EPA

United States 

Environmental Protection 

Agency 

1200 PennsylvaniaAvenue, N.W. 

Washington, DC 20460 April 2016

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 20460
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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Table of Contents

Executive Summary................................................................................................................................................. ii

Introduction ............................................................................................................................................................ iii

Background of the NPL ....................................................................................................................................... iii

Development of the NPL ..................................................................................................................................... iii

Hazard Ranking System ....................................................................................................................................... iv

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

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

Glossary ............................................................................................................................................................... vi

1. List of Commenters and Correspondence .....................................................................................................1

2. Site Description ................................................................................................................................................1

3. Summary 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 Activities .....................................................................................................................................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 HRS Score ................................................................................................................................................26

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

4. Conclusion ......................................................................................................................................................27
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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

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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 sites 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 

(HRS) 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 dangers 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 NCP 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 and, 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 temporary 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 the 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 a 
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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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 what CERCLAfinanced 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 at 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 environment. 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 values 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 hazardous 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 (Sgw) 

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

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• Surface Water Migration (Ssw) 

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

ground water to surface water. 

- drinking water 

- human food chain 

- sensitive environments

• Soil Exposure (Ss) 

- resident population

- nearby population 

- sensitive environments

• Air Migration (Sa) 

- 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 all pathway scores are low, the HRS score is low. However, the HRS score can be relatively 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 site 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.
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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 plant

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 aromatic hydrocarbon 

PRP Potentially responsible party

RI Remedial Investigation

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 Program
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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. (See 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 & Power 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 off 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.
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Figure 1 – Site Location Map 
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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Figure 2 – Property Layout Map
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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. 

Polsinelli 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 contaminant migration from the 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 above 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 impact of LUSTs in facilitating contaminant migration from the contaminated soil 

source. 

• Assigning a toxicity/mobility factor value based on naphthalene. 

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

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

and the toxicity/mobility factor values. 

• Reconsidering the eligibility of municipal wells as targets. 

Based on these issues, Centel asserted that the site score should 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 is adding 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, state priorities, further site investigation, other response alternatives, 

and other factors as appropriate. 
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3.2 Deferral 

Comment: Centel commented that site cleanup should be deferred to the State. Centel commented that it is 

exploring the possibility of enrolling in a voluntary cleanup program (VCP) through the NDEQ. Centel asserts 

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 the 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 listing 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 "Guidance 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 enables States and Tribes, under their own laws, to respond at 

sites that EPA would otherwise not soon address. 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 

concurred 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 remediation is necessary. The NPL is 

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

taken. It is also not relevant at this stage of the Superfund process to address which statutory authorities will be 

used to conduct remedial activities. Furthermore, adding a site to the NPL 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 IowaNebraska Light & Power Co facility to ground water. Centel 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, liability 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). Comments 
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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regarding the likelihood of release due to releases from other facilities are 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 addressed through removal activities 

conducted. Centel asserted 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 EPA

specified cleanup levels. 

Response: The HRS evaluation of the Site properly considered 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 water flow direction was to the southeast and not to the east/southeast as stated 

in 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 

vicinity 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 HRS 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 contaminants 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 levels 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/southeast 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 Figure 3 of this support 
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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

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Figure 3 – Potentiometric Surface Map for “A” Level Monitoring Wells
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Figure 4 – Potentiometric Surface Map for “B” Level Monitoring Wells
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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 LUST related contaminant plumes may have facilitated the 

migration of contaminants from the Site. Centel 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 ground 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 demonstrating 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, the HRS documentation 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 release 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 release, 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 hazardous 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 substance 
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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

be attributable to the site. Use the criteria in Table 2–3 as the standard for determining analytical 

significance. (The criteria in Table 2–3 are also used in establishing observed contamination for 

the soil exposure pathway, see section 5.0.1.) Separate criteria apply to radionuclides (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 Quantitation Limita

No observed release is established.

Sample Measurement≥ Sample Quantitation Limita

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 the 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. Centel 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, pages 59–60 of the 

HRS 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 used 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 composed 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 

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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 

constituents 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 upgradient 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 downgradient 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 plant 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 detected in the field investigation activities..., 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 operations documented identified in ground water downgradient of the facility. (See 

Figures 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 the requirements for establishing this 

significant increase in the HRS are quoted above, the requirements do not specify 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 Site. 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 

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Figure 5 – Expanded Site Inspection Background and Observed Release Well Locations 
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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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. 

