Each service station site presents unique challenges and opportunities for scientists at Environmental Works, Inc. (EWI). For example, our Investigation/Remediation (I/R) department in Kansas City is currently monitoring for petroleum at a site in Northwest Missouri uphill from a perennial stream.
The Missouri Department of Natural Resources (MDNR) tested for and documented petroleum hydrocarbon impacts in the groundwater on site at the station, prompting the need for further testing and assessment. Petroleum hydrocarbon is a term used to describe a large family of several hundred chemical compounds that originally come from crude oil, according to the Agency for Toxic Substances & Disease Registry.
The service station filed a claim with the Missouri Petroleum Storage Tank Insurance Fund (PSTIF), which provides pollution liability insurance to owners and operators who store petroleum products in underground or aboveground tank systems. A $10,000 deductible applies to each incident, and revenues for PSTIF come primarily from a “transport load fee,” which is currently $28 per 8,000 gallons, assessed on each load of petroleum brought into Missouri, according to the PSTIF website. The Missouri PSTIF is one of many such state and federal insurance programs.
EWI was called in to manage the station site, and initiated an ecological risk assessment, according to Suzanne Bailey, Senior Project Manager in I/R. Environmental risk assessments are often mandated by regulators like MDNR as part of the site evaluation process, and results of environmental risk assessments often drive the need for remedial actions and support the derivation of cleanup levels.
The station has not been subject to one particular “catastrophic release,” according to Bailey. Instead, she suspects that any product found on site or downgrade from the station is “probably related to leaking product lines, cumulative spills at the dispenser islands, leaking underground storage tanks, or all of the above.”
The site is made more complicated by the fact that it was built uphill from a hardwood forest with a perennial stream running through it.
“I think the station has been there since the 1970s, and back in that time, nobody really gave any consideration to what environmental receptors (streams, etc.) could potentially be adversely affected by a gas station,” Bailey says. “Given the proximity of the creek to the petroleum release, groundwater flows toward the creek, and we have documented petroleum hydrocarbon impacts in the groundwater, per MDNR, we have to evaluate whether there is potential for impacted groundwater to enter the creek and create an ecological risk. So, that triggers an ecological risk assessment and evaluation of the stream protection pathway.”
EWI installed 17 monitoring wells around the service station property – including “three in the woods,” says Bailey.
“We put wells in between the creek and the petroleum release site (at the station) and will see if groundwater concentrations are high enough to warrant sampling of the creek itself,” she adds.
Next, EWI will conduct quarterly sampling.
“Typically, once we have defined the vertical and horizontal extent of petroleum impacts to soil and groundwater, we move on to doing four to six quarterly groundwater sampling events to establish whether dissolved concentrations in groundwater are increasing, decreasing, or are stable,” says Bailey. “This data is used to indicate whether the petroleum impacts in groundwater are migrating or not. The data will be statistically evaluated, and the results presented to the regulatory agency. If the evaluation indicates increasing or non-stable trends, additional groundwater monitoring events are in order. In such a case, one or two more events may be done and then the data is again examined statistically.”
EWI has not tested the water quality of the stream, yet.
“We have not yet tested the water, as it hasn’t been warranted so far,” says Bailey. “If our groundwater results from wells between the site and the creek are above Missouri water quality criteria, we would recommend testing the water in the creek. If groundwater results are below Missouri water quality criteria, we can assert that impact to the creek is unlikely.”
That said, EWI scientists have inspected the creek every time they have been on site.
“We will also look at the creek to see if there is any indication of petroleum impacts (visible rainbow sheen, for instance),” says Bailey. “So far, we have not seen anything like this on the water. We also have not seen any evidence of stressed vegetation between the creek and the site. We simply have not seen any indication in soil or groundwater of gross contamination.”
According to Bailey, all indications are that the site will not require active remediation, which is a good thing for the station owners, as well as the health of the hardwood forest and perennial stream.
“Active remediation is only warranted when soil and/or groundwater results exceed risk-based target levels and there is no way to develop engineering or institutional controls to prevent risk to potential receptors. So far, our results do not indicate that active remediation will be required at this site,” Bailey says. “The site is an active petroleum fueling station with both gasoline and diesel underground storage tanks and associated underground piping. The tanks are in compliance with Missouri underground storage tank requirements. As long as the site is active and in compliance, it is unlikely that source removal will be required.”