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PUBLIC HEALTH ASSESSMENT

WILLIAMS PIPE LINE COMPANY
SIOUX FALLS, MINNEHAHA COUNTY, SOUTH DAKOTA

ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

In conducting an ATSDR Public Health Assessment, the health assessors identify and review allavailable environmental contamination data for a site. The on- and off-site portions of thissection describe the sampling that has been done and identify contaminants of concern. Thequality of the environmental data is discussed in the Quality Assurance and Quality Controlsubsection. Physical and other hazards not related to toxic substances, if any, are described in thePhysical and Other Hazards subsection. This introductory portion discusses the process forselecting contaminants of concern and Toxic Chemical Release Inventory (TRI) data.

Selection of Contaminants of Concern

ATSDR selects contaminants for further evaluation based upon the following factors:
1) comparison of concentrations of contaminants on- and off-site with values fornoncarcinogenic and carcinogenic endpoints,
2) sampling plan and field and laboratory data quality, and
3) community health concerns.

Identification of a contaminant of concern in the On-site and Off-site Contamination subsectionsdoes not mean that exposure will result in adverse health effects, only that additional evaluationis necessary. The public health significance, if any, of exposure to the contaminants of concern isevaluated in subsequent sections of the public health assessment.

Comparison values for public health assessment are contaminant concentrations in specificmedia that are used to select contaminants for further evaluation. These values includeEnvironmental Media Evaluation Guides (EMEGs), Cancer Risk Evaluation Guides (CREGs),and other relevant guidelines. CREGs are estimated contaminant concentrations based on a oneexcess cancer in a million persons exposed over a lifetime. CREGs are calculated from EPA'scancer slope factors. The identified contaminants of concern are listed in Tables 1 - 5 in Appendix B.

Toxic Chemical Release Inventory (TRI)

A search of the TRI, an EPA database of known spills and releases to the environment, for 1987and 1988, revealed several manufacturers in the area of WPL who use tetrachloroethylene,xylenes and toluene which are contaminants found at the WPL site (19). These releases,however, were to the air and not to the soil or ground water and therefore would not be asignificant source of other contamination in the area.

A. On-Site Contamination

This section identifies the contaminants on the WPL site which are meet ATSDR's guidelines fora contaminant of concern, and also reviews the environmental sampling. It was assumed thatonly adults had any chance of being exposed in determining the contaminants of concern in thepit sludge and soil. This assumption was made because the contaminated sludge and soil is notaccessible to children. The WPL facility is fenced and is guarded on a 24-hour/day basis.

Burn Pit Sludge

Burn pit sludge was sampled by the Ecology & Environment, Inc. for the EPA, during the SiteInspection in March, 1987, and consisted of a grab sample taken 1.5 to 2 feet below the surfaceof the pit. These samples were analyzed by Pace Laboratories (2, 40). WPL sampled the sludgein July, 1988 by dividing the pit into quadrants and taking a sample from 1 foot and 3 feet belowthe surface in each quadrant. A composite of these samples was also combined at the laboratory. Savannah Laboratories provided the analysis for WPL (41). SDDWNR sampled the burn pit inSeptember, 1988 by taking a shallow grab (6 inches deep) and a deep grab of 2 feet. The stateutilized Enesco-Rocky Mountain Analytical Laboratory to perform the analysis (42).

The following chemicals, detected in the burn pit sludge, were identified as contaminants ofconcern: beta benzene hexachloride (BHC); alpha and gamma chlordane; 4-4' DDE (p-p'-dichlorodiphenyldichloroethylene); heptachlor epoxide; and lead (Table 1, Appendix B).

On-Site Soil and Background Soil

All of the metals detected in the on-site soil samples and background sample were within normalregional background levels for soils in the Western United States. All samples were boringstaken over a depth of greater than 3 inches. Chlordane was the only pesticide detected in soilsnear the burn pit as were low levels of bis(2-ethylhexyl)phthalate, naphthalene, phenanthrene andxylenes (Table 1, Appendix B).

Only soil from the WPL disposal/burn pit area has been adequately sampled. There could besignificant contamination of the soil on the rest of the Williams facility.

On-Site Ground Water

Monitoring wells are located throughout the entire WPL property and have been extensively usedto characterize the impact of the various spills. The water from the wells in the northeast area ofthe site was analyzed for a wide range of organic and inorganic chemicals. The other on-sitemonitoring wells were routinely sampled only for benzene, toluene, ethylbenzene, xylenes andnitrates.

Aldrin, arsenic, benzene, beta-BHC, bis(2-ethylhexyl)phthalate, cadmium, fluorene, lead,manganese, mercury, naphthalene, nitrates, and toluene were identified as contaminants ofconcerns in on-site monitoring wells (Table 2, Appendix B). The arsenic levels detected weresimilar to those identified as background for the Sioux Falls area.

Soil Gas

Soil gas sampling measures the concentrations of organic compounds a few inches above theground and is done to identify sources and extent of contamination. Concentrations of soil gasare very dependent on soil temperature, moisture content, soil porosity, and wind speed. Soil gasdata are not appropriate for determining health impact because they don't measure possibleexposure levels. The way health impact could be determined is through sampling of the ambientair near those locations where soil gas is identified.

A limited number of on-site soil-gas samples were collected in 1986 by the EPA ERT in closeproximity to the former residence on the southwest corner of the site (43, 44). No soil gasmeasurements have been taken in the northeastern corner of the site. Benzene, hexane, toluene,and xylene were identified in these measurements.

