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The Minnesota Department of Health (MDH) received a request from the Minnesota PollutionControl 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 theMPCA through its Dump Assessment Program as an "action site", indicating that the site warrantedfurther evaluation due to its potential to adversely impact public health or the environment. Thishealth consultation is based on a site visit conducted by MDH staff on May 26, 2000, private watersupply well sampling conducted by MDH staff on June 28, 2000, and information provided toMDH 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 ofWalker, 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 ofthe dump is beneath the ball fields. The dump area occupies approximately 5 to 10 acres and ismostly 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 thelate 1970s. At that time, the site was covered and seeded with grass. The area immediatelysurrounding the site is largely undeveloped. However, numerous homes are located within one mileof the site. Most of the homes obtain their water from the municipal water system, but severalhomes within one-half mile east of the site have private water supply wells. The nearest homes arelocated less than one-quarter mile east and southeast of the site. The city of Walker has severalmunicipal 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 beapproximately 97,300 cubic yards.


Based on available geologic information provided by STS, soils at the site are composed primarilyof well-drained outwash sand and gravel (STS 2000a). The uppermost bedrock is expected to bePrecambrian metavolcanic rocks at depths greater than 300 feet below grade. Soil boringsconducted by STS confirm the presence of up to 22.5 feet of sandy fill material mixed with wasteoverlying native sand deposits with discontinuous silty clay layers (STS 2000b). The location ofthe borings is illustrated in Figure 2. Cross sections of the dump prepared by STS are presented inFigures 3 and 4.

The surficial groundwater is expected to flow east towards Leech Lake. It is estimated thatgroundwater is located at more than 60 feet below grade. It was not was encountered in any of theborings 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 thickgrass. Very little waste was exposed at the site; it was observed only in the southernmost "toe" ofthe dump, particularly in small erosional gullies. Steep grades also are present in this area. Wastesobserved consisted primarily of metal scrap, 55-gallon drums, tires, appliances, glass, and bags oftrash. Waste was also observed in the wooded area north of the parking lot on the north side of theball 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-highwayvehicle trails. Also, it is likely that during ballgames, children would explore the wooded areasaround 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 boringlocations are shown in Figure 2. The borings encountered a thin layer of sandy fill overlying up to22.5 feet of sandy fill material mixed with waste. This layer, in turn overlies native sands anddiscontinuous silty clay layers. Solid wastes encountered included: glass, wood, concrete, metal,plastic, paper, rubble, brick, and ash.The borings were terminated before they encounteredgroundwater. 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 PIDunits), except in borings B-3 (up to 100 PID units) and B-7 (up to 50 PID units). Methane gas wasalso 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. Ninemetals were detected, but none exceeded applicable MPCA soil screening criteria for the protectionof human health or groundwater. No other compounds were detected. The surface soil analyticalresults are presented in Table 1.

Waste samples from four soil borings were collected at depths of 5 to 17 feet and analyzed forvolatile organic compounds (VOCs), metals, PCBs, PAHs, DRO, pesticides, and herbicides. SevenVOCs (methylene chloride, ethylbenzene, isopropylbenzene, 1,2,4-trimethylbenzene,isopropyltoluene, naphthalene, and xylenes), nine metals, one PCB (Arochlor 1254), and ten PAHswere 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 dermalcontact, inhalation, and/or ingestion does not represent a human health risk. The benzo(a)pyreneequivalent of this sample, which is measurement of the potential toxicity of a mixture of PAHs, wasnine times the SRV. Three of the metals (barium, copper, and lead) were somewhat elevated aboveapparent background levels. DRO was detected in all of the samples, ranging in concentration from25 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 SLVrepresents the concentration of a contaminant in soil above which it is able to leach into thegroundwater at levels in excess of drinking water standards. Other metals detected were withinbackground 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 boringB-2), but this is a frequent lab contaminant and may be a false positive. DRO was detected in onlyone sample, from boring B-4, at very low concentrations (8.7 mg/kg). The soil sample analyticalresults are presented in Table 3.

The MDH collected water samples from three private wells that are located in a direction assumedto be downgradient of the site. The private well locations are shown on Figure 1. The samples wereanalyzed for the presence of 68 volatile organic chemicals (VOCs), 8 metals, nitrate, and 4 indicatorparameters. Barium and copper were detected in all of the wells, and zinc and nitrate were detectedin one well. All of these were detected at concentrations significantly below their respectivedrinking water standards. Arsenic was detected in two wells at concentrations of 6 and 7.5 g/l. Manganese was also detected in two wells, at concentrations (130g/l - 160 g/l) that exceed thecurrent Health Risk Limit (HRL) of 100 g/l. However, the MDH has discontinued the use of thisstandard based on updated toxicological information and is recommending the use of an interimHealth-Based Value (HBV) of 1,000 g/l. The HRLs and HBVs represent levels of contaminationin private drinking water supplies that MDH considers safe for daily human consumption over alifetime. The HRLs have been promulgated into rule, while the HBV's have not. Well owners weresent 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 insoil, water, or air at levels of health concern, or when people are exposed to physical hazards such assharp objects or uneven ground. This requires that both the chemicals (or hazards) are present andthat people are in contact with them.

