ATSDR - Health Consultation - Milltown Reservoir Sediments, Milltown, Missoula County, Montana

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HEALTH CONSULTATION

Environmental Media Investigation Report for Arrow Stone Park in Deer Lodge, Montana
Clark For Operable Unit of the Milltown Reservoir Sediments
National Priorities List Site

MILLTOWN RESERVOIR SEDIMENTS
MILLTOWN, MISSOULA COUNTY, MONTANA

STATEMENT OF ISSUES AND BACKGROUND

Historic mining activities upriver have resulted in the presence of contaminants, including arsenic and other heavy metals, in and along the Clark Fork River (CFR) between Anaconda and Missoula, Montana. This stretch of the CFR has been listed on the National Priorities List as Milltown Reservoir Sediments. The U.S. Environmental Protection Agency (EPA) performed a Baseline Human Health Risk Assessment (HHRA) on the CFR to characterize the range of potential risks to recreational users of the CFR attributable to these mine wastes [1]. Since the HHRA was released, local agencies in Deer Lodge, Montana developed Arrow Stone Park, a public park along the CFR with different usage patterns than those evaluated in the HHRA. In a health consultation on Arrow Stone Park released in March 2001, ATSDR concluded that the existing data do not adequately represent current site conditions and recommended further characterization of the arsenic levels in soil at Arrow Stone Park to assist in public health decision-making [2].

In July 2000, ATSDR offered resources to collect surface soil samples and test them for arsenic. Before agreeing to the sampling, Powell County requested that ATSDR and EPA reach an agreement on the need for testing and the appropriate risk-based concentration (RBC) to use for making decisions based on the results. In July 2001, EPA released a provisional addendum to the HHRA which developed RBCs for exposure of park visitors to arsenic in soil and tailings; this addendum has since been finalized [3]. ATSDR concurred with the chronic RBC of 684 parts per million (ppm) for child recreational users in a letter and draft public health consultation [4], and the sampling was approved by Powell County.

A sampling and analysis plan describing the proposed sampling methodology was developed by ATSDR with input from EPA, Montana Department of Environmental Quality (DEQ), Montana Department of Public Health and Human Services (DPHHS), Powell County, and Montana State University (MSU, under contract to EPA) [5]. The soil sampling was performed on September 24-27, 2001. This report includes the sample findings as well as conclusions reached after presentation of the results to the Powell County Health Board, with personnel from EPA, DEQ, DPHHS, the City of Deer Lodge, the National Park Service, public environmental groups, ARCO (the potentially responsible party for the contamination), and local and regional newspapers in attendance, on December 5, 2001.

Physical Setting and Conceptual Site Model

The location of Arrow Stone Park is shown in Figure 1. Deer Lodge, a residential community of about 3,500 people, is located in Powell County, Montana. The town lies within Reach A of the Clark Fork River Operable Unit of the Milltown Reservoir Sediments NPL Site. Arrow Stone Park stretches along the Clark Fork River from the city limits to the intersection of Interstate 90 and Business 90 (Main Street). Until about twenty years ago, portions of Arrow Stone Park were used as a solid waste dumping area. Within the past five years or so, the community has cleaned up the site and improved several areas with park facilities. ARCO has taken some voluntary actions in areas of Arrow Stone Park to reduce the impact of contaminants, but no formal remediation has occurred.

Arrow Stone Park is split into four subareas, as depicted in Figure 2, and totals approximately 100 acres. Subarea 1 was part of a voluntary demonstration project by ARCO receiving some soil tilling and addition of amendments [6]. Picnic tables, benches, walking paths, and a raft launch are amenities of this subarea [7]. As of fall 2001, the paths and other amenities were becoming overgrown with vegetation due to an apparent lack of use and maintenance. Subarea 2 is the only area of the park that appears to receive regular and frequent use by the public. It also was the focus of voluntary actions including soil tilling and addition of amendments, and parts of it received clean cover soil [6]. This subarea has paths, picnic tables, benches, a fishing deck, and handicapped-accessible rest room, all of which appeared to be well-maintained when ATSDR last visited the site in fall 2001 [7]. Subarea 3 is an undeveloped area of Arrow Stone Park. It contains no amenities [7]. Subarea 4 has a path which is mostly overgrown; there are no other amenities [7]. Powell County only owns the lease on the path and the northern 20% of the subarea shown in Figure 2 ⁽¹⁾. All the subareas have varying levels and types of vegetation and ground cover.

The EPA HHRA addendum describes the conceptual site model for Arrow Stone Park [3]. The population of chief concern for repeated exposures at the park is area residents who may visit the park and be exposed to site soils on a regular basis for a number of years. Possible activities of park visitors include walking, jogging, bike riding, and picnicking. The soil sampling described in this report focused on characterizing chronic arsenic exposures to children aged 1 to 10 years old and visiting the park no more than 48 times per year [3]. Since adults are less at risk than children, conclusions made based on this scenario will be protective of adults as well.

DECISION STATEMENT AND INPUTS NEEDED FOR DECISION

The sampling was designed to determine whether the average arsenic concentrations in current and potential exposure areas exceed EPA's chronic risk-based concentration (RBC) of 684 parts per million (ppm) for child recreational users of Arrow Stone Park. The data needed were concentrations of arsenic in surface soil in the areas that could currently be used and those where development is possible.

METHODS

Locations Sampled

Surface soil sampling (0 to 2 inches) took place in each of the four subareas of Arrow Stone Park. To expedite sampling, the samples were grouped into nine sampling units as described below.

Sampling units 1, 2, and 3 included paths, park bench areas, and other current high use areas such as rest rooms, fishing deck, and raft launch area in subareas 1, 2, and 4, respectively. Children could occasionally play on the ground in these locations. Each subarea may have different contaminant levels due to differing proximity to the alluvial plain (which received higher contaminant deposition).

Sampling unit 4 included the areas around the picnic tables in the park. Children could play in the soil around the tables, resulting in more concentrated exposures.

Sampling unit 5 included bare or poorly vegetated areas in the park. Children playing in the park have a greater chance of being exposed to soil in bare areas. These sample locations were selected by all members of the day's sampling team using the criteria of accessibility and presence of contamination-tolerant vegetation.

Sampling units 6, 7, 8, and 9 included random samples taken in each of the subareas in the park. The random samples were collected to give a more complete picture of arsenic levels in the park, since previous sampling had been biased towards bare or obviously contaminated "slickens" areas.

Because only surface samples were collected, the sample results are limited temporally. Erosion or flood events could wash away the surface soil or deposit new soil. In this event, the soil surface would need to be recharacterized to determine current arsenic concentration.

Sample Collection, Handling and Storage

ATSDR personnel collected surface soil (0 to 2 inches) samples from the locations described above. Personnel from EPA and its contractors MSU and CH2M Hill provided field oversight and assisted in the sampling effort. Sample locations were cited using GPS and photographed. Samples were collected and composited in a manner consistent with and equivalent to EPA's Standard Operating Procedure (SOP) SS-2 and SS-6, as detailed in Standard Operating Procedures for Clark Fork River Superfund Site Investigations [8]. Decontamination of sampling equipment was consistent with SOP G-8 [8]. Samples were shipped under chain of custody to an analytical laboratory (DataChem in Salt Lake City, Utah) for the determination of arsenic concentrations. Details of the sampling activities were documented in a field log book and the chain of custody records.

Laboratory Analysis of Samples

DataChem determined the arsenic concentration of each sample using standard digestion (SW 3051) and detection (SW 6010) methods and protocols. The laboratory agreed to retain samples for six months in the event that re-analysis is requested. No party indicated a desire to analyze split samples.

QA/QC and Data Validation

Duplicate samples were collected for 5 percent of soil samples. Field standards for arsenic in soil (National Institute of Standards and Technology Standard Reference Material (SRM) 2710 and SRM 2711) were added to the sample stream each day as a quality check. Field and equipment decontamination blanks were also collected each day of sampling. The contract laboratory followed EPA-required analytical QA/QC procedures, including laboratory blanks and spikes.

MSU, working under contract from EPA Region 8, Montana Office, validated the laboratory data as specified in EPA guidance documents for data evaluation [9]. Validation included checking the data set for all required laboratory deliverables, checking laboratory reported QC results against the raw data, identifying any out-of-control analytical situations, verifying results for the field standards, assigning appropriate data qualifiers, and making a professional assessment of the data set. The data validation was reported in a memorandum [9]. None of the data collected were rejected. About half the samples were judged to be of enforcement quality. Some of the samples were judged to be of screening quality due to laboratory matrix spike recoveries being outside the acceptable control window. The data were judged to be of sufficient accuracy (bias and precision) to support their intended use [9].

Data Evaluation

Upon receipt of the validated data, ATSDR met with EPA, DEQ, and DPHHS to decide the most effective way to present the data. It was agreed to group the data into exposure units corresponding to the subareas of Arrow Stone Park, as described above and shown in Figure 2. Each subarea had a different number of samples, since sampling was concentrated in the most heavily used areas of the park.

Average values (means and/or medians) and statistical confidence intervals for the soil arsenic data for each subarea were calculated by MSU, under contract from EPA Region 8, Montana Office [10,11]. The calculated 95% upper confidence limit (UCL) is the arsenic value which soil samples have a 95% probability of being below. The data set corresponding to subarea 2 was found to be non-normally distributed,. Therefore, the median was used as an estimate of the average concentration, and a different kind of statistical analysis than the other subareas was used to determine the rank equivalent 95% UCL [10]. In EPA's risk assessment process, both average concentrations (mean and/or median) and 95% UCLs are typically compared to the RBC, with the 95% UCL being more conservative.⁽²⁾

RESULTS AND DISCUSSION

The results of the soil sampling are depicted graphically in Figure 3. This figure shows that the arsenic levels were generally below the chronic RBC. The results are described in more detail by subarea (exposure unit) below.

Subareas 1 and 2

Subareas 1 and 2 are the developed sections of the park; subarea 2 is the most heavily used. The data and summary statistics for subareas 1 and 2 are shown in Tables 1 and 2. For each of these subareas, the 95% UCL (as well as the maximum value) is much lower than the chronic RBC of 684 ppm. Therefore, these subareas are considered safe for the chronic exposures described in the risk assessment addendum [3].

Table 1. Soil Arsenic Results for Subarea 1

Sample ID Type of sample Arsenic concentration in parts per million

5SS-BA12 Bare area 82

3SS-BN1 Bench 30

3SS-BN2 Bench 140

3SS-BN3 Bench 99

6SS-PA1 Path 130

6SS-PA2 Path 340

4SS-PT3 Picnic Table 140

4SS-PT4 Picnic Table 260

4SS-PT5 Picnic Table 520

5SS-R10 Random 140

5SS-R11 Random 38

5SS-R12 Random 370

5SS-R13 Random 350

5SS-R14 Random 130

5SS-R15 Random 270

5SS-R16 Random 21

5SS-R9 Random 150

4SS-S1 Raft launch 37

Mean 180

95% Upper Confidence Limit 250

Table 2. Soil Arsenic Results for Subarea 2

Sample ID Type of sample Arsenic concentration in parts per million

5SS-BA1 Bare area 96

5SS-BA10 Bare area 360

5SS-BA11 Bare area 330

5SS-BA2 Bare area 190

5SS-BA3 Bare area 120

5SS-BA4 Bare area 150

5SS-BA5 Bare area 56

5SS-BA6 Bare area 490

5SS-BA7 Bare area 81

5SS-BA8 Bare area 54

5SS-BA9 Bare area 540

3SS-BN10 Bench 10

3SS-BN11 Bench 10.5

3SS-BN12 Bench 23

3SS-BN4 Bench 19

3SS-BN5 Bench 9.5

3SS-BN6 Bench 29

3SS-BN7 Bench 21

3SS-BN8 Bench 9.5

6SS-PA10 Path 9

6SS-PA3 Path 33

6SS-PA4 Path 52

6SS-PA5 Path 20

6SS-PA6 Path 28

6SS-PA7 Path 11

6SS-PA8 Path 10.5

6SS-PA9 Path 19

4SS-PT1 Picnic Table 39

4SS-PT2 Picnic Table 19

5SS-R1 Random 8.5

5SS-R2 Random 10

5SS-R3 Random 9

5SS-R4 Random 9.5

5SS-R5 Random 31

5SS-R6 Random 9.5

5SS-R7 Random 9

5SS-R8 Random 11

4SS-S2 fishing deck 10

4SS-S3 restroom 45

Median 21

Rank Equivalent 95% Upper Confidence Limit 45

Subarea 3

The data and summary statistics for subarea 3 are shown in Table 3. For this subarea, the 95% UCL is lower than the chronic RBC of 684 ppm. Based on current use and these random sampling results, subarea 3 is considered safe for the chronic exposure scenarios described in the risk assessment addendum. It should be noted, however, that any development in this subarea would result in more targeted exposures, and it would be prudent to perform more characterization should development occur.

Table 3. Soil Arsenic Results for Subarea 3

Sample ID Type of sample Arsenic concentration in parts per million

5SS-UA1 Random 270

5SS-UA2 Random 40

5SS-UA3 Random 9.5

5SS-UA4 Random 82

5SS-UA5 Random 67

5SS-UA6 Random 71

5SS-UA7 Random 110

5SS-UA8 Random 140

Mean 99

95% Upper Confidence Limit 166

Subarea 4

The data and summary statistics for subarea 4 are shown in Table 4. For this subarea, the 95% UCL is higher than the RBC of 684 ppm. This result is partially due to the small number of samples collected, which added uncertainty. Only one sample was actually above 684 ppm arsenic, and this sample was collected from an area of very thick, tall grass, making exposure to soil unlikely. Because of this, and the fact that this section of the park is rarely used, the arsenic concentration in subarea 4 is not considered a problem. Powell County, ARCO, and EPA officials stated that this subarea would not be developed until it is cleaned up, and that the cleanup will be addressed in the record of decision (ROD) for Milltown Reservoir Sediments.⁽³⁾

Table 4. Soil Arsenic Results for Subarea 4

Sample ID Type of sample Arsenic concentration in parts per million

6SS-PA12 Path 530

6SS-PA13 Path 130

6SS-PA14 Path 31

5SS-R17 Random 800

5SS-R18 Random 500

Mean 398

95% Upper Confidence Limit 789

OTHER ISSUES

This sampling effort characterized chronic exposures at Arrow Stone Park. The sampling was not designed to allow decisions to be made regarding risk associated with acute arsenic exposures to children who may exhibit pica behavior (eating soil). This issue was discussed at the Powell County Health Board meeting on December 5, 2001. Because of the large area of the park and the infrequency of pica behavior, it was considered impractical to perform soil testing to assess risk from pica exposure. Instead, the health board has initiated an effort to create and distribute pamphlets to educate parents about the risks associated with arsenic-contaminated dirt and basic hygiene practices that can minimize risk to their children.

CONCLUSIONS

The two developed subareas (1 and 2) in Arrow Stone Park are safe, assuming chronic exposures as described in EPA's HHRA addendum (children 1 to 10 years old who visit the park 48 times a year for many years).

There is no concern at present for the undeveloped subareas (3 and 4) of the park, since arsenic levels and/or use are low.

This sampling effort was designed to characterize risk of chronic exposures to arsenic in soil at Arrow Stone Park. The data cannot be used to determine risk from acute arsenic exposures to children who may eat contaminated soil.

The initiative by the Powell County Health Board to create and distribute educational pamphlets about the risks associated with arsenic-contaminated dirt is a practical way to address acute exposures resulting from pica behavior.

RECOMMENDATIONS

If subareas 3 and/or 4 are developed, ATSDR recommends further arsenic sampling and/or cleanup.

ATSDR recommends that Powell County proceed with its effort to educate parents about the risks to children from eating soil.

