Skip directly to search Skip directly to A to Z list Skip directly to site content




The Oak Grove Sanitary Landfill (Oak Grove SLF) is listed by theU.S. Environmental Protection Agency on the National PrioritiesList. This site is located in Oak Grove Township, in northwestAnoka County, Minnesota. The area surrounding the landfill issparsely populated. The site began operation in 1967 as an opendump. From 1971 through 1984 the landfill operated under asanitary landfill permit issued by the Minnesota PollutionControl Agency. During this period, however, dumping ofindustrial solid and liquid hazardous wastes may also haveoccurred. In 1985, lime sludge from a local water treatmentplant was applied over two-thirds of the landfill as a temporarycover.

The results of two Remedial Investigations of the Oak Grove SLFhave revealed that subsurface soil, cover soil, leachate, anadjacent wetland's surface water and sediment, and a surficialaquifer have been contaminated to varying degrees with volatileorganic, semi-volatile organic, and inorganic chemicals. Adeeper aquifer that is used as the source of potable water bynearby residents was found to contain very low concentrations ofsome organic and inorganic chemicals. However, nearbyresidential wells that draw groundwater from this deeper aquiferare not contaminated.

Based on available information, the Minnesota Department ofHealth has concluded that the Oak Grove SLF site poses noapparent public health hazard under current conditions sincethere are no indications that people either have been or arebeing exposed to levels of site-related contaminants that wouldbe of concern to human health. Therefore, this site is not beingconsidered for follow-up health activities at this time. However, if data become available suggesting that human exposureto hazardous substances at levels of public health concern isoccurring, ATSDR and the Minnesota Department of Health will re-evaluate this site for any indicated follow-up activities.


A. Site Description and History

The Oak Grove Sanitary Landfill (Oak Grove SLF) site is listed onthe U.S. Environmental Protection Agency's (EPA) NationalPriorities List (NPL). The site is located in Oak GroveTownship, in northwest Anoka County, Minnesota (Figure 1). Whilethe entire Oak Grove SLF site encompasses approximately 104acres, only about 45 acres have been actively landfilled. Thislandfilled area is roughly rectangular in shape and rises to amaximum height of approximately 50 feet above the surroundingterrain. At present, the western one-third of the landfill moundis fairly well vegetated with tall grasses. The top portion ofthe eastern two-thirds is covered with lime sludge and is notvegetated; the side slopes are, however, well vegetated. Theareas directly to the west and southwest of the site are sparselypopulated with single-family residences. The owner/operator ofthe landfill and other family members live in homes on the farnorthern portion of the site. A large wetland is locateddirectly south of and adjacent to the landfill (Figure 1). CedarCreek flows through (northeast to west-southwest) and drains thewetland. At its nearest point, Cedar Creek is approximately3,000 feet from the southern edge of the landfilled area. Aborrow pit and a lime sludge-covered area are located directlyeast of the landfilled area. The area further to the east of thelandfilled area is relatively open, undeveloped rural land. There is a well-defined cluster of stressed vegetation in thewetland area adjacent to the southeast corner of the landfillmound.

From 1967 to 1971 the present-day Oak Grove SLF was operated asan open dump which received mixed municipal and industrial solidwastes. In 1971, the Minnesota Pollution Control Agency (MPCA)issued the owner/operator a sanitary landfill permit. The OakGrove SLF was operated as a sanitary landfill under this permituntil 1976, when the operation of the landfill was assumed byNorthwest Disposal, Inc. (a group of nine refuse haulers). Northwest Disposal, Inc. continued to operate the landfill untilJanuary 1984, when the MPCA suspended their operating permit. In1985, Northwest Disposal, Inc. was granted permission by MPCA tocover the landfill with lime sludge from a local water treatmentplant. The lime sludge was applied to the eastern two-thirds ofthe landfill from March to November 1985.

From 1971 through 1983, periodic inspections of the Oak Grove SLFwere carried out by both the Anoka County Health Department andMPCA. Records indicate that while most of the waste in the landfill is commercial and municipal solid waste, unknownquantities of industrial solid and liquid wastes (some of whichmay be regarded as hazardous waste) are also present. Thesewastes included: acidic oil sludge, paint and solvent wastes, foundry sand and sludges, inorganic acids, metal sludges, chlorinated and non-chlorinated organic compounds from pesticide manufacturing, cutting oils, lubricants, cleaning solvents, andinks (1).

Oak Grove Sanitary Landfill and Surrounding Area
Figure 1. Oak Grove Sanitary Landfill and Surrounding Area

The Oak Grove SLF lies on the Anoka Sand Plain. Soils of theAnoka Sand Plain are either sandy and well to excessively welldrained, or organic peat soils with poor drainage. Small lakesand swampy areas are also very common in the plain. As notedearlier, a wetland borders the landfill along its southern edge.

The Oak Grove SLF is situated on glacial drift that ranges indepth from 150 to 250 feet. These sediments contain two aquifersseparated by a layer of glacial till (40 to 80 feet thick) whichacts as a semi-confining layer. The water table aquifer isprimarily an outwash sand which is, at the southern edge of thelandfill, overlain by a peat deposit. The water table is foundwithin the peat layer. The direction of horizontal groundwaterflow in this shallow aquifer is south towards the wetland andCedar Creek. The vertical flow of groundwater in this aquiferappears to be downward in the northern half of the site andupward in the southern half of the site (where it discharges tothe wetland). The semi-confined aquifer beneath the glacial tillis a sand and gravel (deep valley train) aquifer. This deeperaquifer is a source of potable water for many of the residencesin the area (1,2). The area around the Oak Grove SLF isunderlain primarily by the Franconia-Ironton-Galesville aquifer. The groundwater in this bedrock aquifer flows towards the south.

A draft Remedial Investigation (RI) for this site was submittedto MPCA in August 1987. This draft RI was, however, not acceptedby MPCA and a second contractor was selected to: 1) evaluate theoriginal RI, 2) gather additional data to fully characterize thesite, and 3) prepare a new draft RI. Since additional data wereneeded to characterize the site (especially in the case ofgroundwater contamination), the remedy for the Oak Grove SLF wasdivided, by the MPCA and USEPA, into two discrete actions, termed"operable units". The remedy for the first operable unit, sourcecontrol of contaminants from the landfill, will be accomplishedby installing a permanent cover system over the landfill. ARecord of Decision documenting this selected remedy was signed inSeptember, 1988. The remedial design for the final cover isproceeding, but with some delays. The remedy for the secondoperable unit, remediation of contaminated groundwater, will beaccomplished by the continued monitoring of both aquifers presentat the site as well as monitoring of surface water and sediments. Also included in this remedy, for which a Record of Decision wassigned in December, 1990, are institutional controls on theplacement of drinking water wells and natural attenuation of shallow contaminated groundwater. The following documents weremade available to the Minnesota Department of Health (MDH) forreview:

Oak Grove Draft Remedial Investigation Report. MalcolmPirnie, Inc. April 1990.

Draft Report Feasibility Study for Groundwater Operable UnitOak Grove Sanitary Landfill. Malcolm Pirnie, Inc. June1990.

Final Report Remedial Investigation for the Oak Grove Sanitary Landfill. Malcolm Pirnie, Inc. October, 1990.

Oak Grove Sanitary Landfill Declaration for the Record of Decision. U.S. Environmental Protection Agency and theMinnesota Pollution Control Agency. December 1990.

These documents, consultations with MPCA project staff, and sitevisits by MDH staff form the basis for this Health Assessment.

The MDH has written a Preliminary Health Assessment for this site(dated June 27, 1989). This Preliminary Health Assessment wasprepared using the limited data available at that time. Thepresent Health Assessment incorporates more recent and extensivemonitoring data and replaces the 1989 document.

B. Site Visit

Site visits were conducted by MDH and MPCA project staff on June1, 1988, and July 18, 1990. The western one-third of thelandfill was fairly well vegetated with tall grasses and weeds. The remainder of the top of the landfill mound was covered withlime sludge 1 to 1-1/2 feet thick. This area was not vegetatedand had a good deal of refuse (tires, plastics, metal, glass,bedsprings, etc.) sticking out of the surface. There were deertracks visible in the lime cover. Leachate seeps and gullying ofthe lime were seen on the south face of the landfill mound. Inthe wetland area adjacent to the southeast corner of the landfillmound there was a well-defined cluster of stressed vegetation. The landfill site was not fenced.

C. Demographics, Land Use, and Natural Resource Use

The Oak Grove SLF is located in Oak Grove Township in northwestAnoka County, Minnesota. Anoka County is north of Minneapolisand is part of the seven-county Minneapolis-St. Paul Metropolitanarea. Estimates from the Metropolitan Council put the 1989population of Oak Grove Township at 4,967 (1).

The Metropolitan Council estimated that the population within a4-mile radius of the site (includes areas of other townships andcities) in 1989 was 9,821; within a 1-mile radius (includes onlyOak Grove Township) was estimated to be 335. Of the estimated335 persons, approximately ten percent are under 5 years of ageand five percent are over age 62. The owner/operator of thelandfill and other family members live in homes on the farnorthern portion of the site.

Current land uses in the area immediately surrounding the OakGrove SLF are, in general: rural residential to the west; ruralresidential and agricultural cropland to the north; agriculturalcropland, agricultural pastureland, and forested wetland to theeast; and forested wetland, wetland, and upland forest to thesouth.

D. Health Outcome Data

Because there were no data indicating that local residents havebeen or are being exposed to contaminants from the Oak Grove SLF,state and local health outcome data were not examined as part ofthis Health Assessment.


The residents in the vicinity of the Oak Grove SLF are concernedabout the possibility of their wells becoming contaminated withlandfill-derived chemicals and the subsequent potential foradverse health effects if contaminated water is used fordrinking, bathing, food preparation, etc.


In an effort to identify facilities that may currently contributeto the contamination of environmental media (air, soil, water)near and/or on the Oak Grove SLF, MDH searched the 1987, 1988,and 1989 Toxic Chemical Release Inventory (TRI)(8). The TRI wasdeveloped by the U.S. EPA and contains information on estimatedannual releases of chemicals into the environment (air, water,and soil). The chemical release information is provided bynumerous facilities nation-wide.

TRI did not contain any information on reported toxic chemicalreleases in the vicinity of the Oak Grove SLF.

