update no 1 report

Update No 1 Report

for the

Supplemental Site Characterization Report

Tier 1 Risk Assessment

Columbia Missouri FMGP Site

December 2013

Prepared for:

AMEREN SERVICES COMPANY

St. Louis, Missouri

Update No 1 Report

for the

Supplemental Site Characterization Report

Tier 1 Risk Assessment

Columbia Missouri FMGP Site

December 2013

Prepared for:

AMEREN SERVICES COMPANY

St. Louis, Missouri

PSC INDUSTRIAL OUTSOURCING, LP

210 West Sand Bank Road

Columbia, Illinois 62236-0230

Project 624-1302-0002

i Columbia FMGP Site Update No. 1 Report

PSC Project 624-1302-0002 December 2013

TABLE OF CONTENTS

EXECUTIVE SUMMARY ........................................................................................................ 1

1.0 INTRODUCTION ................................................................................................................ 2

2.0 UPDATES TO THE SUPPLEMENTAL SITE CHARACTERIZATION REPORT ... 3

3.0 UPDATES TO THE TIER 1 RISK ASSESSMENT – SITE CONCEPTUAL MODEL 4

3.1 Distribution of COCs in Soil ....................................................................................... 4

3.2 Current/Future Land and Groundwater Use ............................................................ 5

3.3 Known or Proposed Land or Water Use Restrictions .............................................. 5

3.4 Chemicals of Concern .................................................................................................. 6

3.4.1 Chemicals Retained / Excluded for Evaluation ..............................................6

3.5 Exposure Model ............................................................................................................ 7

3.5.1 Domestic Use of Overburden Groundwater ...................................................7

3.5.2 Site Surficial Soil ...............................................................................................9

3.5.3 Site Subsurface Soil ...........................................................................................9

3.6 Saturated Soil Concentration ...................................................................................... 9

3.7 Representative Concentration Calculations .............................................................. 9

3.8 Individual or Representative Concentration Exceedances and Planned Removal

Summary ..................................................................................................................... 10

3.8.1 Evaluation of Exposure Domain and Exclusion Considerations ................10

3.8.2 Exposure Pathway Scenario Evaluation Results ..........................................11

3.8.3 Exposure Scenario Evaluation Summary vs. Planned Removal ................12

4.0 POST-PLANNED REMEDIAL ACTION RISK EVALUATION (TOTAL AND

CUMULATIVE SITE-WIDE) .......................................................................................... 13

4.1 Carcinogenic Risk Evaluation (D)(1) ....................................................................... 13

4.2 Non-Carcinogenic Risk Evaluation (D)(2) ............................................................... 13

4.3 Individual Residual Borehole Risk Evaluation ....................................................... 14

5.0 SUMMARY AND CONCLUSIONS ................................................................................. 15

ii Columbia FMGP Site Update No. 1 Report


LIST OF FIGURES

1 Site Location Map

2 Site Base Map

3 Soil Analytical Sample Depths and Total Borehole Depths

4 Groundwater Monitoring Well Locations

5 Groundwater Results – Benzene, Naphthalene, Benzo(a)Pyrene

6 Soil RBTL Exceedance Summary (0-3’ Interval)





11 Soil RBTL Exceedance Summary (Planned Removal Area/Depth 0-15’)

LIST OF TABLES

1 Soil–Default Target Level Comparison (ND@1xDL)

2 Soil–Default Target Level Comparison ([email protected])

3 Exposure Model–Complete Pathway(s)/Exposure Media-Future Non-Residential Use

4 Groundwater Results: All COC – EOI 2005-2011

5 Groundwater Results: Detected COC Only – EOI 2005-2011

6 Soil RBTL Comparison: Construction Worker Combined Exposure (0-10’)

7 Soil RBTL Comparison: Non-Residential Combined Exposure (0-3’)

8 Soil RBTL Comparison: Non-Residential Indoor Vapor Inhalation Exposure (3-25’)

9 Acceptable Risk Evaluation Summary

LIST OF ATTACHMENTS

1 MDNR Letter Dated June 18, 2013, Re: Columbia FMGP

2 PSC Borehole Logs (SB-19 to SB-28) – 2013 Supplemental Soil Investigation

3 Laboratory Analytical Soil Report – 2013 Supplemental Soil Investigation

4 City of Columbia, MO Zoning District Map (8/17/2012)

5 MDNR Letter Dated November 8, 2013, Re: Columbia FMGP 2013 Borehole Sealing

1 Columbia FMGP Site Update No. 1 Report


EXECUTIVE SUMMARY

Soil remediation at the Columbia [MO] Coal Gas-East Parcel located in Columbia, Missouri is

targeted for the first half of 2014. In preparation for the pending soil remediation, Ameren