ATSDR SITE TEAM

Authors of Report

Jill J. Dyken, Ph.D., P.E.
Environmental Health Scientist
Superfund Site Assessment Branch
Division of Health Assessment and Consultation

John R. Crellin, Ph.D.
Senior Environmental Epidemiologist
Superfund Site Assessment Branch
Division of Health Assessment and Consultation

Regional Representatives

Dan Strausbaugh
Regional Representative
ATSDR Region 8 Montana Office
Regional Operations

Glenn Tucker, Ph.D.
Senior Regional Representative
ATSDR Region 8
Regional Operations

REFERENCES

Roy F. Weston, Inc. Baseline Human Health Risk Assessment for the Clark Fork River Operable Unit of the Milltown Reservoir Sediments National Priority List Site. Prepared for the U.S. Environmental Protection Agency, Region VIII (Montana Office), by Roy F. Weston, Inc., 1998 January.

Dyken, Jill J., Crellin, John R. Public Health Consultation for Arrow Stone Park, Deer Lodge, Powell County, Montana. Atlanta, GA: U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 2001 March 27.

Syracuse Research Corporation. Baseline Human Health Risk Assessment for the Clark Fork River Operable Unit of the Milltown Reservoir Sediments National Priority List Site. Addendum 1. Risk-based concentrations for exposure of recreational visitors at Arrowstone Park to arsenic in soil and tailings. Prepared for the U.S. Environmental Protection Agency, Region VIII, by Syracuse Research Corporation, 2001 October.

Dyken, Jill J., Crellin, John R. Public Health Consultation Concerning Evaluation of EPA's Addendum to the Baseline Human Health Risk Assessment: Risk-based Concentrations for Exposure of Recreational Visitors at Arrowstone Park to Arsenic in Soil and Tailings (draft). Atlanta, GA: U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 2001 August 3.

Dyken, Jill J., Crellin, John R. Environmental Media Investigation Work Plan for Arrow Stone Park in Deer Lodge, Montana. Atlanta, GA: U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 2001 September 18.

ARCO Environmental Remediation LLC. South Deer Lodge Entryway Improvement Project: Arrow Stone Park Data Summary Report. Anaconda, MT, 2000 March 17.

Hanson, Ron. Facilities and Use of Patterns of Arrow Stone Park. Deer Lodge, MT, Powell County, 2000 June 13.

ARCO. Standard Operating Procedures for Clark Fork River Superfund Site Investigations. Anaconda, MT: ARCO, 1992 September.

Neuman, Dennis. Memorandum to Scott Brown (EPA) concerning validation of Arrowstone park soil arsenic data. Bozeman, MT: Montana State University, 2001 October 21.

Neuman, Dennis. Memorandum to Jill Dyken (ATSDR) concerning statistical confidence intervals for Arrowstone park data. Bozeman, MT: Montana State University, 2001 November 6.

Neuman, Dennis. Memorandum to Jill Dyken (ATSDR) concerning statistical confidence intervals for Arrow Stone park data set 4. Bozeman, MT: Montana State University, 2001 November 19.

FIGURES

Figure 1. Location of Arrow Stone Park near Deer Lodge, Montana

Figure 2. Features of Arrow Stone Park, Deer Lodge, Montana

Figure 3. Results of Soil Sampling for Arsenic in Arrow Stone Park

1. According to a conversation with Ron Hanson, Powell County planner, on September 24, 2001.
2. According to conversations with Scott Brown (EPA) on December 4 and 5, 2001.
3. Based on statements by Ron Hanson (Powell County), Barry Duff (ARCO), Scott Brown (EPA), and Bob Fox (EPA) on December 5, 2001.

Table of Contents

Agency for Toxic Substances and Disease Registry, 1825 Century Blvd, Atlanta, GA 30345
Contact CDC: 800-232-4636 / TTY: 888-232-6348

Department of Health and Human Services

Sample ID	Type of sample	Arsenic concentration in parts per million
5SS-BA12	Bare area	82
3SS-BN1	Bench	30
3SS-BN2	Bench	140
3SS-BN3	Bench	99
6SS-PA1	Path	130
6SS-PA2	Path	340
4SS-PT3	Picnic Table	140
4SS-PT4	Picnic Table	260
4SS-PT5	Picnic Table	520
5SS-R10	Random	140
5SS-R11	Random	38
5SS-R12	Random	370
5SS-R13	Random	350
5SS-R14	Random	130
5SS-R15	Random	270
5SS-R16	Random	21
5SS-R9	Random	150
4SS-S1	Raft launch	37
Mean		180
95% Upper Confidence Limit		250