APEA Conference - A Radical Change in Forecourt Drainage Treatment Author - Zoë Sands Oceans ESU Ltd INTRODUCTION Oceans-ESU were invited to speak at the APEA conference due to their involvement in the development of a system that aims to be an alternative to the oil-water separator. As well as product development and technology implementation Oceans-ESU are involved in environmental consultancy in water and wastewater management and the development of contaminated land. This article presents the main drivers for change in the management of water resources at petrol filling stations (PFS), and describes some innovative solutions for consideration in planning new PFS or refurbishing older installations.
DRIVERS FOR CHANGE There are a number of drivers for change within the petrochemical sector at the present time. Firstly environmental liabilities, in terms of required compliance with legislation have greatly increased over the past five to ten years. As large-scale industry has become more compliant the Environment Agency (EA) are beginning to apply more pressure for companies to address the issue of small and diffuse pollution sources. One of these issues is that of levels of hydrocarbons in urban runoff. Accidents such as tanker spillage, pipeline breaks and well blowouts account for less than 10% of the annual discharge into protected groundwater and surface waters. The vast majority of hydrocarbon pollution is from small but frequent spill events. Two main pieces of legislation affect the petrol forecourt operator. Firstly the Environmental Protection Act of 1990, and secondly the Water Resources Act 1991. Between them these allow the enforcement of the ‘‘polluter pays” principle and lay the responsibility firmly at the feet of the site owner to ensure that all reasonable steps are taken to prevent discharge of polluting substances to ground or surface waters. To help operators with understanding and complying with legislation the EA produce a series of pollution prevention guidelines, (PPG’s), two of which (PPG 3 and PPG 7) relate to the design of drainage from petrol forecourts and the design and installation of oil-water separators. The second major driver for change is the increasing environmental awareness of customers, and the growing need for companies to be seen as pro-active in their approach to tackling their internal environmental impact. Companies are reaping the financial benefits of effective environmental management systems, as policies that promote the sustainable use of resources will ultimately lead to lower internal costs, as well as safeguarding against the increasing cost of prosecution for pollution of soil, water or air.
Thirdly, the future will bring increases in charges for use and disposal of water. As the implications of the Water Resources Act, the Groundwater Protection Act (1998), and the Urban Wastewater Directive increase the privatised Water Companies costs so those costs are likely to be passed forward to the consumer. This will increase the cost effectiveness of water re-use and recycling schemes. Hydrocarbon pollution from the forecourt comes primarily from spillage at the pump, this issue is being addressed by those involved in the development of petrol delivery equipment, but any system is likely to be imperfect, and the collection and treatment of the forecourt run-off is likely to have to continue. Currently petrol stations use oil-water separators for treatment of the run-off from under the canopy. These systems where they are managed effectively treat the water to the required standard of less than 5ppm TPH. There are, however, many sites where the systems are imperfect and unacceptable levels of hydrocarbon are released, either due to failing aged equipment, or lack of required maintenance. The oil-water separator requires regular cleaning, and the cost of disposal of the collected floating product and sludge is increasing with rising landfill charges and cost of haulage.
These drivers led Oceans-ESU to seek a sustainable solution to the problem of on-site treatment of forecourt drainage, aiming to provide a low maintenance system that would treat the hydrocarbons rather than simply separating them.
WHY REED BEDS? Reed beds were first used for wastewater treatment in the nineteen sixties, but though they were sporadically installed for domestic and industrial effluent treatment during the sixties and seventies, their popularity really rose during the late eighties and nineties. This coincided with a general increase in awareness about “the environment”, concerns over global warming and the increased powers of enforcement given to the EA. Companies were feeling the major cost implications of installation of wastewater treatment plant, and the revenue requirements of operating and maintaining the installation.
system the wastewater comes into contact with the wide range of micro-organisms that occur in high densities on the surface of the growing media and around the plant roots. Where fine particle size media are used (soils and fine sands), the number of micro-organisms is very significant. Additionally in the soil based system the inherent reactivity of the clay particles and humic particles within the matrix can be exploited as a measurable contributor to the treatment process.