Services desires Missouri Department of Natural Resources (MDNR) approval of this

submittal, along with a PSC risk management plan provided separately, that covers soil

characterization and interim risk assessment updates developed since the MDNR letter dated

June 18, 2013. Following soil remediation, and subsequent groundwater confirmation

sampling activities, a closeout report will be provided for final project closure approval by

MDNR. Future site use will be suitable for non-residential purposes with a non-domestic use

groundwater activity use limitation.



1.0 INTRODUCTION

On behalf of Ameren Services (Ameren), PSC Industrial Outsourcing, LP (PSC) has

prepared this submittal for the Columbia [MO] Coal Gas-East Parcel (MGP) located in

Columbia, Missouri (Site). This submittal has been prepared to provide the results of

soil characterization and risk assessment activities performed by PSC in 2013, which

update the Supplemental Site Characterization Report (SSCR) and Tier 1 Risk

Assessment by Civil & Environmental Consultants, Inc. (CEC) dated August 2007 and

February 2008, respectively. The Missouri Department of Natural Resources (MDNR)

Brownfields/Voluntary Cleanup Program approved the CEC submittals in a letter dated

June 18, 2013.

The Site location in Columbia, Missouri and the current site conditions are illustrated on

two attached figures: Figure 1 (Site Location Map); and Figure 2 (Site Base Map).



2.0 UPDATES TO THE SUPPLEMENTAL SITE CHARACTERIZATION REPORT

Additional characterization of soil was performed during the June 2013 Supplemental

Soil Investigation (SSI) per the SSI Work Plan dated June 5, 2013, with the following

exception. In accordance with comment #6 in the June 18, 2013 MDNR letter (see

Attachment 1), the background arsenic soil sampling locations were eliminated and the

MDNR-provided background concentration for arsenic of 18.1 mg/kg was utilized. The

text below briefly outlines the work performed during the SSI.

Ten (10) direct-push probe locations, SB-19 to SB-28, were completed by Brotcke Well

& Pump, Inc. on June 24-25, 2013. Direct-push probe refusal depths ranged between

14 and 16.5 feet below ground surface (bgs). Soil samples for analysis were collected

as follows:

• 2-3 feet bgs: Six (6) locations - (SB-19, 20, 21, 22, 23, 24, and 26); and

• >3 feet bgs: Ten (10) locations - (seven locations where two samples were

collected for laboratory analysis and three locations where one sample was

collected).

PSC’s borehole logs and the laboratory soil sample analysis report are included as

Attachments 2 and 3, respectively. The soil samples were analyzed for Site chemicals

of concern (COCs) including volatile organic compounds (VOCs), semi-volatile organic

compounds (SVOCs) and inorganic compounds. The new borehole locations, sample

depths, and total borehole depths are summarized on Figure 3, along with those from

the previous (1990-91 and 2007) site investigations. The boreholes were backfilled

with bentonite chips, as documented on the well plugging registration record (ref no.

487067; included in Attachment 2), which was submitted to the MDNR. A letter from

the MDNR dated November 8, 2013 confirmed that these boreholes were plugged

according to Missouri Well Construction rules (Attachment 5).



3.0 UPDATES TO THE TIER 1 RISK ASSESSMENT – SITE CONCEPTUAL

MODEL

Based on the findings from the June 2013 SSI, updates to the Site Conceptual Model

(SCM) in the Tier 1 Risk Assessment are outlined in the following subsections.

