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Methanol: Fate and Transport in the Environment

Rula A. Deeb, Todd L. Anderson, Michael C. Kavanaugh, and Lauren A. Kell

Arcadis U.S., Inc., Emeryville, CA, USA

2.1 Introduction

2.1.1 Release Scenarios

In the United States in 2007, methanol ranked fourth among all chemicals reportedly released by industry to the environment as noted in annual Toxics Release Inventory (TRI) reports required by the U.S. Environmental Protection Agency (USEPA) (USEPA, 2009). These releases were primarily from paper, chemicals, and wood products industries (USEPA, 2009). As shown in Table 2.1, methanol releases from industry in 2006 and 2007 in the United States were primarily to the atmosphere; however, ~15–19% of methanol was directly discharged into groundwater, soil, or surface water during these years. The total reported volume of methanol released to the U.S. environment represents ~1.5% of the total U.S. production volume. In 2001, the United States produced an estimated 3.5–4 million metric tons (mt) of methanol (DeWitt, 2002), with roughly 1.5–2 million of this being “merchant” (for transport/sale) and the remaining 2 million metric tons created and used at the same facility as a feedstock for other products (DeWitt, 2002). Monitoring of methanol in the atmosphere, surface water, or groundwater is generally not required; neither the Clean Air Act (CAA), Clean Water Act (CWA), nor Safe Drinking Water Act (SDWA) includes methanol monitoring requirements. Thus, national monitoring data sets and information on methanol occurrence in air or water are not available (Zogorski et al., 1997).

Table 2.1 Estimated Releases of Methanol in the United States by Industrial Sources.

Source: USEPA (2009).

Reported Release to 2006 (million pounds/year) 2007 (million pounds/year) Atmosphere 145 129 Underground injection 19 13 Land 8 4 Surface water 6 5 Total releases 178 151

This chapter evaluates the fate and transport of methanol in soil, groundwater, and surface water in the context of three methanol release scenarios. The three scenarios are as follows:

Scenario 1: Rail Car or Tank Truck Release. Most of the methanol used in North America is imported from overseas. In one estimate, ~7.1 million metric tons was imported in 2006 (PCI-Ockerbloom & Co. Inc., as cited in Alliance Consulting International, 2008). Another estimate puts this value at 5.4 million metric tons as of 2002 (DeWitt, 2002). Once it reaches a port, it must be transported via rail or truck to its final destination. Approximately 1.6 million “merchant” metric tons produced per year in North America (as of 2006) often must be transported to the point of use as well (PCI-Ockerbloom & Co. Inc., 2008). Rail cars and tanker trucks are the two primary land-based methods of inland transportation of methanol (DeWitt, 2002). An accidental release from a rail car or tank truck could take place in a variety of physiogeographical settings, depending on railway and highway alignments, and possibly including environmentally important features such as the desert, the coast, or drinking water sources. A single rail car could release as much as 30,000 gallons (100 mt) of methanol (DeWitt, 2002; Perry et al., 1984) if fully emptied during such an event. A typical truckload of methanol is 8000 gallons (24 mt) (DeWitt, 2002). To give an example of scale, in 1994, ~1400 truckloads were delivered throughout California (CEC, 1994). Scenario 2: Ship or Barge Release. More than 80% of methanol produced in the world is shipped between continents (Alliance Consulting International, 2008). In 2007, ~40 million metric tons of methanol were consumed worldwide (Alliance Consulting International, 2008). Ocean releases could occur since the vast majority of methanol imported into the United States is by ship, and river releases could occur since barges are used for intergulf or river transport of methanol from regional ports. Typical river barges can carry just under 418,000 gallons, or ~1255 mt (DeWitt, 2002). Deep-sea transport of methanol increased dramatically during the 1980s and 1990s. Smaller to midsize dedicated methanol ocean-going tankers range in size from ~20,000 to 50,000 mt; some dedicated methanol tankers have a capacity of ~100,000 mt (Waterfront Shipping Company Limited, 2010). This corresponds to a volumetric range of oceangoing ship capacities from ~5 to 32 million gallons (MG). Assuming that methanol imported from Canada to the United States is transported entirely by rail (or truck), and methanol imported from the remaining four primary importing countries (Trinidad, Chile, Venezuela, and Equatorial Guinea) is transported by tanker ship, roughly 1.3 billion gallons (BG) of methanol is imported to the United States each year by ship (DeWitt, 2002), corresponding to perhaps 75 tanker trips. Scenario 3: Storage/Fueling Facility Release. The third conceptual scenario involves the accidental release of methanol to the environment at a fueling or a storage facility. Methanol is stored at docks and marine terminals in floating roof tanks; these typically have elaborate leak detection and safety systems. Methanol is also stored in aboveground tank farms with aboveground piping and leak detection and fire suppression systems. While spills may occur in these mass storage facilities, the larger concern is the possibility of releases at smaller distribution facilities and from totes and drums (Alliance Consulting International, 2008). As discussed further in Section 2.2, methanol is a commonly used carbon source for denitrification at wastewater treatment plants throughout the United States.

At distribution facilities, methanol underground storage tank (UST) systems are generally similar to gasoline systems, although some differences in materials used may exist (SWRCB, 1999a). New, upgraded UST systems are double-walled and typically have an interstitial leak detection device or other leak detection mechanism. Leak detection depends upon a number of factors, such as the location, volume, and velocity of the leak. Most commonly, leaks occur at the joints or at the dispenser; if a leak occurs at the dispenser it may not be detected. Leak detection systems can be subject to human error because alarms can typically be just turned off without action being taken. Studies have found that while newer USTs are less likely than older, single-walled tanks to leak, even upgraded USTs experienced leaks (SWRCB, 1999b). Whether leaked material enters the environment also depends on the presence of a catch or drip pan. Because of all the potential leak scenarios from a UST, there are large differences in the amount of fluid that may enter environment in this scenario. It is conceivable that methanol releases may occur at methanol fueling facilities at a rate similar to gasoline UST releases. If methanol USTs are located at or near a gasoline dispensing location, subsurface methanol releases may encounter existing gasoline contaminant plumes. Similarly, methanol releases may also encounter chlorinated solvent plumes or other subsurface contamination. In any case, this third scenario represents another important potential route of methanol release to soil and/or groundwater.

2.1.2 Fate in the Environment

Methanol occurs naturally in the environment because of various biological processes in vegetation, microorganisms, and other living species (ENVIRON, 1996). Nevertheless, a large release of methanol to the surface water, soil, or groundwater has the potential to adversely impact the surrounding environment.

Once released into surface waters or the subsurface environment, the fate of methanol depends on numerous environmental factors including: the nature and quantity of the release and physical, chemical, and biological characteristics of the impacted media. Various reports summarize estimates of possible methanol half-lives (the time required for a 50% reduction in concentration) (Table 2.2) in various environmental media. In the atmosphere, methanol would be photooxidized relatively quickly; its reported half-life ranges between 3 and 30 days. In soil or groundwater, rapid biodegradation is expected as well, with reported half-lives ranging from 1 to 7 days. Finally, in surface water following a pure methanol spill, methanol would also be expected to diminish quickly; reported half-lives are between 1 and 7 days as well. In Table 2.2, reported methanol half-lives are compared to those of benzene to illustrate the relatively rapid degradation of methanol.

Table 2.2 Reported Half-Lives of Methanol and Benzene in the Environment.

Source: Adapted from Howard et al. (1991).

Environmental Medium Methanol Half-Life (Days) Benzene Half-Life (Days) Soil (based on unacclimated grab sample of aerobic/water suspension from groundwater aquifers) 1–7 5–16 Air (based on photooxidation half-life) 3–30 2–21 Surface water (based on unacclimated aqueous aerobic biodegradation) 1–7 5–16 Groundwater (based on unacclimated grab...