PUBLIC HEALTH ASSESSMENT
CITY OF PERRYTON WELL NO. 2
(a/k/a PERRYTON WATER WELL NUMBER 2)
PERRYTON, OCHILTREE COUNTY, TEXAS
The Perryton Water Well Number 2 site is a former public water supply well which is contaminated with carbon tetrachloride, nitrates, and atrazine. This site is in Perryton, Ochiltree County, Texas. The carbon tetrachloride contamination in this water well was first identified in 1989 by the City of Perryton, the Texas Department of Health Water Hygiene Division, and the Texas Water Commission. Because of the carbon tetrachloride in the water, Well Number 2 was taken out of service and has not been used for drinking since June 1989. The source of the contamination has not been identified. Perryton Water Well Number 2 was proposed to the Environmental Protection Agency's National Priorities List in September 1998 and was added to the list in January 1999. The Environmental Protection Agency (EPA) is working with the City of Perryton to develop a treatment plan for Water Well Number 2. An interim remedy for treating and blending the contaminated well water was agreed upon by EPA in September 1999.
Currently, Perryton Water Well Number 2 does not pose a public health hazard because water from the well is not being used and has not been used since the well was disconnected from the city water supply in June 1989.
In the past Perryton Water Well Number 2 posed an indeterminate public health hazard. Available data indicate that in the past, carbon tetrachloride exceeded health-based comparison values; the data were insufficient to reliably reconstruct possible past exposures.
Future use of water from Perryton Water Well Number 2 could pose a public health hazard if people were to use it before it is properly treated to remove the carbon tetrachloride and to reduce the concentrations of nitrates and atrazine. The contaminants of primary concern for future use include carbon tetrachloride and nitrates (the concentration of atrazine decreases to below the Environmental Protection Agency's maximum contaminant level as more water is pumped). If the well water is not treated, chronic exposure to carbon tetrachloride at the reported concentrations could result in an estimated low to moderate increased lifetime risk for developing cancer. In addition, since infants are particularly sensitive to the possible effects of exposure to nitrates, ingestion of this water by infants could result in exposure doses well within the range of doses that have been found to cause methemoglobinemia.
The Agency for Toxic Substances and Disease Registry (ATSDR) was established under the mandate of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980. This act, also known as the "Superfund" law, authorized the U.S. Environmental Protection Agency (EPA) to conduct clean up activities at hazardous waste sites. EPA was directed to compile a list of sites considered hazardous to public health. This list is called the National Priorities List (NPL). The 1986 Superfund Amendments and Reauthorization Act (SARA) directed ATSDR to prepare a Public Health Assessment (PHA) for each NPL site. (Note: Appendix A provides a listing of abbreviations and acronyms used in this report.)
In conducting the PHA, three types of information are used: environmental data, community health concerns and health outcome data. The environmental data are reviewed to determine whether people in the community might be exposed to hazardous materials from the NPL facility. If people are being exposed to these chemicals, ATSDR will determine whether the exposure is at levels which might cause harm. Community health concerns are collected to determine whether health concerns expressed by community members could be related to exposure to chemicals released from the NPL site. If citizens raise concerns about specific diseases in the community, health outcome data (information from state and local databases or health care providers) can be used to address the community concerns. Also, if ATSDR finds that harmful exposures have occurred, health outcome data can be used to determine if illnesses are occurring which could be associated with the hazardous chemicals released from the NPL site.
In accordance with the Interagency Cooperative Agreement between ATSDR and the Texas Department of Health (TDH), ATSDR and TDH have prepared this PHA for the Perryton Water Well Number 2 NPL site. This PHA presents conclusions about whether exposures are occurring, and whether a health threat is present. In some cases, it is possible to determine whether exposures occurred in the past; however, often a lack of appropriate historical data makes it difficult to quantify past exposures. If it is found that a threat to public health exists, recommendations are made to stop or reduce the threat to public health.
The Perryton Water Well Number 2 site includes a contaminated city public water supply well and its associated groundwater plume in the northern part of the Texas Panhandle in Perryton, Ochiltree County, Texas (Figure 1). Well Number 2 was used as a public drinking water supply well until 1989 when carbon tetrachloride was found at concentrations above the Environmental Protection Agency's (EPA's) maximum contaminant level. Perryton Water Well Number 2 is on the north side of the City of Perryton near the intersection of North Amherst Street and Santa Fe Avenue on the 1.7-acre maintenance yard used by the City of Perryton Utilities Department (Figure 2) [1]. Two garages/city maintenance buildings are on the northwest part of this property. Other facilities in the vicinity of this well and the city maintenance yard include the Southwestern Public Service Company to the north, the Southwestern Railroad (formerly Santa Fe Railroad) and the Perryton Equity Exchange to the south, and an electrical substation to the east. The nearest occupied residence is approximately 300 yards west of Well Number 2. The nearest public water supply wells to Well Number 2 are Well Number 1, which is 1,500 feet north of Well Number 2, and Well Number 3, which is 3,000 feet south of Well Number 2. The nearest private water supply well is approximately 1,200 feet southwest of Well Number 2.
