ADMINISTRATIV E

27214

Explanation of Significan t Differences F or The Midvale Slag Operable Unit One Superfun d Site Wincheste *^? /^^/^"^^ *"-e?

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INTRODUCTION

Thi s Explanation of Significan t Differences (ESD) has been prepared to document the changes to

t he Midvale Slag, Operable Unit No. 1 (OU1) Superfun d Site Record of Decision (ROD). The ROD was issued by the U.S. Environmental Protection Agency (EPA) on Apri l 28, 1995. The

selected remedy is described in the ROD as Alternative 3.

T he Utah Department of Environmental Quality (UDEQ) is the lead agency at the site, with

support provided by the EPA. The changes to the ROD have been made as a result of new

information that UDEQ and the EPA received subsequent to the issuance of the ROD. Thi s ESD

will address two changes to the remedy presented in the ROD and are described in detail later in

this document. These changes do not fundamentall y alter the sitewide remedy presented in the ROD. The modified remedy will remain protective of human health and the environment.

Thi s ESD i s prepared in fulfillmen t of EPA' s public participation responsibilities under Section

117(c) of the Comprehensive Environmental Response, Compensation, and Liabilit y Act of

1980, 42 U.S.C. Section 9601, et seq. (CERCLA) , as amended by the Superfun d Amendments

a nd Reauthorization Act of 1986 (SARA), and Section 300.435(c)(2)(i) of the National Oil and Hazardous Substances Contingency Plan (NCP), 40 Code of Federal Regulations (CFR) Part

300. These laws and regulations require EPA to publish an ESD when the remedy to be

implemented differ s significantl y from the remedy described in the ROD.

Thi s ESD and supportin g documentation will become a permanent part of the administrative

record file for the site and is available for public review at the followin g locations:

E PA Superfun d Records Center

9 99 18th Street , Fifth Floor Denver, Colorado 80202 Hours: Monday-Friday 8:00 am"- 4:30pm Telephone: (303)312-6473

Utah Department of Environmental Quality Division of Environmental Response and Remediation

1 68 North 1950 West , First Floor Salt Lake City , Utah 84116 Hours: Monday-Friday 8:00am - 5:00pm Telephone: (801)536-4479
Tyler Branch Library

3 15 South Wood Midvale, Utah 84047

SUMMAR Y OF SIT E HISTORY , CONTAMINATION PROBLEMS, AND SELECTE D

REMEDY

Little information is available describing historical activities on OU1 prior to the 1940's. Before

that time, it is generally believed that the land was used as pasture with no industrial activities. A

1952 aerial photograph of the southern two-thirds of OU1 showed no evidence of

commercial/industrial use or disturbed ground with the exception of a small landfil l (less than 1

acre) and an associated unpaved road. Disposal of domestic trash and household goods occurred

on the southwest corner of the LF Parcel from approximately the 1940's until a landfil l was

established by the county in the 1960's. The South Valle y Water Reclamation District operated

t he Midvale WWTP on the Midvale OU1 Site (LR Parcel) from 1959 until 1986. The plan t

originally consisted of a tricklin g filter system. An aerated lagoon system consisting of three

lagoons was added in 1976 and operated until the closure of the WWTP in 1986. The lagoons

were closed according to an approved Closure Plan and material excavated as part of the Interstate Highway 215 construction project was subsequently deposited on the former lagoon

location. The land to the south of the Midvale Slag OU1 Site was the site of historical smeltin g

activities beginning in 1871 and ending in 1958.

It is the smeltin g activities that are presumed to account for the contaminants detected at OU1. T he former smelter site is being addressed under CERCLA as Operable Unit 2 of the Midvale Slag Site . There are no known discrete waste sources at OU1. The only suspected waste features

within the OU1 boundaries are the small landfil l and abandoned WWTP and associated lagoons. Sit e characterization data suggest that both of the features have not contributed to elevated levels

of the contaminants of concern (arsenic, cadmium, and lead) detected in site soils. It is inferred

from available data that the metal (and metalloid) contaminants detected on OU1 are derived

from discrete waste sources identified on OU2.

T he transport mechanisms postulated to account for contaminants at OU1 include the following:

Win d transport of slag dust onto OU1 from slag piles on OU2.

• Surfac e water transport of slag dust and possible larger particles onto OU 1 from slag pile s

on OU2.

