Niagara Power Project FERC No. 2216

 

DETERMINE IF PROJECT OPERATIONS IMPACT AIR QUALITY

 

HTML Format. Text only

 

Prepared for: New York Power Authority

Prepared by: URS Corporation

 

August 2005

 

___________________________________________________

 

Copyright 2005 New York Power Authority

 

EXECUTIVE SUMMARY

In preparation for the relicensing of the Niagara Power Project (Project), the New York Power Authority (NYPA) is developing information in regard to all aspects of the Project and its potential effect upon its environment. This report documents information related to the determination of whether Project operations impact air quality in the surrounding area.

One of the major components of the Project is the approximately 1,900-acre Lewiston Reservoir, a pumped-storage facility used to store water from the Niagara River for the purpose of power production during peak-use periods. Given the known presence of contaminants in the Niagara River (the source of Lewiston Reservoir water), it has been asked whether the operation of the reservoir might contribute to the volatilization of contaminants from the sediment or water into the atmosphere. Also of concern is the magnitude and influence of heat emissions from Project operations and facilities, including both the Robert Moses Niagara Power Plant (RMNPP) and the Lewiston Pump Generating Plant (LPGP). To address these concerns, the objectives for this study are to (1) evaluate the influence of emissions, including possible volatilization of contaminants from sediment or surface water in the Lewiston Reservoir, and (2) determine the temperature and volume of heat emissions from the RMNPP and LPGP.

Two potential sources of emission from the reservoir were evaluated. The first was the water in the reservoir. Surface water samples collected from the Lewiston Reservoir showed no detectable concentrations of organic compounds, thus eliminating this as an emissions source. The second source evaluated was reservoir sediment that is sometimes exposed during periods of low water in the reservoir. Analysis of reservoir sediment showed the presence of both volatile and semivolatile organic compounds. The only detected volatile compounds were acetone and 2-butanone. Fourteen semivolatile compounds were detected, all of which are polynuclear aromatic hydrocarbon (PAH) compounds. Using equations based on the properties of the sediment and the specific compounds detected, a flux rate (in lb/hr-ft2) was calculated for emissions from the sediment. The compounds with the highest rates of emission were acetone and naphthalene, although other compounds were found. The flux rate for each compound was then multiplied by the area of sediment exposure to determine to the actual emission rate (in lb/hr) from that area.

The area of sediment exposed for emissions varies with the level of water in the reservoir. It is only when the water level in the reservoir reaches El. 631 feet that sediment begins to be exposed. The area exposed ranges from approximately 4 acres at El. 631 feet, to 552 acres at El. 620 feet, the normal low point. The water level in the reservoir is usually at lower elevations toward the end of the week. The total duration of sediment exposure averages approximately 12 hours per week, although this varies due to the seasonal change in operation. Based on 14 years of operating data, the time-weighted average area of exposed sediment was calculated to be 4.5 acres. On average, no portion of the reservoir bottom is exposed more than approximately 7% of the year. Multiplying the flux rate for each compound of concern by the time-weighted average exposed area of 4.5 acres, a total average emission rate of 0.0031 lb/hr was calculated for all compounds.

Using the calculated emission rates and the United States Environmental Protection Agency (USEPA) SCREEN3 dispersion model, ambient air concentrations were calculated for both short-term and long-term scenarios, and then compared to the corresponding New York State Department of Environmental Conservation (NYSDEC) guideline concentrations. Even based on the screening level concentrations, which are conservative, all contaminant concentrations in ambient air are estimated to be well below NYSDEC guideline values. Impacts upon air quality from the reservoir are therefore concluded to be minimal and acceptable.

Heat emissions from the facility also have a limited impact, if any, on the surrounding air quality. The generators, which are the major source of heat at the facility, are water-cooled, using water that is taken from and ultimately returned to the river, thus transferring facility-generated heat to the river as opposed to the atmosphere. The flowrate of the cooling water as compared to the flow of water through the turbines is so low that there is no appreciable rise in the temperature of the water in the tailrace. No heat generated at the facility is of high enough quality for reuse.

 

1.0     INTRODUCTION

The New York Power Authority (NYPA) is engaged in the relicensing of the Niagara Power Project (Project or NPP) in Lewiston, Niagara County, New York. The present operating license of the plant expires in August 2007. As part of its preparation for the relicensing of the Project, NYPA is developing information related to the ecological, engineering, recreational, cultural, and socioeconomic aspects of the Project. This report documents information related to the determination of whether Project operations impact air quality in the surrounding area.

1.1         Background

The 1,880-MW (firm capacity) Niagara Power Project is one of the largest non-federal hydroelectric facilities in North America. The Project was licensed to the Power Authority of the State of New York (now the New York Power Authority) in 1957. Construction of the Project began in 1958, and first electricity was produced in 1961.

The Project has several components. Twin intakes are located approximately 2.6 miles above Niagara Falls. Water entering these intakes is routed around the Falls via two large low-head conduits to a 1.8-billion-gallon forebay, lying on an east-west axis about 4 miles downstream of the Falls. The forebay is located on the east bank of the Niagara River. At the west end of the forebay, between the forebay itself and the river, is the Robert Moses Niagara Power Plant (RMNPP), NYPAs main generating plant at Niagara. This plant has 13 turbines that generate electricity from water stored in the forebay. Head is approximately 300 feet. At the east end of the forebay is the Lewiston Pump Generating Plant (LPGP). Under non-peak-usage conditions (i.e., at night and on weekends), water is pumped from the forebay via the plants 12 pumps into the 22-billion-gallon Lewiston Reservoir, which lies east of the plant. During peak usage conditions (i.e., daytime Monday through Friday), the pumps are reversed for use as generators, and water is allowed to flow back through the plant, producing electricity. The forebay therefore serves as headwater for the RMNPP and tailwater from the LPGP. South of the forebay is a switchyard, which serves as the electrical interface between the Project and its service area.

Operation of the NPP can result in water level fluctuations in the Lewiston Reservoir of 8-18 feet per day, and as much as 36 feet per week.

1.2         Study Objectives

Given the known presence of various contaminants in the Niagara River (the source of Lewiston Reservoir water), it has been asked whether the operation of the reservoir may contribute to the volatilization of contaminants from sediment or water into the atmosphere. Of specific concern is the air transport of contaminants to the Tuscarora Nation, immediately adjacent to the reservoir. Also of concern is the magnitude and influence of heat emissions from the operation of the Project.

The objectives of this study are to (1) evaluate the influence of emissions, including possible volatilization of contaminants from sediment or surface water in the Lewiston Reservoir, and (2) determine the temperature and volume of heat emissions from the Robert Moses Niagara Power Plant and the Lewiston Pump Generating Plant.

1.3         Investigation Area

The investigation area includes the RMNPP, the LPGP, the Lewiston Reservoir, and the areas immediately surrounding these facilities.

1.3.1        Robert Moses Niagara Power Plant

The RMNPP, located at the western end of the forebay, contains 13 individually controlled generating units in a 1,100-foot-long concrete structure located at the base of the gorge wall. Average head is approximately 300 feet. Water from the forebay discharges from each unit through an individual draft tube into a short tailrace channel, which leads directly to the lower Niagara River.

The four-lane Lewiston Road and the four-lane Robert Moses State Parkway traverse the top of the plant. The Power Vista (a visitors center overlooking the Niagara gorge) is on the plants south abutment.

1.3.2        Lewiston Pump Generating Plant

The LPGP is located at the eastern end of the forebay. Its purpose is to pump water from the forebay into the Lewiston Reservoir during periods of low electricity demand, and to generate electricity from release of this stored water during periods of peak demand. Each of the 12 generating units consists of a Francis-type pump-turbine connected to a motor-generator unit. Each electrical unit is rated at 37,500 horsepower (hp) as a motor and 20 megawatts (MW) as a generator. The lower deck of the LPGP serves as a bridge that carries Military Road and the Niagara Expressway (I-190) over the forebay.

1.3.3        Lewiston Reservoir

The approximately 1,900-acre Lewiston Reservoir, which stores water for use as headwater by the LPGP, is impounded by a 6.5-mile-long rock-filled dike (with impervious clay core) anchored at each end of a 1,000-foot-long concrete plant intake structure. The entire shoreline of the Lewiston Reservoir is lined with boulder-size riprap. At its maximum surface elevation, water in the reservoir is about 42 feet deep, and at its minimum, just over 3 feet. The gross storage capacity of the reservoir is 24 billion gallons, with a usable storage capacity of 22.6 billion gallons.

The Niagara Power Project and the Lewiston Reservoir operate on a weekly cycle. On Monday morning, the reservoir is at its highest water level and typically at its lowest on Thursday or Friday evening. Each weekday, water is taken from storage during the daytime peak energy demand periods for power generation. Consequently, the reservoir water level decreases. Then each weekday night (during non-peak energy demand), the reservoir is partially refilled. On the weekend, the reservoir is completely refilled. Daily drawdown is normally 3-18 feet and weekly drawdown 11-36 feet, depending on the season and river flow. Since the storage in the Lewiston Reservoir is used to reallocate Niagara River flow for power generation during peak demand periods, weekly drawdowns are typically greater during the tourist season (21-36 feet) than the non-tourist season (11-30 feet). Weekly drawdowns are also greater during low-flow periods than high-flow periods, as more water is rescheduled to generate electricity during peak demand periods. Portions of the reservoir bottom are sometimes exposed due to drawdown of the water, especially towards the end of the week.

 

2.0     DATA COLLECTION AND ANALYSIS

The estimate of potential emissions from the Lewiston Reservoir described in Section 3.0 is based on data collected specifically for this study, as well as on data collected for other studies related to relicensing. This section identifies the source of the analytical data used, and, for data collected specifically for this study, presents the methods used for collecting and analyzing the samples.

