03-4509. National Oil and Hazardous Substances Pollution Contingency Plan; National Priorities List

AGENCY:

Environmental Protection Agency.

ACTION:

Notice of intent for partial deletion of a portion of the South Indian Bend Wash Site from the National Priorities List.

SUMMARY:

The Environmental Protection Agency (EPA) Region IX announces its intent to delete a portion of the South Indian Bend Wash (SIBW) Site located in Tempe, Maricopa County, Arizona, from the National Priorities List (NPL) and requests public comment on this action. The NPL constitutes Appendix B to the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40 CFR Part 300, which EPA promulgated pursuant to Section 105 of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).

DATES:

EPA will accept comments concerning its proposal for partial deletion for thirty (30) days after publication of this document in the Federal Register and a newspaper of record.

ADDRESSES:

Comments may be mailed to: Melissa Pennington, Superfund Remedial Project Manager, U.S. EPA, Region IX [SFD-8-2], 75 Hawthorne Street, San Francisco, CA 94105, [phone].

Information Repositories: Comprehensive information on the SIBW Site as well as information specific to this proposed partial deletion is available for review at EPA's Region IX office in San Francisco, CA and at the information repositories listed below. There are three Administrative Record files for the SIBW Site: one for the 1993 Record of Decision for VOCs in the Vadose Zone; one for the 1998 Record of Decision for VOCs in Groundwater; and one for the Plug-in Determination issued in January 2002. All three Administrative Record files and the Deletion Docket for this partial deletion are maintained at EPA Region IX's Regional Office Superfund Records Center and the Tempe Public Library. EPA's Superfund Records Center is located at 95 Hawthorne Street (Suite 403S), San Francisco, CA 94105 and the hours of operation are 8-5 p.m., Monday-Friday. The Records Center staff can be reached at [phone]. The location of the other information repository where the Deletion Docket is available for public review is: Tempe Public Library (South Area), 3500 South Rural Road, Tempe, AZ 85282.

FOR FURTHER INFORMATION CONTACT:

Melissa Pennington [phone].

SUPPLEMENTARY INFORMATION:

This partial deletion of the SIBW Site is proposed in accordance with 40 CFR 300.425(e) and the Notice of Policy Change: Partial Deletion of Sites Listed on the National Priorities List. 60 FR 55466 (Nov. 1, 1995).

In July 2002, the City of Tempe (the City) submitted a petition to EPA for Partial Deletion of a portion of the SIBW Site from the NPL. To help facilitate an ongoing redevelopment project, the City requested that EPA delete a 200-acre property known as the McClintock/Rio Salado Brownfield Redevelopment Area (Redevelopment Area). This proposal for partial deletion from the SIBW NPL Site pertains to the former Allstate Mine Supply Subsite, the Maricopa County Landfill, the Old Tempe Landfill, the Resources Reclamation Corporation of America Landfill, the First Street Landfill and the Bennett Family Trust Landfill, which properties comprise that portion of the Redevelopment Area presently part of the SIBW NPL Site. These properties subject to this proposal for partial deletion are collectively referred to hereafter as the “SIBW Landfill Area”. The location of the SIBW Landfill Area is shown on Figure 1. Both Figures 1 and 2 are available for viewing in the Deletion Docket which is maintained at EPA Region IX's Regional Office Superfund Records Center and the Tempe Public Library (details below).

This proposal for partial deletion pertains to all of the soils in the SIBW Landfill Area and a majority of the groundwater underlying the SIBW Landfill Area hereinafter referred to as the “SIBW Deletion Area”. The groundwater included in the SIBW Deletion Area is that groundwater with concentrations of trichloroethylene (TCE) less than 5 parts per billion (ppb). Based on existing data, the groundwater in the middle alluvial unit with concentrations of TCE less than 5 ppb is represented as that portion of the groundwater underlying the SIBW Landfill Area that is not within the 5 ppb TCE contour line as depicted on Figure 2 (available for viewing in the Deletion Docket). Once the partial deletion is effective, the only area remaining on the NPL north of Rio Salado Parkway will be the extent of groundwater contamination in the middle alluvial unit above 5 ppb TCE. This area is shown on Figure 2 (available for viewing in the Deletion Docket) as the overlap of the southeast corner of the SIBW Landfill Area and the 5 ppb TCE contour. This overlap has been estimated to cover approximately 7.4 acres.

Additional data may be obtained prior to the final Notice of Deletion that would allow for refinement of the definition of extent of groundwater contamination exceeding 5 ppb TCE depicted on Figure 2 (available for viewing in the Deletion Docket). Such information would then be set out in the final Notice of Deletion.