Positive soil gas results indicate that ambient air sampling should be done of any dwellings in thearea covered in the soil gas survey. However, the house in the area has subsequently beenremoved.

B. Off-Site Contamination

Off-site Soil

The sampling of soil off-site has been very limited and not systematically done. All of thesamples were taken at a depth of three inches or more. Arsenic was identified as a contaminantof concern (Table 3, Appendix B). The arsenic levels in off-site soil sample were typical for theSioux Falls area. No pesticides were detected in the off-site soil samples.

Off-site Monitoring Wells

The number of monitoring wells off-site is limited, especially to the north and northeast of thesite. Therefore, the extent of groundwater contamination off-site cannot be fully characterized.

Aldrin, ammonia, arsenic, barium, benzene, alpha- and beta-BHC, chlordane,bromodichloromethane, 1,2-dichloroethane, dieldrin, gasoline, heptachlor, heptachlor epoxide,manganese, and nitrates were identified as contaminants of concern (Table 4, Appendix B). Thearsenic levels are typical for the Sioux Falls area. Pesticide contamination in off-site groundwater is primarily in the east and northeast direction from the site. Petroleum hydrocarbons areequally dispersed to the south of the site and to the north and east of the site.

Off-Site Private Wells

Sampling of off-site private wells focused on those wells to the Northeast and to the South of theWilliams facility. Aldrin, alpha-BHC, arsenic, bromodichloromethane, chloroform,chloromethane, 1,2-dichloroethane, lead, manganese, nitrates, and zinc were identified ascontaminants of concern (Table 4, Appendix B). The arsenic levels are typical for the SiouxFalls area.

Municipal Wells

Municipal wells in the Big Sioux Aquifer were sampled in 1987 as part of the EPA siteinvestigation. The City of Sioux Falls supplied sampling data for the municipal well in theSkunk Creek Aquifer from 1987-1991 (45, 46). The maximum levels of arsenic, manganese, andsulfates meet ATSDR's guidelines for contaminants of concerns. No petroleum products,pesticides, or other organic chemicals were detected in the Sioux Falls municipal wells. Becausethese contaminants appear to be naturally-occurring and not site-related, the municipal wells willnot be evaluated further. For information about the possible health impact of the arsenic in theSioux Falls municipal water, read ATSDR's response to public comment 25 on page 68(Appendix C) of this document.

Off-Site Ambient Air

Sampling of ambient air off-site was limited to the investigation of the health complaints at theold Hayward School in 1986. These samples were taken inside the school at locations thatstudents and staff normally occupied and in areas normally unoccupied, such as pipe chases andcrawlways. Benzene, hexane, and pentane were identified as contaminants of concern (Table 5, Appendix B). The old Hayward School is no longer standing and these measurements weretaken within one month of the evacuation of the school.

Off-Site Soil Gas

Soil gas measurements were taken in 1986 surrounding the Hayward School to the south of theWPL site and in 1987 to the north and east of the burn pit as part of the EPA site investigation. The soil gas sampling procedures consisted primarily of field methodologies. The samples takennear Hayward school were verified by gas chromatography/mass spectrometry.

Benzene was identified in the survey done both on the north and south sides. Hexane, toluene,and xylene were identified on the south side. Positive soil gas results indicate that ambient airsampling should be done of any dwellings in the area covered in the soil gas survey. However,the school has subsequently been removed.

C. Quality Assurance and Quality Control

Quality assurance of the data as a whole was acceptable. One holding-time deadline was missedfor the Analytical Results report (2). The effect of this would be to underreport the actualconcentrations of pesticides in ground water from the east side of the site. The silver andselenium values in ground water from the east side were all rejected. In general data packageswere complete and contained adequate chain of custody documentation. Specific examples ofblank contamination or poor data quality were listed in the relevant sections. Data was used froma map on the extent of contamination from the WPL site prepared by the State of South Dakota(17). This map legend merely listed the values that had been detected at various off-sitelocations. Since some of this data was verifiable as a data set from Pace Laboratories, the datagiven on the map was utilized without qualification.

D. Physical and Other Hazards

No unusual physical hazards are currently present at the Williams facility, except those typicalfor a petroleum storage facility. All of the Williams property, including the site of the oldHayward School and the residence, is fenced and patrolled by security guards.

PATHWAYS ANALYSES

In this section of the public health assessment, the possible exposure pathways are evaluated tohelp determine whether persons have, are, or will be exposed to contaminants associated with thesite. This pathway analysis consists of five elements:

(1) identifying contaminants of concern,
(2) determining that these contaminants have/are/will be transported through an environmentalmedium,
(3) identifying of a point of exposure (i.e., a place or situation where humans might be exposedto the contaminated media),
(4) determining that there is a plausible route of human exposure (i.e., can the contaminant enterthe body?), and
(5) identifying an exposed population (i.e., how many people, if any, are at the point ofexposure).

An exposure pathway is considered complete when there is good evidence that all five elementsexist. The presence of a completed pathway indicates that human exposure to contaminants hasoccurred in the past, is currently occurring, or will occur in the future. When one or more of thefive elements of an exposure pathway are missing, that pathway is considered potential. Thepresence of a potential exposure pathway indicates the human exposure to contaminants couldhave occurred in the past, could be occurring now, or could occur in the future. An exposurepathway can be eliminated if at least one of the five elements is missing and will never bepresent. The completed and potential exposure pathways and estimates of the number of exposedindividuals for the WPL site are presented in Tables 6 - 8, Appendix B.

