(1) Unless corrective action is initiated in accordance with ARM Title 17, chapter 56, subchapter 6, owners and operators must immediately investigate and confirm all suspected releases of regulated substances requiring reporting under ARM 17.56.502, within seven days of the discovery of the condition identified in ARM 17.56.502, using either of the following steps, unless both are required by the language of this rule:

(a) Owners and operators must conduct tests (according to the requirements for tightness testing in ARM 17.56.407 and 17.56.408 or, as appropriate, secondary containment testing in ARM 17.56.304(3)(f)(iii)) that determine whether a leak exists in any portion of the tank that routinely contains product, or the attached delivery piping, or both.

(i) Owners and operators must immediately repair, replace, upgrade, or close the PST or UST system, and begin corrective action in accordance with ARM Title 17, chapter 56, subchapter 6 if the test results for the system, tank, or delivery piping indicate that a release exists.

(ii) Further investigation is not required if the test results for the system, tank, and delivery piping do not indicate that a release exists and if environmental contamination is not the basis for suspecting a release.

(iii) Owners and operators must conduct a site check as described in (1)(b) if the test results for the system, tank, and delivery piping do not indicate that a leak exists but environmental contamination is the basis for suspecting a release.

(b) Owners and operators must measure for the presence of a release where contamination is most likely to be present at the PST or UST site. In selecting sample types, sample locations, and measurement methods, owners and operators must consider the nature of the stored substance, the type of initial alarm or cause for suspicion, the type of backfill, the depth of ground water, and other factors appropriate for identifying the presence and source of the release. The department should be consulted to assist in determining sample types, sample locations, and measurement methods. Owners and operators of PST sites and owners and operators of UST sites should refer to the Montana Quality Assurance Plan for Investigation of Underground Storage Tank Releases as a guide in the collection, preservation and analysis of field samples;

(i) if the test results for the excavation zone or the PST or UST site indicate that a release has occurred, owners and operators must begin corrective action in accordance with subchapter 6;

(ii) if the test results for the excavation zone or the PST or UST site are taken according to (1)(b) and do not indicate that a release has occurred, further investigation is not required if approved by the department; and

(iii) the department may reject all or part of the test results, if it has reasonable doubt as to the quality of data or if the sample or test methods are scientifically unsound. In such cases, the department may require resampling, reanalysis, or both. The department will provide the owner or operator with an explanation of its decision to reject any test results.