DE Montana Depar tment -of Environmental Quali ty

May 20, 2020

FINDING OF NO SIGNIFICANT IMPACT

TO ALL INTERESTED GOVERNMENTAL AGENCIES AND PUBLIC GROUPS

As required by state and federal rules for determining whether an Environmental Impact Statement is necessary, an environmental review has been performed on the proposed action below:

Project

Location Project Number Total Cost

Thompson Falls Collection System Expansion and Treatment System Improvements Thompson Falls, Montana C303706 $15,017,390

The City of Thompson Falls (City), through a preliminary engineering report (PER) prepared by Great West Engineering, identified the need to expand the collection system and to upgrade its wastewater treatment facility. Only a portion of the community is served by a municipal wastewater collection and treatment system. The issue of most concern for the City is that portion of the city north of US Highway 200 which is not connected to the municipal system and is served by on-site septic tanks and drainfields. This area contains approximately 560 homes and three schools. The septic systems in this area are aging and some have even failed in recent years. Many of the residential lots are small and owners are unable to install conventional septic systems meeting current design requirements. The quantity and density of these on-site systems present a potential for contamination and pose a threat to human health and natural resources in the area. Existing collection system deficiencies identified in the PER include several lines that have root intrusion and settling issues which require additional maintenance to prevent and clear blockages. In addition, these lines also experience high inflow and infiltration (l&I) of storm and ground waters during the spring month. The City's lift station is over 20 years old and experiences frequent pump maintenance issues resulting in down time for the lift station. The lift station also lacks backup power to maintain operation during power outages and finding parts for the pumps and controls is becoming more difficult. The lift station is located near the bank of the Clark Fork River and there is a risk of wastewater overflowing the wet well and discharging into the river when the lift station is down, threatening public health and safety. The existing asbestos cement force main also requires ongoing maintenance to repair regular breaks. The City's existing aerated lagoon system has some minor operational issues, but can typically meet existing permit limits at current system flows. With expansion of the collection system it will be necessary to make improvements to the treatment system associated with the increased flow and loads including disinfection to meet E. coli limits in the effluent and better biochemical oxygen demand (BOD) and total suspended solids (TSS) removal to meet allocated non-degradation load limits for these parameters in the discharge permit. Additional operational concerns at the lagoons include issues with

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

rags plugging aeration equipment and valves, sludge accumulation, excessive duckweed, and a lack of backup power for operation during outages.

The proposed project consists of constructing a new collection system and three lift stations to serve the unsewered area of Thompson Falls north of Highway 200. The collection system expansion has been divided into four phases to make the project more affordable to residents by giving the City the opportunity to maximize grant funding . Only phases 1 and 2 will be constructed with this project. A few of the existing collection system lines will be rehabilitated to minimize l&I and correct structural deficiencies. In addition, the existing aerated lagoon system will be converted to a complete mix/partial mix aerated lagoon with polishing reactor, and equipped with a new headworks screening system, ultraviolet (UV) disinfection, and backup power.

Federal and State grant/loan programs will fund the project. Environmentally sensitive characteristics such as threatened/endangered species, floodplains, wetlands, and historical sites are not expected to be adversely impacted because of the proposed project. No significant long-term environmental impacts were identified.

An environmental assessment (EA), which describes the project and analyzes the impacts in more detail, is available for public scrutiny on the DEQ web site (http://deq.mt.gov/Public/ea) and at the following locations:

Mike Abrahamson, P.E. Department of Environmental Quality 1520 East Sixth Avenue

Mark Sheets, Mayor City of Thompson Falls 108 Fulton St.

P.O. Box 200901 Helena, MT 59620-09011 mabrahamson@mt.gov

Thompson Falls, MT 59873

Comments on the EA may be submitted to the Department of Environmental Quality at the above address. After evaluating substantive comments received, the Department will revise the environmental assessment or determine if an environmental impact statement is necessary. If no substantive comments are received during the comment period, or if substantive comments are received and evaluated and the environmental impacts are still determined to be non-significant, the agency will make a final decision. No administrative action will be taken on the project for at least 30 calendar days after release of the Finding of No Significant Impact.

Sincerely,

~ SRF Program Manager Water Quality Division Montana Department of Environmental Quality

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

CITY OF THOMPSON FALLS

WASTEWATER IMPROVEMENTS PROJECT

ENVIRONMENTAL ASSESSMENT I. COVER SHEET

A. PROJECT IDENTIFICATION

Applicant: City of Thompson Falls

Address: 108 Fulton St Thompson Falls, MT 59873

Project Number: SRF Project # C303706

B. CONTACT PERSON

Name: Mayor Mark Sheets Address: PO Box 99 Thompson Falls, MT 59873 Telephone: (406) 827-3557

C. ABSTRACT

The City of Thompson Falls (City), through a preliminary engineering report (PER) prepared by Great West Engineering, identified the need to expand the collection system and to upgrade its wastewater treatment facility. Only a portion of the community is served by a municipal wastewater collection and treatment system. The issue of most concern for the City is that portion of the city north of US Highway 200 which is not connected to the municipal system and is served by on-site septic tanks and drainfields. This area contains approximately 560 homes and three schools. The septic systems in this area are aging and some have even failed in recent years. Many of the residential lots are small and owners are unable to install conventional septic systems meeting current design requirements. The quantity and density of these on-site systems present a potential for contamination and pose a threat to human health and natural resources in the area. Existing collection system deficiencies identified in the PER include several lines that have root intrusion and settling issues which require additional maintenance to prevent and clear blockages. In addition, these lines also experience high inflow and infiltration (I&I) of storm and ground waters during the spring month. The City’s lift station is over 20 years old and experiences frequent pump maintenance issues resulting in down time for the lift station. The lift station also lacks backup power to maintain operation during power outages and finding parts for the pumps and controls is becoming more difficult. The lift station is located near the bank of the Clark Fork River and there is a risk of wastewater overflowing the wet well and discharging into the river when the lift station is down, threatening public health and safety. The existing

asbestos cement force main also requires ongoing maintenance to repair regular breaks. The City’s existing aerated lagoon system has some minor operational issues, but can typically meet existing permit limits at current system flows. With expansion of the collection system it will be necessary to make improvements to the treatment system associated with the increased flow and loads including disinfection to meet E. coli limits in the effluent and better biochemical oxygen demand (BOD) and total suspended solids (TSS) removal to meet allocated non-degradation load limits for these parameters in the discharge permit. Additional operational concerns at the lagoons include issues with rags plugging aeration equipment and valves, sludge accumulation, excessive duckweed, and a lack of backup power for operation during outages.

The proposed project consists of constructing a new collection system and three lift stations to serve the unsewered area of Thompson Falls north of Highway 200. The collection system expansion has been divided into four phases to make the project more affordable to residents by giving the City the opportunity to maximize grant funding. Only phases 1 and 2 will be constructed with this project. A few of the existing lines will be rehabilitated to minimize I&I and correct structural deficiencies. In addition, the existing aerated lagoon system will be converted to a complete mix/partial mix aerated lagoon with polishing reactor, and equipped with a new headworks screening system, ultraviolet (UV) disinfection, and backup power. The project is proposed for construction in 2020. The estimated total project cost (including administration, engineering, and construction) for the treatment system improvements is $15,017,390. The City will fund the project through a $750,000 grant from the Treasure State Endowment Program (TSEP); a $187,390 grant from the Department of Natural Resources and Conservation; a $9,182,000 grant from Rural Development; a $4,832,000 loan (2.375% interest rate; 40-year term) from Rural Development; and $66,000 in local funds. The Water Pollution Control State Revolving Fund (WPCSRF) loan program will provide interim financing (1.75% interest rate; 3-year term) equal to the RD loan amount, to cover costs during the construction phase. Environmentally sensitive characteristics such as wetlands, floodplains, threatened or endangered species, and historical sites are not expected to be adversely impacted because of the proposed project. Additional environmental impacts related to land use, water quality, air quality, public health, energy, noise, growth, and sludge disposal were also assessed. No significant long-term environmental impacts were identified. Under Montana law, (75-6-112, MCA), no person may construct, extend, or use a public sewage system until DEQ has reviewed and approved the plans and specifications for the project. Under the Montana Water Pollution Control State Revolving Fund Act, DEQ may loan money to municipalities for construction of public sewage systems. The DEQ, Engineering Bureau, has prepared this Environmental Assessment to satisfy the requirements of the Montana Environmental Policy Act (MEPA) and the National Environmental Policy Act (NEPA).

D. COMMENT PERIOD Thirty (30) calendar days.

II. PURPOSE OF AND NEED FOR ACTION

Only the portion of Thompson Falls located between US Highway 200 and the Clark Fork River is served by a municipal wastewater collection and treatment system. The wastewater issue of most concern to the City is that the portion of the community north of US Highway 200 is not connected to the municipal wastewater system and is served by on-site septic tanks and drainfields. This area contains approximately 560 homes and three schools. The septic systems in this area are aging and some have even failed in recent years. Many of the residential lots are small and owners are unable to install conventional septic systems capable of meeting current design requirements. The quantity and density of these on-site systems present the potential for groundwater contamination and pose a threat to human health and natural resources in the area. While much of the existing collection system was replaced 20 years ago, some portions date back 70 years. These older lines suffer from root intrusions and settling, requiring additional maintenance to prevent and clear blockages. These lines also experience high inflow and infiltration (I&I) of storm and ground waters during the spring months. The City’s lift station is over 20 years old and experiences frequent pump maintenance issues resulting in down time for the lift station. The lift station also lacks backup power to maintain operation during power outages and finding parts for the pumps and controls is becoming more difficult. The lift station is located near the bank of the Clark Fork River and there is a risk of wastewater overflowing the wet well and discharging into the river when the lift station is down for extended maintenance or power outages, threatening public health and safety. The existing asbestos cement (AC) force main also requires on-going maintenance to repair regular breaks. As the collection system is expanded it will be necessary to make improvements to the treatment system associated with the increased flow and loads including the addition of disinfection to meet E. coli limits in the effluent and better BOD and TSS removal to meet the allocated non-degradation load limits for these parameters in the discharge permit. Other operational concerns at the City’s existing lagoon facility include rags plugging aeration equipment and valves, sludge accumulation, duckweed management, and a lack of backup power for operation during outages.

III. ALTERNATIVES INCLUDING THE PROPOSED ACTION AND COSTS Alternatives for treatment and collection were considered separately from each other. A. COLLECTION SYSTEM ALTERNATIVES

In addition to expanding the City’s collection system north of US Highway 200, the collection system alternatives all address deficiencies within the existing system by: 1) reducing inflow and infiltration in one manhole within Solid Rock Estates; 2) replacing 600 feet of failing 6-inch Orangeburg pipe with 8-inch PVC sewer main; 3) replacing 1,300 feet of failing 12-inch AC pipe gravity collection main east of Main Lift Station with 12-inch PVC sewer main; 4) rehabilitating approximately 240 feet of old 8-inch clay pipe in the alley between Hill Street and

Ferry Street with cured-in-place-pipe (CIPP); 5) replacing controls at the Main Lift Station; and 6) installing a backup power generator at the Main Lift Station. Three alternatives for addressing the City’s collection system expansion were evaluated in detail. These included: C-0. No Action C-1. Separate Force Main to Treatment Site C-2. Gravity Collection System to Main Lift Station C-0 NO ACTION – This alternative would not address the primary concern of

the City in that it would not provide sewer service to the unsewered area of the community. This would not address the heath and sanitary concerns associated with the high density of substandard on-site septic systems. In addition, not addressing deficiencies in the existing collection system will require an increase in operation and maintenance efforts associated with elevated I&I and trouble mains. Due to these concerns the “no action” alternative was not given further consideration.