Reed beds are a solution to wastewater treatment that incur lower capital costs than conventional plant, provide reliable and robust treatment performance and have very low operations and maintenance requirements. They are particularly popular for remote locations, without a costeffective sewer connection. Their added benefits of wildlife habitat creation, and the PR possibilities afforded by their installation have made them an attractive alternative. Water Companies have commonly used reed beds for tertiary or stormwater treatment at small and medium scale sewage works. Oceans-ESU have concentrated on industrial wastewater treatment and currently operate systems that were designed for ICI, Air-Products, BP, Corus, BHP and Shell at various locations world-wide. Typical applications include the treatment of hydrocarbon contaminated groundwater, tip leachate, coke oven effluent,
chemical manufacturing plant effluent and piloting the treatment of produced water from oilfields in the Middle East. Reed bed treatment systems are self-contained, artificially engineered, wetland ecosystems, They are designed to optimise the microbiological, chemical and physical processes naturally occurring in the wetland. Wetland plants, such as reeds, transfer atmospheric oxygen down through their roots in order to survive in waterlogged conditions. This creates ‘both aerobic and anaerobic soil conditions, allowing extraordinary microbial species diversity to flourish. These bacteria and fungi can use organic pollutants as a food source, breaking down a wide range of organic chemical products. So, chemicals are not simply stored in the reed bed; they are actually degraded into harmless components. Other contaminants, such as metals, are transformed from a toxic, mobile state and fixed in the soil via complex chemical reactions. Soils adsorption capacity also provides a buffer for peak or shock effluent loads. The complexity of microbial life and powerful reactions within the root zone of the soil based reed bed result in an extraordinary water cleaning capability. This capability is often far less constrained than in many chemical or physical wastewater treatment systems. Reed beds are designed so that the water flows just beneath the surface of the soil. Using the sub-surface flow
REED BEDS ON THE FORECOURT In March 1998 Oceans ESU won European Funding (a Department of Trade and Industry 'Smart' Award) to undertake a feasibility study for the development of reed bed technology for the treatment of hydrocarbon contaminated wastewater from petrol station forecourts. Initially small-scale systems were trialed under laboratory conditions and encouraging results were achieved with Total Petroleum Hydrocarbon (TPH) removal rates ranging from 85 98%, depending upon the soil-type used in the system. The reeds thrived in the wastewater, and new growth occurred throughout the experimental period.
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Larger experimental reed tub systems were established at an outdoor site in winter of 1998, using HDPE containers, of approximately 1 m ³ volume. Loading of these tubs began at the end of May 1999, and has continued into the winter of 2000/2001. Treatment results have been continually good, with results in excess of 98% Diesel Range Organics (DRO) and more than 99% for Petrol Range Organics (PRO). A pilot trial site was also set up in 1998 at a BP forecourt in Sheffield; this facilitated testing the equipment in the “real” situation. Water was drawn from the first chamber of the existing interceptor, passed through the reed tubs and released back into the interceptor. The results from this trial were again positive with outlet levels of TPH well in excess of the current 5ppm required of oil-water separators. A full scale reed tub was installed in Northampton for BP in December 2000. The system measures 2 x 3 x 1m, and was installed into a pre-constructed void. The system is to be closely monitored to assess its performance in situ.
direct use, and the equipment that is required for storing and cleaning the water is minimal. Water enters the storage tank via a vortex filter that uses no external power source. During periods of very low rainfall the tank is topped up by the mains by a delayed action float valve. Water is delivered for use by a booster pump, and dependent upon the applications that the water is destined for UV disinfection may be recommended. Much of the progress in rainwater harvesting has occurred in Germany, where water is universally metered and, in some areas, supplied at 3-4 times the costs of that in the UK. As mentioned earlier in this article the costs for water supply and disposal in the UK are likely to increase. It is also possible that costs will be imposed for the disposal of rainwater from roofs and hardstanding areas. A trial is currently underway in Nottingham to assess the feasibility of imposing this charge, as an incentive to direct stormwater away from the overloaded sewerage system, and into soak-away or re-use systems. Such a charge is very likely to increase the cost effectiveness of rainwater harvesting systems.