Centel 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 assertions regarding the evaluation of waste characteristics: 

3.7.1 Toxicity/Mobility 

3.7.2 Source Hazardous Waste Quantity

3.7.3 Pathway Hazardous Waste Quantity 

3.7.1 Toxicity/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 greatest 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 factor 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 migrate through ground water. Centel also asserted that it would be more appropriate 

to consider naphthalene as the substance with the greatest potential 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 directs: 

For each hazardous substance [for hazardous substances at the site that are available to the 

pathway1

], 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 value 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 

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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 determine a mobility 

value in the instance when that hazardous substance is 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, Calculation 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 substance 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 toxicity 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 

scored 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 2 
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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Benzo(a)pyrene is the hazardous substances with the highest toxicity and mobility factor value, of 

10,000. 

Toxicity/Mobility Factor Value: 1x104

 

(Ref. 1, Table 3-9) 

Centel does not contend that these toxicity values were inappropriately assigned to benzo(a)pyrene or 

naphthalene. 

Regarding the assignment of mobility, page 61of the HRS documentation record 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 therefore 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 factor 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 has 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 waste quantity factor is not appropriately assigned 

because it does not consider that the extent of tar (and hazardous components of the tar) has been 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 Characterization Report, which was estimated 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 hazardous 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. The 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 evaluating source 

hazardous waste quantity. It states in relevant part: 
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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

source.” It states that if the volume cannot be determined then the scorer should assign a value of 0 for the volume 

measure and proceed to section 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: 

Evaluate the area measure using the area of the source...For the migration pathways, 

assign the source a value for area using the appropriate 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. It 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 the HRS, Tier D, was estimated to determine a source waste quantity because the source volume 

could not be adequately determined with reasonable confidence. Pages 38–39 the HRS documentation record at 

proposal documents the estimation of the source area tier 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 

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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 source, as well as releases from the source to shallow ground 

water that were not addressed as part of the removal activities.

Area of Source (ft2

): 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 presence 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 and 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 the 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 quantity 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 waste quantity. Centel commented that 

the pathway 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, the pathway hazardous waste quantity value for ground water (i.e., the 

pathway hazardous waste quantity factor value) should 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 with 
Iowa-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, Hazardous 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 in section 2.4.2. Enter this value in Table 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 

quantity using the Tier A equation of Table 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 waste 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 factor value for the 

pathway from Table 2–6. 
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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Table 2–6—Hazardous Waste Quantity Factor Values

Hazardous waste quantity value Assigned value

0 0

1a to 100 1b

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 migration 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 Table 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 Table 2–6 with and without consideration of the removal action. 

–If the value that would be assigned from Table 2–6 without consideration of the removal 

action would be 100 or greater, assign either the value from Table 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 value that would be assigned from Table 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, page 62 of the 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 

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TABLE 23

SUMMARY OF SOURCE HAZARDOUS WASTE QUANTITY VALUES

Source Number Source Type Source Hazardous Waste Quantity

1 Contaminated Soil >0

Sum 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] 

Hazardous 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 Site and the entire area of tar impact would result in a hazardous waste quantity 

factor value for the ground water pathway of 1. Centel incorrectly 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. 

Furthermore, 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 or D) would not result in a lower 

HRS site score. Using Centel’s suggested 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 

without 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 still be 1 and the corresponding footnote “b” would still apply. For 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 

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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 source 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 targets 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 the 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 well 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 the 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 nearest 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 drinking 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 Table 

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 at proposal, included as Figure 6 of this support document, presented the delineation of the 4-mile TDL 

based on the location 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, there 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 support 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 observation 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 evaluating 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 score 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 

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Figure 6 – 4-Mile TDL Map
Iowa-Nebraska Light & Power Co NPL Listing Support Document April 2016 

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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 

overall 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 sections 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 discussed in detail above in section 3.7.1, 

Toxicity/Mobility, of this support document, 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 

documentation 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 correctly 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-6B.” 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 data 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, and 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 

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4. Conclusion

The original HRS score of this site was 40.80. 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