A. Completed Exposure Pathways

Private Well Pathways

Past, current, and future exposure pathways are possible from contaminated ground water presentin private wells. Please refer to Tables 6 and 8. There are several completed pathways involvingprivate wells and for convenience they will all be discussed under this heading.

    Area Hydrogeology

Groundwater in the area of WPL is located in a water table aquifer (i.e., unconfined conditions)distributed in two geological media beneath the site: a thick glacial outwash and till withinterfingering clay lenses and a fractured sandstone bedrock. The depth to the water table isshallow, ranging from 10 to 20 ft below the ground surface. Flow in this aquifer is to the southin the southwest corner of the property and generally easterly in the eastern and northeasternsections of the property. No adequate estimates of the flow rates could be made due to thequestionable nature of some of the aquifer property data. The value for flow in the outwashaquifer is probably in the range of 0.2 to 10 feet per day. Joints and fractures are the primarygroundwater flow paths in the bedrock portion of the aquifer (4).

The WPL site is located near the confluence of the Big Sioux River and Skunk Creek. Topographic relief at the site is approximately 20 feet. Soils in this area are typical of glacialoutwash deposits in that they are predominantly comprised of sand and gravel with interbeddedlayers or lenses of silt and silty-clay. Area bedrock is Sioux Quartzite, a hard, indurated, well-sorted quartz sandstone thought to be at least 3000 feet thick. Depth to bedrock varies across thesite from 45 feet to outcrops of Sioux quartzite along an east-west ridge north of the site (2).

The Big Sioux and the Skunk Creek outwash aquifers are considered to be the primary sources ofground water for the area. The City of Sioux Falls obtains its water from wells in the Big SiouxRiver outwash aquifer, from one well in the Skunk Creek outwash aquifer, and from the BigSioux River (21). The quartzite ridge north of the site forms a topographic barrier between thesetwo outwash systems, but since it does not extend completely across the river valley outwash, itis not believed that the ridge serves as a barrier between the two aquifers (2). In addition, there isno evidence of an underlying continuous clay layer which could serve as an aquitard (47). Therefore, groundwater movement in the area is such that the two outwash systems may beconsidered to be contiguous. Contaminants from the WPL site have not been detected in theSioux Falls municipal wells.

    Discussion of Contaminant Areas

There appear to be at least three distinct areas of contamination in the shallow groundwater,based on available monitoring data (1, 2). An area of contaminated ground water extends fromthe disposal/burn pit to the northeast at least 1200 feet. Another area of contaminated groundwater plume extends to the south and southwest of the site at least 1000 feet and another area, notfully characterized, extends off the site to the east from the truck-loading area (17, 18). The EPAhas determined that inorganic, pesticide and organic chemicals from the burn/disposal pit aresource of the contaminants in northeast area of contamination (2). The burn/disposal pit area isdesignated as an NPL site. The State of South Dakota documents major spills of nitrates andpetroleum products on WPL as the sources of the south/southwest and east areas ofcontamination (1).

Human exposure to the contaminants through drinking of water from those three areas is knownto be occurring at one well in the northeast area, six in the south/southwest area, and none in theeast area. Several surveys of well users in the area of WPL have been conducted (15, 36). Themost recent (15) was done in 1989 and included 152 residences and businesses nearest theWilliams facility. Responses were obtained from 119 of the 152. Seventy of the 119 residencesor businesses were on municipal water and 49 had only private wells as their source of drinkingwater. The full extent of contamination of private well water is not known.

Based on the well survey and the direction of groundwater flow, there appears to be littleadditional threat of contamination of private drinking water sources in the northeast area. Thecontaminant flow appears to be into an undeveloped area. Most of the residences and businessesin the northeast area are on municipal water. In addition, the pump and treat remediation of thedisposal/burn pit area should eventually lessen the amount of off-site contamination.

There are several residences or businesses in this northeast area which either have not beensampled and/or it is not known what the source of drinking water is. These residences andbusinesses should be surveyed and their wells sampled if they are being utilized as a drinkingwater source.

The one contaminated well in the northeast area which is known to be utilized for drinking wateris located at an auto body repair shop. The maximum levels of contaminants found in this wellare 11 ppm of nitrates, 0.015 ppm of bromodichlormethane, and 0.046 ppm chloromethane. Thepossible health consequences of these levels will be discussed further in the Public HealthImplications section.

The area of contamination on the east of the site is poorly characterized and it is not clear whatdirection the contaminants are moving. All the businesses and residences just across MarionStreet from WPL and at the corner of 12th and Marion are on city water (15). There are severalbusinesses further east of WPL which there are no data on water source or which have onlyprivate wells. These should be surveyed and/or sampled.

The full extent of the area of contamination in the south/southwest is not known. Theremediation at the old Hayward School site should eventually lessen the amount of some of thecontamination from the southwest corner of the facility. However, this remediation probably willnot affect the nitrates would appear to be coming, at least in part, from another site on theWilliams facility.

Based on the survey and the direction of groundwater flow, there are about 45 wells which arestill utilized for drinking water or for which there are no data on usage. Only 14 of these 45 havebeen sampled and six were found to be contaminated at least once. Three of those six are knownto be used for drinking water. Information was not available for the other three, but are assumedto be used for drinking water for this public health assessment.

Nitrates ranging from 12 to 90 ppm are the only contaminants found in four of the six wells inthe southwest/south area. One well had 0.001 ppm of xylene and the other had 0.008 ppmtoluene, 0.1 ppm of xylene, and 0.14 ppm total hydrocarbons (THCs). The levels of these lastthree contaminants did not meet ATSDR's guidelines for a contaminant of concern. The possiblehealth consequences of the nitrate levels will be discussed further in the Public Health Implications section.