2.1         Background

The most exact method to evaluate air emissions is to measure the emissions directly from the source; e.g., to collect and analyze samples directly from a discharge stack. However, analysis of air samples at and around the reservoir would be difficult to collect and would produce data of limited usefulness. Collection of samples would have to be coordinated with periods when the sediment is exposed, which are difficult to predict. Emissions from the reservoir are expected to be of low and highly variable concentration, and therefore difficult to quantify with air samples. It was determined that the best method to evaluate impact would be to estimate (using conservative assumptions) potential emissions based on measured concentrations of detected analytes in the water and sediment.

2.2         2003 Surface Water Chemistry Data

The surface water sample analytical results used for this study were collected as part of the groundwater investigation being conducted by NYPA as part of its relicensing effort (URS Corporation 2004, in prep.).

As part of the groundwater investigation, two surface water sampling events were conducted in 2003. The first was conducted in September-October 2003, and the second in November-December 2003. The goal for each sampling event was the collection of surface water samples from 11 locations in and around the NPP (along with the collection of groundwater samples from several groundwater monitoring locations). Of interest to this study are the two surface water sample locations in the Lewiston Reservoir, namely, SW03-006 and SW03-011, the former located at the western and the latter at the eastern end of the reservoir (Figure 2.2-1). Each was sampled in October and November 2003.

Surface water samples were collected by direct submersion of the sample bottles and capping underwater. Following sample collection, the sample bottles were placed in coolers, iced, and transported via courier to Severn Trent Laboratories of Buffalo, New York, for analysis. The surface water samples were analyzed for an extensive list of organic, inorganic, and biological parameters.

Analytical results from surface water samples collected at two sites in the Lewiston Reservoir in 2003 are presented on Table 2.2-1. Results for organic compounds reveal that both VOCs and SVOCs were below the reporting limit (i.e., were non-detectable) at both surface water sample locations during the two sampling events.

2.3         Previously Collected Sediment Analytical Data

In October 2002, five sediment samples (RES-SED-05 through RES-SED-09) were collected as part of a relicensing study to determine the extent and quality of sediment in the Lewiston Reservoir (ESI 2003). These samples were analyzed for the contaminants of concern being routinely sampled as part of the long-term Niagara River Toxics Management Plan (NRTMP). Since volatile organic compounds (VOCs) are the compounds normally evaluated in air emissions studies, and since only one VOC, namely, tetrachloroethylene (PCE), was targeted by the NRTMP, the ESI 2003 results were not sufficient for the present study.

2.4         2003 Sediment Chemistry Data

Because the sediment samples collected in 2002 did not include analysis for VOCs, five additional sediment samples were collected and analyzed for the full USEPA target compound list (TCL), which includes a number of both volatile and semivolatile organic compounds (SVOCs). Table 2.4-1 shows a complete list of these organic parameters. Analysis was also carried out for other, geotechnical parameters used in the emission calculations.

2.4.1        Sediment Sampling Locations

Sediment sampling locations RES-SED-13 through RES-SED-17 are shown in Figure 2.2-1. Locations were selected according to the following criteria: (1) presence of sufficient volume of sediment for sampling, (2) known exposure of the sampled area during low-water periods, and (3) spatial distribution of sampling locations across the reservoir. For consistency with the number of samples collected in ESI 2003, it was decided to collect five samples.

Using GIS, a figure showing sediment thickness within the reservoir was overlaid with a figure showing the areas of the reservoir exposed during low water elevations (see Figure 2.2-1). Sediment thickness was evaluated in the ESI 2003 report, based on a 2001 bathymetric survey coupled with construction elevations for the reservoir. The area of sediment exposure was determined at a water elevation of El. 620 feet, the operational low level for the reservoir. As shown in Figure 2.2-1, the areas exposed during operation are generally not areas where there has been an accumulation of sediment.

Due to the relatively few areas that were both periodically exposed and projected to contain enough sediment for sample collection, it was decided that only four of the samples could reasonably be collected from the exposed areas. The fifth sample (RES-SED-17) was collected from a location of sedimentation, but one not exposed during low-water periods. The fifth sample also will indicate whether there is any difference in sediment from the exposed and non-exposed areas.

2.4.2        Sediment Sample Collection and Analysis

Although the intent of the sampling effort was to collect samples of sediment that are exposed during low-water periods, the samples were actually collected when reservoir levels were near their highest. The reason for this was that boat access was the only reasonable way to reach the sampling area, and high water was required for such access.

Sediment samples were analyzed for both chemical and physical parameters, including (1) USEPA TCL VOCs, (2) TCL SVOCs, (3) total porosity, (4) total organic carbon, (5) moisture content, and (6) grain size. All sediment samples were collected on October 30, 2003, from a boat. Using latitude and longitude information for the proposed sampling locations and a Global Positioning System, the boat operator was able to anchor the boat within approximately 10 feet of each proposed sampling location. Because the purpose of this study is to evaluate air emissions, and since emissions occur from the surface of the sediment layer, all sediment samples were collected with a Ponar dredge from the top 6 inches (or less) of sediment.

2.4.3        Sediment Analytical Results

Table 2.4.3-1 summarizes detected analytical results for sediment VOCs and SVOCs, and gives the maximum value detected for each compound. For comparison, results from the samples collected in 2002 are also shown on this table.

Analysis of the five samples (RES-SED-13 through RES-SED-17) for VOCs showed the presence of only two, namely, acetone and methyl ethyl ketone (also called 2-butanone). While the concentration of these two compounds was relatively consistent among the five samples, the highest concentrations of both were found in sample RES-SED-17, collected from the area that remains constantly submerged.

With regard to SVOCs, fourteen SVOC compounds were detected in the sediment, all of which are polynuclear aromatic hydrocarbon (PAH) compounds. These are generally compounds that structurally contain two or more molecular ring structures, that have higher molecular weights, and that have lower vapor pressures than other SVOC compounds. Comparison of SVOC results from the 2003 sediment samples to those previously analyzed (RES-SED-05 through RES-SED-09), showed that most of the same parameters were detected, and at similar concentrations. Therefore, as a conservative assumption (from the perspective of environmental effect), the maximum detected value from the samples analyzed for ESI 2003 or the samples analyzed for this study was used as the concentration of that particular contaminant in the calculations presented in Section 3.0.

Results for the geotechnical parameters analyzed on the 2003 samples are presented in Appendix A-2. In general, the results of these analyses are consistent with samples that have been collected previously.

2.4.4        Quality Control

Quality control (QC) samples employed during the sediment sampling program included a field duplicate, matrix spike/matrix spike duplicate (MS/MSD), and a sampling equipment rinse blank sample. A Data Usability Summary Report for the 2003 sampling event is presented in Appendix A, along with the validated analytical results. Of importance to note is that while both acetone and 2-butanone are common laboratory contaminants, there was no evidence of that in the data package, and thus their presence in the sediment cannot be discounted.

 

Table 2.2-1

Surface Water Sample Analytical Results for the Lewiston Reservoir, October and November 2003

Parameter

Units

Results

SW03-006 (south)

SW03-011 (east)

10/07/03

11/24/03

10/09/03

11/24/03

Volatiles

 

g/L

None Detected

Semivolatiles

 

g/L

None Detected

Metals

Arsenic

g/L

10.0 U

10.0 U

10.0 UJ

10.0 U

Cadmium*

g/L

1.0 U

1.0 U

1.0 U

1.0 U

Calcium

g/L

34,800

35,800

34,300

36,000

Lead*

g/L

6.0 U

6.0 U

6.0 U

6.0 U

Magnesium

g/L

8,910

9,100

9,090

9,070

Mercury

g/L

0.200 UJ

0.200 U

0.200 UJ

0.200 U

Potassium

g/L

1,640

2,020 J

1,760

2,050 J

Sodium

g/L

11,000 J

11,400 J

10,400

11,700 J

Miscellaneous Parameters

Alkalinity, Bicarbonate

mg/L

90.2

101

101

98.0

Alkalinity, Total

mg/L

90.2

101

101

98.0

Chloride

mg/L

17.2

20.8

19.8

19.6

Hardness

mg/L

127

132

144

144

Monomethyl mercury

ng/L

0.25 U

0.25 U

0.074 B

0.25 U

Sulfate

mg/L

25.8

27.6

34.1

27.6

Total Dissolved Solids

mg/L

146

163

174

162

Total Organic Carbon

mg/L

1.2

2.0

1.8

2.0

Total Suspended Solids

mg/L

4.0 U

4.0 U

6.0

4.0 U

Bacterial and Microbial Parameters

Heterotrophic Plate Count

CFU/mL

360

620

570

920

Total Coliform

C/100 mL

180

690

600

450

Fecal Coliform

C/100 mL

NA

20

NA

100

E. coli

pos/neg

NA

pos

NA

pos

Pesticides

 

 

 

 

 

delta-BHC

g/L

0.050 U

0.040 J

0.050 U

0.043 J

Note: U - Analyte not detected/associated number is the quantitation limit (QL); J - Reported concentration is an estimated value (UJ indicates an estimated QL); B - Analyte was detected at a concentration above the method detection limit (MDL) but below the QL (applies to metals results only); NA - Sample was not analyzed for this parameter; R - Result rejected, data unusable. With the exception of metals, this table only presents results above the method detection limits. Source: URS Corp. 2004, Groundwater report, in prep.

