(a) A discharger required pursuant to the provisions of this article to conduct unsaturated zone monitoring at a land treatment unit shall comply with the unsaturated zone monitoring and response provisions of this section in conjunction with all other unsaturated zone monitoring and response provisions of this article.

(b) The discharger shall monitor the soil and soil-pore liquid to determine whether constituents of concern migrate out of the treatment zone.

(c) The regional board shall specify the monitoring parameters and constituents of concern to be monitored in the waste discharge requirements. The monitoring parameters to be monitored are those specified pursuant to subsection 2550.8(e) of this article for detection monitoring and subsection 2550.9(e)(2) of this article for evaluation monitoring. The constituents of concern to be monitored are those specified in the water quality protection standard specified for each monitoring and response program. The constituents of concern to be monitored shall include the constituents, including hazardous constituents, that must be degraded, transformed, or immobilized in the treatment zone of the land treatment unit.

(d) The regional board may require monitoring for principal hazardous constituents (PHCs) in lieu of the constituents specified under subsection (c) of this section. PHCs are hazardous constituents contained in the wastes to be applied at the unit that are the most difficult to treat considering the combined effects of degradation, transformation, and immobilization. The regional board may establish PHCs if the regional board finds based on waste analyses, treatment demonstrations, or other data that effective degradation, transformation, or immobilization of the PHCs will assure treatment at at least equivalent levels for the other hazardous constituents in the wastes.

(e) The discharger shall install an unsaturated zone monitoring system that includes soil monitoring using soil cores and soil-pore liquid monitoring using appropriate devices such as lysimeters capable of acquiring soil-pore liquid samples. The unsaturated zone monitoring system shall consist of a sufficient number of sampling points at appropriate locations and depths to yield samples that:

(f) The discharger shall establish a background value for each monitoring parameter and each constituent of concern to be monitored under subsection (c) of this section. The discharger shall propose, for approval by the regional board, the background values for each monitoring parameter and each constituent of concern or the procedures to be used to calculate the background values according to the provisions of subsection 2550.7(e)(10) of this article. The regional board shall specify the background values or procedures in waste discharge requirements according to subsection 2550.7(e)(11) of this article.

(g) Background soil values may be based on a one-time sampling at a background plot having characteristics similar to those of the treatment zone. For new land treatment units, background soil values shall include data from sampling at the proposed plot for the unit.

(h) Background soil-pore liquid values shall be based on at least quarterly sampling for one year at a background plot having characteristics similar to those of the treatment zone. For new land treatment units, background soil-pore liquid values shall include data from sampling at the proposed plot for the unit.

(i) The discharger shall express all background values in a form necessary for the determination of statistically significant increases pursuant to subsection (n) of this section.

(j) In taking samples used in the determination of all background values, the discharger shall use an unsaturated zone monitoring system that complies with subsection (e)(1) of this section.

(k) The discharger shall conduct soil monitoring and soil-pore liquid monitoring immediately below the treatment zone. The regional board shall specify the frequency and timing of soil and soil-pore liquid monitoring in the waste discharge requirements after considering all other monitoring provisions of this article, the frequency, timing, and rate of waste application, the soil permeability, and the maximum anticipated rate of migration. The discharger shall express the results of soil and soil-pore liquid monitoring in a form necessary for the determination of statistically significant increases pursuant to subsection (n) of this section.

(l) The discharger shall propose, for approval by the regional board, consistent sampling and analysis procedures that are designed to ensure sampling results that provide a reliable indication of soil-pore liquid quality and the chemical makeup of the soil below the treatment zone. At a minimum, the discharger shall implement the approved procedures and techniques for:

(m) The discharger shall determine whether there is a statistically significant increase below the treatment zone using a statistical method that provides reasonable confidence that migration from the treatment zone will be identified. The discharger shall propose each statistical method in accordance with the provisions of this subsection and pursuant to the provisions of subsection 2550.7(e)(7) of this article. The regional board shall specify each statistical method pursuant to subsection 2550.7(e)(7) of this article that the regional board finds:

(n) The discharger shall determine whether there is a statistically significant change over background values for each monitoring parameter and each constituent of concern to be monitored below the treatment zone each time the discharger conducts soil monitoring and soil-pore liquid monitoring under subsection (k) of this section.

(o) In determining whether a statistically significant increase has occurred, the discharger shall compare the value of each parameter or constituent, as determined pursuant to subsection (n) of this section, to the background value for that parameter or constituent according to the statistical procedure specified in the waste discharge requirements pursuant to this section.

(p) The discharger shall determine whether there has been a statistically significant increase below the treatment zone within a reasonable time period after completion of sampling. The regional board shall specify this time period in the waste discharge requirements after considering the complexity of the statistical test and the availability of laboratory facilities to perform the analysis of soil and soil-pore liquid samples.

(q) If the discharger determines pursuant to subsection (n) of this section, that there has been a statistically significant increase in the value of a hazardous constituent below the treatment zone the discharger shall:

(r) Upon receiving notice pursuant to subsection (q) of this section or upon the independent confirmation by the regional board, the regional board shall order the discharger to cease operating the land treatment unit. The discharger shall not resume operating the land treatment unit and shall close the land treatment unit unless one of the following actions is taken:

(s) All actions taken by a discharger pursuant to subsections (r)(1) or (r)(2) of this section shall be completed within a time period specified by the regional board, which shall not exceed 18 months after the regional board receives notice pursuant to subsection (q)(1) of this section. If the actions are not completed within this time period, the land treatment unit shall be closed, unless granted an extension by the regional board due to exceptional circumstances beyond the control of the discharger.

(t) If the discharger determines pursuant to subsection (n) of this section that there is a statistically significant increase of hazardous constituents below the treatment zone, the discharger may demonstrate that the increase resulted from an error in sampling, analysis, or evaluation. While the discharger may make a demonstration pursuant to this subsection in addition to or in lieu of the requirements of subsection (r)(1) or (r)(2) of this section, the discharger is not relieved of the requirements of subsections (r) and (s) of this section unless the demonstration made pursuant to this subsection successfully shows that the increase resulted from an error in sampling, analysis, or evaluation. In making a demonstration pursuant to this subsection, the discharger shall: