17.50.1304    GROUND WATER MONITORING SYSTEMS

(1) An owner or operator required to monitor under this subchapter shall install a ground water monitoring system that consists of a sufficient number of wells, installed at appropriate locations and depths, to yield ground water samples from the uppermost aquifer, or underground drinking water source, as required in ARM 17.50.1204, that:

(a) represent the quality of background ground water that has not been affected by leakage from a unit. A determination of background quality may include sampling of wells that are not hydraulically upgradient of the waste management area when:

(i) hydrogeologic conditions do not allow the owner or operator to determine the wells that are hydraulically upgradient; or

(ii) sampling at other wells will provide an indication of background ground water quality that is as representative or more representative than that provided by the upgradient wells; and

(b) represent the quality of ground water passing the relevant point of compliance specified by the department under ARM 17.50.1204(3). The downgradient monitoring system must be installed at the relevant point of compliance specified by the department under ARM 17.50.1204(3) that ensures detection of ground water contamination in the uppermost aquifer, or underground drinking water source, as required in ARM 17.50.1204. When physical obstacles preclude installation of ground water monitoring wells at the relevant point of compliance at existing units, the downgradient monitoring system may be installed at the closest practicable distance hydraulically downgradient from the relevant point of compliance specified by the department under ARM 17.50.1204(3) that ensures detection of ground water contamination in the uppermost aquifer, or underground drinking water source, as required in ARM 17.50.1204.

(2) The department may approve a multi-unit ground water monitoring system instead of separate ground water monitoring systems for each Class II or Class IV landfill unit when the facility has several units, if the multi-unit ground water monitoring system meets the requirements of (1) and will be as protective of human health and the environment as individual monitoring systems for each Class II or Class IV landfill unit, based on the following factors:

(a) number, spacing, and orientation of the Class II or Class IV landfill unit;

(b) hydrogeologic setting;

(c) site history;

(d) engineering design of the Class II or Class IV landfill unit; and

(e) type of waste accepted at the Class II or Class IV landfill unit.

(3) Monitoring wells must be cased in a manner that maintains the integrity of the monitoring well bore hole. This casing must be screened or perforated and packed with gravel or sand, where necessary, to enable collection of ground water samples. The annular space, i.e., the space between the bore hole and well casing, above the sampling depth must be sealed to prevent contamination of samples and the ground water.

(4) The owner or operator of a Class II or Class IV landfill unit required to monitor under this subchapter shall:

(a) submit a ground water monitoring plan to the department for approval that includes:

(i) the location, number, depth, design, installation, development, and decommission of any monitoring wells;

(ii) plans for the design, installation, development, and decommission of piezometers or other measurement, sampling, and analytical devices; and

(iii) discussions of the anticipated ground water monitoring system and schedule of sampling for closed portions of the facility, if applicable;

(b) update the ground water monitoring plan at least once every five years, except that a ground water monitoring plan for a closed facility must be updated at least every ten years; and

(c) notify the department that the approved ground water monitoring systems plan has been placed in the operating record.

(5) The monitoring wells, piezometers, and other measurement, sampling, and analytical devices must be operated and maintained so that they perform to design specifications throughout the life of the monitoring program.

(6) The number, spacing, and depths of monitoring wells must be:

(a) determined based upon site-specific technical information that must include thorough characterization of:

(i) aquifer thickness, ground water flow rate, ground water flow direction, including seasonal and temporal fluctuations in ground water flow; and

(ii) saturated and unsaturated geologic units and fill materials overlying the uppermost aquifer, or underground drinking water source, as required in ARM 17.50.1204, materials comprising the uppermost aquifer, or underground drinking water source, as required in ARM 17.50.1204, and materials comprising the confining unit defining the lower boundary of the uppermost aquifer, or underground drinking water source, as required in ARM 17.50.1204, including, but not limited to, thicknesses, stratigraphy, lithology, hydraulic conductivities, porosities, and effective porosities; and

(b) be certified by a qualified ground water scientist and approved by the department. Within 14 days of this certification, the owner or operator shall notify the department that the certification has been placed in the operating record.

(7) The drilling and construction of a ground water monitoring well at a solid waste management system may be subject to the requirements of Title 36, chapter 21, subchapters 4, 7, and 8.

History: 75-10-204, MCA; IMP, 75-10-204, 75-10-207, MCA; NEW, 2010 MAR p. 317, Eff. 2/12/10.