Chemicals are included in this evaluation based on severalconsiderations. These are as follows: 1) MDH has developedRecommended Allowable Limits (RALs) for contaminants in privatedrinking water supplies (see appendix 3). The RAL reflects themaximum concentration of a contaminant in drinking water that aperson may ingest over a lifetime without risk of adverse healtheffects. Chemicals included on this list are those mostfrequently found in groundwater in Minnesota. RALs for non-carcinogens are often taken from the drinking water healthadvisories published by the EPA Office of Drinking Water (ODW). RALs for carcinogens are derived from the potency slopes from theEPA Carcinogen Assessment Group (CAG) and reflect an estimatedlifetime excess cancer risk of 1 in 100,000. 2) Chemicals thatdo not exceed RALs may present a real or potential health hazardto the public depending on site-specific information andprofessional judgement. In this case, the concern lies with theunknown health consequences of exposure to low concentrations ofmany chemicals simultaneously. Future research data on theadverse health effects of chemical mixtures may necessitatefurther evaluation of this site. 3) Concentrations of chemicalsleaching from landfills are unpredictable. Chemicals are oftenreleased in pulses and monitoring may reflect either peakconcentrations during pulses or lower concentrations foundbetween pulses. In addition, the types of chemicals releasedeither during or between the pulses may be highly variable. Themonitoring results may also be impacted by the variability ofglacial formations typical of Minnesota and the imprecise natureof hydrogeologic characterization.

The following summary is based on data contained in the 1990Draft RI Report (1) and Final RI Report (2).

A. On-Site Contamination

For the purposes of this Health Assessment, all areas exceptCedar Creek are regarded as on-site (see Figure 1).

1. Subsurface Soil

In October and November 1986, three subsurface borings weredrilled into the deep, semi-confined sand and gravel aquifer tocollect samples for geotechnical and chemical analyses. Theborings were installed at the base of the landfill mound at theNE, SE, and SW corners. Four samples were obtained from eachboring hole for a total of 12 soil samples. Samples were takenat depths ranging from 19.5 to 85.5 feet below ground and wereanalyzed for Hazardous Substance List (HSL) compounds.

Two VOCs were detected in the soil samples: chloroform at 0.034and 0.078 mg/kg from the SW boring and xylenes (total) at 0.017and 0.021 mg/kg from the SW and SE borings, respectively. NoVOCs were detected in samples from the NE boring.

The following inorganic chemicals were detected in subsurfacesoil samples: aluminum, arsenic, barium, calcium, chromium,copper, iron, lead, magnesium, manganese, mercury, nickel,vanadium, and zinc. With the exception of magnesium, all themetals were found to be within published background ranges ofmetals in U.S. soils (3,4,5). Magnesium was only slightlyelevated over published background ranges.

2. Landfill Cover Soil

Eight samples of landfill cover soil were collected in November1986 from the interface of the fill and lime sludge cover (thatis, from beneath the lime sludge cover). One soil sample wascollected from the top 3 inches of soil in the sludge-free areaof the western portion of the landfill mound. All nine soilsamples were analyzed for HSL VOCs.

Low concentrations of four VOCs were detected in four interfacesoil samples. These compounds were: trans-1,2-dichloroethene(13 ug/kg), toluene (8.9, 10, and 110 ug/kg), ethylbenzene (23ug/kg), and bromodichloromethane (6 ug/kg). No VOCs weredetected in the sample obtained from the western portion of thelandfill.

3. Soil Gases

Forty-four soil gas measurements were taken in October 1986 atdepths ranging from 1.3 to 3.3 feet below the surface of thelandfill mound.

Organic vapors, primarily methane, were detected under the limesludge cover in the eastern portion of the landfill. Themajority of organic vapors present in the soil in the westernportion of the landfill were also determined to be methane.

4. Leachate

Leachate seeps were sampled at five locations in November 1986: three on the south-southeastern slope, one at the base of thenorthwest slope, and one at the base of the northern slope. Boththe liquid and underlying soil of the leachate seeps wereanalyzed for contaminants; the results are presented separately,below.

- Leachate Seep Liquid

VOCs, semi-volatile organic, and inorganic compounds were detected in the leachate samples from the south-southeastern, northern, and northwest slopes of the Oak Grove SLF. The results are presented below:

I. South-Southeastern Slope
Chemical Concentration Range (ug/L)
Methylene chloride 500-600
Acetone 13,000-19,000
t-1,2-Dichloroethene ND-510
Methyl ethyl ketone ND-18,000
Methyl isobutyl ketone ND-830
Toluene 160-660
Ethylbenzene ND-21
Phthalate esters 35-190
Methylphenols 35-6,900
Aluminum 28-13,500
Chromium 3-102
Mercury 0.37-0.88
Nickel ND-178
II. Northern Slope
Chemical Concentration Range (ug/L)
Methylene chloride 1,900
Acetone 5,400
Methyl ethyl ketone 18,000
4-Methylphenol 6,900
Mercury 0.2
III. Northwest Slope
Chromium 12

ND = Not Detected

- Leachate Seep Soil

VOCs, semi-volatile organic, and inorganic compounds weredetected in the leachate soil samples from the south-southeastern, northern, and northwest slopes of the Oak GroveSLF. The results are presented below:

I. South-Southeastern Slope
Chemical Concentration Range (ug/kg)
Methyl isobutyl ketone ND-660
Toluene 51-640
Ethylbenzene ND-17
Xylenes (total) 32-1,000
Phenol ND-580
Di(2-chloroethyl)ether ND-850
4-Methylphenol 2,000-8,200
Phthalate esters 550-1,300
N-nitrosodiphenylamine ND-650
Aluminum 1,020-1,810
Arsenic 1.4-3.1
Chromium 3.1-3.9
Lead 1.3-4.8
Mercury ND-0.01
Zinc 9.4-72
II. Northern Slope
Chemical Concentration Range (ug/kg)
Methyl isobutyl ketone 640
Toluene 550
Phenol 2,000
4-Methylphenol 13,000
Aluminum 1,660
Chromium 3.9
Lead 6.8
Mercury 0.02
III. Northwest Slope
Chemical Concentration Range (ug/kg)
4-Methylphenol 360
Aluminum 2,540
Arsenic 3.6
Chromium 3.8
Lead 4.9

ND = Not Detected

5. Surface Water

A total of seven surface water samples were collected from thewetland south of the landfill in two separate sampling roundsduring 1986 and 1989. The following contaminants were detected:

Chemical Concentration Range (ug/L)
Benzene ND-25
Chloroethane 93-170
1,1-Dichloroethane 5.4-55
1,2-Dichloroethane ND-23
t-1,2-Dichloroethene ND-12
1,2-Dichloropropane ND-5
Ethylbenzene ND-25
Methyl isobutyl ketone ND-160
4-Methylphenol ND-48
Trichloroethylene ND-3.2
Xylenes (total) ND-18
Arsenic 2.4-10
Barium 99-1,740
Chromium 18-72
Cyanide ND-40
Lead ND-6.4
Nickel 45-96
Zinc 24-43

ND = Not Detected

6. Sediment

Seven sediment samples were taken from the wetland south of thelandfill (from the approximate locations in which the surfacewater samples were obtained) during 1986 and 1989. The followingcontaminants were detected:

Chemical Concentration Range (ug/kg)
Chloroethane ND-140
Chloroform ND-9
Ethylbenzene 2-110
Methyl isobutyl ketone ND-110
N-nitrosodiphenylamine ND-810
Toluene 21-48
Aluminum 19-1,750
Arsenic 0.95-2.4
Barium 12-73
Chromium 0.34-3.4
Lead 0.34-6
Nickel 0.7-2.5
Zinc 0.8-10

ND = Not Detected

7. Groundwater

Monitoring wells were installed adjacent to the landfill in theoutwash sand (water table) aquifer, till, and the deep, semi-confined sand/gravel aquifer. Samples were collected from boththe outwash sand and sand/gravel aquifers during two samplingrounds in January and May 1987. During two subsequent samplingrounds conducted in November 1989 and January 1990, all threeaquifers were sampled. Samples from the first two rounds wereanalyzed for VOCs, semi-volatile organic compounds, and metals;those from the subsequent rounds were analyzed for VOCs, arsenic,and barium. The monitoring data from these wells are discussedby aquifer, below.

Outwash (Water Table) Aquifer

One of three wells screened in this aquifer on the northern edgeof the landfill showed very low levels of toluene (6-7 ug/L),ethylbenzene (1 ug/L), and xylenes (1-8 ug/L); the other twowells showed no detectable levels of VOCs. Di(2-ethylhexyl)phthalate (10 ug/L), arsenic (2.5 ug/L), and barium(25.6 ug/L) were also detected in the well having VOCcontamination. Chromium was detected at 20 ug/L in one of theother two wells.

Six monitoring wells screened in the outwash aquifer adjacent tothe landfill at the base of the southwest, south, and southeastcorners showed contamination. The following contaminants weredetected in one or more of these wells:

Six monitoring wells screened in the outwash aquifer adjacent tothe landfill at the base of the southwest, south, and southeastcorners showed contamination. The following contaminants weredetected in one or more of these wells:

Chemical Concentration Range (ug/L)
Benzene 1-20
Chloroethane 1-540
1,1-Dichloroethane 1-7
1,2-Dichloroethane 2-6.8
1,2-Dichloroethene (total) 0.9-15
Diethyl phthalate 19-24.5
Ethylbenzene 7.4-82
Phenol ND-41
Vinyl chloride 1-9
Xylenes (total) 2-108
Arsenic 12-160
Barium 52-3,290
Chromium 10-25
Nickel 57-223

ND = Not Detected

None of the seven outwash monitoring wells located within thewetland (south of the landfill) had detectable concentrations ofvolatile or semi-volatile organic compounds. Metals includingarsenic (ND-3.3 ug/L), barium (ND-67 ug/L), copper (ND-20 ug/L),and zinc (ND-20 ug/L) were, however, detected in three of thesewells.


The following contaminants have been detected in one or more ofthe six monitoring wells installed adjacent to the landfill atthe south, southwest, southeast, west, north, and east corners:

Chemical Concentration Range (ug/L)
Acrolein ND-6 (J)
Benzene ND-3
Ethylbenzene ND-2
Toluene 0.7-12
Xylenes (total) ND-13
Arsenic 2-6.9
Barium 33.4-251

ND = Not Detected; (J) = Estimated concentration

Sand and Gravel Aquifer

Six monitoring wells have been sampled in this aquifer; threewere located in the zone used for residential water supplies andthree at the top of the aquifer, just beneath the till. Two ofthese wells were located between the landfill and residenceslocated southwest of the landfill. The sampling results arepresented below:

I. Residential Water Supply Zone

Chemical Concentration Range (ug/L)
Ethylbenzene* ND-1 (J)
Toluene ND-5
Xylenes (total) ND-6
Arsenic ND-4.9 (J)
Barium 43-118
Chromium* ND-12
Selenium* ND-5

* = These chemicals were detected only once, at the indicated upper bound, in this portion of the aquifer
ND = Not Detected
(J) = Estimated Concentration

II. Top of the Sand and Gravel Aquifer

Chemical Concentration Range (ug/L)
Di(2-ethylhexyl)phthalate ND-23
Di-N-octyl phthalate* 13
Ethylbenzene ND-0.7 (J)
Toluene ND-3
Xylenes (total) ND-4
Arsenic 3.0 (J)-7.5 (J)
Barium 42.6 (J)-77.1

* = These chemicals were detected only once, at the indicated upper bound, in this portion of the aquifer
ND = Not Detected
(J) = Estimated Concentration

The interpretation of the analytical results for some of theabove chemicals is difficult. In the case of di(2-ethylhexyl)phthalate, it was detected at the same concentration(23 ug/L) in two wells, one upgradient of the site and onedowngradient of the site; these results could not be duplicatedduring subsequent sampling (2). Furthermore, the phthalates arecommon laboratory contaminants. Thus, the origin of this, andpossibly the other phthalate, can't be determined. Arsenic wasalso detected at similar concentrations in both upgradient anddowngradient wells. The detected concentrations of arsenic arequite possibly representative of normal or "background" range ofarsenic levels in confined aquifers in Minnesota. Thisconclusion is based on data provided by the MPCA's GroundwaterDivision which monitors a network of wells throughout the state. Lastly, ethylbenzene, chromium, copper, and selenium were eachdetected only once in the residential water supply zone.

8. Air

On-site air sampling was limited to real-time ambient monitoringwith a photoionization (HNu) instrument during the installationof monitoring wells. No positive HNu readings in ambient air(either in the immediate work area or in the breathing zone) wereobtained during drilling activities.

9. Biota

No biota (game animals, fish, etc.) were sampled as part of theRI.

B. Off-Site Contamination

1. Surface Water and Sediments of Cedar Creek

One surface water and one sediment sample were collected fromCedar Creek at approximately the same location both upstream anddownstream from the Oak Grove SLF in November, 1989. There wereno VOCs detected in upstream or downstream surface water orsediment samples. Arsenic was present at 2.4 ug/L and 3.2 ug/Lin upstream and downstream surface water, respectively; inupstream and downstream sediment arsenic was present at 4.1 ug/kgand 3.4 ug/kg, respectively. Barium was present at 52.2 ug/L and58.6 ug/L in upstream and downstream surface water, respectively;in upstream and downstream sediment barium was present at 118ug/kg and 76.5 ug/kg, respectively.

2. Ground Water

Nearby residential wells located west, southwest, and south ofthe Oak Grove SLF have not been shown to be contaminated witheither organic or inorganic chemicals. Groundwater samples fromresidential wells have been collected and analyzed since 1984;the most recent sampling was carried out by the MPCA inAugust,1991.

C. Quality Assurance and Quality Control

The data supplied are adequate to conduct a Health Assessment forthis site. Sample collection, chain-of-custody, laboratoryanalytical methods, calibration and preventive maintenance ofinstruments, internal quality control, data reduction andvalidation, audits, and data-precision assessment were reviewedby MPCA QA/QC staff and found to be in accordance with the EPA-approved Quality Assurance Project Plan outlined in the RIWorkplan. Chemical analyses were conducted by EPA ContractLaboratory Program (CLP) Laboratories.

D. Physical and Other Hazards

The only apparent physical hazard associated with this site isthe landfill debris (metal, glass, etc.) that is exposed throughthe surface of the landfill mound.


A complete exposure pathway consists of the following fiveelements: 1) a source of contamination (that is, a source that isreleasing contaminants into the environment, such as an inactivelandfill), 2) environmental media (groundwater, surface water,air, soil, etc.), 3) a point of exposure (a point of humancontact with the contaminated environmental medium such as a wellor playground), 4) a route of exposure (ingestion, inhalation,skin contact), and 5) a receptor population (people being exposedat a point of exposure).

A. Completed Exposure Pathways

There are no completed human exposure pathways associated withthe Oak Grove SLF.

B. Potential Exposure Pathways


The landfill is situated on glacial drift that ranges in depthfrom 150 to 250 feet. These sediments contain two aquifers: anupper outwash sand and a lower sand and gravel (deep valleytrain). The aquifers are separated by a layer of glacial tillwhich acts as a semi-confining layer. The horizontal groundwaterflow in the outwash sand aquifer is south towards the wetland andCedar Creek; the vertical flow component is downward in thenorthern portion of the landfill and upward in the southernportion.

