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Sediments in Stewarts Creek



The U.S. Environmental Protection Agency (EPA) Region 6 asked the Agency for Toxic Substancesand Disease Registry (ATSDR) and the Texas Department of Health, Environmental Epidemiologyand Toxicology Division (TDH), to evaluate the potential for contamination from the ConroeCreosoting Company (CCC) site to pose a public health hazard to people living downstream on Stewarts Creek.


Site Description and History

The CCC site is east of the city limits of Conroe, Montgomery County, Texas (Figure 1). It sits onthe north side of State Highway 105 at 1776 E. Davis. Stewarts Creek is to the west; an on-site lakeand Little Caney Creek lie to the east.

From 1946 until 1997, workers at this facility treated lumber with chemicals--creosote,pentachlorophenol (PCP), or copper-chromated-arsenic (CCA)--to preserve the wood for use asfence posts, railroad ties, or utility poles. The Texas Natural Resource Conservation Commission(November 2001) and the EPA (January and November of 2002) documented contamination of sitesoil and sediment with these wood-treatment chemicals [1, 2, 3]. TDH staff noticed heavily stainedsoil areas and chemical odors, particularly around tanks and process areas, when they visited the sitewith EPA and ATSDR regional staff in May 2002.

The EPA began removing tanks, pipes, and other equipment from the site in the Fall 2002. AResource Conservation and Recovery Act (RCRA) vault was built on the site to containcontaminated soil and sediment. Runoff from heavily contaminated areas was redirected andcontained [3]. In the past, rain and runoff that contacted contaminated areas tended to flow into anon-site drainage ditch and then west into Stewarts Creek, which flows south past residential homesand yards that have flooded during heavy rainfall.

In November 2002, to better characterize off-site contaminant concentrations around the CCC site,a contractor for the EPA collected 111 sediment and five soil samples. These samples were analyzedfor semi-volatile organic compounds (SVOCs) and metals [4]. In addition, 101 of the sedimentsamples and all five of the soil samples were analyzed for dioxins/furans. The sediment sampleswere collected along Stewarts Creek, along Little Caney Creek, at the on-site lake, and elsewhereon the CCC site. Soil samples also were collected from three residential yards and a schoolyardalong Stewarts Creek.

Benzo(a)pyrene, an SVOC, exceeded its health-based screening value(1) in 44 of the sediment samplesand in one of the soil samples.

Arsenic exceeded health-based screening values in 75 sediment samples and in all five of the soilsamples (Table 1). However, the levels of arsenic in sediment from Stewarts Creek (not detected to19 mg/kg) and Little Caney Creek (not detected to 4.1 mg/kg), as well as in soil from the residentialyards (2.6-4.7 mg/kg) and the schoolyard (1.5-4.5 mg/kg), were comparable to background soilarsenic concentrations for uncontaminated soil [5]. Therefore, further consideration of arsenic in thishealth consultation was not warranted.

Dioxins, as 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin equivalents (TCDD), exceeded ATSDR's actionlevel for soil of 0.001 milligrams TCDD per kilogram (mg/kg) [6] in one of the 101 sedimentsamples, but did not exceed this value in any of the five soil samples. The sediment sample withTCDD exceeding ATSDR's action level for soil was found where the on-site drainage ditch enteredStewarts Creek. This sediment has since been removed and transferred to the on-site RCRA vault.Since dioxins were below levels of concern in soil and sediment, it is unlikely that significantexposure opportunities existed. Therefore, further consideration of dioxins in this healthconsultation was not warranted.

In April 2003, more-focused sediment sampling was conducted by EPA along two sections ofStewarts Creek: 1) under and near the State Highway 105 bridge over the creek; and 2) near AvenueM. Forty-two (42) sediment samples from each location were analyzed for SVOCs.

For the State Highway 105 bridge location, 28 of the 42 samples exceeded the screening value forthe SVOC benzo(a)pyrene. The maximum level of the benzo(a)pyrene measured at this location was30 mg/kg. This sample was collected in a difficult-to-access area below the bridge. For the AvenueM area, 26 of the 42 samples had levels of benzo(a)pyrene exceeding screening values. Themaximum level of benzo(a)pyrene measured in sediment from the Avenue M area was 1.4 mg/kg.


The environmental sampling data reviewed in this report includes data collected by EPA in 2002 and2003. In preparing this report, TDH and ATSDR relied on those data and assumed adequate qualityassurance/quality control (QA/QC) procedures were followed with regard to data collection, chain-of-custody, laboratory procedures, and data reporting.

Reviewers evaluated the results by comparing the contaminants to screening values and by selectingresults that exceeded the screening level. Benzo(a)pyrene was selected for further consideration.

The most likely exposure route for benzo(a)pyrene in creek sediment or soil is through incidentalingestion of contaminated sediment or soil.(2) To assess the risk for those ingesting sediments, TDHused the following conservative exposure scenario: A worker ingesting 100 mg of sedimentcontaining the highest level of benzo(a)pyrene measured in CCC area sediments (30 mg/kg) duringhis work week for 30 years might have a slightly elevated(1.34 X 10-4) risk of developing cancerover a lifetime of exposure. Because the area that had the highest level of benzo(a)pyrene under andnear the State Highway 105 bridge is not readily accessible, the probability of exposure andsubsequent potential for adverse health outcomes is low.

Similarly, a child or an adult regularly exposed to the maximum level of benzo(a)pyrene (1.4 mg/kg)measured along Stewarts Creek at Avenue M would have no apparent increased risk of developing cancer.


ATSDR's Child Health Initiative

We recognize that the unique vulnerabilities of children demand special attention. Windows ofvulnerability (critical periods) exist during a child's development, particularly during early gestationbut also throughout pregnancy, infancy, childhood, and adolescence--periods when toxicants maypermanently impair or alter structure and function [7].

Unique childhood vulnerabilities may be present because at birth many organs and body systems(including the lungs and the immune, endocrine, reproductive, and nervous systems) have notachieved structural or functional maturity. These organ systems continue to develop throughoutchildhood and adolescence. Children may exhibit differences in absorption, metabolism, storage, andexcretion of toxicants, possibly resulting in higher doses to target tissues. Depending on the media,exposure for children may be more than for adults because of behavior patterns specific to children,such as a tendency to ingest dirt. In an effort to account for children's unique vulnerabilities, and inaccordance with ATSDR's Child Health Initiative [8] and EPA's National Agenda to ProtectChildren's Health from Environmental Threats [9], we used the potential exposure for children as a guide in assessing the potential public health implications of the contaminants.


Based on available information, we have concluded that current and future exposures to the sedimentand soil in and along Stewarts Creek and Little Caney Creek, downstream from the ConroeCreosoting Company site, pose no apparent public health hazard to adults or children. This is eitherbecause contaminants are not present at levels expected to cause a health problem and/or becauseunder current circumstances people are unlikely to come into contact with contaminated sedimentsoften enough or for long enough duration to result in health problems. Therefore, TDH and ATSDR have classified this site as posing no apparent public health hazard.


Actions Completed

  1. EPA has demolished the creosoting/PCP process unit, constructed the RCRA vault on thesite to contain the contaminated material, and has completed moving contaminated soiland material into the RCRA vault.

  2. EPA conducted additional characterization of sediment in Stewarts Creek and LittleCaney Creek and soil in residential yards and a schoolyard downstream of the ConroeCreosoting site in November 2002 and in April 2003.

  3. EPA has redirected site drainage to control surface water runoff. Additional contouring will be completed in the drainage area to direct the flow of rainwater to the creeks.

  4. TDH and EPA contacted and worked with church leaders and leaders of other communitygroups from the nearby neighborhoods to better address community health concernsabout the CCC site.

Actions Recommended

  1. None at this time.

Actions Planned

  1. EPA plans to fence the RCRA vault storage area and to post warning signs.

  2. TDH plans to assist EPA in addressing community health concerns by participating incommunity meetings.

  3. TDH will evaluate additional sampling information as needed and as data becomeavailable. Because the site was proposed for the EPA's National Priorities List, TDH willprepare a public health assessment for the Conroe Creosoting Company site by April2004.


This Health Consultation for the Conroe Creosoting-Stewards Creek Sediment was preparedby the Texas Department of Health (TDH) under a cooperative agreement with the federalAgency for Toxic Substances and Disease Registry (ATSDR). It is in accordance withapproved methodology and procedures existing at the time the health consultation wasinitiated.

Robert Knowles
Technical Project Officer, SSAB, DHAC

The Division of Health Assessment and Consultation (DHAC), ATSDR, has reviewed thishealth consultation and concurs with its findings.

Roberta Erlwein
Section Chief, SPS, SSAB, DHAC, ATSDR


Preparers of the Report

Susan L. Prosperie, M.S., R.S.
Environmental Specialist
Environmental Epidemiology and Toxicology Division
Texas Department of Health

John F. Villanacci, Ph.D.
Environmental Epidemiology and Toxicology Division
Texas Department of Health

ATSDR Regional Representative

Karl Markiewicz, Ph.D.
Regional Representative
ATSDR - Region 6

Jennifer Lyke
Regional representative
ATSDR, Region 6

ATSDR Technical Project Officer

Robert B. Knowles, M.S., R.E.H.S.
Environmental Health Scientist
Division of Health Assessment and Consultation
Superfund Site Assessment Branch
State Programs Section


  1. Texas Natural Resource Conservation Commission. Expanded screening inspectionreport: Conroe Creosoting Company. Austin: Texas Natural Resource ConservationCommission; 2002 June.

  2. Roy F. Weston, Inc. Removal assessment report: Conroe Creosoting, 1776 East Davis,Conroe, Montgomery County, Texas. Washington, DC: US Environmental ProtectionAgency; 2002 March.

  3. US Environmental Protection Agency. Conroe creosoting site, Conroe, Texas: fact sheetno. 2. Washington, DC: US Environmental Protection Agency; 2002 October.

  4. US Environmental Protection Agency Region 6. Sediment sampling data. Dallas: USEnvironmental Protection Agency Region 6; 2002 November.

  5. Agency for Toxic Substances and Disease Registry. Public health assessment guidancemanual. Atlanta: US Department of Health and Human Services; 1993.

  6. Agency for Toxic Substances and Disease Registry. Dioxin and dioxin-like compounds insoil, part 1: ATSDR interim policy guideline. Toxicol Ind Health 1997;13:759-68.

  7. US Environmental Protection Agency Office of Research and Development. Strategy forresearch on environmental risks to children. Washington, DC: US EnvironmentalProtection Agency; 2000 EPA/600/R-00/068, Sect. 1.2.

  8. Agency for Toxic Substances and Disease Registry. Child health initiative. Atlanta: USDepartment of Health and Human Services; 1995.

  9. US Environmental Protection Agency. The children's environmental health yearbook.Washington, DC: US Environmental Protection Agency; 1998.



ATSDR Agency for Toxic Substances and Disease Registry
CCA Copper chromated arsenic
CCC Conroe Creosoting Company
CERCLA Comprehensive Environmental Response, Compensation and Liability Act of 1980
CREG Carcinogenic Risk Evaluation Guide
EMEG Environmental Media Evaluation Guide
EPA United States Environmental Protection Agency
HAC Health Assessment Comparison Value
MRL Minimal risk level
NPL U.S. EPA National Priorities List
PAHs Polycyclic aromatic hydrocarbons
PCBs Polychlorinated biphenyls
PCP Pentachlorophenol
RCRA Resource Conservation and Recovery Act
RfD Reference dose
RMEG Reference Dose Media Evaluation Guide
SARA Superfund Amendments and Reauthorization Act of 1986
SVOCs Semi-volatile organic compounds
TCDD 2,3,7,8-tetrachlorodibenzo-p-dioxin
TDH Texas Department of Health
TNRCC Texas Natural Resource Conservation Commission
VOCs Volatile organic compounds


General Location and Demographic Information
Figure 1. General Location and Demographic Information


Table 1.

Constituents Exceeding Health-based Screening Values in Soil/Sediment Samples Collected November 13, 2003
  Benzo(a)pyrene Range; #/#* Arsenic Range; #/# Dioxins as TCDD equivalents #/#
Sediment Samples (mg/kg)
Stewarts Creek ND-3.0; 32/65 0.9U-19; 40/65 0/60
Stewarts Creek upstream of CCC ND-0.17; 4/7 1.0-5.0; 3/7 0/6
Onsite along Stewarts Creek ND-2.1; 4/5 2.7-22; 4/5 0.001399; 1/4
Little Caney Creek ND-0.39J; 3/26 0.96U-4.1; 21/26 0/24
Lake entry to Little Caney Creek ND; 0/2 4.6-18; 2/2 0/2
Lake ND-1.3; 1/6 1.2-30; 6/6 0/5
Soil Samples (mg/kg)
Residential ND-0.18J; 1/3 2.6-4.7; 3/3 0/3
School yard ND; 0/2 1.5-4.5; 2/3 0/2
Health-based screening values (mg/kg) CREG 0.1 CREG 0.5 <0.001

* #/# Number of samples exceeding health based screening value per total number of samples collected
ATSDR Action Level for TCDD equivalents in soil
ND not detected
estimated value
CREG Cancer Risk Evaluation Guide

1 To assess the potential health risks associated with the contaminants found in the various media (soil and creek sediment), TDH compared each contaminant detected with its health-based assessment comparison (HAC) values for non-cancer and cancer endpoints. TDH used either EPA's reference doses (RfDs) or ATSDR's minimal risk levels (MRLs) to derive the non-cancer HAC values. RfDs and MRLs are based on the assumption that there is an identifiable exposure threshold (both for the individual and for populations) below which there are no observable adverse effects. Thus, RfDs and MRLs are estimates of daily exposures to contaminants that are unlikely to cause adverse non-cancer health effects even if exposure occurs for a lifetime. The cancer risk comparison values used in this consultation are based on EPA's chemical-specific cancer slope factors (CSFs), an estimate of excess lifetime risk of one cancer in one million (1 x 10-6) exposed people and an exposure period of 70 years. TDH used standard assumptions for body weight (15 kilograms, child; 70 kilograms, adult) and soil/sediment incidental ingestion rates (200 milligrams per day, child; 100 milligrams per day, adult) to calculate the HAC values.

Health assessment comparison (HAC) values are guidelines that specify levels of chemicals in specific environmental media (soil, air, and water) that are considered safe for human contact. Because many of the assumptions used to calculate HAC values are conservative with respect to protecting public health, exceeding a HAC valuedoes not necessarily mean that adverse health effects will occur. However, exceeding a HAC value does suggest that potential site-specific exposure to the contaminant warrants further consideration.

2. Although dermal absorption via skin contact with contaminated soil/sediment may have been a concern during heavy rainfall and flooding of yards along the creek, the contaminants in the soil and sediment were more likely to remain joined on the soil/sediment particles than to cling to and absorb into the skin of people who may have come in contact with flood water.

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