The SIBW site was added to the NPL because of widespread groundwater contamination caused by numerous facilities within the City of Tempe. The contaminants of concern (COCs) are volatile organic compounds (VOCs), primarily TCE and tetrachloroethylene (PCE). In order to efficiently manage the site, SIBW was divided into two operable units: a soil operable unit and a groundwater operable unit. In 1993, EPA issued a Record of Decision for VOCs in the Vadose Zone (1993 Soils ROD) at SIBW which required investigation of several facilities referred to as subsites. If the subsite investigations indicated that any subsite posed a continuing threat to groundwater or indoor air quality, then Soil Vapor Extraction (SVE) would be required. To date, EPA has completed or has overseen the investigations of approximately twelve subsites. Among the twelve subsites, SVE was required at one subsite in accordance with the (1993 Soils ROD), SVE was voluntarily conducted by the responsible parties at two of the subsites, SVE was not required at seven of the subsites, and the remaining subsites are still under investigation. None of the subsites still under investigation are part of this partial deletion.

EPA has evaluated all existing data regarding the SIBW Landfills and concluded that the COCs are not present at the five landfills at levels which pose a continuing threat to groundwater or indoor air quality. The Focused Remedial Investigation Report for the Allstate Subsite concluded that this subsite does not pose a continuing threat to groundwater or indoor air quality. Therefore, in accordance with the 1993 Soils ROD, EPA has determined that these subsites do not pose a threat to groundwater and that no further federal CERCLA response actions are required at the SIBW Landfill Area with respect to the groundwater.

The focus of EPA's listing of this Site has been on the groundwater contamination and the sources of groundwater contamination. EPA did not intend to address all areas within the SIBW study area that might be contaminated, only those directly linked to the groundwater contamination. As a result of EPA's investigation, EPA has also determined that the contaminated levels in soil at these subsites do not pose a threat to indoor air. However, no determination has been made as to whether these properties are suitable for unrestricted uses. Any attempt to develop the SIBW Landfill Area should be coordinated with the Arizona Department of Environmental Quality (ADEQ), as well as other appropriate state and local agencies, to ensure that non-CERCLA environmental issues associated with these properties are fully investigated and addressed prior to development.

There are three separate plumes of contaminated groundwater (eastern, central and western), resulting from former disposal practices at various SIBW subsites. The remedies selected for the SIBW groundwater plumes are: monitored natural attenuation in the central and eastern plumes and extraction and treatment via air stripping in the western plume. The groundwater operable unit and the remaining subsites of the soil operable unit will remain on the NPL. This proposal to delete the SIBW Deletion Area from the SIBW NPL Site is based on the determination by EPA and ADEQ that all appropriate federal actions under CERCLA with regard to the SIBW Deletion Area have been completed. Based on EPA's discussions with ADEQ, it has also been determined that ADEQ's Voluntary Remediation Program is an option for addressing any remaining environmental issues at the SIBW Landfill Area.

Table of Contents

I. Introduction

II. NPL Deletion Criteria

III. Deletion Procedures

IV. Basis for Intended Partial Site Deletion

I. Introduction

The United States Environmental Protection Agency (EPA) Region IX announces its intent to delete a portion of the South Indian Bend Wash (SIBW) Site located in Tempe, Maricopa County, Arizona, from the National Priorities List (NPL) and requests public comment on this action. This proposal for partial deletion from the SIBW NPL Site pertains to the former Allstate Mine Supply Subsite, the Maricopa County Landfill, the Old Tempe Landfill, the Resources Reclamation Corporation of America Landfill, the First Street Landfill and the Bennett Family Trust Landfill. These properties subject to this proposal for partial deletion are collectively referred to hereafter as the “SIBW Landfill Area”. The location of the SIBW Landfill Area is shown on Figure 1 (available for viewing in the Deletion Docket).

This proposal for partial deletion pertains to all of the soils in the SIBW Landfill Area and a majority of the groundwater underlying the SIBW Landfill Area hereinafter referred to as the “SIBW Deletion Area'.

The NPL constitutes appendix B to the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40 CFR part 300, which EPA promulgated pursuant to Section 105 of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). This partial deletion of the SIBW Site is proposed in accordance with 40 CFR 300.425(e) and the Notice of Policy Change: Partial Deletion of Sites Listed on the National Priorities List. 60 FR 55466 (Nov. 1, 1995). This guidance allows EPA to delete portions of a site, including deletions by media.

The National Priorities List (NPL) is a list, maintained by EPA, of sites that EPA has determined present a significant risk to human health, welfare, or the environment. This proposal for partial deletion from the SIBW NPL Site pertains to the SIBW Deletion Area defined in the Summary section above (page 2). The location of the SIBW Landfill Area is shown on Figure 1 and the area of groundwater included within the SIBW Deletion Area is shown on Figure 2. Figures 1 and 2 are available for viewing in the Deletion Docket.