There are contaminants in outwash aquifer monitoring wells southand southwest of the landfill (see On-Site Contaminationsection). The combination of the glacial till (acting as a semi-confining layer), wetland soil organic matter (acting as anadsorbent), and upward vertical flow of groundwater are currentlypreventing the movement of contaminants to the lower aquifer. Wetland outwash wells further to the south and southwest are notcontaminated, thus the horizontal component to the groundwaterflow in this aquifer is not transporting contaminants towardlocal residences.

Human exposure to contaminants in the upper outwash aquifer viaingestion of or dermal contact with the water, or inhalation oforganic vapors generated in connection with other uses of thewater will not occur since this aquifer is not used as a sourceof potable water.

Monitoring wells screened in the deeper sand and gravel aquiferwere found to have very low concentrations of three VOCs, two semi-volatile organic compounds, and four inorganic contaminants. This aquifer supplies the potable water for local residents. Theconcentrations of these chemicals are, however, at levels thatwould not be expected to produce adverse effects on human health.

The stressed wetland vegetation located near the southeast cornerof the landfill mound may be the result of contaminant releasevia groundwater. Whether contaminant transport occurs via thispathway or another (i.e. leachate or groundwater), the presenceof stressed vegetation may indicate that landfill contaminantsare being released to the wetland.

There is, however, the potential for local residents to beexposed to landfill contaminants if the contaminants present inthe upper outwash aquifer migrate downward to the deeper aquifer(used as the source of potable water) in the future. It shouldbe emphasized that at this time, the combination of the semi-confining till layer and the upward vertical component of thegroundwater flow in the upper aquifer is acting to prevent themigration of contaminants to the deeper aquifer.


Relatively high concentrations of numerous VOCs, semi-volatileorganic compounds, and inorganic compounds were detected inleachate seep samples. Seeps located on the southern slope ofthe landfill drain directly into the adjacent wetland. Seepssurfacing at other locations along the slopes and base of thelandfill at various times throughout the year may also be apathway of pollutant transport from the landfill.

Leachate seep sediments were also found to be contaminated withVOCs, semi-volatile organic compounds, and inorganic compounds. Surface water runoff could mobilize these contaminants andtransport them away from the landfill mound (that is, into theadjacent wetland area).

The stressed wetland vegetation located near the southeast cornerof the landfill mound may be the result of contaminant releasevia leachate seeps.

Relatively high concentrations of a number of chemicalcontaminants were detected in leachate seeps along the slopes ofthe landfill mound. Trespassers may potentially come intocontact with landfill leachate via dermal contact. However,human exposure is considered to be unlikely since there is noevidence of trespassing at the site.

C. Exposure Pathways Eliminated from Consideration

Subsurface Soil

A comparison of the concentrations of HSL metals in subsurfacesoil with published background concentrations of metals in U.S.soils does not indicate elevated metal concentrations in landfillsoil (3,4,5). The movement of contaminants away from thelandfill mound may be indicated by the detection of chloroformand xylenes (total) at very low concentrations in the SW and SEborings.

Data collected during the RI indicate that subsurface soils atthe base of the landfill from 19.5 to 85.5 feet below groundlevel do not contain elevated levels of HSL metals (as comparedto published background soil metal data), but did contain verylow levels of two VOCs. The concentrations of chloroform (0.034and 0.078 mg/kg) and total xylenes (0.017 and 0.021 mg/kg) in thesubsurface soil were compared with ATSDR derived EnvironmentalMedia Evaluation Guides (EMEGs) and Cancer Risk Evaluation Guides(CREGs). In this case, contaminants that need to be evaluatedfurther for potential noncarcinogenic and carcinogenic healthimpacts following ingestion of the soil. The actualconcentrations of chloroform and xylenes were compared with themost protective EMEGs (that is they were calculated for picachildren or children who have a tendency to ingest largequantities of soil), 20 mg/kg and 4,000 mg/kg, respectively. Since the actual concentration of the two chemicals were farbelow their respective EMEG, no further evaluation of theirpotential noncarcinogenic health impacts was deemed necessary. The subsurface soil concentrations of chloroform were alsocompared to the CREG of 114 mg/kg. Since the actualconcentration of chloroform was far below its CREG, and EPA hasconcluded that xylenes are not classifiable as to humancarcinogenicity (therefore they do not have a CREG) no furtherevaluation of their potential carcinogenic health impacts wasdeemed necessary. Therefore, considering their concentrations inrelation to both EMEGs and CREGs and their inaccessibility tohuman contact, contact with them (if it were to occur) would notbe cause for public health concern.

Landfill Cover Soil

No HSL VOCs were detected in the cover soil from the western one-third of the landfill. Four of eight cover soil samples takenfrom the interface of the fill/lime sludge cover interface hadvery low levels of four VOCs. Since the interface soil iscovered with 1 to 1-1/2 feet of lime sludge, these soils are notbe expected to constitute a point of exposure for thecontaminants.

The cover soil samples in which very low levels of four VOCs weredetected were underneath 1 to 1-1/2 feet of lime sludge. It isexpected that the lime sludge would act as a preventive barrierto human exposure to these contaminants via skin contact,inhalation, and ingestion.

