HEALTH CONSULTATION
WALKER DUMP
WALKER, CASS COUNTY, MINNESOTA
I. SUMMARY OF BACKGROUND AND HISTORY
The Minnesota Department of Health (MDH) received a request from the Minnesota Pollution Control Agency (MPCA) to evaluate potential public health concerns regarding the Walker Dump, located in the city of Walker, Cass County, Minnesota (the site). The site was identified by the MPCA through its Dump Assessment Program as an "action site", indicating that the site warranted further evaluation due to its potential to adversely impact public health or the environment. This health consultation is based on a site visit conducted by MDH staff on May 26, 2000, private water supply well sampling conducted by MDH staff on June 28, 2000, and information provided to MDH by the MPCA and its consultant, STS Consultants, LTD (STS 2000a, STS 2000b).
The site is located on a hilltop approximately one-half mile south of the downtown area of the city of Walker, in a former gravel pit. The property is currently being used for municipal baseball fields. The site location is shown in Figure 1, and a site map is presented in Figure 2. At least a portion of the dump is beneath the ball fields. The dump area occupies approximately 5 to 10 acres and is mostly covered with grass, although the southern "toe" of the dump is wooded.
The dump began accepting wastes in the late 1950s, and it was operated as an open dump until the late 1970s. At that time, the site was covered and seeded with grass. The area immediately surrounding the site is largely undeveloped. However, numerous homes are located within one mile of the site. Most of the homes obtain their water from the municipal water system, but several homes within one-half mile east of the site have private water supply wells. The nearest homes are located less than one-quarter mile east and southeast of the site. The city of Walker has several municipal water supply wells located approximately 1 mile north of the site as shown in Figure 1.
As a public dump, the site likely accepted all types of wastes, including household garbage, autos, tires, and appliances. Only small amounts of waste are currently exposed at the surface of the dump. Based on a Phase II site investigation, the volume of waste at the site is estimated to be approximately 97,300 cubic yards.
Geology/Hydrogeology
Based on available geologic information provided by STS, soils at the site are composed primarily of well-drained outwash sand and gravel (STS 2000a). The uppermost bedrock is expected to be Precambrian metavolcanic rocks at depths greater than 300 feet below grade. Soil borings conducted by STS confirm the presence of up to 22.5 feet of sandy fill material mixed with waste overlying native sand deposits with discontinuous silty clay layers (STS 2000b). The location of the borings is illustrated in Figure 2. Cross sections of the dump prepared by STS are presented in Figures 3 and 4.
The surficial groundwater is expected to flow east towards Leech Lake. It is estimated that groundwater is located at more than 60 feet below grade. It was not was encountered in any of the borings at the site, which were advanced only to depths of 32 feet.
Site Visit
On May 26, 2000, Ginny Yingling of MDH visited the site. The site was well vegetated with thick grass. Very little waste was exposed at the site; it was observed only in the southernmost "toe" of the dump, particularly in small erosional gullies. Steep grades also are present in this area. Wastes observed consisted primarily of metal scrap, 55-gallon drums, tires, appliances, glass, and bags of trash. Waste was also observed in the wooded area north of the parking lot on the north side of the ball fields. It was unclear whether this waste was related to the dump or was more recent in origin.
There was significant evidence of human activity at the site, including numerous off-highway vehicle trails. Also, it is likely that during ballgames, children would explore the wooded areas around the toe of the dump. Abundant wildlife trails and burrows were also observed at the site. No evidence of vegetative stress was observed.
Site Investigation
Fifteen soil borings were advanced by STS at the site using a hollow-stem auger. The boring locations are shown in Figure 2. The borings encountered a thin layer of sandy fill overlying up to 22.5 feet of sandy fill material mixed with waste. This layer, in turn overlies native sands and discontinuous silty clay layers. Solid wastes encountered included: glass, wood, concrete, metal, plastic, paper, rubble, brick, and ash.The borings were terminated before they encountered groundwater. Organic vapor measurements were collected using a photo ionization detector (PID) during drilling. Organic vapors were detected only at very low concentrations (less than 10 PID units), except in borings B-3 (up to 100 PID units) and B-7 (up to 50 PID units). Methane gas was also measured, but detected at very low concentrations (0.6%) in only one boring (B-4).
Surface soil was analyzed from three locations for metals, polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), diesel range organics (DRO), pesticides, and herbicides. Nine metals were detected, but none exceeded applicable MPCA soil screening criteria for the protection of human health or groundwater. No other compounds were detected. The surface soil analytical results are presented in Table 1.
Waste samples from four soil borings were collected at depths of 5 to 17 feet and analyzed for volatile organic compounds (VOCs), metals, PCBs, PAHs, DRO, pesticides, and herbicides. Seven VOCs (methylene chloride, ethylbenzene, isopropylbenzene, 1,2,4-trimethylbenzene, isopropyltoluene, naphthalene, and xylenes), nine metals, one PCB (Arochlor 1254), and ten PAHs were detected. One PAH, benzo(a)pyrene, exceeded its Soil Reference Value (SRV) in boring B-7. The SRV represents the concentration of a contaminant in the soil below which normal dermal contact, inhalation, and/or ingestion does not represent a human health risk. The benzo(a)pyrene equivalent of this sample, which is measurement of the potential toxicity of a mixture of PAHs, was nine times the SRV. Three of the metals (barium, copper, and lead) were somewhat elevated above apparent background levels. DRO was detected in all of the samples, ranging in concentration from 25 to 320 mg/kg. The waste sample analytical results are presented in Table 2.
Soil below the waste horizon from two soil borings was analyzed for VOCs, metals, PCBs, PAHs, DRO, pesticides, and herbicides. The Soil Leaching Value (SLV) for one compound, chromium VI, was exceeded in the sample from B-7. However it should be noted that the sample was analyzed for "total chromium," but compared to the more conservative chromium VI standard. The SLV represents the concentration of a contaminant in soil above which it is able to leach into the groundwater at levels in excess of drinking water standards. Other metals detected were within background concentrations, with the exception of copper in boring B-7 and nickel in boring B-3, which were somewhat elevated. One VOC was detected, methylene chloride (0.64 mg/kg in boring B-2), but this is a frequent lab contaminant and may be a false positive. DRO was detected in only one sample, from boring B-4, at very low concentrations (8.7 mg/kg). The soil sample analytical results are presented in Table 3.
The MDH collected water samples from three private wells that are located in a direction assumed to be downgradient of the site. The private well locations are shown on Figure 1. The samples were analyzed for the presence of 68 volatile organic chemicals (VOCs), 8 metals, nitrate, and 4 indicator parameters. Barium and copper were detected in all of the wells, and zinc and nitrate were detected in one well. All of these were detected at concentrations significantly below their respective drinking water standards. Arsenic was detected in two wells at concentrations of 6 and 7.5 µg/l. Manganese was also detected in two wells, at concentrations (130µg/l - 160 µg/l) that exceed the current Health Risk Limit (HRL) of 100 µg/l. However, the MDH has discontinued the use of this standard based on updated toxicological information and is recommending the use of an interim Health-Based Value (HBV) of 1,000 µg/l. The HRLs and HBVs represent levels of contamination in private drinking water supplies that MDH considers safe for daily human consumption over a lifetime. The HRLs have been promulgated into rule, while the HBV's have not. Well owners were sent letters explaining the results and the implications for their water quality. The private water supply well sample analytical results are presented in Table 4.
Dumps may pose a potential human health risk when people come into contact with chemicals in soil, water, or air at levels of health concern, or when people are exposed to physical hazards such as sharp objects or uneven ground. This requires that both the chemicals (or hazards) are present and that people are in contact with them.
Waste materials in old dumps are often buried beneath a thin layer of whatever type of soil is easily available at the time. Sometimes the cover consists of a waste material such as ash or sand blast sands, which usually contain high concentrations of metals. Often the cover materials are thin or absent in spots, exposing wastes and contaminants. The majority of the site is well covered and vegetated, with erosion exposing wastes only at the southern edge of the dump. Over time, compaction and degradation of the waste result in settling and the emergence of large, sharp objects such as scrap steel, which can become a physical hazard.
Organic waste materials in the dump (if it was not burned regularly) often degrade and generate methane and other gases. Low levels of chemical solvents may also be present in gas produced by old dumps. Together, these gases are referred to as "landfill gases." These gases are frequently explosive and can migrate up to a few hundred feet from the dump site, depending on local conditions. This gas migration can result in explosive levels of methane and concentrations of solvents above health concerns in nearby homes or buildings. Methane gas was only detected at low levels in one boring, indicating that it is naturally escaping or simply not being generated in large quantities within the waste. Low levels of other organic vapors were detected also.
The degradation of solid waste also produces leachate when infiltrating water contacts the waste and dissolves chemicals from it. The SLVs attempt to measure the ability of the waste materials to produce leachate. Only very low levels of one contaminant (DRO) that can be related to the waste materials were found in soil below the waste, indicating that leaching of the waste is not occurring to a large degree. Leachate may discharge to surface water or infiltrate into groundwater. Groundwater contaminated by leachate usually does not have any distinguishing appearance, color, or taste, and people are rarely aware of any problem unless the water is tested.
The Walker Dump is a typical town dump because it was located near the town and accepted all types of wastes. The site, as it exists today, presents little public health hazard. Physical hazards are present, however. Only minor amounts of waste material are exposed at the dump surface. Essentially no methane was detected during the site investigation. There appears to be little chemical risk associated with the site as there appears to be little or no contaminated soil exposed at the surface, and contaminants do not appear to have leached to the water table. Relatively few surface soil samples were collected, however. The analytical results, including the results of private well sampling indicate that widespread groundwater contamination is not likely to be associated with the dump.
There were no detections of common dump related contaminants, such as VOCs, in the private water wells sampled near the site by MDH. Although slightly elevated levels of arsenic were detected in two of the samples, this is not uncommon in glacial deposits in Minnesota and may be naturally occurring. In addition, manganese was detected at concentrations above its HRL, but may also be naturally occurring and is no longer considered to be a health risk at the concentrations detected. It is unlikely therefore, that contaminated groundwater from the site is reaching nearby users.
Agency for Toxic Substances and Disease Registry (ATSDR) Child Health Initiative
ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children make them of special concern to communities faced with contamination of their water, soil, air, or food. Children are at greater risk than adults from certain kinds of exposures to hazardous substances at waste disposal sites. They are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. They are shorter than adults, which means they breathe dust, soil, and heavy vapors close to the ground. Children also weigh less, resulting in higher doses of chemical exposure per body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care.
Children may be attracted to exposed debris areas due to the presence of bottles, shiny metal objects, exposed dirt, etc. The location of the dump in a public recreation area and the abundant evidence of human activity at the site suggests that children are frequenting the site. As a result, they may be coming into contact with exposed waste, which poses a physical risk and potential chemical risk.
Based on a review of available information in MPCA and MDH files, a site visit conducted on May 26, 2000, and analysis of private water supply samples, it appears that this site poses no apparent public health hazard at this time.
MDH's Public Health Action Plan for the site will consist of:
STS 2000a. Draft Phase I Environmental Site Assessment, STS Consultants, LTD. May 15, 2000
STS 2000b. Draft Phase II Environmental Site Assessment, STS Consultants, LTD. October 3, 2000.
James Kelly
Health Assessor
Site Assessment and Consultation Unit
Minnesota Department of Health
tel: (651) 215-0913
Ginny Yingling
Hydrologist
Site Assessment and Consultation Unit
Minnesota Department of Health
tel: (651) 215-0917
Alan Yarbrough
Technical Project Officer
Division of Health and Consultation
State Program Section
Agency for Toxic Substances and Disease Registry
This Walker Dump Health Consultation was prepared by the Minnesota Department of Health under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was begun.
Alan W. Yarbrough
Technical Project Officer, SPS, SSAB, DHAC, ATSDR
The Division of Health Assessment and Consultation, ATSDR, has reviewed this public health consultation and concurs with the findings.
Lisa C. Hayes
for Chief, Superfund Site Assessment Branch, DHAC, ATSDR
Figure 1. Walker Dump Location
Table 1. Surface Soil Analytical Results
Concentrations in mg/kg
| SS-01 (0-1 ft.) |
SS-02 (0-1 ft.) |
SS-03 (0-1 ft.) |
SLV | SRV | |
| Diesel Range Organics | no detects for all compounds analyzed | NE | NE | ||
| Metals EPA 6010 | |||||
| Arsenic | 2.49 | 1.58 | 1.52 | 15.1 | 10 |
| Barium | 19.9 | 21.2 | 19 | 842 | 1,200 |
| Cadmium | 0.0651 | 0.0586 | <0.0498 | 4.4 | 35 |
| Chromium | 12.5* | 12.5* | 11.5* | 18 | 71 |
| Copper | 9.2 | 7.19 | 8.27 | 400 | 100 |
| Lead | 1.39 | 9.58 | 2.08 | 525 | 400 |
| Nickel | 8.15 | 8.8 | 8.72 | 88 | 520 |
| Mercury | <0.0184 | 0.0439 | <0.0191 | 1.6 | 0.7 |
| Selenium | 0.522 | <0.253 | <0.249 | 1.5 | 170 |
| Polychlorinated Biphenyls - PCBs EPA 8020 | no detects for all compounds analyzed | 2.1 | 1.2 | ||
| Polyaromatic Hydrocarbons - PAHs EPA 8270 | no detects for all compounds analyzed | varies | varies | ||
| Pesticides EPA 8081 | no detects for all compounds analyzed | NE | varies | ||
| Herbicides (MDA List 1) | no detects for all compounds analyzed | varies | varies | ||
* = denotes value for total chromium (chromium (III) + chromium
(VI))
SLV = MPCA Soil Leaching Value, Tier 1
SRV = MPCA Soil Reference Value
NE = Not Established
Bold = Concentration above detection limits
| = Concentration exceeds SLV | |
| = Concentration exceeds SRV |
Source: STS 2000b
Table 2. Waste Analytical Results
Concentrations in mg/kg
| B-2 S-04 (7.5-9.5 ft.) |
B-3 S-07 (15-17 ft.) |
B-4 S-03 (5-7 ft.) |
B-7 S-04 (7.5-9.5 ft.) |
SLV | SRV | |
| Volatile Organic Ompounds - VOCs EPA 8260 Methonal Extraction |
||||||
| Methylene Chloride | 0.67 | <0.3 | <0.32 | <0.28 | NE | NE |
| Ethylbenzene | <0.28 | <0.3 | 0.4 | <0.28 | 4.7 | 200 |
| Isopropylbenzene | <0.28 | <0.3 | <0.32 | 1.6 | 18 | NE |
| 1,2,4-Trimethylbenzene | <0.28 | <0.3 | 0.38 | <0.28 | NE | 5 |
| p-Isopropyltoluene | <0.28 | <0.3 | <0.32 | 2.4 | NE | NE |
| Napthalene | <0.28 | <0.3 | 1.9 | 0.43 | 7.5 | 10 |
| M&P Xylene | <0.57 | <0.6 | 0.67 | <0.28 | 45 | 110 |
| Diesel Range Organics | 25 | 36 | 240 | 320 | NE | NE |
| Metals EPA 6010 | ||||||
| Arsenic | 2.14 | 2.71 | 2.04 | 5.07 | 15.1 | 10 |
| Barium | 53.2 | 57.8 | 31.9 | 134 | 842 | 1,200 |
| Cadmium | 0.261 | 0.908 | 0.244 | 0.819 | 4.4 | 35 |
| Chromium | 12.8* | 16.8* | 11.8* | 13.3* | 18 | 71 |
| Copper | 15.9 | 24.9 | 17 | 104 | 400 | 100 |
| Lead | 81.5 | 159 | 30.2 | 90.3 | 525 | 400 |
| Mercury (EPA 7471) | 0.0559 | 0.246 | 0.0271 | 0.0702 | 1.6 | 0.7 |
| Nickel | 9.41 | 14 | 11.4 | 11.1 | 88 | 520 |
| Selenium | 0.405 | 0.301 | <0.299 | 0.372 | 1.5 | 170 |
| Polychlorinated Biphenyls - PCBs EPA 8020 | ||||||
| Arochlor 1254 | <0.037 | 0.15 | <0.04 | <0.044 | 2.1 | 1.2 |
| Polyaromatic Hydrocarbons - PAHs EPA 8270 | ||||||
| Phenanthrene | <0.34 | 3.2 | <0.81 | 28 | NE | NE |
| Anthracene | <0.34 | <0.71 | <0.81 | 9.2 | 942 | 7,880 |
| Fluoranthene | <0.34 | 2.5 | <0.81 | 33 | 295 | 1,080 |
| Pyrene | <0.34 | 2.5 | <0.81 | 29 | 272 | 890 |
| Benzo (a) anthracene | <0.34 | 1.5 | <0.81 | 18 | NE | NE |
| Chrysene | <0.34 | 1.9 | <0.81 | 16 | NE | NE |
| Benzo (b) fluoranthene | <0.34 | 2.4 | <0.81 | 17 | NE | NE |
| Benzo (k) fluoranthene | <0.34 | 0.87 | <0.81 | <7.5 | NE | NE |
| Benzo (a) pyrene | <0.34 | 1.5 | <0.81 | 14 | NE | 2 |