The SIBW study area covers approximately three square miles in Tempe, Arizona. The Site consists of groundwater contaminated with VOCs (primarily TCE and PCE) and soil contamination at the facilities on the surface that have contributed to or are contributing to the groundwater contamination. Groundwater at the Site is present in three separated levels or layers. These layers are referred to as the Upper, Middle, and Lower Aquifers. The groundwater contamination is present as three separate plumes known as the western plume, eastern plume and central plume. Land use in the vicinity of the Site includes residential, industrial/commercial, agricultural, public and private recreational (parks, golf courses, playing fields, etc.), undeveloped open space, and waterways.

There have been two Records of Decision (RODs) issued for SIBW to address VOC contamination at the Site, one for soil and one for groundwater. The soils ROD required Soil Vapor Extraction (SVE) at areas within SIBW (known as subsites) that meet specific criteria which are used to assess whether VOC levels at a subsite pose a threat to groundwater and ambient air. The soils ROD was issued in September 1993. The groundwater ROD required Monitored Natural Attenuation in the central and eastern plumes and extraction and treatment of the western plume. The groundwater ROD was issued in September 1998.

The approximate boundaries for the SIBW Landfill Area are the Rio Salado Parkway, which forms a portion of the boundary to the south; the Salt River to the north; Perry Lane, which makes up most of the western boundary; and the eastern boundary is between Rockford Drive and River Drive. However, the actual boundaries are the boundaries of the SIBW Landfill Area as depicted on Figure 1 (available for viewing in the Deletion Docket). The boundaries of the SIBW Deletion Area are defined as the boundaries of the SIBW Landfill Area (described above) with the exception of the area of groundwater contamination in the middle alluvial unit above 5 ppb TCE. This area is shown on Figure 2 (available for viewing in the Deletion Docket) as the overlap of the southeast corner of the SIBW Landfill Area and the 5 ppb TCE contour. This overlap has been estimated to cover approximately 7.4 acres.

In July 2002, the city of Tempe (the City) submitted a petition to EPA for Partial Deletion of a portion of the SIBW Site from the NPL. To help facilitate an ongoing redevelopment project, the City requested that EPA delete a 200-acre property known as the McClintock/Rio Salado Brownfield Redevelopment Area (Redevelopment Area). EPA is proposing only the SIBW Deletion Area, as defined in the Summary section above (page 2), for deletion from the NPL Site (See Figure 1 which is available for viewing in the Deletion Docket). This is because EPA considers only a portion of the entire 200-acre Redevelopment Area to be part of the SIBW NPL Site. The SIBW NPL Site is defined as the groundwater plumes contaminated with VOCs and the facilities on the surface that have contributed to or are contributing contamination to the groundwater plumes.

The SIBW Landfill Area, which encompasses the SIBW Landfills and the Allstate Subsite, has been thoroughly investigated. In October 2001, a Focused Remedial Investigation Report (FRI Report) was prepared for the Allstate Subsite by EPA's contractor (CH2M Hill) and several documents have been prepared describing the conditions at the SIBW Landfills. In December 1993, ADEQ prepared a draft document entitled “Indian Bend Wash (South) Superfund Site, Tempe, Arizona, Evaluation of Landfills.” In 1999, ADEQ contracted Roy F. Weston to evaluate the existing landfill information and to prepare a report. This document was entitled “Review of Previous Site Characterization Work at Former Landfills”. These documents recommended additional work be performed before a decision could be made regarding remediation at the landfills. In December 2002, EPA's contractor compiled all of the existing landfill data into a technical memorandum. The main objective of this technical memorandum was to utilize data from the landfills as well as groundwater data that had been collected as part of the ongoing groundwater remedy at SIBW to assess whether the soil contamination in, beneath, and in the vicinity of the landfill sites has contributed to the VOC contamination in the groundwater plumes.

For the purposes of this proposal, EPA has evaluated the conclusions regarding the Allstate Subsite in the Allstate FRI Report as well as the data and conclusions in CH2M Hill's December 2002 SIBW Landfill Sites Technical Memorandum. As a result, EPA has determined that the SIBW Landfill Area does not require soil remediation for protection of the groundwater in accordance with the 1993 Soils ROD. Therefore, no further federal CERCLA action is necessary for the SIBW Landfill Area to protect human health and the environment with respect to VOCs in soils contributing to the groundwater contamination. As indicated previously in this document, the 1993 Soils ROD addresses VOCs only. When placed on the NPL, the SIBW Site was defined as groundwater plumes contaminated with VOCs and the surface sources contributing to the VOC contamination in the groundwater. It was never EPA's intention that remediation of the SIBW site would include contaminants other than VOCs. Therefore, this proposed deletion does not draw any conclusions about the potential presence or absence of other contaminants in the SIBW Landfill Area. It is EPA's understanding that further investigation and remediation of the landfill properties will be conducted by the prospective developers prior to redevelopment of the property. ADEQ is in agreement with this approach.