Soil Gases

Soil gas samples taken at the site during the RI demonstrate thepresence of primarily methane. There is the possibility thatmethane vapors can migrate from under the soil cover and into theambient air. However, the concentration of methane would besignificantly reduced by dilution with ambient air. Thus, theconcentration of methane to which residents would be potentiallyexposed to would be well below that which would be of concern tohuman health. The owner/operator of the landfill and otherfamily members live in homes on the far northern portion of thesite. The distance to these residences and the lowconcentrations of methane detected, preclude the possibility ofexplosive levels of methane in the homes. The disruption of thetemporary landfill cover (lime sludge, soil) during remediationcould possibly expose workers to methane. However, monitoringwould alert them to this situation and appropriate actions wouldbe instituted before health problems could arise.

Surface Water and Sediments

Surface water runoff (i.e. rain or snow melt) from the northernone-half of the landfill is directed into low-lying depressions(berm and borrow pit) and to drainage ditches. However, runofffrom the southern one-half of the mound drains directly into thewetland area adjacent to the southern edge of the landfill. Inthis portion of the landfill, runoff water may either washlandfill cover contaminants directly into the wetland or it mayinfiltrate into the landfill and leach contaminants into thegroundwater. Because of the vertical component to thegroundwater flow in this area, the subsequent discharge ofcontaminants into the wetland is likely if contaminants reach thegroundwater.

Surface water and sediments in the wetland immediately adjacentto the landfill mound contained low concentrations of VOCs, semi-volatile organic compounds, and inorganic compounds. Thesecompounds are not expected to impact other areas of the wetlandor Cedar Creek because: 1) even during a very wet summer, thewetland had scattered pockets of standing water and notcontinuous standing water, i.e. there is no direct flow path forcontaminants, 2) Cedar Creek is fairly distant from the landfillmound (greater than 3,000 feet at its nearest point), 3) themovement of contaminants would be retarded by their binding tosoil organic matter in the wetland, 4) contaminant degradationwould occur because of high biological activity in the wetland,5) of volatilization of VOCs from the surface water to ambientair, and 6) the contaminants are present at very lowconcentrations and would become even lower because of dilutionduring transport to these other areas (assuming degradation doesnot occur).

The stressed wetland vegetation located near the southeast cornerof the landfill mound may be the result of contaminant releasevia surface water runoff.

Wetland surface water (and to a lesser extent sediments) near thebase of the landfill contained detectable concentrations of VOCs,semi-volatile organic compounds, and inorganic contaminants. Thewetland surface water is not used as a source of potable water. Trespassers may potentially come into contact with these mediavia dermal contact. However, this exposure pathway is notexpected to be significant because: 1) the amount of standingwater available for contact, even during a wet summer, wasminimal, 2) no evidence of trespassing was noted on site visits,and 3) if contact with surface water were to occur, theconcentration(s) are not at levels that would be of concern (theyare present at levels well below MPCA Surface Water QualityStandards). Thus, significant human exposure to surface water contaminants by ingestion, skin contact, and inhalation (ofvolatile vapors) is not expected to occur.

Sampling data indicate that Cedar Creek is not contaminated atthis time, and because of other factors outlined above, is notexpected to become contaminated under the present conditions.


The potential for wild game living in the wetlands to becomecontaminated by drinking chemically-contaminated surface water isconsidered to be very low. This is based on the following: 1)the area of contaminated surface water near the landfillrepresents a small fraction of the total wetland area that couldbe used for drinking, thus it would be very unlikely that animalswould obtain an appreciable portion of their water from thissource, 2) the concentrations of the contaminants are relativelylow in the surface water, and 3) the chemicals present in thesurface water are not expected to bioconcentrate in aquatic biota(6,7).

Wild animals (especially deer) are known to drink leachate seepliquid (probably as a source of minerals such as salts), thusthis behavior could constitute an exposure pathway for theseanimals. While humans are not expected to drink from theleachate seeps, the seeps may, however, pose a risk to theanimals.

Because stressed wetland vegetation was observed on a site visit,there may be one or more environmental pathways leading to thecontamination of wetland plant biota.

Since the wetland area immediately adjacent to the southern edgeof the landfill mound contains low concentrations of landfillcontaminants, there is the possibility that biota living in thisarea may become contaminated. However, it is unlikely thatingestion of biota would be a human exposure pathway because: 1)the contaminants are not expected to accumulate in the tissues ofthe biota, 2) the contaminants are present in low concentrations,3) the amount of wetland biota ingested by humans, if any at all,would be very limited.

Ingestion of fish from Cedar Creek is not a human exposurepathway since the creek is not contaminated.


Low levels of three VOCs, two semi-volatile organic compounds,and four metals were detected in the deep groundwater aquifer(sand and gravel aquifer) that supplies potable water to localresidents. The concentrations of these chemicals are, however, atlevels that would not be expected to produce adverse effects onhuman health. However, as noted earlier, there is still aquestion as to whether or not some of the chemicals detected inthis aquifer are attributable to the landfill.

There are no data to indicate that local residents are beingexposed to any of these chemicals via residential water use. However, based on: 1) the uncertainty in the evaluation of thesource of these chemicals, 2) their potential toxicity and 3)their frequency of detection relative to the other contaminantsdetected, di(2-ethylhexyl) phthalate and arsenic are discussedbelow.

Relatively high concentrations of numerous VOCs, semi-volatileorganic compounds, and inorganic compounds were detected inleachate seep samples.Human exposure, however, is considered tobe unlikely since there is no evidence of tresspassing at thesite.

