By Mike Pederson, CMWP - Environmental Scientist March 16, 2023
A petroleum release associated with a tank can be found anywhere. In 1984, Congress created the Federal Underground Storage Tank Program and directed the Environmental Protection Agency (EPA) to regulate underground storage tanks. Since then, underground storage tanks have been required to be registered with the State of Minnesota. However, not every tank was accounted for, and some tanks are still being found.
A persistent patch of dead/stressed vegetation could indicate a petroleum release. You may discover a buried tank during construction or landscaping projects. A common sign of a leak is smelling petroleum. A client recently discovered they had a leak from their above ground fuel tank when they began to smell petroleum inside City Hall. At first, they thought the smell was coming from the heater, but after inspecting their crawlspace, they discovered that fuel was leaking from the tank into the crawlspace.
In the case mentioned above, the city reported the leak to the Minnesota Pollution Control Agency (MPCA). A Request for Additional Work letter was sent to the city, which detailed the activities necessary to remedy the petroleum leak. The city then contacted Widseth to provide a proposal to perform the Limited Site Investigation (LSI).
An LSI is conducted by advancing soil borings around the leak site. One boring is generally located in the middle of the leak site to capture the worst-case scenario and is typically used for defining the vertical extent of the contamination and the site stratigraphy. This soil boring is usually drilled to 40 feet, but could be deeper or shallower, depending on the level of contamination and location of the water table. The remaining soil borings are used to define the horizontal extent of the contamination. These soil borings are typically drilled to 25 feet but vary based on site conditions and the level of contamination.
Cores are collected from each of the soil borings and are field tested using a photoionization detector (PID). A reading of 10 parts per million (ppm) or greater indicates that contamination is present in the core. After the soil boring has been drilled to depth, a soil sample is taken from the core, generally where the highest concentration of contamination was detected, at the water table, and/or at the bottom of the soil boring. Soil samples are typically analyzed for diesel range organics (DRO), gasoline range organics (GRO), and petroleum volatile organic compounds (PVOC) if groundwater is present, or volatile organic compounds (VOC) if groundwater is absent.
Grain size analysis is also performed for the soil samples. This is used to determine if an aquifer is present onsite and to characterize the confining layer, if present.
Additionally, if groundwater is present at the site, samples will be collected as well. Groundwater samples are typically analyzed for DRO, GRO, and VOC. Soil gas samples are also collected from the site if needed.
Buildings that are within 100 feet of the leak site will be tested by drilling a soil boring as close to the structure as possible. Also, depending on the site, either ambient air or sub-slab samples are collected from buildings in the immediate vicinity or if the contamination is migrating toward a building. Utilities are also located and mapped to determine the likelihood of contamination.
Properties within 500 feet of the leak site are also contacted and checked to see if water supply wells are present, how they are used, if a basement or sump is present, and if any possible petroleum products are on their property.
In many cases, costs associated with the LSI are at least partially reimbursable through the state's Petrofund. Widseth can assist you with entering all the data, generating figures that are associated with the site, gathering all of the invoices that were related to the tank release, and presenting all of this data in a manner to get the maximum amount of reimbursement related to the leak.
If you suspect there is a petroleum release on your property, contact us so we can provide you a proposal to perform an LSI.