As well as the treatment of hydrocarbon contaminated drainage from the forecourt, reed bed systems can be used as part of a more comprehensive drainage management plan. The application of Sustainable Urban Drainage Systems (SUDS) is becoming more popular across the UK, and was the subject of a Scottish Environmental Protection Agency (SEPA) report published in 1999. SUDS aim to use “natural” systems such as wetlands, ponds and swales to attenuate stormwater flow and filter out pollutants. This has the effect of taking the pressure off overloaded stormdrains and directing much of the stormwater fall back into groundwater via infiltration basins rather than through sewage treatment plants. Natural systems can also be applied for treatment of foul drainage, car wash spent water and oily sludges. They are particularly suitable for rural sites, where land is available for installation.
FORECOURTS OF THE FUTURE
Water management at the forecourts of the future is being driven by pressure from legislation and consumers. Legislation is raising the standards required in environmental performance, with the aim of improving the cleanliness of our soil, air and water resources. As well as applying standards for discharge of pollutants, pressure is also beginning to be applied by the water companies, as they strive to meet their own objectives in the light of new statutory obligations.
At the Northampton site, reed beds have been installed for treatment of the foul drainage from the petrol station and a McDonalds on the same site. Stormwater from the site and roofs is directed through a planted filter and into a stormwater basin prior to final discharge to a local watercourse. It is hoped that this site will provide a showcase for these uses of natural technologies.
Innovative companies are rising to the challenge by developing products that provide sustainable solutions to problematic waste management issues. Natural systems such as reed beds are capable, robust, require little operational input and provide a very real alternative to traditional forecourt solutions. Reducing increasing water bills by managing water demand, and undertaking to re-use or recycle water where possible is likely to become an important aspect of new station design.
RAINWATER HARVESTING
In addition to the sustainable treatment of wastewater from a petrol forecourt, savings can be made through the recycling of water treated on site, and by the collection of rainwater for use in suitable areas. Oceans-ESU teamed up with GTA Ltd at the APEA Conference to present rainwater harvesting as a product for the future.
Improvements in the environmental performance of a PFS can now be made with products that are available at comparable or lower costs to their traditional alternatives. Other water saving and recycling products can be installed that will pay back in increasingly shorter periods as water charges grow.
It is important to first address the health and safety issues concerned with the use of harvested rainwater. The water is safe for no-contact uses such as; Toilet flushing - Urinals - Washing machines - Cleaning purposes - Car washes - Garden watering
FOR FURTHER INFORMATION Reed Beds and Wastewater Management Helen Fazakerley, Oceans-ESU Tel: ++ 44 (0) 1274 480033 h.fazakerley@oceans.co.uk
Before any scheme is implemented a full risk assessment would be undertaken to ensure that the public and employees are protected from any microbiological hazards in the rainwater. The potential for using rainwater or other recycled water on the forecourt is very significant, as water used for the purposes mentioned above typically amounts to more than 60% of total demand in commercial properties. Rainwater can be harvested from the main canopy and kiosk roof for
Rainwater Harvesting
Jeff Horwood Tel: ++ 44 (0) 1444 871444 enq@gtagroup.co.uk 22
Concerns for
TBE Pollution in Groundwater
(A view from the USA)
An article prepared by Shahla Dargahi Farahnak, P.E. and Erin Ragazzi, California, for presentation by Shahla Dargahi Farahnak at the November 2000 APEA Convention, London. MTBE - an oxygenate for better air but a major threat to the quality of groundwater and surface water resources. The use of methyl tertiary butyl ether (MTBE) as an oxygenate additive in gasoline throughout the United State has lead to groundwater contamination that threatens the nation’s drinking water supply and groundwater resources. Most states now routinely require testing for MTBE and other oxygenates at leaking underground storage tank (UST) sites. Drinking water programs are also mandating reporting of detectable levels of MTBE in drinking water samples (Association of State and Territorial Solid Waste Management Officials [ASTSWMO], 2000). It is estimated that 70 percent of all gasoline used in the United States contains MTBE at varying concentrations. MTBE was first used (2-8% by