Water Well Number 2 was drilled in 1946. It is one of twelve wells owned by the City of Perryton to supply municipal drinking water (Figure 3). Until 1989, both Well Number 1 and Well Number 2 supplied water to the northern part of Perryton. Wells Number 3 through 11 supply water to the southern part of Perryton. Well Number 12 has not yet been connected to the Perryton water system.
In early 1989, the city officials requested volatile organic compound analyses of their system to participate in the Wellhead Protection Area program. The initial sample collected in February 1989 indicated one (1) microgram per liter (µg/L) benzene in the northern supply system; however, benzene has not been detected in subsequent samples. The two wells supplying the northern system (Wells Number 1 and 2) and the 75,000 gallon ground storage tank for the northern system were resampled May 9, 1989. No contamination was found in Well Number 1; however, Well Number 2 had a concentration of 25 µg/L of carbon tetrachloride and one (1) µg/L of chloroform. The ground storage tank had a carbon tetrachloride concentration of 11 µg/L. The ground storage tank was immediately flushed and rinsed and Well Number 2 was disconnected from the public water supply system (June 1989). Additional sampling of Well Number 2 by the Texas Department of Health (TDH) and the Texas Water Commission (TWC) in 1989 and 1990 measured carbon tetrachloride concentrations ranging from 9 to 40 µg/L. Chloroform concentrations ranged from below detection to 3.1 µg/L.
The Texas Natural Resource Conservation Commission (TNRCC) and the Environmental Protection Agency (EPA) investigated three possible sources of the carbon tetrachloride contamination. Reportedly, a 30-gallon container of carbon tetrachloride may have been stored in the Well Number 2 pump house; employee accounts could not be substantiated and soil samples collected by the Texas Water Commission around and under the pump house foundation did not contain carbon tetrachloride [1]. However, because of its chemical characteristics (high vapor pressure and low soil adsorption coefficient), carbon tetrachloride would be expected to either evaporate rapidly from the soil or migrate into groundwater [2].
The second possible source of the contamination was a hand-dug well, which was reportedly located about 600 feet northwest of Well Number 2 behind a machine shop and an electrical substation. It was not known if carbon tetrachloride might have been used as a solvent at the machine shop or as a fire extinguishing material at the electrical substation. The exact location of this well was not found [1].
Although the Perryton Equity Exchange is approximately 1,500 feet south of and downgradient from Well Number 2, it was considered as a third possible source for the carbon tetrachloride contamination [1]. The Perryton Equity Exchange is a grain storage facility and a grain elevator. In the past carbon tetrachloride was commonly used as a grain fumigant in grain elevators; EPA has documented groundwater contamination associated with this type of use in other parts of the United States [2]. The grain storage facility has been in operation since 1919 and the grain elevator was built in the 1940s. Well Number 2 is located approximately 130 feet north of a major drainage culvert situated between the city's maintenance yard and the Perryton Equity Exchange.
Because the source of the contamination was not readily apparent, the EPA conducted an Expanded Site Inspection (ESI) in June 1996 again sampling Well Number 2. Carbon tetrachloride was measured at 50.3 µg/L, lead was measured at 60.9 µg/L, and chloroform was measured from 4.2 to 4.9 µg/L. Atrazine (<1 µg/L) and propazine (3.3 to 5.0 µg/L), two herbicides, were tentatively identified in Well Number 2 samples. These data are presented in more detail in the Environmental Contaminant section of this report. No definite source of the contamination was identified during the ESI.
Because Well Number 2 is not available for use, the public water system has had difficulty providing adequate quantities of water to the northern part of town from the remaining well (Well Number 1). Although the City has connected the south water system to the north water system to help maintain supply and water pressure, there are still problems satisfying water demand in the summer. The City of Perryton wants to remedy the problem by treating the groundwater from Well Number 2 to remove the contamination so that this water can be safely used [3].
The Perryton Water Well Number 2 site was proposed to the National Priorities List of Superfund sites September 30, 1998 and was added to the National Priorities List on January 19, 1999 [4]. The EPA proposed treatment plans for the public to review and comment on in August of 1999. The plan selected, called an Interim Record of Decision, was signed on September 22, 1999. It calls for installing a treatment system to remove the carbon tetrachloride from the groundwater pumped from Well Number 2 and then blending this treated water with water from Well Number 1 to reduce the nitrate concentration to a safe level [5, 6].
Two representatives of the Texas Department of Health (TDH), visited the Perryton Water Well Number 2 site on May 27, 1999. TDH met with the City Manager, the Water Superintendent, and the Director of Public Works to brief them on the ATSDR public health assessment process and obtain current information about Water Well Number 2. About one and one half hours were spent examining Well Number 2 and discussing the public water system and past citizen concerns.
The well site is within the fenced City of Perryton maintenance yard. This yard is locked up at night. During the day the yard is open to City employees. Although the immediate area around the well is not currently secured by an intruder-resistant fence, the well opening is secured by a metal plate welded over the opening. No stained soils or other signs of contamination were observed around the well. There was no evidence of trespassers having tampered with this well site.
A representative of TDH attended an EPA public meeting in Perryton on August 24, 1999 to provide information about the Agency for Toxic Substances and Disease Registry's public health assessment process and to solicit community health concerns. Approximately 20 individuals attended this meeting. The community health concerns received have been incorporated into the Community Health Concerns section of this report.
The City of Perryton has a population of 7,607; the population of Ochiltree County is 9,128 [7]. There are 5,003 people living within one mile of the site, according to the 1990 U.S. Census [7]. Currently there are four full-time workers at the city maintenance yard [3]. Within one mile of the Water Well Number 2 site there are 15 churches, three schools and one city park.
According to information in the Expanded Site Inspection [3] and in conversations with City Representatives, the northern water supply system for the City of Perryton serves approximately 1,100 people. The southern supply system serves approximately 6,500 people. During the time that the well contamination was discovered in 1989, 912 people were connected to the northern water system.
Land Use and Natural Resource Use
The Perryton Water Well Number 2 National Priorities List site is in the semiarid High Plains region of Texas. The average temperature range in this area is between 17 and 94 degrees Fahrenheit. Annual precipitation averages around 19.5 inches [8]. There are no perennial surface water bodies within a one mile radius of Well Number 2. Most rainfall drains into playas (ephemeral lakes) which generally are filled with water only during periods of heavy rainfall. Runoff from the Well Number 2 area drains into an east-west drainage culvert on the south side of Santa Fe Avenue (Figure 2). This culvert only flows during heavy rain events and drains into a playa approximately 2.7 miles northeast of Well Number 2 [3]. A release to surface water is not expected since no aboveground sources of carbon tetrachloride have been identified and since carbon tetrachloride readily volatilizes when exposed to the air. There are no drinking water intakes or other resources that rely on surface water near the site.
General Hydrogeology and Public Water Supply Wells
The Ogallala Formation is the principal water-bearing unit of the High Plains Aquifer system. The aquifer system consists of the saturated sediments of the Ogallala Formation. Groundwater in the Ogallala Aquifer is generally under a water table (unconfined) condition, and its flow generally follows the slope of the ground surface flowing toward the south-southeast (Figure 3) [1]. Due to its high porosity and permeability, the Ogallala Aquifer is capable of yielding large quantities of potable water. The depth to groundwater in the Ogallala Aquifer at the site ranges from 260 to 340 feet below the ground surface [3]. The aquifer is the main source of fresh groundwater in Ochiltree County [3].
The City of Perryton receives all of its public water supply from groundwater sources; all 12 of the City of Perryton public water supply wells are completed in the Ogallala Aquifer and are screened at depths ranging from 212 to 637 feet [1, 9]. Well Number 2 is screened between 330 and 415 feet below ground surface [1]. Well Number 1 is the only public water supply well upgradient of Well Number 2. Seven of the ten active public supply wells that supply groundwater to the City of Perryton are within four miles of Perryton Water Well Number 2 (Figure 3). Treating the contamination in Well Number 2 should reduce the likelihood that other area wells will be affected by the contamination in the future.
Until 1989 the northern supply system consisted of Well Numbers 1 and 2 and served approximately 900 people. Currently the northern water system is supplied by Water Well Number 1 and by water from the southern supply system. Since Well Number 2 has been out of service, the city has had to increase pumping from Well Number 1 to compensate for the loss of supply. The southern supply system, which is south of the railroad track, is supplied by Well Numbers 3 through 11. City Representatives have indicated that the water supply to the northern water supply system is inadequate during the summer months.
The EPA Project Manager reported knowledge of one privately owned water well within 1/4 mile of Well Number 2. The presence of this well (~ 1,200 feet southwest of Perryton Water Well Number 2) was verified by City of Perryton officials. Recently the owner expressed interest in having his well tested. Water from this private well is used for drinking [10].
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