3.1 Distribution of COCs in Soil

The soil Type 2 classification determined in the CEC Tier 1 Risk Assessment was

observed in direct-push probe holes SB-19 through SB-28. PSC concludes that the

soil Type 2 classification remains applicable for the Site. Probe refusal depths were

similar to those encountered during the previous site investigations. The general

findings suggest the following:

• Soil samples for SB-19, 20, and 26, in or adjacent the west edge of the

central Metal Storage Building, have impact at levels that indicate soil

remediation beneath the building is not required;

• Subsurface impact extends toward the southwest corner of the property

(as far as SB-23);

• Subsurface impact extends northwest of the slab-at-grade foundation of

Gas Holder GH-3; and,

• Soil impacts extend below the storm water sewer that is present on the

southern one-third of the property (along the south side of Gas Holder

GH-2). Historic photographs of the Site suggest that the storm water

sewer (concrete box culvert) apparently was constructed along the

approximate path of an historic creek, resulting in a suspected

preferential migration pathway.



3.2 Current/Future Land and Groundwater Use

Current and potential future land and groundwater use assumptions for the Site are

discussed below:

Current Land Use

Ameren currently owns the Site property. Zoning reference records for the

property are provided in Attachment 4. The property is located in City Zoning

Map Grid F7, and is zoned as M-1 (General Industrial). The properties

surrounding the Site are zoned either M--1 or C-2 (Central Business).

As of October 2013, Ameren operations have been permanently relocated

from the Site to new facilities. The property is currently vacant and paved

with four slab-on-grade building structures, and is fenced at the property

boundary to limit third party access.

Private utilities on-site (Figure 2) include overhead electric and

communications, and subsurface water, sanitary sewer, storm water, natural

gas, and electric utilities. Public subsurface utilities traversing the site include

sanitary and storm water sewers.

Future Land Use

Ameren intends to make the property available for sale after the completion of

the planned 2014 remedial actions. PSC assumes that Site redevelopment will

be consistent with the current zoning for the Site as General Industrial or

Central Business use, which is consistent with the surrounding property use.

The RMP will include a condition that the Activity Use Limitations (AULs)

will be placed on the property title, limiting future site use to non-residential

use because of the soil remediation objectives planned as part of the RMP.

Groundwater Use

Groundwater is not used at the Site, and the area is supplied by City water for

domestic use purposes currently, which is also the anticipated future status.

3.3 Known or Proposed Land or Water Use Restrictions

Domestic groundwater use is not currently prohibited by City Ordinance or the

property deed. For purposes of site closure and property transfers after the

Remedial Action, an AUL for groundwater use restriction prohibiting the

domestic use of the groundwater within the property boundary will be placed on

the property deed.



3.4 Chemicals of Concern

This section provides an update for the screening of chemicals below the default

target levels (DTLs), including the addition of the June 2013 SSI data.

3.4.1 Chemicals Retained / Excluded for Evaluation

Comment #2 of the MDNR letter dated June 18, 2013, MDNR requested Total

Petroleum Hydrocarbon-Gasoline Range Organics (TPH-GRO) be included in

future evaluations of Site soil although TPH-GRO was not part of the Tier 1

Risk Assessment data comparison set. The 2013 soil sampling TPH-GRO

results exceeded the DTL, so the parameter has been retained in our revised

evaluation as noted below.

Table 1 includes a comparison of the Missouri Risk-Based Corrective Action

(MRBCA) Default Target Levels to maximum and individual COC

concentrations for the selected soil evaluation depth interval. Table 2 presents

the same comparison as Table 1 but presenting one-half the detection limit for

non-detects. There are a total 49 unique COC on each table (Naphthalene was

analyzed by both VOC/SVOC methods).

Two (2) of the 49 parameters historically included with the 1990-1991, 2007,

and 2013 site data sets are considered common laboratory contaminants, and are

not typically associated with coal gasification processes. Therefore, the two

parameters listed below were not deemed necessary to be retained for further

soil evaluation.

- Acetone - 2-Butanone (MEK)*

Of the remaining 47 parameters from the combined soil analysis data sets of the

1990-1991, 2007, and 2013 site investigations, twenty two (22) parameters

listed below had maximum concentrations below the DTL, and were eliminated

from further evaluation.