| Indeno (1,2,3-cd) pyrene | <0.34 | <0.71 | <0.81 | 7.9 | NE | NE |
| Pesticides EPA 8081 | no detects for all compounds analyzed | NE | varies | |||
| Herbicides (MDA List 1) | no detects for all compounds analyzed | varies | varies | |||
* = denotes value for total chromium (chromium (III) + chromium
(VI))
SLV = MPCA Soil Leaching Value, Tier 1
SRV = MPCA Soil Reference Value
NE = Not Established
Bold = Concentration above detection limits
| = Concentration exceeds SLV | |
| = Concentration exceeds SRV |
Source: STS 2000b
Table 3. Soil Analytical Results
Concentrations in mg/kg
| B-2 S-05 (11 ft.) |
B-3 S-10 (23 ft.) |
B-4 S-04 (8 ft.) |
B-5 S-04 (8 ft.) |
B-6 S-02 (2.5-4.5 ft) |
B-7 S-10 (22.5 ft.) |
B-20 S-10 (22.5 ft.)** |
SLV | SRV | |
| Volatile Organic Compounds VOCs EPA 8260 Methanol |
|||||||||
| Methyl Chloride | 0.64 | <0.28 | <0.26 | <0.28 | <0.26 | <0.28 | <0.27 | NE | NE |
| Diesel Range Organics | <8.6 | <9.1 | 8.7 | <8.9 | <8.6 | <6.8 | <8.5 | NE | NE |
| Metals EPA 6010 | |||||||||
| Arsenic | 1.17 | 5.03 | 1.86 | 0.801 | 2.03 | 1.83 | 1.94 | 15.1 | 10 |
| Barium | 39.3 | 39.1 | 14.4 | 36.5 | 10.5 | 45.7 | 27.7 | 842 | 1,200 |
| Cadmium | 0.0968 | 0.47 | 0.0953 | <0.0559 | <0.0506 | <0.0523 | <0.0536 | 4.4 | 36 |
| Chromium | 8.76* | 11.6* | 10.4* | 9.45* | 5.32* | 24.2* | 14.8* | 18 | 71 |
| Copper | 4.19 | 33.4 | 10.6 | 3.72 | 4 | 97.1 | 36.9 | 400 | 100 |
| Lead | 2.03 | 2.92 | 4.27 | 3.6 | 0.775 | 4.41 | 4.86 | 525 | 400 |
| Mercury | <0.0194 | 0.0208 | 0.0352 | <0.0201 | <0.0184 | 0.0251 | <0.021 | 1.6 | 0.7 |
| Nickel | 8.62 | 77 | 9.84 | 5.57 | 5.24 | 13.9 | 9.5 | 88 | 520 |
| Selenium | <0.266 | 0.525 | <0.247 | 0.361 | <0.253 | <0.261 | 0.271 | 1.5 | 170 |
| Polychlorinated Biphenyls - PCBs EPA 8020 | no detects for all compounds analyzed | 2.1 | 1.2 | ||||||
| Polyaromatic Hydrocarbons - PAHs EPA 8270 | no detects for all compounds analyzed | varies | varies | ||||||
| Pesticides EPA 8081 | no detects for all compounds analyzed | NE | varies | ||||||
| Herbicides (MDA List 1) | no detects for all compounds analyzed | varies | varies | ||||||
* = denotes value for total chromium (chromium (III) + chromium
(VI))
SLV = MPCA Soil Leaching Value, Tier 1
SRV = MPCA Soil Reference Value
NE = Not Established
Bold = Concentration above detection limits
| = Concentration exceeds SLV | |
| = Concentration exceeds SRV |
** denotes duplicate of soil sample S-10, boring B-7, 22.5 ft. depth.
Source: STS 2000b
Table 4. Private Well Sampling Analytical
Results
Concentrations in ug/l
| #1 | #2 | #3 | Standard | Source | |
| Volatile Organic Compounds - VOCs | varies | varies | |||
| BDL | BDL | BDL | |||
| Metals | |||||
| Arsenic | <1 | 7.5 | 6 | 50 | MCL |
| Barium | 22 | 63 | 93 | 2,000 | HRL |
| Copper | 23 | 4 | 5 | 1,300 | MCL* |
| Manganese | <10 | 160 | 130 | 1,000 | HBV |
| Zinc | <20 | 62 | <20 | 2,000 | HRL |
| Wet Chemistry | |||||
| Nitrogen, Nitrate & Nitrite | 410 | <50 | <50 | 10,000 | HRL |
| Ammonia Nitrogen | <20 | 0.33 | 0.38 | - | |
| Total Chloride | 4,000 | 1,400 | 1,500 | 250,000 | MCL |
| Total Sulfate | 18,000 | 6,100 | 7,200 | 250,000 | MCL |
BDL - all compounds below lab detection limits
< = Less than laboratory limit of detection
HRL = Health Risk Limit for Groundwater, Minnesota Department of Health
HBV = Health-Based Value for Groundwater, Minnesota Department of Health
MCL = EPA aximum Contaminant Limit
NE = Not Established
Bold = Concentration above detectin limits
| = Concentration exceeds HRL/HBV/MCL |
* = action level for drinking water at the tap.