The further evaluation of the two completed private drinking water exposure pathways will be ofknown exposures. Based on the uncertainty about the extent of contamination and the number ofcontaminants identified in on- and off-site monitoring wells (see Tables 2 and 4, Appendix B),there is a good chance that other exposures are occurring. Additional sampling is needed.

Ambient Air at Hayward School and South Side Residence

Exposure to site-related contaminants in the air occurred at the Hayward Elementary School,which was across 12th Street from WPL and at a residence at the southwest corner of WPL. InMay 1986, gasoline from Tank 1341 on the southwest corner of the WPL property leaked into theground water under the residence and the school (1). The volatile organic compounds in thegasoline infiltrated from the contaminated ground water into the residence and the school. Volatile organic compounds of the petroleum products have a high vapor pressure, that is, theywill become a vapor readily when exposed to air.

The volatile organic compounds in petroleum products are moderately mobile and moderatelypersistent in ground water systems. These compounds will be adsorbed onto the surface of soilparticles as the petroleum product moves through the ground-water system. Changes in theamount of rainfall or the level of the water table may cause the release of these adsorbedconstituents back into the water or into the air.

As described in the Background section, both the residence and the school were evacuated whenhealth effects were experienced by the occupants of the buildings. Length of exposure wasrelatively short, based on the leak occurring in May 1986 and the evacuation of the school inSeptember shortly after the end of the Summer break. The discovery of hydrocarbons in theschool well in 1984 indicates that low level exposures may have occurred before 1986.

B. Potential Exposure Pathways

Soil and Burn Pit Sludge

The primary area of on-site soil contamination is the disposal/burn pit. Organic, pesticide, andmetal contamination is present in the sludge (up to 2 ft depth) at this location (see Table 1 in Appendix B). Historical information indicates that tank sludge was buried on the WPL property;however, specific disposal areas have not been defined, and soil sampling across the site did notreveal significant soil contamination. It is possible that concentrations of contaminants in thesoil have decreased with time through volatilization and leaching. No distressed vegetation wasobserved at the site, although former workers and residents near the site testify of areas of noplant growth (35, 38). There is no information whether these areas are actually contaminated, orwhether the lack of plant growth is due to factors unrelated to the site.

Soil and water contaminants on and off site can be degraded by microorganisms in the soil. Benzene, toluene, and xylene are biodegradable in the environment (49, 50, 51). Pentane, hexane,and heptane are biodegradable, but would tend to volatilize into the air before significantbiodegradation could occur (48). Undecane would undergo biodegradation (48). Thecombustion products would undergo some biodegradation, but would also undergo lightactivated degradation if they are on the soil surface (52). Aldrin is converted to dieldrin by soilmicroorganisms but dieldrin is resistant to further degradation (53). Heptachlor is also convertedto heptachlor epoxide through action of microorganisms, but heptachlor epoxide is resistant tofurther degradation (54). Bis(2-ethylhexyl)phthalate does degrade, but only very slowly in soil(55). The substituted methanes (chloroform, bromochloromethane, etc.) would tend to volatilizebefore degradation. Those substituted methanes that have the fewer number of chlorine andbromine atoms would be most likely to degrade first (chloromethane compared tobromodichloromethane) (48). Biodegradation may not occur as one would expect at the sitebecause other site contaminants may be toxic to the soil microorganisms that are responsible forthe degradation.

Based on the available sampling, this potential exposure pathway is probably restricted to thearea of the burn pit and to those workers frequenting the area. The possible routes of exposurewere ingestion of, skin contact with, and inhalation of soil. Because access to the burn pit area isrestricted, it appears unlikely that exposure could occur now or in the future, especially ifremedial workers take the proper protective measures. This exposure pathway is consideredpotential because it can not be documented that workers and others actually were exposed to thecontaminants in the burn pit sludge and soil.

Off-site Surface Soil

The true exposure to contaminated surface soils is not known as no samples were collected ofsoil samples less than 3 inches deep. The extent of off-site soil contamination is not fullycharacterized. The soils in the area of the WPL facility may have been contaminated by themovement of contaminated ground water through the soil. Persistent compounds remainadsorbed onto soil particles. This would generally be determined in a deep soil sample. Surfacewater runoff, such as what follows a heavy rain, would cause the movement of contaminated soilparticles or even pit contaminants to areas downhill from the site. The grade at the site is verygentle with slopes down to the south and the northeast. Soil gas infiltration will also result incontaminated soil as the contaminant in the vapor state reabsorbs onto soil particles. There is noevidence of bulk spills of petroleum products off-site and there is no evidence of a spring or seepbringing contaminated ground water back to the surface.

Because the data on off-site soil contamination is so limited, this pathway can not be discussedfurther in this public health assessment. Additional sampling of off-site soil is needed.

C. Eliminated Pathways

Surface Water

The nearest natural surface water body, Skunk Creek, lies approximately one mile south of theplant site. The creek is not classified to be used for human drinking water but is to be used forlimited contact recreational purposes, irrigation of crops and wildlife propagation. Themunicipal wells in the Skunk Creek Aquifer are immediately to the north of Skunk Creek andshow no evidence of contamination from the WPL site. The site is located about two milesnorthwest of the confluence of the Big Sioux River , which flows north to south, and SkunkCreek which flows northwest to south east. The graveled and vegetated surface of the sitehinders the amount of surface water runoff and subsequent transfer of contaminants by surfacewater flow. The interceptor trench constructed at the southeast corner of the property also servesto trap any contaminated surface water from the site. Because of these site characteristics thepotential for overland transport of contaminated soil particles is low. This is true for all areas ofthe site except for the old Hayward School area which is currently not vegetated.