- 1,2,3-Trimethylbenzene

- 2-Methylphenol

- 2,4-Dimethylphenol

- 3&4-Methylphenol*

- Anthracene

- Barium

- Benzo(g,h,i)perylene

- Benzo(k)fluoranthene

- Cadmium

- Chromium

- Chrysene

- Fluoranthene

- Isopropyl benzene

- Mercury

- n-Propyl benzene

- Phenol

- Pyrene

- p-Isopropyl toluene

- Sec-Butyl benzene

- Styrene

- Total Cyanide

- TPH - Oil Range Organics

*COC excluded because only an elevated detection limit exceeded the DTL



The remaining twenty five (25) COCs with DTL exceedances retained for further

evaluation included:



- 2-Methylnaphthalene

- Acenaphthene

- Acenaphthylene

- Arsenic

- Benzene

- Benzo(a)anthracene

- Benzo(a)pyrene

- Benzo(b)fluoranthene

- Biphenyl

- Carbazole

- Dibenzofuran

- Dibenzo(a,h)anthracene

- Ethylbenzene

- Fluorene

- Indeno(1,2,3-cd) pyrene

- Lead

- Naphthalene

- Phenanthrene

- Selenium

- Toluene

- TPH Diesel Range Organics

- TPH Gasoline Range Organics

- Xylenes

3.5 Exposure Model

This section includes an updated exposure pathway evaluation (summarized in

Table 3), and discusses pathways eliminated or retained for pathway and soil type-

specific risk-based target level (RBTL) comparisons to applicable soil and

groundwater data for the assumed non-residential future land use scenario to be

used for the property.

3.5.1 Domestic Use of Overburden Groundwater

As acknowledged in comment #4 of the June 18, 2013 MDNR letter, MRBCA

RBTL criteria comparisons for the domestic groundwater use exposure pathway

for groundwater in the overburden have been excluded. As requested in

comment #4, additional detail supporting the exclusion of the domestic

groundwater use exposure pathway for overburden groundwater is discussed

below.

As part of the demonstration for the exclusion of the domestic use of the

overburden groundwater pathway, a groundwater plume stability demonstration

is provided below. Figure 4 illustrates the locations of 11 groundwater

monitoring wells (MW-series) associated with the Site and the 1994 remediation

area west of the Site. Seven (7) of the wells (MW-1, 2, 3B, 4, 5, 6, 8) remain

available for sampling. The remaining four wells were abandoned either during

the 1994 remediation (MW-3), or since the 1994 remediation (MW-7, MW-9,

and MW-10). MW-1 to MW-4 were installed in 1990, and MW-5 to MW-7

were installed in 1991 (Atlantic, 1992). MW-3 was abandoned as part of the

1994 remediation activities, as it was within the excavation area, and was since

replaced by monitoring well MW-3B. Monitoring well MW-8 replaced

monitoring well MW-7, which was damaged and subsequently abandoned.

Monitoring wells MW-9 and MW-10, installed at the same time as MW-8,



were abandoned in 2006 at the request of the property owner when the land on

which they were located (formerly part of an abandoned railroad right-of-way)

was acquired for property expansion.

Groundwater monitoring at the Site was required by an Administrative Order on

Consent (AOC) for the Remedial Action that Union Electric (now Ameren)

entered into with the United States Environmental Protection Agency (USEPA)

Region VII on February 14, 1994. During the biannual sampling events from

2005-2011, which were performed by Environmental Operations Inc. (EOI) on

behalf of Ameren and reported to the MDNR by Ameren, only four (4) of the

remaining monitoring wells (MW-1, MW-4, MW-6, and MW-8) were sampled

in accordance with an approved groundwater sampling plan. Well MW-3B has

not been sampled because of the presence of MGP process residual free product

in the well (which was removed during monitoring events and has diminished to

less than one inch or material). Flow in the overburden groundwater in the

vicinity of the Site has been to the west-northwest (as reported by EOI). MW-1

is the only on-site well, and MW-4 is considered the key down-gradient well for

the Site. Potential off-site COC sources include, but may not be limited to, the

former western MGP area and a former fuel station up-gradient of MW-6 and

MW-8.

Polycyclic Aromatic Hydrocarbon (PAH) and Volatile Organic Compound

(VOC) groundwater results for wells MW-1, 2, 4, 6, & 8 tested during the EOI

2005-2011 biannual monitoring events, are presented on Table 4. Seven (7)

PAH and fourteen (14) VOC COCs were detected at least once, as presented on

Table 5. Groundwater data for the three primary soil COCs, (benzene,

naphthalene, and benzo(a)pyrene) are presented for the 2005-2011 biannual

events on Figure 5. The groundwater concentration trends with time appear to

be stable or decreasing, which suggests that the groundwater use exposure

pathway exclusion for the overburden groundwater is suitable.

Reports referenced for the groundwater exposure pathway exclusion

demonstration included:

• Remedial Investigation Report (Atlantic Environmental - 3/1992);

• 2005 Groundwater Monitoring Event Results (EOI - 8/2005);

• 2007 Groundwater Monitoring Event Results (EOI - 8/2007);

• 2009 Groundwater Monitoring Event Results (EOI - 9/2009); and

• 2011 Groundwater Monitoring Event Results (EOI - 9/2011).

The RMP for the Site remedial actions indicates that Ameren will submit a

groundwater monitoring plan for post-remedial action groundwater monitoring

at the Site.



3.5.2 Site Surficial Soil

Surficial soil exposure pathways deemed complete for non-residential land use

evaluation included:

• Non-Residential Combined* (0 - 3 feet below ground surface) -

*“Combined” refers to the direct contact pathway for outdoor inhalation

(vapors and particulates), ingestion, and dermal exposure pathways in

combination; and

• Construction Worker Combined (0 - 10 feet below ground surface) –

This depth interval is a modification from the 0 - 3 foot interval

considered in the CEC report, and reflects potential future subgrade

construction (e.g. underground parking level).

3.5.3 Site Subsurface Soil

Subsurface soil exposure pathways deemed complete for non-residential land

use evaluation included:

• Non Residential Indoor Inhalation of Vapor Emissions (3 - 25 feet) –

This pathway comparison depth interval was selected assuming

groundwater was not applicable within the overburden.

3.6 Saturated Soil Concentration

As indicated in comment #8 of the June 18, 2013, MDNR letter, MRBCA RBTL

criteria comparisons for saturated soil exposure pathways have been excluded.

3.7 Representative Concentration Calculations

This section includes updated representative concentration considerations based

on the sample location population and exposure pathway route comparison being

considered.

For the COCs retained following the DTL comparison screening, representative

concentrations were calculated for the COCs in an exposure pathway comparison

scenario if the maximum concentration was above the comparison RBTL. The

representative concentration was calculated as the arithmetic average for the

sample population groupings comprising individual sample locations marked as

“Y” below the sample identifications on Tables 6, 7, and 8 (collectively referred to

as “comparison tables” hereafter), which means the result is retained for the

evaluation scenario). The concentration used in the arithmetic average

calculation was the result for detected or estimated results, or one-half the

detection limit if the result was non-detect.



On the comparison tables, the representative concentrations and individual sample

results are color highlighted if they exceed their respective RBTL. Individual

sample results are also underlined if the concentration exceeds 10 times its

calculated representative concentration.

3.8 Individual or Representative Concentration Exceedances and Planned

Removal Summary

This section summarizes the locations with individual sample or representative

concentration-based exceedances of the RBTL or threshold criteria.

3.8.1 Evaluation of Exposure Domain and Exclusion Considerations

For each exposure pathway scenario discussed below, select samples were

excluded from the evaluation set, leaving a grouping of locations to remain

following remediation, which constitute the exposure domain. The exposure

domain is defined by 10 CSR25-18(1)13 as “the area that can result in a

particular receptor being exposed to COCs by a specified exposure pathway”.

Potential exposure across the entire property for future uses is considered likely,

so no specific subarea of interest was evaluated.

