# EPA United States

Environmental Protection Agency 1200 PennsylvaniaAvenue, N.W. Washington, DC 20460 April 20 1 6

O ce of Land and Emergency Management



# Support Document for the

Revised National Priorities List

Final Rule – Iowa-Nebraska Light & Power Co

# Support Document for the

Revised National Priorities List

Final Rule

Iowa

- Nebraska Light & Power Co
April 2016

Site Assessment and Remedy Decisions Branch Office of Superfund Remediation and Technology Innovation Office of Land and Emergency Management U.S. Environmental Protection Agency Washington, DC 20460Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

i Table of Contents

Executive Summary

................................................................................................ ................................................. ii

Introduction

............................................................................................................................................................ iii

Background of th e NPL

....................................................................................................................................... iii

Development of the NPL

..................................................................................................................................... iii

Hazard Ranking System

....................................................................................................................................... iv

Other Mechanisms for Listing ...............................................................................................................................v

Organization of this Document ..............................................................................................................................v

Glossary

............................................................................................................................................................... vi

1. L ist of Commenters and Correspondence .....................................................................................................1

2. S ite Description ................................................................................................................................................1

3. S ummary of Comments ...................................................................................................................................4

3.1 Support for Listing and Other Non-opposition Comments .......................................................................4

3.2 Deferral .......................................................................................................................................................5

3.3 Liability ......................................................................................................................................................5

3.4 Removal Ac tivities .....................................................................................................................................6

3.5 Ground Water Flow Direction ....................................................................................................................6

3.6 Likelihood of Release ...............................................................................................................................10

3.7 Waste Characteristics ...............................................................................................................................14

3. 7.1 Toxicity/Mobility

................................................................................................ ............................................ 14

3.7.2 Source Hazardous Waste Quantity

.................................................................................................................. 16

3.7.3 Pathway Hazardous Waste Quantity

............................................................................................................... 18

3.8 Targets ......................................................................................................................................................22

3.9 H RS Score ................................................................................................................................................26

3.10 Non -Scoring Factual Error .......................................................................................................................26

4. C onclusion ......................................................................................................................................................27Iowa

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ii 

## Executive Summary

Section 105(a)(8)(B) of CERCLA, as amended by SARA, requires that the EPA prepare a list of national priorities among the known releases or threatened releases of hazard ous substances, pollutants, or contaminants throughout the United States. An original National Priorities List (NPL) was promulgated on September 8, 1983 (48 FR 40658). CERCLA requires that EPA update the list at least annually.

This document provides responses to public comments received on the Iowa- Nebraska Light & Power Co site

, proposed on September 30, 2015 (80 FR 58658). This site is being added to the NPL based on an evaluation under EPA’s Hazard Ranking System (HRS) in a final rule published in the Federal Register in March 2016.Iowa

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iii 

## Introduction

This document explains the rationale for adding the Iowa- Nebraska Light & Power Co site in Norfolk, Nebraska to the National Priorities List (NPL) of uncontrolled hazardous waste si tes and provides responses to public comments received on this site listing proposal. The EPA proposed this site to the NPL on September 30, 2015 (80 FR 58658). This site is being added to the NPL based on an evaluation under the Hazard Ranking System (HR S) in a final rule published in the Federal Register in March 2016.



### Background of the NPL

In 1980, Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), 42 U.S.C. Sections 9601 et seq . in response to the dang ers of uncontrolled hazardous waste sites. CERCLA was amended on October 17, 1986, by the Superfund Amendments and Reauthorization Act (SARA), Public Law No. 99-499, stat., 1613 et seq. To implement CERCLA, EPA promulgated the revised National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40 CFR Part 300, on July 16, 1982 (47 FR 31180), pursuant to CERCLA Section 105 and Executive Order 12316 (46 FR 42237, August 20, 1981). The NCP, further revised by EPA on September 16, 1985 (50 FR 37624) and November 20, 1985 (50 FR 47912), sets forth guidelines and procedures needed to respond under CERCLA to releases and threatened releases of hazardous substances, pollutants, or contaminants. On March 8, 1990 (55 FR 8666), EPA further revised the N CP in response to SARA.

Section 105(a)(8)(A) of CERCLA, as amended by SARA, requires that the NCP include

criteria for determining priorities among releases or threatened releases throughout the United States for the purpose of taking remedial action an d, to the extent practicable, take into account the potential urgency of such action, for the purpose of taking removal action.

Removal action involves cleanup or other actions that are taken in response to emergency conditions or on a

short- term or tempo rary basis (CERCLA Section 101). Remedial action is generally long-term in nature and involves response actions that are consistent with a permanent remedy for a release (CERCLA Section 101). Criteria for placing sites on the NPL, which makes them eligible for remedial actions financed by the Trust Fund established under CERCLA, were included in the HRS. EPA promulgated the HRS as Appendix A of the NCP (47 FR 31219, July 16, 1982). On December 14, 1990 (56 FR 51532), EPA promulgated revisions to the HRS in response to SARA, and established the effective date for the HRS revisions as March 15, 1991.

Section 105(a)(8)(B) of CERCLA, as amended, requires that the statutory criteria provided by the HRS be used to prepare a list of national priorities among t he known releases or threatened releases of hazardous substances, pollutants, or contaminants throughout the United States. The list, which is Appendix B of the NCP, is the NPL.

An original NPL of 406 sites was promulgated on September 8, 1983 (48 FR 40658). At that time, an HRS score

of 28.5 was established as the cutoff for listing because it yielded an initial NPL of at least 400 sites, as suggested by CERCLA. The NPL has been expanded several times since then, most recently on September 30, 2015 (80 FR 58620). The Agency also has published a number of proposed rulemakings to add sites to the NPL. The most recent proposal was on September 30, 2015 (80 FR 58658).



### Development of the NPL

The primary purpose of the NPL is stated in the legislative history of CERCLA (Report of the Committee on Environment and Public Works, Senate Report No. 96-848, 96th Cong., 2d Sess. 60 [1980]).

The priority list serves primarily informational purposes, identifying for the States and the public those facilities and sites or other releases which appear to warrant remedial actions. Inclusion of aIowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

iv facility or site on the list does not in itself reflect a judgment of the activities of its owner or operator, it does not require those persons to undertake any action, nor does it assign liability to any person. Subsequent government actions will be necessary in order to do so, and these actions will be attended by all appropriate procedural safeguards.

The NPL, therefore, is primarily an informational and management tool . The identification of a site for the NPL is intended primarily to guide EPA in determining which sites warrant further investigation to assess the nature

and extent of the human health and environmental risks associated with the site and to determine wh at CERCLA

financed remedial action(s), if any, may be appropriate. The NPL also serves to notify the public of sites EPA believes warrant further investigation. Finally, listing a site may, to the extent potentially responsible parties are

identifiable a t the time of listing, serve as notice to such parties that the Agency may initiate CERCLA -financed

remedial action.

CERCLA Section 105(a)(8)(B) directs EPA to list priority sites among the known releases or threatened release of hazardous substances, pollutants, or contaminants, and Section 105(a)(8)(A) directs EPA to consider certain enumerated and other appropriate factors in doing so. Thus, as a matter of policy, EPA has the discretion not to use CERCLA to respond to certain types of releases. Where other authorities exist, placing sites on the NPL for possible remedial action under CERCLA may not be appropriate. Therefore, EPA has chosen not to place certain types of sites on the NPL even though CERCLA does not exclude such action. If, however, the Agency later determines that sites not listed as a matter of policy are not being properly responded to, the Agency may consider placing them on the NPL.



### Hazard Ranking System

The HRS is the principle mechanism EPA uses to place uncontrolled waste sites on the NPL. It is a numerically based screening system that uses information from initial, limited investigations

-- the preliminary assessment and site inspection

-- to assess the relative potential of sites to pose a threat to human health or the enviro nment. HRS scores, however, do not determine the sequence in which EPA funds remedial response actions, because the information collected to develop HRS scores is not sufficient in itself to determine either the extent of contamination or the appropriate response for a particular site. Moreover, the sites with the highest scores do not necessarily come to the Agency's attention first, so that addressing sites strictly on the basis of ranking would in some cases require stopping work at sites where it was already underway. Thus, EPA relies on further, more detailed studies in the remedial investigation/feasibility study that typically follows listing.