Garden Fruits and Vegetables

There are no data available for contaminant levels in the food chain, the extent of gardening inthe area or the fraction of food products consumed that is home grown in the WPL area. However, based on the known extent of the groundwater contamination and usage of groundwater, consumption of garden products does not represent a plausible exposure pathway. It will,therefore, be eliminated from further discussion in the public health assessment.

PUBLIC HEALTH IMPLICATIONS

As discussed in the Pathways Analyses section, private drinking water wells on the northeast andsouth of the site and ambient air in the Hayward School are considered completed exposurepathways. The contaminants of concern in the northeast private drinking water exposurepathway are bromodichloromethane, chloromethane, and nitrate. Nitrate is the only contaminantof concern in the south private drinking water exposure pathway. The contaminants of concernin ambient air pathway are benzene, hexane, and pentane.

Pit sludge/soil and off-site soil were identified as potential exposure pathways, but the off-sitesoil pathway was eliminated from further evaluation in the preceding section. Surface water, andgarden fruits and vegetables were eliminated as exposure pathways. The contaminants ofconcern in the pit sludge/soil pathway are benzene, b-BHC, cadmium, alpha and gammachlordane, chromium, 4,4-DDE, dibenzofuran, heptachlor epoxide, hexane, lead, manganese, 2-methylnapthalene, and napthalene.

The Toxicological Evaluation portion of this section will discuss the possible healthconsequences from exposure to the contaminants of concern in the two private drinking water,ambient air, and pit sludge/soil exposure pathways. Community health concerns will beaddressed in Community Health Concerns Evaluation section and health outcome data in theHealth Outcome Data Evaluation section.

A. Toxicological Evaluation

Introduction

Typically, the toxicological evaluation in a public health assessment involves comparison of theexposure dose for those individuals in an exposure pathway to ATSDR's Minimal Risk Levels(MRLs) or EPA's Reference Doses (Rfd). The MRLs and Rfds are estimates of daily humanexposure to a contaminant below which noncarcinogenic adverse health effects are unlikely tooccur (56). This means that any exposure dose that is below the appropriate MRL or Rfd, doesnot represent a hazard to human health. The finding of an exposure dose above the appropriateMRL or Rfd indicates that evaluation of the toxicological literature needs to be done todetermine whether the specific exposure situation represents a hazard to public health. Theexposure dose, based on the contaminant concentrations and exposure length for the area whereexposure has, is, or could occur, is compared to the MRL or Rfd appropriate for the route andlength of exposure. A qualitative summary of these results can be found in Table 9, Appendix B.

The risk of carcinogenic health effects is also evaluated in this section. EPA's Cancer SlopeFactor for a contaminant is used to calculate the maximum risk from 70 years of exposure. Theactual risk of cancer is probably lower than the calculated number. The method used to calculateEPA's Cancer Slope Factor assumes that high dose animal data can be used to estimate the riskfor low dose exposures in humans (57). The method also assumes that there is no safe level forexposure (58). There is little experimental evidence to confirm or refute those two assumptions. Lastly, the method computes the 95% upper bound for the risk, rather the average risk, whichresults in there being a 95% chance that the risk is actually lower, perhaps several orders ofmagnitude (59).

In this section, the exposure doses and carcinogenic risk will be calculated for each of thecontaminants in the three exposure pathways still being considered. The possible healthconsequences of those contaminants which exceeded health guidelines will then be reviewedalong with those contaminants for which there were no health guidelines.

The Private Drinking Water Completed Exposure Pathways

The contaminants in the two private drinking water exposure pathways includebromodichloromethane, chloromethane, and nitrate. There are no health guidelines forchloromethane, so it will be discussed further in the possible health consequences portion of thissection. The maximum concentrations of bromodichloromethane will be compared tononcarcinogenic and carcinogenic health guidelines. Nitrates are not considered to carcinogenic,so only exposure doses will be calculated.

The exposure doses for ingestion of water were calculated in the following manner. Themaximum concentration for a contaminant was multiplied by the water ingestion rate for adultsof two liters/day or for children, one liter/day. This product was divided by the average weightfor an adult, 70 kg (154 pounds) or for a child, 10 kg (22 pounds). A qualitative summary ofthese results can be found in Table 9, Appendix B. The maximum concentrations of nitrate andbromodichloromethane from the northeast did not exceed the health guideline for the chemical. The maximum concentration of nitrate from the south did exceed the health guideline forchildren and be evaluated further in the possible health consequences portion of this section.

Carcinogenic risk from ingestion of water was calculated through the following. The maximumconcentration of a contaminant was multiplied by the ingestion rate for adults of two liters/day,then this result is divided by the average adult body weight of 70 kg. This product is multipliedby the EPA's Cancer Slope Factor for the bromodichloromethane. This result represents themaximum risk for cancer after 70 years of exposure. Because this is an occupational exposuresituation, it is very unlikely that exposure would be any longer than 35 years. Therefore, theresult was divided by two to adjust for this shorter exposure period.

The calculated maximum risk from ingestion of water contaminated with the maximumconcentration of bromodichloromethane does not represent an increased risk of cancer. Becauseof this, carcinogenic health effects for this chemical will not be evaluated further.

