UST Release Response

UST Release Response guidance

Updated

Five decision units (DUs) are requested for Multi Increment (MI) soil sampling of UST excavations (four walls and floor) when USTs are removed from the ground. The MI soil samples will be obtained from the excavator bucket for 30 to 75+ soil increments per DU. DOH UST recommends 50 to 75+. Minimum soil mass for VOCs is 300g in methanol. SVOCs do not require methanol preservative. Consult your analytical lab for minimum mass by analytes. MI soil samples should be soil only < 2mm particle size. For a UST excavation with one or more USTs of combined volume 6,000 gallons or less – the four walls and floor may be combined into one DU and MI soil sample to be sent to the lab.

  • Additional DUs are requested for fuel piping and beneath fuel dispensers. For fuel piping 60 feet or less, one DU is recommended from native soil of the piping trench after piping removal with additional DUs for additional lengths of 60 feet or less. Dispensers need their own DU after removal as this is a known area for releases.

On neighbor islands, consultants may use alternative methods described in Appendix I and Appendix I.5 of the HEER TGM for alternatives to methanol air transport from neighbor islands.

Soil vapor (SV) site assessments are for gasoline and diesel USTs prior to closure-in-place or for suspected releases of an existing UST system in place. SV site assessments differ from sub-slab intrusion investigations as the purpose is to detect a confirmed release of any quantity vs. the potential hazard of SV intrusion through the foundation of a building. For SV site assessment of in-place USTs, please locate an area of the concrete or asphalt cap over the UST excavation. Following the general guidance of a sub-slab SV intrusion investigation (HEER TGM Section 7), advance the SV probe two feet or more into the pea gravel surrounding the USTs. Two SV samples collected from different locations in the pea gravel above USTs in-place should detect the presence of a confirmed UST release. Triplicate samples (primary + two replicates for QA) are requested for 10% of soil, groundwater, or SV samples collected for analysis. In this case, one of the two samples will be triplicate. In the case of MI soil sampling, we request the triplicate sample be of the floor DU.

Used oil USTs are not able to utilize SV site assessments. DOH UST recommends removal and MI soil sampling for permanent closure of used oil USTs.

SV site assessments for piping – the SV probe should also be advanced into the pea gravel or directly adjacent at the estimated depth of bottom of piping. SV samples should be obtained every 20 linear feet of piping. For both methods, the UST or piping must be under pavement or asphalt. If removing USTs or piping, then Multi Increment (MI) sampling of native soil beneath the pea gravel should be performed instead of SV site assessment.

       If native soil is not present to sample, contact DOH UST Release Response at 808-586-4226.

See Table 9-5 in DOH HEER TGM for required petroleum constituent analyses by fuel type. Unknown USTs need TPH-g, TPH-d, TPH-o and sub-analytes for each on Table 9-5 for soil samples.

Formats for the UST Initial Release Response report and Quarterly Release Response reports may follow the format of Site Investigation reports in DOH HEER TGM 18.5.9. If you have any questions or comments, please contact DOH UST Release Response Section at 808-586-4226 or email.