The HRS uses a structured value analysis approach to scoring sites. This approach assigns numerical valu es to factors that relate to or indicate risk, based on conditions at the site. The factors are grouped into three categories. Each category has a maximum value. The categories are:

• likelihood that a site has released or has the potential to release ha zardous substances into the environment;

• characteristics of the waste (toxicity and waste quantity); and

• people or sensitive environments (targets) affected by the release.

Under the HRS, four pathways can be scored for one or more threats as identified below:

• Ground Water Migration (S gw ) - drinking waterIowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

v • Surface Water Migration (S

sw ) The following threats are evaluated for two separate migration components, overland/flood migration and

gr ound water to surface water. - drinking water

- human food chain

- sensitive environments

• Soil Exposure (S

s )

- resident population - nearby population

- sensitive environments

• Air Migration (S

a ) - population

- sensitive environments

After scores are calculated for one or more pathways according to prescribed guidelines, they are combined using the following root

- mean -square equation to determine the overall site score (S), which ranges from 0 to 100 :



### 4 S + S + S + S = S 2

a 2

s 2

sw 2

gw

If al l pathway scores are low, the HRS score is low. However, the HRS score can be rel atively high even if only one pathway score is high. This is an important requirement for HRS scoring because some extremely dangerous sites pose threats through only one pathway. For example, buried leaking drums of hazardous substances can

contaminate drinking water wells, but

-- if the drums are buried deep enough and the substances not very volatile

-- not surface water or air.



### Other Mechanisms for Listing

There are two mechanisms other than the HRS by which sites can be placed on the NPL. The first of these mechanisms, authorized by the NCP at 40 CFR 300.425(c)(2), allows each State and Territory to designate one site as its highest priority regardless of score. The last mechanism, authorized by the NCP at 40 CFR 300.425(c)(3), allows listing a sit e if it meets the following three requirements:

• Agency for Toxic Substances and Disease Registry (ATSDR) of the U.S. Public Health Service has issued a health advisory that recommends dissociation of individuals from the release;

• EPA determines the site poses a significant threat to public health; and

• EPA anticipates it will be more cost

- effective to use its remedial authority than to use its emergency removal authority to respond to the site.

• 

### Organization of this Document

The following section contains EPA responses to site- specific public comments received on the proposal of the

Iowa -Nebraska Light & Power Co site on September 30, 2015 (80 FR 58658). The site discussion begins with a list of commenters, followed by a site description, a summary of comments, and Agency responses to each comment. A concluding statement indicates the effect of the comments on the HRS score for the site.Iowa

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vi 

### Glossary

The following acronyms and abbreviations are used throughout the text:

Agency U.S. Environmental Protection Agency

APA Administrative Procedure Act

ATSDR Agency for Toxic Substances and Disease Registry

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act of 1980, 42

U.S.C. Sections 9601 et seq ., also known as Superfund

CFR Code of Federal Regulations

CLP EPA Contract Laboratory Program

CRDL Contract- required detection limit

CRQL Contract- required quantitation limit

DL Detection limit

EE/CA Engineering Evaluation/Cost Analysis

EPA U.S. Environmental Protection Agency

ESI Expanded Site Inspection

FMGP Former Manufactured Gas Plant

FR Federal Register

HRS Hazard Ranking System, Appendix A of the NCP

HRS score Overall site score calculated using the Hazard Ranking System; ranges from 0 to 100

LUST Leaking Underground Storage Tank

MCL Maximum contaminant level

μg/kg Microgram per kilogram

MGP Manufactured gas p lant

NCP National Oil and Hazardous Substances Pollution Contingency Plan, 40 C.F.R. Part 300

NDEQ Nebraska Department of Environmental Quality

NPL National Priorities List, Appendix B of the NCP

PAH Polycyclic aroma tic h ydrocarbon

PRP Potential ly responsible p arty

RI Remedial I nvestigation

SARA Superfund Amendments and Reauthorization Act

SCDM Superfund Chemical Data Matrix

SOW Statement of work

SQL Sample quantitation limit

TDL Target distance limit

VCP Voluntary Cleanup ProgramIowa

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1 

### 1. List of Commenters and Correspondence

EPA

- HQ

- SFUND -2015-0578-0004 Correspondence, dated July 7, 2015, from Pete Ricketts, Governor, State of Nebraska.

EPA

- HQ

- SFUND -2015-0578-0005 Comment, dated November 30, 2015, submitted by Adam R. Troutwine, Polsinelli PC on behalf of Centel Corporation and Black Hills/Nebraska Gas Utility Company LLC.

EPA

- HQ

- SFUND -2015-0578-0006 Comment, dated November 30, 2015, submitted by Adam R.

Troutwine , Polsinelli PC on behalf of Centel Corporation and Black Hills/Nebraska Gas Utility Company LLC . (Duplicate

Submission of EPA- HQ

- SFUND -2015-0578-0005)



### 2. Site Description

The Iowa- Nebraska Light & Power Co site (the Site) is located in Norfolk, Nebraska . (S ee Figures 1 and 2 of this support document). The Site is a result of the release of hazardous substances, including benzo(a)pyrene, caused by facility operations at a former manufactured gas facility. The contamination includes contaminated soil and migration of the release to ground water. Evidence of releases from the former manufactured gas plant operations to ground water are documented by the presence of a benzo(a)pyrene in the ground water underlying the contaminated soil source and in monitoring wells downgradient of the soil source. Ground water contamination

from the facility has been found in the interconnected alluvial and chalk aquifer system underlying the facility. Eleven active municipal drinking water wells and 8 other public drinking water supply wells located within the 4

- mile target distance limit (TDL) withdraw water from these aquifer systems . (See Figure 6 of this support document). Populations drinking water from these wells include students, workers, and residents.

The Iowa- Nebraska Light & Po wer facility is located in downtown Norfolk, Madison County, Nebraska. Coal gas was produced at the facility using a water -gas process from approximately 1902 until 1945. Some of these production wastes, including coal tar, were sold and some were disposed of at the facility. Coal tar is primarily composed of polycyclic aromatic hydrocarbons (PAHs), including benzo(a)pyrene, phenolic compounds, light aromatic compounds, various inorganics, and various sulfides.

Between November 2013 and June 2014

, removal activities occurred at the facility as required by the Administrative Settlement Agreement and Order on Consent for Removal Action established with EPA. Contaminated soil and highly concentrated residuals (source material) were excavated and transported o ff the property for disposal. Soil was excavated to depths ranging from 2.5 to 17 feet below ground surface across the majority of the property. Following the removal action, soil samples were collected from the base and walls of the

excavation to evaluate residual soil contamination . The final wall confirmation samples were documented to contain benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, and indeno(1,2,3

- cd)pyrene at concentrations exceeding cleanup levels, documenting that contaminated soil remains at the Site. In addition, the release from the contaminated soil, and possibly from other historic sources, at the facility to shallow ground water was not addressed as part of the removal activities.Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

2 Figure 1 – Site Location MapIowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

3 Figure 2

– Property Layout MapIowa

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4 

### 3. Summary of Comments

Pete Ricketts, Governor of Nebraska, concurred with EPA’s proposal to place the Site on the NPL, asserting the placement of the Site on the NPL is the appropriate approach to address the environmental concerns associated

with the Site.

Pol sinelli PC

, on behalf of Centel Corporation and Black Hills/Nebraska Gas Utility Company (Centel)

, submitted comments in opposition to placing the Site on the NPL. Centel asserted that the organization is currently engaged in discussions with Nebraska Department of Environmental Quality (NDEQ) regarding enrollment in a Voluntary Cleanup Program (VCP), and stated that the Site should not be placed on the NPL if

enrollment occurs.

Centel expressed concern that intermingling of contamination from the Site with contamination from nearby Leaking Underground Storage Tanks (LUSTs) may have facilitated contam inant migration from t he contaminated

soil source.

Centel also commented that the Site should not be listed on the NPL because removal activities conducted at the facility have addressed soil contamination a bove the ground water table.

Centel submitted comments questioning the technical accuracy of the HRS scoring of the Site. Centel commented that correcting for alleged technical errors would reduce the site score to below the NPL eligibility threshold of

28.50. Centel specifically commented on factor values assigned to likelihood of release, hazardous waste quantity

, and toxicity/mobility. Centel asserted that revisions should be made including:

• Identifying that ground water flow is to the southeast and not to the east/southeast.