This proposed deletion specifically addresses the soils at the SIBW Landfill Area and the groundwater beneath the SIBW Landfill Area with concentrations of TCE less than 5 ppb. Groundwater associated with the SIBW Site with concentrations of TCE greater than 5 ppb is being addressed as part of the remedial action at the SIBW Site. The plume south of the SIBW Landfill Area is known as the eastern plume. The remedial design for monitored natural attenuation in the eastern plume is being implemented by an SIBW potentially responsible party. Response activities for the SIBW groundwater plumes are not yet complete and therefore the groundwater operable unit will remain on the NPL. Similarly, the remaining SIBW subsites are not subject to this partial deletion.

The NPL is a list, maintained by EPA, of sites that EPA has determined present a significant risk to human health, welfare, or the environment. Sites on the NPL may be the subject of remedial actions financed by the Hazardous Substance Superfund (Fund). Pursuant to 40 CFR 300.425(e) of the NCP, any site or portion of a site deleted from the NPL remains eligible for Fund-financed remedial actions if conditions at the site warrant such action.

EPA will accept comments concerning its intent for partial deletion for thirty (30) days after publication of this notice in the Federal Register and a newspaper of record.

II. NPL Deletion Criteria

The NCP establishes the criteria that EPA uses to delete sites from the NPL. In accordance with 40 CFR 300.425(e), sites may be deleted from the NPL where no further response is appropriate to protect human health or the environment. In making such a determination pursuant to 40 CFR 300.425(e), EPA will consider, in consultation with the State, whether any of the following criteria have been met:

A. Section 300.425(e)(1)(i). Responsible parties or other persons have implemented all appropriate response actions required; or

B. Section 300.425(e)(1)(ii). All appropriate Fund-financed response under CERCLA has been implemented, and no further response action by responsible parties is appropriate; or

C. Section 300.425(e)(1)(iii). The remedial investigation has shown that the release poses no significant threat to human health or the environment and, therefore, taking of remedial measures is not appropriate.

Deletion of a portion of a site from the NPL does not preclude eligibility for subsequent Fund-financed actions at the area deleted if future site conditions warrant such actions. Section 300.425(e)(3) of the NCP provides that Fund-financed actions may be taken at sites that have been deleted from the NPL. A partial deletion of a site from the NPL does not affect or impede EPA's ability to conduct CERCLA response activities at areas not deleted and remaining on the NPL. In addition, deletion of a portion of a site from the NPL does not affect the liability of responsible parties or impede agency efforts to recover costs associated with response efforts.

III. Deletion Procedures

Deletion of a portion of a site from the NPL does not itself create, alter, or revoke any person's rights or obligations. The NPL is designed primarily for informational purposes and to assist Agency management. The following procedures were followed for the proposed deletion of the SIBW Deletion Area from the SIBW NPL Site:

(1) EPA received and evaluated a petition for partial deletion from the City of Tempe;

(2) The State of Arizona through the Arizona Department of Environmental Quality pledged support for the partial deletion and encouraged EPA to proceed with the deletion process;

(3) EPA preliminarily concurred with the recommendations for partial deletion and prepared the relevant documents;

(4) Concurrent with this national Notice of Intent for Partial Deletion, a notice has been published in a newspaper of record and has been distributed to appropriate federal, State, and local officials, and other interested parties. These notices announce a thirty (30) day public comment period on the deletion package, which commences on the date of publication of this notice in the Federal Register and a newspaper of record.

(5) EPA has made all relevant documents available at the information repositories listed previously.

This Federal Register document, and a concurrent notice in a newspaper of record, announce the initiation of a thirty (30) day public comment period and the availability of the Notice of Intent for Partial Deletion. The public is asked to comment on EPA's proposal to delete the SIBW Deletion Area from the NPL. All critical documents needed to evaluate EPA's decision are included in the Deletion Docket and are available for review at the information repositories.

