Missouri Risk-Based Corrective Action for Petroleum Storage Tank Sites – Evaluating the Utility Receptor Pathway

Environmental Remediation Program fact sheet
07/2019
Division of Environmental Quality Director: Ed Galbraith
PUB2756

Why evaluate utilities?
Section 6.1.2.3 of the Missouri Risk-Based Corrective Action Process for Petroleum Storage Tanks (MRBCA) requires that underground utilities at petroleum release sites be evaluated. This is particularly important when the utilities are or could come in contact with free product, petroleum vapors, or petroleum-contaminated soil or groundwater, as utilities can serve as preferential contaminant migration pathways. Further, studies have demonstrated that petroleum can permeate waterlines and desorb into drinking water supplies, potentially resulting in unacceptable risks from domestic water use and indoor air exposure pathways.

Note: Any drinking water well suspected of being impacted by a petroleum release should immediately be sampled and reported to the Environmental Emergency Response (EER) Hotline at 573-634-2436.

What sites need a utility evaluation?
At all petroleum release sites, the responsible party is required to locate and provide information about underground utilities in accordance with MRBCA Section 5.4.3. A more thorough evaluation is required at petroleum release sites where an underground utility previously has been affected by contamination or a utility is currently in contact with or is likely to come in contact with free product, petroleum vapors, or petroleum-contaminated groundwater or soil.

What actions are required when a waterline is or potentially is in contact with free product, petroleum vapors, or petroleum-contaminated soil or groundwater?

Waterline in contact with free product
Under no circumstances may a waterline remain in contact with free product or petroleum-saturated soil. In these instances, the free product or saturated soil must be removed and the waterline removed and replaced under a corrective action plan (CAP) approved by the department’s Tanks Section. The new waterline must be placed in an uncontaminated area of the site. Alternatively, the waterline may be replaced in the same area after remediation is completed with approval from the Tanks Section. If residual contamination will remain after remediation is complete, the new waterline should be made of petroleum-resistant materials (e.g., ductile iron with fluoroelastomer rubber gaskets, copper piping with no gaskets, etc.) and the waterline trench lined with bentonite barriers where the metal piping connects back to plastic piping, if applicable.

A written construction authorization from the department may be required for community and non-community water suppliers prior to construction, alteration, or extension of these systems as provided in 10 CSR 60-3.010. Therefore, these water suppliers should contact the department’s Water Protection Control Branch – Permit and Engineering Section at 573-751-5924 to determine if a construction authorization is needed prior to constructing, repairing, or rerouting a waterline impacted by the release.

Waterline in contact with petroleum-contaminated soil or groundwater
If a waterline is found to be in contact with contaminated groundwater or soil, the contamination must be remediated and the waterline removed and replaced under a CAP approved by the Tanks Section. The new waterline must be placed in an uncontaminated area of the site. Alternatively, the line may be replaced in the same area after remediation is completed with approval from the Tanks Section. If residual contamination will remain after remediation is complete, the new waterline should be made of petroleum-resistant materials (e.g., ductile iron with fluoroelastomer rubber gaskets, copper piping with no gaskets, etc.) and the waterline trench lined with bentonite barriers where the metal piping connects back to plastic piping, if applicable.

Waterline potentially in contact with free product, petroleum vapors, or petroleum-contaminated soil or groundwater
If a waterline potentially is in contact with free product, petroleum vapors, or petroleum-contaminated soil or groundwater, additional investigation to determine whether the utility is in contact with contamination will be required. This may involve sampling soils or vapors near the utility, conducting groundwater gauging, and providing groundwater elevation data, etc.

If it is demonstrated that the utility is in contact with contamination, the utility service provider and the Tanks Section 573-751-3176 must be informed of the issue as soon as possible. Additionally, sampling of drinking water at the tap must be conducted and follow-up actions taken, in the manner described in this fact sheet.