• Considering the impac t of LUST s in facilitating contaminant migration from the contaminated soil

source.

• Assign ing a toxicity/mobility factor value based on naphthalene.

• Evaluating hazardous waste quantity using the actual area of the tar impacted area

.

• Revising the w aste characteristics factor value based on revisions to pathway hazardous waste quantity

and the toxicit y/mobility factor values.

• Reconsidering the eligibility of municipal wells as targets

.

Based on these issues, Centel asserted that the site score sho uld be reduced to 13.6 which is below the NPL eligibility score of 28.50.



### 3.1 Support for Listing and Other Non-opposition Comments

Comment : The Honorable Pete Ricketts, Governor of Nebraska, expressed support for the proposal to place the Site on the NPL. In his letter to Mark Hague, Acting Regional Administrator, EPA Region 8, he stated, “I concur with EPA's proposal to list the Norfolk site on the National Priorities List.... Based on the available information, the proposed listing is the appropriate approach to address this environmental concern. ”

Response : EPA i s add ing the Iowa

- Nebraska Light & Power Co site to the NPL. Listing makes a site eligible for remedial action funding under CERCLA, and EPA will examine the site to determine what response, if any, is appropriate. EPA will determine the need for using Superfund monies for remedial activities on a site-by- site basis, taking into account the NPL ranking, s tate priorities, further site investigation, other response alternatives,

and other factor s as appropriate.Iowa

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5 

### 3. 2 Deferral

Comment : Centel commented that site cleanup should be deferred to the St ate. Centel commented that it i s exploring the possibility of enrolling in a voluntary cleanup program (VCP) through the NDEQ. Centel assert s that enrollment in this program , to address ground water contamination, would render placing the Site on the NPL unnecessary and duplicative.

Response : Placing the Iowa

- Nebraska Light & Power Co site on the NPL is an appropriate step in addressing the

contamination at the Site, and t he State of Nebraska has also provided support for placing the Site on the NPL

. In a July 7, 2015 letter from Pete Ricketts, Governor of the State of Nebraska (docket ID EPA

- HQ

- SFUND -2015- 0578-0004), to EPA , the Governor stated:

I concur with EPA 's proposal to list the Norfolk site on the National Priorities List. My recommendation is based on written comments received from Norfolk Mayor Sue Fuchtman who

has the full support of the City Council members, in addition to the information that has been provided to me by the Nebraska Department of Environmental Quality and the U.S. Environmental Protection Agency. Based on the available information, the proposed lis ting is the appropriate approach to address this environmental concern.

...

The State of Nebraska will continue to provide cooperative support as we move forward in the Superfund remedial action process.

Furthermore , on May 3, 1995, EPA issued its "Guidanc e on Deferral of NPL Listing Determinations While States Oversee Response Actions." EPA developed the guidance in an effort to enhance the State role in addressing sites. The deferral program is an administrative tool that enable s States and Tribes, under their own laws, to respond at

sites that EPA would otherwise not soon addre ss. In the case of the Iowa

- Nebraska Light & Power Co , EPA has

decided that deferral to the State of the Nebraska is not appropriate, in part, because the State of Nebraska has

conc urred with the proposal to place the Site on the NPL.

Regarding Centel’s specific comment that listing the Site on the NPL would be duplicative of work completed as a part of a VCP , placing a site on the NPL does not represent a decision that r emedia tion is necessary

. The NPL is only identification that a site warrants further investigation . It is not identification that remedial actions will be

taken . I t is also not relevant at this stage of the Superfund process to address which statutory authorities wi ll be

used to conduct remedial activities . Furthermore, adding a site to the NP L does not prevent interested parties from pursuing, or joining , any alternative cleanup program including the voluntary cleanup program.



### 3.3 Liability

Comment : Centel submitted comments questioning the role of other facilities , specifically the nearby Leaking Underground Storage Tank ( LUST ) sites that may have facilitated the migration of contaminants from the Iowa

Nebraska Light & Power Co facility to ground water . Cen tel specifically commented that “ [i] ntermingling of the plumes may facilitate migration of contaminants from the Site.”

Response : In as much as Centel’s comments could be interpreted as raising issues regarding the liability for the release to ground water being evaluated in the HRS documentation record at proposal , l iability is not considered in evaluating a site under the HRS. The NPL serves primarily as an informational tool for use by EPA in identifying those sites that appear to present a significant risk to public health or the environment. Listing a site on the NPL does not reflect a judgment on the activities of the owner(s) or operator(s) of a site. It does not require those persons to undertake any action, nor does it assign any liability to any person. This position, stated in the legislative history of CERCLA, has been explained more fully in the Federal Register (48 FR 40674, September 8, 1983, and 53 FR 23988, June 24, 1988). See Kent County v. EPA, 963 F.2d 391 (D.C. Cir. 1992). CommentsIowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

6 regarding the likelihood of release due to releases from other facilities ar e addressed below in section 3.6

, Likelihood of Release, of this support document.



### 3.4 Removal Activities

Comment : Centel commented that contamination at the facility has been ad dressed through removal activities

conducted. Centel asser ted that the removal action (conducted between November 2013 and June 2014) removed all contaminants in the soil at the Site above the ground water table and stated that the soil was restored to E PA specified cleanup levels.

Response : The HRS evaluation of the Site properly consider ed removal activities and the conditions at the Site post removal activities. The HRS evaluation of the Site was based on current conditions, including the continued presence of contamination in both soil and ground water following these removal activities.

Regarding the consideration of removals in the HRS scoring of a site, Part III Section Q of the Preamble to the HRS, Consideration of Removal Actions (Current Versus Initial Conditions, 55 FR 51568, December 14,1990), explains that EPA will calculate waste quantities based on “current conditions,” which may differ from initial conditions as a result of a response action. The HRS documentation record at proposal explains that the Site was scored based on current conditions following removal activities. The specific technical considerations of removal activities in the HRS scoring of the Site are addressed in detail in sections below.



### 3.5 Ground Water Flow Direction

Comment : Centel submitted comments questioning the ground water flow direction in the vicinity of the Site. Centel commented that the ground wa ter flow direction was to the southeast and not to the east/southeast as statedin the HRS documentation record at proposal, while the municipal wells are located to the east of the IowaNebraska Light & Power Co facility.

Response : The HRS documentation record at proposal correctly identified the ground water flow direction in the

vicinit y of the Iowa

- Nebraska Light & Power Co facility as flowing towards the east/southeast. As discussed in detail below, based on the data available, the ground water flow direction includes both east and southeasterly components. Centel did not disagree with the southeasterly component and did not provide any specific support
for the assertion that the easterly component of the ground water flow direction is suspect.

The H RS does not provide requirements for determining the ground water flow direction or require that ground water flow direction be determined. However, the ground water flow direction was used in the HRS evaluation of the Site to support the attribution of co ntaminants identified in samples from the monitoring wells, used to establish an observed release to ground water , to the Site.

In establishing the ground water flow direction, the HRS documentation record at proposal on page 41 states:

Ground water lev els were measured in all the INL&P monitoring wells during the EE/CA field investigation in July 2009. The depth to ground water at each well relative to the top of casing and the corresponding ground water elevation are presented in Table 3-1, page 57 of Reference 34. The ground water levels were used to generate potentiometric surface maps for water levels measured from both the “A” and “B” wells, Figure 3 -3, page 79 of Reference 34, and Figure 3-4, page 80 of Reference 34. These maps indicate an east/sou theast direction of ground water flow in the surficial aquifer across INL&P.

The flow direction was determined using potentiometric surface maps developed from ground water levels in wells from the vicinity of the Iowa

- Nebraska Light & Power Co facility. (Figures 3 -3 and 3-4 of the EE/CA report are presented below, as Figures 3 and 4 of this support document.) As shown in F igure 3 of this supportIowa

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7 document, the potentiometric surface map presents an easterly component to the ground water flow direction, based on the ground water elevations in wells in the vicinity of the Iowa- Nebraska Light and Power Co facility. This information was used in the HRS evaluation to establish that a localized ground water flow direction of east/southeast is present. Therefore, the ground water flow direction in the vicinity of the facility is to the

east/southeast , as it is described in HRS documentation record at proposal.

