Appendix D - Pre-Hydro Water Quality Study

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Lake Milton Hydroelectric Project Hydro Energy Technologies, LLC

Pre-Hydro Water Quality Study November 11, 2010

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FERC Project No. 13402

Lake Milton Hydroelectric Project

Hydro Energy Technologies, LLC

PRE-HYDRO WATER QUALITY STUDY

By:

31300 Solon Rd Suite 12

Solon, Oh 44139

November 11, 2010





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TABLE OF CONTENTS

1 PROJECT BACKGROUND .............................................................................................................. 3 1.1 STUDY OBJECTIVES .......................................................................................................................... 3

2 PROJECT DESCRIPTION AND PROPOSED OPERATIONS .................................................... 4 2.1 DESCRIPTION OF EXISTING DAM, RIVER AND IMPOUNDMENT .......................................................... 4 2.2 DESCRIPTION OF PROPOSED PROJECT AND OPERATIONS..................................................................11

3 METHODOLOGY ............................................................................................................................18 3.1 LITERATURE REVIEW.......................................................................................................................18 3.2 INSTRUMENTATION..........................................................................................................................18 3.3 SAMPLING METHODS AND LOCATIONS ............................................................................................18 3.4 SAMPLING SCHEDULE ......................................................................................................................24

4 RESULTS AND DISCUSSION ........................................................................................................24 4.1 GENERAL REVIEW OF FACTORS IMPACTING DO AT HYDROPOWER FACILITIES...............................24

4.1.1 Reservoir Factors ..................................................................................................................24 4.1.2 Watershed Factors .................................................................................................................30 4.1.3 Tailwater Factors ..................................................................................................................30 4.1.4 Special Case – Below Ice Oxygen Depletion .........................................................................34

4.2 BIOLOGICAL EFFECTS OF LOW DISSOLVED OXYGEN .......................................................................35 4.2.1 Growth ...................................................................................................................................36 4.2.2 Reproduction .........................................................................................................................36 4.2.3 Behavior and Swimming Performance ..................................................................................36 4.2.4 Early Lifestages .....................................................................................................................37 4.2.5 Fisheries Diversity .................................................................................................................37 4.2.6 Susceptibility to Disease ........................................................................................................38 4.2.7 Trophic Interactions ..............................................................................................................38 4.2.8 Non-Fish Species Response to Low Dissolved Oxygen .........................................................38

4.3 SUMMARY OF RESERVOIR CHARACTERISTICS AT LAKE MILTON .....................................................39 4.4

G

ENERALE

XISTINGW

ATERQ

UALITYD

ATA AT THEP

ROJECTS

ITE................................................39

4.5 PRE-HYDRO DO LEVELS BELOW DAM.............................................................................................40 4.6 PRE-HYDRO TEMPERATURE DATA BELOW DAM .............................................................................42 4.7 PRE-HYDRO DO & TEMPERATURE LEVELS IN LAKE UPSTREAM OF DAM .......................................46 4.8 DISCUSSION OF POTENTIAL MITIGATION MEASURES TO IMPROVE DO LEVELS BELOW DAM .........48

4.8.1 Bypass Flows .........................................................................................................................48 4.8.2 Selective Withdrawal .............................................................................................................48

5 CONCLUSIONS & PROPOSED STANDARDS ............................................................................49 6 REFERENCES ...................................................................................................................................52 APPENDIX A – RAW STUDY DATA ......................................................................................................55





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PRE-HYDRO WATER QUALITY STUDY

LAKE MILTON HYDROELECTRIC PROJECT (FERC #13402)

1 PROJECT BACKGROUND

Pursuant to section 4.38(b) of the Code of Regulations Hydro Energy Technologies, LLC

(HET) has completed the first stage consultation requirements for the proposed

hydroelectric facility at the Lake Milton Dam (FERC # P-13402).

During consultation the USACE requested that data be collected to determine the existing

or “pre-hydro” water quality conditions (specifically dissolved oxygen and temperature).In the Provisional Nationwide Permit issued by the USACE on June 7, 2010 condition 3states the following:

Dissolved oxygen monitoring from August to October is to be conducted to

determine the existing condition of the Mahoning River directly downstream of

the dam. This data will be utilized in mitigating dissolved oxygen levels if

necessary.

1.1 Study Objectives

The primary goal of this study was to determine the existing or “pre-hydro” water qualityconditions (specifically dissolved oxygen and temperature) directly downstream of the

dam from August to October. This information will be used to mitigate dissolved oxygenlevels if necessary during hydro operation. Study objectives include:

a. Estimate the existing range of dissolved oxygen (DO) below the dam in

mg/L as well as in % saturation from August to October.b. Calculate the existing range of water temperature below the dam from

August to October.

c. Determine Pre-hydro DO and temperature levels and stratification patternsin Lake Milton upstream of the dam by depth from August to October.

d. Collect data to determine if hydro operation using gate 2 during the winter

will affect DO and temperature levels downstream or upstream of the dam.





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2 PROJECT DESCRIPTION AND PROPOSED

OPERATIONS

2.1 Description of Existing Dam, River and Impoundment

The original dam located along the Mahoning River was constructed in 1913 by theCity of Youngstown for the purposes of flood protection and water supply to the steel

mills located in the city of Youngstown, Ohio. In 1970 seepage and evidence of

instability on the downstream west abutment was noted. Youngstown relinquished

control of the dam to the Ohio Department of Natural Resources and ODNR began

rehabilitation of the dam which it completed in 1988. Although the dam no longersupplies water to the steel mills in Youngstown, it continues to provide flood protection

to the Mahoning Valley as well as low flow regulation and recreational opportunities tothe area. The dam is operated by the Lake Milton State Park under the supervision of the

Pittsburgh District of the US Army Corps of Engineers (USACE). The nominal surface

area of the existing impoundment created by the existing dam is 1,685 acres.





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LAKE MILTON HYDROELECTRIC PROJECT

FERC # P-13402

STREET LEVEL MAP

Proposed PlantLocation





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FERC # P-13402

PROJECT LOCATION MAP

Proposed Plant

Location





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The proposed hydro plant shown in Figure 2-1 is located on the Mahoning River

and is fed by a total drainage area of approximately 273 square miles. Flow levels at the

proposed site were determined using the data from the USGS gaging station 03091500 onthe Mahoning River located .3 miles downstream of the Milton Dam near Pricetown.

