cleaned up;
no negative comments have
been received on this option
2-25
.AIt W3-3
Excavation and On-Site
Disposal
Yes, existing risk due to
direct exposure is
controlled, if cap integrity is
maintained; rainwater
infiltration is controlled; 00
off-site risks
Yes, would"meet action-
specific and location
specific ARARs; however,
00 chemical specific
ARARs for soils were
identified
Yes, so long as cap
integrity is maintained to
prevent exposure to
contamination
Yes
Potential exposure to
fugitive dust, but no off-site
transport risks
Reduces mobility; if hot
spots are treated on-site or
removed off-site, may
reduce some volume and
toxicity
$ 716,000
The State would sup-port
this option, but has
concems about option
meeting state technical
requirements for an oo-site
landfill
The community wants the
contamination cleaned up,
but has expressed no
specific opinions on how
this s.hould be done
-------
..-.. ....-.
.' ---".. . '..
12.0 The Selected Remedy
Based upon evaluation of the CERCLA requirements, the detailed analysis of the
alternatives using the nine criteria, and public comments, EPA has determined that
the five selected alternatives indicated on Table 13 are the most appropriate
remedies for the Apache Powder Site. The selected remedies will clean up the
nitrate-contamination in the perched groundwater zone and the shallow aquifer and
provide several different cleanup measures for the soils contamination. The
selected remedy for the contaminated soils left on-site will provide a permanent
barrier to the contaminated soil and prevent rainwater from infiltrating the
contaminated soils and carrying the contamination to groundwater. The selected
remedy for the contaminated soils and drummed material selected for off-site
treatment and disposal will permanently remove the contamination from the site
and treat and dispose of the contamination at a permitted facility.
The selected remedy is protective, meets ARARs, is effective for the long-term, and
is permanent. With the exception of the contaminated soils in the inactive
evaporation ponds, the selected remedy for each of the other four media areas
meets the statutory preference for treatment. The selected remedies for the two
groundwater media areas and the on-site clay-capping of the contamination in the
inactive ponds can be constructed, with readily available materials and common
construction techniques. Thus, they are considered implementable. Short-term
risks to workers will be slightly elevated during the capping of the inactive ponds,
but measures will be taken to minimize the impacts. Since the cap will have a
permeability of less than 1 x 10-6 em/see, groundwater will be protected, thus
further reducing the risks posed by the site.
The selected remedy for each of the five media areas is cost-effective.
The State of Arizona concurs with EPA's selected remedies.
During the design process, groundwater analyses will be performed to ensure that
the extraction and treatment of the contaminated shallow aquifer does not unduly
interfere or diminish the existing water resources. Also, the community will have
the opportunity to participate during the selection of the type and final siting of the
constructed wetlands and the recharge phase of treatment of shallow aquifer
groundwater:... Fact sheets will be distributed periodically during the remedial design
phase to keep the community informed during the remedial design phase.
The following are the key components of the selected remedy:
2-26
-------
.' . ~ .. ...'. . ON' ~'.
. .~ .-.. .-..
GROUNDWATER
.
Installing additional groundwater monitor wells to determine the lateral
extent of nitrate contamination in the shallow aquifer and the perched
zone
Conducting a monitoring program to collect chemical water quality
data and water levels
Conducting aquifer tests and groundwater modeling to ascertain
what potential impacts, if any, pumping will have on downstream
water users
Extracting and treating the perched groundwater by forced
evaporation (brine concentrator), in conjunction with treatment
of the company's process V\,dstewaters, to meet the federal and
state drinking water standard of 10 parts per million (ppm) for nitrate.
(Figure 4)
Extracting and treating the shallow aquifer by use of constructed
wetlands to meet the federal and state drinking water standard of 10
parts per million (ppm) for nitrate, and recharging the treatect water
through wetlands, agricultural irrigation, discharge or some
combination of methods as determined during Remedial Design
(Figures 5A and 58)
Monitoring long-term effectiveness and permanence;
Replacement of contaminated shallow aquifer domestic wells with
deep aquifer wells
.
.
.
.
.
.
What Is 8 Brine Concentrator?
-
Figure 4
O The -1t8w8t8r .. pumped
through a heat excll8nger
which 1'81888118 t8rI\p8I8tUnI to the
boiling point.
O Some of the brine W8p0f.'"
. .. It flowa In . failing tUrn
down through the heat transfer
IUb8a and back Into Ih8 aump.
tubn, cau8lng8ome of the bit.. to
8V8porate. M ttKt compr8888d
vapor g/vea up hut, It c:ond8n88
.. dl8Wl8t&.
I:'\. Wnf8w8t8r pa_81hrDugh a
U deaer8torwhleh-
non-c:onclenuble pM8 auch ..
oxygen and carbon dlOxIcf&.
A The Y8p0r~ ItIrougtl
" mist ellmlnatora 8IIcIentera
the vapor comprnaor.
Compl'U88d vapor ftow8 to Ih8
outalcle of the hut Ir8n8fw tubeL
O TM dlat111818 .. pumped b8cIr.
through the heat exchllrlger, .
where It ;1- up beat to tb8
incoming wut8W8t8r. ,
O Hot fMcI combInn wIIIt 1M
brine 8Iurry In the 8ump. The
brfne 8Iurry Ie conat8ntIy
cll'culetad from Ih8 aump to.
IoocIboz at the top of allundl8 of
Mat tranafertub88.
0> Hut from the compI~
vapor .. tranaf8rr8cl to the
c:ooler brine falllnglnalde the
" A am8II amount of ftIt8 brine .
W Ie blown down from the 8UIIIp
to eoMroI the brine d8n81tJ.
----
2-27
-------
. ,..,. .....
.~ ._.. ..'. ...,~...,
TREATMENT WETLANDS
Natural Attenuation Process
1 - Sedimentation I Filtration
2 - Biological Uptake I Oxidation I Reduction
3 - Adsorption I Precipitation
I
BUITE
~
"---
GROUNDWATER
FLOW
WETLANDS
AREA
. ..~ . - .' .. -
. .'--' .... - ..-
Enlargement
SAN PEDRO RIVER
.~
)
t
t
WATER
TABLE
Figure 58: Simplified illustration of . constructed wetlands used for Initial treatment of contaminants
HABITAT WETLANDS
Natural Attenuation Process
1 - Sedimentation I Filtration
2 - Biological Uptake I Oxidation I Reduction
3 - Adsorption I Precipitation
4 - infiltration I Recharge
BUTTE
~
"--
GROUNDWATER
FLOW
WETLANDS
AREA
ORAGONFUES -
mosquIt08 8nd -- ..
food for I8rg8r 8nlma1.
~. -,..
-,..
SAN PEDRO RIVER
oJ.
)
t
t
WATER
TABLE
. .
Rgure 5b: Simplified illustration of . constructed wetlands used for species habitat .00 recharge of treated water
Figures 5A and 58
2-28
-------
"."...- -"- ,'- -- u
" -_.. ~ ... .
SOILS
.
Excavating designated areas to clean-up standards (Table 12);
Consolidating and transporting excavated materials to an off-site
permitted facility for treatment and disposal;
Constructing a low permeability clay cap over the contaminated soils
in the inactive evaporation ponds; .
Monitoring the clay cap on at least an annual basis to ensure that the
integrity of the cap is maintained and that the ponds to not act as
continuing sources of groundwater contamination; and .
Implementing institutional controls so that future use of the site is
compatible with the remedial goals and maintaining the protection
provided by the clay caps
.
.
.
.
12.1 Clean-up Standards
GROUNDWATER
The chemicals of concern for groundwater are arsenic, fluoride, and nitrate in the
perched groundwater zone. Nitrate is the only contaminant of concern in the
shallow aquifer. Federal and State MCLs, which are the same for these
contaminants, are ARARs for groundwater. Table 11 presents the background
levels, Preliminary Remediation Goals (PRGs), Arizona's Health Based G.uidahce
Levels (HBGLs), site-derived, risk-based levels, and drinking water MCLs for the
chemicals of concern in groundwater. EPA's selected clean-up standards are
presented in the last column.
ALTERNATIVE WATER SUPPLY
As discussed in section 4.0, interim actions have been taken to address potential
threats to public health from the domestic use of contaminated groundwater. The.
selected remedy requires t~e provision of an alternative water supply and other
measures as necessary to prevent the domestic use of nitrate-contaminated
shallow aquifer groundwater:
1.
An alternative water supply in the form of the deep aquifer replacement
wells will be supplied to the households that meet the criteria of the
Alternate Domestic Water Supply Plan ("ADWSP") approved by EPA in April
1994.
2.
Identifying the lateral extent of the nitrate-contaminated plume during the
first phases of remedial design will provide the basis for notice of areas of
known shallow aquifer nitrate contamination. (At a minimum, an accurate
plume map will be placed in the site repository at the Benson Library.)
2-29
-------
3.
4.
The existing inventory of private wells in the vicinity of the plume will be
updated periodically. Any identified private wells threatened or potentially
affected by the plume, and without sufficient monitoring data, initially will be
monitored quarterly.
An alternative water supply in a form to be approved by EPA will be
provided to additional households if the household relies on a shallow aquifer
well for domestic water and the water from the well exceeds the federal
drinking water standard of 10 ppm for nitrate in three consecutive quarters
of sampling. (EPA may require an alternative water supply immediately if
level of nitrate significantly exceed the federal drinking water standard.)
........ ... ...... ...... .... .... Table 11 . .. . .... ... ..
Preliminary Remediation Goals (PRGs), Background Levels, Arizona Health Based Guidance Levels
(HBGLS), Site-Derived, Risk-Based Levels, and Arizona Department of Water Quality (ADEQ) Water
. ... <. Quality Standards and Selected. Clean-Up Standards for Chemicals of Concern in . .
. . .... . ... ......: Groundwater at the Apache Powder Site. .. .~< .
Media of
Concern
Perched
Groundwater
ShaDow Aquifer
Groundwater
Footnotes:
Chemical
Site-Oerived ADEQ Water . . ..SeleCted. .
Risked-based Quality . Clean-Up
Background..) Region IX HBGLs Level(b) Standards .Standards
PRGs (Federal MCL)
mgII mgII mg/\ mg/\ mgII mgII .
0.00537 0.000049 0.00002 0.14«) 0.05 0.05
1.4 2.2 0.420 0.38«) 4.0 :.A.O.
0.22 58.0 11.0 6.5«) 10.0 ..10.0
Q.OO537 0.000049 0.00002 0.14(" 0.05 0.05..
1.4 0.420 4.0 .4.0
0.22 11.0 10.0 .10.0 .
Arsenic
Fluoride
Nitrate as nitrogen
Arsenic
Fluoride
Nitrate as nitrogen
(a) Arithmetic mean derived from Remedial Investigation (RI) background samples.
(b) Based on acceptable cancer risk being 1.0E-06 and acceptable non-cancer hazard being 1.0.
(c) Off-slte resident Infant.
Table 11. EPA's Selected Clean~up Standards for Groundwater
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SOILS
Where no ARARs were identified for soils, the cleanup standards for excavation are
based upon health-based levels. Site-Derived, Risk-Based Levels were established
by calculating the chemical concentrations in soil and groundwater that correspond
either to an excess cancer risk of 1.0 x 10-6 or a hazard index of 1.0, based on the
results of the risk assessment. EPA's PRGs were developed to be used as a rapid
reference for screening concentrations in environmental media and as initial cleanup
goals. Arizona's HBGLs for the Ingestion of Contaminants in Soits also were
established as potential cleanup levels and to establish a benchmark for taking
additional action. Table 12 presents the background levels,' PRGs, HBGLs,,'risk-
based levels, and Arizona's Hazardous Waste Management Act (HWMA) treatment
standards for the chemicals in soil. EPA's selected clean-up standards are
presented in the last column. In the absence of an established ARAR, the selected
soil clean-up standard for each compound is the Arizona HBGL.
Table 12
Preliminary Remediation Goals (PRGs), Background Levels, Arizona Health Based Guidance Levels
(HBGLs), Site-Derived, Risk-Based Levels, Arizona Hazardous Waste Management Act (HWMA) Treatment
, ' . Standards, and Selected Clean-Up Standards for ChemIcals of Concern in ..,
., .., Soils at the Apache Powder Site
Arizona Site- Selected
Back- Region IX HWMA Derived Clean-Up
Media of Chemical ground..) PRGs HBGLs Treatment Risked- ,.Standards
Concern Standards based
Level(b)
mgn mgn mgn rngII rngII mgn
Inactive Pond Antimony 4.47 11.0 47.0 38.2«) Capped in
Soils and Arsenic 12.02 0.97ca/23nc 0.76 25.8«) , '. . place
Sediments Barium 125.7 5,500 8,200 1,200«)
Beryllium 0.94 0.4 0.32 513«) .
Chromium (total) 9.78 940.0 1,700 3.83«)
Lead Manganese 14.27 500.0 500.0 NC
Nitrate as nitrogen 383.0 390.0 580.0 1,110«)
140.05 100,000 190,000 84,500«1
',,,,'.,,,:,."".
White Waste Nitrate as nitrogen 140.05 100,000 190,000 84,500(<) ,i::.190,OOO
Materials and Vanadium 16.37 550.0 820.0 753.0«) ':'<:.820.0
Drum Storage Vanadium pentoxide NC 690.0 1,100.0 NC '1;100.0
Area .~ .~: ,", . :,' ; "
,",",'
Wash 3 2,4-Dinitrotoluene (DN'T) 0.0(11) 1.3 2.0 140.0 NC ,:'..140.0,'
(Exduding the 2,6-DNT 0.0(11) 1.3 120.0- 28 NC :':Y;:.:28.0"
Ash and Bum Paraffins a.old) NC NC NC .':0:0"
Area) . Lead 14.27 500.0 500.0 NC 500.0
Table 12. EPA's Selected Clean-up Standards for Soils
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. .-..-.- - .~~ n
. . -..-,.. __,4.'. .
12.2 Remedial Design (RD) Characterization and Analysis
GROUNDWATER
The Feasibility Study (FS) report and the Proposed Plan recommended additional
groundwater investigation and modeling during the first part of the remedial design
(RD). The purpose of these studies would be to define the lateral extent of nitrate
contamination in the perched groundwater zone and the shallow aquifer, and the
effect of various extraction rates on the shallow aquifer's water balance.
Perched Groundwater Zone
Further delineation of the perched groundwater zone will be conducted to the
extent that additional data is needed to assist in locating extraction wells and
determining pumping rates. Because source control is the highest priority
requirement for groundwater protection, emphasis will be placed on gathering this
data and proceeding with the maximum volume of pumping that can be managed
by the brine concentrator as soon as it is on-line in the spring of 1995.
Shallow Aquifer
The FS report also recommended additional groundwater characterization and
analysis to support the design of the shallow aquifer groundwater extraction and
treatment system. Based on data available during the FS, EPA relied on the
assumption that 720 gallons per minute (gpm) would be the required pump rate for
treating the shallow aquifer within a 12 year time-frame, an assumption developed by
Hargis & Associates (H+A) for ANP. However, short term (e.g., less than one year)
aquifer testing and water modeling studies will be completed to determine the impact
of varying pump rates on the water levels in the shallow aquifer and on the San
Pedro River and to gather the appropriate data necessary for designing the well
extraction system. Also, addition~1 monitoring wells also will be installed in the
northwestern portion of the nitrate plume to define the lateral extent of contamination.
The results of these groundwater studies, to be completed early in the RD, will be
shared with the community through fact sheets and/or community meetings prior to
commencing the final design plans for the extraction system. Treatability studies also
will be conducted for constructed wetlands (and, if appropriate, for secondary
treatment options discussed.below) to determine their d~nitrification and/or nitrate
uptake capacities for high nitrate concentrations (300 ppm). The results of the
groundwater modeling will be evaluated to determine if reduced pumping rates
and/or selected "hot-spot" pumping may be necessary to ensure minimal impact on
water resources and the riparian resources of the San Pedro River.
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,.,. ....'...-' .
. . ~ .-. - - - .. . .. .
During the public comment period, some members of the community raised concerns
that the use of constructed wetlands to treat the nitrate-contaminated groundwater in
the shallow aquifer could result in potential evaporation/transpiration loss of valuable
water needed for crop irrigation. A proposal was presented to use agricultural
irrigation as a method for reducing the nitrate levels in the groundwater rather than
other treatment alternatives. EPA initially screened out this alternative primarily
because the ANP facility had insufficient land space suitable for growing agricultural
crops. However, the comments recommended using privately-held farm lands in the
vicinity of the ANP site. (See the Responsiveness Summary, Part III of this ROD, for
EPA's analysis of this proposal.) While EPA is selecting constructed wetlands as the
primary treatment method, EPA will evaluate during RD, a variety of secondary
treatment/recharge options, including habitat wetlands, agricultural irrigation,
discharge to the San Pedro River, or some combination of these.
SOilS
Inactive Ponds
Extensive sampling is not expected to be necessary during RD. However, a limited
amount of characterization sampling will be required to determine whether soils in or
around the inactive ponds require excavation or removal prior to being capped. If
chemicals of concern not previously identified are detected in or around any of the
inactive ponds, the conceptual approach for cleanup of these ponds may need to be
revised. The development of a sampling plan and the completion of this sampling
effort will be completed during the first phase of RD.
White Waste Materials and Drum Storage Area
EPA, in consultation with the State, has determined that the White Waste Materials
and Drum Storage Area will be cleaned up in conjunction with this CERCLA remedial
action for remediation of the historical contamination problems at the site. The State
does not intend to include this area under the State Consent Decree for cleanup of
the active waste management areas of the facility. Final cleanup and confirmatory
sampling will be conducted by ANP as part of EPA's selected CERCLA remedy, not
under the State's Consent Decree.