Waste materials in old dumps are often buried beneath a thin layer of whatever type of soil is easilyavailable at the time. Sometimes the cover consists of a waste material such as ash or sand blastsands, which usually contain high concentrations of metals. Often the cover materials are thin orabsent in spots, exposing wastes and contaminants. The majority of the site is well covered andvegetated, 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 objectssuch as scrap steel, which can become a physical hazard.

Organic waste materials in the dump (if it was not burned regularly) often degrade and generatemethane and other gases. Low levels of chemical solvents may also be present in gas produced byold dumps. Together, these gases are referred to as "landfill gases." These gases are frequentlyexplosive and can migrate up to a few hundred feet from the dump site, depending on localconditions. This gas migration can result in explosive levels of methane and concentrations ofsolvents above health concerns in nearby homes or buildings. Methane gas was only detected at lowlevels in one boring, indicating that it is naturally escaping or simply not being generated in largequantities 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 anddissolves chemicals from it. The SLVs attempt to measure the ability of the waste materials toproduce leachate. Only very low levels of one contaminant (DRO) that can be related to the wastematerials were found in soil below the waste, indicating that leaching of the waste is not occurring toa 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 alltypes of wastes. The site, as it exists today, presents little public health hazard. Physical hazards arepresent, 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 chemicalrisk associated with the site as there appears to be little or no contaminated soil exposed at thesurface, and contaminants do not appear to have leached to the water table. Relatively few surfacesoil samples were collected, however. The analytical results, including the results of private wellsampling indicate that widespread groundwater contamination is not likely to be associated with thedump.

There were no detections of common dump related contaminants, such as VOCs, in the private waterwells sampled near the site by MDH. Although slightly elevated levels of arsenic were detected intwo of the samples, this is not uncommon in glacial deposits in Minnesota and may be naturallyoccurring. In addition, manganese was detected at concentrations above its HRL, but may also benaturally occurring and is no longer considered to be a health risk at the concentrations detected. Itis 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 childrenmake them of special concern to communities faced with contamination of their water, soil, air, orfood. Children are at greater risk than adults from certain kinds of exposures to hazardoussubstances at waste disposal sites. They are more likely to be exposed because they play outdoorsand they often bring food into contaminated areas. They are shorter than adults, which means theybreathe dust, soil, and heavy vapors close to the ground. Children also weigh less, resulting inhigher doses of chemical exposure per body weight. The developing body systems of children cansustain permanent damage if toxic exposures occur during critical growth stages. Most importantly,children depend completely on adults for risk identification and management decisions, housingdecisions, 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 ofhuman activity at the site suggests that children are frequenting the site. As a result, they may becoming 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 May26, 2000, and analysis of private water supply samples, it appears that this site poses no apparent public health hazard at this time.


  1. Exposed waste at the site should be removed and properly disposed, and the propertyshould be posted against illegal dumping.

  2. Areas where erosion is occurring should be covered and regraded to prevent furtherexposure of waste at the site and reduce steep grades.

  3. Institutional controls such as a notice filed with the property deed should beimplemented to record the location of the dump for future reference.


MDH's Public Health Action Plan for the site will consist of:

  1. A letter to the MPCA and to city and county authorities advising them of our recommendations; and

  2. A review of any additional available data, and participation in any meetings or other public outreach activities.


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
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 ofHealth under a cooperative agreement with the Agency for Toxic Substances and DiseaseRegistry (ATSDR). It is in accordance with approved methodology and procedures existingat 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 publichealth consultation and concurs with the findings.

Lisa C. Hayes
for Chief, Superfund Site Assessment Branch, DHAC, ATSDR


Walker Dump Location
Figure 1. Walker Dump Location

Site Map
Figure 2. Site Map

Cross Section
Figure 3. Cross Section

Cross Section
Figure 4. Cross Section


Table 1.

Surface Soil Analytical Results Concentrations in mg/kg
(0-1 ft.)
(0-1 ft.)
(0-1 ft.)
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
(7.5-9.5 ft.)
(15-17 ft.)
(5-7 ft.)
(7.5-9.5 ft.)
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
(11 ft.)
(23 ft.)
(8 ft.)
(8 ft.)
(2.5-4.5 ft)
(22.5 ft.)
(22.5 ft.)**
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
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.

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