This comment results in no change to the HRS score and no change in the decision to place the Site on the N PL.Iowa

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8 F igure 3

– Potentiometric Surface Map for “A” Level Monitoring WellsIowa

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9 F igure 4

– Potentiometric Surface Map for “B” Level Monitoring WellsIowa

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10 

### 3.6 Likelihood of Release

Comment : Centel submitted comments questioning the cause of the migration of contamination from the Site to ground water. Centel asserted that the intermingling of LUS T related contaminant plumes may have facilitated the migr ation of contaminants from the Site. Cen tel further commented that LUST related contamination would be “contributing to the levels of ground water contamination caused by MGP [Manufactured Gas Plant] operations

alone.”

Response : The significant increase in hazardous substance concentrations in ground water was attributed

, at least in part, to a release from the Iowa

- Nebraska Light and Power Co facility . This attribution was conducted consistently with the HRS and was properly presented in the HRS documentation record at proposal. The significant increase in manufactured gas plant related hazardous substances would not be present in ground water,

if it were not for the initial release of hazardous substances to soil from the facility from which the hazardous substances migrated to g round water. Centel contends that the contamination of the Iowa- Nebraska Light & Power Co property might not have migrated into the aquifer nearby if LUSTs did not facilitate the migration of contamination; however, Centel does not dispute that contamination was released from, and has migrated from,

the Iowa- Nebraska Light & Power Co facility or that a significant increase in contaminant concentrations has

been documented in an aquifer at the Site. Additionally, Centel has not provided any evidence demonstr ating that the presence of LUSTs in the vicinity have facilitated the migration of contamination from the soil contamination

at the Iowa- Nebraska Light and Power Co facility

.

Insomuch as these comments question the likelihood of release, t he HRS documenta tion record at proposal established that at least some portion of the significant increase in contamination, including benzo(a)pyrene in the ground water scored is attributable to the Iowa-Nebraska Light & Power Co site.

In evaluating the likelihood of r elease factor, HRS Section 3.1

, Likelihood of release

, states:

For an aquifer, evaluate the likelihood of release factor category in terms of an observed release factor or a potential to release factor.

In establishing an observed release, HRS Section 3.1.1

, Observed r elease

, states:

Establish an observed release to an aquifer by demonstrating that the site has released a hazardous substance to the aquifer. Base this demonstration on either:

• Direct observation

— a material that contains one or more ha zardous substances has been deposited into or has been observed entering the aquifer.

• Chemical analysis

— an analysis of ground water samples from the aquifer indicates that the concentration of hazardous substance(s) has increased significantly above the background concentration for the site (see section 2.3). Some portion of the significant increase must be

attributable to the site to establish the observed release , except: when the source itself consists of a ground water plume with no identified source, no separate attribution is required (emphasis added)

As referenced in HRS Section 3.1.1, quoted above, HRS Section 2.3, Likelihood of release

, further directs

to :

Establish an observed release either by direct observation of the release of a hazardous substance into the media being evaluated (for example, surface water) or by chemical analysis of samples appropriate to the pathway being evaluated (see sections 3, 4, and 6). The minimum standard to establish an observed release by chemical analysis is analytical evidence of a hazardous substanceIowa

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11 in the media significantly above the background level. Further , some portion of the release must

be attributable to the site . Use the criteria in T able 2

– 3 as the standard for determining analytical significance. (The criteria in T able 2 –3 are also used in establishing observed contamination for the soil exposure pathway, see section 5.0.1.) Separate criteria apply to radionucl ides (see section 7.1.1). (emphasis added)

HRS Table 2

- 3 outlines the criteria to determine analytical significance when establishing a significant

increase. It states:

Table 2 –3— Observed Release Criteria for Chemical Analysis Sample Measurement < Sample Q uantitation Limit a

No observed release is established. Sample Measurement ≥ Sample Quantitation Limit a

An observed release is established as follows: • If the background concentration is not detected (or is less than the detection limit), an observed release is established when the sample measurement equals or exceeds the sample quantitation limit. a • If the background concentration equals or exceeds t he detection limit, an observed release is established when the sample measurement is 3 times or more above the background

concentration.

a If the sample quantitation limit (SQL) cannot be established, determine [sic] if there is an observed release as follows:

— If the sample analysis was performed under the EPA Contract Laboratory Program, use the EPA contract

- required quantitation limit (CRQL) in place of the SQL.

— If the sample analysis is not performed under the EPA Contract Laboratory Program, use the detection limit (DL) in place of the SQL.

Pages 44 –58 of the HRS documentation record at proposal establishes that a significant increase in

contaminant concentrations has occurred in the aquifer being evaluated

. Cen tel does not contend that a significant increase in contaminant concentrations in ground water has not occurred.

In documenting that the significant increase is attributable

, at least in part, to the Site, p ages 59 –60 of theHRS documentation record at proposal describe the attribution of the significant increase to the IowaNebraska Light & Power Co site. It states:

The Iowa-Nebraska Light and Power Company operated under numerous names in Norfolk, Nebraska, from about 1907 through the mid- to late -1940s (Refs. 6, p. 3; 8, pp. 8, 9; 9. During this time, the facility operated as a manufactured gas plant (Ref. 7, pp. 3, 5). Operations at the facility used fossil fuel (coal and oil) as a feedstock to produce a combustible gaseous product

that was u sed for lighting and heating (Refs. 8, p. 9; 9, pp. 3-5). The manufacturing process generated several byproducts including tars, sludges, tar liquors and ammonia liquor, spent iron oxide ash, slag, and clinkers (Ref. 19, pp. 3 - 32). The coal tars are comp osed of polycyclic aromatic hydrocarbons (PAHs), phenolic compounds, light aromatic compounds, and small quantities of inorganic constituents (Refs. 8, pp. 9, 11; 19, pp. 9 through 14). ...

Generators produced a combustible gas using coke, steam, and oil products (Ref. 39, p. 6). As the gas cooled through the production process, coal tar would fall from suspension in the gas and become a waste product (Ref. 39, p. 6). A scrubber was used to condense the gas (Ref. 39, p. 6). Coal tar was ultimately separated from the condensate water (Ref. 39, p. 6). Purifier boxes were used to remove sulfides and cyanides from the cool gas. Iron oxides were mixed with fluffing material (primarily wood chips, sawdust and corncobs) in the purifier boxes to provide for additional removal of water vapor and coal tar with the associated hydrogen sulfide and cyanide (Ref. 39, p. 6). After the gas was manufactured, it was stored in gas holders. Coal tar residuals were also present in the gas holders (Ref. 39, p. 6).Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

12 Some of the waste resulting from the production of the manufactured gas, including coal tar, was sold. Some wastes were disposed of at the facility (Ref. 39, p. 7). Coal tar is primarily composed of PAHs, phenolic compounds, light aromatic compounds, various inorganics and various sulfides (Ref. 39, pp. 6, 7). ...As documented in Section 2 of this HRS documentation record, soil samples collected at the facility contained elevated concentrations of the same constituents as were reported in ground water samples collected from on-site monitoring wells and temporary monitoring wells. Background wells did not indicate other potential sources of coal tar related hazardous constituents in the immediate site vicinity. There are no other known source areas at the INL&P facility. The EE/CA described 29 leaking underground storage tank sites within 0.5 mile of the facility and 16 underground storage tanks within 0.25 mile (Ref. 34, pp. 12, 13, 98, 99, 100). These leaking underground storage tanks may be contributing petroleum related

co nstituents to area. Ground water flow is to the east, south east (Ref. 34, pp. 79, 80, 85-88). Most of the USTs and/or LUST sites are located downgradient of both the source and temporary wells used to establish the observed release and/or are located upgr adient of background samples used in the scoring (Ref. 34, p. 105; Figure 2 of this HRS documentation record).

Evidence of releases from the former MGP operations to ground water is evidenced in the presence of DNAPL in ground water underlying and downgr adient of the contaminated soil

source , as documented in the EE/CA ground water investigation (Ref. 34, pp. 36, 37). The approximate extent of DNAPL contamination is shown in Figure 4-11, page 91 of Reference 34. (emphasis added)

These manufactured gas pl ant related contaminants would not be present in ground water if it were not for the

release from the Iowa

- Nebraska Light & Power Co site . This release is acknowledged by Centel in its comment

letter stating that “[c]ontamination from the LUST sites was de tected in the field investigation a ctivities



### ..., thus contributing to the levels of ground water contamination caused by MGP operations alone. ” Based on ground water flow direction and the location of background and release samples relative to the LUST sites, it is reasonable to attribute at least some portion of the increase in contamination levels to the release from the manufactured gas plant operati ons documented identified in ground water downgradient of the facility

. (See Figure s 3, 4

, and 5 of this support document).

