Evaluations Supporting Application for

Evaluations Supporting Application for

Discharger-Specific Water Quality

Standards Variance

for Mercury:

Bad River Band of Lake Superior Tribe of

Chippewa Indians

Diaperville, Birch Hill and Bad River WWTPs

Prepared for:

Bad River Band of Lake Superior

Chippewa Indians

August 17, 2026

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Evaluations Supporting Application for

Multiple Discharger Specific

Water Quality Standards Variance for Mercury:

Bad River Band of Lake Superior Tribe of Chippewa Indians

Diaperville, Birch Hill and Bad River WWTPs

Prepared for:

Bad River Band of Lake Superior Tribe of Chippewa Indians

August 17, 2026

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Evaluations Supporting Application for Water Quality Standards Variance for Mercury

August 17 2026

TABLE OF CONTENTS

1 Introduction......................................................................... 1

1.1 Diaperville WWSL ............................................................. 1

1.2 Birch Hill WWSL ................................................................ 2

1.3 Bad River WWTP ............................................................... 2

1.4 Bad River Watershed ........................................................ 2

1.5 Regulatory Background ..................................................... 4

1.6 Basis for Variance ............................................................. 5

2 Are the sources of pollution human caused? ........................ 7

2.1 History of Atmospheric Mercury Emissions ....................... 7

2.2 Atmospheric Deposition of Mercury near the Bad River

Band Reservation ............................................................. 7

2.3 Conclusion ...................................................................... 12

3 Is attainment of the use prevented? .................................. 13

3.1 Applicable Water Quality Criteria .................................... 13

3.2 Attainment of Criteria in the Bad River Watershed ......... 13

3.3 Conclusion ...................................................................... 15

4 Can the human caused condition be remedied during the

term of the variance? ..................................................... 17

4.1 Atmospheric Mercury Deposition.................................... 17

4.2 Conclusion ...................................................................... 17

5 Highest Attainable Condition ............................................. 18

5.1 Diaperville, Birch Hill and Bad River Treatment Plant

Performance................................................................... 18

5.2 Proposed NPDES Mercury Effluent Limitations ................ 19

5.3 Mercury Minimization Program ...................................... 19

6 Conclusions ........................................................................ 22

7 References ......................................................................... 24

Attachment 1.

Mercury Deposition Data and Calculations

Attachment 2. Mercury Measurements in the Bad

RiverWatershed

Attachment 3. Wastewater Mercury, BOD and Suspended

Solids Data

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LIST OF FIGURES

Figure 1-1. Bad River Reservation and Wastewater Treatment

Plants .............................................................................. 3

Figure 2-1. Location of monitors in 2021 for the (left) Mercury

Deposition Network (MDN), (middle) Mercury Litterfall

Network (MLN), and (right) Atmospheric Mercury

Network (AMNet) in the Great Lakes Region. .................. 8

Figure 2-2. Mercury Concentration in Rainfall in the Eastern

US, 2022 .......................................................................... 9

Figure 2-3. Mercury Wet Deposition for the Eastern US, 2022 .

…………………………………………………………………………………… 10

Figure 3-1. Total Mercury Sample Locations .......................... 14

LIST OF TABLES

Table 1-1. Comparison of Atmospheric Deposition of Mercury

and Wastewater Discharges ……………………………………….. 10

Table 3- 1. Water quality criteria for total mercury ............... 13

Table 3- 2. Mercury Concentrations in the Bad River

Watershed...................................................................... 14

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Evaluations Supporting Application for Water Quality Standards Variance for Mercury

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1 Introduction

The Bad River Band of Lake Superior Tribe of Chippewa Indians (Bad River Band) is in the process of

renewing the National Pollution Discharge Elimination (NPDES) permits for the Diaperville Wastewater

Sewage Lagoon (DWWSL), Birch Hill Wastewater Sewage Lagoon (BHWWSL) and Bad River Wastewater

Treatment Plant (BRWWTP). The current permits expired July 15, 2024. The applications for reissuance

of the permits were submitted on April 3, 2024. These facilities, like most treatment plants in the Great