Upon completion of the thirty (30) day public comment period, EPA will evaluate all comments received before issuing the final decision on the partial deletion. EPA will prepare a Responsiveness Summary for comments received during the public comment period and will address concerns presented in the comments. The Responsiveness Summary will be made available to the public at the information repositories listed previously. Members of the public are encouraged to contact EPA Region IX to obtain a copy of the Responsiveness Summary. If, after review of all public comments, EPA determines that the partial deletion from the NPL is still appropriate, EPA will publish a final notice of partial deletion in the Federal Register. Deletion of the SIBW Deletion Area does not actually occur until the final Notice of Partial Deletion is published in the Federal Register.

IV. Basis for Intended Partial Site Deletion

The following provides EPA's rationale for deletion of the SIBW Deletion Area from the NPL and EPA's finding that the criteria in 40 CFR 300.425(e) are satisfied.

Background

The entire study area of the Indian Bend Wash Superfund Site (Site) covers approximately 13 square miles in Scottsdale and Tempe, Arizona. EPA divided the Site into two areas known as the Indian Bend Wash Area—North (NIBW) and the Indian Bend Wash Area—South (SIBW). EPA is proposing to delete a portion of the SIBW site only; all of the NIBW Site and most of the SIBW Site will remain on the NPL.

As discussed below, there are numerous industrial facilities located within the boundaries of the Site study area. Up until the 1970s, industrial solvents containing VOCs were typically disposed of directly onto the ground or in dry wells. These disposal practices, along with other releases, resulted in soil and groundwater contamination at various locations throughout the Site. The groundwater contamination at NIBW was discovered in 1981 when elevated levels of VOCs, including TCE, were found in drinking water wells. Further investigation of regional groundwater quality led to the discovery and characterization of the three SIBW groundwater contamination plumes (western, central and eastern). The unacceptable risks associated with the contamination at SIBW is based on exposure to groundwater contamination. There were no significant levels of inorganic contaminants found in the groundwater. Therefore, all remedial actions required at the SIBW Site were intended to address VOCs in groundwater and VOCs in soils which could contribute to groundwater contamination.

EPA and the State of Arizona have been involved in investigations and cleanup activities at the Site since the initial discovery of VOCs in the groundwater in 1981. The Site, including both NIBW and SIBW, was placed on EPA's NPL in 1983. On September 27, 1993, EPA issued a Record of Decision for VOCs in the Vadose Zone (the 1993 Soils ROD). This ROD selected soil vapor extraction (SVE) as the remedy for VOCs in soils at SIBW and is discussed in more detail below. EPA also characterized contamination in groundwater and issued a second Record of Decision on September 30, 1998 for VOCs in groundwater at SIBW. The groundwater ROD is not discussed in detail in this document.

The surface portion of the SIBW Site is divided into many small isolated locations where soil contaminated with VOCs was expected to be present. These locations are known as subsites. The 1993 Soils ROD utilized an approach called “Plug-in,” whereby the ROD did not directly apply the SVE remedy to any particular subsite. Rather, the ROD established criteria that EPA uses to determine whether pre-defined conditions exist at any given subsite thereby indicating that a subsite needs to be remediated using SVE. Each individual subsite had to be evaluated by EPA to determine whether it “Plugged-in” to the SVE remedy. These evaluations are based on the data collected at each of the subsites following issuance of the ROD. Implementation of SVE is required for subsites that “Plug-in,” or meet certain criteria, in accordance with the 1993 Soils ROD.

The risks associated with VOCs in the Vadose Zone at the SIBW Landfills and other SIBW subsites were risks solely attributable to the potential for VOCs in soils to enter the groundwater or the air (See Interim Risk Assessment, Operable Unit Feasibility Study, VOCs in Vadose Zone, Appendix A, June 1993). In the Interim Risk Assessment, direct contact and ingestion of VOCs in soil were not considered complete exposure pathways because surface VOCs would likely volatilize before direct contact or ingestion could occur. Therefore, there are no risks associated with direct human exposure to VOCs in soils. The FRI Report for the Allstate Subsite and the SIBW Landfills Technical Memorandum evaluated whether or not VOCs in the Vadose Zone had the potential to impact groundwater or air. If a particular subsite does not meet the plug-in criteria identified in the 1993 ROD, the risks posed by the residual VOC contamination, if any, do not warrant further action.

At the time that the 1993 ROD was issued at SIBW, approximately thirty facilities were considered potential source areas for VOC contamination in the groundwater. Five of these facilities had already been issued unilateral orders to complete site investigations. These five facilities were: DCE Circuits, Eldon Drapery, IMC Magnetics, Prestige Cleaners, and Unitog Cintas. Following additional screening, it was determined that investigations should also be conducted at Arizona Public Service (APS), Circuit Express, Allstate Mine Supply, Desert Sportswear, Cerprobe, Service and Sales, and the City of Tempe Right-of-Way.

