17.30.508 SPECIFIC RESTRICTIONS FOR GROUND WATER MIXING ZONES (1) remains the same.

17.30.517 STANDARD MIXING ZONES FOR GROUND WATER (1) The following criteria apply to determine which discharges qualify for a standard ground water mixing zone:

(a) remains the same.

(b) Disposal systems that discharge to ground water through infiltration, drainfields absorption systems, injection through a disposal well, leakage from an impoundment, seepage from a land application area, or other methods may qualify for a standard mixing zone.

(d) The estimation required in (c), must be based on a calculation of the volume of water moving through a standard cross-section of aquifer. The calculated volume of water moving through the aquifer cross-section is hypothetically mixed with the known volume and concentration of the discharge to determine the resulting concentration at the boundary of the mixing zone. The recommended method to determine the resulting concentration at the boundary of a standard ground water mixing zone is described below:

(viii)(ix) The downgradient boundary of the standard mixing zone extends:

(2)  The department adopts and incorporates by reference Department Circular DEQ-13, entitled "Montana's Policy for Nutrient Trading" (December 2012 edition), which provides procedures and requirements for generating and applying nutrient credits in department-issued discharge permits.  Copies of Department Circular DEQ-13 may be obtained from the Department of Environmental Quality, P.O. Box 200901, Helena, MT 59620-0901.

REASON: The department proposes to replace the word "drainfield" in (1)(b), (1)(d)(ix), and (1)(d)(x) with "absorption system," which is the term used and defined in Department Circular DEQ-4, in order to ensure consistency of terms across different agency rules. No change in the intent or meaning of the rule is proposed. 

The addition of (1)(d)(vi) is proposed to implement Senate Bill 285 from the 2023 legislative session. That bill directed the department to, among other things, adopt criteria for crediting nitrogen attenuation at the drainfield and riparian zone based on soil type in making nonsignificance determinations for non-permitted septic system discharges. New (1)(d)(vi) meets this requirement by providing a method to estimate the reduction in the nitrogen load impacting state ground water and surface water by using Montana's Septic Trading Method in Appendix A of Department Circular DEQ-13 to account for the natural environmental reduction of nitrogen after being discharged to the subsurface from a wastewater absorption system. This method estimates the reduction of the nitrogen wasteload discharged from a wastewater treatment system using an NRCS soil drainage classification for both the soils beneath the absorption system and soils in the riparian area and the distance from the absorption system to the end of the ground water mixing zone or the surface water as applicable. This method was chosen because it has been long-established in Montana, uses readily available information, and addresses the requirement in SB 285 to incorporate drainfield and riparian zone soil attenuation.

The proposed changes to (1)(d)(ix) are necessary to replace inconsistent standard ground water mixing zone lengths that were based on wastewater treatment system size, lot size, subdivision size, and type of water system, which results in widely different standard mixing zones for wastewater treatment systems designed for the same use and the same design wastewater flow. The proposed changes are necessary to provide flexible and consistent standard mixing zone lengths that are based on the most important factors, design flow and the nature of the wastewater discharge. The proposed changes allow more flexibility in assigning standard mixing zone lengths that stay within the lot boundaries that may be necessary under ARM 17.36.122(6). The proposed changes also eliminate unnecessarily long standard mixing zones (up to 500 feet under the current rules) for many small wastewater treatment systems (individual, shared, and multiple-family) that do not provide any environmental benefit over shorter standard mixing zones.

The proposed deletion of (1)(d)(ix)(C) would remove a provision that is unnecessary because source specific mixing zones are available in ARM 17.30.518.

The proposed amendment that adds "industrial wastewater" to (1)(d)(ix)(D) is necessary to provide clarity and consistency for industrial discharges that have characteristics similar to residential wastewater but that discharge other constituents not addressed by the residential strength wastewater definition in DEQ-4 and therefore require longer mixing zones to protect state waters and their uses.  Industrial dischargers may request a different ground water mixing zone length pursuant to the source specific mixing zone requirements in ARM 17.30.518.

The department also proposes to replace the term "single family septic system" with "individual wastewater system" in (1)(d)(ix) and (1)(d)(x), which is the term used and defined in Department Circular DEQ-4, in order to ensure consistency of terms across different agency rules. No change in the intent or meaning of the rule is proposed. 

In (2), the existing Department Circular DEQ-13 is incorporated by reference because Appendix A in that circular contains Montana's Septic Trading Method, which is proposed to be used as described in the proposed changes to (1)(d)(vi).  Department Circular DEQ-13 is available online at: https://deq.mt.gov/files/Water/WQPB/Standards/NutrientWorkGroup/NutrientWorkGroupRulePackage12_13/CircularDEQ13.pdf.

17.30.702 DEFINITIONS The following definitions, in addition to those in 75-5-103, MCA, apply throughout this subchapter (Note: 75-5-103, MCA, includes definitions for "base numeric nutrient standards," "degradation," "existing uses," "high quality waters," "mixing zone," and "parameter"):

(1) through (8) remain the same.

(9)  "Level 1a treatment" means a subsurface wastewater treatment system (SWTS) that:

(a)  removes at least 50 percent, but less than 60 percent, of total nitrogen as measured from the raw sewage load to the system; or

(b)  discharges a total nitrogen effluent concentration of greater than 24 mg/L, but not greater than 30 mg/L.  The term does not include treatment systems for industrial waste.  A level 1a designation allows the use of 30 mg/L nitrate (as N) as the nitrate effluent concentration for mixing zone calculations.

(10)  "Level 1b treatment" means a SWTS that:

(a)  removes at least 34 percent, but less than 50 percent, of total nitrogen as measured from the raw sewage load to the system; or

(b)  discharges a total nitrogen effluent concentration of greater than 30 mg/L, but not greater than 40 mg/L.  The term does not include treatment systems for industrial waste.  A level 1b designation allows the use of 40 mg/L nitrate (as N) as the nitrate effluent concentration for mixing zone calculations.

(11)(9) "Level 2 treatment" means a SWTS wastewater treatment system that:

(27)(28) The department adopts and incorporates by reference:

(a) and (b) remain the same.

(c) Department Circular DEQ-4, entitled "Montana Standards for Subsurface Wastewater Treatment Systems" (2013 2023 edition), which establishes technical standards for construction of subsurface wastewater treatment systems; and

REASON:  The department proposes to remove the definitions of "Level 1a treatment" and "Level 1b treatment" because these treatment technologies have become outdated, making it unnecessary to retain the definitions. Since those treatment levels were added to the rules in 2004, the department has received only one application for such approval, and that system also sought and received level 2 approval.

The department also proposes to replace the term "sewage" in (9)(a) with the term "wastewater," which is the term used and defined in Department Circular DEQ-4, in order to ensure consistency of terms across different agency rules. No change in the intent or meaning of the rule is proposed.

It is necessary to define "level 3 treatment" and "level 4 treatment" in proposed (10) and (11) to incorporate definitions for these improved wastewater treatment technologies currently available for use in wastewater treatment systems. Level 3 and level 4 treatment technologies provide greater nitrogen reduction than the existing definition of level 2 treatment systems. The proposed definitions in (10) and (11) provide the different nitrogen reduction capabilities for level 3 and level 4 treatment technologies prior to discharge. "Level 2 treatment" has been defined in the rule since 1994.  For purposes of nonsignificance determinations in ARM 17.30.715(1)(d)(iii), wastewater treatment systems using level 2 or higher treatment are treated the same.

In conjunction with the proposed amendments to ARM 17.30.715, the department proposes in (19) to add a definition for "ordinary high-water mark." This is necessary to assist the department and public in consistently and accurately defining the distances between a proposed discharge and surface water for purposes of nonsignificance review. The department proposes to use the definition in 23-2-301, MCA, because it is a clear and well-established statutory definition.

It is necessary to update new (28) in order to incorporate by reference the 2023 edition of Department Circular DEQ-4, entitled "Montana Standards for Subsurface Wastewater Treatment Systems," which is the current version of that document.  The 2023 edition of Department Circular DEQ-4 was previously adopted by the department in April 2023 as part of MAR Notice No. 17-421.

17.30.715 CRITERIA FOR DETERMINING NONSIGNIFICANT CHANGES IN WATER QUALITY (1) The following criteria will be used to determine whether certain activities or classes of activities will result in nonsignificant changes in existing water quality due to their low potential to affect human health or the environment.  These criteria consider the quantity and strength of the pollutant, the length of time the changes will occur, and the character of the pollutant. Except as provided in (2), changes in existing surface or ground water quality resulting from the activities that meet all the criteria listed below are nonsignificant, and are not required to undergo review under 75-5-303, MCA:

(d) changes in the concentration of nitrate in ground water which will not cause degradation of surface water if the sum of the predicted concentrations of nitrate at the boundary of any applicable mixing zone will not exceed the following values:

For purposes of this subsection (d), the word "nitrate" means nitrate as nitrogen; and

(g) for nutrients in domestic sewage effluent discharged from a septic wastewater treatment system that does not require an MPDES or MGWPCS permit, except as specified in (1)(d) and (e), which will not cause changes that equal or exceed the trigger values in Department Circular DEQ-7.  Whenever the change exceeds the trigger value, the change is not significant if the changes outside of a mixing zone designated by the department are less than ten percent of the applicable standard and the existing water quality level is less than 40 percent of the standard; and

(4) The following criteria and the criteria in (1)(g) apply to determine whether subsurface wastewater treatment system discharges that are not subject to ground water permitting requirements will result in nonsignificant changes in existing water quality.

            (a) Except as provided in (b), the criteria in (1)(g) apply in either of the following cases:

(i) the ordinary high-water mark of a potentially impacted downgradient state surface water is less than 1/4 mile from any portion of the wastewater absorption system; or

(ii) the ordinary high-water mark of a potentially impacted downgradient state surface water is between 1/4 mile and 1/2 mile from any portion of the wastewater absorption system and:

(A) any of the absorption system soil profiles required by Department Circular DEQ-4 has a limiting layer less than 8 feet below the natural ground surface;

(B) the absorption system soil application rate pursuant to Department Circular DEQ-4 is 0.5 gallons per day per square foot (gpd/ft²) or larger; or

(C) the absorption system soil application rate pursuant to Department Circular DEQ-4 is less than 0.5 gpd/ft² and the soil classification modifier includes extremely cobbly, extremely stony, or extremely bouldery.

            (b) The criteria in (1)(g) do not apply to subsurface wastewater treatment systems that are more than 1/2 mile from a state surface water or to wastewater treatment systems in which the absorption trench is lower in elevation than all downgradient state surface water within 1/2 mile of the absorption system. 

            (c) The distances to surface water in (a)(i) and (a)(ii) include the five-degree expansion of the effluent plume as described for ground water mixing zones in ARM 17.30.517(1)(d)(iii)(B).  The distance is based on the measured ground water flow direction between the absorption system and the ordinary high-water mark of the potentially impacted downgradient state surface water, or the shortest distance between the absorption system and the ordinary high-water mark of the potentially impacted downgradient state surface water when the ground water flow direction is estimated from topography or other method.

            (d) The analysis of impacts to state surface water must use the waste load, as described in ARM 17.30.517(1)(d)(vii)(B), discharged from the absorption system, except when:

(i) the waste load can be reduced pursuant to ARM 17.30.517(1)(d)(vi); or

(ii) a saturated zone solute transport or saturated zone particle tracking model is used to demonstrate that the waste load potentially impacting the state surface water should be reduced.  The model must include site-specific data characterizing the necessary hydrogeologic properties of the water-bearing units in the effluent flow path and calibrated to site-specific data.

(e) Pursuant to 75-5-301(5)(e), MCA, the requirements of (2) do not apply to subsurface wastewater treatment system discharges that are not subject to ground water permitting requirements under 75-5-401, MCA.

(4) remains the same, but is renumbered (5).

REASON: The department proposes in (1)(d)(ii), (1)(d)(iii), (1)(d)(iv), and (1)(g) to replace the term "septic system" with "wastewater treatment system," which is the term used and defined in Department Circular DEQ-4, in order to ensure consistency of terms across different agency rules. No change in the intent or meaning of the rule is proposed.  

The department proposes to amend (1)(d)(iii) to add references to level 3 and level 4 systems, which is necessary to ensure consistency between this rule and the proposed changes to ARM 17.30.702 that add new definitions for such systems. As discussed above, the proposed changes are necessary because certain technologies provide higher levels of treatment than those currently recognized in the rules. Because level 3 and level 4 systems provide even higher levels of treatment than the existing definition of level 2 systems, the proposed rules provide that such systems should be evaluated under the same ground water nonsignificance criteria for level 2 systems in 75-5-301, MCA.

In (1)(g), the department proposes to delete the reference to a nonsignificance limit based on the numeric nutrient water quality standard in Department Circular DEQ-12A. It is necessary to remove any use or reference to Department Circular DEQ-12A to comply with Senate Bill 358 from the 2021 legislative session.

New (4) is necessary to implement Senate Bill 285 from the 2023 legislative session, which requires the department to adopt new criteria to determine when septic system discharges that are not subject to permit requirements result in nonsignificant changes in water quality. These proposed criteria in (4) consider soil type, mixing, nitrogen attenuation, the distance between the subsurface discharge and downgradient surface water, and the comparative elevation of the discharge and downgradient state surface water within 1/2 mile of the absorption system. 

As required by SB 285, proposed (4)(a) limits the adjacent-to-surface-water trigger analysis in (1)(g) to a maximum of 1/4 or 1/2 mile from the drainfield to the state surface water, depending on soil type. These soil types are proposed in (4)(a)(ii)(A) through (C). In (4)(a)(ii)(A), surface water impacts would be considered when the absorption system is between 1/4 and 1/2 mile from surface water and if any of the absorption system soil profiles required by DEQ-4 has a limiting layer less than 8 feet below the natural ground surface. This is necessary to determine nonsignificant impacts for those wastewater discharges that will have less unsaturated soil treatment and, thus, have shorter travel times to surface water and higher risk to impact surface water. In (4)(a)(ii)(B) and (C), the department proposes absorption system application rates and soil classification modifiers to assess the relative travel time and vulnerability of surface waters that are between 1/4 and 1/2 mile distant. The soil application rates are based on soil types and defined for wastewater absorption systems in Department Circular DEQ-4.  Areas with the faster soil application rates listed in the rule (and soils classified as extremely cobbly, stony, or bouldery) are correlated with faster travel times and reduced natural wastewater treatment that increases risk to surface waters; and these wastewater treatment systems, when located between 1/4 and 1/2 mile from high-quality surface waters, are required to undergo assessment of impacts to surface water.  Using the soil application rate and soil classification modifier is necessary to provide a consistent and well-defined process to estimate the relative amount of natural treatment and relative travel time between the wastewater discharge and surface water.  The soil profile information required here is already required for each proposed wastewater absorption system in Department Circular DEQ-4.

Proposed (4)(b) provides that the criteria in (1)(g) do not apply to systems that are more than 1/2 mile from a state surface water or to wastewater treatment absorption system trenches that are lower in elevation than downgradient surface waters. These requirements are necessary to comply with the requirements in SB 285 that the criteria must consider elevation and the horizontal distance between the discharge and the surface water in the direction of ground water flow and that the analysis must be limited to a maximum of 1/2 mile.

New (4)(c) provides requirements for measuring the distance between the absorption system and the state surface water to ensure consistency in determining whether surface water nonsignificance assessments are required for wastewater treatment systems. Two methods of measuring the distance are necessary to account for uncertainty when a measured ground water flow direction is not available.  In cases where the ground water flow direction is not measured, using the closest distance to surface water is necessary to protect surface waters that may be within the 1/4 and 1/2 mile distances specified in (4)(a) depending on the actual ground water flow direction.  In cases where the ground water flow direction is measured, it is necessary to use that information to prevent underestimating or overestimating the distance from a wastewater absorption system to surface water.

As required by SB 285, new (4)(d) accounts for mixing zone dilution and credits nitrogen attenuation at the drainfield and riparian zone. Waste loads are used to determine compliance with the applicable water quality standards and nonsignificance criteria in state waters.  Section (4)(d)(i) refers to the nitrogen waste load reduction described in proposed revisions to ARM 17.30.517(1)(d)(vi). See the reason statement for that rule in this notice of proposed rulemaking for further discussion of that method. Section (4)(d)(ii) provides a method to estimate a reduction in the phosphorus and nitrogen waste load from a wastewater treatment system using site-specific data and modeling. Both of these sections require site-specific data to estimate the waste load reductions. Providing methods to estimate more accurate waste loads entering state waters is necessary to ensure that the correct regulatory requirements for treatment, location, and amount of wastewater are applied. Finally, as required by SB 285, new (4)(e) provides that a discharge that meets the criteria in (1)(g) and (4) is nonsignificant without further review.

(2) Except as provided in (5), a A subsurface wastewater treatment system (SWTS) that does not require an MPDES or MGWPCS permit and meets all of the criteria in (2)(a) (3) and (4) falls within one of the categories in (2)(b) is nonsignificant.

(a)(3)  The SWTS wastewater treatment system, including primary and replacement absorption systems, drainfields must meet all of the following criteria:

(i)(a) the drainfield absorption systems must be 1,000 500 feet or more (400 200 feet or more for lots that meet the criteria in (2)(b)(iv) (4)(b)) from the nearest downgradient high-quality state surface water that might be impacted. Distance between the absorption system and downgradient high-quality state surface water is based on the criteria in ARM 17.30.715(4) This distance may be reduced by 50% (to 500 and 200 feet, respectively) if the drainfield is pressure-dosed;

(ii) if the drainfield is not pressure-dosed:

(A) the soil percolation rate must be between 16 and 50 minutes per inch, if a percolation test has been conducted for the drainfield; and

(B) the natural soil beneath the absorption trench must contain at least six feet of very fine sand, sandy clay loam, clay loam, or silty clay loam;

(iii)  the SWTS must serve no more than two single-family residences, or must serve a facility that produces non-residential, non-industrial wastewater with a wastewater design flow of 700 gallons per day or less;

(b)  the wastewater treatment systems on a lot must have a combined design flow of 600 gallons per day or less, or a combined design flow of 800 gallons per day or less if all the wastewater treatment systems on the lot are level 2, level 3, or level 4 treatment systems;

(c) the wastewater discharge must be residential strength;

(iv) there must be only one SWTS receiving wastewater from the lot;

(v)(d)  the SWTS each wastewater treatment system must be located entirely on the lot where wastewater is produced;

(vi)(e)  the SWTS each wastewater treatment system must meet the current design standards defined in ARM Title 17, chapter 36, subchapter subchapters 3 and 9, and department Department Circular DEQ-4; and

(f) all wastewater treatment systems on the lot must meet the requirements in this rule.

(vii) for lots smaller than 20 acres, and for lots 20 acres and larger on which the drainfield is 500 feet or less from the downgradient property boundary, the background nitrate (as N) concentration in the shallowest ground water must be less than two mg/L.

(A) The department may require multiple ground water samples over a specified time period to determine whether seasonal variation of ground water nitrate concentrations may affect compliance with this requirement.

(b) The SWTS must fall within one of the following five categories:

(i) for category one:

(A) the lot size is two acres or larger;

(B) the percolation rate is 16 minutes per inch or slower, if a percolation test has been conducted for the drainfield;

(C) the natural soil beneath the absorption trench contains at least six feet of very fine sand, sandy clay loam, or finer soil; and

(D) the depth to bedrock and seasonally high ground water is eight feet or greater;

(ii) for category two:

(A) the drainfield is pressure-dosed;

(B) the lot size is two acres or larger;

(C) the percolation rate is six minutes per inch or slower, if a percolation test has been conducted for the drainfield;

(D) the natural soil beneath the absorption trench contains at least six feet of medium sand, sandy loam, or finer soil; and

(E) the depth to bedrock and seasonally high ground water is 12 feet or greater;

(iii) for category three:

(A) the drainfield is pressure-dosed;

(B) the lot size is one acre or larger;

(C) the subdivision consists of five lots or fewer;

(D) there is no existing or approved SWTS within 500 feet of the subdivision boundaries;

(E) the percolation rate is six minutes per inch or slower, if a percolation test has been conducted for the drainfield;

(F) the natural soil beneath the absorption trench contains at least six feet of medium sand, sandy loam, or finer soil; and

(G) the depth to bedrock and ground water is 100 feet or greater;

(iv) for category four:

(4) A wastewater treatment system that meets the requirements in (3) must also meet:

(a)  all the requirements in one of the categories in Table 1; or

(b)  the following requirements:

(A)(i) the wastewater treatment system is in a county where the total number of subdivision lots that were reviewed pursuant to 76-4-101 et seq.Title 76, chapter 4, part 1, MCA, and were created in a that county during the previous 10 state fiscal years is fewer than 150; and

(B)(ii) the lot is not within one mile of the city limits of an incorporated city or town with a population greater than 500 as determined by the most recent census; or and

(iii) the absorption system is pressure dosed.

(v) for category five:

(A) the SWTS is a level II system;

(B) the lot size is two acres or larger;

(C) the bottom of the drainfield absorption trenches is not more than 18 inches below ground surface; and

(D) the depth to limiting layer (based on test pit data) is greater than six feet below ground surface.

(c)

Table 1

FOOTNOTES

(1) "N/A" means not applicable for purposes of this rule. Requirements in all other applicable laws, rules, and circulars must be met.

(2) The reviewing authority may require multiple ground water samples over a specified time period to determine whether seasonal variation of ground water nitrate concentrations may affect compliance with this requirement.

(3) Soil profiles must be conducted in accordance with site evaluation requirements in Department Circular DEQ-4.  Soils that contain 60% or more of a rock fragment (gravel, cobble, stone, or boulder) and are considered extremely gravelly, extremely cobbly, extremely stony or extremely bouldery will not meet this requirement.  All soil profiles for a wastewater treatment system absorption system must meet these soil requirements. The six foot thickness of the specified soil type may be a continuous soil layer or a combination of multiple layers.

(4) Depth below ground surface to ground water and bedrock can be determined using local well logs or other applicable information as approved by the reviewing authority.

(5) For depths shallower than 24 inches, absorption systems must meet the requirements in Department Circular DEQ-4 for shallow-capped absorption systems.

(6)  Category only applies to the gray water discharge. It does not include a blackwater discharge or an alternate system required by Department Circular DEQ-4 that treats gray water and other wastewater from the lot.

(3) A mixing zone is not required for SWTSs that meet the criteria in this rule. However, SWTS drainfields must be located so that there is a 100-foot setback between existing and approved water supply wells and the boundaries of a 100-foot mixing zone that is provisionally designated for purposes of applying this setback.

(4) remains the same, but is renumbered (6).

(5) A 100-foot provisional mixing zone is required for each wastewater treatment system approved as nonsignificant under this rule.  Source specific provisional mixing zones are not allowed.  Provisional mixing zones are subject to the same setbacks and siting requirements as mixing zones but are not subject to the requirements of ARM 17.30.715.

(5) Notwithstanding an activity's designation as nonsignificant in this rule, the department may review the activity for significance under the criteria in ARM 17.30.715(1) based upon the following:

(a) cumulative impacts or synergistic effects;

(b) secondary byproducts of decomposition or chemical transformation;

(c) substantive information derived from public input;

(d) changes in flow;

(e) changes in the loading of parameters;

(f) new information regarding the effects of a parameter; or

(g) any other information deemed relevant by the department and that relates to the criteria in ARM 17.30.715(1) .

(6)(7) The department may determine that the categorical exclusion in (2) does not apply to lots within a specific geographic area do not meet the nonsignificance criteria in (2), and those lots must be reviewed pursuant to ARM 17.30.715. This determination must be based upon information submitted in a petition demonstrating that the categorical exclusions nonsignificance criteria in (2) should not apply within that area.

(a) remains the same.

(b) A petition submitted under this rule must contain the following information:

(i) a legal description of the petition area, which is the geographic area within which the categorical exclusions nonsignificance criteria in (2) would not apply;

(ii) and (iii) remain the same.

(iv) data from ground water samples taken from wells that withdraw water from the uppermost aquifer underlying the petition area or from wells that withdraw water from the uppermost aquifer underlying an area within the same or adjacent county with similar climatic, soil, geologic, and hydrogeologic conditions and a density of individual sewage systems similar to that allowed in (2)(b).  The ground water data must demonstrate that one of the following conditions is met:

(A) nitrate as nitrogen concentrations exceed 5.0 mg/L in ground water samples from more than 25% of at least 30 wells that are not located within a standard mixing zone, as defined in ARM 17.30.517(1)(d)(viii)(ix), for a septic wastewater treatment system; or

(B) remains the same.

(c) Within 90 days after receipt of the information required in (6)(b), the department shall issue a preliminary decision as to whether the petitioner has satisfied the requirements in (6)(b), and describe the reasons for either granting or denying the petition.  The preliminary decision must be mailed to the petitioner and to all landowners or persons with a contract interest in land within the petition area and must include the following information:

(i) through (v) remain the same.

(vi) the name, e-mail address, and telephone number of a person to contact for additional information.

(d) remains the same.

REASON:  This rule sets forth categories of subsurface wastewater treatment systems that cause nonsignificant changes to water quality in addition to those in ARM 17.30.715 and 75-5-317, MCA. Each of the nonsignificant categories in this rule use multiple site-specific, property-specific, and treatment-specific requirements to ensure that small wastewater treatment systems do not degrade state waters and comply with the requirements of 75-5-301, MCA, for nonsignificant activities. The existing rule provides five such categories. In SB 285, the 2023 Legislature directed the agency to create additional nonsignificant ground water and surface water categories of 500 or more feet from surface water that consider soil texture, ground water depths, and other pertinent information.

The proposed changes are necessary to implement this statutory directive. The proposed changes also simplify the rule by providing a table of the categories to allow for easier comparison of requirements that might be applicable to a site; require pressure dosing for more categories than the existing rules, which provides additional environmental protection by providing better distribution of wastewater across the entire absorption system which increases the amount of effluent treatment by the biofilm and soils beneath the absorption system; and encourage the use of wastewater treatment systems that provide higher levels of treatment (levels 2, 3, and 4 treatments) compared to conventional (septic tank and absorption system) wastewater treatment systems by providing three new nonsignificant categories that apply only to level 2, level 3, and level 4 treatment systems. Each of the changes is discussed in more detail below.

            The amendment to (2) is necessary to clarify that the rule applies only to systems that do not require an MPDES or MGWPCS permit. This is not a change in the meaning of the rule, as the design discharge rate in the rule already limits the rule to wastewater treatment systems with lower design flows than those that might require a discharge permit.

            The amendments to (3)(a) maintain minimum distances to surface water for all nonsignificant categories to 200 or 500 feet and remove references to other distances (400 or 1,000 feet) for non-pressure dosed systems. The 500-foot setback for new nonsignificant categories is required in SB 285. The 200-foot setback to surface water applies only to the category in (4)(b) and has not been modified from the existing rule.  Except for new category 9 in Table 1 that requires larger lots than the other categories, pressure dosing is required for all systems seeking to qualify for any of the nonsignificant categories in this rule. Pressure dosing of the absorption systems provides better wastewater treatment, and expanding its requirement in the proposed rule would provide additional protection of state waters. The current setbacks (500 feet and 200 feet, as applicable) in the rule remain unchanged for pressure-dosed absorption systems (and for new category 9 in Table 1) and are necessary to provide protection to state surface waters. The distance between the absorption system and downgradient state surface water is based on the criteria in proposed ARM 17.30.715(4) to ensure consistency across the rules. Finally, it is necessary to delete the percolation rate and soil classification requirements in existing (2)(a)(ii)(A) and (B) for absorption systems that are not pressure dosed because the use of absorption systems that are not pressure dosed is being eliminated in existing (2)(a) as an option for all categories except for new category 9 in Table 1.

The proposed changes to (3)(b) include maintaining similar limits for wastewater flow compared to the existing rule (700 gallons per day (gpd)), but allows for less wastewater discharges from conventional wastewater treatment systems (600 gpd) than level 2, 3, and 4 treatment systems (800 gpd) that provide better treatment including the removal of more nitrogen compared to conventional wastewater treatment systems.  Using different discharge volumes for level 2, 3, and 4 systems would encourage the use of wastewater treatment systems that provide better treatment and have long-term monitoring requirements while allowing for greater flexibility and application of the proposed nonsignificant categories.

            The existing rule in (3)(b) limits the nonsignificant categories to systems that treat single family, shared facilities, or non-residential, non-industrial wastewater. This requirement is unnecessarily complex and has led to confusion. The amendments to (3)(b) and (3)(c) correct this by providing simple and clear criteria for the wastewater discharge requirements that revise the wastewater flow rates in (3)(b) and specify the type of wastewater (residential strength) in (3)(c).

            The amendments to (3)(d) specify that a wastewater treatment system seeking an exemption under the rule must be located entirely on the lot where the wastewater is produced. This is necessary to ensure that systems are not considered nonsignificant if they are primarily or partially located on lots that do not meet the rule requirements.

            The amendment to (3)(e) is necessary to correct an omission in the existing rule and to clarify the rule applies to systems reviewed under ARM Title 17, chapter 36, subchapter 9 in addition to those reviewed under ARM Title 17, chapter 36, subchapter 3.

New (3)(f) requires all the wastewater treatment systems on a lot to meet the rule requirements. This section is necessary because the current rule only allows one wastewater treatment system on a lot, and the proposed revisions to (3)(b) allow more than one wastewater treatment system on a lot.  Without this addition, a lot could contain a combination of wastewater treatment systems that meet one of the nonsignificant categories in the rule and other wastewater treatment systems that do not, which would conflict with the intent of the nonsignificant categories to limit the amount of wastewater discharged on a lot as described in (3)(b).

The existing subsections in (2)(a)(vii) through existing (2)(b)(iii) and (2)(b)(v) are proposed to be moved to new Table 1, which sets forth those requirements in a format that is easier for both applicants to use and for the reviewing authority to review.

Row (i) in Table 1 maintains the existing minimum lot size for existing categories 1 through 4 and provides minimum lot sizes for new categories 5 through 9. This requirement is necessary to limit the density of wastewater treatment systems to protect state waters because discharging excess wastewater in a given area increases the potential to degrade state waters.

Proposed category 9 is for lots that are 20 acres and larger. This category is necessary to account for areas of low density where the cumulative effects of multiple wastewater treatment systems are not a threat to state waters and therefore have less requirements in Table 1.

Row (ii) in Table 1 maintains the existing limitation of maximum number of lots for category 3 and applies that same limitation to category 5. Because those categories may be used on lots as small as one acre, it is necessary to limit the number of lots in the subdivision to ensure that the category is not applied to large, dense subdivisions. The proposed rule also provides that the maximum number of lots includes common developments or phases of a subdivision so that multiple exemptions cannot be stacked on top of each other. This is necessary to protect state waters because discharging excess wastewater in a given area increases the potential to degrade state waters.

Row (iii) in Table 1 limits the maximum background ground water nitrate (as N) concentration for each of the categories. The existing requirements for categories 1 through 4 remain the same. The requirement for categories 5 and 8 would be limited to 2 mg/L to be consistent with the existing categories 1 through 4. A maximum background ground water nitrate (as N) concentration for these categories is necessary to restrict use of the nonsignificant categories when ground water nitrate concentrations indicate the ground water is already being impacted by nitrogen; higher background ground water nitrate concentrations indicate a numerical analysis of impacts to state waters is necessary under ARM 17.30.715 to prevent degradation of state waters. In combination with the minimum lot size in row (i) and the lot limitation in row (ii), this requirement also protects state waters from excessive wastewater discharges in a given area.

The background ground water nitrate concentration row (iii) for category 6 is proposed to be 3 mg/L, which would encourage the use of level 3 and level 4 wastewater treatment systems that provide better nitrogen treatment than level 2 or conventional wastewater treatment systems. A maximum background ground water nitrate (as N) concentration for category 6 is necessary to restrict use of the nonsignificant categories when ground water nitrate concentrations indicate the ground water is already being excessively impacted by nitrogen and a numerical analysis of impacts to state waters is necessary under ARM 17.30.715 to prevent degradation of state waters.  In combination with the minimum lot size in row (i), this requirement also protects state waters from excessive wastewater discharges in a given area.

It is not necessary to limit the maximum background ground water nitrate (as N) concentrations in row (iii) for category 7 because level 4 wastewater treatment is required, and level 4 treatment reduces nitrogen to equal to or less than the ground water nondegradation limit (7.5 mg/L) in ARM 17.30.715.  At that level of wastewater nitrogen treatment, the ground water is protected from degradation; however, it is necessary to maintain other requirements in category 7 to protect surface waters from degradation because, in some circumstances, surface waters can be degraded by wastewater nitrogen (as N) concentrations less than 7.5 mg/L.

For category 9, the maximum background ground water nitrate as (N) concentration (iii) is 4 mg/L. This is larger than the other categories because of the 20-acre minimum lot size required in row (i). The large 20-acre lot size provides protection from dense development that is not available in the other listed categories.  Raising the maximum nitrate (as N) concentration is necessary to increase the applicability of this category in areas where the large lot size requirement provides the primary protection of state waters from degradation.

Row (iv) in Table 1 requires pressure dosed absorption systems for all categories except for category 9. Pressure dosing provides better treatment of wastewater than other methods of disposal and therefore provides additional protection of state waters. Pressure dosing is not required for category 9 because of the low density of development imposed by the 20-acre minimum lot size.

Row (v) in Table 1 modifies the type of soil classification for category 1. The existing rules require soil types with an absorption system application rate of 0.4 gallons per day per square foot (gpd/ft²) or less; adding the proposed new soils (fine sandy loam and loam) adds soils with a 0.5 gpd/ft² application rate. Adding those soils is necessary to include soils that provide good soil treatment similar to the allowed soils in the existing rule to allow additional sites to use this nonsignificant category and still protect state waters from degradation. This requirement is not applicable to proposed categories 5 through 9 because soil requirements for those categories are provided in rows (vi) and (vii). 

Row (vi) in Table 1 requires a minimum soil classification of medium sand, sandy loam, or finer (equivalent to an application rate of 0.6 gpd/ft²) for proposed categories 5 through 8 to provide adequate soil treatment to protect state waters.  These soils can be coarser than those required for category 1 because these categories include additional requirements for level 2, 3, or 4 treatment or for gray water discharges. Soil that is coarser than the required soil classifications have the highest application rate in DEQ-4 and provide less treatment than the required finer soils.

Row (vii) in Table 1 requires an elevated sand mound or a minimum soil classification of medium sand, sandy loam, or finer (equivalent to an application rate of 0.6 gpd/ft²) to provide adequate treatment of wastewater for category 9, which is limited to lots of 20 acres or more. Soil that is coarser than the required soil classifications has the highest application rate in DEQ-4 and provides less treatment than the required finer soils. Allowing for an elevated sand mound is necessary to provide flexibility in applying this category for larger than 20-acre lots even in locations that have coarse soils.

Row (viii) in Table 1 provides the minimum depth required to a limiting layer in the soil profile. The proposed amendment would require that depth be measured below natural ground surface to ensure that the reference point for the depth measurement is applied consistently to all wastewater treatment systems. Under the existing rule, this minimum depth only applies to bedrock or seasonally high ground water. The proposed amendment would measure to the limiting layer instead of bedrock or seasonally high ground water because the current language is missing a third soil factor that would create similar limitations to adequate soil treatment of the wastewater, which is an impervious layer that is not bedrock (an impervious clay layer, for example). The definition of limiting layer is included in DEQ-4, and includes bedrock, seasonally high ground water, and impervious layer; therefore, for clarity and conciseness replacing "bedrock or seasonally high ground water" with the term "limiting layer" is necessary.

The department proposes to modify the minimum depth to a limiting layer, row (viii) in Table 1, for existing category 2 from 12 feet to 10 feet. This change is necessary because determining the limiting layer requires digging a test pit to 12 feet deep which requires excavating a large portion of the future absorption system to make the slope of the test pit safe enough to enter and properly evaluate the soils at that depth. The department also proposes to establish a 10-foot minimum for existing category 3. This change is necessary because the requirements for depth to bedrock and ground water (in row (ix) in Table 1) are proposed to be reduced from 100 feet to 50 feet to allow this category to be applicable in more situations, while still protecting state waters by adding the minimum 10-foot depth to the limiting layer. In both instances, the proposed depth of 10 feet provides 4 feet more soil depth and treatment than is required in Department Circular DEQ-4 for standard depth absorption systems. The depth to a limiting layer is not necessary for proposed categories 8 and 9 because of the dilute gray water wastewater in category 8 and the low density required in category 9.

For proposed categories 5, 6, and 7, the department proposes a minimum depth to a limiting layer of 8 feet below the ground surface in row (viii). Those categories only have one other soil requirement for 6 feet of medium sand, sandy loam, or finer (equivalent to an application rate of 0.6 gpd/ft²). To protect state waters, it is also necessary to require an 8-foot minimum depth to limiting layer because it provides 2 additional feet of soil treatment over what is required in Department Circular DEQ-4 for standard depth absorption systems.

In row (ix) of Table 1, the department proposes to reduce the minimum depth below the natural ground surface to bedrock and ground water for category 3 from 100 feet to 50 feet. This change is proposed in conjunction with the addition of minimum depth to a limiting layer in (viii), which provides 4 more feet of soil treatment. Together, these changes allow more flexibility in using the category, while still maintaining protection of state waters. A minimum depth to bedrock or ground water in (ix) is not required for any categories other than category 3 because the other categories have larger minimum lot sizes; use level 2, 3, or 4 treatment; or are restricted to counties with historically low growth.

Rows (xi), (xii), and (xiii) in Table 1 require level 2; level 2 or 3; or level 2, 3, or 4 treatment systems, respectively.  Rows (xi), (xii), and (xiii) apply to new categories 5, 6, and 7. This is necessary to encourage the use of those systems because they reduce effluent nitrogen concentrations compared to conventional wastewater treatment systems and have required long-term operation and maintenance and effluent sampling requirements that conventional systems do not have.

Row (xiv) in Table 1 provides a maximum depth of the absorption system below the natural ground surface. This is a necessary requirement for all the nonsignificant categories, except the category in (4)(b) for low density counties, to include soil treatment in the upper soil horizons that typically provide the best conditions for wastewater treatment. For categories 1, 2, 3, 8 and 9 this depth is set at 24 inches. This depth is set at 18 inches for categories 4, 5, 6, and 7; these categories have lesser soil or limiting layer requirements because they use level 2, 3, or 4 treatment systems.  Because of that, it is necessary to set the maximum absorption system depth to 18 inches to maximize the soil available for treatment. 

            Proposed category 8 and row (xv) in Table 1 are for gray water discharges that are part of a waste segregation system (as defined in Department Circular DEQ-4). Category 8 is necessary to account for the dilute wastewater in a gray water discharge and to encourage the use of gray water systems that are often used for irrigation purposes during the summer growing season. Encouraging gray water systems is necessary to realize their benefit of reducing effluent discharge to ground water by allowing plants/grass to utilize nitrogen and phosphorus rather than direct it to ground water via wastewater absorption systems.

Footnote (1) of Table 1 is necessary to define "N/A" and to clarify that any requirement that is not applicable in Table 1 only applies to this rule; a wastewater treatment system that is nonsignificant under this rule still has to meet all requirements and design standards for wastewater treatment systems in other applicable rules and circulars.

Footnote (2) in Table 1 is a requirement in the existing rule, at (2)(a)(vii)(A). It has been moved to a footnote to Table 1.  The reference to "department" is proposed to be revised to "reviewing authority."  This amendment is necessary because counties are also authorized to review applications for nonsignificance pursuant to 50-2-116, MCA

In footnote (3) of Table 1, it is necessary to restrict soils with the listed soil modifiers in rows (v), (vi), (vii), and (viii) from meeting the specific soil requirements in Table 1.  Soils with listed classification modifier in footnote 3 are considered to be very limited soils for wastewater treatment according to the 2017 United States Natural Resources Conservation Service (NRCS) Soil Survey Manual.  To ensure categories of nonsignificance have adequate soil treatment, it is necessary to exclude soils with these characteristics.

Footnote (4) of Table 1 provides the type of information that can be used to determine the minimum depth to bedrock and ground water in row (ix). This footnote is necessary to provide consistency and clarity in determining the correct depths.

Footnote (5) of Table 1 is necessary to provide information for row (xiv) on how to correctly install a wastewater absorption system at a shallower depth than a standard system and provide consistency and clarity in implementing the rule.

Footnote (6) of Table 1 is necessary to provide clarity for row (xv) and ensure that category 8 is not applied to the blackwater portion of a waste segregation system nor to an alternate wastewater treatment system (when required in Department Circular DEQ-4) that treats gray water and other wastewater from the lot. This is necessary because those other non-gray water discharges must be evaluated separately for nonsignificance.

Revising the language in (5) is necessary to clarify that any wastewater treatment system that meets the rule requirements as a nonsignificant activity is still required to maintain all applicable setbacks to the 100-foot-long provisional ground water mixing zone that applies to wastewater treatment systems with ground water mixing zones that are approved pursuant to ARM 17.30.517 and 17.30.715.  The revised language is also necessary to clarify that the provisional mixing zone does not need to also meet the requirements of ARM 17.30.715 if it is classified as nonsignificant under this rule, which is also necessary to comply with Senate Bill 285.

Deleting current (5) from the rule is necessary to eliminate redundancy in the rule as the existing petition process new (7) already prohibits specific locations from being classified nonsignificant under this rule and requires those sites to be reviewed pursuant to ARM 17.30.715. Deleting current (5) is also necessary to comply with Senate Bill 285.

Although not explicitly addressed in the rule, cumulative effects of multiple wastewater treatment systems are primarily accounted for in rows (i), (ii), and (iii) in Table 1 and in proposed (3)(b) that provide limits for the minimum lot size, maximum number of lots in a development, maximum background ground water nitrate (as N) concentration, and the maximum discharge rate per lot, respectively.  Combined, those four criteria minimize the potential for excessive cumulative effects from the proposed nonsignficance activities.  The remaining rule requirements including pressure dosing, soil types, soil depths, and higher levels of wastewater treatment all provide additional protection from excessive cumulative effects.

Finally, the department proposes to replace the phrase "septic system" in (7)(b)(iv)(A) with "wastewater treatment system," which is the term used and defined in Department Circular DEQ-4. This change is necessary to ensure consistency of terms across department rules and circulars. No change in intent or meaning is proposed. The remaining changes to the wording of the rule are proposed to improve the readability of the rule. 

17.30.718 CRITERIA FOR NUTRIENT REDUCTION FROM SUBSURFACE WASTEWATER TREATMENT SYSTEM (SWTS) (1) This rule describes the information that must be submitted to obtain a department classification of a SWTS wastewater treatment system as level 1a, level 1b, or level 2, level 3, or level 4 treatment, as those terms are defined in ARM 17.30.702.  The nitrogen treatment efficiency level that a SWTS wastewater treatment system is granted under this rule may be used as the effluent concentration in mixing zone calculations.

(2) A person seeking classification of a SWTS wastewater treatment system as level 1a, level 1b, or level 2, level 3, or level 4 treatment must submit the following background information to the department regarding the SWTS wastewater treatment system, in addition to any other information the department determines is necessary to verify the long-term treatment capabilities of the system:

(a) through (e) remain the same.

(f) information verifying the reliability of the SWTS wastewater treatment system manufacturer and vendor. At a minimum, the vendor or manufacturer must either:

(i) have maintained an office in Montana for the past five years with a significant portion of its business related to design, construction, or installation of SWTSs wastewater treatment systems; or

(ii) remains the same.

(3) A person seeking classification of a SWTS wastewater treatment system as level 1a, level 1b, or level 2, level 3, or level 4 treatment must submit monitoring information as provided in this section.  The department may require additional information (particularly for technologies not included in department Department Circular DEQ-4) if necessary to verify the long-term reliable treatment capabilities of the system.

(a) remains the same.

(b) For a SWTS wastewater treatment system that uses the effluent total nitrogen concentration to determine treatment efficiency, the monitoring must be from at least six systems for approval as a level 2 or level 3 treatment system and from at least 12 systems for approval as a level 4 treatment system. For a SWTS wastewater treatment system that uses the percent total nitrogen removed from measured raw sewage wastewater to determine treatment efficiency, the monitoring must be from at least three systems for approval as a level 2 or level 3 treatment system and from at least six systems for approval as a level 4 treatment system.

(c) For each SWTS wastewater treatment system that is monitored, at least one representative sample of raw sewage wastewater must be collected and analyzed for nitrate (as N), nitrite (as N), ammonia (as N), total kjeldahl nitrogen (TKN) (as N), biological oxygen demand (BOD), and total suspended solids (TSS).  This information will be used to determine the raw sewage wastewater strength, which must not exceed residential strength and have an average TKN or total nitrogen concentration higher than 40 mg/L.  Chemical characterization of raw sewage wastewater must be based on one of the following representative samples:

(i) remains the same.

(ii) if the septic tank or other initial tank is used for treatment beyond primary treatment, the sample should be collected prior to start-up of the SWTS wastewater treatment system from that tank; or

(iii) remains the same.

(d) For level 2 or level 3 treatment approval, each Each SWTS wastewater treatment system must be monitored for one year.  At, and at least one SWTS wastewater treatment system must be monitored for at least two years.  For level 4 treatment approval, each wastewater treatment system must be monitored for one year, and at least two wastewater treatment systems must be monitored for at least two years.

(e) Effluent sampling Sampling frequency must be at least monthly (or equivalent frequency as approved by the department) during the winter months (November through April), and at least quarterly during the summer months (May through October).  At least 50% of the monitoring data from each SWTS wastewater treatment system must be collected during the winter months.  For wastewater treatment systems that use percent total nitrogen removed to determine treatment efficiency, a raw wastewater sample must be collected on the same dates as the effluent samples.

(f) Each effluent sample must be analyzed for nitrate (as N), nitrite (as N), ammonia (as N), TKN (as N), BOD, TSS, and flow. If raw wastewater influent monitoring is conducted concurrently with effluent monitoring, each influent sample must be analyzed for TKN (as N) or total nitrogen.  If the SWTS wastewater treatment system is experiencing significant infiltration and inflow, the department may require that raw wastewater influent samples be collected and analyzed during each effluent monitoring event to determine an accurate representation of the nitrogen-reducing capabilities of the system.

(g) Monitored SWTSs wastewater treatment systems must be in Montana or located in a climate similar to Montana. a location that has an average annual air temperature of 50 degrees Fahrenheit or less.  The temperature must be based on the most applicable active weather station with at least a 20-year record or the most recent 30-year National Oceanic and Atmospheric Administration average annual air temperature.

(h) and (i) remain the same.

(j) The department may waive specific requirements in this rule if:

(i) the monitoring data are substantially equivalent to those requirements.; or

(ii) the SWTS uses a proven nutrient reduction technology listed in DEQ-4 with proprietary variations.

(4) The results data from a SWTS wastewater treatment system that is tested under the EPA/National Science Foundation (NSF) environmental technology verification (ETV) program NSF International/American National Standards Institute 245 (NSF/ANSI 245) certification may be used to demonstrate compliance with the requirements in (3), except that NSF/ANSI 245 data may only be used to replace one-third of the systems required in (3)(b).

(5) In response to a request for classification of a SWTS wastewater treatment system as level 1a, level 1b, or level 2, level 3, or level 4 treatment, the department may, after evaluating the SWTS wastewater treatment system under the criteria in this rule:

      (a) through (d) remain the same.

(6) If a SWTS wastewater treatment system that is classified as level 1a, level 1b, or level 2, level 3, or level 4 treatment is modified, and the modification may have negative effects on the amount of total nitrogen reduction, the department may require that the SWTS wastewater treatment system be re-evaluated under the criteria in this rule.

(7) If subsequent data indicate that a SWTS wastewater treatment system classified as level 2, level 3, or level 4 treatment under this rule is not reliable or cannot meet required nutrient reductions, the department may rescind the classification.

(8) All SWTSs wastewater treatment systems classified as a level 1a, level 1b, or level 2, level 3, or level 4 treatment must have an operation and maintenance (O&M) contract in perpetuity for each system installed. The O&M contract will be required in the subdivision approval, or as a deed restriction if a subdivision plat approval is not required for the property.  O&M must be conducted by the system manufacturer, an approved vendor, or other qualified personnel. The SWTS wastewater treatment system vendor or manufacturer must offer an O&M plan that meets the requirements of this section and the requirements in department Department Circular DEQ-4.  At a minimum, the O&M contract must include:

(a) an on-site inspection of all the major components of the SWTS wastewater treatment system. twice a year for the first two years after use of the system begins, and annually thereafter.  Inspections of suspended growth systems must be twice as frequent.  Inspection items must include verifying proper operation of the visual/audible alarm system required in (9) and determining whether any water treatment devices have been added, modified, or removed from the water system that discharges to the SWTS; and wastewater treatment system. Inspections must be made according to the following schedules:

(i) for a wastewater treatment system with a design flow less than 5,000 gpd that does not require an MPDES or MGWPCS permit, the inspection schedule is semi-annually for the first two years after use of the system begins and annually thereafter;

(ii) for a suspended growth wastewater treatment system with a design flow less than 5,000 gpd that does not require an MPDES or MGWPCS permit, the inspection schedule is quarterly for the first two years after use of the system begins and semi-annually thereafter; and 

(iii) for a wastewater treatment system with a design flow of 5,000 gpd or larger that does not require an MPDES or MGWPCS permit, the inspection schedule is monthly for the first two years after use of the system begins and quarterly thereafter;

(b) annual effluent sampling and analysis for nitrate (as N), nitrite (as N), ammonia (as N), TKN (as N), BOD, TSS, fecal coliform, specific conductance, carbonaceous biochemical oxygen demand (CBOD), field pH, and field temperature.  Effluent sampling must be conducted after all treatment is complete, but before discharge to the absorption area system.  All monitoring data collected from a type of SWTS may be requested, including the identification of the wastewater treatment system manufacturer, must be submitted to the department if requested by the department to verify the total nitrogen reduction is adequate for the approved treatment level. if the department has reason to believe that a type of SWTS that has been approved as a nutrient-reducing system is not meeting the required treatment efficiencies.

(9) All SWTSs wastewater treatment systems classified as level 1a, level 1b, or level 2, level 3, or level 4 treatment must have the following features:

      (a) and (b) remain the same.

(10) A manufacturer of a wastewater treatment system that has been previously approved for level 2 treatment may request approval from the department as a level 3 or level 4 treatment system without submission of additional information if the original level 2 approval includes a total nitrogen concentration or reduction percentage that meets the definition of level 3 or level 4 treatment in ARM 17.30.702.

(11) All level 2, level 3, or level 4 treatment systems, regardless of approval date under this rule, must comply with the requirements in (8).

(12) An approval as level 2, level 3, or level 4 treatment under this rule does not constitute approval under Department Circulars DEQ-2 (2018) or DEQ-4 (2023) and does not constitute approval for any specific project or application of that technology.

REASON: The department proposes to remove references to level 1a and level 1b throughout the rule because they are outdated and unnecessary. Since those treatment levels were added to the rules in 2004, the department has received only one application for such approval, and that system also sought and received level 2 approval. The technology for nitrogen removal has rendered those treatment levels outdated and no longer necessary to include in the rules.

Technological improvements in nitrogen removal have made it necessary to address those systems that provide additional nitrogen reductions. The department proposes to add level 3 and level 4 approvals to provide distinct designations for different amounts of nitrogen treatment instead of the single level 2 designation that does not specifically account for different nitrogen reductions and effluent concentrations in rule.

In (1), it is necessary to replace the word "efficiency" with "level" because efficiency only refers to the effluent percent reduction of a level 2, 3, or 4 treatment system but does not include the other criteria of the definitions for level 2, 3, and 4 (ARM 17.30.702) which is the effluent concentration.  Using the term "level" is necessary to be inclusive, and thus improve rule clarity, of the two criteria used to classify wastewater treatment systems as level 2, 3, or 4.

The proposed amendments in (3)(b) and (3)(c) replace the term "raw sewage" with "raw wastewater," which is the term used and defined in Department Circular DEQ-4. This change is necessary to ensure consistency of terms across department rules and circulars. No change in intent or meaning is proposed.

The proposed monitoring requirements for level 3 systems in (3)(b) and (d) are the same as those existing requirements for level 2 systems because the level 2 requirements are considered adequate to provide the necessary data to classify wastewater treatment systems as level 3. The proposed monitoring requirements for level 4 treatment in (3)(b) and (d) are more extensive than those for level 2 and level 3 systems because the level of treatment for level 4 is a very high level of treatment for an on-site system that requires additional processes compared to level 2 and 3 treatment systems. Additionally, level 4 systems are not required to have a ground water mixing zone to dilute the effluent (although a provisional mixing zone is required to maintain setbacks) because they discharge at or below the nondegradation ground water limit, so it is necessary to require additional data to ensure that such systems can reliably reduce nitrogen at the point of discharge.

In (3)(c), it is necessary to add a lower concentration limit for the raw wastewater total nitrogen (TN) or total kjeldahl nitrogen (TKN) to ensure the wastewater treatment system can treat to the required treatment concentrations or required reductions for level 2, 3, or 4 using typical wastewater instead of dilute wastewater. Using dilute raw wastewater in the testing process provides unrepresentative testing of typical raw wastewater and potentially could allow a system to achieve level 2, 3, or 4 classification even though the system cannot treat typical raw wastewater to the required concentration or percent reduction.

Adding "effluent" to (3)(e) does not change the intent of the rule, but it is necessary to clarify the sampling requirement is for wastewater effluent and not for raw wastewater or some intermediary location in the treatment system. The effluent data is needed to provide the correct information to determine if a system is meeting the required concentrations or percent reductions for level 2, 3, or 4 classification.

The amendment to (3)(e) requires sampling raw wastewater on the same date as effluent sample for systems that use percent reduction to demonstrate compliance with the requirements for level 2, 3, or 4 classification is necessary to ensure that the effluent sample is representative of treatment from raw wastewater with similar characteristics.

The existing rule in (3)(g) requires monitored wastewater treatment systems be located in Montana or in a climate similar to Montana. Because this allowance for a similar climate allows for significant variation in interpretation and application of the rule, the department proposes a specific average annual air temperature of 50 degrees or less, which is approximate to the warmest 30-year average within Montana. The correct temperature range is critical to maintaining the bacterial communities that are necessary to reduce nitrogen concentrations in wastewater, with lower temperatures inhibiting those bacteria. The proposed change is necessary to ensure that systems tested outside of Montana are tested in similar environments. The requirement that such temperature data be an active weather station with at least a 20-year record or the most recent 30-year NOAA average is necessary to ensure such data is reliable and consistent.

The proposed deletion of (3)(j)(ii) is necessary to ensure all systems have similar requirements and have to meet the same testing requirements in (3).

In (4), the department proposes changing the reference to the "EPA/National Science Foundation (NSF) environmental technology verification (ETV) program" to "NSF International/American National Standards Institute 245 (NSF/ANSI 245) certification" because the EPA/NSF ETV program no longer exists.  It was replaced by the NSF/ANSI 245 certification process that is now referenced in the rule. Using the word "data" instead of "results" is necessary to clarify that the data published in the NSF/ANSI 245 certification may be used to determine whether the system meets the requirements of this rule, not the NSF/ANSI 245 certification itself. An NSF/ANSI 245 certification by itself cannot show compliance with the requirements of this rule because the NSF/ANSI 245 criterion is for 50% reduction of TN, which does not meet the defined reduction requires for level 2, 3, or 4 in ARM 17.30.702.

The proposed amendment to (4) limits NSF/ANSI 245 data to replace only one-third of the number of the systems required for testing in (3). This is necessary because the NSF/ANSI 245 testing does not necessarily occur in locations with similar average annual air temperatures as Montana. Since temperature is an important factor in the nitrogen-reducing capabilities of a system, it is necessary to have at least a portion of the data from systems in cold-weather climates similar to Montana.

Section (6) allows the department to require re-evaluation of a system if it is modified. The proposed amendments clarify that re-evaluation is necessary only if the modification has the potential to reduce the system's nitrogen treatment capabilities.

The proposed amendments to (7) are necessary to include reference to "level 2, level 3, and level 4 treatment" to clarify what "classified" refers to in the existing rule.

Existing (8) and (8)(a) provide O&M and inspection requirements for systems approved under this rule.  The proposed changes to (8)(a) are necessary to align this rule with the recent changes to ARM 17.30.1022 in MAR Notice No. 17-433. In that rulemaking, the department redefined the threshold for wastewater treatment systems that require a ground water permit. The proposed amendments to this rule specify that the inspection requirements of this rule do not apply to systems with an MPDES or MGWPCS permit, which is necessary to avoid inconsistent or overlapping inspection requirements imposed by the permit. The department also proposes separate inspection requirements for small and large systems. This is necessary because larger systems have a greater potential to exceed water quality standards than smaller systems if they are not operating correctly.

In (8)(b), the department proposes to modify the parameters required for annual effluent sampling. The modifications are necessary to remove parameters that are not necessary to determine the nitrogen reducing capabilities of level 2, 3, and 4 wastewater treatment systems and have been replaced with parameters that provide better information regarding the proper function of the systems. Total suspended solids (TSS) and fecal coliform have been removed and replaced with a more relevant parameter, field pH.  Field pH is necessary because nitrogen reduction cannot occur if pH is too low. Biochemical oxygen demand (BOD) has been replaced with carbonaceous biochemical oxygen demand (CBOD) because CBOD measures the portion of BOD that is necessary to evaluate proper function of the treatment system. The requirement for temperature monitoring remains the same but includes clarification that the temperature should be measured in the field because the operating temperature is important to the proper functioning of the treatment system.

The department proposes to amend (8)(b) to require that all monitoring data be submitted to the department upon request, including the identity of the wastewater treatment system manufacturer. These changes are necessary to ensure the monitoring data is associated with a particular treatment system and for the department to independently evaluate whether approved systems are meeting the required treatment levels.

New (10) is necessary to clarify that systems with existing level 2 classification approvals that meet the treatment concentrations or percent reduction requirements for level 2, 3, or 4 treatment do not have to submit new information to meet the current rules.  In such a case, additional review is unnecessary.

New (11) is necessary to clarify that level 2 wastewater treatment systems approved prior to the effective date of the proposed rule revisions need to be monitored under the revised proposed monitoring requirements (the same as new level 3 and 4 systems) instead of the existing requirements. This is necessary to eliminate confusion regarding what parameters are required for systems approved on different dates.

New (12) is necessary to ensure that applicants are aware that approval as a level 2, 3, or 4 wastewater treatment system does not constitute plan and specification approval for use on a specific project. Without this addition, there is potential for applicants to incorrectly conclude that the level 2, 3, or 4 treatment classification approval is also approval for use on specific projects. No change in the intent or meaning of the rule is proposed. 

CIRCULAR DEQ-20 1.8  SOURCE SPECIFIC WELL ISOLATION ZONES The Department may approve a source specific well isolation zone (SSWIZ) for existing individual and shared wells that have well logs if the requirements of this standard are met. Wells that were constructed in violation of 76-4-121 or 76-4-130 are not eligible for a source specific well isolation zone request.

REASON: SB 327 from the 2023 legislative session directed the department to allow source-specific well isolation zones that are smaller than 100 feet.  Amendments were made to ARM 17.36.323, 17.36.918, and Circular DEQ 20 in MAR Notice No. 17-430. The amendments to ARM 17.36.323, 17.36.918, and Circular DEQ 20 were intended to be applied to both individual and shared wells.  However, during the drafting of DEQ 20, Section 1.8, "Shared Wells" were mistakenly omitted as being eligible for the SSWIZ. This change ensures there is no conflict between department rules, local health rules, and the design circular.