Regarding contaminant migration from the facility, Centel does not disagree that contamination has migrated from the Iowa- Nebraska Light & Power Co facility to the aquifer and ground water, or that a significant increase in contaminant concentrations has occurred. As t he requirements for establishing this significant increase in the HRS are quoted above, the requirements do not speci fy a method, or cause of migration

, be determined to establish a release to an aquifer beyond the ability to attribute at least part of the significant increase in contaminant levels to the S ite . In addition to a release of contamination (not contested by Centel) the HRS requires that some portion of the release must be attributable to the Site. As established above, the HRS documentation record at proposal properly attributed at least some portion of the significant increase to the Site

.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

13 F igure 5 – Expanded Site Inspection Background and Observed Release Well Locatio nsIowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

14 

### 3. 7 Waste Characteristics

Comment : Centel commented that the waste characteristics factor should be recalculated based on changes to toxicity/mobility , source hazardous waste quantity , and pathway hazardous waste quantity factors

. Centel

asserted that the recalculation should be based on:

• Using naphthalene to assign a toxicity/mobility factor

.

• Using the full delineation of the area of tar in estimating the source hazardous waste quantity value

.

• Using revisions to the source hazardous waste quantity to revise to pathway hazardous waste quantity.

Cente l concluded that a recalculation using the above factors results in a waste characteristics factor of “6, rather than an 18 as currently set out in the HRS Documentation Record. ”

Response : The HRS documentation record at proposal properly evaluated waste characteristics based on appropriate toxicity/mobility and hazardous waste quantity factor values. The following subsections of this support document address specific assertion s rega rding the evaluation of waste characteristics :

3.7.1 Toxicity/Mobility

3.7.2 Source Hazardous Waste Quantity

3.7.3 Pathway Hazardous Waste Q uantity

3 .7.1 T oxicity/Mobility

Comment : Centel asserted that the toxicity/mobility factor should be revised to evaluate naphthalene as the

“ hazardous substance of concern ” instead of benzo(a)pyrene. Centel commented that the appropriate designation of naphthalene as “the hazardous substance of g reatest concern” would reduce the toxicity mobility factor value from 10,000 to 1,000.

Centel commented that the mobility characteristics of naphthalene made this substance the more appropriate

hazardous substance to use to assign the toxicity / mobility f actor value . Centel commented that the organic carbon partitioning coefficient for benzo(a)pyrene is higher than naphthalene, indicating that benzo(a)pyrene is more likely to adhere to soil than migr ate through ground water. Centel also asserted that it would be more appropriate

to consider naphthalene as the substance with the greatest potent ial for ground water migration, because it has the greatest potential to migrate to a receptor

.

Response : The HRS documentation record at proposal properly evaluated benzo(a)pyrene as the substance receiving the highest combined toxicity/mobility factor value, in accordance with the HRS

. In evaluating toxicity and mobility, HRS Sections 3.2.1, Toxicity/mobility direct s:

For each hazardous substance [ for hazardous substances at the site that are available to the pathway 1 ], assign a toxicity factor value, a mobility factor value, and a combined toxicity/mobility factor value as specified in the following sections. Select the toxicity/mobility

factor v alue for the aquifer being evaluated as specified in section 3.2.1.3.

In assigning toxicity, HRS Section 3.2.1.1, Toxicity

, states to, “[a] ssign a toxicity factor value to each hazardous substance as specified in Section 2.4.1.1.”

1 HRS Section 2.4.1.1, Toxicity factor, proscribes the criteria for identifying hazardous substances eligible for evaluating toxicity.Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

15 HRS Section 2.4.1.1, Toxicity factor

, explains how to assign toxicity , “based on quantitative doseresponse parameters” for magnitude of cancer slope factors, non

- cancer toxicological responses of chronic exposure , and non- cancer toxicological responses of acute exposure. To d etermine a mobility

value in the instance when t hat hazardous substance i s in an observed release , HRS Section 3.2.1.2, Mobility

, directs to :

Assign a mobility factor value to each hazardous substance for the aquifer being evaluated as

follows:

• For any hazardous substance that meets the criteria for an observed release by chemical analysis to one or more aquifers underlying the sources at the site, regardless of the aquifer being evaluated, assign a mobility factor value of 1.

HRS Section 3.2.1.3, C alculation of toxicity/mobility factor value , states:

Assign each hazardous substance a toxicity/mobility factor value from Table 3 -9, based on the values assigned to the hazardous substance for the toxicity and mobility factors. Use the

hazardous substa nce with the highest toxicity/mobility factor value for the aquifer being evaluated to assign the value to the toxicity/mobility factor for that aquifer. Enter this value in

Table 3 -1.

In determining the hazardous substance with the highest combined toxic ity mobility value, the HRS documentation record at proposal evaluated the characteristics of hazardous substances at the Site. Page 61 of the HRS documentation record at proposal presents the toxicity and mobility values assigned to hazardous substances

s cored and states:

TABLE 22

TOXICITY/MOBILITY FACTOR VALUES

Hazardous Substance Source

Number Toxicity

Factor

Value Mobility

Factor

Value* Does

Hazardous

Substance

Meet

Observed

Release?** Toxicity/ Mobility

Factor

Value (Ref. 1,

Table 3

- 9) Reference Acenaphthene 1 10 1* Yes 10 2, p. 3 Acenaphthylene 1 1 1* Yes 1 2, p. 3

Anthracene 1 10 1* Yes 10 2, p. 3 Benzo(a)anthracene 1 1,000 1* Yes 1,000 2, p. 3 Benzo(a)pyrene 1 10,000 1* Yes 10,000 2, p. 4 Benzo(b)fluoranthene+ 1

--- 1* Yes

--- 2, p. 4 Benzo(g,h,i)perylene 1 0 1* Yes 0 2, p. 4 Benzo(k)fluoranthene 1 100 1* Yes 100 2, p. 4 Chrysene 1 10 1* Yes 10 2, p. 5

Fluoranthene*** 1 100 1* Yes 100 2, p. 4

Fluorene 1 100 1* Yes 100 2, p. 7 Indeno(1,2,3

- c,d)pyrene 1 1,000 1* Yes 1,000 2, p. 9

2

- Methylnaphthalene 1 1,000 1* Yes 1,000 2, p. 9 Naphthalene 1 1,000 1* Yes 1,000 2, p. 9

Phenanthrene 1 1 1* Yes 1 2, p. 10 Pyrene 1 100 1* Yes 100 2, p. 10

Notes: * Liquid, non

- karst mobility factor value used, or if substance was found in an observed release to ground water, then a mobility factor value of 1 is assigned (Ref. 1, Sec. 3.2.1.2).

** See section 3.1.1 of this HRS documentation record *** This compound is listed as its synonym benzo(j,k)fluorene in Reference 2

+ Compound not listed in Reference 2Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

16 Benzo(a)pyrene is the hazardous substances with the highest toxicity and mobility factor value, of 10,000. Toxicity/Mobility Factor Value: 1x10 4
(Ref. 1, Table 3 -9)

Centel does not contend that these toxicity values were inappropriately assigned to benzo(a)pyre ne or naph th alene

.

Regarding the assignment of mobility, page 61of the HRS documentation reco rd at proposal , quoted above, explains that “if substance was found in an observed release to ground water, then a mobility factor value of 1 is assigned (Ref. 1, Sec. 3.2.1.2).” Both naphthalene and benzo(a)pyrene are documented in an observed release to ground water and were therefor e assigned a value of 1, in accordance with HRS Section 3.2.1.2, quoted above.

The combined toxicity mobility value was then assigned using the substance with the highest toxicity and mobility fa ctor value. Benzo(a)pyrene was assigned a combined toxicity /mobility value of 10,000 and naphthalene was assigned a corresponding toxicity/mobility value of 1,000. Using benzo(a)pyrene to assign a combined toxicity/mobility of 10,000 for the ground water pathway is consistent with the HRS

because benzo(a)pyrene ha s the highest combined toxicity/mobility value

.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.

3.7 .2 Source Hazardous Waste Quantity

Comment : Centel commented that the source hazardous wast e quantity factor is not appropriately assigned because it does not consider that the extent of tar (and hazardous components of the tar) has be en delineated.

Centel asserted that the source hazardous waste quantity should be revised using the following assumptions:

• Contamination exists beneath the entire area addressed in the removal action to a depth of 30 ft below

removal areas.

• Contamination is present in the entire area of tar impact shown on Figure 4-11 of the March 2010 EE/CA

Site Characterizatio n Report, which was estima ted to be 36,000 square ft.

• Contamination can be evaluated using either Tier C or Tier D.

• Material both on and off property should be used in the calculation rather than assuming an unknown quantity, as this “represents the current source of haza rdous substance migration.”

Centel did not estimate a specific source waste quantity value but projected a pathway waste quantity value of 1 based on its calculations, which corresponds to a source hazardous waste quantity value of 100 or less.

Response : The source hazardous waste quantity value presented in the HRS documentation record at proposal was estimated consistent with the HRS as unknown, but greater than zero. T he source hazardous waste quantity was appropriately estimated as an area of contaminated soil of unknown extent, based on the presence of contamination in samples following removal actions. The approach used by Centel to calculate the source hazardous waste quantity is incorrect because it assumes that contamination is continuous throughout the source area and does not take into consideration the conditions following removal activities conducted at the Site.

HRS Section 2.4.2.1, Source hazardous waste quantity, describes the process for e valuating source hazardous waste quantity. It states in relevant part:Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

17 For each of the three migration pathways, assign a source hazardous waste quantity value to each source (including the unallocated source) having a containment factor value greater th an 0 for the pathway being evaluated

.

. . .

For all pathways, evaluate source hazardous waste quantity using the following four measures in the following hierarchy:

• Hazardous constituent quantity. • Hazardous wastestream quantity.

• Volume.

• Area.

HRS Section 2.4.2.1.3, Volume , instructs the scorer to “[ e] valuate the volume measure using the volume of the

source. ” I t states that i f the volume cannot be determined then the scorer should assign a value of 0 for the volume measure and proceed to sectio n 2.4.2.1.4.

HRS Section 2.4.2.1.4, Area , (the tier EPA used to estimate a waste quantity ) states that the scorer should:

E valuate the area measure using the area of the source...For the migration pathways, assign the source a value for area using the ap propriate Tier D equation of Table 2-5.

To calculate the source hazardous waste quantity value, HRS Section 2.4.2.1.5, Calculation of source hazardous waste quantity value

, instructs the scorer to:

Select the highest of the values assigned to the source (or area of observed contamination) for the hazardous constituent quantity, hazardous wastestream quantity, volume, and area measures. Assign this value as the source hazardous waste quantity value. Do not round to the nearest integer.

Page 38 of the HRS documentation record at proposal explains the rationale for evaluating the source hazardous waste quantity for Source 1 based on Tier D, area. The HRS documentation record at proposal documented that the source volume could not be adequately determined. I t states:

The information available is not sufficient to adequately support evaluation of the volume for Source 1 as the full depth of contamination was not determined by sampling. Volume Assigned Value: 0 (Ref. 1, Section 2.4.2.1.3).

Consistent with t he HRS, Tier D, was estimated to determine a source waste quantity because the source volume could not be adequately determined with reasonable confidence. P age s 38–39 the HRS documentation record at proposal documents the estimation of the source area tie r as follows:

As documented in Tables 4 and 9 of this HRS documentation record, soil samples collected from Source 1 revealed the presence of numerous PAH compounds at concentrations above background levels, documenting an area of soil contamination. Table 5 of this HRS

documentation record summarizes observations of contaminated soil. Prior to the November 2013 and June 2014 removal activities, the area of contaminated soil was estimated to be 12,447 square feet, as shown on Figure 2 of this HRS documentation record and using the samples

summarized in Tables 4 and 9 of this HRS documentation record.Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

18 Because contaminated soils were excavated during the November 2013 and June 2014 removal

activities in accordance with the Administrative Settlement Agreement and Order on Consent for Removal Action (Ref. 46, pp. 4, 9, 28, 37, 38), a conservative value of unknown, but greater than 0 is assigned as the Source 1 area assigned value to account for an unknown amount of soil contamination remaining at the s ource, as well as releases from the source to shallow ground water that were not addressed as part of the removal activities.

Area of Source (ft 2 ) : Unknown, but >0 Equation for Assigning Value (Table 2- 5) : A/34,000 Area Assigned Value : >0

Based on the documented conditions at the time of the most recent site assessment

, it was determined that the hazardous constituent quantity , the hazardous wastestream quantity

, and the volume for Source 1 could not be adequately determined because insufficient data was available. Centel did not disagree that a Tier A ( hazardous constituent quantity) or Tier B ( the hazardous wastestream quantity ) estimate could not be adequately determined, according to the HRS. Centel only commented on using Tier C or Tier D to calculate the hazardous waste quantity of Source 1.

The source hazardous waste quantity was estimated in accordance with all HRS procedures. Based on the information available at proposal, it was estimated that prior to November 2013 and June 2014 removal activities, the area of contaminated soil was estimated to be 12,447 square feet based on sampling documenting soil concentrations significantly above background. (See HRS documentation record at proposal page 39). However, as contaminated soil was removed from the property, it was determined that the 12,447 square foot area was not representative of the current area of the source. As quoted above, the HRS documentation record at proposal confirmed the pres ence of soil contamination by documenting that hazardous substances remained present after the removal had been completed, and assigned a conservative value of unknown but greater than zero to account for “an unknown amount of soil contamination remaining at the source, as well as releases from the source to shallow ground water that were not addressed as part of the removal activities.”

Regarding Centel ’s assertion that the fully delineated extent of tar is more appropriate to use to evaluate the source hazardous waste quantity and that it should be reevaluated using removal information an d under either Tier

C or Tier D , this is incorrect in that it does not reflect current site conditions (i.e., post removal conditions). Additionally, it is not known if t he tar is an accurate estimate of the extent of contaminated soil or the amount of contamination that has been released to the soil prior to the removal action. Therefore, the quantity of tar does not provide a complete estimate of the source waste quantit y with reasonable confidence.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.

3.7 .3 Pathway Hazardous Waste Quantity

Comment : Centel submitted comments questioning the appropriateness of the ground water pathway hazardous waste quantity factor value calculation. Specifically, Centel commented that the pathway hazardous waste quantity should be recalculated based on revisions to the source hazardous wa ste quantity. Centel commented that the pa thway hazardous waste quantity factor value for the ground water pathway should be revised based on revisions to the source hazardous waste quantity estimate using the area impacted by tar. Centel asserted that if the source waste quantity were revised, t he pathway hazardous waste quantity value for ground water (i.e., the pathway hazardous waste quantity factor value) shoul d be a 1 instead of 10.

Response : A pathway hazardous waste quantity factor value of 10 for the ground water pathway was correctly assigned in the HRS evaluation of the Site based on the estimated source hazardous waste quantity of unknown but greater than zero for the contaminated soil source. As explained below, the hazardous constituent quantity for

the contaminated soil source was not able to be adequately determined at proposal (Centel did not disagree withIowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

19 this determination), and a pathway hazardous waste quantity factor value of 10 for the ground water migration pathway was correctly assigned to the Site

.

HRS Section 3.2.2, Ha zardous waste quantity , directs that Section 2.4.2 of the HRS be used to evaluate the hazardous waste quantity for the ground water pathway. It states:

Assign a hazardous waste quantity factor value for the ground water pathway (or aquifer) as specified i n section 2.4.2. Enter this value in T able 3

– 1.

HRS Section 2.4.2.1, Source hazardous waste quantity, describes the process for evaluating source hazardous waste quantity. It states , in relevant part:

For each of the three migration pathways, assign a source hazardous waste quantity value to each source (including the unallocated source) having a containment factor value greater than 0 for the pathway being evaluated

.

. . .

For all pathways, evaluate source hazardous waste quantity using the following four measures in the following hierarchy:

• Hazardous constituent quantity. • Hazardous wastestream quantity.

• Volume.

• Area.