Lakes basin, cannot meet water quality-based effluent limits for mercury. These three facilities face an

especially difficult task, because the most stringent Bad River Band water quality criterion for mercury is

an order of magnitude lower than for most Great Lakes basin facilities. This results in a mercury effluent

limit of 0.194 ng/l, versus the water quality-based effluent limit of 1.3 ng/l for most Great Lakes basin

governments. The Bad River Band’s water quality criterion is based on human health protection and

accounts for fish consumption rates typical for its members. The Bad River Band recognizes the need to

protect wildlife (1.3 ng/l criterion for wildlife designated use, consistent with other Great Lakes basin

governments), but the more restrictive Human Health based standard (0.194 ng/l) governs.

The NPDES permits for these facilities should contain water quality-based effluent limits (0.194 ng/l) for

mercury to meet the Band’s water quality criteria for human health. This criterion supports the Cultural

designated use in the Bad River Band’s Water Quality Standards. The limits are, however, much lower

than existing mercury concentrations in surface water in and around the Bad River Band’s reservation.

USGS data indicates that mercury levels in and upstream of the Bad River Reservation are significantly

greater than the water quality criteria due to human-caused conditions due to atmospheric deposition

of mercury. All 67 surface water samples analyzed for total mercury exceeded 0.194 ng/l, the WQS for

mercury. The mean value of 4.2 ng/l is more than twenty times the water quality criteria. The lowest

value (0.34 ng/l) was found in the only lake sample in the dataset. The variance application is for rivers

and swamps, not lakes. The lowest river sample was 0.77 ng/l mercury, four times the water quality

criteria. The source of “background” mercury is atmospheric deposition, driven by the worldwide

mercury air emissions. The Bad River Band of Lake Superior Tribe of Chippewa Indians is therefore

applying for a discharger-specific water quality standards variance for mercury in the DWWSL, BHWWSL

and BRWWTP NPDES permits, based on 40 CFR 131.10(g) Factor 3 (human-caused conditions). The

variance would apply to receiving waters, Hanson Swamp, Birch Hill Swamp and the Bad River

downstream of these facilities, for a 5-year period, starting after EPA approves the variance request.

1.1 Diaperville WWSL

The Diaperville WWSL is an aerobic wastewater stabilization system consisting of two cells. It is located

south of US-2 and west of the Bad River (Figure 1-1). The facility discharges 2.3 MG/year to Hanson

Swamp under NPDES permit WI-0036544. It serves a population of 80 people. The designated uses for

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Hanson Swamp are: Cultural (C1), Commercial (C2), Navigation (N), Wildlife (W2), Aquatic Life and Fish

(A), Recreational (R), and Wetland (W3).

1.2 Birch Hill WWSL

The Birch Hill WWSL is an aerobic wastewater stabilization system consisting of two cells. It is located

south of US-2 and ~18 miles west of Hurley, WI (Figure 1-1). The facility discharges 5.5 MG/year to Birch

Hill Swamp under NPDES permit WI-0036579-5. It serves a population of 290 people. The designated

uses for Birch Hill Swamp are: Cultural (C1), Commercial (C2), Navigation (N), Wildlife (W2), Aquatic Life

and Fish (A), Recreational (R), and Wetland (W3).

1.3 Bad River WWTP

The Bad River Wastewater Treatment Plant is a Sequencing Batch Reactor located north of US-2 near

Odanah, WI (Figure 1-1). The facility currently discharges approximately 0.077 MGD. Treatment consists

of mechanical fine screening, equalization, activated sludge with biological phosphorus removal

supplemented by chemical precipitation and ultra-violet disinfection prior to discharge to the Bad River.

It serves a population of 650 people. Discharges to the Bad River are permitted by NPDES Permit WI0036587-5. The designated uses for the Bad River are: Cultural (C1), Commercial (C2), Navigation (N),

Wildlife (W2), Aquatic Life and Fish (A), Recreation (R), Wild Rice (W1) and Cool Water Fishery (F2).