A. Toxicological Evaluation


Di(2-ethylhexyl)phthalate (DEHP) is absorbed to a limited degree(4 to 25% of administered dose) in humans and to a high degree(40 to 90% of administered dose) in laboratory animals followingoral administration (8,9,10). Once absorbed, DEHP distributes tothe liver, kidneys, and to a lesser extent the brain (10). DEHPis extensively metabolized and eliminated in both the urine andfeces (10). The primary target organs for DEHP toxicityfollowing high dose oral administration are the liver and testes. DEHP and its primary metabolite monoethylhexyl phthalate (MEHP)have been shown to be developmental toxicants in experimentalanimals (10). Hepatic effects most often noted in laboratoryanimals include: peroxisome proliferation, induction ofcytochrome P-450 enzymes, alteration of lipid metabolism, andhepatomegaly (8,9,10). Testicular effects produced in rats andmice are characterized by testicular atrophy and degeneration ordestruction of the seminiferous tubules (8,9). DEHP has not beenshown to be mutagenic in in vitro short term genotoxicity studies(10). The National Toxicology Program has determined that DEHPproduces liver tumors in rats and mice when administered at highdoses in the diet (8). Even though there is inadequate evidencefor the carcinogenicity of DEHP in humans, DEHP is considered tobe a probable human carcinogen because there is sufficientevidence for its carcinogenicity in laboratory animals.


Inorganic, water soluble arsenic (As) compounds are readilyabsorbed (77 to 99% of administered dose) from thegastrointestinal tract following ingestion. Arsenic isdistributed to the liver, kidney, lung, spleen, skin, and hair(11,12). The principal acute health effect produced by Asingestion is severe gastrointestinal irritation (i.e. nausea,diarrhea, and vomiting) (13). Chronic oral exposure torelatively high levels of As (20-60 ug/kg/day; approximately 1-4mg/day for an adult) have been reported to cause anemia,peripheral and central neuropathy, hepatotoxicity,nephrotoxicity, cardiotoxicity, and a group of skin disorderscharacterized by hyperpigmentation and hyperkeratosis insensitive individuals (12,14). Arsenic has not been reported tobe either a developmental or reproductive toxicant, or to bemutagenic in in vitro short term genotoxicity studies (12). Chronic oral exposure to drinking water containing high levels ofAs (mean concentration of 400-600 ug/L) has been shown toincrease the risk of skin cancer in humans (12). Based on thisinformation, EPA has concluded that arsenic is known humancarcinogen.

Three VOCs, benzene, vinyl chloride (both are known humancarcinogens) and 1,2-dichloroethane have been detected in theupper outwash aquifer. These chemicals do not, however,currently pose a threat to human health because humans are not incontact with water from this aquifer (the aquifer is not used asa drinking water supply). They are only briefly mentioned atthis time because they are highly mobile in soil (6,7) and may,after overcoming hydrogeological factors reviewed earlier, leachinto the deeper aquifer in appreciable concentrations. If thesechemicals were to reach the deeper aquifer and contaminateresidential water supplies in the future, appropriate protectiveactions would be taken.

B. Health Outcome Data Evaluation

State local health outcome data were not evaluated as a part ofthis Health Assessment because there were no data indicating thatlocal residents have been or are being exposed to contaminantsfrom the Oak Grove SLF.

C. Community Health Concerns Evaluation

As noted earlier, local residents are concerned about thepossibility of adverse health effects if their wells becomecontaminated with chemicals from the Oak Grove SLF. At thistime, there is no evidence that nearby residential wells arecontaminated with either organic or inorganic chemicals from thelandfill. The potential for these wells to be contaminated withlandfill-derived chemicals is/will be significantly diminished orentirely eliminated because of the following:

  1. The groundwater in the aquifer that supplies local residences with drinking water flows to the southtoward the wetland. Therefore, if this aquifer were tobecome contaminated, local residences are not in thepathway of the contaminant plume.

  2. The groundwater in the contaminated, shallow aquifer does not flow downward toward the deeper aquifer, but instead discharges into the surface water of thewetland south of the landfill.

  3. There is a semi-confining geologic barrier (the "till layer") between the contaminated shallow aquifer andthe deeper aquifer which further prevents the movementof contaminants into the deep aquifer.

  4. The final cover to be installed over the landfill will substantially reduce the movement of chemicals from thelandfill mound to the underlying groundwater.

  5. The installation of new drinking water wells will not be allowed in the contaminated shallow aquifer.

In addition, the Record of Decision signed by the MPCA and EPA in1990 which calls for long-term monitoring of the shallow and deepaquifers, surface waters, and sediments will ensure that localresidents will not be exposed to levels of landfill contaminantsthat would be harmful to their health.

The MDH has prepared a fact sheet for citizens (dated September,1991) containing information regarding contamination issues,health issues, and clean up activities at the Oak Grove SLF(included as Appendix 1 of this document). In addition, MDHstaff contributed to an MPCA fact sheet on health issues (datedNovember, 1990) prepared by the MPCA in response to communitycomments received at a public meeting held on October 24, 1990. MDH staff were also present at the October 24, 1990 publicmeeting to answer health-related questions.

Next Section     Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #