Sabine River Authority of Texas Summary Report MtBE Contamination in Lake Tawakoni from Gasoline Pipeline Rupture INTRODUCTION

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Anissa McCormick
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1 INTRODUCTION On March 9, 2000, a gasoline pipeline several miles northwest of Greenville, Texas ruptured, spilling an estimated 600,000 gallons of reformulated gasoline into a pasture and a tributary of East Caddo Creek. The reformulated gasoline contained methyl tertiary-butyl ether (MtBE), which is difficult to remove from natural waters due to its chemical properties. MtBE has been the cause of significant environmental concern throughout the United States in the last several years because of its tendency to contaminate groundwater. Rainfall the day after the spill flushed a significant amount of the spilled gasoline 28 stream miles downstream into Lake Tawakoni, a reservoir owned and operated by the Sabine River Authority of Texas (SRA). SRA initiated monitoring of the reservoir and East Caddo Creek on March 12. Unless otherwise specified, all discussion of monitoring in this report refers to SRA s activities. The reservoir was monitored on a daily basis for several weeks until MtBE levels dissipated. Monitoring was then shifted to a regular periodic pattern, as well as after each precipitation event in the East Caddo Creek watershed. Monitoring continues in East Caddo Creek and at the head of the Caddo Inlet arm of Lake Tawakoni, where the creek flows into the reservoir, as remediation of the gasoline release is ongoing. 1.1 Physical Setting Lake Tawakoni, owned and operated by SRA, is located approximately 50 miles east of Dallas, Texas in portions of Hunt, Rains, and Van Zandt Counties. Construction on the reservoir began in 1955 and was completed in Lake Tawakoni has a surface area of about 36,700 acres. The reservoir s watershed encompasses approximately 756 square miles (SRA 2000). Three major tributaries drain into the reservoir: the South Fork Sabine River from the west, Caddo Creek from the northwest, and the Cowleech Fork Sabine River from the north. The release occurred in the upper reaches of the Caddo Creek subwatershed near East Caddo Creek, approximately 28 stream miles upstream of Lake Tawakoni. The East Caddo Creek subwatershed accounts for slightly less than eight percent of the reservoir s total drainage area. Figure 1.1 is a map showing the watershed boundaries in the area of Lake Tawakoni and the spill site. Page 3

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3 The United States Geological Survey (USGS) maintains gaging stations in Cowleech Fork and South Fork, but no station is currently present in East Caddo Creek to measure flow. Historical flow measurements conducted by SRA in East Caddo Creek have ranged from less than one cubic foot per second (cfs) to 224 cfs. At the time of the spill, the creek was dry upstream of Interstate Highway 30 (IH-30) and perennial pools were present downstream toward Lake Tawakoni Spill Site Geology The spill site is located on calcareous clay and marl of the lower portion of the Upper Cretaceous Marlbrook Marl Formation. The marl unit is characterized as a medium gray, silty, sandy, calcareous clay unit that weathers light gray. The thickness of the Marlbrook Marl is mapped at approximately 300 feet in Hunt County (BEG 1967). The Marlbrook Marl is underlain by the Pecan Gap Chalk that is characterized as sandy, bedded, bluish white, limesand and chalk. The Pecan Gap Chalk has not been observed in soil borings completed as deep at the site as 18 feet or in excavations completed to date by Explorer during the site clean up operation. The Marlbrook Marl and similar Cretaceous clay formations in the region are known to weather to depths ranging from five to twenty feet below surface grade. The weathered clay zones are typically pervasively jointed and discolored due to movement of precipitation through the zone. Shallow clays within the weathered zone are normally clayey, allowing healing of joint openings during periods of soil wetting. Deeper soils of the weathered clay interval are typically harder and less clayey causing, minimal, seasonal healing and closing of the joint openings East Caddo Creek Geology Quaternary Alluvium and Fluviatile Terrace Deposits of the East Caddo Creek tributary of Lake Tawakoni traverse the outcrops of the Marlbrook Marl, Neylandville Formation, Nacatoch Sand, and the Kemp Clay in ascending order of age. Figure 1.2 is a map depicting the surface geology from the spill site to Lake Tawakoni. Page 5

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5 The Quaternary Alluvium and Terrace Deposits are characterized as clay, silt, sand, and gravel soils that were deposited by the tributary over the Cretaceous formations listed above. Similar to the Marlbrook Marl, the Neylandville and the Kemp Clay formations are calcareous clay units that are mapped to measure approximately 800 feet thick in the area (BEG 1967). The clay formations are anticipated to have weathered zones that extend below surface grade by five to 20 feet. The Nacatoch Sand formation is a silty, fine-grained, sand unit mapped approximately 200 feet thick in the region Regional Structural Geology Cretaceous formations in the region strike northeast and dip to the southeast at approximately ten feet per mile. Northeast-southwest trending, normal faults of the Mexia-Talco Fault System traverse along the western side of Lake Tawakoni and in the Nacatoch Sand outcrop south of the spill site. Displacements along faults of the Mexia- Talco Fault System are pre-quaternary, affecting only Tertiary and older strata Groundwater Resources Minimal groundwater storage and distribution is anticipated in the Marlbrook Marl at the location of the spill site or in the Neylandville and Kemp Clay formations located to the south. Occurrence of a small quantity of perched groundwater is anticipated in these formations in areas of low topography and near surface water. None of the clay formations listed above are classified as aquifers in the state of Texas. Permeabilities of the clay formations are low, but jointing of these formations in the weathered zone typically yields hydraulic conductivity values in the range of 0.03 to 0.3 feet per day. The Nacatoch Sand is characterized as a minor aquifer in the state of Texas. Groundwater in the Nacatoch Sand is utilized as a drinking water resource by private individuals located in the Lake Tawakoni area and to the southeast. East Caddo Creek traverses the Nacatoch Sand outcrop approximately 17 miles downstream of the spill site, although Quaternary Alluvium overlies the Nacatoch Sand in the creek Soils The spill is located in the Leson-Houston Black general soil map unit in Hunt County. The contamination migrated to the Kaufman-Tinn general soil map unit that comprises the riparian areas along the streams that lead to the reservoir. The Leson- Houston Black unit is described as being clayey, deep, gently sloping, and moderately Page 7

6 well drained. It has one to five percent slopes and comprises about thirty percent of Hunt County soils. The spill site is located on Houston Black soils, which comprise about 26 percent of the Leson-Houston Black unit. Houston Black soils are gently sloping in broad areas. Typically, moderately alkaline clay extends to a depth of 64 inches. This soil is black and dark gray with brownish mottles. Below this layer, to a depth of 86 inches, the soil is moderately alkaline shaly clay. The Kaufman-Tinn unit is described as being clayey, deep, nearly level, and somewhat poorly drained. This unit has soils on floodplains that have slopes from zero to one percent. These soils cover 11 percent of Hunt County. Kaufman soils are on the large floodplains of the major rivers and streams carrying mainly calcareous sediment. Typically the soil is black clay to a depth of about 53 inches. East Caddo Creek flows along Kaufman soil beginning at its confluence with Farber Creek, approximately seven miles from Lake Tawakoni and 21 miles downstream from the spill. The creek bed upstream nearly to the spill site consists of Tinn soils. These soils are similar to Kaufman soils except that they are a black clay to a depth of about 76 inches (USDA 1981). 1.2 Sabine River Authority of Texas The Sabine River Authority of Texas (SRA) is a governmental agency of the state of Texas created in 1949 as a conservation and reclamation district with responsibilities to control, store, preserve, and distribute the waters of the Sabine River and its tributary system for useful purposes. SRA s boundaries comprise all of the area lying within the watershed of the Sabine River and its tributary streams within Texas. The watershed area in Texas includes all or parts of twenty-one counties. SRA owns and operates Lake Tawakoni and Lake Fork in Northeast Texas. Toledo Bend Reservoir, on the border of Texas and Louisiana in Southeast Texas, is jointly operated by SRA and the Sabine River Authority of Louisiana. Lake Tawakoni construction began in 1955 and was completed in The primary purpose of Lake Tawakoni is for water conservation and supply. Water is sold by SRA to numerous water customers in the vicinity of the reservoir. The reservoir storage capacity is 927,440 acre-feet at the conservation pool elevation of feet above mean sea level (msl) (SRA 2000). Page 8

7 The city of Dallas has rights to eighty percent of the water available from Lake Tawakoni. The City s raw water intake is located on the southern bank of the mouth of Kitsee Inlet near the main body of the reservoir. The cities of Commerce, Greenville, Wills Point, Point, Emory, Terrell, West Tawakoni, East Tawakoni, and Edgewood also use Lake Tawakoni for their drinking water supply source. Cash Water Supply Corporation (WSC), Combined Consumers WSC, MacBee WSC, and South Tawakoni WSC also supply water taken from the reservoir to cities and unincorporated areas in the vicinity. Figure 1.3 is a map showing the location of each raw water intake in Lake Tawakoni. Public recreational use of the reservoir and its affiliated parks is another benefit of Lake Tawakoni. It is a popular sport-fishing destination, known for excellent sand bass fishing, as well as striper, catfish, and largemouth bass. SRA has constructed picnic tables, comfort stations, boat ramps, and other recreational facilities around the reservoir for the public s use. Wind Point Park, located on 350 acres on the northeast shore of the reservoir, is a major recreational development owned and operated by SRA providing complete facilities for weekend campers. 1.3 Explorer Pipeline Company Explorer Pipeline Company owns and operates a 1,400-mile pipeline system transporting primarily gasoline, fuel oil and jet fuel from Gulf Coast refineries and import facilities in Texas and Louisiana into the mid-western United States. Major city markets served directly include Houston, Dallas, Fort Worth, Tulsa, St. Louis and Chicago. Through connections with other pipelines, Explorer serves more than seventy major population centers in sixteen states. Explorer does not buy or sell petroleum products. It only provides transportation services. Page 9

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9 The pipeline system has been in operation since The mainline pipe is twenty-eight inches in diameter from Port Arthur, Texas to Tulsa, Oklahoma and twenty-four inches in diameter from Tulsa to Hammond, Indiana. The system presently has a line capacity of about 22 million gallons per day on the twenty-eight inch line segment. Explorer is a Delaware corporation and has offices in Tulsa, Oklahoma. Corporate stock is owned by subsidiaries of Chevron, CITGO, Conoco, Marathon, Phillips, Sun, Texaco, and Equilon (a Shell/Texaco joint venture). Approximately half of all present product transport is for non-owner companies. Products move through the pipeline at about four miles per hour for a delivery rate of about 15,000 gallons per minute. Electric motor driven pumps at remotely controlled unattended booster pump stations move the products through the pipeline. According to Explorer, automatic alarm systems enable the central dispatching center to quickly and safely shut down any and all system operations in the event of an emergency (Explorer 2000). 1.4 Properties of MtBE and Other Gasoline Components The product released in the pipeline rupture was refined gasoline reformulated with MtBE for cleaner-burning properties. MtBE was present in the spilled gasoline at a concentration of nine percent by volume. All the components in the gasoline were relatively volatile. MtBE, however, has properties unique to other gasoline compounds that cause it to be a more persistent contamination problem General Gasoline Components Gasoline is a mixture of many different hydrocarbons. Benzene, toluene, ethylbenzene, and xylene (BTEX) are typically the primary gasoline constituents. Benzene, a known carcinogen, was present at a concentration of approximately five percent in the spilled gasoline (Explorer 1999). Other components include trimethylbenzenes, naphthalene, and propylbenzene, although many other hydrocarbons are usually present at low concentrations. Gasoline compounds are usually very insoluble in water, are less dense than water, and evaporate relatively quickly from the water surface. When gasoline comes into contact with surface water, it floats on the surface, forming a separate layer. This property provides opportunities to contain and collect spilled gasoline from water. Page 11

10 Methods used as part of the spill response are discussed in Section 5 (Treatment and Remediation) of this report MtBE Methyl tertiary-butyl ether (MtBE) is a small organic molecule composed of carbon, hydrogen, and oxygen. Most gasoline components, known as hydrocarbons, consist only of carbon and hydrogen. It is the presence of an oxygen atom that provides MtBE with unique properties relative to other gasoline components. MtBE is a primary additive in reformulated gasoline, which is used to CH 3 improve air quality in certain designated areas of the United States that do not meet National Ambient Air Quality Standards H 3 C O C CH 3 set forth in the Federal Clean Air Act of The Reformulated Gasoline CH 3 Program, administered by the EPA, requires a minimum oxygen content of Molecular Structure of MtBE two percent in reformulated gasoline. While other oxygen-rich chemicals, or oxygenates, are available, MtBE is currently the most prevalent additive used to meet the reformulation requirement. Cornbased ethanol is another oxygenate that is used to a lesser degree in reformulated gasoline. The increased level of oxygen in gasoline is intended to promote more complete combustion, thereby reducing emissions of carbon monoxide, nitrogen oxides, and volatile organic compounds. Lowering emissions of these pollutants will reduce groundlevel ozone concentrations to within federally acceptable levels. Houston, Chicago, and seven other cities throughout the United States were required to implement reformulated gasoline by the Clean Air Act of Several other metropolitan areas, including the Dallas/Fort Worth metroplex and St. Louis have voluntarily opted into EPA s Reformulated Gasoline Programs as a method to improve air quality in their respective regions. Page 12

11 MtBE is forty times more soluble in water than other gasoline compounds. At 75ºF, the water solubility of MtBE in oxygenated gasoline containing ten percent MtBE is 5,000,000 ppb, or 0.5%. Pure MtBE is ten times more water-soluble. By comparison, non-oxygenated gasoline has a total hydrocarbon solubility of 120,000 ppb. Because of its affinity for water, MtBE evaporates slowly to the atmosphere from surface waters. The equilibrium that can be established between concentrations of a chemical in the air and water can be described by Henry s Law. Henry s Law constant can be used to compare the volatility of chemicals from water. MtBE has a dimensionless value of 0.022; benzene, which is fairly insoluble in water, has a value of Chemicals with Henry s Law constant values greater than 0.05 are considered to be very volatile from water (Squillace 1998). MtBE will adsorb to granular activated carbon, an effective medium for volatile organic chemical removal from waters. Because of its low molecular weight and high water solubility, MtBE does not adsorb to carbon as cost-effectively as other gasoline components. Frequent replacement or regeneration of the carbon is typically necessary to maintain high removal rates of MtBE from water (Suffet 1999). MtBE is considered by the EPA to be a possible carcinogen based on several research studies. A drinking water advisory published by EPA in 1997 evaluated the toxicity and carcinogenicity of MtBE but did not issue a health effects advisory limit. The advisory indicated that there is little likelihood that MtBE in drinking water will cause adverse health effects at concentrations between twenty and forty ppb or below (USEPA 1997). TNRCC experts have stated that no adverse impact to an individual will occur if water contaminated with 240 ppb is consumed over the period of a lifetime. MtBE is noticeable for its objectionable taste and odor at much lower concentrations than the health-based limits set by EPA or the TNRCC. MtBE tastes and smells like turpentine. The EPA has established a taste and odor threshold of twenty to forty ppb in drinking water for aesthetics purposes. The TNRCC taste and odor threshold for MtBE drinking water contamination is 15 ppb. Page 13

Sabine River Authority of Texas Summary Report MtBE Contamination in Lake Tawakoni from Gasoline Pipeline Rupture 5. TREATMENT AND REMEDIATION

Sabine River Authority of Texas Summary Report MtBE Contamination in Lake Tawakoni from Gasoline Pipeline Rupture 5. TREATMENT AND REMEDIATION 5. TREATMENT AND REMEDIATION Explorer is responsible for the treatment and remediation of areas contaminated by the gasoline spill, including the reservoir. Explorer has worked cooperatively with SRA to