Wash 3 Area (Excluding Ash and Burn Area)
As in the case of the White Waste Materials and Drum Storage area, the State does
not intend to include the Wash 3 Area under the State Consent Decree for cleanup of
the active waste management areas of the facility. With the exception of the area
immediately adjacent to the Ash and Burn Area (also known as the Open Burn/Open
Detonation (OB/OD) which is covered under the jurisdiction of the State's RCRA
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. '''.'''... .... u... ....
interim-status closure requirements, the Wash 3 area will be characterized for final
cleanup and confirmatory sampling as part of EPA's selected CERCLA remedy.
Additional confirmatory sampling will be required both in the area where the
contaminated soils have been stored and in the previously excavated areas prior to
final approval of the completed remedial action.
12.3 Institutional Controls
There will be restrictions on the ANP site to prohibit shallow aquifer groundwater use
for drinking purposes.
There will be restrictions on the uses of the capped areas of the site. Only those
uses that will not adversely affect the cap will be allowed, in order to maintain the
integrity of the caps. Some of the uses that may be compatible with the caps include
recreation (e.g., picnic areas) and light storage. Uses that are unlikely to be
compatible include heavy equipment storage, enclosed buildings, and any structure
that would compromise the integrity of the clay cap during construction.
12.4 Annuallnspection
All components of the remedy will be inspected and evaluated not less than annually.
Special circumstances (such as heavy rains) may require additional inspections.
Groundwater monitoring will be conducted not less than quarterly. The site will also
be inspected to verify the integrity of the clay caps on the inactive ponds, and that
institutional controls are maintained. Operation and maintenance will be conducted to
ensure that the remedy maintains its effectiveness.
12.5 Monitoring - Groundwater
Groundwater monitoring will be conducted throughout both the design and the
implementation of the remedy for several purposes:
1.
To assess the effects of groundwater extraction and pumping on the shallow
aquifer and the baseflow of the San Pedro River.
2.
To assess the effectiveness of groundwater recharge through constructed
wetlands and/or agricultural irrigation.
3.
To monitor the efficiency of the treatment process(es) (e.g., influent, effluent,
intermediate points) to meet and comply with the treatment standards
established in this ROD.
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12.6 Cost
A detailed cost description of each of the components of the preferred remedy for
each of the five media area is included in Appendix E of the F S report. The
estimated cost for the selected remedy is shown in Table 13 as a present worth
value; and includes annual monitoring for 30 years and appropriate 5-year reviews.
TABLE 13
Alternative 1 Site-Wide Costs. Forced Evaporation (Perched), Constructed Wetlands (Shallow
Aquifer), On-Site Capping of Inactive Ponds and Off-Site Fixation I Incineration for Soils
,:Groundwater .
, "',
$ 2.35 M
$ 16.19M
Media
(,sOlis
Inactive Ponds Solis
and Sediments
5-4
Containmen; Bac:klill and clay cap
$1.93 M
White Waste Material
and Drum Storage Area
Wash 3 Area (excluding
Ash and Bum Area)
W3-2
Excavation and backfill; off-site transport to a permitted facility for fixation
and disposal
Excavation and bac:klill; off-site transport to a permitted facility for fixation I
incineration and disposal
$ 0.05 M
WS-2
$ 0.59 ~ .
Total Cost
$ 21.11 M
Table 13. Cost of the Selected Remedy
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12.7 Summary of Major Community and State Concerns
Concerns raised by the community and the State have been addressed and
evaluated. EPA's response to these concerns is contained in Part III of the Record of
Decision (Responsiveness Summary). .
Based on community concerns that the shallow aquifer groundwater might be subject
to excessive evaporation loss if treated solely by constructed wetlands, and a desire
to. use the extracted water prior to recharge, a preference was expressed by some
for agricultural irrigation rather than constructed wetlands as a treatment option. To
address this preference, EPA will consider, during Remedial Design, agricultural
irrigation and other recharge/end use options for the shallow aquifer groundwater.
Additional comments were submitted regarding siting of the secondary stage,
recharge or habitat wetlands away from the ANP operating facility so that the public
could visit the wetlands for recreational or educational purposes without potential
exposure to the day-to-day manufacturing operations at the ANP facility. Decisions
on the final siting of the recharge or habitat wetlands and the potential use of
agricultural irrigation as a component of the secondary stage treatment/recharge will
be made during the remedial design, after additional data collection, characterization,
and analyses.
......
.. ;'...
Members of the community and various state agencies also commented on the
importance of protecting the water resource of the San Pedro River Basin both to
protect riparian resources and to provide sufficient water for downstream users.
Particular intere~t was expressed in the impact that the extraction and treatment
process, including the rate of recharge, will have on the water level in the shallow
aquifer. EPA agrees that additional studies will need to be conducted during the
remedial design to minimize any potential impacts on the water levels.
Other members of the community commented that it was inequitable to install deep
aquifer replacement wells for those households that had been on bottled water and
not to provide some compensation for those landowners who already had installed
deep aquifer wells at their own expense or who had not yet installed wells because of
the shallow aquifer contamination. Comments were also submitted that well owners
with deep aquifer wells would incur increased utility and - pumping costs, because of
additional water demands on the deep aquifer. In order to avoid drilling new deep
aquifer wells, a few comments suggested extending the 81. David water supply
system to accommodate new residents in the area of contaminated groundwater.
To resolve these issues, discussions should be held among landowners, ANP, and
local officials, including the 81. David water supply system officials. EPA will, to the
extent practicable, facilitate such discussions and perform other actions as necessary
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...-..... .:.. .., ...
to protect p~blic health. See Part III (Responsiveness Summary) for a more detailed
discussion of these issues.
13.0 Statutory Determinations
13.1 Protection of Human Health and the Environment
The selected remedy is protective of human health and the environment. The
potential for direct contact with contaminated groundwater and soil will be reduced
significantly by the following mechanisms.
GROUNDWATER
Pumping and treating the perched groundwater by forced evaporation (with a brine
concentrator) and the shallow aquifer by constructed wetlands will greatly reduce
nitrate levels, thereby reducing potential exposures to nitrate via. groundwater andlor
surface water. Replacement of the nitrate-contaminated shallow aquifer domestic
wells will provide significant further reduction in the potential for nitrate exposure.
SOILS
The potential for direct contact with contaminated soils will be greatly reduced by
excavating and removing contaminated soils for off-site transport, treatment, and
disposal at a RCRA permitted facility, and by backfilling the on-site inactive ponds
and covering them with a clay cap. The cap will also reduce significantly the
potential for rainwater to leach contaminants from the soil into a perched groundwater
zone and potentially to the shallow aquifer.
Permanent restrictions will be in place to notify on-site workers and future land
owners of the extent and risks of residual contamination. The restrictions placed on
the ANP property will prevent inadvertent contact with contaminated soils. The
restrictions also will ensure that the integrity of the capping is maintained to
effectively contain the contaminated soils. There are some short-term risks to on-site
workers associated with the inactive ponds while the capping is performed. However,
dust suppression measures will be required to minimize the risk.
13.2 Compliance with Applicable or Relevant and Appropriate Requirements
(AR~Bs)
The selected remedies ~iII comply with all ARARs. The chemical-specific ARARs for
the groundwater cleanup are listed in Table 11. The actic:>n-specific and location-
specific ARARs for the selected remedies are attached as Appendix A.
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13.3 Cost -Effectiveness
EPA believes this remedy will significantly reduce the risks at this site by eliminating
the pathway for direct contact with nitrate-contaminated groundwater and
contaminated soil. This will be done at an estimated cost of $18.5 million for the
groundwater and $2.6 million for the soils, for a total cost of $21.2 million, which EPA
considers commensurate with the risk reduction that will be achieved.
13.4
Use of Permanent Solutions and Alternative Treatment Technologies to the
Maximum Extent Practicable
The selected remedy utilizes permanent solutions and alternative treatment
technologies (or resource recovery) to the maximum extent practicable. The principal
threats of the site, the contaminated groundwater and the soils contamination, will be
treated with one exception. One soils area, the Inactive Pond Soils and Sediments,
was evaluated in the FS and screened out for treatment because it was not found to
be practicable to remove relatively low levels of metal contaminated pond sediments
which were relatively immobile (binding to the soil particles) and were at extremely
low level of risk of transport into the underlying groundwater, if capped in place.
The components of EPA's selected remedy consists of proven technologies, common
construction materials and practices, and incorporates EPA's guidance for closing
surface impoundments to provide a protective, permanent solution to the site
problems.
13.5 Preference for Treatment as a Principle Element
It was determined that treatment of the principal threats of the site was practicable for
the site, with the exception of the soils and sediments located in the inactive ponds
area, as discussed above under Section 12.4.
14.0 Documentation of Significant Changes
There are no significant changes from the Proposed Plan to the Record of Decision.
The Proposed Plan for the Apache Powder Superfund site was released for public
comment on June 23, 1994. EPA has reviewed all written and verbal comments
submitted during the public comment period, and has selected remedies for the five
media areas as conceptually presented in the Proposed Plan. .Qne minor change
relates to the treatment of the shallow aquifer groundwater. While EP A is selecting
constru~ed wetlands as the primary treatment, EPA additionally will evaluate during
remedial design other recharge/end use options. The other four media areas of the
selected remedy have not cl:tanged.
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PART III RESPONSIVENESS SUMMARY
1 .0 Overview
On June 22, 1994, the U.S. Environmental Protection Agency (EPA) issued a
Proposed Plan stating EPA's preference for the cleanup alternatives for the Apache
Powder Superfund Site in St. David, Arizona. A thirty-day public comment period,
following the issuance of the Proposed Plan, ended on July 25, 1994. At a public
meeting held on July 6, 1994, EPA presented the alternatives for addressing the
groundwater and soils contamination at the Site, described EPA's preferred.
alternatives and answered community questions. This Responsiveness Summary is
a written summary of the significant comments received by EPA during the public
comment period and EPA's responses to these comments.
After consideration of the public comments and review of the administrative
record, EPA has selected as the remedy the alternatives identified in the Proposed
Plan. This remedy is embodied and described fully in Parts I and II of the Record of
Decision (ROD). In short, the remedy calls for extraction and treatment of perched
water by a brine concentrator,; extraction and treatment through constructed
.wetlands of the nitrate-contaminated shallow aquifer groundwater; and a variety of
on-site and off-site cleanup methods for the soils. ,..'. . .
The community's response to the Proposed Plan, described more fully in
section 4.0 below, was generally favorable. The community clearly wants cleanup
to proceed, and had little comment on the perched groundwater and soils
alternatives. Most of. the community's comments centered on the use of
constructed wetlands for treating the shallow aquifer groundwater. One area of
concern was the potential loss of water, leading to suggestions of other
alternatives; such as agricultural irrigation or deferment of the shallow aquifer
cleanup.
The comments by state agencies and by Apache Nitrogen Products, Inc.
(ANP), the owner and operator of the Apache site, are discussed in section 5.0
below. The state generally concurs with EPA's remedy selection. ANP generally
supports the perched groundwater and soils remedies with modifications. ANP
favors cleanup of the shallow aquifer but suggests a lower, more selective pumping
rate. ANP prefers the treatment alternative of constructed wetlands to the other
alternatives discussed in the Feasibility Study but urges EPA to consider other
treatment methods, such as agricultural irrigation.
Apache Nitrogen Products, Inc. (ANP) currently is constructing a brine concentrator to trea't
its industrial process wast~water. The perched water is similar enough. to ANP's process
wastewater to make treatment with the same equipment feasible.
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2.0 History of Community Involvement
EPA has conducted an extensive outreach program to involve the community
in activities at the site. For a detailed description of community involvement, refer
to section 5.0 of Part II of the ROD.
3.0 Organization of Responsiveness Summary
3.1 Community Concerns on Major Issues
The community expressed its concerns about the cleanup of the Apache
Powder Site in two principal ways. Many in the community attended and spoke at
the public meeting on the proposed plan held on July 6, 1994. Other community
members submitted written comments to EPA. EPA acknowledges and appreciates
the thoughtful input of the local community, the State, and ANP.
Several major issues were raised by the community during the public
comment period. A summary of those issues and EPA's responses are presented in
section 4.0. Section 4.0 responds to the letters submitted by community members
and the comments made at the publ,ic meeting. These letters and comments cover
a range of issues but with much overlap. For ease of responding, EP~ grouped
these community concerns into six gen.eral subject matter categories. Responses
to more specific or technical comments appear in section 5.0.
EPA is not repeating in this Responsiveness Summary all questions and
answers from the public meeting. A copy of the meeting transcript is included in
the Administrative Record and is available at the public repository in the Benson
Library. '
3.2
Comment Letters Received
In addition to the comments received during the public meeting, EPA
received and considered the following comment letters, a few of which arrived
after the July 25, 1994 close of the comment period.
o
Arizona Department of Environmental Quality, July.25, 2994
o
Arizona Department of Environmental Quality, August 11, 1994
o
Arizona Department of Water Resources; July 25, 1994
o
State of Arizona Office of the Attorney .General, July 25, 1994
o
Kimball & Curry, P.C., on behalf of. Apache Nitrogen Products, Inc.,
July 25, 1994
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o
Julie Stromberg, Ph.D., Arizona State University, Center for Environmental
Studies, June 16, 1994 '
o
Dick Kamp, Border Ecology Project, July 6, 1994
o
Gladys Garno, St. David, Arizona, June 15, 1994
o
John S. Gay, Sahuarita, Arizona, July 5, 1994
o
Mike Kruse, Phoenix, Arizona, July 6, 1994
o
John S. Gay, Sahuarita, Arizona, July 11, 1994
o
Lawrence J. and Patty J. Saunders, St. David, Arizona, July 11, 1994
o
Gerald J. and Farrel H. Kempton, St. David, Arizona, July 20, 1994
o
Thomas Haymore, St. David, Arizona, August 1, 1994
Copies of all written comments are in the Administrative Record and will be
available at the public repository in the Benson Library.
4.0
Summary of Responses to Major Issues and Concerns
In addition to comments received on EPA's selected remedies for the areas
of historical contamination at the ANP site, EPA received comments on air
emissions and other State issues. Because of previous agreements between EPA
and the State on the division of responsibilities for oversight and enforcement of
cleanup activities at the site, EPA forwarded comments relating to State issues to
ADEQ.
4.1 Health Concerns and Site Risks
Groundwater
The potential health threat of nitrate in drinking water is one of the main
concerns posed by the, nitrate-contaminated shallow aquifer groundwater plume
migrating from the Apache Powder site. The ongoing discharge of process
wastewaters to the perched groundwater underneath the evaporation ponds has
resulted in continual contamination of the shallow aquifer. The installation of the
brine concentrator (scheduled for April 1995) will halt this continuing discharge to
the perched groundwater, since the wastewaters will be treated and recycled for
reuse. Additionally, once the brine concentrator is on-line, the perched
groundwater will be extracted and treated by the brine , concentrator, along with the
process wastewaters.
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The, extraction and treatment of the shallow aquifer will begin to clean up
the nitrate contamination over a period of years. In the interim, bottled water has
been supplied to residents to avoid the potential risk of drinking nitrate-
contaminated water above the federal Maximum Contaminant level (MCL) of 10
milligrams per liter (mg/l) or 10 parts per million (ppm), Currently, ANP is installing
new deep aquifer replacement wells under the Alternative Drinking Water Supply
Plan (ADWSP), which is being incorporated as part of this record of decision.
However, a potential risk continues to exist for new residents in the area
who unknowingly may install drinking water wells into the shallow aquifer and
potentially be exposed to nitrate. EPA considers the groundwater contamination at
the site to be a potential health threat, which must be cleaned up to protect human
health. EPA will explore avenues for ensuring that, until the nitrate level in the
shallow aquifer groundwater is reduced to below the MCl, future residents are
aware of the risks of exposure to shallow aquifer groundwater.
Soils
Currently, the site is fenced. Contaminated soils do not pose an immediate
risk, with the possible exception of risk to trespassers who are not knowledgeable
of ' the on-site areas where hazardous substances are stored or contained.
Trespassers could be exposed to some of the surface soil contamination that exists
on the site. Another potential health risk via the soils pathway exists for on-site
workers and nearby residents, if the site were opened up for development. If
contaminated soils were moved or disturbed in the future during the course of
remedial activities, digging the foundations for buildings, or clearing site areas for
construction, disturbed soil could be released to the atmosphere, greatly increasing
the chances for human exposure. EPA considers the soil contamination at the site
a potential health threat requiring either removal or containment, based on
assumptions made for future use of the site. ..
In order to protect the health of the community, the pathway through which
the population can be exposed must be eliminated. EPA has chosen a combination
of methods for protecting people from the contaminated soils, both on-site
containment and off-site treatment and disposal. The metal-contaminated soils and
sediments in the inactive ponds will be covered in place with a low-permeability
clay cap and will remain on site. The clay cap will be a physical barrier between
people and the contaminated soils. Institutional controls (e.g., deed restrictions)
may be put in place to ensure that future use of the inactive ponds area is
compatible with the remedial goals and to maintain the integrity of the clay caps.
The remaining contaminated soils, currently located in the White Waste Material
and Drum Storage Area and in the Wash 3 Area, will be excavated and removed to
an off-site permitted ~azardous waste facility for treatment and disposal.
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4.2 Water Resources - Agricultural Irrigation
A major concern of the community is whether the use of constructed
wetlands to treat the shallow aquifer adequately considers the unique water
resource constraints on this arid part of the southeastern Arizona. Several
comments, including comments from the Arizona Department of Environmental
Quality and ANP, recommended that consideration be given to agricultural irrigation
as either a secondary treatment alternative or for end use.