C-1 SEPARATE FORCE MAIN TO TREATMENT SITE - This alternative

would construct gravity collection main lines within the existing street rights-of-way, and typically located directly underneath the street itself due to construction limitations (i.e., narrow, rock outcrops, etc.) within the alleyways. The predominant slope of the area is from north to south. Individual grinder pumps may be necessary to connect some residences to the gravity collection mains. This alternative will include three new wastewater lift stations. Two of the lift stations (East Preston & Golf Street) will convey wastewater to the third pump station (West Preston). From there, wastewater will be pumped to the treatment site through a new 1,300-foot, 6-inch PVC force main. Each of the new lift stations will include a backup power generator and transfer switch so that it can fully operate during a power outage. The existing on-site septic systems at each residence will be abandoned in-place.

C-2 GRAVITY COLLECTION SYSTEM TO MAIN LIFT STATION - This

alternative would be similar to alternative C-1, but wastewater would be conveyed to the existing Main Lift Station located near the intersection of Maiden Lane and Mill Street. This will require two new crossings of US Highway 200 and the BNSR railway. These crossings will convey all wastewater from the expanded collection system to the existing Main Lift Station. From the Main Lift Station, wastewater will be pumped to the existing treatment site through a new 8-inch force main to replace the existing AC force main. The pumps in the Main Lift Station will be upgraded to convey the additional flow. This alternative includes two new wastewater lift stations. The lift stations (East Preston & Golf Street) will serve to convey wastewater to sewer-sheds within the expanded system that have north-south connections to the existing collection system. Individual grinder pumps may be necessary to connect some residences to the gravity collection mains. Each of the new lift stations will include a backup power generator and transfer switch so that it can fully operate during a power outage. The existing on-site septic systems at each residence will be abandoned in-place.

B. TREATMENT ALTERNATIVES

Four alternatives for addressing the Town’s treatment system needs were evaluated in detail. These include:

T-0. No Action

T-1. Storage and Irrigation T-2. Complete Mix/Partial Mix Aerated Lagoons & Polishing Reactor T-3. Existing Partial Mix Lagoons with Submerged Attached Growth

Reactor (SAGR)

T-0 NO ACTION – The no action alternative consists of making no improvements to the system. Only minimal treatment system improvements would be necessary since the existing treatment system can adequately meet permit limits. Removal of accumulated sludge would still be necessary in the near future. Since the primary intent of the PER is to evaluate the feasibility of providing sewer service to the unsewered area of the community, and it has been shown that lagoon improvements would be necessary to meet current limits due to those extra flows and loads, the “no action” alternative is not a viable option and was not given further consideration.

T-1 STORAGE AND IRRIGATION – This alternative would utilize the existing

lagoon system and construct a new 9-acre storage lagoon cell with capacity to store wastewater effluent beyond the non-degradation allocated load set in the discharge permit. Based on estimated system flows, approximately 75,000 gpd must be stored and irrigated. The stored effluent would be land applied to 21 acres of forestland during the summer months using irrigation equipment. Insufficient land is available within the City’s treatment property boundary. Therefore, a land purchase or lease will be necessary for the irrigation site. A force main to the irrigation site will be necessary. Sludge removal and construction of temporary sludge drying beds are also included with this alternative. Geofabric filter bags would be used to dewater the sludge within the sludge drying beds. These bags can be left in place to dry until an adequate solids content of the sludge is reached. A new headworks screening system and UV disinfection system would be constructed as well.

T-2 COMPLETE MIX/PARTIAL MIX AERATED LAGOONS & POLISHING

REACTOR – With this alternative the influent would pass through a new headworks building housing a mechanical screen to remove material larger than 6 mm in size before entering the lagoon system. A baffle curtain would be installed in two of the existing lagoon cells to create a total of four zones. The first zone will be a complete mix zone which is an aggressively mixed aerated cell that establishes an environment suitable for the rapid removal of BOD and keeping solids in suspension. Aeration and mixing are provided by a combination of fine bubble diffusers and floating mechanical mixers. The second and third zones will be partial mix lagoon cells which have a lower level of aeration and mixing energy to effectively achieve the required BOD removal while utilizing less energy. The fourth zone will be a quiescent settling pond for final TSS removal.

The entire system will have an insulated floating cover to prevent the growth of algae and duckweed and to retain heat to improve treatment and settling in the final zone. The final step in the treatment process is the polishing reactor. This is a fixed film reactor consisting of aerated, submerged, attached growth media modules that maintain a population of bacteria used for final polishing of the lagoon effluent by removing a high percentage of ammonia and further reduce BOD and TSS concentrations. Effluent will be disinfected with a UV system following the polishing reactor before discharging to the river. Existing cell 3 will be used for sludge storage and drying.

T-3 EXISTING PARTIAL MIX LAGOONS WITH SUBMERGED ATTATCHED

GROWTH REACTOR (SAGR) – This alternative would reuse the existing aerated lagoon cells and add a Submerged Attached Growth Reactor (SAGR) after the final lagoon cell to remove ammonia and further reduce BOD and TSS concentrations. The SAGR system consists of two parallel gravel beds that are approximately 7.5 feet deep and are fully aerated with a grid of aeration pipe on the bottom of each bed. New blowers will be needed to provide aeration to the SAGR units. Wastewater is introduced through a distribution header and moves horizontally through the gravel bed. A biofilm grows on the bed to remove BOD/TSS and can also greatly reduce ammonia. To help improve treatment during the winter months, the SAGR units would be constructed below ground and have an insulating layer (e.g., mulch) over the top to help retain heat. The system is relatively easy to operate. The SAGR system would be constructed on City-owned property just west of the existing lagoons. Effluent will be disinfected with a UV system following the SAGR system before discharging to the river. Sludge removal and construction of a temporary sludge drying bed are also included with this alternative. Geofabric filter bags would be used to dewater the sludge within the sludge drying beds as discussed previously.

C. COST COMPARISON - PRESENT WORTH ANALYSIS The present worth analysis is a means of comparing alternatives in present day dollars and can be used to determine the most cost-effective alternative. An alternative with low initial capital cost may not be the most cost-efficient project if high monthly operation and maintenance costs occur over the life of the alternative. A 3% interest factor over the 20-year planning period was used in the analysis. Table 1 provides a summary of the present worth analysis of the feasible collection system alternatives. Table 2 provides a summary of the present worth analysis of the feasible treatment system alternatives.

TABLE 1 - ECONOMIC EVALUATION OF COLLECTION SYSTEM ALTERNATIVES

TABLE 2 - ECONOMIC EVALUATION OF TREATMENT SYSTEM ALTERNATIVES

D. BASIS OF SELECTION OF PREFERRED ALTERNATIVE Selection of the preferred alternative was based upon several criteria, both monetary and non-monetary. The ranking criteria considered are shown in Table 3. The viable collection and treatment alternatives were compared with respect to technical feasibility, environmental impacts, financial feasibility, public health and safety, operational and maintenance considerations, and public comment. Each alternative was assigned a ranking score of 0 to 10 for each category, with 0 representing a negative impact and 10 representing the maximum benefit to the community. The alternatives began with a score of 5 for each criterion, and then

Alternative Total Capital

Cost

Present Worth of Annual O&M Cost

Increase

Present Worth of Salvage Value

Net Present Worth

C-1: Separate Force Main to Treatment Site $18,968,000 $858,500

$1,479,500

$18,347,000

C-2: Gravity Collection System to Main Lift Station $19,369,000 $916,500

$1,455,700

$18,829,800

Alternative Total

Capital Cost

Present Worth of Annual O&M Cost

Increase

Present Worth of Salvage Value

Present Worth of O&M plus Capital

T-1: Storage and Irrigation $6,798,000 $1,898,400

$718,700

$7,977,200

T-2: Complete Mix/Partial Mix Aerated Lagoons w/ Polishing Reactor

$4,462,000 $1,586,000 $284,600 $5,763,400

T-3: Existing Partial Mix Lagoons w/ Submerged Attached Growth Reactor (SAGR)

$5,919,000 $1,541,400

$694,400

$6,766,000

the score was adjusted up or down relative to the benefit of the particular alternative in relation to the other alternatives. The ranking factors were then divided into the relative weight of importance assigned to each evaluation criteria, with the criteria most important to the City receiving higher weighting. The weighted rank scores were then summed, resulting in a total score, with the greatest score indicating the preferred alternatives.

TABLE 3 –WASTEWATER COLLECTION & TREATMENT ALTERNATIVES RANKING

The decision matrix shows that the preferred collection system alternative is C-1; separate force main to treatment site. This alternative ranked higher than the other collection system alternative primarily due to technical feasibility, environmental impacts, and public comment. The preferred treatment alternative is T-2; complete mix/partial mix aerated lagoons with polishing reactor. This alternative ranked higher than the other treatment system alternatives primarily due to financial feasibility and public comment, in comparison to the other treatment alternatives considered.

The estimated total project cost (including administration, engineering, and construction) for the treatment system improvements is $15,017,390. This includes construction of phases 1 and 2 of collection system alternative C-1, and treatment system alternative T-2. The City will fund the project through a $750,000 grant from the Treasure State Endowment Program (TSEP); a $187,390 grant from the Department of Natural Resources and Conservation; a $9,182,000 grant from Rural Development; a $4,832,000 loan (2.375% interest rate; 40-year term) from Rural Development; and $66,000 in local funds. The Water Pollution Control State Revolving Fund (WPCSRF) loan program will

Criterion

Alternative C-1

Alternative C-2

Alternative T-1

Alternative T-2

Alternative T-3

Weight

Score

Points

Score

Points

Score

Points

Score

Points

Score

Points

Financial Feasibility

10

5.1

51

4.9

49

3.6

36

6.4

64

5

50

Technical Feasibility

5

9

45

8

40

5

25

9

45

9

45

Operations and Maintenance Considerations

7

7

49

7

49

7

49

9

63

9

63

Public Health and Safety

10

9

90

9

90

7

70

8

80

8

80

Environmental Impacts

5

9

45

8

40

7

35

9

45

9

45

Public Comment

7

9

63

7

49

7

49

9

63

8

56

TOTAL SCORE

343 317 264 360 339

provide interim financing (1.75% interest rate; 3-year term) equal to the RD loan amount to cover costs during the construction phase.

The financial impact of this project on the system users is shown in Table 4. The existing sewer rate for system users is $40/mo. After the rate increase is imposed, the residential base user rate for existing system users and new users in Special Improvement Districts(SIDs) -1 and -2 will be approximately $65/month. In addition, properties in SIDs -1 and -2 will pay a $300 annual assessment for 20 years on their taxes. This will result in a net effective user rate of $90/month for users in SIDs -1 and -2. Based on the EPA guidance for project affordability, the proposed project will result in a monthly cost per household that is over 2% of the monthly median household income, and therefore, may impose a significant economic hardship on some households.

TABLE 4 - PROJECT AFFORDABILITY

Monthly sewer user cost residential $65.00 Monthly sewer user cost for SID 1 & 2 residents $90.00

Monthly median household income (mMHI)1 $2,549.58 User rate as a percentage of Mmhi 2.5 – 3.5%

1 Based on US Census Bureau 2010 data.

IV. AFFECTED ENVIRONMENT

A. PLANNING AREA AND MAPS

The City of Thompson Falls is located along US Highway 200, in northwestern Montana (see Figure 1). Thompson Falls’ boundary and planning area are shown in Figure 2. This area includes the incorporated limits of the City of Thompson Falls, the wastewater treatment system located northwest of the city, and some adjacent undeveloped lands. Figure 3 shows the collection system layout for the unsewered area north of Highway 200. Figure 4 shows the four phases for the expanded collection system improvements. The existing aerated lagoon system with an overlay of the proposed aeration system design, including the proposed locations of the new headworks building, polishing reactor, and disinfection building is shown in Figure 5.

B. POPULATION AND FLOW PROJECTIONS

The City of Thompson Falls has experienced slight increases and slight

decreases intermittently in the population over the past 20 years. The PER uses a moderate annual growth rate of 0.1% for Thompson Falls. The current population served by Thompson Falls WWTF is 194 people. With expansion of the collection system to serve the entire community the projected design year 2037 population is 1,349.

The average daily flow to the existing WWTF from 194 residents is approximately 33,000 gallons per day (gpd). The proposed treatment system improvements will be designed to handle a design flow of 161,000 gpd to serve a population of 1,349 people. Table 5 summarizes the current and projected population and the average daily flow data.

TABLE 5 – EXISTING AND PROJECTED POPULATION AND WASTEWATER FLOWS

Year Population Average Daily Flow (gal/day)

2017 194 33,240 2037 1,3491 161,000

1 Includes service to entire community

C. NATURAL FEATURES The project area is located in the lower Clark Fork River Basin area which is primarily mountainous and forested, with structurally-controlled valleys. The City of Thompson Falls is situated on the banks of the Clark Fork River proximal to the Thompson Falls Dam. Soils underlying the project areas reflect the near-surface alluvial geology. The soil underlying most of the city belongs to the Elkrock-Selon complex. These soils derive from river terraces and are comprised of primarily silt and gravelly silt. In this case, the river terraces contain a significant fraction of Lake Missoula silt beds left by the formation and repeated draining of Glacial Lake Missoula. The city is underlain predominately by the younger alluvial deposits, although some small areas may have near-surface bedrock or rock outcrops that may impact sewer main and service line installation. Native vegetation surrounding Thompson Falls consists primarily of grasslands and riparian flora in the lower elevations and along some waterways. Most of the uplands comprise conifer forests of various types, depending upon elevation and aspect. The Thompson Falls dam on the Clark Fork is used for hydroelectric production. Some irrigation water may be diverted from the river, but irrigation demands are considerably lower in the region as compared to other areas in the State. Groundwater in the lower Clark Fork River basin is generally found in either bedrock aquifers associated with older metasedimentary rock or within alluvial/fluvial deposits proximal to surface water. Production rates vary widely, from a few gallons per minute (gpm) to 1,500 gpm. Alluvial groundwater can be found reasonably shallow within the existing sewer service area. However, depth to groundwater in the unsewered area of the community north of the highway increases as the ground surfaces slopes away from the river. Water quality will likely improve with the removal of a significant number of individual drainfields. The soils underlying the city are noted in Natural Resources Conservation Service (NRCS) soil mapping as “very limited” for the purposes of septic tank absorption fields. Given this designation and the density of substandard septic systems in the area, strong potential exists for degradation of groundwater, and given the proximity to the Clark Fork River, surface water quality as well. The average high temperature in the Thompson Falls area is 83oF, but can occasionally top 100oF during the summer months. The average low temperature is approximately 28oF, with periods of sub-zero temperatures at times during the winter months. The average annual precipitation rate is 20.19 inches per year, with the drier months being August through September. The average evaporation rate in the area is approximately 32 inches per year.

V. ENVIRONMENTAL IMPACTS OF PROPOSED PROJECT

A. DIRECT AND INDIRECT ENVIRONMENTAL IMPACTS

1. Land Use/Prime Farmland – Land use within the project planning area is predominantly urban-developed. Lands adjacent to the city are generally forestland with areas of cleared rangeland and hay pastures north of the planning area. The improvements at the treatment site will occur within existing boundaries, and expansion of the collection system will be within existing right-of-way. The project area contains soil classified as farmland of local importance, farmland of statewide importance, or prime farmland if irrigated. However, the areas where the improvements will occur have been urbanized and consists of primarily single-family residences with alleyways and paved roads.

2. Floodplains – Based on floodplain maps, the City of Thompson Falls and the project areas are not located within floodplains mapped for FEMA insurance purposes. The Department of Natural Resources and Conservation was contacted regarding the proposed improvements and their comments are summarized at the end of this report.

3. Wetlands – National Wetland Inventory (NWI) mapping data do not reveal

the presence of any wetlands within the boundaries of the City of Thompson Falls. Some wetlands and riparian habitat occur immediately proximal to the Clark Fork River, but the project will not disturb any of these wetland areas. The Army Corps of Engineers was contacted regarding the proposed improvements and their comments are summarized at the end of this report.

4. Cultural Resources and Historical Sites – The Montana State Historic

Preservation Office (SHPO) has conducted a search of the City of Thompson Falls and found that site-specific inventories are not warranted at this time. However, if evidence of culturally-valuable sites is discovered prior to or during construction, the agency will be contacted to determine the appropriate course of action. The State Historical Preservation Office was contacted regarding the proposed improvements and their comments are summarized at the end of this report.

5. Fish and Wildlife – The Montana Natural Heritage Program identified 32

species of concern for Sanders County including: mammals, birds, reptiles, amphibians, fish, and invertebrates. The U.S. Fish Wildlife Services identified the Grizzly Bear, Canada Lynx, Bull Trout, and Whitebark Pine, and Spalding's Campion as threatened species. The area is urbanized and unsuited for the wildlife listed. The project is not located within any designated Sage Grouse habitat. Whitebark pine may exist within the city limits, however the proposed project will disturb ground primarily along paved streets and commonly travelled alleys that do not host large conifers. If any species or habitat are identified prior to the initiation of construction, the contractor will take steps to minimize disturbances. The Montana Fish Wildlife & Parks and the U.S. Fish and Wildlife Services were contacted regarding the proposed improvements and their comments are summarized at the end of this report.

6. Water Quality – The City of Thompson Falls currently discharges to the Clark Fork River with coverage under the Montana Domestic Sewage Treatment Lagoons General Permit MTG580035. The Clark Fork River near Thompson Falls is classified as B-1. Waters classified as B-1 are to be maintained as suitable for drinking, culinary and food processing purposes, after conventional treatment; bathing, swimming and recreation; growth and propagation of salmonid fishes and associated aquatic life, waterfowl and furbearers; and agricultural and industrial water supply. The Clark Fork River at the point of discharge is listed as impaired for dissolved gas supersaturation and fish-passage barrier. There is no TMDL or planned TMDL for this section of the Lower Clark Fork River. Thompson Falls does not have a reasonable potential for exceedances for total nitrogen, total phosphorous, ammonia, nitrate+nitrite; therefore, no water quality-based effluent limits are included in the MPDES permit. At the 20-year design flow of 161,000 gpd, the treatment system would need to treat to an average monthly BOD of 15.6 mg/L and an average monthly TSS of 24.8 mg/L to discharge 100% of the system flow to the Clark Fork River without exceeding the non-degradation allocated load for BOD and TSS specified in the MPDES permit. The City will utilize a fixed film reactor to polish the lagoon effluent, greatly improving BOD and TSS removal such that non-degradation allocated load limits could be satisfied. The facility currently does not employ effluent disinfection; however, it is assumed that a disinfection facility will be necessary with increased system flows to meet E. coli limits, and is included in the proposed project. Expansion of the wastewater collection system to replace the high density of residential drainfields located north of Highway 200 will benefit the local groundwater resources. Portions of the project will replace aging clay tile pipe located within 750 feet of the reservoir on the Clark Fork River. Clay tile pipe contain numerous pipe joints that are highly susceptible to the infiltration of groundwater and/or the exfiltration of sewer that can pollute nearby water resources. Appropriate storm water control will be implemented during construction to protect surface water resources in the area.

7. Air Quality – Short-term negative impacts on air quality are expected to occur during construction from heavy equipment in the form of dust and exhaust fumes. Proper construction practices will minimize this problem. Project specifications will require dust control. No long-term impacts to air quality will occur.

8. Public Health – Public health will not be negatively affected by the proposed project. This project will eliminate the high quantity and density of septic systems within the unsewered area of the city which poses an immediate threat to human health and safety as well as natural resources of the area due to the discharge of inadequately treated sewage. The effluent discharged to the Clark Fork River will be disinfected to protect public health.

9. Energy – The consumption of energy resources directly associated with construction of the recommended improvements is unavoidable, but will be a short-term commitment. There will be a long-term increase in energy consumption due to the need for three additional lift stations to convey wastewater from the unsewered area of the community to the treatment site. In addition, improvements at the treatment site will have increased energy usage associated with the headworks building, increases to the aeration capacity, the use of mixers, and an ultra-violet disinfection system. The long-term energy consumption will be minimized as much as possible by using energy-efficient equipment.

10. Noise – Short-term impacts from excessive noise levels may occur during

construction activities. The construction period will be limited to normal daytime hours to avoid early morning or late evening construction disturbances. No significant long-term impacts from noise should occur as equipment will be housed within structures.

11. Sludge Disposal – Sludge will need to be removed with treatment system

upgrades to ensure proper treatment effectiveness. Sludge will be pumped from Cell 1 and Cell 2 and allowed to dry in existing unused Cell 4 at the treatment site prior to final disposal. Cell 3 sludge will be dried in place and removed from the site when that cell is no longer in use. It is the City’s preference that the dried biosolids would be available for use by interested landowners in accordance with EPA’s 503 Regulations. Specific numeric limits and other requirements for heavy metals, pathogens, and vector attraction must be met prior to the land application of the biosolids. The final sludge disposal plan containing this information must be submitted to the DEQ for review prior to any land application of the biosolids. Another option under consideration is that the dried biosolids will be disposed of in an approved Class II landfill in accordance with EPA’s 258 Regulations Criteria for Municipal Solid Waste Landfills. It is anticipated that dried biosolids would be hauled to the City of Missoula’s landfill for final disposal if this method of disposal is selected.

12. Environmental Justice – Environmental Justice Executive Order 12898: The proposed project will not result in disproportionately high or adverse human health or environmental effects on minority or low-income populations. All base sewer rates will be increased equally and all customers and residents will benefit from improvements to the wastewater system. No disproportionate effects among any portion of the community would be expected.

13. Wild and Scenic River Act – The proposed project will not impact any

rivers designated as wild and scenic by Congress or the Secretary of the Interior.

14. Growth – The City of Thompson Falls has experienced slight increases

and slight decreases in the population over the past 20 years. A moderate annual growth rate of 0.1% has been used to estimate Thompson Falls 20-year design population. The current population served by Thompson Falls WWTF is 194 people. Expansion of the collection system will

immediately serve another 1,120 residents. The design year 2037 population is 1,349.

15. Cumulative Effects – The increased capacity at the wastewater treatment

plant may result in secondary and/or cumulative impacts due to growth of the community and expansion of the service area. Secondary impacts associated with housing, commercial development, solid waste, transportation, utilities, air quality, water utilization, and possible loss of agricultural and rural lands may occur. These secondary impacts are uncertain at this time, and therefore cannot be directly addressed in the EA. However, these impacts will need to be managed and minimized as much as possible through proper community planning. There are several existing city, county and state regulations already in place (i.e., zoning regulations, comprehensive planning, subdivision laws, etc.) that control the density and development of property with regards to water supply, sewage disposal, solid waste disposal, transportation, and storm drainage.

B. UNAVOIDABLE ADVERSE IMPACTS Short-term construction-related impacts (i.e., noise, dust, etc.) will occur, but should be minimized through proper construction management. Energy consumption during construction and its long-term usage for aeration, pumping and disinfecting cannot be avoided. All improvements will occur within the fence line of the existing treatment site and within public right-of-way throughout the community.

VI. PUBLIC PARTICIPATION

The proposed project has been presented at several council and public meetings. Meeting dates include 8/14/17; 2/12/18; 3/5/18; and 1/7/19. The need for the project, the treatment and collection system alternatives considered, estimated project costs, how the improvements will be phased, proposed funding scenarios and the impacts to user rates were discussed at each of these meetings. The meetings were well attended by community members with the highest community attendance at the 1/7/19 meeting. Residents had questions as to how this project will affect their properties and finances.

VII. AGENCY ACTION, APPLICABLE REGULATIONS AND PERMITTING AUTHORITIES

All proposed improvements will be designed to meet state standards in accordance with Circular DEQ-2, and will be constructed using standard construction methods. Best management practices will be implemented to minimize or eliminate pollutants during construction. No additional permits will be required from the State Revolving Fund (SRF) section of DEQ for this project after the review of the submitted plans and specifications. However, coverage under the storm water general discharge permit and groundwater dewatering discharge permit, if necessary, must be obtained from the DEQ Water Protection Bureau prior to the beginning of construction. A 124 Permit from the Department of Fish, Wildlife and Parks, a 404 Permit from the U.S. Corps of Engineers, and a 318 Authorization from the Department of Environment Quality will be obtained for any work that occurs in a streambed or (jurisdictional) wetlands, should it become necessary.

VIII. RECOMMENDATION FOR FURTHER ENVIRONMENTAL ANALYSIS

[ ] EIS [ ] More Detailed EA [ X ] No Further Analysis

Rationale for Recommendation: Through this EA, DEQ has verified that none of the adverse impacts of the proposed City of Thompson Falls wastewater improvements project are significant. Therefore, an environmental impact statement is not required. The environmental review was conducted in accordance with the Administrative Rules of Montana (ARM) 17.4.607, 17.4.608, 17.4.609, and 17.4.610. The EA is the appropriate level of analysis because none of the adverse effects of the impacts are significant.

IX. REFERENCE DOCUMENTS

The following documents have been utilized in the environmental review of this project and are part of the project file:

1. City of Thompson Falls Wastewater System Improvements Preliminary

Engineering Report, prepared by Great West Engineering. January 2018; Revised April 2018.

2. City of Thompson Falls Wastewater System Improvements Environmental Assessment, prepared by Great West Engineering. April 2018.

3. Meeting minutes and summaries, submitted by Great West Engineering. Various

dates between 1/31/17 to 1/7/19.

4. Correspondence from Great West Engineering regarding user rates for proposed project, May 2020.

X. AGENCIES CONSULTED

As part of the Preliminary Engineering Report (PER) process, the following agencies were contacted regarding the proposed construction of this project:

1. The U.S. Fish and Wildlife Service (USFWS) reviewed the proposed project and

provided a list of threatened and endangered species within Sanders County. The species listed within the area include the Grizzly Bear, Canada Lynx, Bull Trout, Whitebark Pine, and Spalding’s Campion.

2. The Montana Historical Society’s State Historic Preservation Office (SHPO) reviewed the proposed project. They commented that if there will be no disturbance to structures over fifty years of age, there is low likelihood cultural properties will be impacted. They felt that a recommendation for a cultural resource inventory is unwarranted at this time. However, should structures need to be altered or cultural materials be inadvertently discovered during the project, SHPO must be contacted and the site investigated.

3. The U.S. Department of the Army Corps of Engineers (USCOE) provided

comments on the proposed project. They indicated that if any work is proposed below the ordinary high-water mark of stream channels, lakes, or wetlands

adjacent to these waters, then a Section 404 permit would apply and authorization from USCOE would be needed.

4. A letter describing the project was sent to the Montana Department of Fish, Wildlife and Parks (FWP) on August 15, 2017. The FWP did not provide any comments.

5. A letter describing the project was sent to the Montana Department of Natural Resources and Conservation (DNRC) on March 12, 2020. The DNRC response stated that Thompson Falls is a FEMA-Sanctioned community and is not currently participating in the National Flood Insurance Program (NFIP). While this community is not currently participating in the floodplain program, the DNRC recommends that any activities that do occur within the FEMA-mapped floodplain be constructed to State and Federal floodplain standards.

DEQ response: Based on the Flood Insurance Rate Map (FIRM), the project areas are not located within any designated floodplains.

EA Prepared by:

Mike Abrahamson, P.E. Date

EA Reviewed by:

~ . Date

i,;;;,, \ J I 2 .-----, -.

,_ ... _ ,. I \ '--1 r-J.'J ···-~/ T ,, 0 CANADA [36

·7r- •-. . ..__ . . .. • ----"--~ I nners E·-·k ·- •·- ·- l \ """' \ l r · "·, ure a GLACIER ·--,; - --· ·--~.--•-·-· - - ..... \ - - -- ------· . .i.---·-·

. - ~ '- - ~~ .,e _,,--_ .__~- Shelby ~- ~ \

Ibby ·:! Kalispel~ ( ~_,.- -~J ~ ~~~ ---------©---- 7 Hav; e ~ - p ~ \ ·' · \ , "" ij '-- @ '-~ ,~ ta -~ \ r-:1, \ , -------0 - ,,..-./ ®. 1

) / l Malta ~asgow ,,,- 2 __ .......... _·t ---

•.1'ATeu~e \. \ Thompso:~-~ D \ \. \., \,,. \..µ _,, §E§ Fort Peck ---.. _____ -Wolf Point / ,, \ \ F~--1111c ' ~ ~~---- ' · \ '861 --\,.❖.,--,,.'"'· , ~ '\ hot~au/\, {1 _ ___,/ -~--..,.. Sidney• -'C/1 ";•lbg g"~ - \ Po'f n : / '\ l,.______ t, ;;r ort Benton ,r ~--- ,---, ,,..___ \ ---" ss{ ' ·~ -~'· 's! ~ ) .Si~ '" reat Falls \ ~ \ \ '--< \ _J Jordan• \ r

Project Location . \ I/ (--~ j ,J , Glendive \ .1

,...._)

\

ISSOUlcv-, _/ ' ·, ~ ,· Lewistown ~- . , r-<~ ~ . C."}00 f8QI ~ ---- .,---+ -, '-. ✓--------1( "''",-,.-- __,,= ) F.tt'(] White '7~ 1·

1

•

----=- t ) i r,...,,,.,._ Helena~ -- Sulphur f...,, ~~ \ ~---- J ~,,.,....-___ ___ _,, • -.. , Springs \_.- , 7 __ .,,..,-, ---..,_ ·

\ _.,.,:J.,J ,♦ 1

◄ ) Q!!IJ \ r,;;,,J ---~ arlowton ' / --@).-.... Miles CitY, _l ______ ~ ( \I ':-----C • \ r f:u~ 'T-~ \ ( -~=::;::::~:;~;;> \ Roundup ~ ' -..,_ ,'·, t ---- Baker - ~ .

/ \ __ \ \., ~ '--. " b ,.r----.._ ':,~ :::;,,-• :, · 4~H I

\ ., A~ onda ,,..,,..,_ Butte ,/ l 1 _

.... -~ ---. .,.~-,.,",! " I ~'\'~\· ~ ~· r , \ :,; ,.._ ' 1-• I . . """· <, '-./ t\ ( '~z•~ Fstoif ·"""~Billings ·-- "\ _ _______.......,..-@- ___ ~

• ' '"',! \ _} / \ (' "'"" ~ ,,,__ Laurel :---,-,-,.,,_ Hardin \ ·

\ \ ( . 1~ t Ji / _Ii,. .... ,, \'r / - ,Broadus I

, c-._ i!II @' ,,,. r.or r> ~ , . , wk,, -~

...... '- • 8Q ~ l o ----I~ --....;. I .Jr' ) Dillon } 1 ~ . \ Red Lodg~

1~ ' ,.\ 1 _____ :!!_·-.

~ ~ J \ "- r ·-:- ·:::::::1· - - -~·-· __ _ )J..,~--{_·_·-·-·-wvoM\'NG r \ ~~', - . t \ ";--,,:r ;She 'd \ - EllO E L 11·, / ·' · ·-. n an B ,.. - · ove -- • . \ ~ Ye11owsi,, """"'~RK ~- ,o. B-7· ( ';:\ ~ °"

Ills \ .-._)('"·.-.;:i.. ~ 1 ··1 '\ r"" . ...) CodY. / ~ , -- \"- - '•1 S • ..,; 1 ~ l m1. _ r --~ ,_,.,.- I· D ',

r I O ~ '-__.~ __ ..,,.. ~- \. .- .

.• ) Ydk,,,,•xcM I • Buff ' \ ~-I '",-:-:- -

~

Montana Department of

ENV][RONME~""TAL QuALl1TY

Figure 1. Site Location Map - City of Thomoson Falls

~

! ~

i :.

i .~~ t-··-~-'. II~ ~

:_J ,N , , , .... _

'.,.-

., I

SC,,LE 1:1 rtCT

Figure 2 PLANNING AREA

CITY OF THOMPSON FALLS WASTEWATER TREATMENT SYSTEM PER · ll ~ ,. -

i e

~ ~

~

' ~ ~

;;.

CITY LIMITS

EXISTING GR AVITY SEWER

EXISTING FORCE MAIN

NEW GRAVITY SEWER

~ engineenng181

soo 1000

~ -tt/H r"l'

Figure 3 COLLECTION SYST~M

ALTERNATIVE C1 - LAYOUT CITY OF THOMPSON FALLS

WASTEWATER TREATMENT SYSTEM PER

PHASE 1

PHASE 2

PHASE 3

- PHASE 4

-

TREATMENT LAGOONS

177 RESIDENTIAL CONNECTIONS

126 RESIDENTIAL CONNECTIONS

- 149 RESIDENTIAL CONNECTIONS

- 101 RESIDENTIAL CONNECTIONS

Ill

~ engineering®

ELEMENTARY & JUNIOR HIGH SCHOOLS

I . i

Fi 'WI 'fllr

~llfl}_I ~

EXISTING 12-INCH SEWER MAIN REPLACEMENT

THOMPSON FALLS CITY LIMITS

□

~ Figure 4

Collection System Project PHASING

CITY OF THOMPSON FALLS WASTEWATER TREATMENT SYSTEM PER

~

SITE CHARACTERISTICS WINTER AIR TEMPERATURE= ·9.5" C ELEVATION: 2550 FT AMSL ATMOSPHERIC PRESSURE: 13.4 PSIG

INFLUENT CHARACTERISTI CS C B005 = 260 MG/L TSS = 300 MG/L NH3 = 30.5 MG/L

EFFLUENT LIMITS CBOD5 = 1 O MG/L TSS = 10 MG/L NH3 = 3.0 MG/L

DES[GN f:LOW = 0.161 MGD

i '

I 1 ' I LEMTEC

l

l LOW RAT

I a ·~ OOUL.ARC

(

SLUDGE STORAGE DRYING CELL

NOTES: DESIGN BASED ON INtMUM INFLUENT TEMPERATURE OF 10• C

~ SCJ.LEl llfECT

eng1neenng®

~ "' - ... __ ... , _ "'~ ... ----NEW OISlNFECTlON BUILDING

(500 SOFT)

' ' Treatment Alternative T-2

COMPETE/PARTIAL MIX LAGOONS W/POLISHING REACTOR

CITY OF THOMPSON FALLS WAS TEWA7ER TREATMENT SYS1EM PER