Owners and operators using groundwater monitoring (testing or monitoring for liquids on the groundwater) must comply with the requirements of this section. Except as otherwise provided in WAC 173-360A-0610(3) or 173-360A-0615(3), groundwater monitoring may be either passive (monitoring for presence of regulated substance) or active (monitoring for presence of tracer compound).

(1) Site conditions.

(a) The regulated substance stored must be immiscible in water and have a specific gravity of less than one.

(b) Groundwater must never be more than twenty feet from the ground surface and the hydraulic conductivity of the soil(s) between the UST system and the monitoring wells or devices must not be less than 0.01 cm/sec (e.g., the soil should consist of gravels, coarse to medium sands, coarse silts or other permeable materials).

(c) The slotted portion of the monitoring well casing must be designed to prevent migration of natural soils or filter pack into the well and to allow entry of regulated substance on the water table into the well under both high and low groundwater conditions.

(d) Monitoring wells must be sealed from the ground surface to the top of the filter pack.

(e) Monitoring wells or devices must intercept the excavation zone or must be as close to it as is technically feasible.

(2) Site evaluations. Within and immediately below the UST system excavation zone, the site must be evaluated to ensure compliance with the requirements in subsection (1) of this section and to establish the number and positioning of monitoring wells or devices that will detect releases from any portion of the tank or piping being monitored that routinely contains product.

(a) Performance. Site evaluations must be performed by or under the direct supervision of a service provider certified in accordance with Part 9 of this chapter.

(b) Reporting. Site evaluations must be reported to the department within thirty days of the installation of the groundwater monitoring system. The report must be submitted with the checklist required for the installation (WAC 173-360A-0300 (5)(b)). The report must be completed by the service provider. The report must identify the service provider and their certification type and number.

(3) Monitoring wells.

(a) Monitoring wells must be clearly marked and secured to avoid unauthorized access and tampering.

(b) Monitoring wells must be constructed, maintained, and decommissioned in accordance with chapter 173-160 WAC.

(4) Monitoring devices or manual methods.

(a) The continuous monitoring devices or manual methods used must be able to detect the presence of at least one-eighth of an inch of free product on top of the groundwater in the monitoring wells.

(b) The continuous monitoring devices must be operated in accordance with the manufacturer's instructions and any conditions or limitations specified in the certification of the equipment.