Besides sample locations not being applicable for the exposure pathway depth

interval of interest on a specific basis, there were other samples excluded from

the evaluations including:

• Locations not included in the Tier 1Risk Assessment data sets (1990-

1991 & 2007) and those without analytical results (B-3 to B-7, B-9 to B-

13, B-22, B-24 to B-32, SB-9);

• Locations outside the property boundaries (B-1, B-2, SB-13, SB-14, and

SB-22);

• Locations at the property boundaries believed to have been remediated in

1994 (B-8);

• Sample duplicates that would bias representative concentration/risk

results; and

• Locations and depths planned for removal during the 2014 Remedial

Action due to direct RBTL, 10x representative concentration

exceedances, or otherwise on a voluntary or as-desired/needed basis (e.g.

un-impacted intervals above impacted intervals, excavation slope

stability requirements, gross visible impact, etc.).

Sample locations and depths retained as part of the exposure domain for the

evaluation scenarios discussed below are marked by “Y” on the comparison

tables, meaning the soil will be left in-place as part of the “residual” exposure



domain. Sample locations and depths excluded from the evaluation tables for

the reasons noted above are marked as “N” on the evaluation tables.

3.8.2 Exposure Pathway Scenario Evaluation Results

Exposure pathway scenario evaluation results are discussed below:

Surficial Soil: Construction Worker Combined (0 - 10 foot interval) – As shown

on Table 6 and Figure 6 (for the 0 - 3 foot interval), the individual

results/maximum and representative concentrations were below the RTBL.

As shown on Table 6 and Figure 7 (for the 3 - 10 foot interval), the individual

naphthalene results for B-14(5-6) and B-16(5-5.7) exceeded the RBTL. The

representative concentration with the individual exceedances excluded was

below the RBTL.

Surficial Soil: Non-Residential Combined (0 - 3 foot interval) – As shown on

Table 7 and Figure 6, the individual results/maximum and representative

concentrations were below the RTBL.

Surficial Soil: Non-Residential Indoor Vapor Inhalation (3 - 25 foot interval) –

The evaluation for this exposure pathway interval is shown on Table 8, and on

Figures 7 through 10. The figures cover the 3 - 10, 10 - 15, 15 - 20, 20 - 25 foot

depth intervals, respectively, as discussed below.

• 3 - 10 Foot Depth Interval (Figure 7) – Individual result or 10x

Representative Concentration exceedances of the RBTL for benzene or

naphthalene occurred at three locations within the planned soil

remediation interval: SB-11(5-7), B-14(5-6), and B-16(5-5.7).

• 10 - 15 Foot Depth Interval (Figure 8) – Individual result or 10x

Representative Concentration exceedances of the RBTL for benzene or

naphthalene occurred at nine locations (not including excluded locations

B-8 and SB-22) within the planned soil remediation interval:

SB-11(12-14), SB-12(10-12), SB-18(11-13), B-16(13.8-14.2), B-

20(13.5-14.5), B-21(12.7-13.2), SB-24(13-14), SB-25(13-14), and SB-

27(13-14).

• 15 - 20 Foot Depth Interval (Figure 9) – Individual result exceedances or

10x Representative Concentration exceedances of the RBTL for

naphthalene occurred at two locations outside the planned soil

remediation interval: B-18 (16.2-16.5) and SB-21(15-16).

• 20 - 25 Foot Depth Interval (Figure 10) – No individual result

exceedances or 10x Representative Concentration exceedances of the

RBTL occurred for this interval.



3.8.3 Exposure Scenario Evaluation Summary vs. Planned Removal

A summary of the benzene and naphthalene RBTL exceedances versus the

planned soil remediation area is shown on Figure 11. RBTL exceedance

locations other than those listed below fall within the planned soil remediation

area/interval (0 - 15 feet):

• B-8(10–11) is at the property boundary where the 1994 remediation

activities ended. It has a benzene non-residential indoor vapor inhalation

exceedance concentration less than 10 times the exposure domain

representative concentration. In addition, construction of a building

would not be anticipated in the vicinity of this location, so receptor

exposure for the non-residential indoor vapor inhalation RBTL

exceedance would not be considered complete regardless;

• B-18(16.2-16.5) has a naphthalene exceedance greater than 10 times the

exposure domain representative concentration, but the cumulative site-

wide risk for naphthalene is within the acceptable risk. This area of the

Site will not be excavated in order to avoid disturbing the sanitary sewer

in this area of the Site;

• SB-21(15-16) has a naphthalene non-residential indoor vapor inhalation

exceedance concentration less than 10 times the exposure domain

representative concentration. This area of the Site will not be excavated

in order to avoid disturbing the sanitary sewer in this area of the Site; and

• SB-22 is located off the property. The sample from a depth of 11-12’

has exceedances of the non-residential indoor vapor inhalation exposure

pathway RBTL for benzene, naphthalene, and 1,3,5-trimethylbenzene.

A building would not be anticipated in the vicinity of this sample

location so receptor exposure for the non-residential indoor vapor

inhalation RBTL exceedance would not be considered complete;

With the planned 2014 Remedial Action, the maximum or representative

concentrations of the exposure domain are less than the RBTL.



4.0 POST-PLANNED REMEDIAL ACTION RISK EVALUATION (TOTAL AND

CUMULATIVE SITE-WIDE)

A description of the total risk and cumulative site-wide risk calculation updates conducted

pursuant to 10 CSR25-18(D)(1,2) are discussed for carcinogenic and non-carcinogenic

scenarios below. These updates pertain to Sections 8.0 and 9.0 of CEC’s Tier 1 Risk

Assessment Report.

4.1 Carcinogenic Risk Evaluation (D)(1)

On Tables 6, 7, and 8, each retained carcinogenic COC has its total risk

calculated. The contributing risk was calculated as either the maximum or

representative concentration times 10-5

and divided by the comparison RBTL. If

the maximum concentration for a retained COC was less than the comparison

RBTL, then the maximum concentration was used to calculate the retained

carcinogenic COC risk. Otherwise, if the maximum concentration for a retained

carcinogenic COC was greater than the comparison RBTL or threshold criteria

concentration, then the representative concentration was used to calculate the

retained carcinogenic COC risk.

Table 9 summarizes the total risk for each retained carcinogenic COC. The total

risk is the sum of all the complete individual exposure risks, which was compared

to the acceptable Individual Excess Lifetime Cancer Risk (IELCR) of 10-5

. The

cumulative site-wide risk was calculated as the sum of the total risks for all

retained carcinogenic COCs, which was compared to the acceptable risk threshold

of 10-4

.

For the planned removal scenario, the only parameter with a total risk above the

acceptable threshold of 10-5

was arsenic, with a value of 1.025x10-5

. This very

slight exceedance is conservative when taking into consideration the planned

removal of the side wall slopes, and is therefore deemed insignificant. The

removal of the 0 - 3 foot soil interval will be greater than the assumed residual

locations evaluated, since an additional perimeter area of 18 feet outside the

planned 15-foot deep removal area will also have the 0 - 3 foot interval removed.

4.2 Non-Carcinogenic Risk Evaluation (D)(2)

On Tables 6, 7, and 8, each retained non-carcinogenic COC has its hazard quotient

calculated. The contributing hazard quotient for a retained non-carcinogenic COC

was calculated as either the maximum or representative concentration divided by

the comparison RBTL. If the maximum concentration for a retained non-

carcinogenic COC was less than the comparison RBTL, then the maximum

concentration was used to calculate the retained non-carcinogenic COC hazard

quotient. Otherwise, if the maximum concentration for a retained non-

carcinogenic COC was greater than the comparison RBTL or threshold criteria

concentration, then the representative concentration was used to calculate the

retained non-carcinogenic COC hazard quotient.



Table 9 summarizes the retained non-carcinogenic COC hazard quotients, the

individual COC-specific hazard index, and the site-wide hazard index. The hazard

quotients were transferred from each complete exposure pathway evaluation. The

COC-specific hazard index (total risk) is the sum of the complete exposure

pathway hazard quotient on an individual basis for each COC. The site-wide

hazard index is the sum of COC-specific hazard indexes. The total risk and site-

wide hazard indexes were compared to the acceptable risk of 1 for both cases. All

non-carcinogenic risk concentrations were below their acceptable risk thresholds.

