(1) (a) If ground water concentration(s) in samples from any facility ground water monitoring well(s) for any Table 1 [ARM 17.50.708] constituent equal or exceed an enforcement standard or show a significant statistical increase above background levels or a statistically significant decrease in pH occurs, the owner or operator must:

(i) Notify the department in writing within 14 days of the discovery.   The notification must specify the parameters and the well(s) involved;

(ii) Begin a program of assessment monitoring and resample all of the ground water monitoring wells for constituents of Table 2 [ARM 17.50.708] within 90 days;

(iii) Collect and analyze a minimum of at least 1 sample from each downgradient well during each sampling event consistent with the methods in the facility's sample and analysis plan approved under ARM 17.50.708;

(iv) For any constituent detected in the downgradient wells as a result of the complete Table 2 analysis, collect and analyze a minimum of 4 independent samples from each well (downgradient and upgradient) to establish background for the constituents detected;

(v) Continue assessment monitoring until the conditions specified in (2) of this rule are satisfied.   During continued assessment monitoring the owner or operator must:

(A) Sample all wells for all Table 2 constituents at least annually;

(B) Sample all wells within 90 days and at least semi-annually thereafter for all Table 1 constituents and all Table 2 constituents detected in the initial, or subsequent annual, Table 2 sampling;

(C) Collect and analyze at least 1 sample from each well (background and downgradient) during each sampling event; and

(D) For any constituent detected in the downgradient wells as a result of the Table 2 analysis, collect and analyze a minimum of 4 independent samples from each well (downgradient and upgradient) to establish background for the constituents detected.

(b) The department may delete any of the Table 2 constituents required under assessment monitoring if it can be demonstrated that the removed constituents are not reasonably expected to be in or derived from the waste contained in the unit.

(c) The department may designate an appropriate alternate subset of wells to be sampled for Table 2 constituents during continued assessment monitoring.

(d) The department may specify an alternative sampling frequency for the full set of Table 2 constituents, or the Table 1 constituents and Table 2 constituents detected during the full Table 2 analysis.   The frequency must be no less than annual and must be based on:

(i) the lithology of the aquifer and unsaturated zone;

(ii) the hydraulic conductivity of the aquifer and unsaturated zone;

(iii) ground water flow rates;

(iv) the minimum distance between upgradient edge of the disposal unit and downgradient monitoring well screen (minimum distance of travel) ;

(v) the resource value of the aquifer; and

(vi) the nature (fate and transport) of any constituents detected in response to this section.

(e) The department may require the owner or operator to sample public or private water supply wells or springs and to determine water level elevations in such wells to determine the extent of ground water contamination.

(f) The relevant point of compliance (POC) to determine if an enforcement standard or preventive action limit has been attained or exceeded is specified as no more than 150 meters beyond the waste management unit boundary and must be located on land owned by the owner of the disposal unit.

(i) The downgradient monitoring system must be installed at the POC specified by the department that ensures detection of ground water contamination in the uppermost aquifer.

(ii) 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 POC specified by the department that ensures detection of ground water contamination in the uppermost aquifer.

(g) The department may approve a multi-unit ground water monitoring system instead of separate ground water monitoring systems for each disposal unit when the facility has several units, provided the multi-unit ground water monitoring system meets the requirement of ARM 17.50.706, and the department determines it is equally or more protective of human health and the environment as individual monitoring systems for each unit. An owner or operator of a facility may submit a written request for approval of a multi-unit ground water monitoring system.   The requirements shall include an evaluation of at least the following factors:

(i) the hydrogeologic characteristics of the facility and surrounding land;

(ii) the climatic factors of the area;

(iii) the volume and physical characteristics of the leachate;

(iv) proximity of ground water users;

(v) the age, and design of the site;

(vi) the classification and quality of ground water;

(vii) the types of waste accepted at the disposal units; and

(viii) the number, spacing, and orientation of the disposal units.

(h) The owner or operator must place in the operating record and submit to the department the results of any sampling required under this rule within 14 days of the receipt of results by the owner or operator.

(i) The owner or operator must notify the department of any detection of any Table 2 [ARM 17.50.708] constituents within 14 days of the receipt of results by the owner or operator.   A copy of the notice must be placed in the operating record.

(j) The owner or operator may demonstrate that a source other than a disposal unit caused the contamination, or that the statistically significant increase resulted from error in sampling, analysis, statistical evaluation, or natural variation in ground water quality.   A report documenting this demonstration must be certified by a qualified ground water scientist and approved by the department and placed in the operating record.   If a successful demonstration is made the owner or operator must continue monitoring in accordance with the detection monitoring program pursuant to ARM 17.50.708.   If a successful demonstration is not made within 90 days, the owner or operator must comply with this rule and initiate assessment monitoring.

(2) If the concentrations of all Table 2 [ARM 17.50.708] constituents are shown to be at or below background values, using the statistical procedures in ARM 17.50.708, for 2 consecutive semi-annual sampling events, the owner or operator must notify the department of this finding and may return to detection monitoring for Table 1 [ARM 17.50.708] constituents.

(3) If the concentrations of any Table 2 [ARM 17.50.708] constituents are above background values, but all concentrations are below the ground water protection standard established under the Montana ground water quality standards, using the statistical procedures in ARM 17.50.708, the owner or operator must continue assessment monitoring on at least a semi-annual basis for all Table 1 [ARM 17.50.708] constituents and all Table 2 constituents detected in the initial assessment monitoring.

(4) If 1 or more Table 2 [ARM 17.50.708] constituents are detected at statistically significant levels above the ground water protection standard established under (5) of this rule in any sampling event, the owner or operator must, within 14 days of this finding, place a notice in the operating record identifying the Table 2 constituents that have exceeded the ground water protection standard and notify the department and all appropriate local government officials.   The owner or operator also:

(a) (i) Must characterize the nature and extent of the release by installing additional monitoring wells as necessary;

(ii) Must install at least 1 additional monitoring well at the facility boundary in the direction of contaminant migration and sample this well for all Table 2 constituents;

(iii) Must notify all persons who own the land or reside on the land that directly overlies any part of the plume of contamination if contaminants have migrated off-site if indicated by sampling of wells; and

(iv) Must initiate an assessment of corrective measures   within 90 days; or

(b) May demonstrate that a source other than a disposal unit caused the contamination, or that the statistically significant increase resulted from error in sampling, analysis, statistical evaluation, or natural variation in ground water quality.   A report documenting this demonstration must be certified by a qualified ground water scientist and approved by the department and placed in the operating record.   If a successful demonstration is made the owner or operator must continue monitoring in accordance with the assessment monitoring program pursuant to this rule, and may return to detection monitoring if the Table 2 [ARM 17.50.708] constituents are at or below background as specified in (2) of this rule.   Until a successful demonstration is made, the owner or operator must comply with (4) of this rule, including initiating an assessment of corrective measures.

(5) The ground water protection standard (enforcement standard) for each Table 1 and Table 2 [ARM 17.50.708] constituent must be:

(a) For constituents for which a maximum contaminant level (MCL) has been promulgated under the Montana ground water quality standards, the MCL for that constituent;

(b) For constituents for which MCLs have not been promulgated, the background concentration for the constituent established from wells in accordance with ARM 17.50.708;

(c) For constituents for which the background level is higher than the MCL identified under (a) above or health based levels identified under (d) below, the background concentration; or

(d) The department may establish alternative ground water protection standards (enforcement standards) for which MCLs have not been established based on the following criteria:

(i) The level is derived in a manner consistent with US EPA guidelines for assessing the health risks of environmental pollutants (51 FR 33992, 34006, 34014, 34028, September 24, 1986) ;

(ii) The level is based on scientifically valid studies conducted in accordance with the Toxic Substances Control Act Good Laboratory Practice Standards (40 CFR, Part 792) or equivalent;

(iii) For carcinogens, the level represents a concentration associated with an excess lifetime cancer risk level (due to continuous lifetime exposure) with the 1 x 10^-4 to 1 x 10^-6 range; and

(iv) For systemic toxicants, the level represents a concentration to which the human population could be exposed to on a daily basis that is likely to be without appreciable risk of deleterious effects during a lifetime.   For purposes of this subsection, systemic toxicants include toxic chemicals that cause effects other than cancer or mutation.

(6) (a) Within 90 days of finding that any of the constituents listed in Table 2 [ARM 17.50.708] have been detected at a statistically significant level exceeding the ground water protection standards defined under (5) of this rule, the owner or operator must initiate an assessment of corrective measures.   Such an assessment must be completed within a reasonable period of time, not to exceed an additional 60 days, and be submitted to the department.

(b) The owner or operator must continue to monitor in accordance with the assessment monitoring program as specified in this rule.

(c) The assessment shall include an analysis of the effectiveness of potential corrective measures in meeting all of the requirements and objectives of the remedy as described under (7) of this rule, addressing at least the following:

(i) The performance, reliability, ease of implementation, and potential impacts of appropriate potential remedies, including safety impacts, cross-media impacts, and control of exposure to any residual contamination;

(ii) The time required to begin and complete the remedy;

(iii) The costs of remedy implementation; and

(iv) The institutional requirements such as state or local permit requirements or other environmental or public health requirements that may substantially affect implementation of the remedy(ies) .

(d) The owner or operator must discuss the results of the corrective measures assessment, prior to the selection of remedy, in a public meeting with interested and affected parties.

