Sponsored by API

UST Vapor Leak Research
Gary Lynn, NHDEP, Concord, NH

Monitoring Small Releases from USTs and assessing Vadose Zone Infiltration 
Gary Robbins, U. Connecticut, Storrs, CT

Evaluation of Maryland’s Enhanced UST Regulations for Mitigating Groundwater Contamination Risk from Small Gasoline Leaks
Cynthia Cogan, ENSR, Westford, MA  

UST Vapor Leak Research

Gary S. Lynn, New Hampshire Department of Environmental Services, 29 Hazen Drive, Concord, New Hampshire 03302, Tel: 603 271-8873, Fax: 603 271-2181, Email: glynn@des.state.nh.us

The State of New Hampshire has encountered significant MtBE contamination problems at operating service stations that it has attributed to tank system vapor releases.  State sponsored research is being conducted to foster understanding of the releases and practical ways to mitigate them.  The research partnership includes DES, the University of New Hampshire, a large northeast/mid Atlantic oil company and equipment vendors (US EPA and API also provided supplemental funding and assistance).  Seven operating service stations were instrumented to collect continuous data on groundwater levels, subsurface temperatures and tank internal pressure.  On a weekly basis data was collected on groundwater quality in the well nearest to the tanks and soil vapor levels at the nearest monitoring well and tank pad well.  Additional data was collected on gasoline deliveries, tank inspections, leak repairs and A/L ratio modifications.  After an initial month long baseline monitoring period, six of the service stations were modified.  The following modifications were evaluated: 1) SVE system installation and startup, 2) vent processor installation and operation, 3) ORVR compatible nozzle and clean air separator installation, 4) pressure decay test and leak repairs, 5) monthly inspection and leak repairs and 6) ISD system monitoring and repairs.  After approximately three months of operation and data collection on the modified systems, the service stations transitioned from gasoline containing MtBE to gasoline with ethanol.  The data collection continued to capture the response in the MtBE contamination levels in groundwater once MtBE was no longer present in the ongoing vapor releases.   Preliminary findings will be discussed on: a) the main sources and relative size of vapor leaks, b) the impact of A/L and nozzle type on tank system pressures, c) the success of the technologies in controlling releases and d) the response time in various geologies once releases are reduced.

Monitoring Small Releases from USTs and Assessing Vadose Zone Infiltration

Gary A. Robbins, Department of Natural Resources Management and Engineering, University of Connecticut, 1376 Storrs Road, Storrs, CT 06269-4087, Tel: 860-486-2448, Fax: 860-486-540, E-mail: gary.robbins@uconn.edu
Judith C. Rondeau, Department of Natural Resources Management and Engineering, University of Connecticut, 1376 Storrs Road, Storrs, CT 06269-4087, Tel: 860-486-2448, Fax: 860-486-2840, E-mail: judith.rondeau@uconn.edu

In conducting near-field UST monitoring over several years, we have observed periodic spikes in MTBE ground water contamination in the absence of BTEX. MTBE levels may exceed thousands of parts per billions. Based on the work of others, the likely source of the MTBE contamination spikes is periodic vapor releases. Conceptually, MTBE vapors will rapidly partition into vadose zone soil moisture or a shallow water table, given its low Henry's Law constant.  In these environments, BTEX constituents would readily biodegrade. Accumulations of MTBE in soil moisture can be periodically flushed from the vadose zone by direct infiltration beneath the asphalt, by a rise in the water table in response to precipitation and by infiltration in upgradient recharge areas. Direct infiltration may occur during precipitation events at downspout locations adjacent to on-site buildings, from dry wells beneath pump islands which drain station canopies, and from cracks in the asphalt. Furthermore, it is possible that water migrating downward at these locations rapidly moves laterally in the coarse subbase of the asphalt. We have implemented a monitoring program at several gas station sites to evaluate the magnitude, duration and configuration of the water table rise beneath the asphalt in response to precipitation events.  The monitoring program entails the installation of pressure transducers in wells in the near field along with an on-site rain gauge to document the water table response. 

Evaluation of Maryland’s Enhanced UST Regulations for Mitigating Groundwater Contamination Risk from Small Gasoline Leak

Cynthia L. Cogan, PE, ENSR, 2 Technology Park Drive, Westford, MA, 01886, Tel: 978-589-3000, Fax: 978-589-3100, Email: ccogan@ensr.aecom.com
Maya Desai, PG, ENSR, 2 Technology Park Drive, Westford, MA, 01886, Tel: 978-589-3000, Fax: 978-589-3100, Email: mdesai@ensr.aecom.com
Elizabeth Perry, PG, ENSR, 2 Technology Park Drive, Westford, MA, 01886, Tel: 978-589-3000, Fax: 978-589-3100, Email: eperry@ensr.aecom.com

The State of Maryland promulgated new regulations in January 2005 to require owners of new and existing UST systems in areas of the State defined as “High Risk Groundwater Use Areas” to implement groundwater monitoring and additional leak testing to prevent releases of petroleum products into groundwater sources used for drinking water.

ENSR conducted an evaluation of the new UST regulations in order to: 1) perform a cost evaluation for implementing the new regulations for existing sites; and 2) evaluate the effectiveness of the new regulation to better detect releases from existing gasoline UST systems in high risk groundwater use areas.

Maryland estimates that 750 UST systems are located in high-risk areas.  ENSR evaluated a sample of 30 UST systems and estimated the cost to install monitoring wells and perform the first year testing requirements to be $13,500.  The annual cost of compliance with the regulations was estimated to range from $5,640 to $6,300.  It was also estimated that approximately 7% of the UST systems in the state will be required to comply with the new regulations.

ENSR used the simple BIOSCREEN model (EPA, 1996) and a number of assumptions to evaluate the effectiveness of the new UST regulations.  Assumptions related to quantity and duration of release, concentration, specific gravity and solubility of MTBE, dilution factor, groundwater flow velocity and elapsed time and monitoring well distance relative to the point of release.  The modeling suggested that small releases of reformulated gasoline will result in MTBE plume migration and the releases will be detected by the 180 day monitoring cycle required by the new regulations.

Maryland’s new UST regulations will likely detect or prevent several different types of gasoline leaks that previously went undetected   The regulations target a relatively small number of UST  systems located within high risk groundwater use areas and are, therefore, considered to be cost effective. 

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