4.3 Individual Residual Borehole Risk Evaluation

Tables 9-1 to 9-4 of CEC’s Tier 1 Risk Assessment report calculate the

carcinogenic and non-carcinogenic risks by individual location to remain outside

the exposure domain. Tables 6, 7, and 8 of this report calculate these risks using

the parameter groupings indicated below:

COCs Used For Location Risk Calculation (See table COC highlighting)

Carcinogenic (yellow highlight) Non-carcinogenic (blue highlight)

Benzene Ethylbenzene

Naphthalene Toluene

Benzo(a)Anthracene 1,2,4-Trimethylbenzene

Benzo(b)Fluoranthene 1,3,5-Trimethylbenzene

Benzo(a)Pyrene Xylenes

Carbazole Acenaphthene

Dibenzo(a,h)Anthracene Acenaphthylene

Indeno(1,2,3-c,d)Pyrene Fluorene

Arsenic 2-Methylnaphthalene

Phenanthrene

Lead

Selenium

TPH – Gasoline Range Organics

TPH – Diesel Range Organics

COCs Not Used in Grouping For Location Risk Calculation (No highlight)

Biphenyl

Dibenzofuran

None of the individual borehole carcinogenic and non-carcinogenic risks exceeded their

individual acceptable risk criteria of 10-5

and 1, respectively.



5.0 SUMMARY AND CONCLUSIONS

The PSC 2013 soil characterization update identified additional impact beyond that

covered in the CEC2007 report. The PSC 2013 Tier 1 risk assessment identified soil

impact risks to be addressed under a separate risk management plan (RMP). The soil

remediation of interest based on this risk assessment update consists of subsurface soil

(primarily 3-15 feet) around the vicinity of Gas Holder #2 and #3, and the concrete box

culvert.

Following soil remediation activities, a final groundwater sampling event will be

performed, and a final remediation/risk assessment close out report will be submitted to

MDNR for site closure. The close out report will provide an overview of the

performance based remediation activities and confirmation results, the groundwater

results, and the post-remediation final risk assessment.

Based on the post-remediation cumulative site-wide risk, the residual impact will be

proposed to remain in place for a MDNR-approved closure that will allow for future

non-residential site use and include a non-domestic groundwater activity use limitation.

LIST OF FIGURES

1 Site Location Map

2 Site Base Map

3 Soil Analytical Sample Depths and Total Borehole Depths

4 Groundwater Monitoring Well Locations

5 Groundwater Results – Benzene, Naphthalene, Benzo(a)Pyrene






11 Soil RBTL Exceedance Summary (Planned Removal Area/Depth 0-15’)

LIST OF TABLES

1 Soil–Default Target Level Comparison (ND@1xDL)

2 Soil–Default Target Level Comparison ([email protected])

3 Exposure Model–Complete Pathway(s)/Exposure Media-Future Non-Residential Use

4 Groundwater Results: All COC – EOI 2005-2011

5 Groundwater Results: Detected COC Only – EOI 2005-2011

6 Soil RBTL Comparison: Construction Worker Combined Exposure (0-10’)

7 Soil RBTL Comparison: Non-Residential Combined Exposure (0-3’)

8 Soil RBTL Comparison: Non-Residential Indoor Vapor Inhalation Exposure (3-25’)

9 Acceptable Risk Evaluation Summary

LIST OF ATTACHMENTS

1 MDNR Letter Dated June 18, 2013, Re: Columbia FMGP

2 PSC Borehole Logs (SB-19 to SB-28) – 2013 Supplemental Soil Investigation

3 Laboratory Analytical Soil Report – 2013 Supplemental Soil Investigation

4 City of Columbia, MO Zoning District Map (8/17/2012)

5 MDNR Letter Dated November 8, 2013, Re: Columbia FMGP

Attachment 1

MDNR Letter Dated June 18, 2013, Re: Columbia FMGP

Attachment 2

PSC Borehole Logs (SB-19 to SB-28) – 2013 Supplemental Soil Investigation

Attachment 3

Laboratory Analytical Soil Report – 2013 Supplemental Soil Investigation

Attachment 4

City of Columbia, MO Zoning District Map (8/17/2012)

Attachment 5

MDNR Letter Dated November 8, 2013 Re: Columbia, MO FMGP Site

update no 1 report

Documents