An irrigation proposal was presented by a member of the agricultural
community, identifying owners of approximately 1,000 acres of privately-owned
land adjacent to the ANP site who would be interested in taking the nitrate-
contaminated water for crop irrigation. The identified 1,000 acres were on both
the east and the west side of the San Pedro River. To date, the contaminated
nitrate plume has only been detected on the west side of the river, with the
exception of a small area near the Pomerene Canal north of site. Only low levels of
nitrate contamination (3-5 ppm) in the range normally expected in an agricultural
area have been detected on the east side of the river. For this reason, EPA
believes consideration of agricultural irrigation should be limited to the west side of
the river to eliminate any potential risk of introducing levels of nitrate above the
federal Maximum Contaminant Leyel (MCL) of 10 ppm and the consequent risk of
contaminating any drinking water wells.
EPA agrees that the agricultural irrigation concept should be evaluated during
the first phase of remedial design (RD). EPA plans to include several studies,
including but not limited to gathering data on the concentrations of nitrate in
various portions of the plume, water balance, the potential land acreage both on
and off the ANP site, the geological characteristics of the areas considered for
irrigation (clay versus alluvium), the crops available for irrigation, and the efficiency
of these crops to take up nitrate. Based on the findings of these studies, it may be
feasible to incorporate the use of agricultural irrigation either as secondary
treatment following primary treatment in a constructed wetlands or as an end use if-
the influent levels of nitrate can be reduced to levels that can be efficiently treated
by the crops. However, until these studies are completed, EPA believes it is
premature to alter the selection of constructed wetlands for treatment of the nitrate
in the shallow aquifer.
In conversation, some members of the agricultural community have
expressed an interest in developing educational programs in the use of constructed
wetlands and/or crop irrigation to inform the community on environmental
protection and enhancement and good farming/ranching management practices.
4.3 Water Resources - Riparian Protection
Many members of the community and various state agencies commented on
the importance of protecting the water resources of the San Pedro River Basin, and
to maintain or, if possible, enhance the riparian resources. Concerns were raised
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that extracting and pumping the shallow aquifer groundwater to treat and remove
the nitrate may potentially damage these ecological resources.
EPAconcurs and has determined that various types of hydrogeological
studies should be conducted during RD to evaluate the hydraulic connection
between the shallow aquifer and the San Pedro River. These studies include, but
are not limited to, aquifer testing, updated water quality testing, and groundwater
modeling. In addition, refinement of the assumptions on pumping rates and the
location of extraction wells will be developed during RD to minimize any impact on
the flow of the San Pedro River. Water levels also will be monitored during
operations so that adjustments to the pumping rates can be made, as necessary.
EPA also will consider measures during RD for enhancing existing riparian resources
by careful consideration of the siting and construction design (including choice of
vegetation) for the constructed wetlands.
4.4 Water Resources - Downstream Users
Other members of the community commented that pumping and extracting
the groundwater from the shallow aquifer for treatment by constructed wetlands
may continue to exacerbate an already lowered water table. As stated above, EPA
concurs that additional studies need to be conducted during the first phase of RD
to minimize any impact on the San Pedro River Basin and the availability of water
for downstream users. EPAwili ensure that the RD will effectively address
recharge to the shallow aquifer groundwater.
4.5 Water Resources - Deep Aquifer Replacement Wells
Some members of the community commented that it was inequitable to
install deep replacement wells for households that had been on bottled water due
to the nitrate contamination of their shallow aquifer drinking water wells, while not -
providing monetary compensati?n for those land owners who installed a deep
aquifer well (because of prior knowledge of the shallow aquifer nitrate
contamination) or who have delayed installing either a shallow or deep aquifer well.
Some of the comments. requested that EPA do something about this matter.
The purpose of replacement well installation is to protect the health of
people who otherwise would have the potential for unsafe exposure to nitrate-
contaminated shallow aquifer groundwater. Those who have drilled their own deep
aquifer wells, fortunately, have eliminated their own risk of exposure. EPA
general~y does not have the authority to intercede in private party disputes
regarding alleged property damage or losses~ .
. .
. A few comments stated that, because of additional water demands on the
deep aquifer, certain wells that previously had been artesian would require the
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installation .of pumps, resulting in increased costs. EPA is aware that the
installation of new deep wells may impact the availability of water for other nearby
wells. EPA also recognizes that some landowners have incurred or may incur
expenses due to the lowering of deep aquifer water levels (whether the lowering of
deep aquifer levels was due to new deep well installation or other possible causes).
Because the ANP site is not located in an area designated by the Arizona
Department of Water Resources as an Active Management Area (AMA), there are
no legal restrictions that would prohibit parties from drilling wells on their property
to withdraw water from either the shallow or deep aquifer. EPA believes requiring
cleanup of the shallow aquifer and ensuring safe water for those who have relied
on the shallow aquifer for domestic use are appropriate measures to protect human
health and the environment, and EPA will seek to avoid possible inadvertent
negative impacts of the selected remedy.
Other comments recommended that the St. David water supply system be
extended to accommodate new residents in areas of nitrate-contaminated
groundwater that otherwise will be forced to drill deep aquifer wells. EPA also
recognizes that future population growth, including the need to supply potacble
water, will continue to be a concern in the Benson/St. David area. To resolve
these issues, discussions should be held among landowners, ANP, and local
representatives, including the St. David water supply system officials. EPA will, to
the extent practicable, facilitate such discussions and will perform other actions as
necessary to protect public health.
4.6 Effectiveness of Remedy
Four of the five selected remedial actions in the ROD received general
concurrence by the community, with the exception that ANP did not concur with
EPA's recommendations for additional soil sampling. For details, see section 5.4
for EPA's responses to ANP's comments.
However, the selection of constructed wetlands to treat the nitrate-
contaminated shallow aquifer received numerous comments, as discussed above.
EPA believes many of these concerns will be resolved during the first phase of the
remedial design at the conclusion of the various studies previously discussed. EPA
agrees that the shallow aquifer extraction system, including the siting of the
extraction wells and the recharge locations, including pumping rates, needs to be
carefully reviewed and considered once additional, updated data are gathered.
Additionally, if new information .becomes available supporting the inclusion of an
agricultural irrigation component, EPA could modify the remedy, if appropriate.
However, until these additional analyses are completed during remedial design, any
specific changes to the selected use of constructed wetlands for treatment of the
shallow aquifer would be premature.
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5.0 Detailed Response to Comments
This portion of the Responsiveness Summary responds to more specific or
technical comments made or submitted during the public comment period. These
include the comments by the state agencies, ANP and certain community
members. This section also includes responses to specific questions raised during
the public meeting that were not answered at the public meeting or in the previous
section.
5.1 Comments from Arizona Department of Environmental Quality (ADEQ) -Letters
of July 25, 1994 and August 11, 1994
1.
General Comment: "The Arizona Department of Environmental Quality
(ADEQ) concurs with EPA's proposed groundwater and soil cleanup
alternatives at the Apache Powder Superfund Site, as generally outlined in
the above referenced Proposed Plan".
Response: Thank you for the comment.
2.
Caooing of the Inactive Ponds: Regarding the proposed alternative for the
inactive ponds at the site (capping), ADEQ wishes to emphasize the
importance of the development of a plan to monitor the integrity of the caps
and to verify that the ponds do not act as a continuing source of
groundwater contamination. Monitoring methods may include collection of
physical data associated with the ponds, such as unsaturated zone'
monitoring, in addition to visual inspections of the capped ponds.
Response: EPA will take these recommendations into account during the design of
the remedy and the development of monitoring plans to ensure that the
ponds do not act as a continuing source of groundwater contamination.
ADEQ will have the opportunity to review and submit comments on the
monitoring plans before EPA approves them. ..
3.
Future Use of Inactive Ponds: ADEQ recommends that continued
consideration be given to the development of a mechanism(s) restricting
future use of the capped, inactive ponds. These mechanisms may include
deed restrictions, notice to the deed and/or fencing.
Response: EPA shares these concerns and has included institutional controls in the
ROD. Any future site use must be consistent with the remedy and not
compromise the integrity of.the caps on the inactive ponds.
4.
Post-Closure'M0nitorina for Inactive Ponds: In the event additional sampling
during the RD phase at the site' ind~cates that inactive pond sediments cao
be classified as a Resource Conservation and Recovery Act (RCRA)
Hazardous Waste, then post-closure monitoring' and notice to the deed may
be required. .
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"' ., -., "" "
Response: EPA agrees that if any inactive pond sediments are determined to be a
RCRA hazardous waste, the ROD may need to be revised to provide post-
closure monitoring and/or other requirements.
5.
Reconsideration of Agriculture Use Alternative for Shallow Aquifer: The
determination of the preferred remedial alternative for the contaminated
shallow aquifer should include a reconsideration of the agricultural use
alternative. This alternative, or a combination of wetlands and agricultural
use, may offer an effective method of treatment.
Response: Based on current information and the nine criteria analysis, EPA
believes that the use of constructed wetlands is the best alternative for
treating the shallow aquifer. The effectiveness of agricultural irrigation as a
method of ' treatment depends on many variables, such as the concentrations
of nitrate in the influent to be treated. Agricultural irrigation, as an
alternative for secondary treatment or end use, will be further evaluated
during the initial stages of RD. Until additional analyses are completed
during RD on the concentrations of nitrate in various portions of the plume
and on the potential land acreage and crops available for irrigation, any
specific changes to the selected use of constructed wetlands would be
premature.
6.
Crop Irriqation as Secondary Treatment of Water: ADEQ believes that the
irrigation proposal warrants consideration by the EPA as secondary treatment
of the (shallow aquifer ground) water. Such treatment mayor may not
replace a secondary wetlands treatment system, depending on the amount
of water which can feasibly be distributed to the farmers.
Response: As stated in EPA's response to ADEQ's comment #5 above (p.3-9),
EPA intends to have additional analyses completed during RD to explore the
potential use of crop irrigation as secondary treatment or end use.
7.
Factors to be Considered to Ensure Nitrate Contamination is Not Spread to
Previouslv Uncontaminated Soils and Groundwater: Given the extremely
high nitrate content of the shallow aquifer groundwater (approximately 300
parts-per-million, or 810 Ibs of nitrogen per acre foot of water, in some
locations), ADEQ is concerned that applying the groundwater to various
parcels in the St. David area may create a high potential for spreading
contamination to previously non-contaminated soils and groundwater. Thus,
various factors should be considered for each farm, including soil type and
properties, method and. procedures of irrigation, pumping rates,
concentration of nitrates in the groundwater at the time of the application,
and nitrogen consumptive use of the crops. These factors and conditions
mayva~furmtofurm.
ADEQ feels that a high degree of assurance that contaminants will not be
spread to other areas is needed, prior to approval of the irrigation proposal.
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Thus, it would be appropriate to reduce nitrate concentrations through a
primary treatment system initially, prior to applying the groundwater on the
fields. In addition, groundwater monitoring should be conducted in
association with each farm to ensure that impacts to the underlying
groundwater are not significant.
Response: EPA concurs with ADEQ's comments and recommendations. As stated
in EPA's responses to ADEQ's comments #5 (p.3-9) and #6 (p.3-9) above,
EPA will take measures to ensure that the necessary data is gathered and
analyzed regarding the agricultural irrigJation option during the first phase of
RD to fully evaluate the technical feasibility of this proposal.
8.
Avert Imoact on the Base Flow of the San Pedro River: One of ADEQ's
primary concerns with a shallow aquifer remedy at the site involves the
hydraulic connection between the shallow aquifer and the San Pedro River
(SPR). The selected remedy should be designed to avert an impact to the
base flow of the SPR. Additional information on the effects of the remedy
on the SPR will be obtained early in the remedial design phase. Such data
may suggest that a substantial amount of treated water should be returi1ed
to the SPR, either directly or indirectly, to sustain current base flows.
Depending on factors such as irrigation methods used on the various farms.
and the location of the farms relative to the SPR, the irrigation proposal may
not support recharge to the SPR.
Response: EPA concurs that additional studies will need to be done during the first
phase of the remedial de~ign on the hydraulic connection between the
shallow aquifer and the SPR to ensure that pumping and extracting of
shallow aquifer groundwater does not adversely impact the base flow of the
SPR.
9.
Arizona Water Qualitv Standards: Treated water to be returned to the
aquifer and/or the SPR must meet Arizona Water Quality Standards. This
should be specified in the final ROD as an applicable or relevant and
appropriate requirement.
Response: EPA concurs with this comment. Please see page 2-30 of the ROD.
10.
Details of an Agricultural Irriaation Alternative: ADEQ has raised several
. issues regarding an irrigation alternative, including long-term commitments
from farmers using water, restrictions on the farm size, compliance with
State regulations when applying water, and siting of the farms near the San
Pedro River and the primary treatment stage of the constructed. wetlands.
Response: EPA b~Jieves that these are important issues which require further
.consi~eration during RD, when a more complete evaluation of the irrigation
alternative will be conducted. . . . .
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5.2 Comments from Arizona Department of Water Resources (ADWR)
1 .
General Comment: "The Department concurs with the Proposed Plan with
the understanding that downstream water rights holders are not affected,
that base flows in the San Pedro River are maintained to app~opriate levels
and that any water withdrawn be put to reasonable and beneficial use."
Response: Thank you for the comment. See EPA's response to ADWR's comment
#2 (p.3-11) below.
2.
Groundwater Withdrawals Performed Pursuant to Remedial Actions at the
Apache Powder Company (A PC) Superfund Site Mav Result in Neaative
Impacts to Downstream Users: Any groundwater withdrawals performed
pursuant to remedial actions at APC that affect base flows in the San Pedro
River (SPR) may be considered surface waters and may result in negative
impacts to downstream surface water right holders. If downstream rights
holders were affected, those rights holders would have the option to take
legal action in state court.
Response: EPA acknowledges the potential impact that pumping and extraction
could have on the base flows in the SPR and downstream surface water
right holders. As stated in the response to ADEQ's comment #8 (p.3-10).
EPA will require additional studies during the RD to ensure that pumping and
extracting of shallow aquifer. groundwater does not adversely impact the
base flow of the SPR.
3.
Withdrawn Water Must be Put to Reasonable and Beneficial Use: In order to
be consistent with applicable laws, water withdrawn pursuant to remedial
actions must be put to reasonable and beneficial use.
Response: EPA concurs with this comment.
5.3
Comments from the State of Arizona Office of Attorney General on EPA's
Feasibility Study
1.
Reauest for Corrections to Citations in the Applicable or Relevant and
Appropriate Reauirements (ARARs) Tables in the Feasibilitv Study (FS): The
Arizona AG's Office has requested corrections to the following tables: Table
3-2 (Potential Chemical Specific ARARs for Groundwater), Table 3-5
(Chemical Specific ARARS for Soil, Wash 3 Area (Excluding the Ash and
Burn Area), and Table 3-6 (Potential Action-Specific ARARs for the Apache
Nitrogen Products, Inc. Site) in EPA's Feasibility Study (FS).
Response: EPA has made the requested changes. See Table 11 (p.2-30) and
Table 12 (p.2-31) and Appendix A (p.2-39) of the ROD for corrected
versions of Tables 3-2, 3-5, and 3-6.
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5.4
Comments from Kimball & Curry on behalf of Apache Nitrogen Products,
Inc.,. (ANP) ..
1.
Inclusion of Previous Comments on RifFS in the Administrative Record:
Numerous documents containing comments by and on behalf of ANP
previously have been submitted to EPA regarding various aspects of the
RifFS and relating to the proposed remedy. At the time that these
comments were submitted, ANP requested that they be included in the
administrative record of this matter. ANP repeats that request by this
reference, and requests that EPA respond to ANP's previous comments as
provided in 40 C.F.R. Section 300.815.
Response: Given the general reference to previous submissions, EPA cannot
identify with specificity the documents and comments to which ANP is
referring. EPA has attempted to include all correspondence by and on behalf
of ANP regarding the RI/FS and relating to the proposed remedy in the
administrative record. EPA has considered the documents and comments
contained in the administrative record. EPA is responding to ANP's
comments submitted during the comment period, and believes that these
responses, plus the responses to other comments, adequately address issues
raised by ANP in documents contained in the Administrative Record.
2.
Inclusion of ANP's Document. "Risk Assessment, Apache Nitroaen
Products" in the Administrative Record: There is one document, "Risk
Assessment, Apache Nitrogen Products" (Woodward-Clyde Consultants,
July 13, 1992), which contained comments previously submitted by or on
behalf of ANP relating to selection of the proposed remedy and which is not
referenced in the Proposed Plan or the final RI or FS reports. In case this
document has not already been included in the administrative record, a copy
is enclosed for inclusion in the administrative record and response by EPA.
Response: ( EPA will include ANP's document, "Risk Assessment, Apache Nitrogen'
Products" in the administrative record. EPA relied on the Baseline Public
Health Evaluation/Ecological Assessment (PBHE/EA) prepared by ICF
Technology Incorporated for EPA in September 1992. EPA has reviewed
ANP's risk assessment in conjunction with completing the Record of
Decision and has concluded that there are no major disparities between
EPA's selected remedy and ANP's findings in the risk assessment.
3.
Validitv of ANP's June 25. 1993 Proposal for Remedial Action: By letter
dated June 25, 1993, ANP. submitted a proposal for remedial action, based
upon the RI/FS prepared by Hargis +. Associates. ANP continues to believe
that the proposal made last year is a valid approach to remediation. EPA's
proposed plan is similar to ANP's plan with respect to most of the areas at
the site, with the exception of the remediation of the shallow aquifer. ANP's
proposal provided for a more selective approach to pumping from the
shallow aquifer for treatment. ANP believes that public comments made at
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the July 6, 1994 public meeting regarding water conservation and concerns
regarding the impacts of pumping on the flow of the San Pedro River stated
in EPA's FS support ANP's more selective approach to pumping, which
would reduce the pumping rate. ANP believes that this approach would be
fully protective of human health and the environment. At worst, ANP's plan
might take a few years longer to achieve cleanup goals in the shallow
aquifer. However, a reduced pumping rate would reduce the risk of adverse
impact to the flow of the San Pedro River and alleviate the other concerns
regarding water conservation.