(7) (a) Based on the results of the corrective measures assessment conducted under (6) of this rule, the owner or operator must select a remedy that, at a minimum, meets the standards listed in (b) below.   The owner or operator must notify the department, within 14 days of selecting a remedy, that a report has been placed in the operating record describing the selected remedy and how it meets the standards in (b) below.

(b) Remedies must:

(i) Be protective of human health and the environment;

(ii) Attain the ground water protection standard as specified pursuant to (5) of this rule;

(iii) Control the source(s) of releases so as to reduce or eliminate, to the maximum extent practicable, further releases of Table 2 [ARM 17.50.708] constituents into the environment that may pose a threat to human health or the environment; and

(iv) Comply with standards for management of wastes as specified in (8) of this rule.

(v) Be approved by the department.

(c) In selecting a remedy that meets the standards of (7) (b) of this rule, the owner or operator shall consider the following evaluation factors:

(i) The long and short-term effectiveness and protectiveness of the potential remedy(ies) , along with the degree of certainty that the remedy will prove successful based on consideration of the following:

(A) Magnitude of reduction of existing risks;

(B) Magnitude of residual risks in terms of likelihood of further releases due to waste remaining following implementation of a remedy;

(C) The type and degree of long-term management required, including monitoring, operation, and maintenance;

(D) Short-term risks that might be posed to the community, workers, or the environment during implementation of such a remedy, including potential threats to human health and the environment associated with excavation, transportation, and redisposal or containment;

(E) Time until full protection is achieved;

(F) Potential for exposure of humans and environmental receptors to remaining wastes, considering the potential threat to human health and the environment associated with excavation, transportation, redisposal, or containment;

(G) Long-term reliability of the engineering and institutional controls; and

(H) Potential need for replacement of the remedy.

(ii) The effectiveness of the remedy in controlling the source to reduce further releases based on consideration of the following factors:

(A) The extent to which containment practices will reduce further releases;

(B) The extent to which treatment technologies may be used.

(iii) The ease or difficulty of implementing a potential remedy(ies) based on consideration of the following types of factors:

(A) degree of difficulty associated with constructing the technology;

(B) expected operational reliability of the technologies;

(C) need to coordinate with and obtain necessary approvals and permits from other agencies;

(D) availability of necessary equipment and specialists; and

(E) available capacity and location of needed treatment, storage, and disposal services.

(iv) Practicable capability of the owner or operator, including a consideration of the technical and economic capability.

(v) The degree to which community concerns are addressed by a potential remedy(ies) .

(d) The owner or operator shall specify as part of the selected remedy a schedule for initiating and completing remedial activities.   Such a schedule must require the initiation of remedial activities within a reasonable period of time taking into consideration the factors set forth in (i) -(viii) below.   The owner or operator must consider the following factors in determining the schedule of remedial activities:

(i) Extent and nature of contamination;

(ii) Practical capabilities of remedial technologies in achieving compliance with ground water protection standards established under (5) of this rule and other objectives of the remedy;

(iii) Availability of treatment or disposal capacity for wastes managed during implementation of the remedy;

(iv) Desirability of utilizing technologies that are not currently available, but which may offer significant advantages over already available technologies in terms of effectiveness, reliability, safety, or ability to achieve remedial objectives;

(v) Potential risks to human health and the environment from exposure to contamination prior to completion of the remedy;

(vi) Resource value of the aquifer including:

(A) current and future uses;

(B) proximity and withdrawal rate of users;

(C) ground water quantity and quality;

(D) the potential damage to wildlife, crops, vegetation, and physical structures caused by exposure to waste constituent;

(E) the hydrogeologic characteristic of the facility and surrounding land;

(F) ground water removal and treatment costs; and

(G) the cost and availability of alternative water supplies.

(vii) Practicable capability of the owner or operator; and

(viii) Other relevant factors.

(e) The department may determine that remediation of a release of Table 2 [ARM 17.50.708] constituent from a disposal unit is not necessary if the owner or operator demonstrates to the department that:

(i) The ground water is additionally contaminated by substances that have originated from a source other than a disposal unit and those substances are present in   concentrations such that cleanup of the release from the disposal unit would provide no significant reduction in risk to actual or potential receptors; or

(ii) The constituent(s) is present in ground water that:

(A) Is not currently or reasonably expected to be a source of drinking water; and

(B) Is not hydraulically connected with waters to which the hazardous constituents are migrating or are likely to migrate in a concentration(s) that would exceed the ground   water protection standards established under (5) of this rule; or

(iii) Remediation of the release(s) is technically impracticable; or

(iv) Remediation results in unacceptable cross-media impacts.

(f) A determination by the department pursuant to (7) (e) of this rule will not affect the authority of the state to require the owner or operator to undertake source control measures or other measures that may be necessary to eliminate   or minimize further releases to the ground water, to prevent exposure to the ground water, or to remediate the ground water to concentrations that are technically practicable and significantly reduce threats to human health or the   environment.