1.4 Bad River Watershed

The Bad River Watershed Association’s 2008 Strategic Plan describes the watershed:

The Bad River Watershed (BRW) drains over 1,000 square miles along Wisconsin’s north shore. The

headwaters are found in the Chequamegon-Nicolet National Forest. The lower one-third of the

watershed is land of the Bad River Band of Lake Superior Tribes of Chippewa Indians Reservation. Small,

rural communities including Mellen, Odanah, Gurney, Mason, Grand View, Delta and Marengo are

scattered throughout the watershed. The Kakagon Slough/Bad River Slough, located at the mouth of the

watershed on Lake Superior, is the largest and possibly most pristine freshwater estuary remaining on

Lake Superior. As the only remaining extensive coastal wild rice wetland in the Great Lakes Basin, the

Kakagon Slough provides abundant habitat for wild rice, which is highly important to the Tribe’s culture,

and also provides exceptional habitat for a variety of wildlife. The Watershed is made up of seven sub

watersheds - the Upper Bad River draining 137 square miles, the Lower Bad River draining 123 square

miles, Tyler Forks draining 78 square miles, the Marengo River draining 217 square miles, the Potato

River which drains 140 square miles and the White River sub watershed which drains 360 square miles.

The smaller Beartrap Creek sub watershed is included in this watershed as it too drains into the Kakagon

Sloughs. The BRW contains one of the most diverse assemblages of fish in the Lake Superior Basin, many

of which are listed as “species of management concern” by the Bad River Tribe, U.S. Fish and Wildlife

Service and/or Wisconsin Department of Natural Resources (WDNR). Major land uses within the rural

Bad River watershed include agriculture (10%), wetlands (16%) and forest (74%). Originally, large white

pine forests covered the watershed. A large logging enterprise grew in the area. By the early 1900s the

logging industry had completely depleted the forests. Forests are in recovery but with aspen as the major

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forest component replacing the original conifers. Though the water resources of the BRW are currently in

good condition, several impacts to water quality indicate they may no longer be termed “pristine”. Prior

to the formation of the BRWA, comparably little data on water chemistry existed. The need for data to

responsibly make decisions affecting water resources in the basin was a major impetuous for the

formation of the BRWA.

Figure 1-1. Bad River Reservation and Wastewater Treatment Plants

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1.5 Regulatory Background

A multiple discharger-specific water quality variance is a time-limited water quality criterion change for

a specific pollutant, allowing the Bad River Band relief from meeting the mercury WQBEL. Federal

regulations allow the flexibility to adopt a variance based upon one of the six use attainability factors

outlined in 40 CFR §131.10(g). A variance serves as the applicable water quality standard for the permit,

and only applies to the permittees (in this case, Diaperville WWSL, Birch Hill WWSL and Bad River

WWTP) specified in the variance. Federal regulations require that where a tribe adopts a water quality

standards variance, the tribe must retain the underlying designated use and criterion addressed by the

variance; all other applicable standards not specifically addressed by the variance remain in effect.

The six use attainability factors (40 CFR §131.10(g)) that may be used to justify a variance include:

1. Naturally occurring pollutant concentrations prevent the attainment of the use; or

2. Natural, ephemeral, intermittent or low flow conditions or water levels prevent the attainment

of the use, unless these conditions may be compensated for by the discharge of sufficient

volume of effluent discharges without violating State water conservation requirements to

enable uses to be met; or

3. Human caused conditions or sources of pollution prevent the attainment of the use and cannot

be remedied or would cause more environmental damage to correct than to leave in place; or

4. Dams, diversions or other types of hydrologic modifications preclude the attainment of the use,

and it is not feasible to restore the water body to its original condition or to operate such

modification in a way that would result in the attainment of the use; or

5. Physical conditions related to the natural features of the water body, such as the lack of a

proper substrate, cover, flow, depth, pools, riffles, and the like, unrelated to water quality,

preclude attainment of aquatic life protection uses; or

6. Controls more stringent than those required by sections 301(b) and 306 of the Clean Water Act

would result in substantial and widespread economic and social impact.

In this case, the proposed variance is based on Factor 3: Human caused conditions or sources of

pollution prevent the attainment of the use and cannot be remedied or would cause more

environmental damage to correct than to leave in place.

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1.6 Basis for Variance

The widespread contamination caused by global air emissions and subsequent deposition of mercury

justifies a discharger-specific variance based on Factor 3: human caused conditions or sources of

pollution prevent the attainment of the use and cannot be remedied or would cause more

environmental damage to correct than to leave in place. This report addresses specific parts of Factor 3

to support the variance request:

•

Is the source of pollution human-caused?

•

Is attainment of the use prevented?

•

Can the human-caused condition be remedied?

•

What is the Highest Attainable Condition?

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2 Are the sources of pollution human caused?

The first determination to be made is whether the sources of mercury are human caused. This section

describes the human activities that led to mercury contamination in the Bad River Watershed.

2.1 History of Atmospheric Mercury Emissions

Mercury concentrations in the Bad River watershed are driven by atmospheric sources that are still

increasing and show no signs of abating in the near term. While natural sources of mercury to the

atmosphere exist, they are dwarfed by anthropogenic sources. The United Nations 2018 Global Mercury

Assessment found that “Human activities have increased total atmospheric concentrations [of mercury]

by about 450% above natural levels.” This report further concluded that “Estimated global

anthropogenic emissions of mercury to the atmosphere for 2015 are approximately 20% higher than

they were in updated estimates for 2010.” The report further concludes that “Reductions in mercury

emissions and resulting declines in atmospheric concentrations may take time to show up as reductions

of mercury concentrations in biota” (UN Environment, 2019).

2.2 Atmospheric Deposition of Mercury near the Bad River Band Reservation

The National Atmospheric Deposition Program (NADP) has been monitoring mercury in the atmosphere

and in deposition since the 1990s. Figure 2-1 shows the location of monitors utilized to collect mercury

deposition data near the Great Lakes.

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Figure 2-1. Location of monitors in 2021 for the (left) Mercury Deposition Network (MDN), (middle) Mercury

Litterfall Network (MLN), and (right) Atmospheric Mercury Network (AMNet) in the Great Lakes Region.

NADP developed annual gradient maps of precipitation-weighted mean mercury concentration (ng/l)

and wet mercury deposition (ug/m2). The 2022 maps are shown in Figure 2-2 and Figure 2-3. Data from

these figures is used to illustrate the source of water quality criteria violations in the Bad River

watershed.

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Figure 2-2. Mercury Concentration in Rainfall in the Eastern US, 2022

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Figure 2-3. Mercury Wet Deposition for the Eastern US, 2022

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Data from the three monitoring locations closest to the Bad River Band Reservation are tabularized in

Attachment 1. The data for the years 2018 – 2022 were used to estimate the average concentration of

mercury in precipitation on the Bad River Band Reservation. The annual average mercury concentration

in rainfall for this period ranged from 8.9 ng/l to 13.5 ng/l. The 5-year average was 11.4 ng/l, which is

nearly sixty times the Bad River Band water quality criterion (0.194 ng/l).

Wet deposition data from the three closest NADP monitoring sites were averaged from 2018-2022 to

estimate wet deposition on the Bad River watershed (2750 km2) and Bad River Band Reservation (504

km2). The estimated annual mercury deposition for this period was 53 lbs/year on the Bad River

watershed and 9.7 lbs/year on the Bad River Band Reservation (Table 2-1).

Wet deposition dwarfs the combined annual mercury discharges from the three treatment plants

(0.0082 lbs/year) that are seeking a mercury variance. Table 2-1 provides an estimate of wet deposition

on the wastewater sewage lagoons, Bad River Band Reservation and Bad River watershed. It also

provides mercury discharge data for the three wastewater plants and compares the discharges to wet

deposition values, as described below.

The annual mercury discharge from Birch Hill WWSL is 0.00031 lbs/year, or 0.003% of the estimated wet

deposition on the Bad River Band Reservation and 0.0006% of the estimated mercury deposition on the

Bad River watershed. Estimated annual wet deposition onto the 0.022 km2 lagoons is 0.00042 lbs/year,

somewhat greater than the estimated annual discharge from the lagoons of 0.00031 lbs/year.

The annual mercury loading from Diaperville WWSL is 0.00019 lbs/year, or 0.002% of the estimated wet

deposition on the Bad River Band Reservation and 0.0004% of the estimated mercury deposition on the

Bad River watershed. Estimated annual wet deposition onto the 0.016 km2 lagoons is 0.00031 lbs/year,

somewhat higher than the estimated annual discharge from the lagoons of 0.00019 lbs/year.

The annual mercury loading from Bad River WWTP is 0.0077 lbs/year, or 0.08% of the estimated wet

deposition on the Bad River Band Reservation and 0.01% of the estimated mercury deposition on the

Bad River watershed.

The estimated total mercury discharge from Bad River Band’s three treatment plants combined is

0.0082 lbs/year. This is <0.02% of the estimated wet deposition of mercury onto the Bad River

watershed and <0.1% of the wet deposition of mercury onto the Bad River Band Reservation.

Attachment 1 provides detailed calculations.

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Table 2-1. Comparison of Atmospheric Deposition of Mercury and Wastewater Discharges

Further evidence that atmospheric deposition, not Bad River Band wastewater discharges, is causing

non-attainment of water quality criteria is found by evaluating Bad River watershed samples

downstream of the wastewater treatment plant discharges. There are six sample locations downstream

of the wastewater discharges that were sampled 29 times. For the entire watershed, 14 locations were

sampled at total of 68 times. The average total mercury concentration in samples downstream of

wastewater discharges is 3.6 ng/l, compared to 4.2 ng/l watershed wide. The median total mercury

concentration in samples downstream of wastewater discharges is 2.7 ng/l, compared to 4.3 ng/l

watershed wide. Detailed sample results are found in Attachment 2.

2.3 Conclusion

Atmospheric mercury deposition from worldwide emissions has led to significant mercury

contamination of the Bad River Watershed. Streams and wetlands in the Bad River Band Reservation do

not meet water quality criteria because of human-caused atmospheric mercury deposition. World-wide

mercury emissions are continuing to increase. Table 2-1 estimates that the average annual mercury

deposition onto the Bad River Watershed is 53 lbs. Conservatively we can assume 1% of the

atmospherically deposited mercury enters the Bad River. That gives an annual mercury contribution of

0.53 lbs. By contrast, the treatment plants covered by this variance application discharge 0.0094 lbs of

mercury annually, less than 2% of the presumed atmospheric contribution to the river.

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3 Is attainment of the use prevented?

The second determination to be made in evaluating Factor 3 is whether conditions in the Bad River

Watershed prevent the attainment of the Bad River Band water quality criteria. As described below,

mercury concentrations in and upstream of the Bad River Band Reservation consistently exceed both

human health and wildlife-based water quality criteria.

3.1 Applicable Water Quality Criteria

Bad River Band’s water quality standards specify both human-health and wildlife-based criteria for

mercury. The 0.194 ng/l mercury limit in the Diaperville WWSL, Birch Hill WWSL and Bad River WWTP

NPDES permits are based on the Human Health based criteria found in Table 3-1.

Table 3-1. Water quality criteria for total mercury

Total Mercury

Human Health (ng/L)

Wildlife (ng/L)

0.194

1.3

Note that for mercury, the human health cancer and non-cancer water quality criteria are the same. The

evaluations described in this section of the report therefore address both cancer and non-cancer

criteria.

3.2 Attainment of Criteria in the Bad River Watershed

The Bad River Band and United States Geological Survey (USGS) have measured total mercury in river

and lake samples on and upstream of the Bad River Band Reservation sixty times since 2010. All results

exceeded the Bad River Band’s mercury water quality criteria (criteria) of 0.194 ng/l by a wide margin.

The mean mercury level was 4.2 ng/l, more than twenty times the criteria. The lowest river sample

contained 0.77 ng/l mercury, still almost four times the criteria. The single sample from a lake (0.34 ng/l

at Lake Site 3) also exceeded the criteria. Existing conditions in the Bad River watershed do not meet the

Bad River Band’s mercury criteria. Figure 3-1 shows sample locations. Table 3-2 summarizes mercury

sample results for the Bad River Watershed. All mercury sample results are tabularized in Attachment 2.

Nonattainment is not caused by upstream point source discharges of mercury. The largest upstream

point source is the Mellen WWTF, which discharged 0.0009 lbs of mercury per year from 2020-2025

(WDNR’s WQBEL development document). In Section 2.3 of this document, we conservatively

estimated annual atmospheric contribution to the Bad River as 0.53 lbs per year. The Mellen WWTF

discharges less than 0.2% of the atmospheric mercury contribution.

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Figure 3-1. Total Mercury Sample Locations

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Table 3-2. Mercury Concentrations in the Bad River Watershed

Mean

Concentration

(ng/L)

Median

Concentration

(ng/L)

Maximum

Concentration

(ug/l)

Minimum

Concentration

(ug/l)

Water Quality

Criterion

(ug/l)

Number

of

Samples

4.2

4.3

10.4

0.34

0.194

60

Total Mercury

3.3 Conclusion

The Bad River Band water quality criteria for mercury are not being attained in the Bad River Watershed

upstream of the three discharges covered by this variance application. The largest upstream point

source discharge of mercury to the Bad River Watershed is less than 0.2% of the atmospheric

contributions to the Bad River. USGS data shows that the mean and median mercury concentration in

the watershed are more than twenty times the Bad River Water Quality criteria. Even the lowest river

sample (of 59 samples) mercury concentration is four times the Bad River Water Quality criteria.

Atmospheric deposition is the primary driver of non-attainment.

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4 Can the human caused condition be remedied during

the term of the variance?

Another question to be addressed about Factor 3 is whether the human-caused conditions can be

remedied during the term of the variance. The proposed term of the variance is five years, consistent

with the term of the DWWSL, BHWWSL and BRWWTP NPDES permits. The variance could be renewed,

as appropriate, for future NPDES permit terms based upon a showing that the factors addressed in this

report have not changed. This section of the report discusses atmospheric mercury deposition trends,

and the likelihood of human caused water quality criteria exceedances in the Bad River Watershed

abating over the next five years.

4.1 Atmospheric Mercury Deposition

The primary source of mercury to the Bad River Watershed is atmospheric mercury deposition

originating from worldwide mercury emissions. There are no significant air emissions on the Bad River

Band Reservation. While awareness of this issue has spawned reductions in emissions from some

sectors, worldwide mercury emissions to the atmosphere are still increasing. The United Nation’s 2018

Global Mercury Assessment estimates that 2015 anthropogenic global mercury air emissions were 2200

tonnes, 20% higher than their 1818 tonnes estimate for 2010. Even more discouraging, the

anthropogenic emissions are only 30% of total atmospheric emissions. Environmental processes

comprise 60% of global atmospheric emissions, much of which involves recycling of anthropogenic

mercury previously deposited to soils and water. The remaining 10% comes from natural sources, like

volcanos. Even if anthropogenic releases decline over the next five years, releases from environmental

processes (currently twice the anthropogenic emissions) will lag as mercury previously deposited on

soils and water continues to be remobilized. While there are no estimates as to how long it will take for

either anthropogenic or environmental processes to decrease significantly, a major turnaround in the

next five years is not possible. Since mercury concentrations in the Bad River Watershed are over

twenty times the Bad River Band’s water quality criteria, it is safe to conclude that mercury

concentrations in the Bad River Watershed will remain well above 0.194 ng/l for more than five years.

4.2 Conclusion

The driver for Human-Caused mercury contamination is atmospheric deposition from world-wide

mercury sources. The United Nations’ most recent estimate shows that worldwide anthropogenic

mercury emissions are continuing to increase. The United Nations also estimates that environmental

processes emit twice as much mercury to the atmosphere as anthropogenic sources. Since much of the

mercury emitted by environmental processes is ‘recycled’ from previous anthropogenic emissions, there

will be a time lag between reductions in anthropogenic emissions and environmental process emissions.

Current mercury concentrations in the Bad River Watershed are more than twenty times the Water

Quality Criteria. There is no chance that the mercury criteria will be met during the next five years.

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5 Highest Attainable Condition

5.1 Finally, a variance under Factor 3 must identify the Highest Attainable

Condition that can be achieved during the term of the variance. For the

Bad River Band, this entails interim effluent limits for the three

wastewater treatment plants and implementation of pollutant

minimization plans for each treatment plant. The Bad River Band is

emphasizing Pollutant Minimization as the best path to attaining the

water quality criteria for mercury. Another alternative, wastewater

treatment, transfers mercury from one environmental medium to

another, while not eliminating all pathways to the environment. For

sanitary wastewater treatment, mercury is transferred to biosolids which

are placed in landfills. This mercury is cycled back to wastewater

treatment plants in the form of landfill leachate. Prevention and source

reduction can ultimately eliminate mercury entry into the environment.

While the Bad River Band will continue to optimize wastewater

treatment, pollutant minimization will be emphasized. Diaperville, Birch

Hill and Bad River Treatment Plant Performance

All three wastewater treatment systems are constructed and operated to meet technology based

effluent limits for BOD and suspended solids. Treatment of municipal effluents to meet technologybased limits is known to reduce mercury concentration. USEPA Industrial Pretreatment Guidance1

suggests a median mercury removal rate of 60% in an activated sludge treatment plant. The Bad River

WWTP utilizes activated sludge treatment. The Diaperville and Birch Hill systems utilize wastewater

stabilization lagoons. Treatment processes in lagoon systems are like activated sludge, so mercury

removal through lagoons is expected to be similar. Mean influent and effluent mercury levels from 2019

– 2023 and percent removals for each system were:

Diaperville WWSL (n=10): 40 ng/l and 10 ng/l, 75%

Birch Hill WWSL (n= 10): 83 ng/l and 6.8 ng/l, 92%

Bad River WWTP (n = 25): 84 ng/l and 33 ng/l, 61%

The actual mercury removal rates for these three systems are better than the median removal rate

(60%) for activated sludge plants. This is especially impressive for the lagoon systems, as they are less

efficient at suspended solids reduction. Furthermore, lagoons are subject to atmospheric deposition

approximately equal to the mass of mercury in their discharges (Attachment 1). If atmospheric

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deposition is added to the wastewater influent, mercury removal rates would be even higher than

reported above. All three plants are removing more mercury than expected.

5.2 Proposed NPDES Mercury Effluent Limitations

Mercury data for Bad River Band’s three treatment facilities is found in Attachment 3. Effluent mercury

concentrations are variable at these facilities, presenting a challenge for setting interim effluent limits.

Mercury contamination is widespread in the environment, making obtaining representative samples at

the parts per trillion level a real challenge. Bad River Band staff have improved mercury sampling

technique in recent years. As a result, the inexplicable spikes in both influent and effluent mercury

results will decline going forward. Using existing data, the “Highest Attainable Condition” proposed is

the upper 95% confidence interval for existing effluent data. Using this technique, effluent limits for Bad

River Band facilities would be:

Diaperville WWSL– 21 ng/l

Birch Hill WWSL – 9.8 ng/l

Bad River WWTP – 51 ng/l

Inserting these proposed effluent limits (red font) into effluent data shows reasonable compliance for

the lagoon systems (90%):

Diaperville WWSL: 54, 21, 11, 9.9, 5.9, 5.9, 4.3, 4.0, 2.8, 2.1 and1.5 ng/l. Historic non-compliance: 10%

(1 of 10).

Birch Hill WWSL: 16, 9.8, 9.8, 9, 8, 7.1, 6.5, 3.3, 2.8, 2.8 and 2.4 ng/l. Historic non-compliance: 10% (1 of

10).

For the Bad River system, effluent data is highly variable, ranging from 1.2 to 160 ng/l. Influent mercury

concentrations range between 9 and 450 ng/l. Historic non-compliance with an effluent limit equal to

the upper 95% confidence interval is quite high, 27%. While improved sampling technique will reduce

data variability, a strong focus on mercury minimization is appropriate for this system. Sampling to

isolate and eliminate mercury sources is appropriate and is provided for in the Band’s proposed

Pollutant Minimization Plan for Bad River SBR.

The proposed effluent limit (red font) is inserted into effluent data:

Bad River WWTP: 160, 85, 82, 80, 69, 54, 51, 39, 35, 23, 22, 19, 12, 11, 9.2, 5.4, 4.5, 3.7, 3.5, 2.7, 2.0, 1.8

and1.2 ng/l. Historic non-compliance: 27% (6 of 22).

5.3 Mercury Minimization Program

The Bad River Band has developed facility-specific Mercury Minimization Plans to further reduce

mercury discharges during the life of the proposed variances. Key components of those plans include:

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(a) Education on what individuals can do to minimize mercury discharges to the

environment

(b) Household hazardous waste collection

5.3.1.b Testing the effectiveness of chairside amalgam traps at the dental facility (Bad River WWTP).

5.3.1.c Where appropriate, collection system testing to identify mercury sources

(a) .

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6 Conclusions

Worldwide anthropogenic mercury emissions and resulting deposition on land and water have made

complying with the Bad River Band’s water quality criteria for mercury impossible at this time. This

justifies a discharger specific variance for mercury at the three facilities treating community wastewater

based on 40 CFR §131.10(g) Factor 3, human caused conditions or sources of pollution prevent the

attainment of the use and cannot be remedied or would cause more environmental damage to correct

than to leave in place. Specifically, this report demonstrates:

•

The source of pollution is human-caused;

•

Attainment of the use is prevented; and

•

The human-caused condition cannot be remedied over the term of the variance.

For the term of the variance, the Bad River Band proposes a Highest Attainable Condition:

•

•

Mercury effluent limits representing the 95th percentile concentration for each of the three

facilities covered by this variance:

o

Diaperville WWSL: 21 ng/l as a monthly average.

o

Birch Hill WWSL: 9.8 ng/l as a monthly average.

o

Bad River WWTP: 51 ng/l as a monthly average.

The Bad River Band will implement facility-specific Pollutant Minimization Plans attached to this

variance application. Those plans include:

o

Education on what individuals can do to minimize mercury discharges to the

environment

o

Household hazardous waste collection

o

Testing the effectiveness of chairside amalgam traps at the dental facility (Bad River

WWTP).

o

Installation of chairside amalgam traps at new dental facilities (Bad River WWTP).

o

Where appropriate, collection system testing to identify mercury sources.

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7 References

Bad River Watershed Association Strategic Plan, Adopted January 2008

Local Limits Development Guidance Appendices, EPA 833-R-04-002B, July 2004

National Atmospheric Deposition Program (NRSP-3). 2022. NADP Program Office, Wisconsin State

Laboratory of Hygiene, 465 Henry Mall, Madison, WI 53706

UN Environment, 2019. Global Mercury Assessment 2018. UN Environment Programme, Chemicals and

Health Branch Geneva, Switzerland ISBN: 978-92-807-3744-8

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Attachment 1. Mercury Deposition Data and

Calculations

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Attachment 2. Mercury Measurements in the Bad

River Watershed

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Mercury Measurements Downstream of Bad River Band Wastewater Treatment Plants Discharges

Evaluations Supporting Application for Water Quality Standards Variance for Mercury

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Attachment 3. Wastewater Mercury, BOD and

Suspended Solids Data

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