Water sampling for waterlines in contact with free product, petroleum vapors, or petroleum-contaminated soil or groundwater
In addition to notifying the utility service provider and the Tanks Section as soon as possible upon discovering that a waterline is in contact with free product or petroleum-contaminated soil or groundwater, the responsible party must collect samples of drinking water at the tap to determine whether the water can be used safely until the waterline can be replaced or relocated and the contamination remediated. Tap samples must be collected from the on-site building, the building immediately upstream of the contamination, and the building immediately downstream of the contamination as follows:

Laboratory detection limits for all chemicals of concern (COCs) must be at or below the risk-based target levels for groundwater domestic use in order to continue using the water. If the sample results indicate COCs are present at any concentration in the water, the responsible party shall notify the utility service provider and the Tanks Section as soon as possible. Immediate confirmation sampling will be required.

If COC concentrations in the water exceed levels protective of drinking water, the responsible party must arrange for a source of clean drinking water for building occupants. Additionally, any and all filters used to treat drinking water in the facility must be replaced. An existing water treatment system for the building may not be relied upon to reduce concentrations of petroleum COCs to acceptable levels unless the responsible party can demonstrate to the department that the existing system is designed for and capable of removing petroleum COCs from the water.

After the waterline is no longer in contact with free product or contaminated soil or groundwater due to waterline replacement, waterline relocation, remediation, or some combination thereof, waterlines will need to be flushed to remove residual contamination from the system. Post-flushing water sampling may be required by the department to confirm that petroleum COCs are no longer present.

As contaminants in drinking water can volatilize into indoor air, indoor air sampling conducted in accordance with methods found in either the U.S. Environmental Protection Agency’s Office of Solid Waste and Emergency Response (OSWER) Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air or the Interstate Technology & Regulatory Council’s (ITRC’s) Petroleum Vapor Intrusion: Fundamentals of Screening, Investigation, and Management may be required depending on COC concentrations in the water and how the water is used within the building. If required, results of this vapor sampling must be compared to the indoor air risk-based target levels in Table 7-1 or 7-2 of MRBCA, dependent upon the use of the building (i.e., residential or non-residential).

Vapor intrusion
In addition to the vapor exposure that can occur as COCs volatilize from impacted drinking water, utility lines (in particular sewer lines) and utility trenches can serve as potential conduits for vapor migration and vapor intrusion into buildings. This can occur if contamination has infiltrated the utility itself or vapors are migrating along the utility trench. The following outlines the steps the responsible party must take if petroleum vapors are migrating along utility corridors or contamination has infiltrated a utility.

Utility infiltrated by petroleum contamination
If contamination has infiltrated a utility, the responsible party must contact the department’s EER Hotline at 573-634-2436, the utility service provider, and the Tanks Section as soon as possible. In addition, the responsible party must immediately take steps to repair the utility and/or remediate contamination to prevent additional infiltration of contamination and vapor migration.

After the responsible party has taken all actions required by EER, and EER has released the site to the Tanks Section, the Tanks Section may require routine weekly vapor monitoring of the utility, if warranted based on site-specific conditions, including documented petroleum infiltration into the utility. When required, vapor monitoring will continue until such time as sampling or screening demonstrates no ongoing threat from petroleum contamination to the utility, the utility corridor, or any buildings to which the utility connects.

When vapor monitoring is required, it will include monitoring of any buildings connected to the impacted portion of the utility. Monitoring shall be conducted using an explosimeter and a photoionization detector (PID) as follows:

Vapor migration along utility corridor
If vapors are known or thought to be preferentially migrating along a utility corridor, vapor screening of the utility access points and points of ingress into the building will be required. If such screening detects petroleum vapors in a building connected to the utility, or if petroleum odors are present in a building, indoor air sampling as described in the section above (Water sampling for waterlines in contact with free product, petroleum vapors, or petroleum-contaminated soil or groundwater) will be required. Where vapors are found to be entering into a building along a utility, the ingress point of the utility must be sealed or reconstructed to permanently prevent vapors from entering the building. The method to be used to prevent future vapor intrusion must be proposed in a work plan submitted to the Tanks Section for review and approval.

Other exposure pathways
If a utility trench contains petroleum-contaminated soil or groundwater, the construction worker dermal contact pathway (for soil, groundwater, or both) is considered complete. Risk from this pathway must be appropriately evaluated and any associated unacceptable risks addressed through a CAP approved by the Tanks Section.