Response: EPA concurs with ANP's assertion that the June 25, 1993 proposal for
remedial action has merit, and EPA has considered this proposal in selecting
its remedy. However, for purposes of preparing EPA's FS Report, EPA did
not alter the assumptions made by Hargis + Associates regarding the
quantities of soil and volume of groundwater requiring remediation. Rather
than spend additional dollars on a new theoretical model, EPA continued to
use Hargis + Associates existing data and assumptions for the purposes of
preparing EPA's revised FS report. However, EPA believes additional data
gathering and analyses (groundwater modeling, aquifer tests, etc.) need to
be performed during the first phase of remedial design to determine if
modifications or adjustments can be made to the cleanup remedy. EPA
agrees that more refinement of the assumptions on pumping rates and the
location of extraction wells should be developed during remedial design to
account for seasonal weather conditions, the specific subsurface geology of
the recharge location, and to minimize the impact on the flow of the San
Pedro River or on the water rights of downstream users. See EPA's
responses to ADEQ's comment #8 (p.3-10) and ADWR's comment #2
(p.3-11).
4.
Use of Constructed Wetlands is Preferred bv ANP for the Shallow Aauifer:
With respect to the proposed method of treatment, the use of constructed
wetlands is preferred by ANP over the other treatment methods for the
shallow aquifer discussed in the FS. However, ANP requests that EPA give
serious consideration to comments made by local landowners regarding the
use of water pumped from the shallow aquifer for irrigation use. As long as
irrigation use would not increase the costs of the project and as long as.
water rights issues can be resolved, ANP would support this alternative
approach.
Response: EPA concurs with ANP that potential irrigation use as a component of
the treatment remedy for the shallow aquifer ~hould be considered in more
detail. EPA believes this option for agricultural use as secondary treatment
or as end use should be analyzed in greater detail during the first phase of
remedial design. See EPA's responses to ADEQ's comments #5 (p.3-9), #6
(p.3-9), #7 (p.3-9), and #10 (p.3-10).
3-13
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5.
EPA's Assessment That Use of the Shallow Aauifer for Drinkina Water
Pre~ents the Onlv Risk to Public Health or the Environment: ANP wishes to
highlight that EPA's own assessment indicates that use of the shallow
aquifer for drinking water pres"ents the only risk to public health or the
environment. Notably, the only designated use for which a state numerical
aquifer water quality standard exists is for drinking water. As EPA is aware,
ANP is currently installing deep aquifer drinking water wells for those
residences where shallow aquifer drinking water wells have been shown to
have nitrate concentrations above the maximum contamination levels
("MCLs"). This project will be completed within a few weeks, and will result
in the replacement of all residential wells where there has been a verified
exceedance of the MCL.
Response: EPA has highlighted the risk posed to infants if nitrate-contaminated
groundwater is ingested. However, as stated in EPA's risk assessment, RI
report, and FS report, health risks also are posed by the perched
groundwater which continues to contaminate the shallow aquifer and by the
soils contamination on the site. "
6.
Cut-Off of Nitrate Flows to the Shallow Aauifer Will Stronalv Attenuate the
Nitrate Concentrations in the Shallow Aauifer: Once pumping of the perched
aquifer begins, the cut-off of flows to the shallow aquifer will strongly
attenuate the nitrate concentrations in the shallow aquifer as fresh upstream
water flows mix with the remaining waters in the shallow aquifer. As the FS
admits, even if no action is taken, "dispersion and dilution of the COC's to
concentrations that would not exceed MCL would occur over a period of
several years." Although ANP does not suggest that the no-action"
alternative be adopted, it does believe that EPA should more seriously
consider a modified alternative GS':'1 B that includes institutional controls and
discrete groundwater pumping. Again, EPA states on page 5-6 that this
alternative would "reduce the potential for exposure to surface water and
groundwater containing concentrations in excess of the MCLs on a short-
term basis," and "on a long-term basis, natural dilution from recharging and
dispersion caused by surface water flows and groundwater movements and
natural biological degradation would reduce concentrations of the COC's to
concentrations less than the MCLs and allow removal of the restrictions on
use of the groundwater."
Response: EPA is aware that some dispersion and dilution would occur in the
shallow aquifer. However, the timeframe required is not short-term. Hargis
+ Associates concluded in ANP's FS report that the time-frame is up to 90
years for attenuation to reach MCLs if no action is taken on the shallow
aquifer, assuming the perched groundwater is pumped and treated. ANP's
FS further states that even if the shallo~ aquifer is pumped and treated at a
rate of 500 gpm, the treatment period is still 35 years to reach 10 parts per
million (ppm), according its calculations. EPA agrees that discrete pumping
3-14
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may be an appropriate approach to ensure there are not adverse impacts on
the base flow of the San Pedro River. However, until additional
hydrogeological studies are conducted during RD, the optimum pumping
rates, (including consideration of discrete pumping) cannot be selected.
7.
ANP Believes That ADWR's Authority Could Restrict the Drilling or Use of
Wells in the Shallow Aouifer. TherebY Makino .the No Action Alternative an
Imclementable Oction: EPA did not evaluate the no action alternative for the
shallow aquifer because it believed that there were no state or federal laws
or regulations "that could restrict the drilling and the use of wells in the
shallow aquifer." Of course, given that ANP currently is providing drinking
water wells to affected residences. the only potential exposure which could
cause a risk is nitrate contaminated groundwater from new drinking water
wells, and EPA's statement that state regulations could not restrict the
drilling and use of new wells in the shallow aquifer is not wholly accurate.
First, all of the residences which have or will receive new, deep aquifer
drinking water wells have agreed to not use the shallow aquifer for drinking
water purposes. In addition, Arizona laws and regulation allow the
Department of Water Resources ("DWR") to limit the installation and
construction of new wells. All wells must be registered with the State, and
construction of new wells must be approved before installation. At that
time, DWR has the opportunity to review well siting and could prohibit the
approval of a drinking water well in an 'area of poor water quality. Given
that authority, ANP believes that the GS-1 B alternative is implementable,
would be protective of the health and the environment, and should be
considered more fully prior to issuance of the ROD.
Response: EPA does not concur with ANP's position on the extent of ADWR's
authority regarding "the restriction of drilling and the use of wells in the
shallow aquifer". At the public meeting, a question was asked whether
there was a potential for deed restrictions to be placed on private property
adjacent to the site. The question was answered by a representative of
ADWR, who stated that ADWR does not have the authority to deny the
drilling of wells or the proper drilling of wells or extraction of groundwater in
this area, since it is a non-active management area. Because the site is not
located in an active management area in which ADWR regulates water rights
and water use, EPA did not consider the no action alternative a protective or
an implementable alternative. Even if the State had the authority to restrict
well drilling, EPA does not consider such institutional controls to be an .
adequately implementable or protective alternative.
8.
ANP Believes a Sufficient Remedy is to Cut-Off of the Perched Zone. and
Install Deec Aouifer Drinkino Reolacement Wells. Combined with Discrete
Shallow Aouifer Groundwater Pumoino and Treatment in Scecific Areas of
Low Flow Where Nitrate Concentrations Aooear to Accumulate: With the
cut-off of the perched zone, and the installation of drinking water
. replacement wells, ANP believes that this will be a sufficient remedy to
3-15
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address the requirements of CERCLA. Moreover, ANP could combine this
wit~ discrete pumping and treatment in specific areas of low flow where
nitrate concentrations appear to accumulate.
Response: EPA agrees that cut-off of the perched zone will reduce nitrate flow to
the shallow aquifer and that installation of deep aquifer replacement wells
will reduce the potential risk of exposure to nitrate in the shallow aquifer.
But these reductions alone would not be an adequate' remedy. (See EPA's
responses to ANP's comments #6 (p.3-14) and #7 (p.3-15).) The.
presumption of nitrate accumulating in certain areas of the shallow aquifer is
questionable. The appearance of nitrate accumulation in specific areas may
be due to the locations and construction details of existing wells. Based on
existing data, the effectiveness of discrete pumping in terms of meeting
remedial action objectives cannot be estimated. Additional hydrogeological
studies must be completed to determine the exact number and location of
extraction wells necessary to hydraulically control and remediate the nitrate-
contaminated shallow aquifer groundwater. See EPA's responses to ADEQ's
comment #8 (p.3-10), ADWR's comment #2 (p.3-11), and ANP's comments
#3 (p.3-12) and #6 (p.3-14).
9.
ANP and the Local Community Believe That Heavy Pumpina of the Shallow
Aauifer is the Wrona Solution and That The Benefits Should be Investigated
of Pumpina Water From the Shallow Aauifer For Use Directly to Irriaate
Aaricultural Crops or to Support the Riparian Area: Public comment at the
recent public hearing indicated that the local community also believes that
heavy pumping of the shallow aquifer is the wrong solution. Although ANP
has not had the opportunity to fully investigate whether water pumped from
the shallow aquifer could be used directly for irrigated agriculture or to
support the riparian area, these alternatives al50 should be evaluated prior to
issuance of the ROD. The benefits that this water could provide would
justify abandonment of the wetlands alternative.
Response: EPA concurs that either an end use or a secondary treatment option of
agricultural irrigation or riparian enhancement should be evaluated during the
first phase of RD for shallow aquifer groundwater. At this time, however,
EPA does not concur with ANP's statement that these potential uses of the
shallow aquifer groundwater will ~e of sufficient benefit to not require
primary and/or secondary treatment by constructed wetlands. Unless
additional analyses (to be conducted during the first phase of RD) indicate
that "the concentrations of nitrate in the shallow aquifer are much lower than
previous sampling has indicated, initial primary treatment of the groundwater
by constructed wet.lands will be necessary. Blending of the contaminated
groundwater within .the plume may be .feasible for reducing the concentration
of influent. Blending may be possible by inserting mixing devices into the
piping system for the extraction wells; but, most likely a constructed
wetlands "holding" pond would be needed, bo~h as a large mixing vessel for
completing the blending. and as a storage vessel during rainy or freezing
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10.
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conditions, when the water could be mismanaged if suddenly released or
allowed to flood.
ANP Believes EPA's Selection of the Caooina Alternative for the Inactive
Ponds Offers a Protective Yet Cost-Effective Remedial Solution. But Does
Not Believe That Additional Characterization of These Ponds is Required:
ANP also believes the EPA selection of the capping alternative for the
inactive ponds offers a protective yet cost-effective remedial solution,
because this alternative will prohibit the further mobilization of any pollutants
or contaminants in these ponds. However, ANP does not agree that
extensive additional characterization of the ponds is required during the
remedial design phase.
Response: EPA concurs that the capping of the inactive ponds is a protective and
cost-effective solution. However, EPA does not concur that no additional
soil characterization in the inactive ponds is necessary. EPA will require that
at least a minimal level of baseline data, to be determined during RD, be
collected from each of the inactive ponds prior to final capping and closure.
The number of samples required during RD will vary with each pond,
depending on the number of samples collected during prior investigations.
The rationale for this requirement is that the investigative studies conducted
during the PI and the RI focused on establishing the presence of
contamination, not the extent of contamination. The sediments and
surrounding soils of many of the inactive ponds were never sampled during
these prior investigations.. In order to determine the lateral extent of capping
required at the edges of the inactive ponds as well as to document the
characteristics of the soils being capped, EPA will require additional
characterization as part of the final remedial design and remedial action for
these inactive ponds.
11.
ANP Believes that the Management (Either Throuqh On-Site Storaqe or Off-
Site Disposal or Treatment) of the Contaminated Soils in the White Waste
Materials and Drum Storage Area (Vanadium Pentoxide) Are Required Under
the State's Consent Decree (CD)' Since No Soecific Exemption for the
Characterization and Manaaement of These Materials Was Included Under
the CD: EPA's preferred remedial alternative for the white waste materials
and the vanadium pentoxide is off-site disposal. At this time, ANP is
required under the Consent Decree it recently entered into with the State of
Arizona and the ADEQ to characterize all waste materials on the site and
properly manage those materials, either through on-site storage or off-site
disposal or treatment. The CD does not include an exemption for the white
waste or vanadium pentoxide. Because there is no specific exemption for
these materials, ANP believes that these materials can be managed under the
CD and in a manner that actually will expedite the removal of the materials
from the Apache site. ANP believes that the handling of these materials
should be deleted from the ROD, and EPA should allow prompt management
of the materials under the CD.
3-17
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...... . ,.....
Response: EPA does not concur with ANP's position that the contaminated soils in
the YVhite Waste Materials and Drum Storage Area, including the vanadium
pentoxide, should be managed under the State's CD rather than under the
EPA ROD. EPA has contacted. the State of Arizona regarding ANP's
interpretation of the lead responsibility for these areas, and the State
concurs with EPA that the White Waste Materials and Drum Storage Area
contamination should be addressed under the CERCLA ROD. EPA and the
State of Arizona previously agreed that EPA's ROD will cover specific areas
of historical contamination, including the White Waste Materials and Drum
Storage Area, while the State's CD will cover areas of active hazardous
waste management.
12.
ANP Believes that the Excavated Soil from Wash 3 Currentlv Stored On-Site
Also Should be Manaaed Under the State's Consent Decree (CD): ANP
believes that the excavated soil from Wash 3 that currently is stored on-site
also should be managed under the CD. As it is, the drums of soil are being
stored on-site awaiting the issuance of the ROD and the final excavation of
Wash 3. The management of these soils under the CD would expedite their
removal from the Apache site.
Response: EPA does not concur with ANP that the cleanup of the Wash 3
contaminated soils should be managed under the State's CD. EPA has
contacted the State of Arizona regarding ANP's interpretation of the lead
responsibility for this area, and the State concurs with EPA that the Wash 3
Area contamination should be addressed under the CERCLA ROD. The Wash
3 Area also was included in EPA's ROD, based on prior agreements between
EPA and the State of Arizona, as discussed above under EPA's response to
ANP's comment #11 (p.3-17). .
13.
ANP Aarees That the Excavation and Off-Site Disposal of the Contaminated
Soils Is The Most Practicable Remedial Action for the Wash 3 Area.
However. ANP Does Not Aaree That Additional Soils Characterization is
Necessarv: Although ANP agrees that the excavation and off-site disposal
of the Wash 3 soils is the most practicable remedial action to address Wash
3, ANP does not agree with the EPA's determination that additional
characterization of the Wash 3 Area is necessary. .
Response: EPA does not concur with ANP that additional characterization of the
Wash 3 Area is not necessary prior to final removal of contaminated soils.
EPA is aware that characterization sampling was conducted by ANP during
the course of conducting Phases I-IV of the Wash 3 investigation, and the
initial removal of drums and contaminated soils to an on-site central
accumulation area. ANP's sampling and removal of dinitrotoluene (DNT)-
con.taminated soils was based on an. assumption that 200 mg/kg (ppm) DNT
would be sufficient as a cleanup standard (based on Hargis + Associates'
risk calculation of 10-4). However, becaus.e EPA has selected-the State's soil
cleanup standard for DNT of 140 mg/kg, additional surface soil sampling will
3-18
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14.
. . . - . ... ~ ,'. ..'.
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be required to ensure that ANP has cleaned up the Wash 3 area to this
standard. In addition, because of the potential for lead to migrate from the
Ash and Burn Area to other surrounding areas within the Wash 3 Area,
additional surface soil sampling will be required for lead.
ANP Disaarees With EPA's Statement in the EPA Rl and FS Reports That
ANP's RI and FS Reports Were "Incomplete" Because of ".. .Unresolved
Technical Differences. Missina Data and New Information" and ANP Counter
Araues That ANP Excluded Certain Disputed PI Data From ANP's RI and FS
Reports Because of Poor Qualitv Control. Inappropriate Sampling
Methodologv. and Erroneous Interpretation of the Data: In both the RI and
FS produced by EPA/Bechtel, it is alleged that ANP's RI and FS report were
"incomplete" because of "...unresolved technical differences, missing data
and new information..." However, the technical differences are not outlined
nor are the differences discussed in terms of how these differences are
handled in the reviewed documents. Review of the document indicate that
the interpretation of the data and resulting conceptual model of groundwater
flow and fate and transport of compounds of concern did not change. The
only change apparent from the original ANP RI and FS is the inclusio-n of the
EPA Preliminary Investigation (PI) data and interpretations from the PI. The
ANP documents use these data selectively because of poor quality control,
inappropriate sampling methodology and erroneous interpretation of the
data....Due to these problems with the PI data, ANP did not include these
data in the RI. However, the fact that these data were not used did not
impact the conclusions or interpretations in the ANP RI or FS. In fact, the
EPA proposed remedy for soils and groundwater do not differ from the
remedial actions proposed by ANP with the exception of the shallow aquifer
treatment technology.
Response: ANP has selected one of the three reasons offered by EPA, "missing
data", as the primary basis for EPA's determination that ANP's RI and FS
reports were determined to be inadequate by EPA and, therefore, revised.
While the missing PI data, as discussed by ANP, was one reason EPA'
revised ANP's RI and FS reports, the other two reasons were of equal if not
more important weight.
During the period of 1989 through 1993, continual "unresolved technical
differences", with the State of Arizona and EPA disagreeing with ANP,
existed regarding the extent and levels.of nitrate contamination in the
shallow aquifer. ANP's unwillingness to revise or correct hydrogeological
evaluations and conclusions in both ANP's RI and FS, after repeated
requests by EPA, was one of the primary reasons EPA determined that
ANP's RI and FS reports were inadequate and required revisions by EPA.