HRS Section 2.4.2.1.1, Hazardous constituent quantity, explains how to evaluate Tier A, the hazardous constituent quantity of a source. It states, in relevant part:

Evaluate hazardous constituent quantity for the source (or area of observed contamination) based solely on the mass of CERCLA hazardous substances (as defined in CERCLA section 101(14), as amended) allocated to the source ...

Based on this mass, designated as C, assign a value for hazardous constituent quantity as follows:

• For the migration pathways, assign the source a value for hazardous constituent

quantit y usi ng the Tier A equation of T able 2 –5.

. . .

If the hazardous constituent quantity is not adequately determined, assign the source (or area of observed contamination) a value for hazardous constituent quantity based on the available data and proceed to section 2.4.1.2.

To calculate a hazardous wast e quantity factor value for a pathway, HRS Section 2.4.2.2, Calculation of hazardous waste quantity factor value, states, in part:

Sum the source hazardous waste quantity values assigned to all sources ... for the pathway being evaluated and round this sum to the nearest integer, except: if the sum is greater than 0, but less than 1, round it to 1. Based on this value, select a hazardous waste quantity fac tor value for the pathway from T able 2 –6.Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

20 Table 2 –6— Hazardous Waste Quantity Factor Values

Hazardous waste quantity value Assigned value

0 0

1 a to 100 1 b

Greater than 100 to 10,000 100

Greater than 10,000 to 1,000,000 10,000

Greater than 1,000,000 1,000,000

a If the hazardous waste quantity value is greater than 0, but less than 1, round it to 1 as specified in text.

b For the pathway, if hazardous constituent quantity is not adequately determined, assign a value as specified in the text; do not assign the value of 1.

For a migrati on pathway, if the hazardous constituent quantity is adequately determined (see section 2.4.2.1.1) for all sources (or all portions of sources and releases remaining after a removal action), assign the value from Table 2

– 6 as the hazardous waste quantity factor value for the pathway. If the hazardous constituent quantity is not adequately determined for one or

more sources (or one or more portions of sources or releases remaining after a removal action) assign a factor value as follows:

• If any target for that migration pathway is subject to Level I or Level II concentrations (see section 2.5) , assign either the value from T able 2

– 6 or a value of 100, whichever is greater, as the hazardous waste quantity factor value for that pathway.

• If none of the targets for that pathway is subject to Level I or Level II concentrations, assign

a factor value as follows:

– If there has been no removal action, assign either the value from table 2 –6 or a value of 10, whichever is greater, as the hazardous waste quantity factor value for that pathway.

– If

there has been a removal action:

– Determine values from T able 2 –6 with and without consideration of the removal action.

– If the val ue that would be assigned from T able 2 –6 without consideration of the removal action would be 100 or greater, assign either the value f rom T able 2 –6 with consideration of the removal action or a value of 100, whichever is greater, as the hazardous waste quantity factor value for the pathway.

– If the val ue that would be assigned from T able 2

– 6 without consideration of the removal action would be less than 100, assign a value of 10 as the hazardous waste quantity factor value for the pathway ... [emphasis added]

Page 62 of the HRS documentation record at proposal explains that the hazardous constituent quantity has not been adequately determined for the ground water pathway because there was insufficient data to adequately determine the total mass of all CERCLA hazardous substances in the source. Additionally, p age 62 of th e HRS documentation record at proposal explains the calculation of the pathway hazardous waste quantity factor value for the ground water pathway:Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

21 TA BLE 23 SUMMARY OF SOURCE HAZARDOUS WASTE QUANTITY VALUES

Source Number Source Type Source Hazardous Waste Quantity

1 Contaminated Soil >0

S um of Values: >0

In accordance with Section 2.4.2.2, a minimum value of 10 was used for the Hazardous Waste Quantity Factor Value because Hazardous Constituent Quantity has not been adequately determined for Source 1, and none of the targets for the ground water pathway is subject to Level I or Level II concentrations (Ref. 1, Sec. 2.4.2.2). [emphasis added]

H azardous Waste Quantity Factor Value: 10 (Ref. 1, Section 2.4.2.2)

The HRS documentation record at proposal followed the HRS and determined that the source hazardous waste quantity was estimated as unknown, but greater than zero. Based on Table 2-6 of the HRS, this corresponds to an assigned value of 1; footnote “ a” of Table 2

- 6 directs that a value of 1 be assigned when the source waste quantity value is between 0 and 1. However, as directed in footnote “b”, the value of 1 is not applied because the hazardous constituent quantity has not been adequately determined; footnote “b” then directs that the pathway hazardous waste quantity be based on the text in the remainder of HRS Section 2.4.2.2.

As presented above, the text in HRS Section 2.4.2.2 directs that when a complete Tier A hazardous constituent quantity has not been adequately determined, the HRS evaluation proceeds to evaluate a pathway hazardous waste quantity factor value taking into consideration Level I/II targets and removal actions at the Site. Because no target wells were considered to be subject to Level I or II concentrations (i.e., contaminated at levels that met observed release criteria), the HRS directs to evaluate the pathway waste quantity based on removal actions. Since a removal action has occurred, HRS Section 2.4.2.2 directs that the pathway hazardous waste quantity factor value

be assigned a value of 10. This section instructs to assign a value of 10 if the value assigned from HRS Table 2 -6, without the consideration of a removal action, would be less than 100.

Regarding Centel ’s comments that the application of Tier C or Tier D to the known area and depth of

contamination removed at the S ite and the entire area of tar impact would result in a hazardous waste quantity

factor value for the ground water pathway of 1. Centel incorrec tly interprets a Tier C or Tier D estimate for a Tier A (hazardous constituent quantity) estimate that was actually determined. However , a Tier A estimate cannot be adequately determined and cannot be used to assign the hazardous waste quantity.

Furthe rmore, even if Centel’s estimate of the source were used to determine the source hazardous waste quantity based on the contaminated soil removed and the tar impacted area and evaluated in accordance with Tier C or Tier D, the result would only raise the source hazardous waste quantity value and does not impact the ground water pathway hazardous waste quantity factor value . Therefore, using Centel’s suggested source dimensions to evaluate the source hazardous waste quantity based on volume or area (Tiers C o r D) would not result in a lower HRS site score. Using Centel’s suggest ed 12,447 square feet (area prior to removal ) or 36,000 square feet ( in the EE/CA Site Characterization Report [Reference 34 of the HRS documentation record at proposal]), with or

witho ut using a depth of 30 feet to calculate a volume or area estimate, results in a source hazardous waste quantity volume value of 21.5 or an area value of 1.5. If both of these values are entered into HRS Table 2 -6, the corresponding assigned value would st ill be 1 and the corresponding footnote “b” would still apply. F or the same reasons explained above, the assigned pathway hazardous waste quantity value would remain 10.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

22 

### 3.8 Targets

Comment : Centel submitted comments questioning the eligibility of the municipal wells scored as potential targets. Centel commented that the “contaminant plume has never reached the Elkhorn River or the municipal wells east of the Site,” in the over 70 years that no new sourc e material has been added.

Response : Wells located within the four mile TDL drawing from the alluvial and Niobrara chalk aquifer systems being evaluated, including municipal wells east of the Site, were correctly included and scored as eligible potential targets in the HRS documentation record at proposal in accordance with the HRS. The HRS scoring of the Site properly included the municipal and community wells as subject to potential contamination, and Centel does not provide a new population score. The HRS does not direct the scorer to consider ground water flow direction when determining the potential target factor value in the ground water pathway or when delineating the

TDL.

To evaluate t argets the ground water pathway in the HRS requires that the distance of each well be evaluated to determine if the wells are eligible for consideration. HRS Section 3.0.1.1, Ground water target distance limit

, states:

The target distance limit defines t he maximum distance from the sources at the site over which targets are evaluated. Use a target distance limit of 4 miles for the ground water migration pathway, except when aquifer discontinuities apply (see section 3.0.1.2.2). Furthermore, consider

any w ell with an observed release from a source at the site (see section 3.1.1) to lie within the target distance limit of the site, regardless of the well’s distance from the sources at the site.

To determine what qualifies as a target in the ground water pathway, HRS Section 3.3, Targets , instructs the

scorer to:

[e]valuate the targets factor category for an aquifer based on four factors: nearest well, population, resources, and Wellhead Protection Area. Evaluate these four factors based on targets

within t he target distance limit specified in section 3.0.1.1 and the aquifer boundaries specified in section 3.0.1.2. Determine the targets to be included in evaluating these factors for an aquifer as specified in section 3.0.

To evaluate targets, HRS Section 3. 3.1, Nearest well, states that:

[i]n evaluating the nearest well factor, include both the drinking water wells drawing from the aquifer being evaluated and those drawing from overlying aquifers as specified in section 3.0. ...

Assign a value for the neares t well factor as follows:

• If one or more drinking water wells is subject to Level I concentrations, assign a value of 50.

• If not, but if one or more drinking water wells is subject to Level II concentrations, assign a

value of 45.

• If none of the d rinking water wells is subject to Level I or Level II concentrations, assign a

value as follows:

...

– If not, determine the shortest distance to any drinking water well, as measured from any source at the site with a ground water containment factor value greater than 0. Select a value from T able 3–11 based on this distance. Assign it as the value for the nearest well factor.Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

23 To determine eligible populations associated with drinking water wells, HRS Section 3.3.2, Population

, states:

In evaluating the population factor, include those persons served by drinking water wells within the target distance limit specified in section 3.0.1.1.

To evaluate populations associated with points of withdrawal, HRS Section 3.3.2.1, Level of contamination

, states:

Evaluate the population served by water from a point of withdrawal based on the level of

contamination for that point of withdrawal. Use the applicable factor: Level I concentrations, Level II concentrations, or potential contamination.

If no samples meet the criteria for an observed release for a point of withdrawal and there is no observed release by direct observation for that point of withdrawal, evaluate that point of withdrawal using the potential contamination factor in section 3.3.2.4. ...

For the potential contamination factor, use population ranges in evaluating the factor as specified

in section 3.3.2 .4. ...

Users of ground water not scored as subject to actual contamination, and within the 4- mile TDL, are evaluated using the potential contamination factor. HRS Section 3.3.2.4, Potential contamination , directs

a scorer to:

Determine the number of people served by drinking water from points of withdrawal subject to potential contamination. Do not include those people already counted under the Level I and Level

II concentrations factors.

Assign distance -weighted population values from Table 3-12 to this population ...

The HRS documentation record at proposal defined a target distance limit for the Site. Reference 3 of the HRS package a t proposal, included as Figure 6 of this support document, presented the delineation of the 4- mile TDL

based on the loca tion of Source 1. Reference 3 states that “[t]he radius rings are drawn from the outside of the boundaries of Source No. 1. The boundaries of Source No. 1 are shown in Figure 2.”

Pages 67 –68 of the HRS documentation record at proposal provide further information regarding the inclusion of target wells scored as subject to potential contamination. These pages state:

3.3.2.4 Potential Contamination

The public water supply system for the City of Norfolk includes 11 active permanent municipal wells (Refs . 17, pp. 1, 2; 27; 41). These wells are reported to range in depth from 50 to 130 feet bgs (Ref. 17, pp. 3 - 14). The city has two water treatment facilities referred to as the east and west treatment plants (Refs. 17, p. 1; 41, p. 1). Eight municipal wells (wells 681, 682, 692, 691, 752, 751, 921, and 20031) are associated with the west treatment plant, and three wells (wells 281, 471 and 551) are associated with the east treatment plant (Ref. 17, pp. 1, 2).

...

In addition to the City of Norfolk wells, t here are numerous other community water supplies

within the 4

- mile radius of the INL&P facility.Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

24 Reference 3 of the HRS package at proposal presents the location of the wells evaluated as targets subject to potential contamination. (See Figure 6 of this s upport document). This figure documents that the wells are located

within the 4

- mile TDL, making these wells (including the municipal wells to the east of Iowa

- Nebraska Light and Power Co property) eligible for scoring according to the HRS.

Pages 67 and 68 of the HRS documentation record at proposal, quoted above, and Reference 3 of the HRS package at proposal document that these wells (including the municipal wells that draw from the interconnected aquifer system) are considered potential targets located within the TDL. In accordance with the HRS, it is appropriate to evaluate these wells as potential targets in the HRS site evaluation because these wells are within the TDL and draw from the aquifer system subject to potential contamination. 2

Regarding Centel’s assertion that contaminants have not been documented to have migrated to the municipal

wells east of the Iowa -Nebraska Light and Power Co property, the presence of actual contamination in a well is not required by the HRS to evaluate a well as subject to potential contamination. HRS Section 3.3.2.1, Level of

contamination , quoted above, directs the scorer to evaluate a point of withdrawal without samples meeting observed release criteria or without a documented observed release by direct observatio n using the potential contamination factor. The HRS does not specify that actual contamination must be documented to evaluate a point of withdrawal as subject to potential contamination. The HRS evaluation of the Site followed the HRS requirements in evalu ating the municipal wells because the municipal wells were eligible to be scored as targets using the potential contamination factor even though there had been no documented observed release to these

wells.

This comment results in no change to the HRS sc ore and no change in the decision to place the Site on the NPL.

2 For further information on why the HRS does not consider ground water flow direction in evaluating potential contamination in the ground water pathway, please see Section L of the preamble to the 1990 HRS. (55 FR 51551).Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

25 F igure 6 – 4- Mile TDL MapIowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

26 

### 3.9 HRS Score

Comment : Centel submitted comments asserting that revisions to HRS scoring factors should be made, correcting

for alleged errors in scoring. Centel commented that naphthalene should be used for the assignment of a toxicity mobility value and “the Toxic/Mobility Factor will be reduced from 10,000 to 1,000, which will reduce the

over all HRS score for the Site.” Centel asserted that this would result in a waste characteristics value of, “6, rather than an 18.” Centel concluded that correcting for the toxicity/mobility factor, the hazardous waste quantity factor, and the waste characteristics would result in an HRS score of 13.6; which is below the NPL threshold

value of 28.50.

Response : The Iowa

- Nebraska Light and Power Co site was correctly scored in the HRS documentation record at proposal in accordance with the HRS. The responses to comments in the preceding section s demonstrate that the HRS documentation record at proposal followed the HRS requirements for scoring the Site.

Regarding the scoring of the toxicity/mobility factor, as discusse d in detail above in section 3.7.1, Toxicity/Mobility, of this support docume nt, benzo(a)pyrene was correctly identified as the hazardous substance with the highest combined toxicity/mobility value. Accordingly, the corresponding assignment of 10,000 for the toxicity/mobility, based on the data associated with benzo(a)pyrene, is appropriate.

Regarding Centel’s assertion that the appropriate waste characteristics value is 6 rather than 18, the discussion above in sections 3.7.3, Pathway Hazardous Waste Quantity, of this support document, demonstrates that a toxicity/mobility factor value of 10,000 and a pathway hazardous waste quantity factor value of 10 are appropriate, resulting in a waste characteristics value of 18.

Therefore, Centel’s suggested site score of 13.6 is incorrect and the site score of 40.80 calculated in the HRS

d ocumentation record at proposal is correct. The discussions above explain that each of the Site evaluation scoring factors, alleged to be inaccurate by Centel, were correctly calculated in accordance with the HRS. Therefore, the HRS site score was correctl y determined in accordance with the HRS as 40.80, and this score exceeds the NPL eligibility threshold of 28.50 of greater.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.



### 3.10 Non-Scoring Factual Error

Comment : Centel questioned the accuracy of the HRS documentation record at proposal’s description of the boring from well MW-6B. Centel commented that page 58 of the HRS documentation record at proposal was not accurate in stating that “tar was encountered in the boring from Well MW-6 B.” Centel asserted that boring log presented in the EE/CA Site Characterization Report (Reference 34 of the HRS documentation record at proposal) only documented a tar/petroleum odor. Centel commented that the absence of tar in this boring is confirmed by the ground water monitoring da ta from wells MW -6A and 6B.

Response : EPA acknowledges Centel’s correction to the HRS documentation record at proposal. This inconsistency does not impact any scoring factors, an d Centel has not asserted that this error would result in any change to the HRS site score.Iowa

- Nebraska Light & Power Co NPL Listing Support Document April 2016

27 

## 4. Conclusion

The origi nal HRS score of this site was 40.8 0. Based on the above response to comments, the score remains unchanged. The final scores for the Iowa

- Nebraska Light & Power Co site are:

Ground Water 81.60

Surface Water Not Scored Soil Exposure Not Scored

Air Not Scored

HRS Site Score 40.80