Steve Bullock, Governor I Tom Livers, Director I P.O. Box 200901 I Helena, MT 59620-0901 I (406) 444-2544 I www.deq.mt.gov

May 3, 2019 Sent via electronic mail Mr. Matt Guptill Decker Coal Company, LLC 12 Lakeshore Drive Decker, MT 59025 Subject: Deer Creek AVF Partial Determination; Presence or Absence and Significance Dear Matt: The Department of Environmental Quality (DEQ) has completed its determination of the Deer Creek AVF. This includes the presence and absence determination as well as the significance determination for the Deer Creek valley adjacent to East Decker Mine. This can also be found on DEQ’s website here: http://deq.mt.gov/Public/ea/coal Please feel free to contact Mike Glenn at 406-444-3401, if you have any questions.

Sincerely,

Chris Yde, Supervisor Coal Section Coal and Opencut Mining Bureau Phone: 406-444-4967 Fax: 406-444-4988 Email: CYde@mt.gov Cc: Jeff Fleischman, Office of Surface Mining Erica Trent, Office of Surface Mining Enclosure: Deer Creek AVF FC: 624.168

1

Gilbert, Sharona

From: Gilbert, SharonaSent: Friday, May 3, 2019 1:32 PMTo: 'm.guptill@deckercoal.com'; Bill Pruitt (b.pruitt@deckercoal.com)Cc: jfleischman@osmre.gov; Trent, Erica; Shaeffer, Elizabeth (eshaeffer@osmre.gov); Giovetti, Debbie

(dgiovetti@osmre.gov); 'mcalle@osmre.gov'; Bartlett, Franklin P (fbartlett@osmre.gov); DEQ AEMD Coal

Subject: AVF Cover Letter_Deer Creek.pdfAttachments: AVF Cover Letter_Deer Creek.pdf; Deer Creek_AVF_Final.pdf

Please see attached correspondence. Have a great day! Sharona Gilbert  Program Support Specialist Coal Section Coal and Opencut Mining Bureau Ph: 444-4966 Fax: 444-4988   The best laid schemes o' Mice an' Men, Gang aft agley ~Robert Burns 

MONTANA DEPARTMENT OF ENVIRONMENTAL QUALITY

Partial Alluvial Valley Floor Determination

Presence or Absence and Significance for Deer Creek, Adjacent to East Decker Mine

Coal and Opencut Mining Bureau, P.O. Box 200901, Helena, MT 59620

May 2019

1

Table of Contents Regulatory Framework ................................................................................................................................... 2

I. Presence or Absence .............................................................................................................................. 2

Analysis of Presence or Absence ................................................................................................................ 2

Introduction ............................................................................................................................................ 3

1. Unconsolidated Streamlaid Deposits ................................................................................................. 4

Geology and Soils.................................................................................................................................... 4

Geomorphology ...................................................................................................................................... 5

1.1 Deer Creek .................................................................................................................................. 5

Geology and Soils.................................................................................................................................... 5

Hydrology ............................................................................................................................................... 5

2. Sufficient Water to Support Agricultural Activities: ............................................................................... 6

a. The Existence of Current or Historic Flood Irrigation ..................................................................... 6

b. Capability of the Area to be Flood Irrigated ................................................................................... 7

c. The Existence of Subirrigation ........................................................................................................ 8

Presence or Absence Conclusion .............................................................................................................. 13

II. Significance ........................................................................................................................................... 13

Statutory Exclusions ................................................................................................................................. 13

Landowner/Ranch operator Interviews ............................................................................................... 14

Summary ....................................................................................................................................................... 14

References ................................................................................................................................................ 16

2

Regulatory Framework The Montana Strip and Underground Reclamation Act (MSUMRA) § 82-4-201 through 82-4-254, MCA, and its implementing rules, Administrative Rules of Montana (ARM) 17.24.301 through 17.24.1309, specifically § 82-4-227(3) (b) (i) MCA, and ARM’s 17.24.301 and 17.24.325 set forth the process for identifying an alluvial valley floor (AVF) located in the arid and semi-arid lands of Montana. ARM’s 17.24.325 and 17.24.805 are utilized to define the significance of an AVF. Any mine proposal or mine related disturbance within a valley holding a stream, or adjacent to and connected to a valley holding a stream, must have an AVF determination. MSUMRA requires protection of identified AVFs from impacts of coal mining that are adverse to agricultural activities or farming.

An AVF determination consists of three separate evaluations. The first evaluation determines the presence and extent or absence of AVFs based on defined criteria. The second evaluation determines the significance of the AVF for adversely affected agricultural or farming operations. ARM 17.24.805 requires that in making this significance determination, the department consults with the affected landowner(s). The third evaluation determines the essential hydrologic functions of each AVF, see ARM 17.24.325. If the first evaluation determines that no AVF is present, then further evaluation is not warranted. If an AVF is identified, then significance of the AVF must be determined, and the essential hydrologic functionality of that AVF must also be determined.

As explained in detail, below, both geologic and hydrologic criteria must be met to designate an AVF. The key to the existence of an AVF is the presence of both geomorphic characteristics and water availability for agricultural activities or farming.