The second major reason for the revisipns was "new information", regarding
treatment technologies for treating the perched and shallow aquifer
3-19
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15.
groundwater. In early 1994, EPA became aware that ANP had proceeded to
design a brine concentrator to treat its process wastewaters and potentially
the contaminated perched groundwater. However, this treatment technology
(forced evaporation) was not selected for detailed analysis as a treatment
alternative for the perched groundwater in ANP's FS report.
Additionally, only a limited number of biological treatment technologies were
mentioned for treatment of the shallow aquifer groundwater. Of these, only
anaerobic denitrification in reactor tanks was retained for detailed analysis in
ANP's FS report. There are several treatment technologies involving
anaerobic denitrification, including constructed wetlands, which are viable
methods for denitrifying nitrate and which appear more cost-effective than
the physical treatment technologies (e.g., reverse osmosis, electrodialysis
reversal) evaluated in the ANP FS report. Because of the volume of water
requiring treatment, the estimated cost for treatment of the contaminated
shallow aquifer comprises an estimated 75% or more of the total projected
costs for the site cleanup required under CERCLA. According to the
literature, significant cost savings can be realized by the use of constructed
wetlands. EPA believes that ANP and the public have benefited from EPA's
further consideration and selection of this option.
, '
ANP Takes Exception with EPA's UnwillinQness to AcknowledQe the Validitv
of ANP's Risk Assessment Prepared bv Woodward-Clvde Consultants,
Especiallv Given the Inadequacies of EPA's Draft Baseline Public Health
Assessment (BPHE) Report: All references to the Risk Assessment (RA)
document prepared for ANP by Woodward-Clyde Consultants were deleted
from the EPA final 'documents, and large sections of the RI and FS have been
changed to include risk evaluations that were not available to ANP during the
preparation of the ANP RI a.nd FS. While the EPA took exception to the
independent RA conducted by ANP, the work is valid and was necessary due
to inadequacies of the draft Baseline Public Health Assessment (BPHE) report
prepared by EPA. ANP's review of the BPHE found significant problems with -
the approach in the BPHE, and provided comments to EPA. At the time, EPA
indicated that no additional work was planned to correct the inadequacies in
the BPHE report. However, it is apparent that the BPHE was revised and the
results of the revisions were included in the EPA's final RI and FS. In the
final analysis, these changes do not result in significant differences in ANP's
proposed remedial actions and the EPA proposed remedy, although they
could make a difference in setting cleanup levels. Again, the major
difference being the recommended treatment technology to be used to
remediate the shallow aquifer groundwater.
Response: EPA did not acknowledge the validity of ANP's,risk assessment
primarily because it did not include the data from the PI in its calculations.
. EPA did not revise the 1992 EPA BPHE document. The changes or additions
noted in EPA's RI and FS reports in the presentation of the risk assessment
data were a result of a reevaluation of the BPHE data by EPA's contractors
3-20
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. (Bechtel Environmental, Inc.) during the process of preparing the revised RI
and FS reports.. In addition to reformatting the data already included in the
1992 BPHE into a more readable format, one additional set of calculations
was completed to establish a site-specific risk level based on the data in
both the PI and the RI. These new, additional calculations were added as an
additional column to several tables in EPA's RI and FS reports for analytical
purposes to provide a full range of possible cleanup standards for
consideration and final selection in the ROD.
16.
ANP Aqrees That Some Refinement of the Data Are Needed and Some
Specific Desiqn-Related Data Are Yet to be Gathered. But ANP Believes That
EPA's Recommendations For Further Soils and Groundwater Investiqation
and Characterization During RD Constitutes a Larqe Site Assessment Effort
and That It is Premature to Identifv These Data Needs: Recommendations
for further investigations required for developing a remedial design of the
selected remedies are presented. However. details regarding these
"required" investigation is limited. These investigations are significant
efforts that. as outlined, imply major expenditures. Although ANP agrees
that some refinement of the data are needed and some specific design-
related data are yet to be gathered. it appears that the recommendations in
these documents constitute a large site assessment effort. H + A believes
that some of the required data will be collected as part of source control
work conducted by agreement with the Arizona Department of
Environmental Quality (ADEQ). Examples of these data include the
additional work in the perched groundwater area planned as part of the
Aquifer Protection Permit (APP) studies that will define the extent of the
perched groundwater system, and soils sampling that is proposed for RCRA
closure and non-RCRA closure of some of the facilities on the plant site.
The work to be conducted for ADEQ as part of the recently-signed Consent
Decree and investigations for the Aquifer Protection Program (APP) -
application will supply additional data regarding soils and pond sediments for
some of the active pond areas. Additional sampling at some of the inactive
ponds can be included in that sampling to evaluate the potential size of the
areas around the ANP ponds that needed to be remediated or capped. The
waste and drum storage area will also supply additional soils data.
Therefore, H + A believes that the need for additional characterization work
should be determined at the time the RD/RA plans are developed.
Some of the soil sampling described in the EPA document also may not be
necessary. Previous sampling in the inactive pond areas indicate that the
areas impacted by ANP wastes are not extensive. It is possible that
investigation of selected inactive ponds can guide the remediation efforts
without extensive and expensive sampling at all locations.
3-21
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Response: If missing data will be gathered as part of other investigative or source
con~rol efforts (for example, characterization of the perched groundwater)
conducted by ANP in response to the State's CD, EPA agrees that additional
data gathering may be unnecessary. Assuming that any data collected by
ANP would be provided to EPA readily upon request, EPA concurs that it
may be possible to keep additional sampling requirements to a minimum.
However, EPA does not concur with ANP's assessment that sufficient soils
and groundwater characterization data have been collected to date, with the
exception of some specific design-related data. EPA believes additional soil
sampling is required in the area of the Inactive Ponds (see EPA's response to
ANP's comment #10 (p.3-17)) and in the Wash 3 Area (see EPA's response
to ANP's comment #13 (p.3-18)). Additionally, EPA believes additional
characterization is required to define the vertical and lateral extent of the
nitrate-contamination in the shallow aquifer in the areas north and north-
west of the site study area (see EPA's response to ANP's comment #17
(p.3-22)).
The full extent of this additional characterization work may not be easy to
define at one time during the RD/RA planning stage. EPA believes this -
sampling work will likely be completed in multiple phases, commencing with
some sampling in the pre-design phase, followed by some sampling during.
the development of the RD plans and drawings, some sampling during the
actual removal of the contaminated soils or extraction of the contaminated
groundwater, and some sampling after completion of the RA to ensure
compliance with the ROD cleanup standards and to monitor the success of
tpe remediation.
At a minimum, a certain level of base-line water and soils data will need to
be collected in the near future, since over two years have elapsed since any
on-site data has been collected. The only data collected during the last two
years in areas of the site covered by EPA's ROD have been a limited amount
of water quality data from shallow aquifer private wells identified for
replacement in the Alternative Domestic Water Supply Plan (ADWSP). All
other data collected in the last two years have been data collected to
support the State's CD for aquifer protection. or for hazardous waste
management, in areas of the site study area not covered by EPA's ROD.
17.
ANP A9rees That Some Additional Data Will Be Needed for Final Desian of
. the Groundwater Extraction and Treatment System, But ANP Believes That it
is Premature to Identifv Data Collection Needs Since Other Samolin9
Activities Reauired For Either the Installation of the DeeD Aauifer
ReDlacement Wells or For ADEQ as Part of State's CD Will Suoolv Additional
Data: Some of the additional data needs alluded to in the EPA RI and FS
documents will be necessary for final design of the groundwater extraction
system and treatment system, but H + A feels that it is premature to identify
data collection needs. at this point. Sampling to be conducted for the well
replacement work under the alternative drinking water supply activities will
3-22
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~ . . .... . - - .
provide additional current and future data on the extent of the shallow
aquifer contamination and the effects that source control will have on the
groundwater system.
Response: EPA does not concur with ANP's conclusion that it is premature to
identify specific data collection needs until other site cleanup activities have
been completed, as detailed above in EPA's response to ANP's comment
#16 (p.3-21). In particular, EPA strongly believes that the full lateral extent
of the nitrate-contaminated shallow aquifer plume should be defined.
Sufficient, accurate data must be available to landowners planning to install
wells north and north-west of the ANP property. The current lack of data on
the location of the leading edge of the contaminated plume is unacceptable,
if the public is to be duly and properly informed about potential risks.
Additionally, monitor wells should be installed to monitor the performance
and effectiveness of the constructed wetlands treatment system. If the
extraction and treatment process is working, eventually there should be
nitrate reductions at the north end of the plume.
18.
ANP Believes That Drillinq of Additional Monitor Wells to the North and
Northwest of the Site Study Area May Not Be Necessary to Characterize the
Extent of the Nitrate Concentrations in the Shallow Aquifer Groundwater
Requiring Remediation: H + A also believes that some of the work
recommended by EPA may not be necessary. For example, EPA
recommends drilling monitor wells to the north and northwest of the site
study area. In addition to sampling conducted as part of the Alternative
Drinking Water Supply Plan (ADWSP), there may be private shallow aquifer
wells in these area that can be sampled initially.to determine if any or all of
the wells proposed by EPA are necessary to determine if groundwater in this
area contains nitrate-N concentrations that require remediation.
Response: EPA does not concur with ANP's statement that drilling of additional
monitor wells to the north and northwest of the site study area may not be
necessary. Monitor wells of a known design (e.g., where the screened
interval is known) are needed to collect accurate water quality and water
level data, to determine more accurately the extent of contamination and the
direction in which the plume is moving. Even if a sufficient number of .
production wells exist in appropriate locations, the water levels reflect local
conditions due to pumping and the part.of the aquifer from which water for
the sample is being with withdrawn. In many instances, the screened
interval on existing production wells is unknown or inappropriate. The data
collected for the ADWSP does not address these data needs. (Also, see
EPA's response to ANP's comment #17 (p.3-22)).
19..
ANP Believes the Costs For Performinq Further Investiqation for DeveloDinq a
Remedial Design Could Add Substantial Costs to the Remedial Alternatives,
Particularly Because the ScoDe of These RD Investiaations Were Not
Defined: The FS did not incorporate costs for performing the RD
3-23
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investigations. These costs could add substantially to the estimated costs of
the, alternatives, particularly because the scope of the RD investigations is
not defined. For example, additional work is proposed for Wash 3. A year
ago H + A provided EPA with a Phase IV report that described the clean-up
status of Wash 3. All 2,6- and 2,4-dinitrotoluene (DNT) drums and known
contaminated materials were removed and contained. Post-removal sampling
was performed and results reported to EPA. This document was referenced
in the FS, yet EP A states on p. 1-32 that "The characterization... of DNT
in...Wash 3...is not complete."
Response: EPA does not concur with ANP's comments that further sampling and
investigative work will add substantial costs to the RD/RA cost estimates.
Five areas have been identified in the ROD for design and remediation,
including three areas with soil contamination. As discussed above under
EPA's responses to ANP's comments #10 (p.3-17) and #13 (p.3-18),
additional soil samples may need to be collected and analyzed. Even if it
were determined that 100 additional samples (at an estimated cost of
$1,000 per sample, including sample collection, analysis, and management
oversight) were required, the total cost for additional soils characterization
would be only another $100,000, on top of the $2.57 currently estimated
for the soils cleanup portion of the ROD.
Regarding a requirement to characterize the perched groundwater
contamination, ANP expressed in comment #16 (p.3-21) that ANP will be
completing this work 'as part of its separate requirements under the State's
CD. The shallow aquifer groundwater contamination is the remaining area
requiring additional characterization. The nitrate plume in the shallow aquifer
already has been characterized reasonably well on the south and eastern
edges as it migrates in a north-easterly direction from the site along the San
Pedro River. A good data base has been developed for the area of the plume
just north of the ANP site, as a result of the recent sampling conducted in
conjunction with the installation of .deep aquifer replacement wells for
residences with contamis:'ated shallow aquifer wells. The data gaps for
characterization of the shallow aquifer have been described in detail under
the response to ANP's comment #17 (p.3-22) above. At a minimum,
additional monitoring wells will need to be installed to identify the leading
edge of the plume. If it were determined .that twelve wells would be
required to define the '~nose" of the plume (at a cost of $20,~00 per wen,
including drilling, analysis, and management oversight), the total costs would
be approximately $240,000.
An estimated additional $340,000 ($100,000 for soils and $240,000 for
groundwater) of site characterization costs is n01 a significant sum when
contrasted with the overall remedial cost estimate of $21.1 million, and
when one considers that the site study area encompasses over 1,.000 acres.
3-24
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20.
;",
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EPA's Clean-UD Goals Were Not Clearlv Stated. Which Could Have a
Sianificant Bearing on the Costs of the RD/RA: The clean-up goals are not
clearly stated. This, of course, has a significant bearing on both the costs of
the remedial action and the RD investigation.
Response: EPA did not include EPA's cleanup standards in the Proposed Plan
because the selection of final cleanup standards is a component of EPA's
final decision-making documented in the ROD. However, EPA's FS Report
included several tables in sections 2.0 and 3.0 summarizing State of Arizona
and federal soil and groundwater Preliminary Remediation Goals (PRGs),
background levels, Health Based Guidance. Levels (HBGLs), Site-Derived,
Risk-Based Levels, Maximum Contaminant Levels (MCLs), and Health
Advisories. While cleanup standards affect costs, in the case of the ANP
site, EPA believes that the costs should not vary significantly from the
estimated costs in EPA's FS report. The reason is that groundwater cleanup
is the most costly component of the ROD ($18.5 million). The cleanup
standard for nitrate, the primary contaminant of concern, is the federal and
state MCL of 10 ppm. This standard was the same basis for cost estimates
prepared for EPA's FS report (and summarized in EPA's Proposed Plan) and
used by ANP's contractor for ANP's FS report.
21.
In the case of soil costs, because most of the contaminated soils covered by
this ROD are already drummed (vanadium pentoxide), accumulated in a
central storage area (dinitrotoluene), or will be contained in place (metals and
nitrate in the inactive ponds), there probably are not extensive areas for
which additional excavation will be required. Even though some cleanup
levels may vary from those used for purposes of the cost estimates in the FS
Report, the costs for cleanup of the soils areas should not vary significantly.
ANP Believes That EPA's FS Did Not Consider Anv actions Short of Full-
Scale Clean-uc of the Shallow Aquifer (For Examcle a Combination of
Pumcina in "Hot Soots" and Allowina the Remaining- Lower Concentration.
Portions of the Aquifer to Self-Cleanse). With the Excection of the No Action
Alternative: With the exception of the no action alternative, the FS did not
consider any options short of full-scale clean-up of the shallow aquifer. The
ANP FS, for example, considered a combination of pumping in "hot spots" .
and allowing the remaining, lower concentration, portions of the aquifer to
self-cleanse. Additionally, EPA made several assumptions regarding the
selected remedial action that need to be refined and may affect the
estimated total cost of the shallow aquifer remediation. As previously stated
to -EPA, ANP intends to begin source control as soon as the brine
concentrator is completed and tested. This will probably happen prior to
construction of the shallow aquifer extraction well system and the wetlands
and will probably have an impact on nitrate-N concentrations in the shallow
aquifer. This could affect the amount of water that needs to be pumped and
treated and therefore the length of time for cleanup to occur, both of which
impact cleanup cost estimates significantly.
3-25
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"..":':. ,,"..,,"
Response: EPA did not develop multiple alternatives with various pumping rates
for ~he FS report because, until additional groundwater modeling and aquifer
tests are conducted, it is premature to assume the optimum pumping rate(s).
See EPA's responses to ANP's comments #6 (p.3-14), #7 (p.3-15), and #8
(p.3-15). For purposes of comparing the various treatment technologies
(physical, biological, and chemical), EPA used the assumptions of H + A's
groundwater model that a pumping rate of 720 gpm would be needed to
clean up the aquifer in the shortest time frame (12 years).
22.
Rather than expand EPA's FS report to include numerous options that may
not be applicable to the particular situation at the site, EPA assumed that
additional analyses would be completed during the initial stages of remedial
design after new, updated data are gathered. Various factors (season of the
year, the subsurface geophysical conditions, the precise location of "hot
spots") need to be evaluated to determine optimum pumping rates for
containing or controlling the migration of the plume and optimum recharge
rates for returning the treated groundwater back to the shallow aquifer.
ANP Believes There May Be an ImDact on the Amount of Water That Needs
to be Pumoed and Treated From the Shallow Aauifer and the Corresoondina
Costs. Once the Brine Concentrator is Comoleted and Tested and Source
Control Measures Beain:
Response: EPA agrees that there may be an impact on the amount of water that
needs to be pumped and treated from the shallow aquifer and the
corresponding costs, but EPA does not believe the impact will be so great
that there will not be a need to remediate the shallow aquifer. RD will
include monitoring this expected impact, as soon as the brine concentrator
goes on line in April 1995. An initial focus should be placed on monitoring
the impact of ceasing the discharge of ANP's process wastewaters to the
active, unlined evaporation ponds, combined with extracting the perched
groundwater from the underlying contaminated zone. ..
23.
