Interstitial Monitoring Release Detection Method
(1)An owner and permittee may use an interstitial monitoring system as a release detection method if:
(a)The system is designed, constructed and installed in accordance with a national code of practice or industry standard and the interstitial monitoring system is an approved leak detection system (method and equipment) for that system as listed by a national organization (e.g., the National Work Group on Leak Detection); and
(b)The system is able to detect a leak from any portion of an UST or underground piping that routinely contains a regulated substance.
(2)An owner and permittee must meet the following requirements for the specific type of UST system or piping:
(a)Multiwalled UST systems. The sampling or testing method must be able to detect a release through the inner wall in any portion of the UST.
(b)UST systems with a secondary barrier within the excavation zone. The sampling or testing method used must be able to detect a liquid between the UST system and the secondary barrier.
(A)The secondary barrier around or beneath the UST system must consist of artificially constructed material that is sufficiently thick and impermeable (at least 10-6 cm/sec for the regulated substance stored) to direct a liquid to the monitoring point to allow its detection;
(B)The secondary barrier must be compatible with the regulated substance stored so that a liquid from the UST system will not cause a deterioration of the barrier or allow a release to pass through the barrier;
(C)For USTs with corrosion protection, the secondary barrier must be installed so that it does not interfere with the proper operation of the corrosion protection system;
(D)Groundwater, soil moisture or rainfall cannot render the testing or sampling method used inoperative so that a release could go undetected for more than 30 days or one day if used for pressurized underground piping;
(E)Before installation, an owner and permittee must have the site assessed to demonstrate that the secondary barrier is always above the seasonal high groundwater level and not in a 25-year flood plain, unless the barrier and monitoring system are designed for use under such conditions; and
(F)An owner and permittee must mark and secure monitoring wells at all times to prevent unauthorized access and tampering.
(c)USTs with an internally fitted liner. An automated device must be able to detect a release between the inner wall of the UST and the liner, and the liner must be compatible with the regulated substance stored.
(d)Double walled pressurized piping. Interstitial monitoring devices must be installed in any sump unless the piping is continuously double-walled through the sump.
(3)An owner and permittee must monitor the UST and underground suction piping for a leak at least every 30 days and record the results for each month.
(4)An owner and permittee must monitor pressurized underground piping for a leak at least every 30 days and record the results for each month.
(5)Beginning October 1, 2020, owners and permittees must follow OAR 340-150-0310 (Spill and Overfill Prevention Equipment and Testing Requirements)(8) to ensure that containment sumps used for interstitial monitoring of piping are operating properly and will prevent releases to the environment.
(6)An owner and permittee must retain at a minimum the most current 12 consecutive months of release detection records. Records must include, at a minimum, the date the system was checked, observations made and the name or initials of the person conducting the monitoring. In addition, records for electronic systems must include: power status (on or off), alarm indication status (yes or no) and sensor malfunction noted (yes or no).
(7)An owner and permittee must report to DEQ any leak test observations, alarms or results indicating the possibility of a release to the interstitial area within 24 hours as a suspected release (OAR 340-150-0500 (Reporting Suspected Releases)) and immediately begin investigation in accordance with 340-150-0510 (Suspected Release Investigation and Confirmation Steps).
Rule 340-150-0465 — Interstitial Monitoring Release Detection Method,