In February 1994, EPA issued a Plug-in Determination requiring implementation of SVE at the DCE Circuits Subsite. This work has been conducted with fund-lead money and is currently nearing completion. APS made the determination that SVE was appropriate at its site in lieu of conducting additional investigations. APS implemented SVE successfully at its subsite, and EPA approved its closure report in April of 2001, documenting that soil cleanup had been completed at the APS Subsite.

In January 2002, EPA issued a Plug-in Determination that documented EPA's subsite-specific decision for the following seven SIBW subsites: Eldon; Circuit Express; Allstate Mine Supply; Desert Sportswear; Cerprobe; Service and Sales; and City of Tempe Right-of-Way. In the January 2002 Plug-in Determination, EPA concluded that all seven subsites fall within the Remedy Profile defined in the 1993 Soils ROD and that the subsites contain VOCs in soils at concentrations that do not exceed the Plug-In Criteria. Therefore, SVE was not required for any of these subsites.

The remaining SIBW subsites (IMC Magnetics, Prestige Drapery, and Unitog) are still being evaluated. EPA will address these subsites in future Plug-in Determinations.

Current Surface Conditions at the SIBW Deletion Area

The Allstate Subsite is located at 1926 East First Street, Tempe, Arizona. It is also within the footprint of the Maricopa County Landfill discussed below. Prior to 1963, the property was vacant and undisturbed.

From 1963 to 1976, the property was used in a gravel sorting operation and construction equipment and/or dumpsters became noticeable onsite. During this timeframe, the property served as a storage yard for A&B Enterprises (A&B). A&B was an operation that repaired garbage dumpsters. The repairs included painting, welding, and use of paint thinners.

Beginning in approximately April 1976, Allstate Mine Supply, Inc. and Canyon State Chemical, Inc. used this property to blend soaps, solvents, and other chemicals into finished products to be sold to clients. The products were “specialty cleaning products” which are made by compounding liquid raw materials (chemicals) onsite. The compounding, storing and shipping of raw materials and finished products occurs in 55-gallon drums.

EPA's FRI Report for the Allstate Mine Supply Subsite (Allstate FRI) found that VOCs are present in the soil vapor at the Allstate Subsite to a depth of approximately 43 feet below ground surface (bgs). Although as many as 10 VOCs were detected at the subsite, only 1,1,1-TCA and PCE were consistently present in both shallow and deep samples. Total xylenes were detected at depth in all three sampling events in 1998 and the 1999 sampling event. The maximum concentrations of these contaminants are as follows: PCE at 28 μg/L, 1,1,1-TCA at 210 μg/L, and total xylenes at 88 μg/L. In 1988, 1990 and 1994, shallow soil vapor data were collected for this subsite. Three sampling events were conducted in 1998 (August, September and November) and one sampling event was conducted in July 1999 from one soil vapor monitoring well (SVWM-6). Both shallow and deep soil vapor samples were collected. The soil vapor data show that PCE appears to persist through time and throughout the length of the vadose zone. 1,1,1-TCA and 1,1-DCE appear to decrease with time and depth in the vadose zone. Total xylenes are at the highest concentrations at 43 feet bgs and appear to be decreasing over time. The levels of VOCs at the Allstate Subsite were not high enough to cause the subsite to Plug-in to the 1993 Soils ROD.

The landfill properties are located along the north side of Rio Salado Parkway approximately one quarter of a mile east of McClintock Drive. The landfill property boundaries are shown on Figure 1 (available for viewing in the Deletion Docket). Since these landfills operated sometimes on top of one another, each landfill will be discussed separately. Since the state, county, and local government agencies did not keep information on landfill activities until after the landfills were closed, little information is available. Most of the information available is from site investigation activities that began around 1988 as part of the SIBW Superfund Site investigation. Five landfills were operated on the property in the vicinity of the proposed redevelopment project in Tempe, Arizona. These landfills are: Maricopa County Landfill; Old Tempe Landfill; Resources Reclamation Corporation of America; First Street Landfill; and the Bennett Family Trust Landfill.

The Maricopa County Landfill operated on the southwest portion of the landfill area properties and consisted of approximately 40 acres. The landfill has two distinct areas, a northern portion and a southern portion, based on apparent differences in fill material, time of emplacement, and soil vapor sampling results.

A number of buildings were constructed on the southern portion of the landfill. None of the buildings were associated with the landfill operations. The buildings housed many industrial businesses, most notably the former Allstate Mine Supply. The Allstate Subsite was investigated as a separate and distinct subsite of SIBW as discussed above.

