SEVEN POINTS SANITATION SITE
MABANK, KAUFMAN COUNTY, TEXAS
The Texas Natural Resource Conservation Commission (TNRCC) requested that the Texas Department of Health (TDH) evaluate the potential health risks associated with exposure to soil, liquid/sludge waste, and drinking water on the former Seven Points Sanitation Site. The site is located in a sparsely populated area, approximately 3.5 miles northwest of Mabank, Kaufman County, Texas, and is adjacent to Cedar Creek Reservoir. Seven Points Sanitation is a sixteen acre inactive landfill that operated from 1974 to 1984. From 1974-1976, Seven Points Sanitation operated as an unregistered landfill. In 1976, the TDH Region 5 office received a report from the Tarrant County Water Control Board of unauthorized landfill operations adjacent to the Cedar Creek Reservoir. In 1978, the owner obtained a TDH approved operating permit to receive non-hazardous waste at a rate of eight tons per day for ten years. Because the surface soils are predominately highly permeable, a clay liner was recommended but never implemented. During the ten years of operation, Seven Points Sanitation landfill was inspected 35 times by TDH and received 31 documented compliance violations. A 1984 court injunction ordered all activities to cease until the facility became compliant with TDH operating rules.
Following the 1984 court injunction to cease all operations, the TDH Region 5 office collected five samples from containers of liquid/sludge wastes marked "poison" abandoned at the landfill's south pond area. Surrounding soils were described as blue-stained. Results indicated elevated copper and sulfate, and the presence of organic wastes. Corrosive tests revealed hazardous levels of both caustic and acid waste. The site was abandoned in poor condition in 1984. After an issuance of contempt for failure to comply with the court order, a 1986 judgement assessed a fine against the owners.
The property owners declared insufficient funds for remediation and the site was referred to the EPA Superfund Program in 1988 for further action. A Preliminary Assessment was completed by the EPA in 1989. The Preliminary Assessment documented 14 domestic wells within one mile and two drinking water intakes at four and seven miles downstream from exposed surface wastes; however, the site received a low priority qualifier. The EPA contractor concluded that the site did not warrant inclusion on the National Priority List, but recommended a site inspection based on State records. A decision of "No Further Remedial Action Planned" under Superfund was entered and the site was referred to the State. No closure activities or efforts to improve the condition of the landfill have been completed to date.
In 1996, as part of the U.S. Environmental Protection Agency (EPA) Site Investigation, the following observations were made: the surface was virtually devoid of vegetation, there was evidence of severe erosion, the site was used to store junk, at least two ponds containing water were observed on-site, as well of evidence of recent burning of tires and other items. The EPA collected seven soil samples and four groundwater samples to assess soil contamination and migratory pathways to surface water and groundwater (Appendix; Table 1). In 1997, as a follow-up to the EPA Site Investigation, the TNRCC collected six well water samples and eleven soil samples from the former Seven Points Sanitation Site (Appendix; Table 2).
Health Assessment Comparison Values
To assess the potential health risks associated with contamination at this site we compared contaminant concentrations to health assessment comparison (HAC) values for non-carcinogenic endpoints. HAC values are media specific contaminant concentrations that are used to screen contaminants for further evaluation. Non-cancer comparison values are based on the Agency for Toxic Substances and Disease Registry's (ATSDR's) minimal risk levels (MRLs), the U.S. Environmental Protection Agency's (EPA's) references doses (RfDs), or other non-carcinogenic health-based comparison values. MRLs and RfDs are estimates of a daily human exposure to a contaminant that is unlikely to cause adverse non-cancer health effects over a lifetime. Exceeding a HAC value does not imply that a contaminant represents a public health threat but suggests that the contaminant warrants further consideration.
Results of water taken from residential wells were compared to EPA's maximum contaminant levels (MCLs); lead concentrations were compared to EPA's Action Level for this contaminant. MCLs are chemical-specific maximum concentrations allowed in water delivered to the users of a public water system. Maximum contaminant levels are considered protective of public health over a lifetime (70 years) at an exposure rate of two liters per day. MCLs may be based on available technology and economic feasibility. Although MCL's apply to public water systems, they can be used as a guide when assessing the public health implications of contaminants found in water from private water wells. Although EPA's Action Level for lead in drinking water is not directly analogous to an MCL, it also can be used as a guide when assessing the public health significance of lead in drinking water.
Results of the EPA Site Investigation
A drinking water sample collected from a domestic well 900 feet northeast of the suspected contamination in the south pond basin (sample DW-03) contained an iron concentration of 384 micrograms per liter (ug/L) at the tap, exceeding the secondary Maximum Contaminant Level for iron of 300 ug/L. The secondary MCL for iron was established for aesthetic purposes; therefore, a slight exceedance of the MCL in sample DW-03 does not pose a health threat.
Lead was detected at a concentration of 39 ug/L in a background drinking water sample collected from a domestic well 1,000 feet south of the site entrance (DW-04). A drinking water sample from a domestic well 650 feet west of the area of suspected contamination in the south pond basin contained 93 ug/L lead and 42 ug/L lead in duplicate samples (DW-01, DW-02). All three samples exceed EPA's Action Level for lead in drinking water of 15 ug/L.
TNRCC Sample Results
In contrast to the EPA findings, the TNRCC did not find lead in any of the residential well water samples. The concentration of antimony found in the soil sample (SO-11) from the ash pile of the Hunter residence, (23.7 mg/kg) slightly exceeded the HAC value of 20 mg/kg for a child. The concentration of manganese found in the soil sample (SO-12) from the Penix residence (303 mg/kg) slightly exceeds the HAC value of 300 mg/kg for a child. A child would have to ingest over 200 milligrams of contaminated soil every day before the reference dose for either of these contaminants was exceeded. Based on this information we would not anticipate either of these contaminants to present a health threat. The concentration of lead found in the soil sample (SO-11) from the ash pile of the Hunter residence (544 mg/kg) exceeds the clean-up level for lead in soil commonly used in residential yards in Texas (500 mg/kg) and would present a potential health threat if the concentration measured in this sample was representative of the lead levels in the whole yard and young children frequently played in the contaminated soil.