• Fallout of smelter fume onto OU1 from smelter chimneys on OU2 and/or the south

chimney on OU1 of the Sharon Steel site.

• Deliberate placement of slag and possible other smelter waste onto OU1 to fill wetlands

or other low areas, and to sand roads in the Winchester Estates development during snow

or ice events.

T he major components of the selected remedy, as presented in the ROD, include the following:

• Excavating native surface soils at 14 residential yards (Parcel WENW ) to a minimum
depth of 18 inches with confirmatory sampling to identif y areas requiring additional

excavation. Clean fill is to be imported to restore the original grade, and each yard will

be restored as closely as possible to its original condition. The wastes, being nonhazardous, would be transported to the nearest solid waste (RCRA Subtitle D) landfill . • Placing a compacted permeable soil cover (Non-RCRA Cap) over exposed native soils in

the undeveloped residential area (Parcel WESE) . The cap would be accomplished using a

portion of existing clean fill from the LG and LR parcels. Thi s remedial action would be

coupled with erosion controls (grading and revegetation, and ground water monitoring). T he final compacted surface will be covered with topsoil and revegetated with native

plant s to minimize erosion by wind and surface water.

• Implementin g deed restrictions or other institutional controls on the remaining parcels of

the operable unit to prohibit residential land use unless additional remediation to

residential soil clean up levels occurs.

DESCRIPTION OF THE SIGNIFICANT DIFFERENCES AND THE BASI S FOR

THOS E DIFFERENCES

T he firs t change is the elimination of the requirement to place a 2-foot-thick permeable soil cover

over contaminated soil on Parcel WESE . Instead of covering contaminated soil on the WESE Parcel, contaminated soil will be excavated and relocated to Midvale Slag Operable Unit 2. The

second change is to eliminate the requirement to not breach the monolayer soil cover on Parcel WESE . The ROD required, as a measure to prevent future development activities from

breaching the soil cover, that deed restrictions or other institutional controls be implemented on

the WESE parcel. Thi s control is no longer necessary due to the remedy change on that parcel.

The changes reflected in this ESD are based on new information that the UDEQ and the EPA

received subsequent to the issuance of the ROD. The UDEQ determined that the information

support s the need to correct and/or clarify certain aspects of the remedy described in the ROD. These changes do not fundamentall y alter the overall approach of the sitewide remedy.

Modificatio n of two foot permeable soils cover on Parcel WESE : The ROD requires a 2-footthick monolayer soils cover on Parcel WESE . A vegetation plan would then be implemented

with drought tolerant plant species consistent with the local ecosystem. Continued site

investigations concurrent with the remedial design have indicated that, contaminated soils are

generally within the uppermost 6 inches for the majority of the site. Due to the proximity of the Midvale Slag OU2 Site , it is more economical to excavate and relocate the contaminated soils.

Thi s modificatio n to the ROD offers two advantages; one, it is more economical; and two it

provides for clean, developable property. Initial cost comparisons indicate that possibly 30 to 40

percent reduction in total remediation cost for the WESE parcel may be realized. Thi s savings

can be mostly attributed to the fact that lower costs are incurred in excavating, loading, hauling,

and unloading 6 inches of material than would be if 18 inches of fill material were excavated,

loaded, hauled, and unloaded with similar haul distances. Thi s change is in compliance with all Applicable or Relevant and Appropriate Requirements.
Elimination of controls implemented for the protection of the permeable soil cover: Due to the

remedy change and elimination of the permeable soil cover, the need to protect the cover is no

longer needed. Thi s leaves the WES E parcel more developable by not restricting future

excavation.

SUPPORT AGENCY COMMENT S

T he EPA concurs with the remedy changes presented in this ESD. AFFIRMATION OF THE STATUTOR Y DETERMINATIONS

Considering the new information that has been developed and the changes that have been made

to the selected remedy, UDEQ and EPA believe the remedy: remains protective of human health

and the environment; complies with applicable or relevant federal and state requirements

appropriate to this remedial action at the time the original ROD was signed; is cost effective; and

utilizes permanent solutions to the maximum extent practicable for this site.

PUBLIC PARTICIPATION ACTIVITIE S

Notice is hereby made that this ESD and its supporting documentation is available for review

through the administrative record file located at the above listed locations.