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(1) All facilities required to monitor ground water are required to prepare a site specific hydrogeological and soils report of the facility. Four copies of the report must be transmitted to the department. The report must contain sufficient data and plans to provide the department with a sound basis to determine the adequacy of the proposed ground water monitoring system. At a minimum, the scope of each report will include the following components:

(a) The owner or operator shall conduct a program to evaluate hydrogeologic conditions at the facility. This program shall provide the following information:

(i) A description of the regional and facility specific geologic and hydrogeologic characteristics affecting ground water flow beneath the facility, including:

(A) regional and facility specific stratigraphy;

(B) structural geology;

(C) depositional history;

(D) identification and characterization of areas and amounts of potential recharge and discharge;

(E) a discussion of regional deeper aquifers of significance;

(F) regional and facility specific ground water flow patterns;

(G) characterization of seasonal variations in the ground water flow regime;

(H) resource value of the uppermost aquifer; and

(I) identification and description of the confining layers present, both above and below the saturated zone(s) .

(ii) An analysis of any topographic features that might influence the ground water flow system (springs, sinkholes, lineaments, outcrops, rivers, and other surface water or topographical features.

(iii) Based on field data, tests, and cores, preparation of a representative and accurate classification and description of the hydrogeologic units which overlie the uppermost aquifer or which may be part of the leachate migration pathways at the facility (including saturated and unsaturated units) , including:

(A) hydraulic conductivity, effective porosity, and porosity (from slug testing, pumping tests or laboratory methods) ;

(B) lithology, grain size, sorting, degree of cementation;

(C) an interpretation of the relative degree of interconnections between saturated zones; and

(D) the leachate attenuation capacity and mechanisms of the natural earth materials.

(iv) Based on field studies and cores, structural geology and hydrogeological cross sections showing the extent (depth, thickness, lateral extent) of hydrogeological units which may be part of the leachate migration pathways and identifying:

(A) laterally extensive and hydrogeologically significant sand and gravel layers in unconsolidated deposits.

(B) cross sections should include significant aquifers beneath the uppermost aquifer, particularly if the uppermost aquifer is thin or laterally discontinuous, as well as applicable confining layers;

(C) zones of fracturing or channeling in both horizontal and vertical directions in consolidated or unconsolidated deposits;

(D) zones of higher permeability or lower permeability that might direct and restrict the flow of contaminants;

(E) the uppermost aquifer; and

(F) water bearing zones above the first confining layer that may serve as a pathway for leachate migration including perched zones of saturation.

(v) Based on data obtained from ground water monitoring wells installed upgradient and downgradient from the waste disposal areas, a representative description of water level or fluid pressure monitoring will be prepared including:

(A) water level contour and/or potentiometric maps;

(B) hydrogeologic cross sections showing hydraulic gradients;

(C) the flow system including the vertical and horizontal components of flow; and

(D) any temporal changes in hydraulic gradients.

(vi) A description of manmade influences that may affect the hydrogeology of the site (schedules and volumes of production for local water supply wells, pipelines, drains, ditches, septic tanks, etc.) .

(vii) The hydrogeological report shall include a description, construction facts, location, elevation, well log, sampling history and operational history of all existing wells for monitoring ground water quality and static water level elevation at the facility.

(viii) The quality of ground water monitored by the ground water monitoring well network will be analyzed and the results included with the hydrogeological report. At a minimum the parameters listed in Table 1 [ARM 17.50.708] are required for each existing monitoring well.

(ix) The report shall include and explain all calculations supporting ground water flow directions and velocities, determinations of hydraulic conductivity, transmissivity, porosity, permeability, and estimated leachate transport times.

(x) Characterization of the soil and rock units above the water table in the vicinity of the landfill, including, but not limited to, the following information:

(A) USCS soil classification;

(B) surface soil distribution;

(C) unsaturated zone hydraulic conductivity;

(D) porosity;

(E) soil organic content;

(F) soil pH;

(G) particle size distribution;

(H) moisture content, specific capacity, infiltration rate;

(I) soil stratification effect on unsaturated flow;

(J) mineral content; and

(K) soil boring information gathered in the following manner:

(I) all borings shall be within 300 feet of the limits of waste filling (if practical) ;

(II) borings shall extend a minimum of 20 feet below the base of waste disposal areas, or to bedrock, whichever is less;

(III) Sufficient soil borings must be done to define the soil and bedrock conditions.   The initial drilling must include borings positioned throughout the site; within each geomorphic feature including ridges, knolls, depressions, and drainage swales; and within any geophysical anomalies already identified. The minimum required number of borings for this initial drilling is as follows:


0-10 acres          15 borings

11-20 acres         add 1 boring per additional acre

20-40 acres         add 1 boring per additional 2 acres

41 or more acres    add 1 boring per additional 4 acres

75% of the required number of boring may be conducted with a backhoe to a depth of 10 feet.


(IV) samples of all significant hydrostratigraphic units encountered during soil boring will be described in full in a report appendix;

(V) borings not converted to wells shall be abandoned in accordance with the well abandonment specifications herein; and

(VI) a boring log shall be submitted for each boring.   Each boring log shall include soil and rock descriptions, methods of sampling, sample depths and elevations, date of boring, land surface elevation, bottom of boring elevation, moisture content, and consolidation test results such as blow counts, vane sheer or pocket penetrometer.   If the boring is converted to a well, include the water level at time of drilling, dates of water level measurements and a well construction diagram.

(xi) An appendix shall be included which lists the references used and includes any additional data not previously presented, supplemental design calculations, material specifications, well construction specifications, and other appropriate information.

(b) The facility owner or operator or their consultant must perform the hydrogeological and soils study in a professional and workmanlike manner. If the operator fails to provide the necessary hydrogeological and soils information required by the department, then the owner must do so. Additional studies may be required if the department determines that the studies will lead to increased protection of public health and natural resources. A report will not be considered complete until it is approved in writing by the department.

(c) The hydrogeological and soils report must be completed for new and existing facilities within the following time frames:

(i) applicants for new facilities must submit a complete report before the department will consider an application to be complete;

(ii) existing, operating facilities must submit a complete report within the following time frame:

(A) a work plan must be submitted 90 days after notification by the department;

(B) a revised work plan must be submitted 15 days after the department comments are received;

(C) the hydrogeologic and soils report must be submitted 180 days after the work plan is approved by the department; and

(iii) facilities which serve a geographic area with a population of 5,000 or more persons that accepted solid waste after October 1, 1989, and have ceased taking waste prior to October 9, 1993, must submit to the department a complete report. The report must be submitted no later than one year after the department requests the report.   Closure will not be final until the department approves of the report.

(d) A work plan must be submitted to the department for approval at least 180 days in advance of any applicable deadline specified in ARM 17.50.701(2) .

History: 75-10-204(5), MCA; IMP, 75-10-204, 75-10-207, MCA; NEW, 1991 MAR p. 1937, Eff. 10/18/91; AMD, 1993 MAR p. 1645, Eff. 10/9/93; TRANS, from DHES, 1995 MAR p. 2253.

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