volume) to enhance fuel octane in 1979, to transition from leaded to unleaded fuel. The 1992 Oxyfuel and 1995 reformulated gasoline (RFG) programs were initiated by the United States Environmental Protection Agency (US EPA) to meet requirements of 1990 Clean Air Act amendments. The Oxyfuel program requires use of gasoline with 2.7% oxygen (by weight) in areas with high levels of carbon monoxide during the fall and winter. Ethanol (blended at 7.3% by volume) and MTBE (blended at 15% by volume) were the oxygenates of choice for meeting these requirements. The RFG program requires 2% oxygen (by weight) throughout the year in the most polluted metropolitan areas (including most of California). The primary oxygenate of choice to meet the year-round requirements and to get cleaner burning fuel with low emissions was MTBE, and hence the statewide use of MTBE (at 11% by volume) began in California (United States Environmental Protection Agency [US EPA], 1998). The petroleum industry preferred MTBE over ethanol for octane enhancement and RFG because it is less expensive, more compatible (compared to ethanol) with gasoline, can be blended at the refinery and distributed with gasoline through pipelines, and generates a lower vapor pressure gasoline. MTBE is a colorless liquid at room temperature that is highly water-soluble (30 times more soluble than benzene), is poorly adsorbed to soils (hydrophilic) and therefore migrates with groundwater, and responds very slowly to biodegradation. Wide-spread use of MTBE at high concentrations, combined with chemical properties that
render it resistant to breakdown create the potential for high source area concentrations, long plumes in groundwater, and long residence times in the subsurface (State Water Resources Control Board [SWRCB], 2000). MTBE’s distinctive turpentine-like odor and taste render drinking water resources unacceptable to consumers at extremely low concentrations and well below the health advisory levels. In California, odor and taste thresholds for MTBE in water have been reported to range from 15 to 95 parts per billion by volume [ppbv] and a secondary maximurn contaminant level [MCL] of 5 ppbv has been established (Regional Water Quality Control Board [RWQCB], 2000). Anecdotal acute health effects that have been attributed to MTBE exposure include headache, nausea or vomiting, a burning sensation in the nose or mouth, coughing, dizziness, disorientation, and eye irritation. Furthermore, MTBE is an animal carcinogen, although it has not yet been determined to cause cancer in humans. Additionally, the health effects of MTBE’s primary metabolites (such as tertiary-butyl alcohol [TBA] and formaldehyde) may be responsible for increased health effects associated with exposure to MTBE (Froines et al, 1998). Additional study and evaluation is being performed to further determine and evaluate the health affects of MTBE and its primary metabolites.
Several analytical methods have been established that detect the presence of MTBE in gasoline and environmental samples. Analytical methods used to detect MTBE and other oxygenates in gasoline include ASTM D 4815 and ASTM D 5599. Method SW8260 is used to detect MTBE in environmental samples; misidentification of MTBE has been noted with Methods SW8015 and SW8021 (Rhodes and Verstuyft). Due to the slow degradation, lack of absorption to soil, and mobility of MTBE in water, remedial technologies that clean-up MTBE are vital. Remedial technologies available to treat water contaminated with MTBE include air stripping, advanced oxidation processes (AOPs), granular activated carbon (GAC), and synthetic resin sorbents (The California MTBE Research Partnership, 2000). Major MTBE contamination and impact on drinking water wells has occurred nation-wide, and at dozens of sites in California. MTBE is a frequent and widespread contaminant in shallow groundwater at leaking underground storage tank (UST) facilities throughout California. In California, the cities of Santa Monica and South Lake Tahoe have had their drinking water supplies contaminated with MTBE. The city of Santa Monica lost 50% of its total water supply with concentrations of 610 ppbv reported in the Charnock aquifer (the city’s major drinking water source) and up to 190,000 ppbv in the groundwater directly beneath a leaking UST (McClurg, 1998). The groundwater supply was deemed unusable for drinking water due to gasoline and MTBE Contamination. The responsible party (Mobil Oil) was ordered to clean up the groundwater and provide an alternate drinking water supply for the affected community until the contamination is removed (Cal EPA, 1997). In Lake Tahoe, six of their 36 drinking water wells were shut down due to MTBE contamination that ranged from 1 ppbv to 26 ppbv. Additionally, more than 300 releases of MTBE from leaking UST systems have been reported in Santa Clara County, with MTBE concentrations ranging from 1ppbv to 4 million ppbv (McClurg, 1998). Other potential sources of MTBE releases to the subsurface environment are above ground storage tanks, spills, and transfer pipelines. MTBE has also been detected in reservoirs and lakes throughout California. In a 1997-98 survey to assess the prevalence of MTBE in groundwater and surface water supplies, MTBE was detected at least once in 9% of wells in 17 states (30 in 342 wells), and MTBE was detected at least once in 8.7% of surface waters (92 surface waters in 12 states) in 8 states (Gullick and LeChevallier, 2000). While precipitation of MTBE from the air contributes as a source of surface water contamination, spills or exhaust emissions of recreational boats and personal watercraft (such as jet skis), are additional sources of MTBE contamination in surface water. As a result, the use of personal watercraft has been banned or limited on drinking water reservoirs across California. Despite the fact that MTBE is credited for helping reduce the levels of benzene, a known human carcinogen, in air by 50%, due to its threat to groundwater aquifers and drinking water reservoirs, its health effects, and the challenges of removing it from contaminated water; California is looking forward to the mandated phase out of MTBE by December 2002 (McClurg, 1998 and Davis, 1999). The MTBE phase out decision in California was supported by a series of studies that evaluated the
occurrences and risks associated with MTBE. Generally, about 30% of California’s water is supplied by groundwater. In some areas groundwater is the only source of drinking water. US EPA and other states (such as Connecticut) are also evaluating the phase out of MTBE. New York has already banned the use of MTBE as an additive to gasoline sold in its state (State of New York, 1999) and Colorado plans to phase out MTBE by April 30, 2002. Many other states have passed laws to limit the percentage of MTBE in fuel to less than 2% by volume or are implementing programs to evaluate future MTBE phase out (ASTSWMO, 2000). On July 27, 1999 a Blue Ribbon Panel commissioned by US EPA recommended amending the Clean Air Act to provide the authority to significantly reduce or eliminate the use of MTBE, ensuring air quality gains are not diminished as use of MTBE is reduced or eliminated, and replacing the existing oxygen requirement contained in the Clean Air Act with a renewable fuel standard for all gasoline (ASTSWMO, 2000).
Release of MTBE from new and upgraded UST system A US EPA mandate required upgrade of all the USTs to provide corrosion protection and spill and overfill protection by December 22, 1998. In California, secondary containment of tanks and pressurized piping has been required since 1984. Tank owners were required to install both cathodic protection and lining to upgrade their tanks and to replace all corrodible piping or protect it from corrosion by the December 1998 upgrade deadline. Despite all these improvements, MTBE continues to be detected at UST sites and in the subsurface environment. In 1998, California’s Governor directed the UST program to convene an advisory panel to evaluate the effectiveness of the new and upgraded UST systems in preventing the release of oxygenates into the environment (SWRCB, 1999a, 1999b, 1999c, and 1999d). The panel’s findings indicated that both equipment specific issues and the human factor may be contributing to continued releases from upgraded systems. MTBE detected at new and upgraded UST sites has been attributed to a variety of factors including: 1) past contamination, 2) spills during fuel delivery to the tank, 3) releases of fuel from single-wall components of UST systems at rates less than the detection rates designed for leak detection devices, 4) release of MTBE in vapor phase from single-wall vapor recovery lines and other tank top fittings, 5 ) surface spills during fuel dispensing and subsequent surface infiltration, 6) permeation through flexible piping or other UST components, and 7) diffusion from loose joints, seals, and tank top fittings. Permeation and surface infiltration have not been proven to be likely sources of the MTBE problem in California. Further research to determine the extent to which MTBE is released from UST systems in vapor phase is needed. However, improper installations as well as UST system deficiencies appear to be the major contributing factors to ongoing undetected releases from UST systems. The requirements for new and upgraded UST sites differ across the United States and are established and enforced by the individual states. All states must enforce regulations that are as stringent as the Federal regulations, but many states, including California and Florida, have additional regulations for UST systems that are even more stringent than those established by the Federal government.
The presence of MTBE in groundwater across the United States can be attributed to problems associated with UST equipment and human factors. UST component and equipment deficiencies that are potential contributing factors to MTBE and oxygenate release to the subsurface environment Results of studies conducted by the State of California and information received from contractors, inspectors, and other state regulators have identified the following suspected sources of releases from UST systems and have suggested potential solutions to address these UST system deficiencies:
Product Piping System Problem: Single-wall piping is a problem because leaks from piping allow a release to directly impact the surrounding environment. Pressurized piping is also riskier than suction piping. Other piping problems associated with UST systems include: 1) releases from piping may result from mismatched fittings, connections, and gaskets, 2) the integrity of secondary containment specifically flexible piping, swing joints, flex connectors, and unions is questionable, 3) poor installation and 4) freezing water in rigid fiberglass piping. Solution: Installation of secondary containment on pressurized piping, initial post-installation testing of both primary and secondary piping, proper installation of secondary containment of piping to make it water tight and free of condensation, continuous leak detection, and periodic testing of secondary containment including all sumps will reduce the risk of release of MTBE into the environment. Under-Dispenser Piping Problem: Releases from the dispenser may result from the failure of meter seals, the routine replacement of fuel filters, the frequent replacement of meters, the breakdown of impact valves, and weak unions. Solution: The installation of under-dispenser containment that is protected from corrosion (including all transition piping in contact with the backfill) and is equipped with a continuous leak detection system connected to an audible and visual alarm or capable of dispenser shut-down would provide protection from releases to the environment. Turbine Area Problem: Leaks in the turbine area may be due to lack of routine maintenance, a leak in the swing joint under the turbine, leaks during servicing, and bolts on the turbine shaft that may rust off. Solution: Turbine containment boxes should be properly installed and sealed to prevent water intrusion and release of the primary piping leaks into the environment. Additionally, the turbine containment boxes should be reliably monitored using continuous electronic sensors connected to audible and visual alarms that are also connected to the pumping system. A program to implement a post-installation test and periodic testing of sumps should also be in place.
Leaking Spill Containment Problem: Spill containment (generally holds five gallons) connected to the tank’s fill pipe is used to capture fuel spilled during routine fuel deliveries; however, releases may occur from the spill containment due to improper design, installation, or operation and maintenance. Liquid from fuel spilled during deliveries is often left in the spill containment and not properly drained back into the tank. Spill containment that is not liquid-tight allows releases directly into the surrounding environment. Additionally, spill containment box bellows may separate from concrete surface support and cause release of vapors and gasoline over the top of the spill container and into the environment. Spill containment systems that are manufactured by the joining of two containment pieces (bottom surface and side wall containment) are subject to a higher rate of damage due to roughness of the cam lock adapter connections during routine fuel deliveries. Solution: Improved design, installation, operation, and maintenance of spill containment will help prevent leakage. Routine testing to confirm the spill containment is liquid-tight is also essential. A more drastic but protective solution is to contain the fill and spill containment in fill sumps that are connected to the tank. This will practically eliminate the potential threat of release of gasoline vapors and liquid from the fill area components into the surrounding backfill. Loose Tank Riser Adapters Problem: Tank risers often contribute to releases. Damage to the tank fill riser occurs as jarring of the adapter connections during routine fuel deliveries, improper installation (threaded onto tank incorrectly) and/or damage from corrosion. Direct releases into the environment may not be immediately detected because tank risers are not routinely tested. Solution: Tank risers should be contained inside secondary containment (such as a fill sump with a continuous leak detection device) and have corrosion protection. Additionally, proper installation and routine maintenance are necessary so fill risers will function properly. Leak Detection Programs Problem: There is evidence that leak detection programs may not be performing as intended. This finding is based on the fact that only 4% of releases reported during a 24 month study period were discovered by a leak detection program (SWRCB, 1 9 9 9 ~ )This . may be due to releases occurring below detection level of existing methods and devices, systems not operating as expected, systems deactivated with the leak detection program not in place, or the reports and alarms by leak detection methods and systems are ignored by owners and operators. Solution: Additional research including a field evaluation of leak detection equipment should be conducted to evaluate the effectiveness of these systems. More rigorous training and inspection programs and follow up on reported leak test results would encourage owners and operators to implement a more effective leak detection program and reduce or prevent costly releases of MTBE and fuel into the environment.
Human factors and training issues that contribute to increased risk of release of MTBE and other oxygenates into the subsurface environment. Improvements made to UST equipment and systems, installation of cathodic protection, mandatory secondary containment, and implementation of sensitive leak detection methods will not solve the problem of leaking USTs unless proper installation, periodic maintenance, and an adequate inspection program is in place. Poor installation practices and lack of periodic maintenance are major factors blamed for release of MTBE and fuel from new state-of-the art UST systems. A new law passed in California (Senate Bill 989) that became effective January 1, 2000 requires: improved licensing and manufacturer certification for installation contractors, licensing requirements for contractors performing maintenance and annual certification of leak detection equipment, and training requirements for tank owners and operators and government inspectors. This new law imposes requirements for periodic testing of secondary containment, installation of dispenser containment boxes at all UST sites, and completion of an enhanced leak detection test at three-year intervals at all UST facilities with single-wall components within 1,000 feet of public drinking water wells (Farahnak, 2000). The new law also mandates a field-based research study to better evaluate the effectiveness of UST systems and to determine the potential for release of vapors to the environment from UST systems and vapor recovery equipment. As part of the field-based research study, the UST systems at 180 sites throughout California will be tested using the Tracer0 Tight test method. Researchers predict that even if MTBE were to be removed from gasoline today, a significant but currently unknown number of community water wells may be at risk and the risk of contamination will continue for the next decade (Zogorski, 2000). Today we are moving to make sure that MTBE is significantly reduced or eliminated from gasoline. However, in the future we may want to think
twice about blending fuel with environmentally persistent man-made chemicals such as MTBE. First we have to fully address equipment failures and deficiencies, improving training and qualifications of those dealing with UST equipment. Most of all before we add an additive to our fuel, we must phase out old systems that provide inadequate protection against release to the environment.
MTBE in groundwater of England and Wales Dr Alwyn Hart Environment Agency, National Groundwater and Contaminated Land Centre, Olton Ct, 10 Warwick Rd, Solihull, B92 7HX.
Introduction In the United States, oxygenate ether compounds such as methyl-tertiary-butyl-ether (MTBE) were incorporated into motor fuels to meet the requirements of the Clean Air Act in order to improve combustion and hence air quality. In the UK and Europe, the switch to unleaded fuels, along with efforts to improve combustion, has also led to the introduction of ethers such as MTBE, primarily to achieve mandated octane levels. However, recently MTBE has come to be seen as one of the most significant pollution threats facing the US. For although it may benefit air quality, poor management of stored fuel and leaks from underground tanks have brought major groundwater pollution problems. In England and Wales, the situation was less clear. The Environment Agency, in collaboration with the Institute of Petroleum, has recently assessed the known incidence of MTBE pollution of groundwater and the resulting risk to public drinking water abstractions. The result of eight months research, including data from over 800 site investigations and nearly 3000 samples, is the most comprehensive study of its kind believed to have been conducted in Europe. The work has formed the basis for the current Environment Agency thinking and position on MTBE and these will also be discussed.
Why protect groundwater ? Quite simply, in England and Wales groundwater directly supplies around one-third of all our drinking water. However, the actual amount varies depending on location from just a few percent in Wales to over three quarters of all public water supplied in the south-east of England. Groundwater is also in reality just one part of a global water cycle; pollution entering the groundwater may be carried back to the surface and threaten the more familiar surface water features, wildlife etc. Groundwater is also notoriously difficult and expensive to clean up once contaminated. The pollution and loss of an entire city’s water supply through leaking fuel tanks as happened in California would cost millions of pounds to repair.
Why is MTBE of such concern ? Briefly, the relatively high water solubility, lack of sorption to aquifer solids and low biodegradability of MTBE mean that once it enters the groundwater, it has the potential to travel hundreds of metres (sometimes over a kilometre) from the site of a spill or leak. Its very low taste (10-100 mg/l) and odour (0.05 ppm) threshold mean that it has the potential to make large volumes of potable groundwater undrinkable.
In contrast to MTBE, the next most water soluble components of gasoline: benzene, toluene, ethylbenzene and xylenes (BTEX) travel more slowly from the site of a spill or leak and are often rapidly biodegraded by naturally occurring microorganisms.
Joint study of MTBE in UK Groundwater Against this background, the Environment Agency joined forces with the Institute of Petroleum to carry out a study of MTBE and other ether oxygenates in groundwater in England and Wales. The data were acquired through the use of questionnaires, interviews and analysis of site investigation reports and groundwater quality monitoring databases held by many parties: oil companies, petrol retailers, water companies and the Agency itself.
Major findings of the study The major oil companies provided information on over 2,000 retail, depot and terminal sites which have been investigated for soil and groundwater contamination. Ether oxygenates had been specifically looked for at 40% of these investigated sites, and were detected (primarily MTBE) in groundwater or perched water at approximately 29% and 25% percent of these petrol retail and distribution sites respectively. Forty of the sites contaminated with MTBE are located above high vulnerability aquifers (water bearing rocks).
The Agency already have a number of tools for assessing and managing risk to groundwater from activities or pollution incidents at the ground surface. By comparing the locations of all the retail sites in England and Wales with the Agency’s groundwater vulnerability maps, it is apparent that 44% of petrol stations on high vulnerability major aquifers and 6% of those on high vulnerability minor aquifers are within an abstraction source catchment. These catchments are the land areas where groundwater is collected and used for public water supply. This indicates that perhaps only six of the 40 sites on high vulnerability aquifers (commonly used for public water supply) are likely to lie within a source catchment zone and therefore could present a risk to PWS wells. Note that the 2,000 sites which were originally considered were the likely high risk sites from the oil company estates. In all, the Agency and the water companies supplied data
on almost 3,000 groundwater samples from 940 observation boreholes or PWS wells which have been analysed for ether oxygenates. Of the 255 PWS wells regularly sampled for ether oxygenates by the water companies, 32 (12.5%) contained MTBE above the detection limit of 0.1 mg/l. Only three contained MTBE at concentrations in excess of the low end of the taste threshold range(5 mg/l). There is only one case in the UK where MTBE has been detected in mains water by the public.
Modelling the future A model was developed to predict the overall risks associated with MTBE contamination of groundwater throughout England and Wales, both now and in the future. The model predicts MTBE is not a problem waiting to happen, based on current usage.
However, the model also predicts the consequences of increasing the concentration of MTBE in gasoline in the UK. The number of PWS boreholes containing MTBE at concentrations exceeding the taste threshold increase from 0.3% at 1% (v/v) MTBE in gasoline (the current situation), to 4% impacted at 5% (v/v) MTBE and to 8% impacted at 15% (v/v) MTBE.
Overall conclusions The report concludes that ether oxygenates such as MTBE do not currently pose a major threat to public water supplies derived from groundwater in England and Wales. Predictive modelling indicates that this is likely to remain the case in the future providing there is no major increase in the percentage of MTBE used in gasoline sold in the UK. If, however, the concentration of MTBE in gasoline was increased to 5% (v/v) or greater, there could be an order of magnitude increase in the number of PWS boreholes impacted with concentrations of MTBE above the taste threshold. This still leaves some doubt over small private water supplies which were not considered by the study. Why are England and Wales so different to the USA ?
We identified several reasons for this: The concentration of MTBE used in UK petrol is one tenth that used in the USA. We use small numbers of high yielding deep wells to provide drinking water from deep consolidated sandstone and chalk aquifers. High water consumption and low recharge in California have resulted in heavily depressed watertables and virtually all infiltration in urban areas is abstracted.
regions of England and Wales. More comprehensive site investigations be carried out at petroleum sites in areas where PWS wells are potentially vulnerable. Review of laboratory analytical methods for MTBE. Caution be exercised with respect to any increase the concentration of MTBE in petrol. The full report (A Review of Current MTBE Usage and Occurrence in Groundwater in England and Wales. Environment Agency R&D Publication 97) is available from The Stationery Office , The Publications Centre PO Box 276 London SW8 5DT tel0171 873 0011 Internet: www.theso.co.uk.
Key recommendations of the report The report recommends that: Increased monitoring for MTBE in groundwater to cover all
For more information contact Dr Alwyn Hart at the National Groundwater and Contaminated Land Centre.