ANP Believes There Will Likely Be A Lengthenina in the Proiected Cleanuo
Time Beyond 12 Years (Since the Estimated 12 Year Cleanuo Time Was
Based on the Theorv That the Flushina Effects of the Iniection Wells Would
Increase the Gradients Around the Extraction Wells and Soeed Uo the
Remediation Process). If theProoosed Wetlands Replace the Iniection Wells
For Recharge: Another factor not considered in EPA's FS is the fact that the
proposed wetlands will replace the injection wells used in the numerical
modeling conducted fQr the FS. The injection wells were simulated in the
modeling effort to shorten cleanup time. This is based on the theory that
flushing effe~ted of the treated water and the increase in gradients around
the extraction wells in high concentration areas of the a.quifer would speed
up the remediation pro.cess. The impact of using the wetlands recharge
option instea.d of injection wells is not known at this time: Howe"er, it is
likely the impact yvill be that the cleanup time using the wetlands recharge
3-26
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met~od will lengthen the cleanup time beyond the 12 years estimated using
injection wells and potentially increase the cost of the remedy. In any case,
there may be opportunity to refine the design and decrease or avoid
increasing costs by evaluating a "hot spot" cleanup scenario, customizing
the extraction well system design based on conditions after source control is
implemented, or reevaluating the location and design of the wetlands
treatment system.
Response: EPA is. aware that alterations in the basic conceptual design, including
the use of recharge wetlands versus the use of reinjection wells, may alter
cleanup times and long-term projections. As stated earlier in response to .
ADEQ's comments on impacts of pumping on the San Pedro River base flow,
EPA concurs with the need to complete a revised groundwater model for the
site.
24.
Certain Directions and Comments Provided to ANP Durino the Preparation of
ANP's FS Drafts Precluded OPtions Involving Wetlands and Aoricultural
Treatments and the Blendino of Perched Groundwater in the Brine
Concentrator to be Used for Source Control. While EPA's Contractor (Bechtel
Environmental) was Not Limited by These Constraints:
Response: EPA reconsidered various treatment technologies when EPA
revised ANP's FS report. EPA reevaluated the use of the brine concentrator
for treatment of the perched groundwater and the use of biological treatment
technologies (including constructed wetlands) for treatment of the shallow
aquifer groundwater. EPA believes that ANP and the public have benefited
from EPA's further consideration of these options.
25.
EPA's RI Report States That ANP is the Only Source of Nitrate Within the
Study Area. While the EPA FS Report States That the Pomerene Canal and
Local Septic Systems May Be Sources of Nitrate:
Response: Based on the available data, EPA believes that ANP, as a result of the
company's manufacturing of nitric acid, is the primary source of nitrate
within the study area, and, in particular, is the primary or only source nitrate
contamination on the west side of the San Pedro River. However, some low
levels of nitrate contamination in the range of 2-5 ppm can be detected in
shallow aquifer wells on the east side of the San Pedro River, in the vicinity
of St. David. These levels are consistent with the expected "background"
levels of groundwater nitrate contamination detected in any agricultural or
rural area where there are irrigation ditche~, a large number of farms applying
fertilizers to crops, and local septic systems. None of the nitrate levels
detected on the east side of the river in the vicinity of the ANP site study
area exceed the federal maximum contaminant level (MCL) of 10 ppm, with
the exception of one private well adjacent to the Pomerene Canal. In
3-27
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general, these" background" nitrate levels range from 20 to 1 00 times lower
thaI) the levels detected in wells completed in the nitrate-contaminated
shallow aquifer plume on the west side of the San Pedro River.
5.5. Comments from Border Ecology Project dated July 5, 1994.
1.
Development of a Wetlands Holds Promise as a Remediation Strateav as
Lana as Fauna, Flora (or Humans) Are Not Exposed to a Contaminated Area:
The development of a wetlands as a major component of an Apache Powder
remediation strategy appears to hold promise, assuming that the wetlands
does not, itself, become a collector of contamination nor a magnet that
attracts fauna, flora (or humans) to a contaminated area.
Response: The use of constructed wetlands to treat the nitrate contamination in
the shallow aquifer most likely will attract fauna and flora (and perhaps
humans). However, the luring of any of these species to the wetlands is not
considered to be placing any of these species at risk, with the exception of
infants if they should ingest the nitrate-contaminated water. Nitrate is the
only contaminant of concern in the shallow aquifer groundwater. There are
no metals or other organic compounds of concern that have been detected
above background in the shallow aquifer. . The only other water quality
characteristic of the shallow aquifer is a high concentration of total dissolved
solids' (TDS), primarily sulfate. The constructed wetlands should be
successful at both denitrifying and removing the nitrate, but also filtering and
reducing the TDS levels.
Nitrate, which acts as a nutrient, should enhance the growth of the flora,
which in turn should provide more habitat for the fauna. According to the
U.S. Fish and Wildlife Service, certain amphibians could be at risk from the
nitrate. Fortunately, none of these species are known to inhabit this
particular vicinity of the San Pedro River. If humans are attracted to the
constructed wetlands, the appropriate signs and/or fencing will be needed to
ensure that no one drinks water from the constructed wetlands area. .
2.
The Role of Aoache Nitrogen Products as a Maior Sino Ie Source Air Polluter
Was Not Addressed bv EPA's Proposed Plan: During the June 7
presentation by EPA and consultants at the Water Resource Center, I was
aware that the role of Apache Nitrogen Products as a major single source air
polluter was not addressed. I have not researched emissions data for these
brief comments. Suffice it to say that the visible plume at Apache --
measured by opacity -- has increased markedly, if irregularly, over the past
year or two; concurrent with an expansion in production at the plant.
Arizona Dept. of Environmental Quality (ADEQ) has issued a. revised air
pollution permit that allows this increased producHon. Part of the da~a
gathering process to develop groundwater remediation should include:
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A.
Distribution of concise forms to area residents living within 5 miles of
the plant to determine whether they feel excessive air pollution is a
problem. Anonymity should be guaranteed. . .
B.
Examination of current continuous emissions monitoring (as well as
any ambient monitoring data) for criteria and NESHAP (National
Emission Standards for Hazardous Air Pollutants) pollutants under the
1990 Clean Air Act and Arizona law to determine the potential
hazards to health and the environment.
C.
Creation of a multi-topographical air quality model to ensure that an
enforceable continuous emissions limit is established that could not
impact sensitive individuals with respiratory problems nor any flora
and fauna that grow currently or could grown in the region should a
wetlands be established.
D.
I have frequently seen a plume of smoke miles in length extending
from the plant, that is clearly not an acceptable emission. Apache, as
part of a long term remediation of groundwater strategy, should not be
permitted to aerially pollute the ecology that it is going to create while
cleaning up its past. .
Response: EPA is aware of the history of air pollution issues at the site. Because
the ADEQ is the lead agency for air emissions compliance, EPA forwarded
these recommendations to ADEQ. ADEQ has asked EPA to include the
following responses to these recommendations. For additional comments or
questions regarding air emissions compliance, please contact ADEQ at (602)
628-6738 or (602) 628-6717.
A.
Individuals are encouraged to telephone ADEQ at 628-6738 with complaints
in regard to air pollution at the ANP facility. The ADEQ Southern Regional
Office (628-6738) logs all complaints. Anonymity is permissible; however,
individuals are encouraged to be prepared to give specific descriptions, times
and dates of events. Citizens may call and register as many complaints about
a source (of air pollution) as they feel necessary. All complaints are
documented and filed at ADEQ. The complainant receives a copy of the
complaint along with the source (ANP). Response actions to the complaints
are handled by the ADEQ inspector responsible for the facility. The follow-
up inspection is done in accordance with EPA's Clean Air Act enforcement
inspection levels (levels 0-4).
Also, in 1995 as part of the Title V permit process, ANP will be undergoing
review for a Title V permit. Citizens can comment at public hearings and
meetings held in conjunction with the new permit process, on whether they
feel that source air pollution is effecting them or whether increased pollution
control is required.
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The above described complaint response protocol and inspection
methodology are standard for every major source currently permitted by
ADEQ's Air Quality Division. At thistime~ADEQ does not believe that a.
deviation from department policy is warranted for this specific .source (ANP).
However, .if new or increased air pollution- should occur, ADEQ believes that
adequate citizen input will be available through the forthcoming public
hearing process mandated in the Title V air quality permitting process.
B.
Current continuous emissions monitoring (CEM) is done and annually audited
on'the state level. Quarterly reports are submitted for review and periodic
4nspections determine source c.ompliaAce with the criteria pollutant
standards. The regulated pollutant is nitrog.en oxide (NOx) and is measured
at the stacks of nitric acid plants #3 and #4.
C.
The current permit specifically limits emissions into the atmosphere of the
contaminants nitric acid, ammonium nitrate particulate and amm'onia. In
addition the sources are subject to Arizona Air Pollution rules and the Code
of Federal Regulations (CRF 40, part 60). Conservative dispersion modeling
calculations of the maximum ground-level pollutant concentrations, due to
plant emissions, show that no ambient air quality standards (based on health
effects) should be violated. .
D.
Sighting of smoke plumes: ADEQ research shows that under normal
conditions, emissions from the plant should fall within health standards.
During the oxidation process, water sometimes reacts with n!tric acid to
generate a puff of what appears to be white smoke. Chemicals are present
only in trace amounts that pose virtually no health risk. Puffs of brown
smoke containing nitrous oxide sometimes are generated during the nitric
acid manufacturing process. The NOx is present only in trace a"mounts and
poses virtually no risk. Plant upset conditions are to be reported to ADEQ
within 24 hours; causes are investigated and trends documented.
3.
U.S. Taxpaver Should Not Pay for the Apache Cleanup Costs: The Arizona
or U.S. taxpayer should not be required to pay for any of the cost of
Apache's cleanup -- from monitoring to control.
Response: Consistent with EPA's approach at Superfund sites nationwide, EPA
intends to seek cost recovery from ANP for all costs incurred by EPA to
oversee or conduct any response actions at the site. EPA also will negotiate
with ANP or, if necessary, take enforcement actions to have ANP perform
the work required by the ROD. A central feature of Superfund is that those
who caused or contributed to the contamination are responsible for the costs
of investigation and cleanup.
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5.6.
1.
Comments from Julie Stromberg, Assistant Research Professor, Arizona
State University, Center for Environmental Studies
Be ~areful In Considering the Idea of Constructed Wetlands: First of all, I
would be very careful in considering the idea of constructed wetlands,
particularly if they are to accomplish the dual purposes of nitrate reduction
and habitat creation. Dr. Joy Zedler of San Diego State, and others, have
done much work assessing the functioning of constructed wetlands, and
found that despite aU good intentions they genera.lly do not function near the
level of their natural counterparts and do not have long-term sustainability.
It is true that cienegas are a rare ecosystem type in the Southwest, but it
al50 has not been demonstrated that we know how to recreate them,
especially when we are trying to achieve water purification as a main goal.
Response: EPA appreciates your comments and realizes that combining the goals
of treatment of nitrate-contaminated groundwater and habitat creation would
require careful planning and execution. In regards to the success of
constructed wetlands, a recent EPA study completed in August 1993,
"Habitat Quality Assessment of Two Wetland Treatment Systems in the Arid
West: A Pilot Study", was designed primarily to examine methods and the
usefulness of various wetland indicators for assessing the habitat quality of
six wetlands treatment systems (WTS), constructed for treating municipal
wastewater in the United States. This report focused on two of these sites,
located in Show low, Arizona, and Carson Valley, Nevada. A comparison of
various wetland indicator values (e.g., vegetation, invertebrates, site
morphology, birds) concluded that most indicator values from these two
WTS were within the range of non-WTS (natural systems), and that the
density and richness of bird species were above the range of values for non-
WTS. Preliminary results of the two WTS studied indicated that the habitat
condition is comparable with that of non-WTS in this arid region. A copy of
this report will be made available for public review at the information
repository in the Benson library.
2.
However, to clarify EPA's proposal, the initial or primary treatment would
occur in a series of lined, highly managed constructed wetlands ponds with
a primary objective to denitrify by an estimated reduction of 70% the nitrate-
contaminated influent. The establishment of habitat for species (under more
cienega-like conditions) would be a component of the secondary stage
"leaky" or recharge wetlands, where the previously treated influent nitrate
levels should be much lower than at the primary stage. The creation of
these "cienega-type" wetlands would be treated as a pilot and, depending on
the final siting location for the secondary stage recharge wetlands, mayor
may not be feasible.
Wetland Construction Would Result in loss of Water (That Currentlv
Sustains Riparian Veqetation) From the Floodplain Aauifer: Wetland
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construction would result in loss of water from the floodplain aquifer, water
- that currently sustains existing ~iparian vegetation. A careful water budget
for all' proposed methods should be prepared so that potential loss of riparian
vegetation can be'determined: The benefits from the constructed wetland
vegetation can then be weighted against the 1055 of riparian floodplain
vegetation. This analysis might 'reveal the denitrificatio[l tanks (no
Evaporation-Transpiration (ET)) to 'be a'desirable option.
Response: EPA is aware of the water balance issue, especially in this particular
area of the San Pedro River that is located in close proximity to the San
Pedro River National Conservation Area established by Congress to protect'
riparian resources. Groundwater modeling is planned for the initial stages of
remedial design to ascertain the impacts of various pumping options and
extraction locations on the base flow in the San Pedro River. See EPA's
response to ADEQ's comment #8 (p.3-10) and ADWR's comment #2 (p.3-
11 ).
3,.
Recommend Waitina Before Commencina Any Treatment Since Natural Rates
of Nitrate Reduction. In the Absence of New Discharge. May Be More RaDid
Than Are Presently Predicted: Before making a decision regarding the water
purification treatment, be it constructed wetlands or denitrification tanks, I
would suggest waiting a couple of years after the time when discharge of
nitrates to the shallow aquifer ceases. If my question was answered
correctly, then the numbers were calculated based on the assumption that
"natura'" purification would occur solely by physical processes (Le., dilution,
etc.). Biological processes were ignored, and could be substantial. We have
been conducting some studies on the effluent dominated Santa Cruz River,
and these studies suggest that the cottonwood-dominated floodplain can
help to remove the nitrates, through direct uptake and enhanced growth
rates (also found by Dr. Karpiscak of the Office of Arid Lands Studies at the
University of Arizona), as well as by providing an environment for bacterial
activity. The point of this is that natural rate of reduction. in the absence of
new discharge, may be more rapid than are presently predicted; this in turn
may mean that less water-intensive or less costly treatment are in order. I
know that people want action now, but given that this problem has been
around decades, another year or two of data collection should not be an
unreasonable request.
Response: EPA recognizes that once ANP's process wastewater discharge is
ceased_and the extracted perched groundwater begins to be processed
through the brine concentrator (estimated to be on-line by April 1995), there
could be alteration to the current characteristics of the nitrate-contaminated
shallow aquifer . Additionally, dilution plus the contribution of the biological
processes already available in the existing San Pedro River Basin may
contribute to reduced levels of nitrate in a more timely manner than currently
predicted. In response to these possibilities, very focused monitoring of the
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shallow aquifer is planned as soon as the brine concentrator commences
operation. See EPA's response'to ANP's comment #22 (p.3-26) for a more
detailed response. , " .
5.6. Comments/Questions from Private Citizens - Grouped by Category
NOTE: The written comment letters, received during the thirty-day public
comment period of June 22 - July 25, 1994, are included in the
administrative record. In addition; the oral questions and comments,
received by EPA from private citizens at the July 6, 1994 public meeting, are
included in the written transcript, which also is part of the administrative
record located in the information repository in the Benson Library.
ANP's History of Environmental Problems
1.
Apache Powder Has Willfullv Created Manv Serious Environmental' Problems
and Has Not Reduced the Harmful Effects. Resultino In the R.esidents Being
the Victims of Apache's Misuse of the Environment: Several community
members expressed anger at ANP's actions to date, as summarized below:
A.
It is our feeling that Apache Powder Company has made little effort to
do the necessary clean up or pay for the' extensive damage they have
done in the St. David area. Contamination has continued during the
whole Superfund study. This is clear evidence to us of a very
calloused attitude. Talk and promises sound good, however the token
fine assessed by the State of Arizona is hard evidence that they have
little fear of being forced to deal fairly in resolving these problems,
now or ever.
B.
Apache Powder is the offender. They caused the problem. They
should pay fully for the cleanup. They'should be forced to place fail-
proof processes into operation. They should be monitored in every
phase of their future manufacturing processes. Their previous.
performance clearly shows that nothing should be left to "good faith"
performances on their part.
C.
Apache Powder must be closely monitored. These people are not
good neighbors and will circumvent requirements to save costs. How
long have health officials known that nitrates are harmful? If Apache
Powder is such a good community citizen, why didn't they act on
their own to reduce known harmful effects on the public? As you
may feel from my expressions, ('m very concerned and I'm very angry
at Apache Powder. They have raped the environment and they
continue to do so and will continue in the future if someone doesn't
monitor them closely.
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Response: EPA is 'aware of a high level of distrust among certain members of the
community regarding ANP's past practices and commitment to clean up the
site. As discussed in EPA's respo'nse to comment #3 (p.3-30) of the Border
Ecology Project" EPA ~onsiders ANPto be the responsible party for the
contamination and the cleanup. EPA expects ANP to fulfiH its responsibilities'
to both reimburse EP~ for costs already incurred and to perform remedial
work, and will aggressively use its statutory powers if ANP does not comply
voluntarily. These powers include ordering ANP to perform remedial work,
with penalties for non-compliance. EPA is encouraged by ANP's recent
commitment in a consent decree to undertake work for the State, and EPA
has confidence that the State will strictly oversee that work.
Expenses Incurred by Landowners to Dr;1I Deep Wells
Concerns Regardinq Deee Aquifer Wells: Several community members
expressed concerns about ANP's drilling of deep aquifer wells as
replacements for shallow aquifer wells contaminated by ANP's operations.
These concerns include the expenses incurred by landowners for drilling their
own deep wells, the effects of the new wells on the level of the deep
aquifer, and the option of city water rather than deep wells. These
comments are summarized below:
2.
A.