The Ambient Air Completed Exposure Pathway

The contaminants in this pathway are benzene, hexane, and pentane. Direct comparison of themaximum concentrations for benzene and hexane were made to the appropriate acute MRL(benzene), RfC (hexane), and CREG (benzene). Both benzene and hexane exceeded the healthguidelines, and they, along with pentane which had no health guidelines, will be evaluatedfurther in the possible health consequences portion of this section.

The Pit Sludge/Soil Potential Exposure Pathway

The contaminants in this pathway were included because they exceeded CREGs (benzene, b-BHC, chlordane, 4,4-DDE, and heptachlor epoxide) or because there were no comparison values(lead, 2-methyl naphthalene, and naphthalene). For those contaminants for they were available,none of the maximum concentrations exceeded noncarcinogenic health guidelines. Theevaluation of the risk of carcinogenic health effects for the first group follows as does adiscussion of the possible health consequences of exposure to the second group.

Carcinogenic risk from soil ingestion was calculated through the following. The maximumconcentration of a contaminant was multiplied by the soil ingestion rate for adults of 0.0001kg/day, then this result is divided by the average adult body weight of 70 kg. This product ismultiplied by the EPA's Cancer Slope Factor for the contaminant. This result represents themaximum risk for cancer after 70 years of exposure. Because this is an occupational exposuresituation, it is very unlikely that exposure would be any longer than 35 years. Therefore, theresults were divided by two to adjust for this shorter exposure period.

Cancer slope factors were available for benzene, b-BHC, chlordane, 4,4-DDE, and heptachlorepoxide (60). The calculated maximum risk from ingestion of soil contaminated with themaximum concentrations of these chemicals does not represent an increased risk of cancer. Because of this, carcinogenic health effects for those contaminants in the pit sludge/soil forwhich cancer slope factors were available, will not be evaluated further.

Possible Health Consequences

The possible health consequences of benzene, chloromethane, dibenzofuran, hexane, lead, 2-methyl naphthalene, naphthalene, nitrate, and pentane are described in the following paragraphs.

Benzene

Benzene is a naturally occurring substance produced by volcanoes and forest fires and is presentin many plants and animals, but benzene is also a major industrial chemical made from coal andoil (49). In industry benzene is used in other processes, as well as being used to make some typesof plastics, detergents, and pesticides. It is a component of gasoline and found in cigarette smoke(49).

The primary effects of exposure to benzene either from inhalation or ingestion are to the blood-forming organs, depression of the immune system and reproductive effects. Symptoms includeheadache, dizziness, drowsiness, and nausea. Benzene may also cause irritation of the eyes andskin (49). Exposure to benzene at occupational levels is known to cause leukemia in humans.

The known exposure levels at the old Hayward School in 1986 were high enough to haveresulted in some of the symptoms reported by the students and staff. Because the knownexposures were probably only a few weeks, the students and staff should not experience anyincrease in their risk for cancer.

Chloromethane

Chloromethane is a clear, colorless, nearly odorless gas. It is produced naturally by some plants,rotting wood, and when grass, wood, charcoal, and coal burn (61). It is also producedindustrially for use in making silicones, agricultural chemicals, and butyl rubber. In addition, ithas been used in the past as the cooling compound in refrigerators instead of Freon.

Exposure to chloromethane has been studied in humans and animals only for the inhalation routeof study (61). Because the exposure at WPL was through ingestion of water, the possible healthconsequences of this exposure can not be evaluated.

Dibenzofuran

Dibenzofuran is released to the environment in air emissions from the combustion of coal, trash,and diesel fuel and in wastewater from coal tar, coal gasification, and shale oil operations (62). Itis commercially made for use as an insecticide and for organic synthesis (63). There are notoxicologic data available for dibenzofuran, so the possible health consequences can not bedetermined (63).

Hexane

Hexane is an organic solvent that is widely used and in low concentrations, is approved for use infood products. Exposure to hexane is usually through inhalation, as was the case with exposuresat the old Hayward School in 1986. Symptoms of exposure to hexane can include giddiness,headache, eye and throat irritation, blurred vision, and numbness (64). Studies of workersindicate that those symptoms would not occur until the concentrations were at least 50 times thelevels identified at the school (64).

Lead

Lead is a naturally occurring element in the environment. Lead is widely used for the productionof storage batteries, pipes and solders, chemical, gasoline additives, and paints. Exposure to leadoccurs from the ingestion of water transmitted in lead pipes and when children ingest paint chipsor soils contaminated with lead (65).

Three literature reviews have evaluated the relationship between concentrations of lead in soiland blood lead levels in children (66-68). All three concluded that soil lead levels of 1000 partsper million (ppm) would increase concentrations in blood from 0.6 to 65 micrograms/deciliter(ug/dL) with an average increase of 4-5 ug/dL. This wide range was due to different sources oflead, exposure conditions, and exposed populations. The health effects associated with such anincrease would depend partly on the existing body burden of lead.

Actual health impact depends on factors such as the age and nutritional status of the childcontacting the soil, the frequency of contact, the rate of soil ingestion, the type of lead, and thecharacteristics of the soil. The limited nature of the sampling and that only one of nine sampleshad detectable levels preclude making any conclusions on the possible health consequences fromingestion of lead.

The maximum concentrations of lead in pit sludge/soil could represent a health threat if childrenwere to regularly ingest the contaminated material. However, since the contaminated area isfenced and guarded, it is very unlikely that children would ever be exposed.

