Missouri Risk-Based Corrective Action for Petroleum Storage Tank Sites: Evaluating the Utility Receptor Pathway - PUB2756

Why evaluate utilities?

Section 6.1.2.3 of the Missouri Risk-Based Corrective Action (MRBCA) Process for Petroleum Storage Tanks 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 department's Environmental Emergency Response Spill Line 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 according to 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 Underground Storage 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 department approval. 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 before construction, alteration or extension of these systems, as provided in Code of State Regulations 10 CSR 60-3.010. Therefore, these water suppliers should contact the department’s Water Protection Program at 573-751-5924 to determine if a construction authorization is needed before 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 department-approved CAP. 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 complete, with department approval. 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 is potentially 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, providing groundwater elevation data, etc.

If it is demonstrated that the utility is in contact with contamination, the utility service provider and the department’s Underground Storage 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 department’s Underground Storage Tanks Section as soon as possible upon discovering 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:

• Collect all samples after water in the line has been stagnant for at least eight hours, or as long as reasonably possible
• Collect samples upstream of any treatment systems (e.g., water heater, water softener, filtration, etc.)
• Collect the first sample immediately upon opening the tap (to determine impact in the building’s plumbing)
• Collect the second sample after running the tap for three minutes (to determine impact in the service connection)
• Collect the third sample after running the tap for six minutes (to determine impact in the water main)

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 must notify the utility service provider and the department’s Underground Storage 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. The department may require post-flushing water sampling to confirm that petroleum COCs are no longer present.

As contaminants in drinking water can volatilize into indoor air, indoor air sampling conducted according to 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 Environmental Emergency Response Spill Line at 573-634-2436, Underground Storage Tanks Section and the utility service provider as soon as possible. In addition, the responsible party must immediately take steps to repair the utility or remediate contamination to prevent additional infiltration of contamination and vapor migration.

After the responsible party has taken all actions required by the department, and Environmental Emergency Response has released the site to the department’s Underground Storage Tanks Section, the 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 must be conducted using an explosimeter and a photoionization detector (PID) as follows:

• Begin monitoring at the utility access point nearest to the contamination, or the point at which the contamination is presumed to have entered the utility or utility corridor. Work outwardly along the utility in both directions from the known or presumed source to determine whether vapors are present, where vapors may be entering the utility and the extent of the contamination.
• At the top of each utility access point, take readings for oxygen and percentage explosive level. Repeat the measurements at mid-depth of the access point and at the water level or the bottom of the point, whichever is first encountered.
• When present along and proximate to the affected utility, take explosimeter and PID readings at lift stations, buildings and other structures, making certain to include all such features connected to the affected utility. Note the location of all monitoring points and include addresses and owner information for buildings. All monitoring points should be identified on a site map showing the affected utility, nearby buildings and other relevant features.
• For buildings, check for vapors in basements and sewer drains and near foundation joints, seams and cracks. If petroleum odors, PID readings or vapors are detected in buildings connected to the utility, indoor air sampling according methods found in either OSWER or ITRC guidance documents referenced above will be required. Vapor sampling results must be compared to the indoor air risk-based target levels in Table 7-1 or 7-2, as appropriate, of the MRBCA document. Additionally, relocation of workers or occupants of any impacted structure may be required if warranted based on COC concentrations in indoor air.

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 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 department 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 department-approved CAP.