What will EPA do to help an owner of a parcel just around the corner
from Apache Powder, who has steadily improved the property and
saved money to drill a shallow aquifer well and then discovers that he
will have to drill a much deeper well because of the contaminated
groundwater?
8.
I was forced to drill a deep artesian well in order to assure myself of
nitrate-free water. This was a great expense to me because of the
high probability of contaminated groundwater. I would have preferred
the cheaper cost of drilling for (shallow aquifer) ground water, but was
unable to gamble on nitrate-free water in case the (shallow aquifer)
ground water was contaminated.
C.'~
Should Apache Powder continue the project of drilling deep wells for a
select few property owners, they should also be required to pay for all
additional operational costs this drilling causes to those with existing
domestic deep wells.
D.
We continue to express our disagreement on this item. There are two
problems we see with this decision. Ffrst, it is discriminatory in that it
does not treat all affected property owners equally. Other families
have previously drilled wells to provide their families with usable
domestic water. If there is to be a program of providing deep water
3-34
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wells for some families, there should be payment for all privately
drilled domestic wells in the Superfund area.
Effects of New Wells on the Level of the Deep Aquifer
E.
Stop Apache's discriminating drilling into the deep aquifer. It's
lowering the deep aquifer now! My artesian well's static level drops
each time' another well is drilled. I'm being punished with reduced
flow and increased pumping costs because Apache Powder polluted
the ground water. I hold Apache Powder and those who forced this
decision on them responsible. This was a very short-sighted solu'tion
for a few house holds. How does it help future landowners who may
have valid claims against Apache Powder? How does it help me when
I had to drill into the deep aquifer at my expense to get pollution-free
water?
F.
One possible solution to make up for the added (deep aquifer) wells
they propose to drill would be a Record of Decision measure by EPA
to require them to reuse their treated water in an amount equal to, or
greater than, that which will be pumped from all drilled deep domestic
wells. If the treated water is as pure as it has been reported to be,
Apache Powder could greatly reduce the daily pumping from their
deep wells by using treated water in their manufacturing processes.
By so doing they would protect the current deep well water level.
G.
Second, with the drilling of each well, the deep water table drops'.
The Carnes deep well for example, with the related pumping
associated with purging that well, caused well owners to experience a
lowering of the water level in their deep wells. Heretofore, each has
had domestic water,in a free-flowing form. With the drilling of several
such wells, we will likely lose the free flow and be forced to make
extra expenditures to purchase pumps for our wells. This will also
require us to pay monthly utility charges to deliver our water to our
homes.
Option of City Water Rather Than Deep Wells
H.
There were and are now other solutions. The extension of the St.
David water system, at the expense of Apache Powder, is the best
solution. It would benefit those whose wells are now polluted, those
in the future whose wells become polluted, and it would provide for
growth. New customers should be charged in lieu of construction
cost which could be rebated to Apache Powder. That way Apache
Powder could recover some of their costs. How much will they
recover from continued deep well drilling costs now?
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I.
Our recommendation is to stop all this discriminatory drilling of the
deep wells immediately~' 'In exchange for wells, provide city water to
each affected househotd in the Superfund area. This extension of the
St. David water system should be paid for by Apache Powder. In
addition, they should pay all monthly service fees for enough water to
meet normal domestic needs. This charge should continue until such
time as the surface water becomes clear of all the contaminants' .
Apache Powder has deliberately injected into it over the years. While
some argue that private drilling will eventually do the same damage to
deep well owners as the current Apache Powder drilling, it should be
pointed out that one is free enterprise and the other is an unjust
imposition upon non-offending neighbors by a company which has
been judged to be in violation of environmental law.
Response: Community members are understandably concerned about the many,
ramifications of new deep aquifer drilling. EPA has been attempting to work
with the community and ANP to protect public health within EPA's
regulatory authority. In 1989, EPA required ANP to supply bottled water to
households that were using contamin'ated shallow wells for drinking water.
In 1994, ANP began installing deep aquifer replacement wells for those
households on bottled water. This plan was not discriminatory because
EPA's mandate was to protect the health of those relying on contaminated
water, which does not extend to households that already had potable water.
In approving the Alternative Domestic Water Supply Plan (ADWSP), EPA '
considered the option of city water. EPA ultimately approved deep wells
based on the preferences of the households on bottled water.
EPA recognizes that future population growth, including the need for potable
water, will continue to be a concern. Resolution of these issues will require
discussions among landowners, 'ANP, and local officials, including the 5t.
David water system operators. EPA will, to the extent practicable, facilitate
such discussions and will perform other actions as necessary to protect
public health.
EPA further recognizes that some landowners have incurred or may in the
future incur expenses in drilling their own wells, or expenses by virtue of the
lowering of the deep aquifer. Generally, EPA does not have the authority to
intercede in disputes between private parties regarding alleged damages to
property. EPA's authority and its priorities, are to protect public health and
the environment by cleaning up the shallow aquifer and ensuring safe water
to those who have relied on the contaminated shallow aquifer.
Regarding ANP's use of deep wells for its operations, EPA expects this to
reduce dramatically once the brine concentrator goes on-line in April 1995.
ANP currently withdraws approximately 135 gallons per minute (gpm) from
the deep aquifer. In the future, only "make-up" water is expected to be
3-36
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3.
withdrawn, since all the treated wastewater will be recycled into ANP's plant
operations. .
. .
Impact of Pumping on Base F!ow of the San Pedro River (ShC!lIow Aquifer
and Surface Water)
Shallow Aquifer PumoinQ as a Cleanup Measure. Several comments.
expressed concern regarding the impact of pumping on the shallow aquifer
and the surface water. These comments are summarized below:
A.
We feel strongly that no decision by EPA should call for heavy
pumping of surface water as part of the clean up process. Secretary
of Interior Bruce Babbit recently commented on the dropping water
table in the San Pedro Basin and expressed concern about how to
resolve the matter. He felt that the problem was so severe that it
merits extension of the CAP canal system to Sierra Vista. It is far
better to stop all contamination of the ground water and then do
follow up studies to determine what kind of surface water clean up
will take place naturally.
B.
The wetlands decision is a very costly solution with unknown
consequences on the ground water level. There most .Iikely will be a
lowering of the water table causing users additional. pumping costs.
Many more people may be affected. The San Pedro River is a
beautiful and precious resource and hasty decisions may adversely
affect it. Who would want to be responsible for damaging it because
of hasty decisions? Defer your decision for a period of five years.
Continue to monitor pollutants in existing wells and test wells. Please
don't be in a hurry to spend money and take unknown risks.
Response: EPA concurs that additional studies will need to be conducted to
determine the impact of the remedy on the shallow aquifer and the base flow
of the San Pedro River. Final decisions on the location of extraction wells
and pumping rates, including whether certain areas are "self-cleansing", will
not be made until these studies are completed.
However, in regards to wetlands being a cause of groundwater loss, any
treatment alternative (other than no action) will require extraction, treatment,
and !.echarge or reinjection of the groundwater, and as a result, some water
loss. With wetlands, one would have optimum flexibility to pump at various
rates or not to pump at all and hold the water in the wetlands (if necessary
due to storm conditions or other circumstances). Additionally, when
compared to other nitrate treatment alternatives, constructed wetlands are a
less expensive alternative both in terms of initial capital costs and long-term
operations and maintenance costs than all other applicable treatment
technologies.
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See EPA's responses to ADEQ's comment #8 (p.3-10), ADWR's comment
#2 (p.3-11), ANP's comments #6 (p.3-14), #21 (p.3-25), and #22 (p.3-26),
and the Center for Environmental Studies, Arizona State Uni'!ersity's
commerit #2 (p.3-3.1), for additional details. .
Use of Constructed Wetlands to Treat the StJallow Aquifer
4.
Wetlands ProDosal for Shallow Aauifer Clean-uD. We have two major
problems with the wetlands conc~pt. First is the. increased well owner costs
in pumping water from a lowered water table. This, in effect, transfers
cleanup costs from Apache Powder to every well owner in this portion of the
San Pedro Basin. Second, we are very concerned about federal funds paying
for a project on private land. Here we have the tax payers paying a major
portion of the cleanup costs and Apache Powder continues to pollute at
taxpayers' expense. The proposed wetlands would very likely be unavailable
to the public for park purposes, as it would be on Apache Powder property.
Response: As stated in EPA's responses to the citizens' comments included under
#2 (p.3-34) above, the lowering of the water table due to additional wells
being installed into the deep aquifer and any consequent additional pumping
costs to adjacent well owners is a private party issue that is generally
outside the scope of EPA's authority.
Regarding federal funds being spent at the taxpayer's expense, EPA will seek
cost recovery from ANP for all costs incurred by EPA to oversee or conduct.
any response actions at the site. EPA also will negotiate with ANP or, if
necessary, take enforcement actions to have ANP perform the work required
by the ROD.
In response to an interest in public access to the wetlands, during the
remedial design phase the final siting location will be determined. Although
the primary focus will be on selecting a location where treatment can occur
safely and cost-effectively, consideration will be given to siting the
secondary phase recharge wetlands in a location available to the public for
viewing.
5.
Excellent Idea to Construct Wetlands: Excellent idea to construct artificial
wetlands for the shallow aquifer remediation, as constructed wetlands are
very effective in treatment of contaminated water.
Response: Thank you for the comment.
6.
Does This Process (Constructed Wetlands) Take Lots of Water?
Response: The use of constructed wetlands is a treatment technology (a biological
treatment technology) similar to the use of reverse osmosis or electrodialysis
3-38
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reversal (physical treatment technologies), which can be used to treat
wastewater. . It takes no more .or less water than any other treatment
technology. The amount of water treated by the ~echnology is dependent on
the extraction rate. ANP's consultant (Hargis & Associates) estimated in
1992 that approximately 720 gpm should be extracted from the shallow
aquifer to treat the nitrate-contamination by reverse osmosis. This
calculation will need to be updated based on new aquifer tests and revised
groundwater modeling.
EPA does anticipate some net loss of water. through evaporation. Water loss
in a wetlands can be due to two factors: infiltration through the bottom and
evaporation-transpiration (ET) off the surface. Both of these factors are a
function of the surface area given a constant flow rate. The primary
wetlands will be lined with a liner to not allow any infiltration loss. The ET
losses will vary with the growing season, the relative humidity, the
temperature, and the wind speed. Generally, this is about equal to the open
water evaporation loss in the region.
7.
What is the Dailv Water Reauirement (for the Constructed Wetlands)?
Response: See EPA's response to citizen comment #6 above (p.3-3B).
B.
Where Will Aoache Get The Water (for the Constructed Wetlands)?
Response: The water to be treated in the constructed wetlands would be .
extracted from the area of the nitrate-contaminated plume in the shallow
aquifer. See Figure 2 on page 2 of EPA's Proposed Plan, dated June 22,
1994.
9.
Who Will Bear The Cost of This Exoerimentation (Constructed Wetlands)?
Response: ANP is responsible for the cleanup costs for treating the nitrate-
contaminated shallow aquifer plume.
10.
Where Does Aoache Plan to Do This Exoerimentation (Constructed
Wetlands) ?
Response: The exact siting of the constructed wetlands will not be determined
until the RD stage. However, at this point in time, EPA anticipates that the
wetlands will be sited on property owned and operated by ANP.
11 .
What Facts Provide Assurance That the Contaminants Will Not Be
Transferred to Another Area and Conseauentlv Nothina Gets Handled?
Response: Based on the literature and studies of currently operating wetlands, it is
anticipated that constructed wetlands will be quite efficient at removing
nitrate, the one contaminant of concern, from the shallow aquifer'
3-39
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groundwater. The contaminated water will be pumped from the shallow
aquifer and piped to the constFucted wetlands with a well extraction system
similar to the type of sys1ems used for any other treatment technology. . The
primary treatment wetlands will be lined with a .syn.thetic liner to prevent
recharge of untreated' water. See EPA's response to citizen comment #6
(p.3-38) above. .
12.
Provide a List of ODe rations and Their Duration in Other States That Have
Done This ExDerimentation (Constructed Wetlands) With Organic
Contaminants With No ComDlaints?
Response: An EPA paper published in September 19.92, entitled "Con"Structed
Wetland Design -- The First Generation", inventoried 150 constructed
wetlands systems for the treatment of municipal and industrial wastewaters
in the United States. The paper summarizes some of the results from the
inventory, including: location, type, vegetation, design flow, loading rates,
and costs for wetlands systems, where available. A copy of this paper will
be made available for public review at the information repository in the
Benson Library.
Some of the inventoried wetlands systems for municipal and industrial
wastewaters described in this publication may be treating organic
contaminants mixed in with domestic wastewater.. However, fortunately in
the case of the ANP site, there are no organic contaminants in the shallow
aquifer groundwater. Because the contamination is singularly composed of
nitrate, a wetlands systems for the Apache site would be designed for
treating nitrate only.
Another EPA publication, "Report on the Use of Wetlands for Municipal
Wastewater Treatment and Disposal", dated October 1987, also will be
placed in the information repository. This report discusses the use of both
natural and constructed wetlands for municipal wastewater treatment and
disposal. A list of technical references also is included.
Use of Brine Concentrator to Treat the Perched Groundwater
13.
Brine Concentrator is a Good Solution for the Perched Water. Several
. community members commented that the use of forced evaporation (a brine
concentrator) for treating the perched groundwater was a good choice, as
long as it was monitored for compliance. These comments are summarized
below:
A.
The brine concentrator is a good solution to clean up the perched
water and to reduce deep water pumping by Apache Powder.
,
( ,.
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B.
We fully support this recommendation. We cautiously point out,
however, that it is just a turn of a valve to continue to dump
contaminated water into unlined ponds instead of the flqw of properly
treated environmentally safe water. We needed to hear that failure of
the process would close down the plant. . We also need to hear about
the necessary enforcement to cause this to be practice, not just
promise.
Response: As stated under EPA's respon~e to the citizen comments included
under #1 (p.3-31) above, EPA intends to monitor ANP's cleanup activities
covered under the ROD.
14.
Use of Agricultural Irrigation to Treat the Shallow Aquifer
Leaching Contaminants From the Surface Water bv PumoinQ It Onto Private
Land. This is a move in the wrong direction for many reasons. This option
creates even more problems. There will be an even greater lowering of the
water table, as very little of the irrigation water will return to the surface
water reserves. The cost of pumping will increase for everyone. It might
also provide a screen for Apache Powder to continue their polluting
processes.
Response: Improper management of agricultural irrigation could result in the
recycling of the contamination back into the shallow aquifer. See EPA's
response to ADEQ's comment #7 (p.3-9). EPA believes that additional
studies need to be conducted during the first phase of remedial design to
determine if agricultural irrigation is technically feasible and impJementabJe as
part of the remedy. See EPA's responses to ADEQ's comments #5 (p.3-9)
and #6 (p.3-9).
15.
Farmers Have Interest in UsinQ Shallow Aquifer Groundwater With Nitrate
Contamination on Their GrowinQ Grasses and Use of Nitrate-Contaminated
Water Could Offset Current Pumoinq. I have two good artesian wells on my
property that are near Escalante Crossing which have flowed since we
bought the property about 20 years ago, and have several 3 to 5 foot
diameter cottonwood trees near them which make me think the old artesian
wells have flowed for maybe 100 years. I am not sure of the exact date,
but both of these wells quit flowing about 3 to 6 months ago.
Over the past years, I have read articles in the newspapers, and heard talks
that the water table in the Sierra Vista - Fort Huachuca area is going down
and there is a cone of depression in the water table in this area. This makes
me think that water from this area that in past years flowed toward the St.
David area, either underground, or in the, "perennial" river may no long
come.
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.....-...-'. ..- .... .
In today's Tucson newspaper, the Arizona Daily Star, under precipitation it
states: normal to date is 3.11.ihches, actual to date is 3.01 inches, and
normal annual rainfall is 12.0 inches. Tucson may not be St. David, but this
whole part of the ~tate is a desert and we should conserve what water we
have. .
Therefore, for the above reasons and other similar information, I think
constructed wetlands will be too much of a water waste for here. I have
talked to five of six farmers .- ranchers in the area that either adjoin, or are
close to Apache's property, and they all showed interest in using some of
the shallow aquifer groundwater with nitrate contamination .on their growing
grasses and any water received from Apache would allow them to not pump
an equal amount.
Response: EPA is aware 01 the interest in agricultural irrigation on the part 01
certain members 01 the community as an alternative to the use of
constructed wetlands to treat the nitrate-contaminated shallow aquifer
groundwater plume at the ANP site. As stated in EPA's responses to
ADEQ's comment #5 (p.3-9) and ANP's comment #9 (p.3-16), agricultural
irrigation will be evaluated during RD as a secondary treatment and/or end
use option.
16.
Aoricultural Irrioation ProDosal Submitted bv Community Member. At the
public meeting in St. David on July 6th about the Apache Powder Superfund
site it was suggested by several officials that I write a letter explaining my
suggestions further. I am no expert on this subject, but hope the names,
addresses, acres, and costs are approximately correct.
For costs, I am using pages E-23 to E-27 in the Volume 4 Notebook (EPA's
Feasibility Study) in the Benson Library... I would like to suggest that you go
directly from several of these (extraction) wells to farmers' fields, and maybe.
make another extraction well as they are only $24,750 each, so you can cut
your (piping) sizes to 4" or 6", and cut the total 33,000 feet (for the
treatment system piping).
On page E-25 you itemize the costs to build two 9.0 acre ponds, which adds
up to $2,226,000 and two 4.5 acre secondary ponds, which will cost
$320,000. The total to build these ponds is $2,546,000, which you do not
need to spend if you put the water on fields growing crops. (In this total
you have 18 acres, plus 9 acres worth of plants at $8,000 per acre, which
you will not have to spend because each farmer will have his fields
planted.)...