 

Table 2.4-1

USEPA TCL Volatile and Semivolatile Organic Compounds

Volatiles

1,1,1-Trichloroethane

Bromomethane

1,1,2,2-Tetrachloroethane

Carbon Disulfide

1,1,2-Trichloro-1,2,2-trifluoroethane

Carbon Tetrachloride

1,1,2-Trichloroethane

Chlorobenzene

1,1-Dichloroethane

Chloroethane

1,1-Dichloroethene

Chloroform

1,2,4-Trichlorobenzene

Chloromethane

1,2-Dibromo-3-chloropropane

Cyclohexane

1,2-Dibromoethane (Ethylene dibromide)

Dibromochloromethane

1,2-Dichlorobenzene

Dichlorodifluoromethane

1,2-Dichloroethane

Ethylbenzene

1,2-Dichloroethene (cis)

Isopropylbenzene (Cumene)

1,2-Dichloroethene (trans)

Methyl acetate

1,2-Dichloropropane

Methyl Ethyl Ketone (2-Butanone)

1,3-Dichlorobenzene

Methyl tert-butyl ether

1,3-Dichloropropene (cis)

Methylcyclohexane

1,3-Dichloropropene (trans)

Methylene Chloride

1,4-Dichlorobenzene

Styrene

2-Hexanone

Tetrachloroethene

4-Methyl-2-Pentanone

Toluene

Acetone

Total Xylenes

Benzene

Trichloroethene

Bromodichloromethane

Trichlorofluoromethane

Bromoform

Vinyl Chloride

Semivolatiles

1,1-Biphenyl

Benzo(a)pyrene

1,2,4-Trichlorobenzene

Benzo(b)fluoranthene

1,2-Dichlorobenzene

Benzo(g,h,i)perylene

1,3-Dichlorobenzene

Benzo(k)fluoranthene

1,4-Dichlorobenzene

Bis(2-Chloroethoxy)methane

2,4,5-Trichlorophenol

Bis(2-Chloroethyl)ether

2,4,6-Trichlorophenol

Bis(2-Chloroisopropyl)ether

2,4-Dichlorophenol

Bis(2-Ethylhexyl)phthalate

2,4-Dimethylphenol

Butylbenzylphthalate

2,4-Dinitrophenol

Caprolactam

2,4-Dinitrotoluene

Carbazole

 

Table 2.4-1 (CONT.)

USEPA TCL Volatile and Semivolatile Organic Compounds

Semivolatiles (cont.)

2,6-Dinitrotoluene

Chrysene

2-Chloronaphthalene

Dibenz(a,h)anthracene

2-Chlorophenol

Dibenzofuran

2-Methylnaphthalene

Diethylphthalate

2-Methylphenol (o-cresol)

Dimethylphthalate

2-Nitroaniline

Di-n-butylphthalate

2-Nitrophenol

Di-n-octylphthalate

3,3-Dichlorobenzidine

Fluoranthene

3-Nitroaniline

Fluorene

4,6-Dinitro-2-methylphenol

Hexachlorobenzene

4-Bromophenyl-phenylether

Hexachlorobutadiene

4-Chloro-3-methylphenol

Hexachlorocyclopentadiene

4-Chloroaniline

Hexachloroethane

4-Chlorophenyl-phenylether

Indeno(1,2,3-cd)pyrene

4-Methylphenol (p-cresol)

Isophorone

4-Nitroaniline

Naphthalene

4-Nitrophenol

Nitrobenzene

Acenaphthene

N-Nitrosodimethylamine

Acenaphthylene

N-Nitroso-di-n-propylamine

Acetophenone

N-Nitrosodiphenylamine

Anthracene

Pentachlorophenol

Atrazine

Phenanthrene

Benzaldehyde

Phenol

Benzo(a)anthracene

Pyrene

 

 

Table 2.4.3-1

Volatile and Semivolatile Compounds Detected in Sediment Samples

Parameter

(units are ug/kg)

RES-SED-05

RES-SED-06

RES-SED-07

RES-SED-08

RES-SED-09

RES-SED-13

RES-SED-14

RES-SED-15

RES-SED-16

RES-SED-17

Maximum Detected

VOCs

 

 

 

 

 

 

 

 

 

 

 

Acetone

NA

NA

NA

NA

NA

25.5

26

25.6

31.1

44

44

Methyl Ethyl Ketone (2-Butanone)

NA

NA

NA

NA

NA

5.23

5.64

4.79

6.45

9.23

9.23

 

 

 

 

 

 

 

 

 

 

 

 

SVOCs

 

 

 

 

 

 

 

 

 

 

 

Acenaphthylene

170

170

180

340

220

94

 

113

 

130

340

Anthracene

250

230

240

430

280

79.4

 

101

 

107

430

Benzo(a)anthracene

480

360

280

450

260

217

54.3

129

64.2

300

480

Benzo(a)pyrene

710

570

490

840

560

250

65.8

167

93.2

356

840

Benzo(b)fluoranthrene

860

670

670

1100

750

259

70.3

162

141

393

1,100

Benzo(g,h,i)perylene

200

200

190

310

190

299

 

269

 

255

310

Benzo(k)fluoranthene

630

540

380

690

480

176

 

117

114

269

690

Chrysene

800

640

620

1100

640

261

70.3

181

102

386

1,100

Fluoranthene

1000

880

710

1200

750

439

103

262

144

576

1,200

Fluorene

330

330

380

710

470

 

 

 

 

 

710

Indeno(1,2,3-cd)pyrene

240

220

210

350

210

573

 

347

 

569

573

Naphthalene

170

130

99

160

64

 

 

 

 

 

170

Phenanthrene

410

340

310

540

290

144

 

89.7

 

197

540

Pyrene

1100

850

750

1300

870

307

 

202

140

364

1,300

 

Figure 2.2-1

Lewiston Reservoir Surface Water and Sediment Sampling Locations

[NIP General Location Maps]

 

1.0     CALCULATED EMISSIONS FROM THE LEWISTON RESERVOIR

Two potential sources exist for contaminant emissions from the Lewiston Reservoir. One is the reservoir surface, and the second is the reservoir sediment during bottom-exposure periods. Both these sources, and their respective volatilization pathways, are evaluated in the following sections.

1.1         Contaminant Emissions from the Reservoir Water Surface

With no detectable VOCs or SVOCs in the water, no basis exists for estimating contaminant emissions from the water surface. Contaminant emissions from the reservoir water surface are therefore assumed to be negligible and acceptable.

1.2         Contaminant Emissions from Reservoir Sediment

Given that organic compounds have been detected in the sediment of the Lewiston Reservoir, and that the contaminated sediment is periodically exposed during low water levels in the reservoir, it is possible for contaminant vapors to be emitted from reservoir sediment at such times. Because direct measurement of vapors would be both difficult and inconclusive, it was decided that the best method would be to calculate potential emissions by using contaminant concentrations in the sediment in appropriate equations and models.

1.2.1        Calculation of Emission Rates

Because sediment is not typically a source of vapor emissions, no models specific to estimating the emission of organic contaminants from sediment could be found. All equations used in this evaluation are actually for estimating contaminant emissions from soil. However, given that the only potential for contaminant emissions from sediment is during sediment exposure, there is essentially no difference between the exposed sediment and soil, and thus the equations used have been considered appropriate.

Due to the operation of the reservoir and the specific conditions of the sediment, the process of contaminant emissions from the reservoir is complicated. In order to simplify the calculations, the following assumptions were made:

         All parameters affected by ongoing changes in the reservoir, such as moisture content, are assumed to be constant. Reasonably conservative assumptions were made for the value of all such parameters.

         Air emission occurs only when the sediment is exposed, with the actual duration and area of sediment exposure to be factored into the calculations.

         Organic compound concentrations to be used in emissions calculations are the highest values detected in sediment samples.

         The compound concentration in sediment remains constant over time (even though a certain mass is lost to the atmosphere if volatilization is actually occurring).

Appendix B shows the calculation that was performed to estimate the emission rate for all organic compounds detected in the sediment. In general, the compound concentration in the sediment is used to calculate the corresponding concentration in the vapor phase (i.e., soil gas concentration). Using the soil gas concentration then, the emissions rate (or vapor flux rate) may be calculated. Finally, multiplying the vapor flux rate by the area from which the vapors are being emitted provides the total emissions from the reservoir.

The soil gas concentration and vapor flux rates are separately determined for each of the contaminants detected in the sediment. The concentration and flux rate for each contaminant is affected by such factors as its vapor pressure (i.e., tendency to volatilize), its tendency to adsorb to soil particles, and its diffusion rate through soil and air. Most of the contaminants detected are SVOCs, which have a higher tendency to remain adsorbed to the soil, and which volatilize at comparatively low rates. Table 3.2.2-1 presents a summary of the maximum contaminant concentrations detected in the sediment, and the corresponding vapor flux rate calculated for each. As shown on the table, the calculated flux rate was highest for acetone, followed by naphthalene, and methyl ethyl ketone.

1.2.2        Duration and Area of Sediment Exposure

Because the contaminants in the sediment have the potential to emit vapors only when the sediment is exposed, a major factor in determining contaminant emissions from the reservoir is the duration and area of sediment exposure in the reservoir. The vapor flux rate is multiplied by the exposed sediment area to determine the overall contaminant emission rate.

The area of sediment exposed varies with the level of water in the reservoir. The water level in the reservoir ranges from a high of El. 659 feet to a low of El. 620 feet, but it is only below El. 631 feet that any portion of the sediment is exposed. The area exposed ranges from approximately 4 acres at El. 631 feet to 552 acres at El. 620 feet. The water elevation in the reservoir is usually at lower elevations toward the end of the week.

Water levels in the Lewiston Reservoir are recorded hourly. URS evaluated 14 years of operating data from 1991 through a portion of 2004. Table 3.2.3-1 summarizes the water level data for the reservoir in one-foot increments. Data that were not recorded or that were in error were excluded from the analysis. Each years data were evaluated separately, and showed that some variability exists from year to year in the length of time that sediment is exposed. The length of time that the reservoirs water level was in the range allowing sediment exposure varied from an annual low of only 1% to a high of 13%. The average percent of time during which sediment is exposed over the 14 years for which data exist is 7% (12 hours per week). Although there is some seasonal variation in the exposed area, that was not evaluated for this report. The data also show that over the last 14 years, the water level in the reservoir was at its low of El. 620 for a total of only 8 hours.

Using the exposed area that corresponds to each water elevation (by increments of one foot) in the reservoir, and the length of time that the reservoir was at that water level, a time-weighted average area of exposed sediment from all 14 years of data was calculated to be 4.5 acres. On an annual basis, the time-weighted average ranged from a low of 0.2 acres in 1997 to a high of 12 acres in 1994.

1.2.3        Total Contaminant Emissions from Sediment

To determine the actual pounds per hour of emissions from exposed sediments, the flux rate for each contaminant was multiplied by 4.5 acres (the time-weighted average exposed area), to arrive at the emission rates summarized on Table 3.2.2-1. The average emission rate for all contaminants was then calculated to be 0.0031 lb/hr. Also shown on Table 3.2.2-1 are the emission rates calculated for 12 acres, the highest annual time-weighted exposed area.

1.3         Total Estimated Contaminant Emissions

Since emissions from the water surface are negligible, the only source of emissions is the reservoir sediment. The emission rates estimated in Section 3.2 and summarized on Table 3.2.2-1 comprise the total emissions from the Lewiston Reservoir. Section 4.0 presents the evaluation of the potential impact of these emissions on the surrounding community.

 

Table 3.2.2-1

Estimate of Contaminant Emissions from Exposed Sediment in the Lewiston Reservoir

Contaminant

Maximum Concentration Detected in Sediment

Calculated Contaminant Flux "J"

Emission Rate From 4.5-acre Area

Emission Rate From 12-acre Area

ug/kg

lb/h-ft2

lb/h

lb/h

Acetone

44

1.25E-08

2.44E-03

6.51E-03

Methyl Ethyl Ketone (2-Butanone)

9.23

7.28E-10

1.43E-04

3.80E-04

Acenaphthylene

340

1.63E-10

3.20E-05

8.52E-05

Anthracene

430

2.80E-11

5.49E-06

1.47E-05

Benzo(a)anthracene

480

1.87E-13

3.67E-08

9.80E-08

Benzo(a)pyrene

840

3.65E-14

7.15E-09

1.91E-08

Benzo(b)fluoranthrene

1100

2.05E-12

4.01E-07

1.07E-06

Benzo(g,h,i)perylene

310

1.70E-14

3.33E-09

8.89E-09

Benzo(k)fluoranthene

690

9.59E-15

1.88E-09

5.01E-09

Chrysene

1100

5.91E-12

1.16E-06

3.09E-06

Fluoranthene

1200

4.97E-12

9.74E-07

2.60E-06

Fluorene

710

1.08E-10

2.12E-05

5.66E-05

Indeno(1,2,3-cd)pyrene

573

4.58E-15

8.97E-10

2.39E-09

Naphthalene

170

2.19E-09

4.30E-04

1.15E-03

Phenanthrene

540

2.88E-11

5.64E-06

1.50E-05

Pyrene

1300

3.38E-12

6.62E-07

1.77E-06

TOTAL

 

 

3.08E-03

8.21E-03

 

Table 3.2.3-1

Reservoir Level Data

Reservoir Water Level Elevation

Exposed Area at Elevation

Year

Totals for all Years

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

ft

acres

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

 

620

552

-

-

-

-

-

-

5

2,760

3

1,656

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

 

621

443

3

1,330

4

1,774

5

2,217

33

14,632

21

9,312

-

-

-

-

-

-

-

-

-

-

1

443

-

-

9

3,991

-

-

 

622

314

8

2,514

17

5,342

32

10,055

39

12,255

50

15,711

-

-

-

-

16

5,028

3

943

-

-

11

3,457

7

2,200

13

4,085

-

-

 

623

252

10

2,521

32

8,067

36

9,076

64

16,134

55

13,865

-

-

-

-

17

4,286

6

1,513

-

-

23

5,798

16

4,034

25

6,302

-

-

 

624

186

18

3,343

28

5,200

36

6,685

59

10,956

53

9,842

-

-

-

-

19

3,528

22

4,085

2

371

26

4,828

20

3,714

39

7,242

-

-

 

625

141

28

3,938

46

6,469

32

4,500

67

9,422

61

8,578

-

-

-

-

21

2,953

25

3,516

13

1,828

32

4,500

28

3,938

34

4,781

-

-

 

626

96

43

4,133

46

4,421

64

6,152

84

8,074

83

7,978

3

288

-

-

27

2,595

47

4,518

13

1,250

28

2,691

39

3,749

40

3,845

1

96

 

627

74

51

3,774

71

5,254

70

5,180

115

8,510

120

8,880

23

1,702

3

222

34

2,516

63

4,662

18

1,332

41

3,034

50

3,700

41

3,034

5

370

 