Naphthalene and 2-Methylnaphthalene

Naphthalene is an organic chemical that has the characteristic smell of mothballs. the major usesof naphthalene are in the manufacture of dyes and resins, and in mothballs. Naphthalene isreleased to the air from the burning of coal and oil and is a normal constituent of petroleum fuels. Little is known about the release of 2-methylnaphthalene. Hemolytic anemia (the breakdown ofred blood cells) is the primary health concern for humans exposed to naphthalene and 2-methylnaphthalene for either short or long periods of time. Systemic effects include nausea,diarrhea, kidney damage, respiratory effects, and liver damage (69).

The levels of naphthalene and 2-methylnaphthalene on-site are much less than those known tocause hemolysis or liver damage. Infants, however may be more susceptible to the effects ofnaphthalene as jaundice was reported among infants who were exposed to mothball treatedclothing or blankets (69).

Nitrates

Nitrates in the groundwater near the WPL site may be related to site activities. Nitrates arecommon in fertilizer products and are formed from ammonia-based fertilizer products. Nitratecompounds are used as cetane enhancers in diesel fuels (60, 62). Nitrates found in off-sitegroundwater are of special concern for young infants due to the conversion of nitrates to nitritesin the intestines. Infants less than six months old and especially those under three months of ageare particularly susceptible to methemoglobinemia which is caused by ingestion of watercontaining elevated levels of nitrates. Methemoglobinemia is the condition where thehemoglobin in the blood which normally carries the oxygen is converted to a form that cannotcarry oxygen. This would manifest as some of the symptoms of oxygen deficiency, i.e., turningblue and gasping for breath. While some cases of methemoglobinemia have been reported withassociated water nitrate levels of less than 50 mg/L, most cases occur with nitrate levels of 90mg/L or more. Nitrate concentrations off-site are reported at a range of 11-99 mg/L, and may beharmful to newborns.

Pentane

Exposure to pentane vapors occurred in the past at the old Hayward School. Pentane is anorganic solvent, a constituent of petroleum products, and is highly flammable. Pentane is mostcommonly found in the vapor state. Symptoms of exposure can include a sensation ofexhilaration, dizziness, headache, loss of appetite, loss of feeling, muscle weakness, nausea,confusion, and the inability to do fine work (62, 64). The maximum concentration of pentanefound at the old Hayward School (11.2 mg/m3) is about 10 times lower than the National Instituteof Occupational Safety and Health's (NIOSH) eight-hour exposure limit for pentane of 350mg/m3 (70).

B. Health Outcome Data Evaluation

In a public health assessment, available health outcome databases are identified for the area nearthe site. From those available data, ATSDR selects health outcomes for further evaluation thatare biologically plausible or are community health concerns.

For biological plausibility, the decision to evaluate available health outcome data depends on theexistence of a completed exposure pathway for a chemical suspected to cause the health outcomeof concern. The selection of a noncarcinogenic health outcome is based on a review of thetoxicologic literature for a contaminant of concern.

Designating a chemical as a carcinogen (for purposes of health outcome data evaluation) is basedon:

(a) classification by the National Toxicology Program (NTP)(1) in its Annual Report on Carcinogens as a "known human carcinogen" or "reasonably anticipated to be a carcinogen"; or
(b) classification by the International Agency for Research on Cancer (IARC)(2) as a 1, 2A, or 2B carcinogen; or
(c) classification by the United States Environmental Protection Agency (EPA)(3) as an A, B1, or B2 carcinogen.

A latency period of at least 10 years between exposure and diagnosis has been observed in moststudies of human cancer. If exposure began less than 10 years prior to the latest data available,analysis of health outcome data for cancer incidence or mortality is not likely to be useful,particularly if the exposure level is low.

Another important factor is the difference in size between the population at risk of exposure tosite contaminants and the smallest population unit for which health outcome data are available. For example, any effect from a site would likely not be observed if the population at risk is 100and the population unit for which health outcome data are available is 100,000.

Even when health outcomes do not meet ATSDR's guidelines for biological plausibility, healthoutcome data can be evaluated to address community health concerns.

For WPL, infant and cancer mortality data are not evaluated here because the disparity inpopulation size between the WPL area and the smallest unit (Minnehaha County) for which dataare available.

Learning Disabilities

The Sioux Falls School District classifies students as having a learning disability (LD), if thechild manifests a disorder in one or more of the basic psychological processes involved inunderstanding or in using spoken or written language (32). Such a disorder may be a diminishedability to listen, think, speak, read, write, spell, or do mathematical calculations in the presence ofaverage intelligence, adequate sensory/motors systems, and adequate learning opportunities. WISC-R and WAIS-R tests and standard achievement tests are utilized in this evaluation (32).

The only available data on the number of LD by school for the Sioux Falls School District werefor the 1990-91 school year (33). Fifty-three of the 518 (10.2%) students at the new HaywardSchool were considered to have LD, while 649 of 9051 (7.2) had LD in the school district as anwhole (32). Hayward had the second highest rate of LD of the 21 elementary schools in thedistrict. When they provided these LD data, the Sioux Falls School District advised that thepercent LD is higher for the northern half of school district where Hayward is located (32). Thepercent LD for the 10 schools in the northern half is 8.2, while it is 6.4 for 11 southern schools. The percent LD for the Hayward School is not statistically greater than the percent LD for thenorthern schools, but is for the school district as a whole.

These results for Hayward School include students were at the old Hayward School in September1986 (mostly those in grades 4-6), and many who were not. Data on LD for the years between1986 - 1990 and by grade are needed to fully evaluate the possible relationship between theincident in 1986 and LD. Unfortunately, those data are not available from the Sioux Falls SchoolDistrict or the State of South Dakota, the only two possible sources (32-34).

Learning Disabilities (LD) is a general term for a mixed group of disorders whose symptomsinclude significant difficulties in the acquisition and use of listening, speaking, writing,reasoning, mathematical abilities, or social skills (71). These disorders are intrinsic (i.e., theirsource is mainly internal, rather than due to social factors) to the individual and are presumed toresult from central nervous system dysfunction. LDs may occur at the same time as otherhandicapping conditions but are not a direct result of them.

Learning disabilities are associated with lower socioeconomic status, males, genetic factors, verylow birth weight, seizure disorders, lead exposure, and prenatal maternal alcohol abuse (65, 72). While solvents are known to cause neurotoxic effects, it is not known whether exposure to thesechemicals can contribute to the onset of LD (71, 73).

C. Community Health Concerns Evaluation

We have addressed each of the community health concerns as follows:

1. Did the children and staff of the Old Hayward School suffer any long-term health effects as aresult of exposure to vapors in the school?

    As discussed in the Toxicological Evaluation section, the known exposure levels at the old Hayward School in 1986 were high enough to have resulted in some of the symptoms reported bythe students and staff. Because the known exposures were probably only a few weeks, thestudents and staff should not experience any increase in their risk for cancer. Exposures wouldhave had to been for several years before there would have been any increase in cancer risk.

2. Will the exposure to vapors in the old Hayward School impair the children's learning ability inany way? Is the rate of learning disabilities 42% for children who attended Old HaywardSchool?

    While solvents found at Hayward in 1986 are known to cause neurotoxic effects, it is not knownwhether exposure to these chemicals can contribute to the onset of LD (71, 73). There is additional information on LD in the preceding section.

    As discussed in the preceding section, there are no data which identify the percent LD forchildren who attended the old Hayward School. However, given that the percent LD for 1990 is10.2% and that most of the members of grades 4-6 attended the old school in 1986, it is veryunlikely that the percent LD for those who went to the old Hayward is 42%. For that to be so,nearly all the 53 LD students at Hayward in 1990 would have to have attended the old Hayward.

3. Is the off-site soil contamination high enough to warrant concern?

    The known contaminant levels do not represent a health threat.

4. Is it possible for site contaminants to pollute garden fruits and vegetables? Is it safe for me togarden?

    Yes, it is safe to garden. Small amounts of the contaminants may be on or in the vegetables. Washing will remove contaminants on the surface of vegetables. Given the low levels of thecontaminants in the soil, the amount in the flesh of the vegetables would be very small.

5. Are the levels of vapors in residences and business high enough to be a concern?

    The levels of chemical vapors in homes and residences in the area of WPL have not beenquantitatively measured. The Sioux Falls Fire Department has used instruments that can detectfor the presence of very high explosive levels of vapors in homes and businesses in the area ofWPL. These instruments are not sensitive at low levels and they do not indicate precisely whichvapors are present.

6. Are workers on the WPL site in any great danger?

    The actual working conditions on the WPL site do not fall within the scope of this public healthassessment. The conditions encountered by workers on the site may pose various hazards such asentering a tank to clean or repair it or the actual handling of petroleum products on a daily basis. The Occupational Safety and Health Administration (OSHA) and National Institute forOccupational Safety and Health (NIOSH) have established protocols for these circumstances and,if followed, will promote worker safety and health.

7. Is the municipal well in the Skunk Creek Aquifer safe now and for future consumption?

    The sampling results for this well indicated no significant contamination problems. The samplesfrom the Skunk Creek Aquifer municipal well showed levels of sulfates that exceeded the EPAProposed Maximum Contaminant Levels. The sulfate levels may be an indicator of water qualityin the area of the city well. However, the City of Sioux Falls lowers the sulfate levels toacceptable limits by mixing the water from the Skunk Creek Aquifer with water from other citywells. The city also maintains a monitoring well north of the Skunk Creek Aquifer well and alsouses a private well as an observation point for contaminants flowing from the north. The citybelieves this monitoring system provides for an adequate warning should contaminants movefrom the WPL towards the city well.

8. Will the residents and employees of the school and businesses in the area who consumed wellwater have any long-term health effects?

9. Should residents in the area continue using private wells?

    Based on the known data on extent of contamination and the direction of groundwater flow,residents north and west of WPL can continue to use their wells without concern forcontamination from WPL. Those residents living to the south, east or northeast of WPL shouldconsider having their private well tested if it has not been. The Sioux Falls Health Departmentshould be contacted for information on testing. The City of Sioux Falls has installed municipalwater lines, so that all concerned residents in the vicinity of WPL may have municipal water ifthey desire it.

10. Has the source of pesticide contamination in the burn pit area and off site been identified?

    The Site Investigation Analytical Results report concluded that the WPL burn pit was the sourceof the pesticide contamination to the northeast of the WPL site. WPL and the other investigatorshave not determined how the pesticides got into the burn pit.

11. Is there any relation of the WPL site to dead trees to the west of the site?

    The sampling reports that we analyzed did not include any off-site samples taken from the westside of the WPL site. We cannot say at this time if the dead trees are related to the WPL site.

12. Will children at a day care facility off the south side of the WPL site suffer any health effectsfrom the site?

    Based on the information reviewed in this public health assessment, it is unlikely that the soil ordrinking water at this facility are contaminated with site-related substances. There is no evidenceof off-site soil contamination on the south side of WPL. This faculty is probably on public drinking water. While the exact location of this day care facility is not known, it is not located in the area of known groundwater contamination.(4) No samples were taken in areas designated as childcare centers.


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