My well pumps about 200 gpm and I irrigate about two acres at a time,
using furrow irrigation, so I suppose that 720 gpm would irrigate about
seven acres at a time using flood or furrow irrigation. But for people with
sprinklers this could be different. But in any case, we would mostly be using
3-42
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the same amount of water in the same way as we do now, so there would
be 27 acres that we would be-saving the evaporation from...
I would suggest anytime there is rain that the wells be turned off. Because
if a 1 inch rain were to occur while irrigating, there is a good chance that the
nitrate water could go off of the property, it was intended to irrigate...
..
Dr. Gearheart, from Arcata, California, was one of the speakers at the July
6th meeting. After the meeting, he was kind enough to give me a paper on
which he had figured the number of acres necessary to handle the nitrogen
load at the 720 gpm and the 300 pounds of nitrogen per acre that I had
mentioned during the meeting. At 300 ppm, the 720 gpm produces 2,600
pounds of nitrogen per day. This means one needs 8.6 acres per day, or a
total of 3,000 acres.
Paul Brick, a San Pedro NRCD (Natural Resources Conservation District)
member talked to Dave Matthews, who is the District Conservationist for the
Soil Conservation Service. Dave felt that most crops in this area only need
200 pounds of nitrogen per acre, and he figured at 200 ppm, one would only
require about 4 inches of water to get the 200 Ib/acre. At 200 gpm, one
needs 884 acres total. .
Below are some names and addresses of some people that I know are near
ANP and would like to cooperate to conserve water in this area.
Response: EPA will review the suggestions in your proposal in conjunction with.
evaluating agricultural irrigation as a treatment option either for secondary
treatment or as an end use. See EPA's responses to ADEQ's comment #5
(p.3-9) and ANP's comment #9 (p.3-16) for further details.
Cleanup of Contaminated Soils
17.
Cleanup of Buried Wastes. We are in complete agreement with the proposed
soils removal in areas of dumping of solid wastes. We recommend extensive
testing of their property with metal detectors as well as chemical detection
equipment to make certain that every solid waste dump site has been
discovered. Then EPA should enforce the cleanup of all buried materials
located on their property. It is our impression, which has been reinforced by
other local witnesses, that the company still operates on a basis "if it is not
seen, it is not a serious environmental problem".
Response: EPA will be overseeing the cleanup of the contaminated soils during the
remedial action. During the remedial design phase EPA will be incorporating
the advice of technical experts on the appropriate level of sampling and
monitoring required to ensure that the three areas of soils contamination are
cleaned up as required in the ROD. EPA's efforts, combined with the soils
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characterization requirements in the State's Consent Decree, will greatly
assist in the discovery and identification of any previously unkn<1Wn areas of
contamination. .
Cost of Remedy
18.
Cost of Remedv: The cost of the remedy seems very high. Can this cost be
brought down?
Response: When the total cost is broken down into its five sub-component costs,
an estimated $2.3 million is for cleanup of the perched groundwater, an
estimated $2.6 million is for soils cleanup, and the remainder of $16.2
million is for constructed wetlands to clean up the shallow aquifer. The
component with most potential for cost-savings is the constructed wetlands
alternative for cleanup of the shallow aquifer. The costs for the shallow
aquifer cleanup were based on the assumption that 720 gallons per minute
(gpm) would be pumped from three extraction wells and would be piped over
certain distances. During the .initial stages of remedial design, EPA will
require additional groundwater modeling and aquifer testing studies to refine
this conceptual model to account for seasonal fluctuations in demand and
the ability to maintain recharge at certain rates. In addition, the design will
include evaluating the optimum siting location for the wetlands. - Data
gathered and analyzed during these studies may help reduce costs. EPA also
will be overseeing the analysis of the potential use of agricultural irrigation to
determine if additional cost savings can be attained by adding this
component either as secondary treatment or as end use of the treated water.
Status of ANP's Current Operations and Cleanup Activities/Future Monitoring
19.
Give a Current Update of ANP's Operation. Including: (a) Expansion of the
Plant: (b) Names of Products Beinq Produced; (c) Condition of ANP's
Equipment: (d) Ash Disposal and Burn Area; (e) Drum Storaqe: and (f) Status
of Compliance with EPA's Remedial Projects.
Response: Because the Arizona Department of Environmental Quality (ADEQ) is
the lead agency for overseeing ANP's active day-to-day operations, EPA
forwarded your question to ADEQ. The following responses are based on
the information provided by ADEQ. For additional information or questions
regarding the status of ANP's active operations addressed in the responses
to questions (a) through (d) below, please contact ADEQ at (602) 207-4191.
(a)
ANP has been expanding its production of nitric acid and ammonium
nitrate based products, and currently is closing down its
manufacturing of commercial explosive products. ANP currently is
recommissioning a second nitric acid plant, referred to as Ammonium
3-44
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(b)
(c)
20..
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Oxidation Plant #3 (AOP #3). AOP #3 is scheduled to be in full
service in the fall of 1994.
The products currently being produced by ANP are nitric acid, solid
and liquid ammonium nitrate, blasting agents, and nitrogeneous
fertilizer. ANP also distribute,s explosives materials to mining
companies.
ANP has been in operation since 1922. However, the equipment and
structures currently in use date from the late 1970's. Older ,historic
areas of plant operations are closed or are in the process of being shut
down. Some of the corresponding equipment is being dismantled and
salvaged. Given the corrosive nature of the products manufactured at
the plant, operating equipment requires continual maintenance.
(d)
The Ash and Burn Area located in Wash 3 will be closed and
remediated under the State's CD. ANP has had interim status under
the Resource Conservation and Recovery Act (RCRA) for treatment of
explosive wastes in this area. The Ash and Burn' Area, also known as
the Open Burn/Open Detonation (OB/OD) Area, currently is undergoing
closure review by ADEQ under its RCRA program authority.
(e)
The Drum Storage Area will be cleaned up in conjunction with the
other areas of historical soils contamination identified in EPA's ROD.
The area currently is used for the storage of drums containing
vanadium pentoxide and storage of some nitrate-contaminated soils.
During the remedial action under this ROD, these contaminated
materials will be removed and treated off-site, prior to disposal. After
removal of these materials, the Drum Storage Area will be resampled
to ensure that the cleanup standards established in the ROD are met.
(f)
ANP completed a remedial investigation (RI) report and a feasibiity
study (FS) report for the site. However, as stated in EPA's FS report,
issued in June 1994, EPA determined ANP's RI and FS reports to be
incomplete because of unresolved technical differences, missing data,
and new information. See EPA's response to ANP's comment #14
(p.3-19).
What Are The Boundaries (North, South. East, and West) in St. David and
Benson of the Contaminated Perched Groundwater and the Shallow Aauifer
Groundwater Plume?
Response: The general boundaries of both the perched groundwater and the
shallow aquifer plume are shown on Figure 2 on page 2 of EPA's Proposed
Plan, dated June 1994. However, as stated at the public meeting held on
July 6, 1994 in 5t. David, additional data will be gathered during the first
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phase of remedial design to further define these boundaries. See EPA's
response, to ANP's comments #16 (p.3-21), #17 (p.3-22), and #18 (p.3-23).
21.
Which Ponds Are Unlined of the Following List: 1 A. 1 B. 2A. 2B. 6B. 7.
Dynagel. and Siudae? '
Response: All of these ponds are unlined. During ANP's cleanup activities under
EPA's ROD and the State's CD, all of the active and inactive evaporation
ponds, will be close'd and covered with a clay cap. The capped ponds will be
monitored in the future to ensure the integrity of the caps.
22.
What Action Will Aeache Take to Clean Ue Ponds 2A and 2B. Which
Contain Most of the Metal Contaminants? .
Response: Ponds 2A and 2B are addressed under the State's CD for final cleanup
, and closure. Based on discussions between EPA and the State, the capping
of the active ponds, including Ponds 2A and 2B, will be completed in a
manner similar to the capping of the historical inactive ponds covered under
EPA's -ROD. The caps will restrict direct contact and eliminate potential
exposure to the contaminated soils left in place in the ponds.
23.
Will a Different Tyee of Cleanue Procedure Be Reauired for Pond 7. Where a
Lot of Nitrate-Nitrogen Was Found?
Response: No, all of the inactive ponds will be capped in a similar manner, with
the contaminated s,oils and sediments left in place. The clay caps will be
monitored as part of a long-term operations and maintenance plan to ensure
that rainwater does not migrate through the cap and cause any further
migration of contaminants.
Geology of the St. David Clay Formation
24.
What Documented Data Backs Ue That the St. David Clay is 400 Feet Thick
and Imeermeable? .
Response: Data obtained from the drilling logs for local wells indicate that the St.
David clay is hundreds of feet thick in the Middle San Pedro Basin, including
the St. David area. Permeability tests conducted by Hargis and Associates
indicate that the St. David clay has' an extremely low vertical permeability
(-10.8em/see). For additional information on the stratigraphy of the area
around the ANP site, please refer to ANP's RI and hydrogeological reports
and EPA's RI report in the information repository in the Benson library.
25.
Are the Different Tyees of Soils and Stratums In and Around 51. David Part
of This 400 Foot (St. David Clay) Or Is This In Reference to the Land
(Subsurface Geology) Around the Aeache Plant?
3-46
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Response: The St. David clay is a distinct geologic unit.
26.
How Far Below The Surface Does the Impermeable Clay BeQin?
Response: The subsurface geology of the area around the ANP site is comprised of
alluvial deposits at or near the surface adjacent to the San Pedro River, with
the St. David clay underlying these deposits at levels ranging from 10 to
more than 300 feet (Gray, 1965).
27.
Have Tests Been Done For Contaminants Below the Impermeable Clay? If
So. Please Provide the Findings.
Response: Groundwater sampling from the deep aquifer, which is located beneath
the St. David Formation at depths greater than 300 feet, has been
/ conducted by both EPA as part of the Preliminary Investigation (PI) and by
ANP as part of the RI. The sampling results detected elevated levels of
naturally-occurring fluoride, strontium, and arsenic. None of the
contaminants associated with ANP's explosives manufacturing processes
have been detected in the deep aquifer.
28.
What Type of Clay is Found in the St. David (Formation). Dry or Wet?
Response: The moisture content of the St. David clay is spatially variable. Details
of the variability have not been characterized. Clays, by their natlJre, tend to
retain relatively significant amounts of moisture relative to other lithologies,
such as silts, sands, and gravels.
29.
Do FreQuent Earth Vibrations by the Use of Heavy EQuipment Over a Period
of Time Create Cracks or Fractures In Any Type of Clay?
Response: It is not known whether the use of heavy equipment over a period of
time will create cracks or fractures in any type of clay, withOut specific
studies being complet~d. It is very unlikely that heavy equipment would
fracture the St. David clay, due to its plasticity and the lithostatic pressures
it is subjected to at greater depths. Any cracking would only occur locally at
the ground surface in areas where the clay may be dry.
30.
Does Dry Clay Have Desiccated Cracks or Fractures?
Response: Dry clay may crack due to shrinkage associated with moisture loss.
31.
What is the Composition or the Properties of the St. David Clay?
Response: The Upper St. David Formation consists primarily of lacustrine
unconsolidated and consolidated red and brown clays and silts.
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32.
Constructed Wetlands for Treatina MuniciDal Wastewater or Other Inoraanic
or Oraanic ComDounds (Not Detected in the Shallow Groundwater at the
ANP Site): .
The following questions are asked in reference to the booklet, "A Natural.
System for Wastewater Reclamation and Resource Enhancement, Arcata,
California", which was distributed at a te'chnical meeting held in Tucson,
Arizona on June 7, 1994. (A copy of the booklet will be made available for
public review at the information repository in the Benson library.) The
booklet describes the seven basic components of Arcata's present
wastewater treatment plant. These components are the headworks, primary
clarification, solids handling, oxidation pond, treatment ~arshes,
enhancement marshes, and disinfection. Two of these components are
constructed freshwater wetlands which receive partially treated wastewater
for further treatment by marsh plants, soils and their associated
microorganisms. The wetlands components are a cost-effective system that
further treat the wastewaters, enhance the receiving water, and provide a
wetland ecosystem and habitat for fish, shorebirds, waterfowl, raptors and
migratory birds.
Please note that the Arcata wastewater treatment system is not a
comparable system to the selected constructed wetlands treatment system
for the ANP site. The ANP wetlands system will be designed to remove only
nitrate, not the numerous compounds and constituents (sewage, gray water,
storm water runoff, etc.) found in municipal wastewater. The Arcata
wetlands system was used as an example in an EPA technical meeting held
in June 1994 for the following purposes: (1) to illustrate what a constructed
wetlands looks like, and (2) to demonstrate how nitrate (at domestic
wastewater concentrations) is treated and removed in a constructed
wetlands system.
A.
It (the Arcata wastewater treatment system) is "aimed at removina
inoraanic materials from the raw sewaae". What about oraanic
contaminants such as : benzene. carbon tetrachloride. 1,2-
dichlorethane. trichloroethvlene. 1. 1-dichloroethane. and vinvl
chloride. which are known cancer causing chemicals?
Response: The phrase" aimed at removing inorganic materials from the raw
sewage" is a phrase in the Arcata brochure describing the "headworks"
component of Arcata's wastewater treatment plant. The headworks is the
first phase in the treatment process where the influent of raw sewage and
wastewater is received. The headworks consists of various technologies
"aimed at removing inorganic materials". The reference to organic matter is
human organic waste material, not chemical organic compounds (Le.,
benzene, carbon tetrachloride, vinyl chloride, etc.). The headworks is not a
component of the constructed wetlands project for the ANP site.. None of
the chemically manufactured organic compounds listed. above were detected
3-48
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in the shallow aquifer. The only contaminant of concern in the shallow
aquifer is nitrate, a by-product of ANP's nitric acid manufacturing
processes.
B.
What are the inaredients used in Arcata's two clarifiers?
Response: The "ingrediems" processed by the two clarifiers in Arcata's
wastewater treatment plant are wastewater containing raw sewage, and
other possible waste products (for example, storm 'water runoff, pre-treated
industrial wastewaters). The two clarifiers (which are one part of the seven.
part Arcata municipal treatment system) perform the primary clarification by
settling out any remaining suspended material that passes through the
headworks. See response to citizen question #32, A (p.3-48) above. This
primary clarification component would not be part of the ANP constructed
wetlands treatment process, since only nitrate (not raw sewage or other
wastewaters) is being treated.
_. '--..' C.
Arcata's treatment marshes "reduce the levels of suspended solids
and BOD concentrations". What happens to the remainina waste that
they do not handle?
Response: The purpose of Arcata's treatment marshes (constructed wetlands) is
to reduce the levels of suspended solids and BOD (Biological Oxygen
Demand) concentrations that remain in the oxidation pond effluent after
secondary treatment. The treatment marshes are the fifth stage of the
Arcata treatment system, following the headworks, primary clarification,
sludge pumping, digestion, and methane recovery (cogeneration)
components, and the oxidation ponds. At the point these pre-treated
wastewaters enter Arcata's treatment marshes, the wastewater has received
primary treatment and secondary treatment, and the "treatment marshes",
planted with hardstem bulrush (Scirpus acutus), are performing further
treatment. Any remaining waste materials after this phase of treatment are
pumped to the "enhancement marshes" for a final stage of further treatment
to ensure that the effluent meets federal and state water quality
requirements.
D.
"Chlorine aas is used" to disinfect Arcata's waste water. In the Arcata
system. "double chlorination" occurs in two chlorine basins. Chlorine
is a poisonous greenish-yellow diatomic aas that is very irritatina to
the nose. throat. and lungs. with suffocating odor. What is a safe
distance so that the surrounding community will not smell or breathe
the chlorine aas? .
Response: Chlorine is required in the Arcata municipal wastewater treatment
system to kill any pathogens or other organisms commonly found in
wastewater composed of human waste materials to properly disinfect it prior
to release to the environment. As stated above in EPA's respons~s to citizen
3-49
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questions #32, A and B (p.3-4;8) above, the shallow aquifer is contaminated
with nitrate, not human waste .materials. A chlorination disinfection stage
would nDt be a component of the ANP constructed wetlands system.
E.
What haooens to chlorine aas when it accidentallv combines with rare
gases or nitrogen? .
Response: As stated in EPA's response to ci~izen question #30, D (p.3-49) above,
the use of chlorine gas is not a component of the constructed weth;mds
system selected for the ANP site. .
F.
.In the Arcata system (anv free chlorine remainina. in the final effluent
after the 60 minute contact time) "is removed with sulfur dioxide".
Sulfur dioxide is a share. strong. suffocatina odor. What is a safe
distance so that the surroundina community will not smell or breath
the sulfur dioxide? .
Response: Because chlorine will not be needed or used in the constructed
wetlands system for the ANP site, sulfur dioxide will not be used. See
EPA's responses to citizen questions #32, D (p.3-49) and E (p.3-50) above.
Concerns about exposure to either chlorine or sulfur dioxide (resulting from
treatment of the nitrate-contaminated shallow aquifer by constructed
wetlands at the ANP site) should be put aside, since these chemicals will not
be used. .
G.
Does sulfur dioxide smell like rotten egas?
Response: Sulfur dioxide does not smell like hydrogen sulfide (a rotten egg smell).
Howev.er, as stated in EPA's response to citizen question #30, F (p.3-49)
above, sulfur dioxide will not be used during the treatment of the nitrate-
contaminated shallow aquifer groundwater in the constructed wetlands at
the ANP site. .
H.
Does water enhance the smell of sulfur dioxide?
Response: As stated in EPA's responses to question #30, F and G (p.3-50) above,
sulfur dioxide will not be used during the treatment of the nitrate in the
shallow aquifer groundwater at the ANP site.
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