Figure 2-1 – Mahoning River Watershed

USGS

Gaging

Station

Proposed

Hydro Site





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Figure 2-2 and Table 2-1 represent the daily mean flows from August

1979 to August 2009 for the Mahoning River at the Pricetown gaging station:

Mahoning River FDC

0

500

1,000

1,500

2,000

2,500

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

% Time Flow Exceeded

F l o w ( c

f s )

Figure 2-2

% Time Flow Exceeded Q (cfs)

0 2,430

5 1,110

10 835

15 615

20 466

25 362

30 289

35 247

40 213

45 186

50 172

55 162

60 152

65 138

70 12975 115

80 97

85 85

90 70

95 47

100 13 Table 2-1





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Monthly mean data from the USGS Station from years 1979 to 2009 was used to

create the hydrograph and data table for the Mahoning River labeled Figure 2-3 and

Table 2-2 respectively.

Mahoning River Hydrograph

0

50

100

150

200

250

300

350

400

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

M e a n F l o w ( c

f s )

Figure 2-3

Month Mean Flow (cfs)

Jan 320

Feb 338

Mar 365

Apr 290

May 290

Jun 284

Jul 251

Aug 256

Sep 276

Oct 237

Nov 240

Dec 298Mean 287.1

Table 2-2







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downstream. The Corps' policy for our projects is for non-degradation of water quality. What we

would do, is gather and collect lake and downstream data to define the current state, then

calibrate a model. Then we would model various scenarios and see what happens. I would start by

modeling the parameters water temperature and dissolved oxygen, but there may be other

parameters. The CE-QUAL and CE-QUAL2 models have been used at other reservoir projects,

but there may be other models.

Werner

Mean Lake Elevation

934

936

938

940

942

944

946

948

950

E l . ( f t ) 1990-2007

Jan 2008- Aug 2009

1990-2007 942.59 942.35 943.65 946.73 948.03 948.19 948.19 948.21 948.03 947.27 945.03 942.95

Jan 2008- Aug 2009 940.02 941.13 942.93 947.35 948.32 948.46 948.38 948.09 948.04 947.31 944.93 942.53

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 2-4 – Mean Historical Lake Elevations obtained from the USACE Pittsburgh District

2.2 Description of Proposed Project and Operations

The current design (Figure 2-5) uses the existing intake and connects a 800 mm

diameter 650 KW S-Type Kaplan Turbine to the exisiting 60" outlet pipe on gate 2 belowthe dam. The proposed powerhouse would be constructed over the existing discharge

location where the turbine and generator will be housed. The proposed location of the

turbine and powerhouse are shown in Figure 2-6 & Figure 2-7.





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Figure 2-5

NEW TRASH RACK WITH 1” BAR SPACING INSTALLED OVER EX.

TRASHRACK

NEW 800 MM DIA.

TUBULARHORIZONTAL

KAPLAN

Spillway

Using Ex.

Gate 2

Conduit


FERC # P-13402

PROJECT PLAN - PROPOSED





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Figure 2-6 - Photo of existing dam and outlet works

Figure 2-7 – Conceptual Sketch of Dam and Proposed Powerhouse

Proposed

Powerhouse

Location

Existing

Spillway Existing OutletWorks





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FERC # P-13402

PROFILE – EXISTING CONDITIONS





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NEW

TRASHRACK

WITH 1” BAR SPACING

INSTALLED

OVER EXISTING

EX. APRONS

ELECTRIC ACTUATORSFOR SLUICE GATES

962.4

EXISTING

STRUCTURE

AIR VENT

SLOT FOREMERGENCY

BULKHEAD

EX. SLUICE GATES

EXISTING 60” DIA.CAST IRON CONDUIT

SLUICE GATE STEM

907.0

EX. END SILL

922.0

915

USE EXISITN

STILLING BASIN

USE EXISITNG 3’CONCRETE FLOOR SLAB AS

SYSTEM FOUNDATION

SUMMER POOL EL. 948.0

WINTER POOL EL. 940.8

EX. SPILWAY CREST EL. 951

INVERT EL. 913.0

901.0

TAILWATER LEVEL El 908.0


FERC # P-13402

PROJECT PROFILE - PROPOSED

PROPOSED 800 MM DIA.

HORIZONTAL TUBULAR

KAPLAN TURBINE

PROPOSED POWERHOUSE

CONSTRUCTED OVEREX. STRUCTURE

SILT BUILD UP

1” BAR SPACING

.25” BAR THICKNES

1” BAR WIDTH





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The proposed flow operations during hydro operation do not modify lake

elevations or discharge levels dictated by the USACE. The only modification is thetiming of which gates are used. Since the 250 cfs capacity turbine will be installed on

gate 2, all flows up to 250 cfs are proposed to be discharged through gate 2 so that hydro

power production can be continuous throughout the year except during winter whenwater is typically discharged through the lower gates.

All flows above 250 cfs would be discharged through an alternate gate. Table 2-3and Figure 2-8 show how the proposed gate use schedule would differ from existing

operations. The total flow use curve is shown in Table 2-4.

CURRENT DISCHARGE CAPACITY AT LAKE MILTON (CFS)

Lake E. (ft) GV 1 GV 2 GV 3 GV 4 Total

940 600 600 690 0 1890

942 620 620 700 0 1940

948 690 690 770 0 2150

952 740 740 810 0 2290

DISCHARGE CAPACITY WITH HYDRO (CFS)

Lake E. (ft) GV 1 GV 2 GV 3 GV 4* Total

940 600 250 690 690 2230

942 620 250 700 700 2270

948 690 250 770 770 2480

952 740 250 810 810 2610 Table 2-3 – Gate Discharge Capacity at Lake Milton (Current and with Hydro)

*Gate 4 is currently inoperable and will be repaired by HET if Hydro is approved.





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Flow Duration Curve November to April 1978-2008

0

500

1,000

1,500

2,000

2,500

0 10 20 30 40 50 60 70 80 90 100

% Time Flow Exceeded

F l o w ( c f s )

Total Flow

Hydro Flow

Figure 2-8

% Time Flow Ex. Total Flow (cfs) Hydro (cfs) Other 60" Discharge Pipes (cfs)

0 2,430 250 2218

5 1,110 250 898

10 835 250 623

15 615 250 403

20 466 250 25425 362 250 150

30 289 250 77

35 247 247 35

40 213 212 1

45 186 186 0

50 172 172 0

55 162 162 0

60 152 152 0

65 138 138 0

70 129 129 0

75 115 115 0

80 97 97 0

85 85 85 0

90 70 70 0

95 47 47 0

100 13 0 13 Table 2-4 – Total Flow Use Curve





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3 METHODOLOGY

3.1 Literature Review

A literature review was conducted to present a brief summary of general factors

impacting DO levels at hydro power facilities. Included is a discussion of the specific

site conditions at the Lake Milton Project and how these specific reservoir and rivercharacteristics might influence DO levels during hydro operation. Also included is a

summary of the biological effects of low DO.

3.2 Instrumentation

HET used the YSI ProODO Optical Dissolved Oxygen Meter for this study. This is anaccurate portable unit measuring dissolved oxygen (in either mg/L or % saturation) as

well as temperature and barometric pressure with short term data logging capability (80

hours or more of up to 2,000 data points). The data sheet for this unit is shown in Figure

9 and Figure 10.

Additionally DO and other water quality measurements taken by the OEPA in 2006 at the

project site as well as temperature data from USGS gage 03091500 located .3 milesdownstream of the Milton Dam near Pricetown as well as USGS gage 03090500 located

upstream of the proposed project below the Berlin Dam will be used to supplement data

obtained by HET. Water quality data at Berlin Lake provided to HET from the USACE

Pittsburgh District in 2009 was also used in this analysis.

3.3 Sampling Methods and Locations

Condition 3 of the provisional NWP 17 states that the testing must occur directly downstream of the dam. Therefore samples were taken within the stilling basin directly below

the dam as well as further down stream and in the lake at varying depths (Figure 14).

HET took spot samples as well as continuously logged data (Figure 11 and Figure 12).





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Figure 9





20

Figure 10







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Figure 13 – General HET Sampling Locations

Stilling Basin

WWTP Outfall

CR @ Gas

Line

Pricetown @

Northbridge

Upstream of

Dam @ the

Intake at Varying

De ths





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Figure 14 – Sampling locations


FERC # P-13402

PLAN & PROFILE OF EXISTING DAM

GATE 4

GATE 3

GATES

1&2

Upstream

of Dam

Samples Taken

at 5 Ft.

Increments





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3.4 Sampling Schedule

A total of 219 Samples were taken from August 9th

, 2010 to October 6, 2010. All flows were

discharged through gate 2 during the study therefore most samples were taken directly

downstream of gate 2 where the most re-aeration was occurring and DO levels were the highest.More samples were taken in August and September as DO levels are typically lowest during

these two months. HET used spot sampling as well as continuous logging with 1 hour intervals.There were 42 samples in August that were not used (not included in the 219 total) due to excess

algae growth on the probe during logging compromising the results. The sample summary is

shown in Table 5 and the raw data is included in Appendix A.

Table 5: Summary of Samples Used in this Study

Month Gates 1&2 Gate 3 Gate 4 Lake Other Total

Aug 70 27 2 16 2 117

Sep 68 4 4 9 4 89

Oct 2 1 1 9 0 13

Total 140 32 7 34 6 219

4 RESULTS AND DISCUSSION

4.1 General Review of Factors Impacting DO at Hydropower Facilities

Sections 4.1 and 4.2 including all tables and figures are taken entirely from the 2002 EPRI reportentitled Maintaining and Monitoring Dissolved Oxygen at Hydroelectric Projects: Status Report

which provides an excellent summary of issues related to dissolved oxygen at hydro projects

located at reservoirs. The sections directly taken from the EPRI report are shown in italics.

4.1.1 Reservoir Factors

Reservoir processes that affect DO are significantly influenced by the physical characteristics of

reservoirs. Probably the most significant characteristics are the volume and through-flow of the

project, which can be represented by the calculated retention time (summer volume/average flow

rate) of water in the project. Run-of-river projects typically have retention times of less than

about 25 days; storage projects typically have retention times greater than about 200 days.“Transitional” projects have retention times that fall within the range of about 25 to 200 days.

At summer pool, Lake Milton has a storage capacity of 24,000 acre feet and a mean flow of

287.1 cfs which calculates to an average retention time of 42.1 days.

Thermal Stratification





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Retention time and depth of outlet are the main factors that affect thermal stratification within

reservoirs, which, in turn, affect the routing of “density currents” through reservoirs. An

understanding of these density currents is important to determining how DO is affected at

various locations within reservoirs.

Figure 15 illustrates typical temperature profiles depicting annual stratification patterns for various types of reservoir projects. Thermal stratification begins when the reservoir surface

water warms and floats on top of the colder water in the reservoir. Figure 16 illustrates the

relationship between density and temperature of water. As the warm season progresses, the

epilimnion enlarges due to solar incidence and mixing caused by wind energy. The metalimnion

also increases in volume due to the withdrawal of hypolimnetic water through the outlets, as well

as the spring and summer inflows that are cooler than the epilimnion but warmer than the

hypolimnion. These inflows seek an appropriate water depth in the metalimnion having a density

somewhere between the epilimnion and the hypolimnion. The metalimnia and hypolimnia in

hydropower reservoirs are very dynamic due to the relatively high flows through these projects

and the use of lower level outlets. It is in these two layers where density currents occur and DO

is dominated by consumption processes and not replenished by the atmosphere or algal productivity.

In deep storage reservoirs, stratification is strong (large difference in temperature between the

top and bottom) and generally persists through the summer and fall. Quite often the colder water

in the reservoir originally during the winter may remain in the hypolimnion until the next fall.

This is especially true if the outlet is at a mid-level point within the reservoir and the withdrawal

zone does not extend to the reservoir bottom.

In transitional reservoirs, thermal stratification is somewhat weaker than in storage

impoundments because the cold winter inflows are released more rapidly from the bottom. The

winter water is replaced by warmer inflow water as the warming pattern progresses into thesummer and fall. Usually these types of reservoirs will maintain some form of stratification even

though it will be weaker than that of storage impoundments. Transitional reservoirs that have

storage impoundments a short distance upstream will not demonstrate this typical thermal

pattern if the inflows remain cold through the summer and fall because cold inflows drop

beneath the warm surface and continue to maintain the strong thermal stratification.

For run-of-river reservoirs, the colder water is released even more rapidly and the resulting

stratification is weaker, particularly in June, July, and August. Often during these latter two

months stratification may not even occur, except under low flow conditions such as those that

occur during droughts.

At Lake Milton Thermal Stratification is minimal in August (see section 4.7) and resembles that

of a run of river reservoir. The reservoir is relatively shallow (40 ft at the intake during summer)and two of it’s 4 intakes are located at the bottom and the other two are approximately 7 ft higher

than the bottom but would generally still be considered low level intakes. A summary of the

reservoir characteristics at Lake Milton are shown in

Table 8 in section 4.3 of this report.





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Figure 15





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Figure 16

Environmental Processes in Reservoirs that Affect DO

The environmental processes that affect DO can be separated into three longitudinal zones and

four thermal layers. The longitudinal zones include the riverine, transitional, and lacustrine

zones. The thermal layers include the epilimnion, the warmer portion of the metalimnion (which

usually is composed of interflows that result from inflows to reservoirs during the months of May

through September), the cooler metalimnion (which usually represents inflows during the months

of March and April), and the hypolimnion. In the areas of the U.S. where inflows are comprised

of significant amounts of snowmelt, cooler inflows may persist until June. These zones and layers

are illustrated in Figure 17 showing that DO within a reservoir is usually low immediately above

the sediments and in the warmer metalimnion, which occupies a comparatively larger portion of

the reservoir.





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Figure 17





29

Table 6





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As discussed in the previous section, the lower layers are density currents that essentially are

isolated layers that do not mix in the reservoir until the temperatures of the layers become about

the same as the epilimnion, usually in the fall of each year. Hence, to determine how the DO

balance is affected in a reservoir, it is important to analyze the changes that take place in each

layer of water. The longitudinal zones are useful for describing the changes in water quality as

the water passes through the reservoir. Table 6 presents a limnological description of the processes involved in these zones and the resulting DO dynamics.

4.1.2 Watershed Factors

Clearly, the amount of precipitation and inflow temperatures affect thermal stratification, but

other factors can also be important. For example, the size of the watershed draining into the

reservoir affects not only the amount of flow through the reservoir but the natural organic

loading and other non-point sources of nutrients to the reservoir as well. Precipitation intensity

and frequency also affect the transport and timing of watershed water quality constituents such

as organic matter. Since thunderstorms occur more frequently in the southeast (Kennedy and

Gaugush 1988), the reservoirs in this region may receive greater loads.

Regarding streamflow patterns, upstream reservoir projects significantly alter the natural

hydrologic runoff, e.g., high spring natural runoff quantities can be shifted to late summer and

fall high volume reservoir releases. Such a shift in flow quantity significantly affects downstream

reservoir processes affecting DO.

Another significant watershed factor that affects DO levels is the dominant source of inflow. The

typical storage impoundment will have one or two primary sources of inflow, accounting for 70

percent or more of the reservoir inflow volume. However, some impoundments can have

significantly dispersed inflow quantities coming from multiple tributaries. Such dispersed inflows

can complicate significantly the reservoir processes that may affect DO within a reservoir. Anupstream (reservoir) with low-level releases can significantly alter temperature in the inflow.

(EPRI 1990).

Reservoirs having watersheds with significant snowmelt during the spring can exhibit the

same DO dynamics seen for southeastern reservoirs. However, these dynamics will lag in time

corresponding with the temperature and peak inflow hydrology that is characteristic in the

northern regions. In the south, the peak inflow hydrology is dominated by more direct runoff

from spring rains that occur during March through May.

4.1.3 Tailwater Factors

The DO in the tailwater is affected primarily by characteristics of the hydropower releases,

various tailwater hydraulic conditions, the presence of aquatic weeds, and various DO

consumption processes. Mechanistic formulations for riverine DO predictions can be found in a

comprehensive review by Bowie et al. (1985). A qualitative description of the factors is provided

here.





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Characteristics of DO in Reservoir Releases

The large volume of reservoir releases usually dominates water quality in tailwaters. Hence,

changes in operational characteristics can significantly change DO in downstream reaches and

cause both short- and long-term cyclical variations.

The cyclical nature of DO in a tailwater is significantly affected by the mode of operation for

hydro generation and must be considered in determining the exposure characteristics of

sitespecific DO variation to aquatic life. For instance, brief exposures of fish to DO levels as low

as 3 mg/L may not be harmful (EPRI 1990).

Because of the dominant influence of flow and release DO level on downstream DO levels,

seasonal variations in these factors are important. High release flow and DO is common in the

winter. Low flow and high DO is common in the spring during filling of the reservoirs

concurrent with cold water temperatures. Flows increase with summer power generation and

low DO is common in summer and fall due to warmer water being released from within the

reservoir.

Re-Aeration

Atmospheric re-aeration occurs at the air-water interface and affects dissolved oxygen

concentrations throughout the water column by turbulent mixing of surface water to deeper

depths. The re-aeration rate is usually stated as a product of a re-aeration coefficient, K 2 (see

EPRI 1990 Appendix C) and the DO deficit below saturation. Expressions for the reaeration

coefficient have been developed by many investigators, where K 2 is directly related to mean

velocity and inversely related to mean depth, suggesting a dual effect of an increase in flow on

K 2. However, increased depth is more significant than increased velocity, so the reaeration rate

typically decreases with higher flow in most rivers (see Figure 18). Higher flows also reduce thetravel times between two river stations, decreasing the opportunity for re-aeration as well as the

re-aeration coefficient.

Figure 18







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Aquatic vegetation (algae, macrophytes) contributes oxygen to the water column during

photosynthesis and consumes oxygen for respiration. Photosynthesis is roughly confined to the

third of the day with the highest solar radiation, while respiration is more evenly distributed

throughout the day and night (depending primarily on temperature). Photosynthetic oxygen

production can be quite high, normally exceeding respiration demand during this third of theday (except perhaps on overcast days), while respiration demands prevail at night when there is

no photosynthesis. Thus, the aquatic plant community can be a net source of oxygen in daytime

hours and a net demand for oxygen at night. Depending on the aquatic plant density, respiration

during low flow can create localized reaches of low DO in pre-dawn hours that are lower than

the low DO caused by dam releases. Daily average production and demand may vary, but are

often in approximate balance with one another in the range of 5 to 10 g O2 /m2 /d each.

Sediment Oxygen Demand (SOD)

Bacterial decomposition of organic matter (leaf litter, dead bacterial growth, and dead aquatic

plants) in sediments also consumes oxygen from the water column. Another source of organicdeposits is particulate matter from wastewater treatment plant discharges. Respiration of the

benthic community during decomposition of organic sediments can create significant oxygen

demands, especially in pools where organic deposits may be significant and the residence time of

water over the sediments is prolonged. Sediment oxygen demand of most river mud falls in the

range of 0 to 2 g O2 /m2 /d, but can exceed 10 g O2 /m2 /d downstream from municipal and industrial

discharges.

Research conducted by Mackenthun and Stefan (1993) on the effects of near bottom flow

velocities on SOD indicates that oxygen demand increases linearly with water velocity over the

range of velocities tested (1.0 to 10.0 cm/s [0.03 to 0.33 ft/s]). In quiescent lake water in

Minnesota, average SOD values range from 0.5 to 2.0 g/m2

/d (Fang and Stefan 1993). Therefore,SOD can double if flow velocities are minimally increased (on the order of 1.0 cm/s (0.03 ft/s).

Poorly designed lake aerators systems can disturb sediments and lower or negate their ability to

aerate the hypolimnion (see further discussion in Section 4 – Hypolimnetic Aeration).

Other Factors

Temperature plays a role in tailwater atmospheric heat exchange due to solar and atmospheric

radiation. Heat transfer and release temperatures both effect the temperatures of tailwaters.

Heat transfer plays the dominant role during times of low flow, while release temperatures are

more influential during periods of high flow. Solar radiation also provides energy for plant

photosynthesis with associated oxygen production. As discussed earlier, temperature determines

both the saturation oxygen concentration and the rates of most physical and biochemical

processes affecting DO. The rates of many biochemical processes can double with a 10 _C (50ºF)

rise in temperature in the range of temperatures found in many tailwaters.

There are additional factors specific to certain tailwaters that may have important effects on the

local oxygen budget. These include: oxidation of reduced chemical elements (iron, sulfide, and





34

manganese) in releases, quantity and quality of tributaries, presence of toxic compounds, and

respiratory demands of localized heavy concentrations of mussels or other fauna.

4.1.4 Special Case – Below Ice Oxygen Depletion

Low dissolved oxygen conditions can also arise in colder climates during the winter months that

may kill fish. This “winterkill” condition is common in eutrophic lakes and reservoirs that have

long periods of ice and snow cover. Severe oxygen depletion under ice leads to fish losses.

Winterkill usually occurs when a water body is entirely ice- and snow-covered. Open ice allows

for a greater level of light penetration and subsequent photosynthetic activity of plants and

algae. Photosynthetic activity, in turn, produces oxygen. Dissolved oxygen levels are, therefore,

lowest when light penetration is minimized by snow and ice cover. Often times, DO depletion is

coupled with the build-up of toxicants such as ammonia (NH 3) and hydrogen sulfide (H 2S) (Fast

1994).

Two processes lead to low DO concentrations under ice-cover: (1) respiratory oxygen demand and other oxidation processes exceed the level of oxygen output from photosynthesis and (2) the

total oxygen reserve at the time the water body freezes over is insufficient to compensate for

oxidation and respiration losses during time of ice-cover (Fast 1994).

Minimum fish requirements for DO are lower under ice-cover than during other times of the

year due to lower fish activity levels and subsequent low metabolic rates. Wetzel (1983) suggests

that fish can survive at DO levels as low as 2 mg/L when water temperatures range from 2º to

5ºC (36º to 41ºF). Other researchers have indicated that fish will survive at even lower DO

levels (Table 7) and that tolerance is species- and lifestage-specific.

Table 7





35

Lakes and reservoirs most likely to be affected by winterkill are shallow, eutrophic, have little

water flow-through, have mucky, silty or black organic bottom sediment and whose shorelines

have a large amount of submergent or emergent plant vegetation (Piening 1977, Nickum, 1970).

Analysis of oxygen depletion rates under 70 Canadian lakes by Mathias and Barcia (1980),

indicates that the principal source of DO depletion occurs in the sediments rather than in thewater column. Sediments in eutrophic lakes consumed oxygen three times as fast as oligotrophic

lakes (0.23 vs. 0.08 g/m2 /d). According to a literature review conducted by Ellis and Stephan

(1989), the biochemical oxygen demand associated with the decomposition of organic materials

in the sediments of ice-covered lakes may be the largest demand on DO.

It is very difficult to assess the effects of winterkill management practices, because there is little

opportunity to establish a control time or period. Comparing across years within the same water

body is confounded by considerable year-to-year variation. Site-specific variation between water

bodies even geographically proximate does not lend itself to valid comparisons. Only prevention

of winterkill over many seasons, especially in water bodies that only occasionally experience

winterkill (i.e., once every three, five or ten years) can convincingly demonstrate winterkill prevention techniques. Few experiments have provided such a rigorous assessment, but most

provide value judgments regarding a winterkill prevention techniques’ efficacy.

Several of the technologies used to mitigate low DO levels in reservoir releases during warm

months can also be utilized for mitigating factors that cause winterkill conditions. Designing

wintertime aeration systems may be complicated by severe weather and icing conditions. In

addition, some technologies that cause mixing of stratified water layers may cause ice to weaken

or disappear. If the ice surface is used recreationally (e.g., skating, ice fishing), such options

may not be feasible. Wintertime aeration systems are not addressed specifically in this report.

4.2 Biological Effects of Low Dissolved Oxygen

Dissolved oxygen (DO) is one of the most influential water quality parameters on the health of

aquatic ecosystems and fisheries populations. When DO concentration fall below certain levels,

water becomes incapable of sustaining aquatic life. Above the lethal limit, DO acts as a limiting

factor to the growth of fish.

A full discussion on biological responses of fish, based on the investigation of numerous studies,

is included in EPRI 1990 (Section 5). A brief summary of those findings is included here, with

the addition of recent studies.

The focus of the discussion below is on salmonids (Family Salmonidae), as there are morestudies investigating the effect of low DO on these species than with other species, since they are

readily available, easy to maintain and of great economic importance. Although it could be

argued that low DO concentrations have adverse effects on all species of fish in all water body

types, in the following discussion secondary emphasis has been placed on those species likely to

be impacted by hydropower operation. Discussion is grouped by physiological responses or

population responses to varying dissolved oxygen concentrations.





36

4.2.1 Growth

In general, for salmonid species, as dissolved oxygen levels decrease there is a corresponding

drop in median growth rates. The effects of low DO are amplified at higher water temperatures

as a result of increased metabolic activity (EPRI 1990).

4.2.2 Reproduction

Very little information is available on the effects of low dissolved oxygen on the fecundity,

fertility and reproductive success of fish. What information that does exist (EPRI 1990) suggests

that low dissolved oxygen has a negative effect.

4.2.3 Behavior and Swimming Performance

Fish can detect zones of low dissolved oxygen and will actively try to avoid them. Early

lifestages (e.g., larvae, juveniles) fish appear less able to detect areas of low DO and are,

therefore, less able to avoid them. The distribution of fish within a body of water can be affected by the avoidance behavior of some fish species to areas of low DO.

There is often a strong link between DO levels and water temperatures. In a thermally stratified

water body experiencing hypolimnetic DO depletion, DO and temperature are two of the most

influential factors affecting the distribution of fish species. As water below the thermocline

becomes depleted of DO, fish are faced with a trade-off between moving to shallow warmer

water with higher levels of DO and associated heat stress or remaining in cool, DO depleted

waters and the associated hypoxic stress. Below are some recent examples of studies conducted

on the effects of low DO on the behavior (especially habitat selection) of fish.

Aku et al. (1997) compared the vertical distribution of cisco (Coreonus artedi) in a basin of alake during and after oxygenation to an unoxygenated lake. The use of hypolimnetic oxygenation

increased dissolved oxygen concentrations and expanded cisco habitat up to 9 m (29.5 ft) in

depth. Expansion was limited by water temperature.

Bodensteiner and Lewis (1992) observed that freshwater drum (Aplodinotus grunniens)

aggregated in pockets of warm backwater eddies in winter. These warmer areas had higher

dissolved oxygen levels than other, cooler portions of the river. The authors speculate that

winterkills may be associated with periodic man-made or natural disruptions to thermal refuges

and subsequent drops in dissolved oxygen levels.

Jones and Reynolds (1999) compared the parental care and hatching success in subsequent brood cycles of the common goby (Pomatoschistus microps) reared in hypoxic and normal

oxygen conditions. In low dissolved oxygen, males increased the amount of time and the tempo

with which they fanned eggs in the nest. In addition, they spent less time engaged in nest-

building activities. Males under low oxygen conditions lost more weight than those in normal

oxygen conditions, and were more likely to abandon a second brood. Hatch weight and survival

of offspring did not differ between those reared in hypoxic and normal oxygen conditions,

although eggs hatched an average of one day earlier under normal oxygen conditions.





37

Knights et al. (1995) used radiotelemetry to observe the winter habitat selection of bluegills

(Lepomis macrochirus) and black crappie (Pomoxis nigromaculatus) under varying levels of

dissolved oxygen, water temperature and current velocity. When DO concentrations were above

2 mg/L, both species selected areas with water temperatures greater than 1 C (34ºF) with no

detectable current. When DO dropped below 2 mg/L, fish moved to areas of higher DO despitelower temperatures and current velocities at or above 1 cm/s (0.03 ft/s). For these warmwater

species, DO appears to be the dominant factor in the trade-off between temperature and

dissolved oxygen.

Matthews and Berg (1997) observed the habitat selection of rainbow trout (Oncorhynchus

mykiss) in a California stream whose temperatures frequently rises to lethal levels. Distribution

in two stream pools (pools 1 and 2) was largely based on temperature and dissolved oxygen.

Pool 1 was observed to have a bottom temperature of 21.5 C (70.7ºF) and a top temperature of

28.9 C (84.0ºF), while pool 2 had a bottom temperature of 17.5 to 21 C (63.5º to 89.8ºF) and a

surface temperature of 27.9 C (82.2ºF). After August 5, when stream temperatures were

dangerously high, no trout were found in pool 1. Pool 2, however, contained trout throughout the study period. Most trout were found in the region of the pool with the lower temperature

where dissolved oxygen was lowest. For this coldwater species, temperature appears to be the

dominant factor in the trade-off between temperature and dissolved oxygen.

4.2.4 Early Lifestages

For salmonid species, whose earliest lifestages occur in gravel substrates, low dissolved oxygen

in the intergravel spaces can delay development and hatching, and increase the mortality of

embryos.

Although the early lifestages of salmonids do not have a greater need for dissolved oxygen thanother lifestages, intergravel dissolved oxygen levels are typically lower than overpassing waters.

Intergravel DO levels are dependent upon DO diffusion rates, rates of water convection, and

rates of respiration of intergravel organisms. Studies and field observations indicate that DO

levels in natural salmonid redds are approximately 3 mg/L lower than overpassing water (EPRI

1990).

For non-salmonids, early lifestages tend to be more sensitive to the adverse affects of low DO

than other lifestages. In the range of 3 to 6 mg/L, several investigations show a reduction in

survival and significant damage to early lifestages. Susceptibility to low levels of DO among

non-salmonids is species-specific. Largemouth bass, black crappie, white bass and white sucker

appear to be more tolerant of low DO levels than channel catfish, walleye, northern pike and smallmouth bass.

4.2.5 Fisheries Diversity

Previous studies have looked at the abundance of fish and their relative health in relation to

dissolved oxygen levels. There is some indication that lower levels of dissolved oxygen may

negatively influence the diversity of fish communities. These types of studies are limited,





38

however, in their ability to quantify the long-term effects of exposure to low levels of DO on fish

communities (EPRI 1990).

4.2.6 Susceptibility to Disease

Fish show an increased susceptibility to disease when exposed to low levels of dissolved oxygen.Caldwell and Hinshaw (1995) observed significant variation in mortality rates of rainbow trout

associated with different levels of dissolved oxygen when fish were exposed to the bacteria

Yersinia ruckeri. Interestingly, increased mortality was observed in both hypoxic and hyperoxic

conditions relative to normal oxygen conditions.

4.2.7 Trophic Interactions

Provided that there is a species-specific response of organisms to low levels of DO, there could

be possible disruptions to organism interactions when exposed to non-lethal but reduced levels

of DO. Breitburg et al. (1997) showed that low dissolved oxygen affects predation rates in a

“zooplankton – fish larvae – larval predator food web”. For example, low non-lethal levels of dissolved oxygen greatly increased predation of larval fish by sea nettles. Changes in species

interactions varied according to each species physiological tolerance for low dissolved oxygen

levels and the subsequent effects of low DO on escape behavior, swimming response, and feeding

behavior. Low DO may greatly affect the relative importance of differing energy pathways.

Although this research was conducted to evaluate low DO in an estuarine environment, it is

possible that a similar disruption in trophic interactions may occur in riverine or lacustrine

environments.

4.2.8 Non-Fish Species Response to Low Dissolved Oxygen

As shown in the example above, DO levels affect all aquatic organisms, not just fish. Dinsmoreand Prepas (1997a and b) describe the changes in Chironomus spp. abundance and biomass and

the changes in macroinvertebrate abundance and diversity following hypolimnetic oxygenation

in a eutrophic lake. Hypolimnetic oxygenation occurred in the northern basin of Amisk Lake

from 1988 to 1981. During that time, mean summer DO levels in the deep hypolimnion (25 m [82

ft]) rose from a pre-treatment level of 0.0 mg/L to 2.7 mg/L. Profundal (15 to 25 m [49 to 82 ft])

Chironomus spp. abundance increased from <100 to >2000 per m3. Unlike previous studies,

measures of diversity (Shannon-Weaver indices) decreased with increased oxygenation. Similar,

but less pronounced, patterns of density and abundance occurred in the south basin undergoing

smaller increases in DO levels. A nearby reference lake showed no change in macroinvertibrate

communities during the same study period. Response to oxygenation among several

macroinvertebrates was species-specific with some species increasing in abundance and densitywhile other species declined.

Nie et al. (1999) observed tadpole habitat selection during the warmer months at two ponds. One

pond, exposed and shallow, was wind mixed and experienced complete water column turnover.

A second pond, protected and deeper, experienced incomplete water turnover. It was found that

DO in the second pond fell below critical levels at depths of less than 2 m (6.6 ft). When this





39

occurred, the tadpoles favored depths near 2 m (6.6 ft), reversing their winter tendency to move

towards shore and shallower water.

4.3 Summary of Reservoir Characteristics at Lake Milton Table 8: Summary of Lake Milton Reservoir Characteristics

Lake Characteristics Lake Milton Classification

Retention Time (Days) 42.1 Transitional

Approximate Depth (ft) at Summer Pool

at Dam

40 Run of River

Aug/Jul Thermal Stratification Minimal Run of River

Dam Intake Location Bottom N/A

Modification of Flows Yes Transitional

Upstream Resevoir Yes N/A

Type of Reservoir Upst Transitional N/A

Mean Flow (cfs) 287.1 N/A

Drainage Area (sq mi) 273 N/ASource of Inflow Approx 91% from Berlin

and 9% other drainage and

tributaries

N/A

Type of Tailwater Shallow and Fast N/A

4.4 General Existing Water Quality Data at the Project Site

Existing Water Quality Data for this segment of the Mahoning River is shown in Table 9.

Table 9: Water Quality Data from EPA Sampling For Mahoning River Upstream and Downstream

of Proposed Project (OEPA, 2008)

Location

Drainage

Area (sq.

miles)

Current

Aquatic

Life Use

Attain-

ment

Status IBI MIWB QHEI ICI

Mahoning River UST of

Lake Milton (RM 70.7)248 WWH Partial 28-30 8.41-9 78.5 30

Mahoning River DST of

Lake Milton (RM 62.7) 274 WWH Partial 26-34 8.14-9.18 80.5 34







41

DO (%) Levels Below Dam

0

20

40

60

80

100

120

7 8 9 10 11

Month

D O ( % )

All HET Samplesin varyingLocations belowthe Dam

HET MedianValues

EPA 2006Samples

Figure 21

Figure 22 – Water Quality measurements taken on September 6, 2010

Stilling Basin

8 mg/L94.4 % sat

23.7 C

WWTP Outfall

8 mg/L

93.9 % sat

23.6 C

CR @ Gas Line

7.54 mg/L

88.4% sat

23.3 C

Pricetown @

Northbridge

8.1 mg/L

94.1% sat

22.8 C





42

4.6 Pre-Hydro Temperature Data Below Dam

Approximately 91% of the Inflow at Lake Milton is from the Berlin Lake Dam, a 70 foot

deep reservoir operated by the USACE located about 8 miles upstream of the proposed project(Figure 23). Berlin’s intake is at the bottom of the dam releasing the cooler water settling at the

bottom during the summer (Figure 24). This cool water flowing in from Berlin is warmed inLake Milton as evidenced by the warmer mean outflows below the Lake Milton Dam (Figure

25). In general 2010 temperature samples obtained by HET during the study as well as the data

obtained from the USGS gage were warmer than average temperatures below the dam duringAugust and closer to the mean in September and October (Figure 27 & Figure 28).

Project

Location

Figure 23





43

Berlin Thermal Stratification

0

10

20

30

40

50

60

70

80

7.0 9.0 11.0 13.0 15.0 17.0 19.0 21.0 23.0 25.0 27.0

Temp (C)

D e p t h ( f t )

Apr

May

Jun

Jul

Aug

Figure 24 – Mean Thermal Stratification Patterns at Berlin Dam 1969 to 2009 (reservoir 8 mi upstream 70 ft

deep with low level intake). Data was obtained from the USACE in 2009.

Mean Temperature Data from USGS gages

0

5

10

15

20

25

jan feb mar apr may jun jul aug sep oct nov dec

T e m p ( C )

Milton Outflow Temp

Inflow from Berlin

Figure 25 – Mean Temperature Data from USGS gages upstream and downstream

of the proposed project (1992-2010 for Lake Milton outflow and 1969-2009 for

Berlin outflows).

Approx. Intake

El. At Berlin

Dam







45

Temperature Data (C) below Lake Milton Dam

0

5

10

15

20

25

30

7 8 9 10 11

Month

T e m p e r a t u r e ( C O

All HET Samples atvarying locationsbelow dam

HET median Values

Figure 28 – Temperature Data obtained from the 2010 HET study directly below

the dam





46

4.7 Pre-Hydro DO & Temperature Levels in Lake Upstream of Dam

The data shows that Lake Milton behaves like a run-of-river reservoir in terms of thermal

stratification patterns (Figure 29). During the study period (August to October) stratification wasgreatest in on August 30

th, 2010, and by October 6, 2010 the lake was completely unstratified

and mixing was complete. The lake will likely remain uniform top to bottom until the weatherbegins to warm in the spring.

Lake Temperature Upstream of Dam

0

5

10

15

20

25

30

35

40

45

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0

Temp (C)

D e p t h

16-Aug

30-Aug

18-Sep

6-Oct

Figure 29 – Temperature Profile of Lake Milton at the Dam Intake (note complete mixing

and lack of thermal stratification by Oct 6th

)

In general dissolved oxygen levels at the dam intake mirrored temperature patterns

showing the greatest top to bottom disparity in August and mostly uniform levels top to bottomwere reached by October 6th (Figure 30 and Figure 31).

of Intakes 1 & 2

of Intakes 3 & 4





47

Lake DO levels

0

5

10

15

20

25

30

35

40

45

0 2 4 6 8 10 12

DO (mg/L)

S a m p l e D e p t h ( f t )

Aug-16

30-Aug

18-Sep

6-Oct

Figure 30

DO (%) Upstreeam of Lake Milton Dam

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100 120 140

DO (%)

D e p t h ( f t ) 16-Aug

30-Aug

18-Sep

6-Oct

Figure 31

. of Intakes 1 & 2

of Intakes 3 & 4

of Intakes 1 & 2

of Intakes 3 & 4





48

4.8 Discussion of Potential Mitigation Measures to Improve DO Levels Below Dam

4.8.1 Bypass Flows

Bypass flows involve discharging flows through one of the existing non-hydro gates. Changes in

the timing and duration of flow releases, as well as spilling or sluicing water, increasing mixing

flows can all be used to boost DO levels (Peterson et al. 2001).

Benefits

Bypass flows are the existing condition as well as the least invasive mitigation for low DO

levels. No additional structures, machinery or pipelines are required. Bypass flows can beincreased incrementally until either the minimum standards are reached or 100% of the flow is

being bypassed.

Cost

Any flow that is bypassed is flow that is not converted in to renewable energy. The over use of

bypass flows can threaten project feasibility and financial sustainability.

4.8.2 Selective Withdrawal

Selective withdrawal is a method of improving water quality both downstream and upstream of a

dam. DO concentrations downstream of a reservoir are improved by withdrawing water at an

elevation above the thermocline. DO concentrations in a stratified reservoir can be increased by

discharging water from the hypolimnion layer, however, this approach will decrease DOdownstream. The feasibility of incorporating a selective withdrawal system to enhance DO

levels depends on many factors, including the configuration of the discharge structure, reservoir

stratification cycle, energy budget, reservoir water quality distribution and characteristics,economics of modifications, and competing objectives (EPRI 1990).

The Lake Milton Dam already has the infrastructure in place to use selective withdrawaltechniques. Using the existing vertical wet well that extends throughout the depth of the

reservoir, water may be drawn from different elevations by actuating a series of gates or raising

or lowering a bulkhead (Figure 32). There is some trade off with selective withdrawal including:

Improving water quality downstream may decrease water quality in the reservoir and

vice-a-versa. Drawing water from above the thermocline will increase DO levels downstream but

would also increase temperature levels downstream where as drawing from the

hypolimnion will decrease DO downstream but would lower water temperatures

downstream.





49

Figure 32

5 CONCLUSIONS & PROPOSED STANDARDS

The pre-hydro DO levels below the Lake Milton Dam are well above the state average. This ismost likely due to the re-aeration that currently occurs in the tailwaters beginning with the

discharge splashing and spraying out of the outlet pipes and continuing with the shallow fast

moving conditions of the river extending for several miles. Based on the results of this studyHET proposes the following standards and operating procedures August to October:





50

1. Minimum Acceptable DO Levels & Temperature Range to be Maintained During

Hydro Operation

Table 10: Proposed Minimum DO Levels to be Maintained During Hydro Operation

State

Average

State

Min

Level

State M

Leve

mg/L % Sat Temp © mg/L % Sat Temp © mg/L mg/L % Sat

August 3.19 - 7.48 37.8 - 89.2 19.7-26 6 70 19.7-26 5 4 110

September 6.23 - 8.31 71.5 - 92.7 15.8-29.2 6 70 15.8-29.2 5 4 110

October 6.56 - 8.82 67.3 - 90.5 10.2-22.5 6 70 10.2-22.5 5 4 110

Proposed Min Acceptable

Levels During Hydro

Pre-Hydro Sample Range (Includes

HET, EPA & USGS Data)

2. Proposed Mitigation for Lowered DO levels or Out of Range Water TemperatureDuring Hydro Operation - If levels drop below the proposed standards, HET will use

bypass flows until DO levels reach 6 mg/L and 70% saturation and temperature is within the

pre-hydro range. HET proposes to use the selective withdrawal method as a secondarymitigation option if hydro operation is significantly reduced from August to October (more

than 40% of the total flow is being bypassed). If no combination of bypass flows and

selective withdrawal methods are able to maintain the pre-hydro standards, hydro operation

will be shut down and 100% of flows will be bypassed (existing condition), until theproposed standards can be met.

3. DO Monitoring During Hydro Operation – HET will provide continuous, monitoring of

DO levels below the dam during hydro operation from August to October for the first 3 yearsof operation. HET will use the YSI Pro ODO and post the real time data (mg/L and % sat)

on the internet. The website address will be provided to all interested parties. Temperature

and flow will continue to be monitored by the USGS gage .3 miles down stream and the datacan be access through the USGS website.

4. Proposed Winter Hydro Operations - According to the ERPI report (1990) reservoirs thatlack thermal stratification in the winter (such as Lake Milton) allow mixing of the water from

all elevations. Therefore elevation of the intake is not a critical factor in the winter in terms

of DO and temperature at Lake Milton. So the current practice of switching to the lowergates in the winter is not consequential in terms of temperature and dissolved oxygen above

or below the dam. According to the EPRI report (1990) this practice makes sense for somestorage reservoirs several hundred feet deep which typically use mid level intakes and where

extreme stratification occurs in the late summer and fall (temperature range of approximately20 degrees Celsius or more). Lake Milton does not meet any of these criteria. It is shallow

(approximately 40 ft in the summer and 32 feet in the winter when the gate switch occurs),

all intakes are toward the bottom, it has a short retention time of approximately 42 days whilestorage reservoirs have retention times of 200 days or greater, and there is minimal





51

stratification in the late summer (difference of less than 6 degrees Celsius compared to the 20

degrees or more that typify storage reservoirs).

According to the results of this study HET submits that operating the hydro turbine from

gate two during the winter will not alter DO or temperature levels in the lake or

downstream during the winter and should be authorized. HET is willing to test the DOand temperature levels at the dam intake at varying depth intervals each fall to confirm full

mixing has occurred top to bottom prior to operating the turbine during the winter. If full

mixing has occurred (as determined by uniform DO and temperature levels top to bottom)HET proposes that full turbine operation is authorized for the winter from gate 2. If full

mixing has not occurred prior to switching to the lower gates, HET will not operate the

turbine until either full mixing occurs and is documented or until HET can provide other

sufficient documentation that there will be no negative impacts to water quality by operatingthe turbine from gate 2 during the winter.

Other general conclusions reached based on the results of this study include the following:

Lake Milton behaves like a Run of River Reservoir in terms of thermal

stratification during the late summer. Minimal stratification occurred in the late

summer during this study with a maximum temperature disparity of about a 6

degree Celsius from surface to bottom.

Although the turbine will release water more gently and provide less initial re-aeration, the shallow fast moving tailwaters below the Lake Milton dam provideample opportunity for re-aeration of discharge flows for several miles. So

although there may be some temporary decrease in DO levels within the stilling

basin during hydro operation compared the pre-hydro condition, it is anticipated

that levels remain within the pre-hydro range (min 6 mg/L or 70% saturation) andwill continue to re-aerate as flows travel down stream.

The methodologies used in this study are based on recommendations from the EPRI (1990)

report and are more than adequate for determining the pre-hydro DO levels. The proposedstandards to be maintained during hydro operation are well above the state average and

consistent with the data obtained during this study.





52

6 REFERENCES

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Bodensteine, L. R. and W. M. Lewis. 1992. Role of Temperature, Dissolved Oxygen, and

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Peterson, M. J., G. F. Čada and M. J. Sale. 2001. Non-Structural Approaches for Addressing

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Perch, and Bluegill to Oxygen Concentrations under Simulated Winterkill Conditions. Copeia1:125-133.

Piening, R. 1977. Potential Winterkill Lakes in Walworth, Kenosha, and Racine Counties,Wisconsin 1935-1975. Fish Management Report 92. Wisconsin Department of Natural

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APPENDIX A –

Raw Study Data





56





57





Documents

Appendix D - Pre-Hydro Water Quality Study