The Old Tempe Landfill was located on the northeast corner of the landfill properties and consisted of approximately 11.5 acres. This landfill operated between 1971 and 1977, prior to which it was a gravel quarry. Conflicting information exists regarding the operating timeframe of this landfill. According to various property owners in the area, the landfill was operated as a municipal landfill by the cities of Tempe, Mesa, Phoenix, and Scottsdale from 1968 to 1979. The landfill primarily accepted solid waste; however, liquid and/or hazardous wastes may also have been accepted, although never verified. Resources Reclamation Corporation of America (RRCA), discussed below, purchased the property and continued the municipal landfill operations from 1978 to 1982.

The RRCA property totaled approximately 104 acres and included the area of the First Street Landfill, the Old Tempe Landfill, and adjacent parcels in the northwest corner of the landfill properties. The landfill accepted demolition debris, municipal solid wastes, and recyclable material, including metals, glass, and paper from the Cities of Tempe and Mesa, Arizona and reportedly did not accept any liquid or hazardous wastes. Additionally, RRCA was supposedly producing combustible materials for fuel cubes (refuse-derived fuel) from non-recyclable products received at the landfill. RRCA disposed of the wastes over the area of the Old Tempe Landfill. The First Street Landfill property consisted of approximately 80 acres and included the area of the Old Tempe Landfill. The First Street Landfill accepted demolition debris and was to accept only inert materials such as dirt, concrete, and asphalt. Wood and uncontained refuse was also allowed if it was buried above the historical high water level.

The Bennett Family Trust Landfill is located adjacent to the First Street Landfill and is comprised of approximately seven acres. Little information is available for this property. The Bennett Family Trust obtained the property in the 1970s and used an onsite pit for storage of automobiles related to their scrap yard. The pit was susceptible to flooding, so the Bennetts decided to fill the pit with clean material. Supposedly, the Bennetts observed every load of material used to fill the pit and did not allow wood, garbage, tires, or the like to be disposed of in the pit.

The VOCs identified in the shallow soil-vapor within the SIBW Landfill Area include TCE, PCE and 1,1,1-TCA. These VOCs were identified because they were pervasive and persistent with respect to the three shallow soil vapor studies. In addition to the VOCs identified above, methane is also present in soil vapor at the SIBW Landfills. The methane concentrations are well below the lower explosive limit for methane, but still may cause a potential explosion risk if the gases build up inside of a structure.

The highest concentrations of 1,1,1-TCA or PCE observed within the SIBW Landfill Area were associated with the Allstate Subsite. None of the VOCs of concern were detected in the soil beneath the SIBW Landfills at concentrations that suggest that there could be a continuing source contamination to the groundwater into the future. 1,1,1-TCA contamination is present in soil vapor at concentrations ranging from 0.68 mg/L to 210 mg/L. The samples that contained the highest measured concentrations of 1,1,1-TCA are near the drywell on the former Allstate property. Data from SVMW-6, located at the former Allstate property, exhibited concentrations of 1,1,1-TCA that decreased with depth suggesting the 1,1,1-TCA source is above 30 feet bgs.

Within the SIBW Landfill Area, PCE contamination is present in soil vapor at concentrations ranging from 0.24 mg/L to 30 mg/L. The samples that contained the highest measured concentrations of PCE are associated with the former Allstate property. PCE concentrations appear to be decreasing with depth, peak at approximately 30 feet bgs, and decrease below 30 feet bgs at the former Allstate property.

TCE was observed only once within the SIBW Landfill Area in shallow soil vapor at a concentration of 0.55 mg/L in 1990. This TCE concentration was observed in SVMW-6 in 1998 and 1999 which is located at the former Allstate property. Unlike 1,1,1-TCA and PCE, the TCE concentrations do not appear to follow any identifiable pattern related to depth.

The 1993 Soils ROD identified very specific criteria that determines whether or not soil remediation is required at SIBW subsites. The subsite must meet the following criteria in order for EPA to require soil remediation:

(1) Present cancer risk (incremental risk) of more than one in one million to a person from both ingestion of VOCs in groundwater and inhalation of VOCs during other household uses of groundwater, such as showering, over a lifetime;

(2) Present a cancer risk to a person of more than one in one million from inhalation of air above the soils at the subsite itself, over a lifetime;

(3) Present a hazard index for non-cancer effects of more than one to a person from both ingestion of VOCs in groundwater and inhalation of VOCs during household uses of groundwater, over a lifetime;

(4) Present a hazard index for non-cancer effects of more than one to a person from inhalation of air above the soils at the subsite itself, over a lifetime; and

(5) Increase the concentration of VOCs in groundwater (incremental concentration) by an amount greater than the federal Maximum Contaminant Level (MCL) under the Safe Drinking Water Act.

The maximum concentrations of 1,1,1-TCA, TCE and PCE in soil gas at the SIBW Landfill Area were obtained from sample points at the Allstate facility, which did not plug in to the 1993 soils ROD Remedy. Therefore, since the concentrations observed on the landfill properties are less than or equal to the concentrations observed at the Allstate Subsite, EPA has determined that the landfill properties would not meet any of the criteria listed above and therefore would not Plug-in to the 1993 soils ROD Remedy.

In conclusion, the concentration of VOCs detected in soil gas at the SIBW Landfill Area do not require any soil remediation to be conducted under CERCLA.

Current Groundwater Conditions at the SIBW Deletion Area

There are three separate plumes of contaminated groundwater (eastern, central and western), resulting from former disposal practices at various SIBW subsites. The primary contaminants of concern in the groundwater are VOCs, primarily TCE and PCE. EPA characterized contamination in groundwater and issued a Record of Decision on September 30, 1998 for VOCs in groundwater at SIBW (Groundwater ROD). The remedies selected for the SIBW groundwater plumes are: monitored natural attenuation in the central and eastern plumes and extraction and treatment via air stripping in the western plume. The cleanup levels for the SIBW plumes are based on the federal Safe Drinking Water Act Maximum Contaminant Levels (MCLs). The MCL for both TCE and PCE is 5 parts per billion (ppb).

The plume of groundwater with concentrations of TCE above 5 ppb in the vicinity of the SIBW Landfill Area is the eastern plume. This plume is located approximately 100 to 200 feet below ground surface (bgs) in a formation known as the Middle Alluvial Unit. The groundwater included in the SIBW Deletion Area is not part of the eastern plume and contains concentrations of TCE less than 5 ppb. Based on existing data, the groundwater in the middle alluvial unit with concentrations of TCE less than 5 ppb is represented as that portion of the groundwater underlying the SIBW Landfill Area that is not within the 5 ppb TCE contour line as depicted on Figure 2 (available for viewing in the Deletion Docket). Once the partial deletion is effective, the only area remaining on the NPL north of Rio Salado Parkway will be the extent of groundwater contamination in the middle alluvial unit above 5 ppb TCE. This area is shown on Figure 2 as the overlap of the southeast corner of the SIBW Landfill Area and the 5 ppb TCE contour. This overlap has been estimated to cover approximately 7.4 acres.

Additional data may be obtained prior to the final Notice of Deletion that would allow for refinement of the definition of extent of groundwater which is presently above 5 ppb TCE depicted on Figure 2 (available for viewing in the Deletion Docket). Such information would then be set out in the final Notice of Deletion.

Community Relations Activities

Community interest in this site has been relatively low. With the exception of persons wanting to purchase property in the area, very few calls are received from citizens interested in activities at SIBW. EPA issued a fact sheet in February 2002 which described the January 2002 Plug-in Determination for seven (7) SIBW Subsites including the Allstate Subsite. EPA has also conducted two formal public meetings. The first was on July 7, 1993 and was to present the proposed Soil Vapor Extraction Plug-in Remedy and the second was on September 24, 1997 to present the proposed groundwater remedy.

Current Status

The SIBW Landfill Area has been investigated and the plug-in analysis has been performed in accordance with the 1993 Soils ROD. As prescribed by the ROD, SVE remediation is not required and therefore, no further federal CERCLA action is necessary at the SIBW Landfill Area to protect human health and the environment with respect to VOCs in soils. However, any attempt to develop the SIBW Landfill Area should be coordinated with the Arizona Department of Environmental Quality (ADEQ), as well as other appropriate state and local agencies, to ensure that non-CERCLA environmental issues associated with these properties are fully investigated and addressed prior to development of the area. In accordance with 40 CFR 300.425(e)(1)(ii), EPA has determined that all appropriate Fund-financed response under CERCLA has been implemented in accordance with the 1993 Soils ROD, and no further response action by responsible parties is appropriate.

While EPA does not believe that any future response actions at the SIBW Deletion Area will be needed with respect to CERCLA, if future conditions warrant such action, the proposed deletion area of the SIBW Site remains eligible for future Fund-financed response actions. In order to be eligible for future Fund-financed response actions the deleted portion of the SIBW site would either have to be re-listed on the NPL or an imminent and substantial threat would have to be documented that would warrant a CERCLA removal action. Furthermore, this partial deletion does not alter the status of the groundwater operable unit or the remaining subsites of the SIBW Site which are not proposed for deletion and remain on the NPL.

In a letter dated July 2, 2002 the State of Arizona through its Department of Environmental Quality, has pledged its support for the partial deletion of this portion of the SIBW Site.

Dated: February 14, 2003.

Keith Takata,

Acting Regional Administrator, Region IX.