628

48

52

2,514

88

4,255

96

4,642

152

7,349

145

7,011

53

2,563

11

532

48

2,321

77

3,723

17

822

60

2,901

65

3,143

72

3,481

18

870

 

629

34

81

2,757

108

3,676

91

3,097

151

5,140

164

5,582

49

1,668

24

817

64

2,178

108

3,676

39

1,327

73

2,485

77

2,621

82

2,791

15

511

 

630

15

93

1,429

116

1,782

130

1,997

162

2,489

178

2,734

54

830

21

323

82

1,260

138

2,120

66

1,014

82

1,260

81

1,244

88

1,352

18

277

 

631

4

99

362

143

523

158

578

174

636

232

848

104

380

61

223

112

409

158

578

76

278

113

413

116

424

85

311

34

124

 

632

0

126

-

146

-

211

-

204

-

247

-

118

-

62

-

138

-

186

-

72

-

134

-

129

-

118

-

42

-

 

633

0

145

-

159

-

238

-

217

-

305

-

147

-

83

-

190

-

211

-

109

-

152

-

136

-

129

-

44

-

 

634

0

156

-

161

-

240

-

224

-

277

-

180

-

92

-

242

-

261

-

127

-

163

-

181

-

151

-

63

-

 

 

Table 3.2.3-1 (CONT.)

Reservoir Level Data

Reservoir Water Level Elevation

Exposed Area at Elevation

Year

Totals for all Years

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

ft

acres

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

 

635

0

207

-

201

-

279

-

235

-

286

-

220

-

158

-

277

-

296

-

175

-

186

-

196

-

160

-

61

-

 

636

0

171

-

232

-

278

-

235

-

313

-

242

-

200

-

300

-

308

-

182

-

222

-

210

-

172

-

74

-

 

637

0

147

-

231

-

283

-

235

-

315

-

270

-

221

-

354

-

328

-

220

-

244

-

254

-

220

-

83

-

 

638

0

148

-

236

-

303

-

252

-

310

-

314

-

274

-

383

-

349

-

234

-

254

-

276

-

255

-

82

-

 

639

0

152

-

281

-

294

-

229

-

330

-

391

-

257

-

377

-

415

-

280

-

265

-

290

-

256

-

113

-

 

640

0

168

-

302

-

253

-

264

-

286

-

389

-

276

-

383

-

406

-

305

-

306

-

272

-

280

-

110

-

 

641

0

149

-

312

-

298

-

257

-

320

-

422

-

366

-

406

-

423

-

382

-

325

-

318

-

284

-

134

-

 

642

0

159

-

346

-

349

-

320

-

308

-

436

-

381

-

343

-

431

-

387

-

357

-

332

-

291

-

119

-

 

643

0

180

-

321

-

368

-

360

-

338

-

450

-

369

-

375

-

417

-

492

-

422

-

362

-

331

-

119

-

 

644

0

172

-

345

-

349

-

391

-

410

-

489

-

461

-

376

-

381

-

539

-

401

-

406

-

317

-

109

-

 

645

0

169

-

391

-

380

-

427

-

409

-

506

-

414

-

391

-

390

-

514

-

429

-

408

-

350

-

138

-

 

646

0

189

-

379

-

455

-

380

-

438

-

471

-

441

-

462

-

399

-

510

-

428

-

435

-

372

-

168

-

 

647

0

169

-

394

-

431

-

396

-

389

-

472

-

405

-

418

-

385

-

522

-

462

-

457

-

372

-

158

-

 

648

0

135

-

472

-

450

-

420

-

402

-

460

-

445

-

464

-

436

-

504

-

438

-

430

-

389

-

165

-

 

649

0

151

-

484

-

409

-

353

-

352

-

449

-

503

-

452

-

358

-

501

-

462

-

433

-

460

-

155

-

 

650

0

159

-

458

-

352

-

336

-

314

-

405

-

506

-

355

-

336

-

488

-

437

-

424

-

444

-

197

-

 

 

Table 3.2.3-1 (CONT.)

Reservoir Level Data

Reservoir Water Level Elevation

Exposed Area at Elevation

Year

Totals for all Years

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

Ft

acres

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

Total # of hours at elevation

(Area) x (Total # of hours)

 

651

0

112

-

415

-

320

-

279

-

266

-

390

-

501

-

289

-

286

-

455

-

432

-

419

-

447

-

150

-

 

652

0

103

-

369

-

279

-

293

-

227

-

324

-

457

-

305

-

236

-

445

-

361

-

408

-

415

-

148

-

 

653

0

94

-

402

-

271

-

225

-

217

-

298

-

414

-

227

-

203

-

325

-

355

-

389

-

412

-

157

-

 

654

0

76

-

323

-

206

-

172

-

145

-

221

-

299

-

214

-

174

-

273

-

338

-

296

-

377

-

122

-

 

655

0

70

-

228

-

182

-

112

-

107

-

141

-

315

-

201

-

119

-

197

-

230

-

256

-

308

-

121

-

 

656