(8) (a) Based on the schedule established under (7) (d) of this rule for initiation and completion of remedial activities, the owner/operator must:

(i) Establish and implement a corrective action ground water monitoring program that:

(A) at a minimum, meets the requirements of an   assessment monitoring program under this rule;

(B) indicates the effectiveness of the corrective action remedy; and

(C) demonstrates compliance with ground water protection standard pursuant to (5) of this rule.

(ii) Implement the corrective action remedy selected   under (7) of this rule; and

(iii) Take any interim measures necessary to ensure the protection of human health and the environment.   Interim measures should, to the greatest extent practicable, be consistent with the objectives of and contribute to the performance of any remedy that may be required pursuant to (7) of this rule.   The following factors must be considered by an owner or operator in determining whether interim measures are necessary:

(A) time required to develop and implement a final remedy;

(B) actual or potential exposure of nearby populations   or environmental receptors to hazardous constituents;

(C) actual or potential contamination of drinking water supplies or sensitive ecosystems;

(D) further degradation of the ground water that may occur if remedial action is not initiated expeditiously;

(E) weather conditions that may cause hazardous constituents to migrate or be released;

(F) risks of fire or explosion, or potential for exposure to hazardous constituents as a result of an accident or failure of a container or handling system; and

(G) other situations that may pose threats to human health and the environment.

(b) An owner or operator may determine, based on information developed after implementation of the remedy has begun or other information, that compliance with the requirements of (7) (b) of this rule are not being achieved through the remedy selected.   In such cases, the owner or operator must implement other methods or techniques that could practicably achieve compliance with the requirements, unless the owner or operator makes the determination specified in (8) (c) of this rule.

(c) If the owner or operator determines that compliance with the requirements of (7) (b) of this rule cannot be practically achieved with any currently available methods, the owner or operator must:

(i) Obtain certification of a qualified ground water scientist and approval by the department that compliance with requirements under (7) (b) of this rule cannot be practically achieved with any currently available methods;

(ii) Implement alternate measures to control exposure of humans or the environment to residual contamination, as necessary to protect human health and the environment; and

(iii) Implement alternate measures for control of the sources of contamination, or for removal or decontamination of equipment, units, devices, or structures that are:

(A) Technically practicable; and

(B) Consistent with the overall objective of the remedy.

(iv) Submit to the department for approval a report justifying the alternative measures 14 days prior to implementing the alternative measures and place a copy of the report in the operating record.

(d) All solid wastes that are managed pursuant to a remedy required under (7) of this rule, or an interim measure required under (8) (a) (iii) of this rule, must be managed in a manner:

(i) That is protective of human health and the environment; and

(ii) That complies with applicable federal Resource Conservation and Recovery Act requirements.

(e) Remedies selected pursuant to (7) of this rule must be considered complete when:

(i) The owner or operator complies with the ground water protection standards established under (5) of this rule at all points within the plume of contamination that lie beyond the ground water monitoring well system established under ARM 17.50.706.

(ii) Compliance with the ground water protection standards established under (5) of this rule has been achieved by demonstrating that concentrations of Table 2 [ARM 17.50.708] constituents have not exceeded the ground water protection standard(s) for a period of three consecutive years using the statistical procedures and performance standards in ARM 17.50.708(12) and (13) .   The department may specify an alternative length of time during which the owner or operator must demonstrate that concentrations of Table 2 [ARM 17.50.708] constituents have not exceeded the ground water protection standard(s) , taking into consideration:

(A) extent and concentration of the release(s) ;

(B) behavior characteristics of the hazardous constituents in the ground water;

(C) accuracy of monitoring or modeling techniques, including any seasonal, meteorological, or other environmental variabilities that may affect the accuracy; and

(D) characteristics of the ground water.

(iii) All actions required to complete the remedy have been satisfied.

(f) Upon completion of the remedy, the owner or operator must supply the department within 14 days with a certification that the remedy has been completed in compliance with the requirements of (e) above and a copy must be placed in the operating record.   The certification must be signed by the owner or operator and by a qualified ground water scientist and approved by the department.

(g) When, upon completion of the certification, the owner or operator determines that the corrective action remedy has been completed in accordance with the requirements under (e) above, the owner or operator will be released from the requirements for financial assurance for corrective action under ARM 17.50.540.

(9) (a) The department hereby adopts and incorporates by reference:

(i) 51 FR 33992, 34006, 34014, and 34028 (September 24, 1986) , containing EPA guidelines for assessing the health risks of environmental pollutants; and

(ii) 40 CFR, Part 792, setting standards ensuring scientifically valid laboratory studies.

(b) Copies of the above may be obtained from the Department of Environmental Quality, PO Box 200901, Helena, MT 59620-0901 [(406)444-1430].