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(1) In order to determine the full extent and location of soils contaminated by the release and the presence and concentrations of free and dissolved product contamination in the surface water and in ground water, owners and operators must conduct a remedial investigation of the release, the release site, and the surrounding area possibly affected by the release if any of the following conditions exist:

(a) there is evidence that ground water wells have been affected by the release (e.g., as found during release confirmation or previous corrective action measures);

(b) free product is found to need recovery in compliance with ARM 17.56.602(1)(c);

(c) there is evidence that contaminated soils may be in contact with ground water (e.g., as found during conduct of the initial response measures required under ARM 17.56.602); or

(d) the department requests a remedial investigation, based on the known or potential effects of contaminated soil or ground water on nearby surface water, ground water, and human health.

(2) After reviewing information required under ARM 17.56.602 and 17.56.603, the department may determine that no additional investigation or corrective action is necessary; however, the department may require the owners and operators to initiate and continue compliance monitoring as determined by the department.

(3) A remedial investigation generally is an expanded site assessment more detailed in scope than the initial response and abatement measures under ARM 17.56.602, which must define the nature, extent, and magnitude of contamination and identify threats to public health, welfare and to the environment. A remedial investigation work plan must be submitted to the department prior to implementation by the owners and operators. The department shall submit a copy of a work plan from any owner or operator who is or may be seeking reimbursement to the appropriate local government office with jurisdiction over corrective action of the release. The office shall respond with any comments within 15 days of receipt of the plan and the department shall approve or disapprove the plan within 15 days of receipt from the local government. The following information is required to complete the remedial investigation:

(a) site map(s) showing all sampling locations, including the site(s) of:

(i) borings;

(ii) monitoring wells;

(iii) recovery wells;

(iv) vapor survey points; and

(v) sites where any other samples were taken.

(b) soil and bedrock technical information and map(s), including:

(i) soil type, thickness, and classification below the site of the release;

(ii) unconsolidated material and bedrock type, thickness, and formation name below the site of the release;

(iii) boring logs and monitoring well logs (description of well, well construction methods, sediment odors, and blow count);

(iv) soil characteristics (grain size, sorting, origin, texture, permeability, classification);

(v) observed contamination (visual, odors, and vapor survey results); and

(vi) laboratory analytical results.

(c) ground water technical information and map(s), including:

(i) general description and characteristics of aquifers and unsaturated zone below the site of the release, including:

(A) hydraulic characteristics;

(B) depth to water table;

(C) surveyed water elevations and contours (potentiometric surface);

(D) direction of ground water flow;

(E) rate of ground water flow;

(F) perched conditions; and

(G) connections to other aquifers.

(ii) location, ownership, use and construction of all municipal, domestic, irrigation, industrial and monitoring wells within ½ mile of the site;

(iii) sampling description;

(iv) results of laboratory analysis.

(d) surface water technical information and map(s), including:

(i) location and use of all surface water within one mile of site;

(ii) ground water/surface water discharge points;

(iii) sampling description; and

(iv) results of laboratory analysis.

(e) description of and map(s) showing the extent of free product and vapors discovered, whether as a result of current or past vapors/seepage, in basements and other subsurface structures and utilities. The description must include a copy of the vapor survey.

(f) technical conclusions, which must be stated with reasonable professional certainty and under the standard of care applicable, must include at least:

(i) source of the release;

(ii) current extent of and potential for the release (determined with field or laboratory analytical detection equipment) in or through the following media:

(A) soil; lateral and vertical extent of fuel-soaked soil;

(B) free product; areal extent;

(C) water; dissolved phase (water soluble constituents);

(D) vapor;

(g) sampling summary charts, which clearly identify by the date on which the samples were taken, all of the following: sample ID#, sampling location, sample type, date analyzed, laboratory conducting the analysis, analytical method, and results of the analysis.

(h) laboratory report sheets.

(4) If a remedial investigation has been conducted, owners and operators must submit a report containing the information collected under (3) within 120 days of release confirmation. If investigation extends beyond the time for submission of the report, owners and operators must also submit an additional follow-up completion report according to a schedule established by the department.

History: 75-11-319, 75-11-505, MCA; IMP, 75-11-309, 75-11-505, MCA; NEW, 1989 MAR p. 1912, Eff. 11/23/89; TRANS, from DHES, 1995 MAR p. 2259; AMD, 2003 MAR p. 1079, Eff. 5/23/03; AMD, 2007 MAR p. 2124, Eff. 12/21/07; AMD, 2016 MAR p. 1694, Eff. 9/24/16.

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