I. Presence or Absence

Analysis of Presence or Absence Section 82-4-203(3)(a), MCA, defines an AVF as: “the unconsolidated stream-laid deposits holding streams where water availability is sufficient for subirrigation or flood irrigation agricultural activities.” Section 82-4-203(3)(b), MCA, distinguishes “upland areas that are generally overlain by a thin veneer of colluvial deposits composed chiefly of debris from sheet erosion and deposits by unconcentrated runoff or slope wash, together with talus, other mass movement accumulation, and windblown deposits” from AVFs. Uplands is further defined in ARM 17.24.301 (136) as “with respect to alluvial valley floors, those geomorphic features located outside the floodplain and terrace complex, such as isolated higher terraces, alluvial fans, pediment surfaces, landslide deposits, and surfaces covered with residuum, mud flows or debris flows, as well as highland areas underlain by bedrock and covered by residual weathered material or material deposited by sheetwash, rillwash, or wind.”

Alluvium and colluvium are deposits of materials resulting from erosion and deposition. Alluvium is a general term for materials deposited by water, including gravel, sand, silt, clay, and all the variations and mixtures of these. Unless otherwise noted, alluvium is unconsolidated (Brady and Weil, 2010). Colluvium is a deposit of rock fragments and soil material accumulated at the base of steep slopes as a

3

result of gravitational action (Brady and Weil, 2010). Both transport processes result in unconsolidated material on the earth’s surface.

According to the Dictionary of Geologic Terms, colluvial is defined as “Consisting of alluvium in part and also containing angular fragments of the original rocks.” Colluvium may be mixed with alluvium. Various processes may account for this. For example, alluvial stream channel deposits may slide down terrace banks resulting in new colluvial deposits.

The definition of AVF is further clarified as “unconsolidated streamlaid deposits holding streams” as “all flood plains and terraces located in the lower portions of valleys which contain perennial or other streams with channels.” ARM 17.24.301(132). This definition of unconsolidated deposits allows for colluvium as defined above to be contained in a terrace or floodplain of an AVF. Therefore, the presence of surface colluvium does not exclude a stream from AVF status. The underlying geology rather than surface deposition dictates a determination of alluvial or colluvial character in a valley floor.

ARM 17.24.325(2)(b) sets forth the procedure for determining the presence or absence of an AVF:

Based on the investigations conducted under [ARM 17.24.325(2)(a)], the department shall make a written determination of the extent of any alluvial valley floors within the study area and whether any stream in the study area may be excluded from further consideration as lying within an alluvial valley floor. The department shall determine that an alluvial valley floor exists if it finds that: (i) unconsolidated streamlaid deposits holding streams are present; and (ii) there is sufficient water to support agricultural activities as evidenced by: (A) the existence of current flood irrigation in the area in question; (B) the capability of the area to be flood irrigated, based on typical regional agricultural practices, historical flood irrigation, stream-flow, water yield, soils, water quality, and topography; or (C) subirrigation of the lands in question, derived from the ground water system of the valley floor; and (iii) the valley does not meet the definition of upland areas in ARM 17.24.301. (c) If the department determines in writing that an alluvial valley does not exist pursuant to (b), no further consideration of this rule is necessary;

Finally stream valleys “adjacent” to proposed mining operations must be evaluated for the presence or absence of AVFs. “Adjacent” is also a defined term under MSUMRA and means in pertinent part, “the area outside the permit area where a resource or resources, determined in the context in which the term is used, are or could reasonably be expected to be adversely affected by proposed mining operations.” § 82-4-203(2), MCA.

Introduction Decker Coal Company (DCC) has requested an alluvial valley floor determination for a portion of the Deer Creek Drainage (Study Area) depicted on Map 1. Deer Creek is an intermittent stream located adjacent to the current East Decker Mine. Deer Creek is a tributary of the Tongue River with a drainage area of approximately 55 square miles. The East Decker Mine is in Big Horn County, roughly five miles north of the Montana and Wyoming border. The current permit area is approximately 4,361 acres. The East

4

Decker Mine is located at the southeast end of the Tongue River Reservoir, approximately five miles northeast of Decker, MT, and 18 miles northeast of Sheridan, WY. An evaluation of evidence supporting the presence or absence of an AVF in the Study Area is presented in this document.

1. Unconsolidated Streamlaid Deposits

Geology and Soils As explained above, the first step in determining the presence or absence of an alluvial valley floor is to identify valleys with streams holding unconsolidated streamlaid deposits. Unconsolidated stream laid deposits are alluvium.

In this tributary of the Tongue River drainage the parent materials for alluvium are derived from the Fort Union formation where the streambed of Deer Creek is eroding westward toward the Tongue River. Geology of the Fort Union formation consists of: clay shale, siltstone, and sandstone and includes the Tongue River member, Lebo shale member, and Tullock member in its overall stratigraphy. Alluvial materials are formed in a setting where more erosion resistant sandstone and clinker capped buttes are underlain by softer strata (USDA 1980). Through time, erosion and deposition have eroded the parent materials depositing them in the drainages and lowlands as alluvium. The alluvium is sorted into finer silts and clays on floodplains that lie over clinker gravels and fine sands. Monitoring well logs may refer to alluvium using any of these material names. As defined above alluvium is unconsolidated material.

Soil types of these geologic units are expected to have similar characteristics. Soils of the Deer Creek Study Area are in loamy, clayey, or silty soil texture classes. Coarse fragments, when present, are found further below ground surface. Soil survey and drill log data indicate the finest particle sized soils, silty and clayey loam, are found in surface soil layers (horizons). These surface horizons rest on varying types of unconsolidated materials and loam in channel bottoms and on terraces. Many of these soil types have mixed layers consisting of scoria gravels which occur at the greatest depths in the soil column. This is a typical layering of soil horizons. When water transports earthen materials the largest particles, gravels and then sands, settle out first. As sediment rich water slows down, smaller and smaller particles settle out. The smallest and lightest particles, silty then clayey particles, settle out last generally to be found in the surface horizons.

Prime Farmland soil Soils that meet requirements of prime farmland are investigated in the permitting process and indicate an enhanced ability to cultivate the land surface. As part of the permitting process, Decker Coal Co. determined if prime farmlands are present. The Natural Resources Conservation Service (NRCS) was consulted and concurred that there were no prime farmland soils present unless irrigation is present. Alluvial Valley Floor determination is not tied to Prime Farmlands, as it pertains to the permitting process or the AVF determination; however, prime farmland soils do indicate areas viable for cultivation in a valley floor. Decker Coal Co. has addressed permitting concerns regarding prime farmlands, which can be found in Sections 306 and 324 of the permit application.

5

Geomorphology Geomorphology of tributaries to the Tongue River fit into two general categories. The first category includes streams where erosional and depositional zones have created meanders within a lower gradient valley consisting of alluvium. A second category includes erosional streams where the channel is held in an incision formed on a steeper gradient slope and lacks major depositional zones and meanders. The category two channels usually represent upland tributaries to larger streams of the first category. Deer Creek is considered a category one stream, with a reach, referred to as the Dry Arm, meeting category two classifications.

Category one low gradient valleys may support agricultural production adjacent to the active stream channels. In contrast, category two erosional channels flow through rangeland, where runoff could be directed to flood irrigation on a lower gradient valley, or used in stock watering ponds, but generally is not captured for use directly from the main channel.

1.1 Deer Creek

Geology and Soils Multiple sources of information indicate the presence of unconsolidated material in the Deer Creek Study Area. Geologic maps published by the Montana Bureau of Mines and Geology indicate that unconsolidated alluvial material is present in the lower Deer Creek Valley (Vuke et al 2001). Subsurface unconsolidated material thickness ranges from not present in upland areas to over 90 feet thick in the lower Deer Creek valley near the Tongue River. This is based on drill logs and data included in the permit application and the request for an alluvial valley floor determination submitted to DEQ by DCC (DCM 2016). Data indicate soil textures ranging from fine sands to clayey loams and below the soils various unconsolidated materials ranging from fine sand and clay to coarse gravels. Geology in the Deer Creek Drainage meets criteria of unconsolidated streamlaid materials required for identification of an AVF.

Hydrology Deer Creek is an intermittent stream with a drainage area of approximately 55 square miles. Groundwater and surface water within an adjacent to the East Decker Mine are monitored as part of the annual hydrology monitoring required for the current East Decker Mine permit. Some of these surface water monitoring sites are in Deer Creek and some groundwater monitoring wells are in Deer Creek alluvium. Additional monitoring stations were installed for the Deer Creek AVF investigation. Data from these monitoring sites, submitted to DEQ in annual monitoring reports and the DCC request for AVF determination, were used to evaluate the presence of hydrologic conditions necessary for the existence of an AVF (DCC 2015, DCC 2016, DCM 2016).

Surface flow in Deer Creek is highly variable. In general, the highest flows are associated with spring snowmelt or exceptional precipitation events. Three active surface water monitoring stations (LDC-14, DCHR-14, and DCCR-14) and many historic surface water monitoring stations are present in the Study Area (Map 2). Long term surface water monitoring at station SFDC-14 near the upstream extent of the Study Area showed peak flows ranging from zero to over 60 cfs. Long term surface water monitoring at station DCHR-14, downstream of the county road crossing in T9S R41E Section 10, showed peak flows ranging from less than 5 cfs to over 300 cfs. At the most downstream monitoring station, LDC-14 located

6

less than one mile from the Tongue River Reservoir, long term monitoring showed peak flows ranging from less than 5 cfs to over 800 cfs. This 800 cfs peak flow event was an outlier as typical peak flows range from 10 to 60 cfs.

Data from alluvial wells and shallow piezometers located in the Deer Creek alluvium were evaluated to determine depth to groundwater in the Deer Creek Valley. Alluvial well and piezometer locations are shown on Map 2. Immediately downstream from the eastern edge of the Study Area, groundwater levels in wells 226381 and 226281 are over 10 feet below ground surface. Moving downstream less than one half mile, groundwater levels are 6-7 feet below ground surface at Piez 3. Continuing downstream, groundwater levels are 4-9 feet below ground surface in the vicinity of Piez 2 and well 225681, then progress to 7-10 feet below ground surface at Piez 1 and alluvial well 237882. Alluvial groundwater level drops below 10 feet from the ground surface near alluvial well 117874. Groundwater returns to within 10 feet of the ground surface elevation downstream of alluvial well 235582. Alluvial groundwater levels downstream of well 235582 are most likely influenced by the Tongue River Reservoir elevation, at higher reservoir stages. The alluvial aquifer is hydrologically connected to the Tongue River Reservoir. The Tongue River Reservoir water elevation typically exceeds the Tongue River Dam’s primary spillway elevation for a limited time in the spring. Measured groundwater elevation in 235582 is below the reservoirs principal spillway elevation indicating that during a portion of the year the Tongue River Reservoir may influence alluvial groundwater elevation.

Available geological information along with surface and groundwater data suggest there are unconsolidated alluvial deposits that convey water in the Deer Creek Valley. Surface flows are highly variable; however, present. Shallow groundwater, within eight feet of the ground surface, has been recorded throughout portions of the Study Area in alluvial deposits. This information indicates that portions of the Study Area may meet the requirements of an AVF, as stated in ARM 17.24.325(2)(b).

2. Sufficient Water to Support Agricultural Activities: The presence of irrigation sufficient to support agricultural activities or farming must be determined. See Section 82-4-203(3)(a), MCA; 17.24.325(2)(b). The three criteria to determine if there is sufficient water to support agricultural activities or farming are discussed in subsections a-c. See ARM 17.24.325(2)(b)(ii).

a. The Existence of Current or Historic Flood Irrigation Flood irrigation is defined as “supplying water to plants by natural overflow or the diversion of flows, so that the irrigated surface is largely covered by a sheet of water.” ARM 17.24.301(44). Surface water management structures such as dams or spreader and containment dikes indicate the existence of current or historic flood irrigation. Of these water management structures, dams and spreader dikes can be found in the Study Area and are visible on aerial images.

There are several irrigation ditches on Deer Creek associated with terminated or withdrawn surface water rights. According to water right data, available from Montana Department of Natural Resources and Conservation (DNRC) records, the surface water rights were established from 1907 to 1915 and subsequently dismissed in 2010 by the Montana Water Court. This indicates that flood irrigation was

7

attempted in this area but did not persist. All active water rights in the Deer Creek alluvial valley are listed as groundwater source and used for stock watering.

Though flood irrigation was attempted in the past and there are remnant structures present in the area, no current water rights for surface water indicate these attempts were unsuccessful. Dams and spreader dikes are not maintained. Also, individuals who had surface water rights, let them lapse in 2010. Water rights are very difficult to obtain and would therefore be maintained if they were in any way beneficial. This suggests that there is no benefit of flood irrigation in the study area.

b. Capability of the Area to be Flood Irrigated An area has the capacity to be flood irrigated if there is enough available water to support flood irrigation and there is an appropriate location on the landscape to irrigate with that water. Water availability and appropriate landscape locations for flood irrigation in the Study Area are discussed below.

Long-term monitoring of flow at surface water sites show high flows during some precipitation events and occasional years with no flow at all. Peak flows are highly variable from year to year with maximum flows ranging from zero cfs to 800 cfs. The highest flows are typically observed in the spring and early summer coinciding with the period of highest average precipitation. These data indicate that during some years in some locations there may be enough surface water available to support flood irrigation. However, the flow events that would be required to inundate pastureland happen too infrequently to maintain consistent flood irrigation. Though portions of the Study Area were previously flood irrigated, the lack of consistent flows would make flood irrigation unreliable and likely led to those water rights expiring.

Surface water quality in Deer Creek is variable. Total Dissolved Solids (TDS) in samples from Deer Creek ranged from 130 to 8,060 mg/l and electrical conductivity (EC) ranged from 137 to 7670 µS/cm. During major precipitation or snowmelt events the surface water in Deer Creek typically exhibits low dissolved solids. When flow is not influenced by a major precipitation event alluvial groundwater contributes a larger portion of surface flow and the TDS is typically much higher. Elevated soil EC is associated with reduced yield and quality of cultivated species (United States Soil Conservation Service 1997). The EC levels observed in Deer Creek may cause reduced crop yield if used for irrigation (Kotuby-Amacher et al. 2000).

Soils in the Deer Creek valley show variable suitability for agricultural use and flood irrigation. In general, the soils adjacent to Deer Creek, in the study area, are dominated by loam textured material with slopes of less than four percent. Some of this area is classified by the NRCS as prime farmland if irrigated. The NRCS also classifies some of the Deer Creek valley as saline land. These saline areas exhibit soil conductivities of 8-16 mmhos/cm and are not classified as prime farmland. Soil information submitted with the AVF request indicates that the areas of saline land are less extensive than what is depicted on NRCS soil maps.

There are terraces, adjacent to the channel over much of Deer Creek’s length, that currently support pastureland. This vegetation community consists primarily of crested wheatgrass. Flood irrigation water rights were previously held in the Study Area but were dismissed in 2010. This suggests that there were

8

areas with suitable topography to flood irrigate in the Deer Creek Study Area. Irrigation structures persist although they are no longer functional as diversions have failed over time with no maintenance.

Portions of the Deer Creek valley have the capability to be flood irrigated. In the Study Area, there is enough available water, in some years, to support flood irrigation and there is an appropriate location on the landscape to irrigate with that water based on soils and topography. Consistent flood irrigation may not be possible due to variations in water availability. Opportunistic flood irrigation is possible based on the stream flow, soils, water quality, and topography discussed above.

While portions of the study area are suitable for flood irrigation, surface water flows are highly variable and unpredictable. It has also been demonstrated that the quality of the surface water could have negative impacts on cultivated crops. Additionally, surface water rights would have to be reestablished in order for flood irrigation to be re-implemented in the area.

c. The Existence of Subirrigation Areas with unconsolidated streamlaid deposits that are subirrigated are AVF’s. Subirrigation occurs when groundwater is close enough to the surface to support agricultural activities or farming. This happens when water reaches the root zone of the plants being grown. According to ARM 17.24.301 (118) “Subirrigation” means, with respect to alluvial valley floors, the supplying of water to plants from a sub-surface zone where water is available and suitable for use by vegetation. Subirrigation may be identified by:

(a) diurnal fluctuation of the water table, due to the differences in nighttime and daytime evapotranspiration rates;

(b) increasing soil moisture from a portion of the root zone down to the saturated zone, due to capillary action;

(c) mottling of the soils in the root zone;

(d) existence of an important part of the root zone in the capillary fringe or water table of an alluvial aquifer; or

(e) an increase in streamflow or a rise in ground water levels, shortly after the first killing frost on the valley floor.

The portion of the Study Area that is subirrigated was delineated using evidence of the conditions described above. This effort was limited by the available data. The following analysis of subirrigation will focus on ARM 17.24.301 (118) (a), (d), and (e) because those components of this rule can be evaluated using available evidence.

Groundwater elevation in shallow alluvial wells was evaluated for the presence of daily fluctuations indicating the effects of evapotranspiration (ET). These daily fluctuations, referred to as diurnal fluctuations, are indicative of ET lowering shallow groundwater levels and have been used to estimate ET rates in numerous studies (summarized in Gribovszki et al. 2010). During daylight hours, when ET is

9

actively occurring, groundwater levels continually decline as water is lost to the atmosphere. During night hours, after ET has ceased, groundwater levels recover as recharge from adjacent areas occurs.

Hydrographs depicting continuous groundwater elevation data, from 2015 and 2016, were reviewed to identify the presence of diurnal trends in piezometers Piez 1, Piez 2, and Piez 3, and wells 225681, and 237882. The hydrograph for groundwater well 225681 could not be evaluated from December 7, 2015 to July 14, 2016 because no continuous groundwater elevation data were available during that time period. The monitoring points listed above were selected for evaluation because they were located adjacent to Deer Creek, equipped with pressure transducers, and the depth to water in each well was less than the predicted limit for subirrigation based on rooting depth and capillary fringe estimates.

Diurnal fluctuations in groundwater, indicating the effects of ET, were observed in Piez 3 and well 225681 (Figure 1 and Figure 2). During July and August of 2015 and 2016 diurnal fluctuations are present in the continuous groundwater elevation data from Piez 3 and 225681. No clear diurnal fluctuations were observed in Piez 1, Piez 2, or well 237882.

Figure 1. Diurnal fluctuations of the water table in well 225681.

3523.40

3523.60

3523.80

3524.00

Gro

undw

ater

Ele

vatio

n (ft

)

Deer Creek Alluvial Well 225681

10

Figure 2. Diurnal fluctuations of the water table in piezometer Piez 3.

Capillary fringe refers to the ability of water to rise in the soil column above the water table due to capillary action. Pore sizes of the material above the water table determine the thickness of the capillary fringe. Montana DEQ defined the maximum depth of the water table below ground surface that still provides the potential for subirrigation to be approximately 7.5 feet (3 feet average rooting depth plus 4.5 feet of predicted capillary rise in the soil from the water table) for the Deer Creek Alluvial Valley. This was determined using soil test pit data for both rooting depth and soil composition.

According to the East Decker Northeast Extension Soil Survey, the maximum rooting depth for alluvial soils ranged from 14 to 60 inches, with an average of 36 inches. This 36-inch average rooting depth, or three feet, is considered the rooting depth in the Study Area for this analysis. Some plants species, like alfalfa, can develop root systems to depths of 14 feet or more (Dollhopf, et al., 1982). The three-foot average rooting depth observed in the Study Area is likely due to the relatively low abundance of alfalfa in the Deer Creek valley. The East Decker Northeast Extension Vegetation and Land Use Inventory, indicates that crested wheatgrass dominates the plant community in the Pastureland land use category and bluebunch wheatgrass dominates the grazing land use category in the Study Area. These species have a much shorter rooting depth compared to alfalfa and thus the three feet observed average rooting depth is an appropriate average for the Study Area.

The Study Area soils capillary potential, or the vertical distance water can move above the water table, was calculated using laboratory data presented in the East Decker Northeast Extension Soil Survey. The soil survey results include the physical parameters of each of the soil types in the pits that were dug in Deer Creek. Those physical parameters include the amount of sand, silt, and clay components of each soil type. Using that information, the amount of capillary potential for each soil type is determined and then

3553.35

3553.40

3553.45

3553.50

3553.55

3553.60

3553.65

3553.70

Gro

undw

ater

Ele

vatio

n (ft

)Deer Creek Piezometer Piez 3

11

a total capillary potential for each soil column is calculated. Capillary potentials ranged from 38 inches to 70 inches and average 52 inches. This value was rounded up to 54 inches, or approximately 4.5 feet of capillary potential in the soils for Deer Creek.

Groundwater modeling, provided by Decker Coal Company as part of the AVF assessment of Deer Creek, shows depth to groundwater across the Study Area in 2-foot intervals (DCM 2016 Exhibit 325 5-1). Though the maximum depth to groundwater useable by plants was calculated as 7.5 feet (capillary potential of the soil plus rooting depth), the 8-foot contour was chosen as the maximum depth to groundwater useable by plants to match the 2-foot contours of the groundwater model and be conservative. The area where groundwater was modeled to be 8-feet or less from ground surface and alluvial deposits were present, as identified by the Montana Bureau of Mines and Geology in Vuke et al 2001, is shown on Map 2. The green shading on Map 2 represents the area within the Deer Creek alluvial valley that has the potential for subirrigation based on capillary action, rooting depth, and depth to groundwater. The AVF shading presented is DEQ’s best approximation based on the available data. Further refined surface topography mapping may cause the boundary of the shading to shift slightly.

Further investigations of the soil profile data included looking for the presence of soil mottling. This would be found if portions of the soil profile were regularly inundated with water. Soil mottling occurs when saturation creates reducing conditions and iron coatings from mineral grains are removed or depleted. When the soluble reduced iron (Fe II) encounters more aerobic zones it is oxidized and precipitates as Fe III oxide. Reduced iron is grey to blue-green while oxidized iron is reddish. This contrast in color creates a unique mottled appearance (Brady and Weil 2010). Photos of select soil pits were included in the East Decker Northeast Extension Soil Survey. These did not show any evidence of soil mottling in the areas investigated. However, many photos were of soil pits in upland areas and photos typically showed only the first five feet of the soil profile.

Seasonal fluctuations are common in shallow groundwater systems, where groundwater levels are dependent on recharge and loss due to atmospheric conditions. In general groundwater levels reach their maximum following winter and early spring after precipitation events that create recharge (rain or snowmelt). These high levels decline as a result of evaporation and vegetative transpiration. In early fall, ET rates decline due to shorter days, cooler temperatures, and vegetation senescence (hibernation or frost kill). Thus, shallow groundwater levels start to recover in the fall as ET markedly declines. Observation of increasing shallow groundwater levels in early fall is an indication that subirrigation may be occurring.

An increase in groundwater levels in the early fall occurred in Piez 3 and in well 225681. In early October 2015 groundwater levels began to rise drastically in well 225681. An increase in groundwater in Piez 3 also occurred during early October 2015, although the rise was not as pronounced. In September 2016 groundwater levels began to rise drastically in well 225681(Figure 3). Groundwater level also increased in Piez 3 during September 2016, although the rise was not as pronounced compared to well 225681(Figure 4). No appreciable increase in groundwater levels was observed during late September 2016 in Piez 1 or 237882. The Groundwater level in Piez 2 fell below the measurable limit for the

12

pressure transducer in the well by early July of 2016 and did not exhibit significant recharge until February of 2017.

Figure 3. Groundwater elevation July 15, 2016 to October 31, 2016.

Figure 4. Groundwater elevation May 1, 2016 to October 31, 2016.

3523.00

3523.50

3524.00

3524.50

3525.00

3525.50

3526.00

3526.50

3527.00

3527.50

3528.00

7/14/2016 8/3/2016 8/23/2016 9/12/2016 10/2/2016 10/22/2016

Elev

atio

n (ft

)

Deer Creek Alluvial Well 225681

Groundwater

Ground Surface

3553.000

3553.500

3554.000

3554.500

3555.000

3555.500

3556.000

3556.500

3557.000

3557.500

3558.000

3558.500

4/25/2016 5/25/2016 6/24/2016 7/24/2016 8/23/2016 9/22/2016 10/22/2016

Gro

undw

ater

Ele

vatio

n (ft

)

Date

Deer Creek Piezometer Piez 3

Groundwater

13

The presence or absence of strong seasonal patterns and diurnal fluctuations in alluvial wells may be explained by differences in depth to groundwater. Groundwater levels in Piez 3 and 225681 were less than five feet from the ground surface throughout the growing season in 2016. Groundwater levels in Piez 1 were more than five feet from the ground surface throughout the growing season in 2016. Groundwater levels in 237882 were more than seven feet from the ground surface throughout the growing season in 2016. Groundwater levels in Piez 2 increased dramatically in winter then dropped dramatically in early summer. In early June groundwater levels in Piez 2 were more than five feet from the ground surface and by late July groundwater had dropped to over nine feet below ground surface and remained over nine feet below ground surface for the rest of the 2016 growing season. The two wells that exhibited diurnal fluctuation of the water table and a rise in groundwater levels in the fall were in areas where groundwater was less than five feet from the ground surface throughout the growing season.

Multiple lines of evidence were evaluated to draw conclusions about the presence of subirrigation in the Study Area. In some portions of the Study Area, evidence of subirrigation, including the existence of an important part of the root zone in the capillary fringe was identified. Diurnal fluctuation of the water table, and an increase in ground water levels after vegetation senescence was also identified. Multiple lines of evidence indicate that subirrigation occurs in portions of the Study Area.

Presence or Absence Conclusion An AVF is defined by having unconsolidated streamlaid deposits which are either flood or subirrigated. As described above, there is evidence within the Study Area of the presence of an AVF. Unconsolidated deposits are present in and adjacent to the defined channel of Deer Creek. The unconsolidated deposits depict one half of the AVF potential, while flood irrigation or subirrigation depicts the other half. The Study Area has limited potential for flood irrigation. However, flood irrigation was attempted in the past and evidence of water management structures remain. There is evidence of subirrigation in a portion of the Study Area. Based on soils and vegetation it can be expected that areas with water within eight feet of the surface can be subirrigated. Evidence of diurnal fluctuation of the water table during the growing season in some alluvial wells supports this. The presence of unconsolidated deposits and subirrigation confirms that an AVF is present along Deer Creek. The extent of the area identified as AVF is depicted on Map 2.

II. Significance

Statutory Exclusions Once the presence of an AVF is confirmed, the department must address the statutory exclusions described in 17.24.325(3)(a)(ii). If statutory exclusions apply, an AVF is deemed insignificant, and the operator is not required to provide information explaining whether the operation will avoid interrupting, discontinuing, or precluding farming on the AVF and whether the operation will cause material damage to the quality and quantity of water supplying the AVF.

ARM 17.24.325(3)(a)(ii)(A –C) define the statutory exclusions for significance. They are included below:

14

(A) the premining land type is undeveloped rangeland that is not significant to farming; (B) any farming on the alluvial valley floor that would be affected by the coal mining operation is of such small acreage as to be of negligible impact on the farm's agricultural production. Negligible impact of the proposed operation on farming is based on the relative importance of the affected vegetation and water of the developed grazed or hayed alluvial valley floor area to the farm's production over the life of the mine; or (C) the circumstances set forth in ARM 17.24.802(3) exist.

Statutory exclusions are applicable to the Deer Creek AVF. Any farming along the identified AVF is of such small acreage and low frequency as to be of negligible impact on the ranching operation. Production that may be affected within the Study Area is on minimal acreage and a landowner/operator interview confirms that it is not relied on for farming or ranching. A summary of the ranch operator interview is included below, and the interview questionnaire is attached. DEQ interviewed Mr. Mark Moreland who operates a ranch of approximately 23,000 acres, of which a portion is in the study area. The interview indicates exclusion (B) applies to this alluvial valley floor. The total area of AVF identified is approximately 325 acres, which represents approximately 1.4% of the total land utilized by Mr. Moreland’s ranch for grazing. Based on the statutory exclusion ARM 17.24.325(3)(a)(ii)(B) there is no significant AVF present in the lower Deer Creek valley because the AVF in the study area is of such small acreage as to be of negligible impact on Mr. Moreland’s operation.

Landowner/Ranch operator Interviews A requirement of significance determination under rule ARM 17.24.805 states, “In making the determination of “significance”, the department shall consult with the affected landowner(s).” Decker Coal Company or its Parent company owns the land where the AVF was identified. However, one ranch operator currently leases the land for cattle production. Mark Moreland operates a cattle ranch in the Deer Creek valley. The Department conducted an interview with Mr. Moreland on August 21, 2018. The interview questionnaire is attached as Appendix A.

Mr. Moreland leases a portion of the Study Area and lives upstream of the mine in the Deer Creek Valley. Mr. Moreland’s ranch utilizes approximately 23,000 acres. There are 1,201 acres deeded with 21,799 leased acres. There are no crops accept dryland hay farmed on the ranch. There is no irrigation on the ranch. The floodplain of Deer Creek is not critical to operations and is only utilized in very wet years and may only constitute about one percent of the 23,000 acres utilized. This indicates 98% - 99% of the ranch is upland grazing land as the entire area is grazed. Mr. Moreland’s operation runs approximately 1,500 head of cattle for four months a year. There is no winter feeding in turn reducing the requirement to produce hay in large quantities. Based on comments from the ranch operator, Mark Moreland, this AVF has a negligible impact on his ranching operation.

Summary The lower Deer Creek valley has been evaluated for the presence of an AVF. Evidence demonstrating the presence of an AVF was found. Based on the presence of an AVF in the lower Deer Creek valley a significance determination was required.

15

Pursuant to ARM 17.24.325(3)(a)(ii)(A–C), DEQ utilized existing scientific data and surface operator information to determine whether any statutory exclusions were applicable to the significance determination for Deer Creek. Under exclusion (B), if agricultural acreage is impacted but the acreage is negligible to the farm or ranch operation, the AVF is considered insignificant. Due to the negligible size of impacted acreage in the Deer Creek AVF, the AVF is considered insignificant to agriculture.

Since the AVF meets the criteria for statutory exclusions, DCC is not obligated to “submit the information required in ARM 17.24.325(3)(c)(ii)(B) and (C), and the department is not required to make the findings of ARM 17.24.325(3)(f)(ii)(A) and (B).” as stated in ARM 17.24.325(3)(a)(ii).

16

References

American Geologic Institute. Dictionary of Geological Terms, Revised Edition. Anchor Press 1976

Brady, Nyle C., Weil, Ray R., 2010. Elements Of The Nature And Properties Of Soils, Third Edition, Prentice Hall/Pearson.

Dollhopf, D. J., J.D. Goering, C.J.Levine, S.A. Young and E.L. Ayers, 1982. Crop response to subirrigation in alluvial valley systems, Montana Agricultural Experiment Station, Reclamation Research Program, MSU, Bozeman, Research Report 900.

Decker Coal Company (DCC), 2015. 2015 Annual Hydrology Report. Submitted to Montana Department of Environmental Quality in December 2015.

Decker Coal Company (DCC), 2016. 2016 Annual Hydrology Report. Submitted to Montana Department of Environmental Quality in December 2016.

Decker Coal Mine (DCM), 2016. Alluvial Valley Floor Assessment – Deer Creek Valley. Submitted to Montana Department of Environmental Quality in January 2016.

East Decker Northeast Extension Soil Survey (Soil Survey), 2016. Northeast Extension Soil Survey. Submitted to Montana Department of Environmental Quality in April 2017.

Gribovszki, Z., J. Szilágyi, and P. Kalicz (2010), Diurnal fluctuations in shallow groundwater levels and streamflow rates and their interpretation: A review, J. Hydrol., 385(1–4), 371–383, doi:10.1016/j.jhydrol.2010.02.001.

Kho, Jeff, Practical Calculations for Groundwater and Soil Remediation, 2d ed., Taylor and Francis Group, Boca Raton, FL, 2014, p. 30.

Kotuby-Amacher, Jan, Rich Koenig, Boyd Kitchen. 2000. Salinity and Plant Tolerance. Utah State University Extension AG-SO-03

USDA, 1980.; Geological Parent Materials of Montana Soils. Montana Agricultural Experiment Station, Montana State University – Bozeman, MT and USDA Soil Conservation Service. pp 74-81.

United States Soil Conservation Service, 1997. National Engineering Handbook: Irrigation Guide. U.S. Dept. of Agriculture, Soil Conservation Service, 1997. Print.

Vuke, S.M., Heffern, E.L., Bergantino, R.N., and Colton, R.B., 2001, Geologic map of the Birney 30' x 60' quadrangle, eastern Montana: Montana Bureau of Mines and Geology Open-File Report 431, 12 p., 1 sheet, scale 1:100,000.

Deer Creek

9S 41E9S 40E

8S 41E8S 40E

9S 42E

8S 42E

10S 42E

Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS UserCommunity

$

LegendStudy Area BoundaryEast Decker Permit BoundaryDeer CreekDeer Creek Drainage Basin PreminePLSS

Projection: NAD83 Montana State Plane - Meters

East Decker MinePermit ID: C1983007

Deer Creek AVFAugust 2018

Map 1. Area Overview

0 1 20.5 Miles

!(

!( !(!(

!(

!(

!(!(!(!(!(!(!(

!(!(

!(!(

!(!(!(!(!(

!(

!(

!(

!(

!(

#

#

#

#

#SFDC-14

UCC-75

DCHR-14

DCCR-14

LDC-14 (PT)

Piez 3

Piez 2

Piez 1

117874

124274

225481225581225681

225781225881

226281226381

235482235582 235782

235882235982236082 236382236482

237282

237582

237782 237882237982238182

Deer Creek

Midd

le Cr

eekCoal Creek

9S 41E

8S 41E

9S 40E

8S 40E

11

12

01

13

3332 34 3531

15

2322

08

1614

36

17

1009

07

21

18

06 05

20

04 03 02

1924

36

14

23

12

01

11

13

25

24

02

30 29 28 27 26

35

25

Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS UserCommunity

$

LegendEast Decker Mine Permit BoundaryStudy Area BoundaryDeer Creek AVF

!( Deer Creek Alluvial Wells# Deer Creek Surface Water Monitoring Sites

StreamsPLSS

Projection: NAD83 Montana State Plane - Meters

East Decker MinePermit ID: C1983007

Deer Creek AVFSeptember 2018

Map 2. AVF Extent

0 0.5 10.25 Miles

AVF Ranch Operator Significance Interview 17.24.805

Ranch Operator

Drainage (s) addressed

Date

General Agricultural Type

FarmingRanchingFarming and Ranching

Total Acreage Under Production (Farming)

What crops are produced

Do you implement crop rotation

Total Acreage Flood Irrigated

Average yield of Flood Irrigated fields

Total Acreage Subirrigated

Average yield of Subirrigated fields

How critical is the floodplain to sustain operations

Total Acreage Upland

Total acreage Grazed

How many head of livestock do you run