Lower Okanogan River Basin DDT 

and PCBs Total Maximum Daily Load 

Submittal Report 

October 2004 

Publication Number 04-10-043 

Lower Okanogan River Basin DDT 

and PCBs Total Maximum Daily Load 

Submittal Report 

Prepared by: 

Mark Peterschmidt 

Washington State Department of Ecology 

Water Quality Program

October 2004 

Publication Number 04-10-043 
For additional copies of this document contact: 

Department of Ecology 

Publications Distribution Center 

P.O. Box 47600 

Olympia, WA 98504-7600 

Telephone: (360) 407-7472 

Adams

Benton Asotin

Chelan

Clallam

Clark

Columbia

Cowlitz

Douglas

Ferry

Franklin Garfield

Grant

Grays

Harbor

Island

Jefferson

King

Kitsap

Kittitas

Klickitat

c Lewis

Lincoln

Mason

Okanogan

Pacifi

Pend

Oreille

Pierce

San Juan

Skamania

Spokane

Stevens

Thurston

Skagit

Snohomish

Wahk

Walla

Walla

Whatcom

Whitman

iakum Yakima

Northwest

425-649-7000

Southwest

360-407-6300

Eastern

509-329-3400

Central

509-575-2490

Headquarters (Lacey) 360-407-6000

TTY (for the speech and hearing impaired) statewide is 711 or 1-800-833-6388

Regional

Office

location

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Yakima

Lacey

Bellevue

If you need this publication in an alternate format, please contact us at 360-407-6404 or TTY 

(for the speech and hearing impaired) at 711 or 1-800-833-6388. 
Table of Contents 

List of Tables.................................................................................................................................iii 

List of Figures................................................................................................................................. v 

Executive Summary........................................................................................................................ 1 

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

Components of the TMDL.............................................................................................................. 4 

Background..................................................................................................................................... 5 

Applicable Criteria.......................................................................................................................... 9 

Water Quality and Resource Impairments.................................................................................... 11 

Technical Approach and Results .................................................................................................. 12 

Technical Assessment Objectives and Strategy........................................................................ 12 

Methods..................................................................................................................................... 13 

Results of 2001-2002 Sampling................................................................................................ 16 

Loading Capacity.......................................................................................................................... 27 

Daily DDT and PCB Loads to the Lower Okanogan River and Osoyoos Lake....................... 27 

Source Assessment........................................................................................................................ 32 

Load Allocations........................................................................................................................... 35 

Load Reductions........................................................................................................................... 38 

Seasonal Variation ........................................................................................................................ 42 

Margin of Safety ........................................................................................................................... 42 

Summary Implementation Strategy .............................................................................................. 43 

Activities that Support this TMDL ............................................................................................... 49 

Implementation Strategy............................................................................................................... 49 

Supporting Regulations and Land Management Plans................................................................. 49 

Reasonable Assurance .................................................................................................................. 49 

Public Participation....................................................................................................................... 50 

References..................................................................................................................................... 51 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page i 
Definitions and Acronyms............................................................................................................ 53 

Appendix A................................................................................................................................. A-1 

Summary of Public Involvement ............................................................................................ A-2 

Responses to Public Comments on the Lower Okanogan River Basin DDT and PCB 

Submittal Report Draft............................................................................................................ A-3 

Appendix B................................................................................................................................. B-1 

Page ii Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
List of Tables 

Table 1: Criteria from Chapter 173-201A WAC .......................................................................10 

Table 2: Human Health Criteria from 40CFR131.36 (July 1, 2000 edition).............................10 

Table 3: Impaired Waterbodies Addressed in this TMDL.........................................................11 

Table 4: Samples Collected During Ecology’s 2001-2002 Assessment of DDT and 

PCBs in the Lower Okanogan River Basin..................................................................14 

Table 5: DDT and PCB Concentrations in Lower Okanogan River Water, May, 2002............17 

Table 6: DDT Concentrations in Tributary Streams of Osoyoos Lake and the Lower 

Okanogan River, April-May, 2001a ............................................................................18 

Table 7: DDT and PCB Concentrations in Lower Okanogan River Basin STP Effluent, 

2001-2002 ....................................................................................................................19

Table 8: DDT and PCB Concentrations in Lower Okanogan River Basin STP Sludge 

June 2001 (ng/g,dw).....................................................................................................20 

Table 9: DDT & PCB Concentrations in Osoyoos Lake Sediment Core Collected June, 

2001 (ng/g, dw)............................................................................................................20 

Table 10: DDT and PCB Concentrations in Lower Okanogan River Sediment Core 

Collected September, 2001 (ng/g, dw) ........................................................................21 

Table 11: DDT and PCB Concentrations in Fillet of Fish from the Lower Okanogan 

River, 2001 (ng/g, ww)...............................................................................................25 

Table 12: Weighted Mean DDT Loads in Tributary Streams of Osoyoos Lake and the 

Lower Okanogan River Based on Water Column Samples Collected 1995-

2002 (mg/day)..............................................................................................................28 

Table 13: Mean DDT and PCB Loads in Lower Okanogan River Basin STPs Based on 

Whole Effluent Samples (DDT) and PCB Concentrations in STP Sludge 

Collected 2001-2002 (mg/day) ....................................................................................29 

Table 14: Total Load Delivery, Measured Loads, Theoretical Loads, and Loading 

Capacities of DDT and PCBs at Several Osoyoos Lake and Lower Okanogan 

River Reaches (mg/day)...............................................................................................31 

Table 15: Measured Loads of DDT and PCBs at Several Lower Okanogan River 

Reaches Compared to Loads Estimated from Re-suspension of Surficial 

Osoyoos Lake Bed Sediments (mg/day)......................................................................35 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page iii 
Table 16: DDT and PCB Load Allocations for Individual Tributary streams (mg/day) .............36 

Table 17: DDT and PCB Waste Load Allocations for STPs (mg/day)........................................37 

Table 18: DDT and PCB Load Allocations for Bottom Sediments (mg/day) .............................38 

Table 19: Required DDT and PCB Load Reductions and Reserve Capacity (-) at 

Osoyoos Lake and Lower Okanogan River Reaches (mg/day)...................................39 

Table 20: BSAFs at Osoyoos Lake and Several Lower Okanogan River Reaches.....................40 

Table 21: Reductions or Reserve Capacity (-) in Sediment DDT and PCB 

Concentrations (ng/g OC) Required to Meet Load Allocations ..................................41 

Table 22: Load Reductions Required to Meet Criteria within Individual Tributaries and 

STPs (mg/day) .............................................................................................................41 

Page iv Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
List of Figures 

Figure 1: Okanogan River Watershed.............................................................................................6 

Figure 2: Location of Lower Okanogan River and Osoyoos Lake tributary 

streams.............................................................................................................................7 

Figure 3: Lower Okanogan River and Similkameen River average monthly flows 

(figure adapted from WEST Consultants, Inc. and Hammond, Collier, 

& Wade-Livingstone, Inc., 1999)..................................................................................15 

Figure 4: T-DDT and t-PCB concentrations in Osoyoos Lake sediment core .............................22

Figure 5: T-DDT and t-PCB concentrations in lower Okanogan River sediment 

core ................................................................................................................................23 

Figure 6: Lipid-normalized t-DDT concentrations in lower Okanogan River fish 

muscle ordered by mean length of fish in each composite (Lg=large, 

Md=medium, Sm=small) and location for each species. ..............................................26 

Figure 7: Lipid-normalized t-PCB concentrations in lower Okanogan River fish 

muscle ordered by mean length of fish in each composite (Lg=large, 

Md=medium, Sm=small) and location for each species. ..............................................26

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page v 
Page vi Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Executive Summary 

Basin: Okanogan River (Washington) 

Key Impaired Resources: Water Quality 

Uses Affected: Water Supply (Domestic), Harvest of aquatic organisms 

Type of Impairment: Concentrations of DDT, 4,4’-DDD, 4,4’-DDE and PCBs in fish 

Tissue, DDT in Water 

Pollutant: DDT, 4,4’-DDD, 4,4’-DDE and PCBs 

Contribution Factors: Historic agricultural, industrial, commercial and residential 

practices. 

The Okanogan River originates in the Cascade Mountains north of the international border 

between British Columbia and Washington State. The Okanogan River is characterized by a 

series of lakes north of international boundary and a free flowing river flowing out of lake 

Osoyoos, which straddles the boundary, 78 miles to it’s confluence with the Columbia River. 

The Okanogan River’s primary tributary is the Similkameen River, which enters 5 miles south of 

Lake Osoyoos. The Similkameen River normally contributes three quarters of the combined 

flow in the Okanogan River. The Similkameen River originates on the east slopes of the 

Cascade Mountains along the international boarder and meets the Okanogan River at Oroville, 

Washington. Agriculture, forestry, mining, and recreation are the major land-use activities in the 

Okanogan watershed. 

Under Section 303(d) of the federal Clean Water Act, the Okanogan River and several tributaries 

have been listed by Washington State for non-attainment of the EPA human health criteria for 

DDT and PCBs in edible fish tissue and for non-attainment of Washington State chronic criteria 

for DDT in water. Therefore, a Total Maximum Daily Load (TMDL) project was conducted for 

the portion of the river that flows through Washington State, as required by the Clean Water Act. 

The source of these contaminants appears to be the legacy from historic agricultural and 

industrial activities common throughout the Okanogan River watershed. 

The chemical characteristics of DDT and PCBs cause them to be classified as persistent, 

bioaccumulative toxins. These contaminants are a legacy of past activities as their use has been 

banned in both the United States and Canada for more than 25 years. Due to the legacy nature of

the contamination, substantial mitigation of the DDT and PCB contamination, both directly and 

indirectly, has already occurred in the Okanogan Basin. Direct actions include the banning of 

these materials from use; while, indirect actions include irrigation improvements that have 

reduced the loss of agricultural topsoil that potentially could carry pesticide residues to the 

Okanogan River and associated waterbodies. The DDT and PCBs in the lower Okanogan River 

Basin TMDL continues to promote community actions that address DDT and PCB 

contamination, along with new actions of source identification and development of management 

strategies to address any sources of contamination subsequently revealed. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 1 
Page 2 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Introduction 

Section 303(d) of the federal Clean Water Act mandates that the state of Washington establish 

Total Maximum Daily Loads (TMDLs) for surface waters that do not meet water quality 

standards, designed to protect, restore and preserve water quality, after application of 

technology-based pollution controls. The U.S. Environmental Protection Agency (EPA) has 

established regulations (40 CFR 130) and developed guidance (EPA, 1991) for setting TMDLs. 

Under the Clean Water Act, every state has its own water quality standards designed to protect, 

restore, and preserve water quality. The state’s water quality standards consist of both (1) 

designated uses, such as supporting cold water biota and providing a drinking water supply, and 

(2) criteria, usually numeric, required to achieve those uses. When a lake, river or stream fails to 

meet the water quality standards after application of required technology-based controls, the 

Clean Water Act requires the state to place the water body on a list of "impaired" water bodies 

and to prepare an analysis called a Total Maximum Daily Load. 

The goal of a TMDL is to ensure that the impaired water will attain water quality standards. A 

TMDL includes a written, quantitative assessment of water quality problems and of the sources 

that cause them. The TMDL determines the amount of a given pollutant that can be discharged 

to and assimilated by the water body and still meet standards; this is called the loading capacity. 

The TMDL also allocates that load among the various sources, both point and non-point. 

The TMDL must also consider seasonal variations and include a margin of safety that takes into 

account any lack of knowledge about the cause of the water quality problem or its loading 

capacity. The sum of the individual allocations and the margin of safety must be equal to or less 

than the loading capacity. 

In addition to the mandatory components of a TMDL, the general purposes of this document are 

to: 

• Summarize data that document which stream segments exceeded standards for DDT and 

PCBs. 

• Summarize the results of a technical assessment which identified probable sources of 

DDT and PCB contaminant loading that cause increases in contaminant concentrations in 

fish tissue and tributary waters. 

• Summarize actions recommended for meeting water quality standards. 

• Summarize monitoring that should be used to track TMDL implementation and 

determine progress toward attaining water quality standards. 

A Detailed Implementation Plan (DIP) will be developed within a year of TMDL approval by 

EPA, to expand the initial implementation strategy into a working plan. Further public input will 

be sought to help prepare the DIP, which will identify how, when, and where voluntary 

restoration activities will be implemented. Details of a monitoring plan will be developed. The 

Washington State Department of Ecology (Ecology) and other entities will provide technical 

assistance and seek additional funding for these activities. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 3 
This TMDL addresses the 303(d) listed water quality impaired water bodies for the DDT and 

PCBs in the lower Okanogan River basin on the Okanogan River, Lake Osoyoos and the 

tributary streams Tallant Creek, Elgin Creek and Ninemile Creek, as well as the unlisted 

tributaries of Antoine Creek and Mosquito Creek. Antoine and Mosquito Creeks do not meet the 

state water quality standards based on the 2001-2002 sampling study. The specific water body 

identification numbers and impairments being addressed by this TMDL are: Okanogan River 

segment ID YN58LL for 4,4’-DDD, 4,4’-DDE, PCB-1254 and PCB-1260 in fish tissue; Lake 

Osoyoos ID 060VKD for 4,4’-DDD, 4,4’-DDE in fish tissue; and all of the following water 

bodies for exceeding state chronic criteria for DDT: Tallant Creek ID LD33FC; Elgin Creek ID

KR66GR; Ninemile Creek ID IP09QF; Antoine Creek ID NN36KM; and Mosquito Creek ID 

QH83DF. 

Components of the TMDL 

The five components of a TMDL, as required by the Clean Water Act and applied to this TMDL, 

are described below: 

Loading Capacity 

The loading capacity is the maximum amount of pollutant that a water body can receive without 

violating water quality standards. The loading capacity is allocated between waste load 

allocations, load allocations, natural background, and a margin of safety. No natural background 

value exists for DDT and PCB compounds, therefore no allocation is made for it in this TMDL. 

Waste Load Allocations 

A waste load allocation is that portion of a receiving water's loading capacity that is allocated to 

point sources of pollution. There are four permitted wastewater discharges to the Okanogan 

River and its primary tributary, the Similkameen River. These permitted discharges represent 

the municipal wastewater treatment plants in Oroville, Tonasket, Omak and Okanogan. 

allocations were calculated for these permitted discharges based on their respective design 

capacities and the water quality standards for DDT, DDE, DDD and PCBs. 

Load Allocations 

A load allocation is that portion of the receiving water's loading capacity that is allocated to nonpoint sources of pollution or to natural background sources. Load allocations for this TMDL are 

based on the concentration of contaminants in fish tissue in the mainstem Okanogan River and 

based on the Washington State chronic criteria for DDT in water for selected tributaries. 

Margin of Safety 

EPA requires that a TMDL include a margin of safety to account for any lack of knowledge 

concerning the relationship between loads and water quality. This TMDL relies on a margin of 

safety implicitly included in the conservative assumptions that were calculated into the 

Page 4 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
regulatory numerical values contained in the National Toxics Rule and the Water Quality 

Standards for Surface Waters of the State of Washington. 

Seasonal Variation 

Seasonal variation, or the changes in loading rates due to changing conditions associated with the 

annual change in seasons, has been accounted for by sampling during both high flow and low 

flow events. Additionally, the human health and chronic aquatic life criteria for DDT and PCBs 

are driven by long-term exposures. Since the accumulation of DDT and PCBs in fish is a timeintegrative process, and the chronic aquatic life criteria are based on long-term exposures, 

seasonal variations in loads are not an important factor in determining load allocations for these 

parameters. 

Background 

The Okanogan River flows from its headwaters in British Columbia (B.C.) through north-central 

Washington, where it discharges into the Columbia River near the town of Brewster. The 

Okanogan River basin drains approximately 8,900 square miles of area. The uplands consist 

mostly of forests and rangelands, while the fertile valley bottom provides one of the most 

productive orchard regions in B.C. and Washington (Figure 1). 

Most of the Okanogan River basin lies north of the Canadian border, where its flow is regulated 

by four lakes along the river’s mainstem. All of the lakes are located north of the U.S.-Canada 

border except the 14,150-acre Osoyoos Lake, which straddles the border. The lower Okanogan 

River flows out of Osoyoos Lake (elevation 915’ m.s.l.) at the city of Oroville and flows 79 

miles southward to its confluence with the Columbia River (779’ m.s.l.). The Similkameen 

River joins the Okanogan River just downstream of Oroville, where its flow is increased by an 

average of 400 percent. About 20 small tributary streams also drain the 2,600 mi

2 of the

Washington portion of the basin (hereinafter referred to as the lower Okanogan River basin). 

Most of the tributaries are small or intermittent, contributing little to the overall flow of the lower 

Okanogan River (Figure 2). 

The lower Okanogan River basin is located within a semi-arid region that has an annual 

precipitation of approximately 20 inches in the higher elevations of the basin fringes, to as little 

as 10 inches near the valley bottom. Surface hydrology generally follows a snowmelt regime, 

with low flows occurring September-March. Several of the small streams are diverted for 

irrigation and flow only during releases from their storage reservoirs. 

The basin is sparingly populated, with 39,564 residents in Okanogan County according to the 

2000 census. The cities of Omak and Okanogan have a combined population of about 7,000. 

Other population centers include the cities of Oroville (≈ 1,600) and Tonasket (≈ 1,000). The 

southern portion of the lower Okanogan River provides the western boundary of the Colville 

Indian Reservation from river mile (RM) 38.6 downstream to its confluence with the Columbia 

River. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 5 
Land cover is primarily forest and rangeland, especially in the uplands. Near the valley bottom,

orchards and pasture/hay are the primary agricultural uses. Fruit orchards have a long history in 

the Okanogan valley, with the first planted in 1857. By 1916 there were approximately 12,000 

acres of irrigated orchards in the lower Okanogan River valley. Fruit orchards presently 

comprise about 2 percent or approximately 37,000 acres of the land area. The upper Okanogan 

River basin (north of the Canadian border) has a similar composition of orchard lands, providing 

over 99 percent of the tree fruit grown in British Columbia (Sinclair and Elliott, 1993).

Okanogan R.

Similkameen R.

Okanogan Lk. Columbia

River

50 0 50 Miles

N

Watershed boundary

Figure 1: Okanogan River Watershed

Page 6 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
    

	

 

	



	












	







	












 




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Figure 2: Location of Lower Okanogan River and Osoyoos Lake Tributary Streams 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 7 
Page 8 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Applicable Criteria 

Within the state of Washington, water quality standards are published pursuant to Chapter 90.48 

of the Revised Code of Washington (RCW). Authority to adopt such rules, regulations, and 

standards as are necessary to protect the environment is vested with the Department of Ecology. 

Under the federal Clean Water Act, the EPA Regional Administrator must approve the water 

quality standards adopted by the State (Section 303(c)(3)). Through adoption of these water 

quality standards, Washington has designated certain characteristic uses to be protected and the 

criteria necessary to protect these uses [Washington Administrative Code (WAC), Chapter 173-

201A]. 

Streams in the lower Okanogan Basin watershed have the following designated uses assigned in 

Chapter 173-201A WAC, Table 602. The designated uses are: 

• Aquatic Life Uses 

o Non-Core Salmon/Trout: Salmon and trout spawning, non-core rearing, and 

migration. For the protection of spawning, non-core rearing, and migration of salmon 

and trout, and other associated aquatic life. 

• Recreational Uses 

o Primary Contact 

• Water Supply Uses 

o Domestic Water 

o Industrial Water 

o Agricultural Water 

o Stock Water 

• Miscellaneous Uses 

o Wildlife Habitat 

o Harvesting 

o Commerce/Navigation 

o Boating 

o Aesthetics 

This TMDL is designed to address impairments of designated uses caused by DDT and PCB 

concentrations in fish tissues and surface waters. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 9 
Chapter 173-201A WAC contains DDT and PCB criteria to protect aquatic life (Table 1). 

Because this criteria does not include a human health component and does not protect all 

designated uses (i.e. use of water as a domestic supply and harvesting of organisms), the Clean 

Water Act requires the additional use of the water quality criteria set in National Toxics Rule, 

Chapter 40 of the Code of Federal Regulation part 141.36 (40CFR131.36). The National Toxics 

Rule (NTR) defines the criteria for DDT, DDD, DDE and PCBs for the protection of human 

health. The numeric criteria are given in Table 2. 

Table 1: Criteria from Chapter 173-201A WAC 

Toxics Substances Criteria (μg/L) 

 Freshwater 

Substance Acute Chronic 

DDT (and metabolites) 1.1a 0.001b 

Polychlorinated Biphenyls (PCBs) 2.0b 0.014b 

Notes to Table 1:

a. An instantaneous concentration not to be exceeded at any time.

b. A 24-hour average not to be exceeded. 

Table 2: Human Health Criteria from 40CFR131.36 (July 1, 2000 edition)

Human Health

(10-6 risk for carcinogens)

for the consumption of: 

Water & Organisms Organisms Only

 (#) Compound 

CAS 

Number (μg/L) (μg/L) 

(108) 4,4'-DDT 50293 0.00059 0.00059 

(109) 4,4'-DDE 72559 0.00059 0.00059 

(110) 4,4'-DDD 72548 0.00083 0.00083 

Page 10 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Water Quality and Resource Impairments 

The lower Okanogan River, Osoyoos Lake and their Washington State tributaries of Ninemile 

Creek, Similkameen River, Tallant Creek, and unnamed (Elgin) creek were included in 

Washington’s 1998 list of impaired waters compiled under Section 303(d) of the Clean Water 

Act due to water quality impairments by DDT, 4-4’-DDD, 4,4’-DDE, PCB-1254, PCB-1260, 

Dissolved Oxygen, Fecal Coliform, Arsenic, and Temperature. In addition to the 303(d) listed 

impaired waters the lower Okanogan River tributaries Antoine Creek and Mosquito Creek were 

found to be impaired by DDT (Serdar 2003). This TMDL addresses the water quality 

impairments from DDT, 4,4’-DDD, 4,4’-DDE, PCB-1254, PCB-1260 included in Table 3. 

Table 3: Impaired Waterbodies Addressed in this TMDL 

Waterbody

Old 

Segment No. 

New

Segment No.

Township, 

Range 

& Section Impairment(s) 

Years listed 

on the 

303(d) List: 

Okanogan 

River 

WA-49-1010 YN58LL 31N, 25E, 

Section 27

Exceeds NTR criteria for 

4,4’-DDD, 4,4'-DDE, 

and PCB-1254 in fish 

tissuea

1996 

1998 

Okanogan 

River 

WA-49-1010 YN58LL 31N, 25E, 

Section 34

Exceeds NTR criteria for 

PCB-1260 in fish tissuea 1996 

1998 

Osoyoos Lk. WA-49-9260 060VKD 40N, 27E, 

Section 22

Exceeds NTR criteria for 

4,4’-DDD, 4,4’-DDE 

in fish tissueb

1996 

1998 

Tallant Creek WA-49-1017 LD33FC 32N, 25E, 

Section 02

Exceeds Washington

State 

chronic criteria for 

DDT in waterc

1998 

Elgin Creek 

(listed as 

Unnamed 

Creek) 

WA-49-1022 KR66GR 33N, 26E, 

Section 03

Exceeds Washington

State 

chronic criteria for 

DDT in waterc

1998 

Ninemile 

Creek 

WA-49-1049 IP09QF 40N, 27E, 

Section 15

Exceeds Washington

State 

chronic criteria for 

DDT in waterc

1998 

Antoine Creek NN36KM 38N, 27E 

Section 27

Exceeds Washington

State 

chronic criteria for 

DDT in waterd

Unlisted but 

impaired 

Mosquito 

Creek 

QH83Df 38N, 27E 

Section 27

Exceeds Washington

State 

chronic criteria for 

DDT in waterd

Unlisted but 

impaired 

NTR=National Toxics Rule a Davis and Serdar, 1996 b Johnson and Norton, 1990 

c Johnson et al., 1997 d Serdar, 2003 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 11 
Technical Approach and Results 

An approach of mass balancing was used in the Lower Okanogan River Basin DDT and PCBs 

Total Maximum Daily Load TMDL evaluation for DDT and PCB compounds in the lower 

Okanogan River basin. The mass balancing was used to evaluate the sources of contaminant 

loading and their potential impacts to the water quality in the basin. This study approach used 

several techniques for the collection of surface water data, sediment data, fish tissue data and 

discharge information from the NPDES permitted dischargers. Data collected was used to assess 

potential DDT and PCB sources and to compare data from the current study to other data 

sources. (Serdar 2003) 

Technical Assessment Objectives and Strategy 

During 2001 – 2002, Ecology collected data necessary to conduct a TMDL assessment for the 

geographic area and parameters covering the lower Okanogan River and all of its tributaries from 

the Canadian border (RM 82.5) to its mouth near Brewster, including the southern portion of 

Osoyoos Lake (RM 79.0 – 82.5). The TMDL concerns 4,4’-DDD, 4,4’-DDE, 4,4’-DDT, t-DDT, 

and PCBs (as Aroclors or t-PCB). Objectives of the sampling were to assess DDT and PCB 

loads to the lower Okanogan River and Osoyoos Lake, assess DDT and PCB concentrations in 

edible fish tissue, and reconstruct historic DDT and PCB levels in sediments. This was 

considered necessary to achieve the goal of the lower Okanogan TMDL project – to determine if 

and where DDT/PCB loading may be reduced and how this may affect their concentrations in 

fish tissue. 

Early in the planning process it was recognized that this would not be a traditional TMDL. First, 

although DDT and PCBs have been banned for decades, they persist in the environment and 

generally have become non-point contaminants often dissipated and dispersed far from their 

original sources. Second, the listings in the lower Okanogan River and Osoyoos Lake are based 

on fish tissue, adding layers of complexity to calculating loads and load allocations, customary 

elements of a TMDL assessment. 

The need to approach this TMDL assessment from a broad geographical perspective was also 

recognized as a potential difficulty early in the planning process. The distribution of agricultural 

lands and results of previous Ecology studies suggested DDT contamination existed throughout 

the lower Okanogan River valley. The geographical locations of PCB contamination were less 

certain, but the problem was addressed basin-wide rather than focusing on a single listed river 

reach. 

Given these and other considerations, four sampling components were identified to carry out the 

TMDL assessment: 

• Re-assessment of DDT and PCB loads transported to the lower Okanogan River and 

Osoyoos Lake through tributaries and discharged by municipal sewage treatment plants. 

• Measurement of DDT and PCB concentrations in the water column of the lower 

Okanogan River. 

Page 12 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
• Analysis of DDT and PCB concentrations in edible fish tissue from the lower Okanogan 

River. 

• Analysis of DDT and PCB concentrations in sediment cores from the lower Okanogan 

River and Osoyoos Lake. 

The following sections describe methods for collecting data for these study components and 

sample results. A TMDL analysis is then performed to quantify loads to the lower Okanogan 

River and Osoyoos Lake. Also included is a quantitative analysis of DDT/PCB accumulation by 

fish in the lower Okanogan River and Osoyoos Lake. These analyses were performed using data 

collected during 2001-2002, as well as previous Ecology data and data collected by other 

agencies. 

Methods 

Sampling Strategy

Sample types, sample locations, and analyses were all conducted to best meet the project 

objectives. Table 4 summarizes samples collected during 2001-2002. 

Lower Okanogan River and Osoyoos Lake tributaries were sampled for DDT in the present 

assessment during the high flow season (April-May) when more streams contain water than other 

times of year. Previous sampling of tributary streams was conducted during low flows (JulyAugust) (Johnson et al., 1997). PCBs were not analyzed in water from tributaries since they are 

extremely difficult to detect in water without expensive specialized methods. There is also little 

reason to suspect these streams contain measurable PCBs since they are primarily an industrial 

and urban contaminant. 

Water from the three municipal sewage treatment plants (STPs) discharging to the lower 

Okanogan River or Similkameen River – Oroville, Omak, and Okanogan – were also sampled 

for DDT and PCBs (Tonasket STP began discharging to the Okanogan River after sampling for 

this project had been completed). STPs may act as funnels for DDT in urban areas (Reif, 1990) 

possibly due to improper disposal or storage and historic non-agricultural insecticidal uses such 

as mosquito control. Previous studies have not adequately investigated DDT in STP effluent. 

PCBs were also sampled in STP effluent since STPs represent the few places in the basin where 

PCBs may be present at detectable concentrations, due, for instance, to the high density of 

electrical transformers in the service area compared to other parts of the basin. The only known 

analysis of PCBs in a lower Okanogan River basin water sample was from Okanogan STP 

effluent analyzed in 1988 by Reif (1990). No PCBs were detected in this sample. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 13 
Table 4: Samples Collected During Ecology’s 2001-2002 Assessment of DDT and PCBs in the 

Lower Okanogan River Basin 

Location Whole Watera Sediment/Sludgeb

Fish 

Tissuec

Osoyoos Lake -- 

Core – DDT/PCBs + 

chlorinated pesticides -- 

Mainstem Okanogan River 

Oroville Reach DDT/PCBs -- DDT/PCBs 

Riverside-Omak Reach DDT/PCBs -- DDT/PCBs 

Malott-Monse Reach DDT/PCBs 

Core – DDT/PCBs + 

chlorinated pesticides DDT/PCBs 

Tributary Streams 

DDT

(DDT/PCBs in Similkameen R.) -- -- 

STPs DDT/PCBs Sludge – DDT/PCBs -- 

a

ancillary analyses included TSS, TOC, and field parameters b

ancillary analyses included TOC and 210Pb c

ancillary analysis included percent lipids 

STP sludge was also examined for DDT and PCBs since it provides a more feasible media for 

detection of these chemicals due their tendency to sorb to organic-rich solids. In the absence of 

detectable concentrations in effluent, sludge was used to calculate crude estimates of DDT and 

PCB loads via STPs. 

High flow data were collected to supplement previously reported low flow data in order to 

address potential seasonal variation. Water column samples were collected at three locations in 

the lower mainstem Okanogan River in May during the rising limb of the season hydrograph 

(Figure 3), since rising flows are most likely to entrain DDT-containing particulate matter. 

Samples were also analyzed for PCBs. Sampling locations were at the Osoyoos Lake outlet to 

assess contaminant loads from across the border; at Riverside just upstream of the largest urban 

center in the lower Okanogan River basin; and at Malott below urban centers and near the 

Okanogan River mouth. Samples were also collected at the mouth of the Similkameen River. 

Page 14 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Figure 3: Lower Okanogan River and Similkameen River Average Monthly Flows (figure adapted 

from WEST Consultants, Inc. and Hammond, Collier, & Wade-Livingstone, Inc., 1999) 

To assess the geographical distribution of contaminants in lower Okanogan River fish, three 

species were sampled from the upper river (Oroville reach, RM 77.3 – 76.4), middle river 

(Riverside-Omak reach, RM 41.0 – 30.7), and lower river (Monse reach, RM 10.5 – 4.9). These 

three reaches also encompass three of the population centers and public boat launches along the 

river. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 15 
Species analyzed were common carp (Cyprinus carpio), mountain whitefish (Prosopium 

williamsoni), and smallmouth bass (Micropterus dolomieui). These are the three most common 

resident game species in the lower Okanogan River and represent different feeding behaviors and 

habitat uses. Edible tissue (fillet) was analyzed for DDT and PCBs. Results were provided to 

Washington State Department of Health (WDOH) for their assessment of any potential human 

health risks associated with consumption of each species. 

Sediment cores were collected to reconstruct historical DDT and PCB concentrations from

sediment deposits. Two to four decades have passed since DDT and PCBs were banned or their 

use peaked in the U.S. and Canada, and concentrations in the aquatic environment have since 

been declining. However, existing lower Okanogan River basin data are not sufficient to gauge 

trends over time. In the absence of previously established baselines, sediment coring is the best 

method to reconstruct historic contamination levels. 

Due to the high laboratory costs associated with analyzing multiple sediment horizons, coring 

was limited to two sites: southern Osoyoos Lake and the mouth of the Okanogan River near 

Monse. These sites may represent the only locations in the basin with sediment deposits deep 

enough to reconstruct contamination levels going back several decades. 

Field procedures, sampling locations, laboratory procedures and data quality assurance 

procedures are contained in the Okanogan Technical Assessment Report (Appendix B, Serdar 

2003). 

Results of 2001-2002 Sampling 

Complete results of 2002-2002 sampling are in Appendix F. 

DDT and PCBs in the Lower Okanogan River Mainstem Water Column

Table 5 shows results of water column sampling conducted in the lower Okanogan River during 

May 2002. Comparable concentrations of 4,4’-DDE and 4,4’-DDD (0.14 – 0.29 ng/l) were 

found at all three lower Okanogan River sites. None of the nine PCB Aroclors analyzed were 

detected at practical quantitation limits of 0.64 – 0.67 ng/l. 

These results represent the first time DDT compounds have been detected in the water column of 

the lower Okanogan River. Previous sampling during 1995 by Johnson et al. (1997) failed to 

detect DDT in the lower Okanogan River at a practical quantitation limit of 1 ng/l. Therefore, it 

is impossible to determine if the 2002 results represent a change from 1995 levels. The May 

2002 concentrations probably would have gone undetected had Metro Environmental Laboratory 

(MEL) not used the large volume injection to achieve low quantitation limits (≤0.1 ng/l). 

Page 16 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Table 5: DDT and PCB Concentrations in Lower Okanogan River Water, May, 2002 

Location RM Date

Flow

(l/s) 

TSS 

(mg/l) 

4,4'-DDE 

(ng/l) 

4,4'-DDD 

(ng/l) 

4,4'-

DDT 

(ng/l) 

t-DDT 

(ng/l) 

PCBsa

(ng/l) 

Okanogan R. @ 

Zosel Dam 77.4 5/13/02 33,131 18 0.23 0.29 u(0.080) 0.52 u(0.66)

Okanogan R. @ 

Riverside 40.6 5/13/02 137,620 20 0.22 0.14 u(0.076) 0.36 u(0.66)

Okanogan R. @ 

Malott 17.0 5/14/02 146,681 26 0.17 0.16 u(0.10) 0.33 u(0.64) a

Results shown are for PCB Aroclors 1268, 1262, 1260, 1254, 1248, 1242, 1232, 1221, and 1016 

u=undetected at practical quantitation limit in parentheses 

DDT in Osoyoos Lake Tributaries and Lower Okanogan River Tributaries

DDT concentrations in water collected near the mouths of Osoyoos Lake and lower Okanogan 

River tributaries are shown in Table 11. These represent all of the tributary streams found 

flowing during the April and May 2001 sampling events, except for the Similkameen River 

which was sampled during May, 2002. In all, 18 streams were sampled and 13 were found 

flowing during both April and May sampling events. This is about twice the number of streams 

sampled during July-August 1995 even though the 2001 water year was extraordinarily dry. 

DDT was detected in water from 12 streams with t-DDT concentrations ranging from 0.4 – 9.2 

ng/l. 4,4’-DDE was the primary metabolite detected, with 4,4’-DDT present at the second 

highest concentration, unlike lower mainstem Okanogan River samples which had no measurable 

4,4’-DDT. Low concentrations of 2,4’-DDT (≤0.5 ng/l) were also detected in several creeks. 

Antoine Creek had 2,4’-DDD at 1.3 ng/l during April 2001 sampling. 

Elgin Creek in the lower part of the basin (RM 28.4) had the highest t-DDT concentrations, 

followed by Antoine Creek and Nine Mile Creek, which is an Osoyoos Lake tributary. This 

partially mirrors the 1995 study which found these streams to have some of the highest DDT 

concentrations and is indicative of a pattern showing streams with high DDT concentrations in 

the upper and lower parts of the basin (RM 61-80 and RM 15-28). Little or no DDT was found 

in the middle basin (RM 32-57), especially RM 32-51 where no DDT at all was detected. 

Tallant Creek was not sampled in the present study because it was dry. This creek generally 

contains water only during late summer or early autumn due to releases from Leader Lake, its 

primary source. When Tallant Creek was sampled in 1995, t-DDT concentrations up to 500 ng/l 

were found and Tallant Creek contributed about 75% of the DDT load to the lower Okanogan 

River during that period. 

No DDT was detected in the Similkameen River during May 2002 sampling even though the 

large volume injection method used for this sample provided quantitation limits an order of 

magnitude lower than in other tributaries. PCBs Aroclors were also analyzed in the 

Similkameen River water sample, but none were detected at a quantitation limit of 0.67 ng/l. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 17 
Table 6: DDT Concentrations in Tributary Streams of Osoyoos Lake 

and the Lower Okanogan River, April-May, 2001a

Location RM Date

Flow

(l/s)

TSS

(mg/l)

4,4'-DDE

(ng/l)

4,4'-DDD 

(ng/l) 

4,4'-DDT

(ng/l)

t-DDT

(ng/l)

Nine Mile Creek 80.2 4/17/01 99 12 1.8 0.4 1.3 3.5

“ 5/16/01 32 u(1) 1.4 0.6 1.5 3.5

Tonasket Creek 77.8 4/17/01 361 4 1.5 u(0.8) 1 2.5

“ 5/16/01 26 9 1.2 u(1.7) 1.1 2.3

Similkameen River 74.1 5/13/02 113,551 14 u(0.067) u(0.067) u(0.080) nd

Mosquito Creek 67.4 4/11/01 0.24 7 0.8 0.7 u(0.8) 1.5

“ 5/16/01 0.5 2 1.7 0.4 1.4 3.5

Whitestone Creek 62.4 4/11/01 114 10 0.6 u(0.8) u(0.8) 0.6

“ 5/16/01 85 5 0.4 u(1.6) u(1.6) 0.4

Antoine Creek 61.2 4/17/01 10 12 5.2 1.1 1.7 8.0

“ 5/16/01 31 16 1.8 0.5 1 3.3

Siwash Creek 57.3 4/16/01 24 1 0.5 u(0.8) u(0.8) 0.5

“ 5/16/01 0 -- -- -- -- --

Bonaparte Creek 56.7 4/11/01 62 21 0.4 u(0.8) u(0.8) 0.4

“ 5/17/01 153 55 0.4 u(1.7) u(1.7) 0.4

Aeneas Creek 52.9 4/16/01 95 u(1) 0.4 u(0.8) u(0.8) 0.4

“ 5/17/01 78 2 0.4 u(1.6) u(1.6) 0.4

Chewiliken Creek 50.7 4/11/01 9 u(1) u(0.8) u(0.8) u(0.8) nd

“ 5/17/01 0 -- -- -- -- --

Tunk Creek 45.0 4/16/01 106 2 u(0.9) u(0.9) u(0.9) nd

“ 5/17/01 197 16 u(1.7) u(1.7) u(1.7) nd

Johnson Creek 40.6 4/16/01 79 11 u(0.8) u(0.8) u(0.8) nd

“ 5/17/01 29 12 u(1.7) u(1.7) u(1.7) nd

Wanacut Creek 35.0 4/12/01 29 1 u(0.8) u(0.8) u(0.8) nd

“ 5/17/01 14 1 u(1.7) u(1.7) u(1.7) nd

Omak Creek 32.0 4/12/01 382 5 u(0.8) u(0.8) u(0.8) nd

“ 5/15/01 596 35 u(1.7) u(1.7) u(1.7) nd

Elgin Creek 28.4 4/12/01 27 7 3.7 0.4 1.8 5.9

“ 5/15/01 19 20 5.8 0.9 2.5 9.2

Salmon Creek 25.7 4/17/01 284 1 0.4 u(0.9) u(0.9) 0.4

“ 5/15/01 0 -- -- -- -- --

Tallant Creek 19.5 4/16/01 0 -- -- -- -- --

“ 5/15/01 0 -- -- -- -- --

Loup Loup Creek 16.9 4/16/01 0 -- -- -- -- -- 

“ 5/15/01 3 u (1) 0.7 u(1.6) 0.7 1.4

Chiliwist Creek 15.1 4/16/01 71 11 0.4 u(0.8) u(0.8) 0.4

“ 5/16/01 27 1 u(1.7) u(1.7) u(1.7) nd a

Similkameen River samples May, 2002 

u=undetected at practical quantitation limit in parentheses 

nd=not detected

DDT and PCB Concentrations in STPs

Three municipal sewage treatment plants (STPs) were sampled for DDT and PCBs during 2001. 

The Omak STP and Okanogan STP discharge treated effluent directly to the Okanogan River 

Page 18 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
while the Oroville STP effluent is discharged to the Similkameen River approximately four miles 

upstream of the formal confluence with the Okanogan River. Samples of final effluent were 

collected on three occasions and sludge was collected once. 

Table 7 shows results of DDT and PCB analysis of STP effluent samples. Table 8 shows results 

of sludge samples analyzed for DDT and PCBs. DDT was detected in Oroville and Okanogan 

STP effluent on two occasions, with t-DDT concentrations (0.7 – 1.8 ng/l) comparable to those 

found in tributary streams. No evidence of PCBs were found in a scan of the April, 2001 and 

May, 2001 samples. Samples collected during May, 2002 were analyzed for PCBs only using a 

large volume injection method. A low concentration of PCB-1248 (0.39 ng/l) was found in 

Okanogan STP effluent, but no other PCBs were detected. 

DDT and PCBs were detected in sludge from all three STPs, with the highest concentrations 

from the Oroville STP. The t-PCBs were found at higher concentrations than t-DDT in sludge 

unlike effluent samples where DDT concentrations were higher. This may suggest that, while 

both DDT and PCBs are present in STPs, PCBs are more strongly sequestered in solids. The 

Omak STP consistently showed the lowest concentrations of DDT in both media and of PCBs in 

sludge, even where the TSS and TOC content – factors often correlated with higher 

concentrations of organochlorine compounds – was highest. 

Three of seven PCB Aroclors analyzed in sludge were detected; PCB-1260, -1254, and -1248. 

These are the most common Aroclors detected in Washington’s freshwater aquatic environment 

both statewide (e.g. Hopkins et al., 1985; Davis et al., 1995; Davis and Serdar, 1996) and at sites 

with known PCB sources (e.g. Ecology, 1995). As mentioned previously, PCB-1248 was the 

only Aroclor detected of the nine analyzed in effluent samples. 

Table 7: DDT and PCB Concentrations in Lower Okanogan River Basin STP Effluent, 2001-2002 

Location RM Date

Flow

(l/s) 

TSS 

(mg/l) 

4,4'-DDE 

(ng/l) 

4,4'-DDD 

(ng/l) 

4,4'-DDT 

(ng/l) 

t-DDT 

(ng/l) 

PCBsa

(ng/l) 

Oroville STP b 4/17/01 6 1 0.5 u(0.9) 0.6 1.1 nd*

5/16/01 7 u(1) u(1.7) u(1.7) 0.7 0.7 nd*

5/14/02 7 u(1) na na na na u(0.63)c

Omak STP 29.9 4/17/01 24 2 u(0.8) u(0.8) u(0.8) nd nd*

5/17/01 26 4 u(1.6) u(1.6) u(1.6) nd nd*

5/13/02 26 3 na na na na u(0.66)

Okanogan 

STP 24.8 4/16/01 16 4 0.7 u(0.8) 0.6 1.3 nd*

5/17/01 16 4 0.4 0.4 1 1.8 nd*

5/14/02 11 5 na na na na 0.39d

a

Results shown are for PCB Aroclors 1268, 1262, 1260, 1254, 1248, 1242, 1232, 1221, and 1016 b

Similkameen River mile 4.0 c

Practical quantitation limit was 0.94 ng/l for PCB-1254 d

Concentration of PCB-1248. Other Aroclors undetected at a practical quantitation limit of 0.65 ng/l 

u=undetected at practical quantitation limit in parentheses 

nd=not detected

*no practical quantitation limit determined 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 19 
Table 8: DDT and PCB Concentrations in Lower Okanogan River Basin STP Sludge 

 June 2001 (ng/g,dw)

Location %TOC

4,4'-

DDE 

4,4'-

DDD 

4,4'-

DDT t-DDT 

PCB1260 PCB1254 PCB1248 t-PCBa

Oroville STP 36.7 180 26 36 242 48 130 95 273

Omak STP 40.3 68 u(45) 23 91 41 100 63 204

Okanogan STP 32.0 110 23 40 173 51 120 63 234

a

Aroclors 1242, 1232, 1221, and 1016 not detected at practical quantitation limits of 43 ng/g (Oroville STP), 45 ng/g (Omak 

STP), and 42 ng/g (Okanogan STP) 

u=undetected at practical quantitation limit in parentheses 

DDT and PCB Concentrations in Sediment Cores

Sediment cores were collected to reconstruct the history of DDT and PCB deposition in Osoyoos 

Lake and the lower Okanogan River. A relatively deep core (approximately 45 cm) was 

obtained at the southern end of Osoyoos Lake (Table 9). Penetration was not as deep in the core 

collected near the Okanogan River mouth (Table 10). Deposition of fine sediments near the 

mouth of the Okanogan River may not have occurred until the formation of Lake Pateros 

(consequently backing-up the Okanogan River near the mouth) in 1967, and, therefore, bottom

sediments pre-dating 1967 are probably absent at this site. 

Table 9: DDT & PCB Concentrations in Osoyoos Lake Sediment Core 

Collected June, 2001 (ng/g, dw) 

Depth 

Interval 

(cm)

Year 

Deposited %TOC

4,4'-

DDE 

4,4'-

DDD 

4,4'-

DDT 

tDDT PCB1260 PCB1254 PCB1248 tPCBa

0-1 2001.0 4.37% 35 43 3 81 u(2.8) u(2.8) 1.1 1.1

1-2 1999.0 3.78% 32 42 0.79 75 u(5.4) u(5.4) u(5.4) nd

2-3 1998.8 4.25% 75 77 96 248 u(5.4) u(5.4) 2.2 2.2

3-4 1998.5 4.03% 34 39 13 86 u(5.3) u(5.3) u(5.3) nd

4-5 1998.3 4.47% 39 44 u(5.3) 83 u(2.6) 0.79 u(2.6) 0.79

6-7 1996.5 4.23% 37 20 1 58 u(2.5) 0.74 u(2.5) 0.74

8-9 1993.5 4.05% 37 38 13 88 u(2.3) u(2.3) 1.2 1.2

10-11 1991 3.93% 38 43 4 85 u(2.2) u(2.2) 1.1 1.1

13-14 1988 3.99% 35 45 4.8 85 u(2.0) u(2.0) 1.0 1.0

16-17 1985 3.72% 39 47 1.8 88 u(1.9) 0.75 u(1.9) 0.75

19-20 1981 3.60% 36 54 6.4 96 u(1.7) u(1.7) 0.85 0.85

23-24 1976 3.04% 92 150 12 254 u(3.3) 2.7 2.0 4.7

27-28 1967 2.43% 42 92 1.6 136 u(2.9) 1.4 u(2.9) 1.4

31-32 1957 2.12% 21 48 3.5 72 u(2.7) u(2.7) u(2.7) nd

35-36 1945 1.93% 3.7 8.6 u(0.61) 12 u(2.5) u(2.5) u(2.5) nd

39-40 1932 1.76% 2.2 5.1 u(0.56) 7.3 u(2.2) u(2.2) u(2.2) nd

44-45 1917 1.76% u(0.55) 0.22 u(0.55) 0.22 u(2.2) u(2.2) u(2.2) nd a

Aroclors 1242, 1232, 1221, and 1016 not detected at practical quantitation limits of 1.7 – 5.4 ng/g

u=undetected at practical quantitation limit in parentheses

Page 20 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Table 10: DDT and PCB Concentrations in Lower Okanogan River Sediment Core 

Collected September, 2001 (ng/g, dw)

Depth 

Interval 

(cm)

Year 

Deposited %TOC

4,4'-

DDE 

4,4'-

DDD 

4,4'-

DDT 

tDDT PCB1260 PCB1254 PCB1248 t-PCBa

0-2 2001 1.95% 6.9 1.9 u(0.63) 8.8 u(2.5) 0.89 u(2.5) 0.89

6-8 1998 1.72% 7.1 2.2 u(0.53) 9.3 u(2.1) 0.74 u(2.1) 0.74

12-14 1995 1.62% 7.5 2.6 u(0.49) 10 u(2.0) 1.1 u(2.0) 1.1

18-20 1992 1.48% 6.8 2.5 u(0.45) 9.3 u(1.8) 0.88 u(1.8) 0.88

24-26 1988 1.40% 8.0 3.0 u(0.44) 11 u(1.8) 1.1 u(1.8) 1.1

28-30 1984 1.41% 9.9 4.4 0.65 15 0.44 1.5 u(1.7) 1.94

30-32 1981 1.44% 14 8.0 1.1 23 0.74 2.1 u(1.7) 2.84

a

Aroclors 1242, 1232, 1221, and 1016 not detected at practical quantitation limits of 1.7 – 2.5 ng/g

u=undetected at practical quantitation limit in parentheses 

Sediments in the core from Osoyoos Lake dated from 1917 whereas the oldest horizons from the 

river mouth were deposited circa 1981, although the lack of background 210Pb from the mouth 

leaves some doubt about the accuracy of age estimates at this site. Sedimentation rates appear to 

be about three times higher near the mouth (1.6 cm/yr) compared to southern Osoyoos Lake (0.5 

cm/yr). 

DDT concentrations in the Osoyoos Lake core were an order of magnitude higher than sediments 

of approximately equal age from the Okanogan River mouth. Differences between these 

locations are probably due to dilution by relatively clean sediments from the Similkameen River 

which supplies the vast majority of sediments to the lower Okanogan River (Ehinger, 1994). 

Evidence indicating the Similkameen River provides a diluting influence comes from data 

showing low (≤2 ng/g) to undetectable DDT concentrations and other chlorinated organics in 

Similkameen River bottom sediments (D. Hurst, written communication; Johnson and 

Polotnikoff, 2000). Similkameen River sediments have also been shown to contain very little 

organic carbon content which probably accounts for the lower TOC in sediments from the 

Okanogan River mouth. 

The reconstructed history of DDT contamination in Osoyoos Lake shows initial DDT 

concentrations barely detectable or very low from 1917 until 1945 (Figure 4), where its presence 

may be due to limited mixing by burrowing organisms. DDT concentrations rose sharply after 

1945, peaked around 1976, then declined sharply between 1976 and 1981. DDT concentrations 

show little change during the subsequent two decades. 

A large spike in DDT concentrations was seen in sediments deposited around late 1998 or early 

1999. Concentrations of t-DDT (250 ng/g) were triple those seen during the 1980s and 1990s 

(60-100 ng/g). This sample had a remarkably high concentration of 4,4’-DDT relative to 4,4’-

DDE and 4,4’-DDD, constituting 39% of t-DDT. Other horizons had 4’4-DDT making up a 

maximum of 15% t-DDT, but was generally 5% or less. The high proportion of 4,4’-DDT 

coupled with the anomalous concentration suggests the occurrence of a large disturbance and 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 21 
subsequent input of agricultural soils where DDT is degraded at a much slower rate than in the 

aquatic environment (Harris et al., 2000). The presence of high levels of undegraded DDT could 

possibly have resulted from a spill or illegal dumping during the late 1990s. 

DDT concentrations at the Okanogan River mouth show a decreasing trend in the 1980s 

followed by steady concentrations during the last decade (Figure 4). The decline in DDT 

concentrations during the 1980s is most likely the tail end of a longer and steeper decline, but the 

limited core depth only permitted analysis back to 1981. The late 1990s spike seen in Osoyoos 

Lake DDT concentrations did not appear in the sediment core from the mouth. It is possible that 

it could have been missed if this spike was a singularly discreet episode. Alternatively, it may 

take several years for a contaminant pulse to travel from Osoyoos Lake sediments to the mouth 

of the Okanogan River. 

PCB concentrations in core samples were low, with concentrations generally around 1 ng/g tPCB (Figures 3 and 4). The pattern of PCB concentrations in both cores appeared to mirror 

DDT concentrations, including a late 1990s spike in the Osoyoos Lake core. The peak PCB 

concentration was found in the 1976 horizon in Osoyoos Lake sediments followed by a sharp 

decline 5 years later. No PCBs were detected in sediments deposited in 1957 or earlier. 

Unlike DDT concentrations which were much higher in Osoyoos Lake sediments, PCB 

concentrations were similar in core samples from both locations. This may suggest that lowlevel PCB sources such as STPs between the lake and the river mouth keep depositional areas 

enriched with low levels of PCBs. 

0

50

100

150

200

250

300

1915 1930 1945 1960 1975 1990 2005

Year

t-D

D

T (ng/g, dw)

0

5

10

15

20

25

30

t-P

C

B (ng/g, dw)

DDT

PCB

Figure 4: T-DDT and t-PCB Concentrations in Osoyoos Lake Sediment Core 

Page 22 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
0

5

10

15

20

25

1980 1985 1990 1995 2000 2005

Year

t-D

D

T (ng/g, dw)

0

1

2

3

4

5

t-P

C

B (n

g

/g, d

w)

DDT

PCB

Figure 5: T-DDT and t-PCB concentrations in lower Okanogan River sediment core

DDT and PCB Concentrations in Fish Tissue

Carp, mountain whitefish, and smallmouth bass were collected from three locations on the lower 

Okanogan River during 2001, except for carp which were not found at the Monse location. 

Samples at each location were sorted by size to assess this as a factor affecting contaminant 

accumulation. Samples were analyzed for DDT, PCBs, and lipid content in fillet. Table 11 

shows the results. 

Concentrations of t-DDT ranged from 30 to 600 ng/g, while t-PCB concentrations were much 

lower, ranging from 2 ng/g or less to 40 ng/g. Mountain whitefish and carp generally had much 

higher DDT and PCB concentrations than smallmouth bass. 

4,4’-DDE was the primary DDT component, exceeding the NTR criterion of 32 ng/g in all 

samples except smallmouth bass from the Riverside-Omak location. 4,4’-DDD concentrations 

were much lower with only one sample – Riverside-Omak carp – exceeding the NTR criterion of 

45 ng/g. None of the samples exceeded the 4,4’-DDT criterion. 

PCB-1254 made up the highest proportion of t-PCB in most samples, followed by PCB-1260 and 

PCB-1248. PCB-1242 was not detected aside from a low concentration (4.0 ng/g) in one 

Riverside-Omak carp sample. All carp and mountain whitefish met or exceeded the NTR 

criterion for PCBs (5.3 ng/g). In contrast, only one of the nine smallmouth bass samples had tPCB greater than the criterion. 

Lipid content, size, and location all appear to be factors in DDT and PCB concentrations within 

each species. Figures 6 and 7 show lipid-normalized t-DDT and t-PCB concentrations grouped 

by species for each location. Carp and mountain whitefish collected at the Oroville location 

clearly had higher lipid-normalized t-DDT concentrations than from other sites. Smallmouth 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 23 
bass from Monse had lipid-normalized t-DDT concentrations slightly higher than those collected 

from the Oroville and Riverside-Omak locations. 

Lipid-normalized t-PCB concentrations generally followed the same location pattern as with 

lipid-normalized t-DDT; the highest concentrations were at Oroville, followed in decreasing 

order by Riverside Omak and Monse. However, carp from Oroville and Riverside-Omak had 

similar concentrations, and the lipid-normalized t-PCB concentrations in the large-sized 

smallmouth bass from Monse were much higher than those from other locations. 

In nearly all cases, the largest fish composites (greatest mean total length) had the highest t-DDT 

and t-PCB concentrations for each species at each site. This was generally the case in lipidnormalized concentrations as well. It should be noted that species were not sampled by size 

class in order to compare locations according to size. For instance, carp size classes are not 

necessarily a valid comparison between Oroville and Riverside-Omak, since all composites from 

Riverside-Omak had a larger or nearly equal average size than those from Omak. Grouping by 

size was done to assess the relationship with contaminant concentrations within each location. 

Page 24 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 25 

Table 11: DDT and PCB Concentrations in Fillet of Fish from the Lower Okanogan River, 200

Sample 

No. (02-) Species Location 

N Per 

Comp. 

Mean 

Length 

(mm)

Mean 

Weight

(g) 

Mean 

Age 

(yr)

Lipid 

(%)

4,4'- 

DDE 

4,4'- 

DDD 

4,4'- 

DDT t-DDT 

128230 CARP Oroville 8 552±25 2,135±432 nc 1.04 290 37 u(1.6) 327 128231 “ “ 8 514±7 1,749±93 nc 0.84 410 24 u(1.5) 434 128232 “ “ 7 463±37 1,348±354 nc 1.55 210 38 0.6 249 128233 “

Riv. - 

Omak 8 619±20 3,345±385

nc 

3.43 270 41 u(1.5) 311 

128234/35 “ “ 8 584±12 2,740±481 nc 3.00 220 29 u(1.6) 249 

128236 “ “ 8 550±13 2,393±320 nc 3.09 210 26 u(1.6) 236 128237 MTWF Oroville 8 363±21 315±76 5 0.79 460 38 17 515 128238 “ “ 8 330±7 229±54 4 1.31 330 21 9.8 361 128245 “ “ 8 290±14 167±21 2 1.17 150 19 5.1 174 

128239/40 “

Riv. - 

Omak 10 365±19 453±87

6 

4.26 520 62 17 599 

128241 “ “ 10 334±13 331±69 5 4.70 330 39 13 382 128249 “ “ 10 284±20 209±48 3 4.58 160 19 6.0 185 128242 “ Monse 9 326±48 301±134 4 2.96 110 14 3.2 127 128243 “ “ 9 246±7 127±18 2 3.07 120 16 3.7 140 128244 “ “ 8 220±15 81±14 2 1.55 73 4.9 2.8 81 128246 SMBS Oroville 1 424 1,111 5 3.21 230 44 14 288 128247 “ “ 4 316±28 472±138 nc 1.39 64 11 2.3 77 128248 “ “ 1 248 206 1 1.60 100 3.5 0.8 104 128250 “

Riv. - 

Omak 7 350±56 685±377

4 

1.17 78 6.5 3.1 88 

128251 “ “ 7 287±11 320±47 3 1.42 55 2.9 1.6 60 128252 “ “ 7 213±28 133±50 1 0.95 25 1.7 0.8 28 128253 “ Monse 5 327±12 496±41 3 1.35 150 14 3.0 167 128254 “ “ 5 276±32 276±98 3 1.12 89 11 1.6 102 128255 “ “ 5 200±10 98±18 1 0.70 59 3.4 0.8 63 

aAroclors 1268, 1262, 1242, 1232, 1221, and 1016 not detected at practical quantitation limits of 2.7 – 5.4 ng/g bIncludes 4.0 ng/g PCB-1242 

MTWF=mountain whitefish SMBS=smallmouth bass nc=not calculated u=undetected at practical quantitation limit in parentheses 

nd=not detected
0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

Lg Md Sm Lg Md Sm Lg Md Sm Lg Md Sm Lg Md Sm Lg Md Sm Lg Md Sm Lg Md Sm

t-DDT (ng/g lipid)

CARP

Oroville Riv-Omak Oroville Riv-Omak Monse Oroville Riv-Omak Monse

MOUNTAIN WHITEFISH SMALLMOUTH BASS

Figure 6: Lipid-Normalized t-DDT Concentrations in Lower Okanogan River Fish Muscle Ordered 

by Mean Length of Fish in each Composite (Lg=large, Md=medium, Sm=small) and Location for 

each Species

0

500

1,000

1,500

2,000

2,500

3,000

3,500

Lg Md Sm Lg Md Sm Lg Md Sm Lg Md Sm Lg Md Sm Lg Md Sm Lg Md Sm Lg M

t-PCB (ng/g lipid)

Oroville Riv-Omak Oroville Riv-Omak Monse Oroville Riv-Omak Mo

d Sm

CARP

nse

MOUNTAIN WHITEFISH SMALLMOUTH BASS

Figure 7: Lipid-Normalized t-PCB Concentrations in Lower Okanogan River Fish Muscle Ordered 

by Mean Length of Fish in Each Composite (Lg=large, Md=medium, Sm=small) and Location for 

each Species

Page 26 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Loading Capacity 

The following sections contain a TMDL analysis of DDT and PCBs in the lower Okanogan 

River basin using the data collected during 2001-2002, or in some cases historical data 

(Appendix A) to describe or quantify DDT and PCB loading to the lower Okanogan River and 

Osoyoos Lake. 

Daily DDT and PCB Loads to the Lower Okanogan River and 

Osoyoos Lake 

DDT Loads Delivered Through Tributary Streams

Loads were calculated using the following equation: 

Load (mg/day) = Cw x (10-6 mg/ng) x Q x (86,400 s/day)

Where: 

• Cw (concentration in water) = concentration of DDT or PCBs in water 

(ng/l) 

• Q (discharge) = instantaneous flow, unless stated otherwise (l/s) 

DDT loads in tributaries were measured during a total of four rounds of sampling conducted 

during 1995 and 2001 (Table 12). As mentioned previously, sampling during 1995 represented 

low-flow conditions, with many stream channels dry and others (e.g. Tallant Creek) flowing due 

only to release of stored irrigation water (T. Neslen, OCCD, personal communication). To 

account for the intermittent flow (and resultant loading) in some streams, weighted mean loads 

were calculated for each stream by multiplying the mean loads by the percentage of times the 

stream was found flowing during sampling visits. The following formula describes calculation 

of the weighted mean load for each tributary: 

Weighted Mean Load = (sum of n loads/n) x (n/number of sample attempts)

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 27 
Table 12: Weighted Mean DDT Loads in Tributary Streams of Osoyoos Lake and the Lower 

Okanogan River Based on Water Column Samples Collected 1995-2002 (mg/day)

Location RM 

Samples/ 

Attempts 4,4'-DDE 4,4’-DDD 4,4’-DDT t-DDT 

Okanogan R. @ 

Osoyoos, BC 91.2 1/1 0.0 0.0 0.0 0.0

Haynes Creek (BC) 82.8 1/1 1.3 0.0 0.0 1.3

Nine Mile Creek 80.2 4/4 6.6 2.1 4.9 13.6

Tonasket Creek 77.8 2/4 12.4 0.0 8.4 20.8

Similkameen River 74.1 2/2 0.0 0.0 0.0 0.0

Mosquito Creek 67.4 3/4 1.0 1.0 0.0 2.0

Whitestone Creek 62.4 4/4 6.7 0.0 0.0 6.7

Antoine Creek 61.2 4/4 4.8 0.6 1.0 6.4

Siwash Creek 57.3 1/4 0.3 0.0 0.0 0.3

Bonaparte Creek 56.7 3/4 1.9 0.0 0.0 1.9

Aeneas Creek 52.9 3/4 1.5 0.0 0.0 1.5

Chewiliken Creek 50.7 1/2 0.0 0.0 0.0 0.0

Tunk Creek 45.0 2/4 0.0 0.0 0.0 0.0

Johnson Creek 40.6 2/4 0.0 0.0 0.0 0.0

Wanacut Creek 35.0 2/4 0.0 0.0 0.0 0.0

Omak Creek 32.0 3/4 0.0 0.0 0.0 0.0

Elgin Creek 28.4 4/4 14.4 0.6 7.1 22.0

Salmon Creek 25.7 1/4 2.5 0.0 0.0 2.5

Tallant Creek 19.5 2/4 46.6 10.5 68.6 125.7

Loup Loup Creek 16.9 2/4 trace 0.0 trace 0.1

Chiliwist Creek 15.1 2/4 0.6 0.0 0.0 0.6

Total = 100.4 14.7 90.1 205.2

trace = <0.05 mg/day

The t-DDT load from all tributaries combined average 205 mg/day, with 4,4’-DDE and 4,4’-

DDT comprising the bulk (93%) of the t-DDT load. Most of the DDT load delivered to the 

lower Okanogan River through tributary streams is from Tallant Creek (61% of t-DDT ), even 

though this stream was found to be flowing during only two of four attempts to sample it. Flow 

in Tallant Creek is limited to a few months per year when water is released from Leader Lake for 

irrigation. Therefore, DDT loads from Tallant Creek are probably best described as 

comparatively large, episodic, and difficult to accurately quantify without intensive 

investigation. 

Page 28 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 29 

Ninemile, Tonasket, and Elgin Creeks together account for a large remainder of the DDT loads 

from tributaries (27% of t-DDT). Ninemile and Elgin Creeks were among the four streams to 

have measurable DDT loads during all 1995 and 2001 sampling events. Whitestone and Antoine 

Creeks also had measurable DDT loads during all rounds of sampling. 

Mean DDT loads were higher during 1995 compared to 2001 (307 mg t-DDT /day vs. 104 mg tDDT/day, respectively) due primarily to the Tallant Creek samples collected during 1995. 

However, mean loads were similar between years when the contribution from Tallant Creek is 

removed (55 mg t-DDT /day in 1995; 104 mg t-DDT/day in 2001). 

Notable is the absence of any DDT load from the Similkameen River, which has the potential to 

deliver large loads due to its high flow. For instance, had 4,4’-DDE been detected at the very 

low practical quantitation limit (0.07 ng/l) during 2002 sampling, the resulting daily load (660 

mg/day) would have been an order of magnitude higher than the average daily loads of all other 

tributaries combined during 2001. 

DDT and PCB Loads Delivered Through STPs

Daily DDT and PCB loads from the Oroville, Omak, and Okanogan STPs are shown in Table 13. 

Loads were calculated from effluent sampling conducted during April and May 2001, and in 

May, 2002. 

Table 13: Mean DDT and PCB Loads in Lower Okanogan River Basin STPs Based on Whole 

Effluent Samples (DDT) and PCB Concentrations in STP Sludge Collected 2001-2002 (mg/day) 

Location RM n

4,4'-

DDE 4,4’-DDD 4,4’-DDT t-DDT t-PCBa

Oroville STP b 3 0.1 0.0 0.4 0.5 0.1 

Omak STP 29.9 3 0.0 0.0 0.0 0.0 1.3 

Okanogan STP 24.8 3 0.8 0.3 1.1 2.2 1.3 

a

Results shown are for PCB Aroclors 1260, 1254, 1248, 1242, 1232, 1221, and 1016 b

Similkameen River mile 4.0. The Similkameen River enters at Okanogan River mile 74.1 

Daily loads of DDT and PCBs were low at all three STPs sampled. Oroville and Okanogan 

STPs had daily DDT loads similar to the lowest measured loads in tributary streams. Daily loads 

in effluent were 2.7 mg t-DDT/day and 0.4 mg t-PCB/day from all three STPs combined. 

As shown previously, PCBs were present at substantial concentrations in sludge from all three 

treatment plants (200-270 ng/g t-PCB, dw). Since PCBs were difficult to detect in water, 

estimates can be made of PCBs discharged from STPs in the form of suspended particulate 

matter in effluent. Assuming the suspended solids in effluent are composed primarily of sludge, 

the estimated t-PCB load from STPs combined is approximately 2.7 mg/day using the following 

formula: 

mg PCB/day = mg PCB/kg sludge x (mg sludge/l effluent x [kg/106

 mg]) x l effluent/day 

Using sludge concentrations to estimate DDT loads yields an average combined t-DDT load of 

1.7 mg/day, similar to the combined load measured from whole effluent samples (2.7 mg tDDT/day). 
Page 30 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 

Calculation of DDT and PCB Loads and Loading Capacities of Osoyoos Lake and the Lower 

Okanogan River

Loads measured and delivered to the lower mainstem Okanogan River, theoretical loads based 

on tissue concentrations, and the lower Okanogan River’s capacity to assimilate DDT and PCBs 

are presented in this section and Table 14. 

Delivered loads are the weighted mean loads from tributary streams and STPs (12 and 13) and 

combined for each Okanogan River reach. 

Measured loads in the lower mainstem Okanogan River were calculated from DDT and PCB 

concentrations analyzed during May, 2002 (Table 5) and daily flows recorded at USGS gaging 

stations at Oroville, near Tonasket, and at Malott. 

Theoretical loads in this report represent the all the aquatic environmental impacts on fish tissue 

contaminant levels. This aquatic environment impact includes contaminant exposures from 

water, sediments and the food chain in the Okanogan River as a water contamination 

concentration that would reasonably be expected to result in fish tissue contamination that has 

been observed in the most recent Okanogan River fish tissue samples. Theoretical loads were 

determined using DDT and PCB concentrations in fish tissue back-calculated to water 

concentrations using BCFs for each chemical. The most contaminated species from each reach 

was used to calculate theoretical loads (mountain whitefish for lower Okanogan River reaches 

[Table 11], lake whitefish for Osoyoos Lake [Appendix A]). 

Loading capacities were calculated using NTR human health criteria and Ch. 173-201A WAC 

chronic aquatic life criteria (Table 1). Flows used to calculate loading capacities were harmonic 

means recorded at USGS gaging stations (Table 2). 

 

DDT loads delivered through tributaries and STPs were generally one to three orders of 

magnitude below the measured loads, theoretical loads, and the loading capacities of each reach 

indicating that exogenous DDT input accounts for only a minor amount of the load in the lower 

mainstem Okanogan River and Osoyoos Lake. 

Since no PCBs were detected in lower Okanogan River water it is not feasible to compare 

delivered loads to measured loads. Like DDT, however, delivered PCBs appear to be orders of 

magnitude below theoretical loads and loading capacities in all reaches except Osoyoos Lake 

where PCBs were undetectable in edible fish tissue. 

PCBs loads consisted of a trace amount (0.1 mg t-PCB/day) from the Oroville STP, representing 

about 0.01% of the loading capacity of the Okanogan River near Tonasket based on the State 

criterion. The combined t-PCB loads from the Omak and Okanogan STPs (2.6 mg t-PCB/day) 

was about 0.3% of the loading capacity of the Okanogan River at Malott. 
Table 14: Total Load Delivery, Measured Loads, Theoretical Loads, and Loading Capacities of DDT and 

PCBs at Several Osoyoos Lake and Lower Okanogan River Reaches (mg/day)

Reach RM 4,4'-DDE 4,4’-DDD 4,4’-DDT t-DDT t-PCB

Osoyoos Lake; RM 91.2- 79.0

Total load delivered to reach (tribs.) 91.2 – 80.2 8 2 5 15 0 

Theoretical Load (US Waters) 82.5 – 79.0 17,000 10,000 770 25,000 0 

Loading cap. @ Osoy. Lk. outlet 79.0 800 1,100 800 1,400 230

Near Oroville; RM 79-77.4

Total load delivered to reach (tribs.) 77.8 12 0 8 21 0 

Cumulative load 77.8 12 0 8 21 0 

Measured load @ Oroville 77.4 660 830 0 1,500 0 

Theoretical Load 77.3 – 76.4 7,800 650 280 8,700 820a

Loading capacity @ near Oroville 74.1 800 1,100 800 1,400 230 

Near Tonasket; RM 77.4-50.7

Total load delivered to reach (tribs. and STPs) 74.1 – 52.9 16 2 1 19 traceb

Cumulative load 77.4 – 52.9 680 830 1 1,500 traceb

Measured load @ Riverside 40.6 2,600 1,700 0 4,300 0

Theoretical Load 41.0 – 30.7 41,000 4,900 1,500 45,000 6,500a

Loading capacity near. Tonasket 50.7 3,900 5,500 3,900 6,500 1,100

Near Malott; RM 50.7-17.0

Total load delivered to reach (tribs. and STPs) 50.7 – 19.5 64 11 77 152 3b

Cumulative load 50.7 – 19.5 2,700 1,700 77 4,500 3b

Measured load @ Malott 17.0 2,200 2,000 0 4,200 0 

Theoretical Load 10.5-4.9 13,000 1,500 400 13,000 2,600a

Loading capacity @ Malott 17.0 4,000 5,600 4,000 6,700 1,100

Mouth; RM 16.0-0.0

Total load delivered to reach (tribs.) 16.9 – 15.1 1 0 0 1 0 

Cumulative load 17.0 – 15.1 2,200 2,000 0 4,200 0 

Theoretical Load 10.5-4.9 13,000 1,500 400 13,000 2,600a

Loading cap. @ Okan. R. mouth 0.0 4,000 5,600 4,000 6,700 1,100

trace = <0.5 mg/day a

Results shown are for PCB Aroclors 1268, 1262, 1260, 1254, 1248, 1242, 1232, 1221, and 1016 b

Results shown are for PCB Aroclors 1260, 1254, 1248, 1242, 1232, 1221, and 1016 

Using Washington State and NTR DDT criterion, the measured loads in the lower Okanogan 

River did not exceed loading capacities except for t-DDT in the Oroville reach where it was 15% 

above the loading capacity. Measured loads of 4,4’-DDE, 4,4’-DDD, and 4,4’-DDT were below 

the loading capacities at Oroville when the NTR criteria were used to calculate the loading 

capacities of these compounds. 

Although measured loads of DDT shown in Table 14 represent the only instance when accurate 

instantaneous load assessments have been available for the lower mainstem Okanogan River, 

these loads may actually overestimate annual average DDT loads in the water column. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 31 
Measured loads were calculated during high-flow conditions in May when TSS concentrations 

are typically at or near their annual peak, suggesting that DDT (which sorbs to particulate matter) 

may also be at its highest concentration. A potentially more accurate measurement of average 

annual loads could be obtained from tissues in fish, which integrate concentrations over time and 

space. 

Theoretical loads of DDT and PCBs were much higher than measured loads in all reaches of the 

lower Okanogan River, with the exception of 4,4’-DDD at Oroville where the theoretical and 

measured loads were similar. The comparatively high theoretical loads (derived from tissue 

concentrations) indicate that the relationship with measured loads (derived from water column

concentrations) is inconsistent with the BCFs used to link tissue and water concentrations. The 

BCFs for both DDT and PCBs appear to overestimate the theoretical water concentrations that 

should lead to certain concentrations in tissue. 

Source Assessment 

Historical DDT use in the Okanogan Basin, primarily on orchard and other agricultural lands, 

has resulted in contamination of the aquatic environment. Although banned in the U.S. as a 

pesticide in 1972, DDT and its breakdown products have persisted, accumulating at high 

concentrations in lower Okanogan River and Osoyoos Lake fish as shown in this and other 

investigations (e.g. Johnson and Norton, 1990; Davis and Serdar, 1996; Serdar et al., 1998). 

PCBs are a ubiquitous environmental contaminant and, like DDT, they have persisted in the 

aquatic environment and continue to accumulate in fish tissue even though production of PCBs 

was banned 25 years ago. However, due to the difficulty in detecting PCBs in the water column, 

little effort has been made to track down the source(s) of PCBs in the lower Okanogan River 

system. 

It is notable that while PCBs in edible fish tissues may be a human health concern at the levels 

reported here (2 – 42 ng/g); it is not uncommon to find similar levels in other Washington waters 

where no discernible sources of PCB exist (Davis and Johnson, 1994; Davis et al., 1998). 

Conversely, waterbodies with known point sources of PCBs such as the Spokane River have 

PCB concentrations in fish one to two orders of magnitude higher than those found in the lower 

Okanogan River (Ecology, 1995). 

The source of DDT delivered to tributaries has not been examined. Presumably, DDT bound to 

agricultural soils makes its way to streams directly or through rivulets formed during rainstorms, 

snowmelt, or irrigation. Due to the low solubility of DDT compounds in water, the mechanism

of delivery probably involves particle transport rather than leaching and dissolution of DDT. 

Transport of agricultural soil particles to streams depends on a variety of factors. Within 

streams, increasing flows result in higher TSS concentrations. For streams where DDT was 

detected during all four rounds of sampling, flows were a major positive determinant of TSS 

concentrations in Ninemile Creek (r2

 = 0.89), Antoine Creek (r2 = 0.89) and Elgin Creek (r2 = 

0.94) but less so in Whitestone Creek (r2

 = 0.27). However, higher concentrations of DDT 

compounds were not a function of higher TSS concentrations, and in some cases (Ninemile and 

Page 32 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Elgin) showed a negative relationship with TSS. Only Whitestone Creek showed DDT 

concentrations highly dependent on TSS (t-DDT; r2

 = 0.97). 

Differences in TSS levels among tributaries account for about 25-40% of the variation in 

concentrations and loads of DDT based on an analysis of pooled tributary data. However, the 

regression used to explain this relationship is leveraged largely by data from Tallant Creek with 

high TSS (122 mg/l) and exceptionally high DDT (0.5 μg t-DDT/l). Absent the Tallant Creek 

data, TSS does little to explain DDT concentrations. 

The lack of a strong functional relationship between TSS and DDT concentrations suggests 

suspended solids in the water columns of tributaries are largely composed of particles other than 

contaminated soils. In general, orchards and other agricultural lands in the lower Okanogan 

River Basin are on shallow slopes, soils are well-drained, grass is maintained as ground cover in 

orchards, and irrigation is sprinkler or drip rather than rill and furrow. These conditions do not 

lend themselves to substantial erosion of agricultural soils as occurs, for instance, in the lower 

Yakima River Basin where TSS and DDT are highly correlated in tributaries (Johnson et al., 

1988; Joy and Patterson, 1997). 

During the initial investigation of DDT in Okanogan basin streams, GIS covers were used to 

overlay DDT concentrations on the amount of steep slopes and percentage of orchard lands in 

each tributary basin. Although this was conducted only on a cursory basis, these factors 

appeared to correlate poorly with DDT concentrations in streams (A. Johnson, Ecology, personal 

communication). 

In urban areas, STPs may serve as a funnel for waterborne contaminants. The wastewater 

system could potentially deliver contaminants such as DDT that were used historically for nonagricultural purposes such as mosquito control and carried off soil via stormwater to STPs. DDT 

and PCBs could also potentially end up in STPs as a result of improper storage and disposal. 

Other possible DDT and PCB sources and delivery mechanisms that were not revealed by 

sampling may include groundwater, deposition of airborne material, illegal dumping, and erosion 

of contaminated bank material. It is also possible that the streams sampled deliver large DDT 

and PCB loads that were not captured during sampling, and therefore tributary sampling 

conducted during 1995 and 2001 was not representative. Another possibility is that small nearbank drainages went unnoticed during tributary sampling. 

These sources and delivery mechanisms probably contribute unaccounted quantities of DDT and 

PCBs to some extent. However, if the continual delivery of significant DDT quantities to the 

lower Okanogan River and Osoyoos Lake through one or more of these mechanisms results in 

water column concentrations comparable to fish tissue concentrations (using a BCF conversion), 

then the water column concentrations should be present at higher concentrations. 

In consideration of the factors previously mentioned, it is unlikely that significant exogenous 

sources of DDT and PCBs have gone unaccounted. There are essentially two scenarios to 

explain DDT and PCB accumulation in fish tissues. The first explanation is that the BCF used to 

calculate the NTR water criteria for DDT and PCBs are inaccurate. These BCFs (53,600 for 

DDT and 31,200 for PCBs) were derived specifically for criteria development, not for siteLower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 33 
specific assessment. It is possible that at least some species in the lower Okanogan River 

concentrate DDT and PCBs by factors one to two orders of magnitude higher than the criteria 

BCF. 

A higher BCF for DDT in fish makes it possible to explain high tissue concentrations relative to 

water. For the present DDT listings in the lower Okanogan River and Osoyoos Lake, BCFs 

ranging from 66,000 to 2,800,000 would explain reported tissue concentrations at DDT 

concentrations in water. These BCFs are not unreasonable considering EPA cites seven 

examples of field-measured BCFs for DDT in freshwater fish (whole body) greater than one 

million (Ambient Water Quality Criteria for DDT; EPA, 1980a). BCFs are generally lower for 

muscle than whole body, but EPA (1980a) lists BCFs of 460,000 and 370,000 for lake trout 

(Salvelinus namaycush) and cisco (Coregonus sp.) muscle, respectively. EPA reports a narrower 

range freshwater fish BCFs for PCBs in their criteria development document for PCBs (EPA, 

1980b), with a maximum whole body BCFs of 270,000 (Pimephales promelas; Aroclors 1242 

and 1260) and muscle BCFs less than 10,000 (Salvelinus fontinalis and Oncorhynchus mykiss

[formerly Salmo gairdneri]). 

The second plausible explanation for high DDT and PCBs in fish relative to water column

concentrations is that the exposure route is something other than water. Specifically, fish may be 

accumulating DDT and PCBs through contaminated sediments or diet. The lack of significant 

exogenous DDT sources combined with high fish tissue concentrations suggests that the bed 

sediments are the primary route of exposure in lower Okanogan River and Osoyoos Lake fish. 

It is not unreasonable to assume that re-suspended Osoyoos Lake sediments account for nearly 

all of the measured DDT loads in the lower Okanogan River. Osoyoos Lake bed sediments resuspended during high flows, spring turnover, or other perturbations may account for the 

disparity between DDT load delivery and measured loads in the water column of the lower 

mainstem Okanogan River. These differences can be explained by assuming suspended solids in 

the water column are composed of re-suspended surficial (top 2-cm) Osoyoos Lake bed 

sediments. Table 15 compares measured loads with loads calculated by assuming TSS at the 

Osoyoos Lake outlet is composed of the same material as the top 2-cm of the Osoyoos Lake 

sediment core. Loads from re-suspended Osoyoos Lake bed sediments match well with the 

measured DDT loads at Riverside and Malott, although measured loads at Oroville should be 

approximately 150% higher. Relative concentrations of DDT compounds in measured loads (i.e. 

4,4’-DDE ≈ 4,4’-DDD >> 4,4’-DDT) are similar to concentrations in Osoyoos Lake bed 

sediment, further indicating that measured loads may originate from sediment re-suspension. 

CCT conducted a longitudinal transect of DDT in 40 lower Okanogan River sediments from the 

Osoyoos Lake outlet to the mouth during 2001 (Hurst and Stone, 2002; D. Hurst, written 

communication). Aside from two locations, little DDT was found. Sixty percent of the sites had 

DDT (t-DDT) less than the detection limit (0.5 ng/g) and another 35% had concentration 1-10 

ng/g (mostly less than 2 ng/g). The only significant DDT levels were found just below the 

Osoyoos Lake outlet (but upstream of Zoesel Dam) at 46 ng/g t-DDT and just downstream of 

Elgin Creek (260 ng/g t-DDT). The site upstream of Zoesel Dam probably collects much of the 

same settling particulate material as southern Osoyoos Lake since it is within the impounded 

reach of the river (although technically not part of Osoyoos Lake). 

Page 34 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
The reason for the high DDT in sediments downstream of Elgin Creek is not certain, although 

this stream has chronically high DDT concentrations and moderate TSS levels. The Elgin Creek 

site may also be one of the few locations in the lower mainstem Okanogan River where very fine 

material is able to accumulate. Visual inspection reveals only a few large areas of fine sediment 

deposits in the mainstem river, an observation shared by investigators conducting the CCT 

survey.

Table 15: Measured Loads of DDT and PCBs at Several Lower Okanogan River Reaches 

Compared to Loads Estimated from Re-suspension of Surficial Osoyoos Lake Bed Sediments 

(mg/day)

Reach RM 

4,4'-

DDE 

4,4’-

DDD 

4,4’-

DDT t-PCBa t-DDT 

Measured load @ Oroville 77.4 660 830 0 1,500 0 

Measured load @ Riverside 40.6 2,600 1,700 0 4,300 0

Measured load @ Malott 17.0 2,200 2,000 0 4,200 0 

Loads calculated from re-suspension of surficial (top 2-cm) Osoyoos Lk. bed sediments 1,700 2,200 100 4,000 30 

a

Results shown are for PCB Aroclors 1260, 1254, 1248, 1242, 1232, 1221, and 1016 

Load and Wasteload Allocations 

DDT and PCB Load Allocations in Tributary Streams

DDT and PCB load allocations (LAs) for tributary streams are shown in Table 16. LAs were set 

at loading capacities. For tributaries with weighted mean loads below loading capacities, LAs 

were set at current loading levels. Since DDT and PCBs are persistent bioaccumulative 

chemicals and have not been found at acutely toxic concentrations in the present study, LAs for 

tributary streams may be set at monthly or even yearly averages, but are expressed as daily loads 

for consistency within this report. 

Setting LAs for the Okanogan River at Osoyoos, B.C. and the Similkameen River was more 

difficult since no DDT or PCBs have been detected at either location, yet they potentially deliver 

substantial DDT/PCB loads even while concentrations remain undetectable. Major differences 

in laboratory quantitation limits between sampling conducted during 1995 and later in 2002 

made a logical approach to LAs even more difficult. 

LAs for the Okanogan River at Osoyoos, B.C. (where the river enters Osoyoos Lake) were set at 

loading capacities for this location. Setting LAs for the Okanogan River at Osoyoos, B.C. is 

more practical than setting LAs farther downstream in mid-lake at the Canadian border. 

For the Similkameen River, LAs were set at average loads calculated from flows and one-half 

the practical quantitation limits during sampling in 1995 and 2002. Although this may initially 

seem an arbitrary approach, LAs are well within the loading capacities of the Similkameen River 

and account reasonably well for the increased DDT loads measured in the lower Okanogan River 

downstream of the Similkameen River confluence. (see Table 14). 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 35 
The following streams would require load reductions in order to meet LAs; Haynes Creek (4,4’-

DDE, t-DDT), Ninemile Creek (4,4’-DDE, 4,4’-DDT, t-DDT), Tonasket Creek (4,4’-DDE, 4,4’-

DDT, t-DDT), Mosquito Creek (4,4’-DDE, 4,4’-DDD, t-DDT), Whitestone Creek (4,4’-DDE), 

Antoine Creek (4,4’-DDE, t-DDT), Elgin Creek (4,4’-DDE, 4,4’-DDT, t-DDT), and Tallant 

Creek (4,4’-DDE, 4,4’-DDD, 4,4’-DDT, t-DDT). 

Table 16: DDT and PCB Load Allocations for Individual Tributary streams (mg/day)

Stream/Reach RM 4,4'-DDE 4,4'-DDD 4,4'-DDT t-DDT t-PCB 

Osoyoos Lake; RM 91.2-80.2

Okanogan River @ Osoyoos BC 91.2 796.3 1133.8 796.3 1349.7 229.5

Haynes Creek BC 82.8 0.3 0.0 0.0 0.5 0.1

Ninemile Creek 80.2 2.0 2.1 2.0 3.4 0.6

Sum = 798.6 1135.9 798.3 1353.6 230.2

Near Oroville; RM79-77.4 

Tonasket Creek 77.8 4.9 0.0 4.9 8.4 1.4

Sum = 4.9 0.0 4.9 8.4 1.4

Near Tonasket; RM 77.4-50.7 

Similkameen River 74.1 998.7 998.7 1028.1 3025.6 791.0

Mosquito Creek 67.4 0.4 0.5 0.0 0.6 0.1

Whitestone Creek 62.4 5.9 0.0 0.0 6.7 1.7

Antoine Creek 61.2 1.9 0.6 1.0 3.3 0.6

Siwash Creek 57.3 0.3 0.0 0.0 0.3 0.1

Bonaparte Creek 56.7 1.9 0.0 0.0 1.9 0.8

Aeneas Creek 52.9 1.5 0.0 0.0 1.5 0.8

Chewiliken Creek 50.7 0.0 0.0 0.0 0.0 0.1

Sum = 1010.6 999.8 1029.1 3039.9 795.2

Near Malott; RM 50.7-17.0 

Tunk Creek 45.0 0.0 0.0 0.0 0.0 1.1

Johnson Creek 40.6 0.0 0.0 0.0 0.0 0.4

Wanacut Creek 35.0 0.0 0.0 0.0 0.0 0.2

Omak Creek 32.0 0.0 0.0 0.0 0.0 4.3

Elgin Creek 28.4 1.8 0.6 1.8 3.1 0.5

Salmon Creek 25.7 2.5 0.0 0.0 2.5 1.0

Tallant Creek 19.5 0.2 0.3 0.2 0.4 0.1

Sum = 4.5 0.9 2.0 6.0 7.6

Mouth; RM 17.0-0.0 

Loup Loup Creek 16.9 0.0 0.0 0.0 0.1 0.1

Chiliwist Creek 15.1 0.6 0.0 0.0 0.6 0.4

Sum = 0.6 0.0 0.0 .07 .05

Page 36 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
DDT and PCB Waste Load Allocations in STPs

DDT and PCB waste load allocations (WLAs) for STPs are in Table 17. WLAs were determined 

from design criteria flows and criteria concentrations for DDT and PCBs. Like the LAs for 

tributaries, WLAs are expressed as daily loads for consistency but may be set as monthly or 

yearly averages. 

Table 17: DDT and PCB Waste Load Allocations for STPs (mg/day)

STP RM Design Flow (l/s) 4,4'-DDE 4,4'-DDD 4,4’-DDT t-DDT t-PCB

Orovillea e 21.6 1.1 1.6 1.1 1.9 0.3

Tonasketd 56.4 17.5 0.9 1.3 0.9 1.5 0.5

Omakb 29.9 82.8 4.2 6.0 4.2 7.2 1.2

Okanoganc 24.8 23.7 1.2 1.7 1.2 2.0 0.3

Criteria (ng/l) = 0.59 0.83 0.59 1.0 0.17

a

NPDES permit WA-002239-0 

b

NPDES permit WA-002094-0 

c

NPDES permit WA-002236-0 

d

NPDES permit WA-005233-7 

e

Similkameen River mile 4.0. The Similkameen River enters at Okanogan River mile 74.1 

Daily loads measured during 2001-2002 (Table 13) are generally consistent or lower than WLAs. 

Exceptions are small exceedances of t-PCB at Omak and Okanogan STPs, and t-DDT at the 

Okanogan STP. It is not known if the potential discharge of contaminants is within the Tonasket 

WLA. The current discharge for the city of Tonasket has not been sampled due to the Tonasket 

WWTP beginning its discharge to the river after the samples were taken for the current TMDL 

assessment report. 

DDT and PCB Load Allocations for Sediments

Table 18 shows DDT and PCB load allocations for exogenous sources (tributary streams and 

STPs), bottom sediments, and loading capacities of successive Osoyoos Lake and lower 

Okanogan River reaches. LAs for bottom sediments were calculated as the difference between 

the cumulative LAs/WLAs and the loading capacity of each reach. 

LAs for the Okanogan River at Osoyoos, B.C. constitute all of the loading capacities at Osoyoos 

Lake and the Okanogan River at Oroville. The added loading capacity of the Similkameen River 

provides for bottom sediment DDT LAs of about one-half the loading capacities at reaches 

below Oroville. However, little capacity is available for bottom sediment PCB LAs at any of the 

reaches. This is due to the relative uncertainty regarding PCBs in the Similkameen River which

in turn is a function of the relatively high practical quantitation limits for PCBs. A greater 

degree of certainty that PCBs were much lower in the Similkameen River would add capacity for 

a PCB LA in bottom sediments. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 37 
Table 18: DDT and PCB Load Allocations for Bottom Sediments (mg/day)

Reach RM 4,4'-DDE 4,4'-DDD 4,4'-DDT t-DDT t-PCB

Osoyoos Lake

Cumulative LAs (tribs.) 91.2-80.2 798.6 1135.9 798.3 1353.6 230.2

Bottom sediments 82.5-79.0 0 -12.4 0.3 0 0 

Loading capacity 79.0 798.6 1123.5 798.6 1353.6 230.1

Near Oroville

Cumulative LAs/WLAs (tribs.and STPs) 91.2-77.8 803.5 1135.9 803.2 1362.0 231.6

Bottom sediments 79.0-77.4 0.2 -5.3 0.4 0.2 0.0

Loading capacity 77.4 803.7 1130.6 803.7 1362.2 231.6

Near Tonasket

Cumulative LAs/WLAs (tribs.and STPs) 

91.2 – 

52.9 1816.1 2138.6 1834.3 4405.3 1027.6

Bottom sediments 77.4-50.7 2038.4 3283.9 2020.2 2127.8 83.1

Loading capacity 50.7 3854.5 5422.5 3854.5 6533.1 1110.6

Near Malott

Cumulative LAs/WLAs (tribs.and STPs) 

91.2 – 

19.5 1826.0 2147.2 1841.7 4420.5 1036.7

Bottom sediments 50.7-17.0 2113.7 3395.1 2097.9 2256.9 98.5

Loading capacity 17.0 3939.7 5542.3 3939.7 6677.4 1135.2

Mouth

Cumulative LAs/WLAs (tribs.and STPs) 

91.2 – 

15.1 1826.6 2147.2 1841.7 4421.2 1037.2

Bottom sediments 2113.1 3395.1 2097.9 2256.2 98.0

Loading capacity 3939.7 5542.3 3939.7 6677.4 1135.2

Load Reductions 

Load reductions required to meet DDT/PCB LAs are shown in Table 19. On a reach-by-reach 

basis, no load reductions are required to meet LAs through delivery from tributaries and STPs 

since substantial reserve capacity exists at all reaches. As mentioned previously, however, some

load reductions are needed to meet loading capacities in certain tributary streams and STPs. 

Major load reductions from bottom sediments will be required to meet LAs for all reaches except 

where reserve capacities exist for 4,4’-DDD and 4,4’-DDT at Malott and the mouth, and 4,4’-

DDT near Tonasket. No load reductions are required to meet t-PCB LAs in Osoyoos Lake since 

PCBs have not been detected in fish from this location. 

Page 38 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Table 19: Required DDT and PCB Load Reductions and Reserve Capacity (-) at Osoyoos Lake and 

Lower Okanogan River Reaches (mg/day)

Reach RM 4,4'-DDE 4,4’-DDD 4,4’-DDT t-DDT t-PCB 

Osoyoos Lake 

Tribs. (reduction) 91.2-80.3 -790.7 -1133.8 -793.4 -1338.7 -230.2

% reduction 0% 0% 0% 0% 0%

Sediments (reduction) 82.5-79.2 17114.1 10238.0 777.7 28117.7 0.0

% reduction 100% 100% 100% 100% 0%

 

Oroville 

Tribs. (reduction) 91.2-77.8 -783.2 -1133.8 -789.9 -1326.3 -231.6

% reduction 0% 0% 0% 0% 0%

Sediments (reduction) 79.0-77.4 7933.9 664.0 265.8 8858.8 829.5

% reduction 100% 100% 100% 100% 100%

 

Reach RM 4,4'-DDE 4,4’-DDD 4,4’-DDT t-DDT t-PCB 

Near Tonasket 

Tribs. and STPs (reduction) 91.2 – 52.9 -1779.5 -2134.9 -1819.6 -4350.3 -1027.5

% reduction 0% 0% 0% 0% 0%

Sediments (reduction) 77.4-50.7 39000.5 1587.9 -572.2 45230.8 6408.0

% reduction 95% 33% 0% 96% 99%

 

Malott 

Tribs. and STPs (reduction) 91.2 – 19.5 -1725.1 -2132.1 -1750.2 -4213.1 -1034.0

% reduction 0% 0% 0% 0% 0%

Sediments (reduction) 50.7-17.0 10367.9 -1915.2 -1790.8 11986.8 2467.0

% reduction 83% 0% 0% 84% 96% 

 

Mouth 

Tribs. and STPs (reduction) 91.2 – 15.1 -1725.1 -2132.1 -1750.2 -4213.1 -1034.5

% reduction 0% 0% 0% 0% 0%

Sediments (reduction) 17.0-0.0 10367.9 -1915.2 -1790.8 11986.8 2467.5

% reduction 83% 0% 0% 84% 96% a

Results shown are for PCB Aroclors 1268, 1262, 1260, 1254, 1248, 1242, 1232, 1221, and 1016 

Reductions in DDT and PCB Concentrations in Bottom Sediments

Accumulation of a contaminant through all components of the aquatic environment is often 

referred to as bioaccumulation, with the numerical relationship described by bioaccumulation 

factors (BAFs). For fish, BAFs are probably more appropriate than BCFs to describe the 

contaminant link with the aquatic environment because BCFs substantially underestimate the 

bioaccumulation potential for hydrophobic chemicals that are resistant to metabolism and 

degradation such as DDT and PCBs (EPA, 2000). 

Biota-sediment accumulation factors (BSAFs) are the simplest model to explain the relationship 

between contamination of an organism and bottom sediments. BSAFs are essentially the ratio of 

contaminant concentrations in tissue to concentrations in sediment and may be used in situations 

where the concentration ratios do not change substantially over time, both the organism and food 

are exposed to the contaminant, and sediment concentrations are representative of those in the 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 39 
vicinity of the organism. For hydrophobic chemicals such as DDT and PCBs, this relationship is 

more accurately defined by factoring in tissue lipid and sediment organic carbon which strongly 

influence the uptake and retention of these chemicals. Site-specific BSAFs may then be 

calculated using the formula: 

BSAF = (Ct/fl)/(Cs/foc) 

where: 

Ct = contaminant concentration in tissue 

Cs = contaminant concentration in sediment 

fl = lipid fraction in tissue 

foc = fraction of organic carbon in sediment 

Current data on DDT and PCB in sediments and fish tissue were used to establish site-specific 

BSAFs at Osoyoos Lake and several lower Okanogan River reaches (Table 25). Data used were 

mean DDT, PCB, and TOC concentrations in the surficial layers (top 2-cm) of sediment cores 

collected from Osoyoos Lake (Osoyoos Lake and Oroville BSAFs) and from the Okanogan 

River mouth (Riv-Omak and Monse BSAFs). Fish tissue data were the same as those used to 

calculate theoretical loads. 

BSAFs generally ranged by approximately an order of magnitude (2.3 – 34.9) demonstrating a 

fairly good correlation between DDT/PCB concentrations in sediment and tissue. The BSAF for 

PCB at Oroville was very high due to low lipid content of fish combined with low PCB level in 

sediments. High BSAFs for 4,4’-DDT at Riverside-Omak and Monse were driven by very low 

concentrations in sediment. 

Reductions in sediment DDT/PCB concentrations required to meet LAs at several Osoyoos Lake 

and lower Okanogan River reaches were calculated by applying BSAFs to required reductions in 

tissue concentrations (Table 26). Except for PCBs in Osoyoos Lake, complete (100%) or near 

complete reductions are needed to meet LAs in the Osoyoos Lake and Oroville reaches, 

reflecting the LAs given to sediments in these reaches (0 mg/day). Large percent reductions are 

also needed for 4,4’-DDE, t-DDT, and PCBs in sediments in the lower reaches, but reserve 

capacities exist in most cases for 4,4-DDD and 4,4’-DDT. 

Trends in sediment DDT and PCB concentrations obtained from sediment cores suggest in most 

cases these required reductions will not be met in the near future. Concentrations have remained 

stable for the past two decades in the Osoyoos Lake sediments and for the past decade in 

sediments at the Okanogan River mouth. 

Table 20: BSAFs at Osoyoos Lake and Several Lower Okanogan River Reaches 

Location 4,4'-DDE 4,4'-DDD 4,4'-DDT t-4,4'-DDT t- PCBa

Osoyoos Lake 12.6 6.0 10.2 8.9 11.3b

Oroville 34.9 2.3 21.7 16.8 129.1

Riv-Omak 21.1 9.1 162.1c 19.0 15.1

Monse 11.3 4.9 77.1c 10.1 10.4 a

Results shown are for PCB Aroclors 1268, 1262, 1260, 1254, 1248, 1242, 1232, 1221, and 1016 b

One-half practical quantitation limit (10 ng/g) used as tissue concentration c

One-half practical quantitation limit (0.032 ng/g) used as sediment concentration 

Page 40 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Table 21: Reductions or Reserve Capacity (-) in Sediment DDT and PCB Concentrations (ng/g OC) 

Required to Meet Load Allocations 

Reach 4,4'-DDE 4,4’-DDD 4,4’-DDT t-DDT t-PCBa

Osoyoos Lake

Current conc. 822 1,043 46.5 1,912 13.5

Reduction required to meet LA 822 1,030 48.0 1,905 0.0 

Percent reduction 100% 99% 100% 100% 0% 

Oroville 

Current conc. 822 1,043 46.5 1,912 13.5

Reduction required to meet LA 820 1,043 46.5 1,912 13.5 

Percent reduction 100% 100% 100% 100% 100%

Near Tonasket 

Current conc. 354 97.4 1.6b 453 45.6

Reduction required to meet LA 336 37.8 -0.4 431 45.6 

percent reduction 95% 39% 0% 95% 100% 

Malott 

Current conc. 354 97.4 1.6b 453 45.6

Reduction required to meet LA 308 -97.4 -6.7 398 45.6 

Percent reduction 87% 0% 0% 88% 100% 

Mouth 

Current conc. 353 97.4 1.6b 453 45.6

Reduction required to meet LA 308 -97.4 -6.7 398 45.6 

Percent reduction 87% 0% 0% 88% 100% a

Results shown are for PCB Aroclors 1268, 1262, 1260, 1254, 1248, 1242, 1232, 1221, and 1016 b

One-half practical quantitation limit (0.032 ng/g) used as sediment concentration 

Load Reductions in Individual Tributaries and STPs

Table 27 shows load reductions needed to bring individual tributaries and STP in line with 

Washington State and NTR criteria. In general, required load reductions are less than 10 

mg/day. Tallant, Elgin, Tonasket, and Ninemile Creeks will require the largest load reductions. 

Three of these streams – Tallant Creek, Elgin Creek, and Ninemile Creek – are currently on the 

303(d) list for t-DDT. The Okanogan STP was the only one of the three STPs requiring load 

reductions for DDT and PCBs. 

Table 22: Load Reductions Required to Meet Criteria within Individual Tributaries and STPs 

(mg/day)

Location RM 4,4'-DDE 4,4'-DDD 4,4'-DDT t-DDT t-PCBa

Haynes Creek BC 82.8 1.0 0 0 0.8 0 

Nine Mile Creek 80.2 4.6 0 2.8 10.2 0 

Tonasket Creek 77.8 7.4 0 3.5 12.4 0

Mosquito Creek 67.4 0.6 0.5 0 1.4 0 

Whitestone Creek 62.4 0.8 0 0 0 0

Antoine Creek 61.2 2.8 0 0 3.1 0 

Elgin Creek 28.4 12.5 0 5.3 19.0 0

Okanogan STP 24.8 0 0 0.3 0.8 0.2 

Tallant Creek 19.5 46.4 10.2 68.4 125 0 a

Results shown are for PCB Aroclors 1268, 1262, 1260, 1254, 1248, 1242, 1232, 1221, and 1016 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 41 
Seasonal Variation 

Seasonal variation has been addressed through sampling during low flow and high flow events. 

Use of weighted mean loads also incorporates flows and contaminant concentrations measured at 

various times of the year. 

Both the human health and chronic aquatic life criteria for DDT and PCBs are driven by longterm exposures. Acute toxicity is not considered to be a concern at concentrations in the lower 

Okanogan River basin (EPA, 1980a; EPA, 1980b). Since the accumulation of DDT and PCBs in 

fish tissues is a time-integrative process, and the chronic aquatic life criteria are based on longterm exposures, seasonal variations in loads are not an important factor in determining load 

allocations for these parameters. 

Margin of Safety 

The federal Clean Water Act requires that a margin of safety be identified to account for 

uncertainty when establishing a TMDL. The margin of safety can be explicit in the form of an 

allocation, or implicit in the use of conservative assumptions in the analysis. 

A large portion of the Margin of safety in this TMDL is the long standing bans on use of these 

persistent compounds in the environment. As the reduction of contaminants in the system is 

observed, no new sources will occur. The non-point nature of DDT and PCBs and the difficulty 

to directly control their discharge to the water have abated over time and the improvements to 

land and water management within the valley assures improving long term control of non-point 

contaminant migration pathways. This TMDL also relies on the conservative means by which the 

criteria have been set for the DDT and PCB related contaminants for the margin of safety. 

Additionally; this margin of safety is enhanced by the legacy nature of the contaminants 

addressed in this TMDL, the concentrations of contaminants should continue to decline even 

after the regulatory criteria have been met. 

Page 42 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Summary Implementation Strategy 

Introduction

Pursuant to the 1997 Memorandum of Agreement between Ecology and the EPA, a Summary 

Implementation Strategy (SIS) is included in this submittal report for the Okanogan River DDT 

and PCB Total Maximum Daily Load Project. This goal of this SIS is to present a clear, concise 

and sequential concept of how suspended DDT and PCB pollution will be reduced within the 

Lower Okanogan basin in order to meet the fish tissue and surface water criteria for DDT and 

PCBs. It is anticipated that implementation of the TMDL will return this water body to 

conditions that meet the targets and criteria noted above by July and 2054. The SIS complies 

with the federal mandate of the Clean Water Act, State laws to control point and non-point 

source pollution, and the 1997 Memorandum of Agreement between EPA and Ecology. 

A citizen’s workgroup that was formed as the Implementation Committee under the Okanogan 

Watershed Water Quality Management Plan served as citizen representatives in the development 

of this TMDL and implementation strategy. Groups represented in the TMDL workgroup 

include irrigated agriculture, ranchers, conservation districts and natural resource agencies, 

recreational interests, as well as numerous other interested parties or stakeholders, agencies and 

organizations. There is a high level of cooperation and communication between project 

participants, and their continued active pursuit of the goals TMDL’s and watershed management 

plan, many of which are shared by both the TMDL and the Okanogan Watershed Water Quality 

Management Plan, will ultimately ensure the success of this TMDL. 

The strategy to implement the TMDL is based upon actions already taken to address contaminant 

sources, the continuation of the many existing efforts, and the implementation of new actions. 

The non-point sources (load allocations) will be addressed by the use of best management 

practices (BMPs). Point sources (NPDES dischargers) are already working to understand the 

source of contaminants in their discharges and will continue to work under the NPDES program

to reduce their contaminant loading to the Okanogan River. The principal focus of this TMDL 

implementation strategy will be to continue the removal of potential sources of contamination 

from the watershed and the implementation of seasonal and year-round BMPs to prevent the 

entry of persistent residues of DDT and PCBs into area waterbodies. Additionally, continued 

monitoring of implementation activities and fish tissue contaminant levels and water quality are 

essential in assessing the natural attenuation of contaminants. 

This SIS will serve as guidance for developing a Detailed Implementation Plan (DIP) during the 

one-year period after the TMDL has been approved. The DIP will describe specific 

implementation activities that need to be performed to achieve the TMDL targets. The DIP will 

also present a thorough plan for monitoring implementation of this TMDL. It is anticipated that 

implementation of this TMDL will document long-term reductions in the DDT and PCBs in fish 

from the Lower Okanogan River Basin. 

The technical assessment report identified the sediments within the Okanogan River as the 

primary load of contaminants. The restoration timeframe for this TMDL is primarily dependent 

on the natural breakdown of these persistent chemicals in the environment. Limited early data 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 43 
on fish tissue concentrations suggest a downward (improving water quality) trend in fish tissue 

concentrations when compared to data reported from the latest TMDL study. Data collection 

and analysis for fish tissue prior to the TMDL Technical Assessment report is insufficient for the 

establishment of baseline data. The downward trend cannot be determined due to the limited 

amount of the early data. The current TMDL assessment report does provide sufficient data for 

reference by future fish tissue studies 

Implementation Activities 

This TMDL is addressing water quality impairment from legacy loading. The primary actions 

for reducing DDT and PCB in the environment was the regulatory ban on DDT use in 1972 and 

the 1979 ban on PCB production, and the subsequent phase-out and control of PCB products. 

A downward trend in DDT and PCB concentrations following the above bans is evident in the 

sediment cores from the south basin of Lake Osoyoos and the lowest segment of the Okanogan 

River. This downward trend, however, is not continuous in the Lake Osoyoos coring and 

exhibits an anomalous spike of high concentration in the past decade. This trending data 

suggests two courses of actions are needed to address continuing inputs of DDT to the 

watershed; continued implementation of BMPs to reduce pesticide residues reaching the affected 

surface waters and efforts to remove DDT containing products for the watershed. 

Implementation Activities for Non-Point Sources 

Several tributary streams within the Okanogan Basin were identified as carrying DDT 

contamination. Specific source areas of non-point contamination were not apparent and not 

identified by the technical assessment. 

Lands that were in agricultural production during the time period that DDT was in common 

usage are considered potential sources of DDT due to the residues of DDT that persist in the 

soils. Erosion of these lands can be the source of contaminated river systems as shown in the 

report: A Suspended Sediment and DDT Total Maximum Daily Load Evaluation Report for the 

Yakima River. In that report DDT loading to the Yakima River was found to correlate strongly 

with the amount of sediment derived from agricultural runoff. Irrigation practices in the lower 

Okanogan River basin do not produce the amounts of sediment loading to the river that were 

seen in the Yakima example, even though pesticide application practices were similar in both 

basins at the time, which suggests that agricultural soil losses in the Okanogan are not as great a 

source of DDT as in the Yakima River area surface waters. 

Historical improvements in irrigation delivery systems in the lower Okanogan River basin have 

resulted in the current irrigation systems efficiently providing water to the lands. According to 

the Okanogan Conservation District, irrigation practices that result in significant soil loss, such 

as open rill irrigation, are no longer practiced in the lower Okanogan Basin. Investigations in the 

lower Okanogan River basin by Ecology and the Colville Confederated Tribes did not document 

the discharge of irrigation drains in the Okanogan valley. 

Experience in other irrigated river basins, like the lower Yakima River Basin, has shown that a 

movement to enclosed irrigation systems, like sprinklers or drip systems, effectively reduces the 

amount of pesticide residues carried from agricultural lands into nearby surface waters. 

Page 44 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Continuing improvements to irrigation efficiency and water delivery systems may continue to 

decrease the soil that migrates directly from the agricultural lands. Therefore, working with 

irrigation water management to produce efficient irrigation practices will also reduce the 

transport of DDT residues from the agricultural lands. 

BMPs that work directly with the riparian lands located between the current and former 

agricultural lands to reduce losses of soils that potentially contain pesticide residues are actively 

promoted through programs including: EQUIP, CREP, CRP, and Ecology administered grants of 

Centennial Clean Water funds, 319 funds and Salmon Recovery Funds. These funding sources 

are not dedicated only for projects that reduce DDT in surface waters, but are directed toward 

reducing a variety of pollutants. Many of the projects, such as exclusion fencing to restrict cattle 

from riparian areas that are promoted for environmental restoration and preservation can have 

the side benefit of DDT reduction through the prevention of erosion. 

Potential sources of DDT contamination, other than agricultural soil erosion, have been 

suggested for the tributary streams. An example of this is a complaint that has been filed with 

the Ecology that an old orchard dump in the vicinity of Highway 20 crossing Talent Creek may 

be a continuing source of DDT contamination. Such complaints regarding inappropriate disposal 

will be investigated though the Washington State Model Toxics Control Act and other State 

regulations as appropriate. 

Removing potential sources of DDT in the watershed is an important step in reducing the 

contamination in the Okanogan watershed. Programs for the collection of banned pesticides, 

including DDT, have been successfully implemented in both Washington and British Columbia, 

removing many stored pesticides from the watershed. The waste pesticide pickup programs, 

such as the one conducted by the Washington Department of Agriculture, reduces the potential 

of inappropriate disposal or accidental loss of DDT, or any other waste pesticide, in the 

watershed. Losses of DDT-containing materials could result from catastrophic losses from

storage facilities through flood, fire, or inappropriate disposal activities. Such a disposal or 

catastrophic loss of stored materials could account for the spike in concentrations found in the 

sediment core from southern Lake Osoyoos. 

Addressing PCB contamination in the lower Okanogan River Basin is more problematic than 

addressing the DDT pesticide. The primary uses of PCB were not intended for dispersal into the 

environment, but its environmental persistence is similar to that of DDT. Efforts to reduce PCB 

releases to the environment will include education efforts for disposal of potential PCBcontaining materials common to industry, small businesses and households. Proper disposal of 

items and materials that potentially contain PCBs may be achieved through the existing moderate 

risk waste facility operated by Okanogan County. An experimental effort to collect and test 

sediment from storm drains in municipal areas has been proposed for the municipalities of 

Tonasket and Okanogan. This effort has the potential to collect PCBs from the urban 

environment and analytically test collected materials to determine the success of the project and 

its potential future applications in the valley. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 45 
Implementation Activities for Point Sources (NPDES) 

The NPDES permitted dischargers in the Lower Okanogan Basin are the municipal wastewater 

treatment plants in Oroville, Tonasket, Omak and Okanogan. These facilities are the only 

potential point sources in the TMDL study area. 

The NPDES discharge permits for the cities of Oroville Omak and Okanogan have recently been 

renewed. Coordination between the NPDES permit development and the ongoing development 

of this TMDL has resulted in each of these permits containing requirements to investigate the 

wastewater collection systems for the sources of DDT and PCBs in their effluent. An effort is 

being made to undertake a coordinated investigation of wastewater collection systems of these 

municipalities and the wastewater collection and treatment system for the city of Tonasket. The 

purpose of investigating the wastewater collection systems is to determine if there is a discreet or

concentrated source of contaminants entering the systems that may be addressed efficiently 

before the contaminants enter the wastewater treatment plants. 

The city of Tonasket was not included in the sampling for the technical assessment study as it 

was not discharging to the river at the time of the study. The city of Tonasket has since 

completed construction on an upgraded wastewater treatment system and is now discharging to 

the river. The NPDES permit was not conditioned with a requirement for investigating potential 

sources of DDT. However, the city of Tonasket has expressed a willingness to participate in 

DDT studies in anticipation of their next permit cycle. 

Monitoring Strategy 

The persistent natures of DDT and PCBs in the environment truly make them a legacy of past 

practices. While these toxic compounds continue to persist in the environment their effective 

levels are reduced over time through degradation and by natural attenuation through dilution and 

capping. The natural processes resulting in the lower exposure of aquatic life to the 

contaminants will play a major role in the success of this TMDL. Monitoring fish tissue 

concentrations of these contaminants will be the most effective means to judge the progress of 

environmental improvement. 

Analytical testing results for fish tissue sampling for the 2003 TMDL Technical Assessment 

report show DDT and PCB values that appear to be substantially lower than the fish tissue 

samples that were taken in the period of 1984 – 1995. Unfortunately, there is insufficient data 

from 1985-1995 to determine if this apparent reduction of contamination in fish tissue is truly 

significant. The fish tissue data from the 2003 Technical Assessment report will serve as the 

baseline data to judge progress of environmental improvement. Repeating the fish tissue 

sampling efforts on a regular cycle of 5 years is recommended for the tracking of effective water 

quality improvements. 

Responsible Entities and Actions 

The Okanogan Conservation District administers most of the incentive based or grant funded 

programs for the restoration and preservation of riparian lands, and the reductions of soil losses 

on agricultural lands. It is important that the Okanogan Conservation District continue to serve 

Page 46 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
this role of coordinating grant funded projects in the watershed as they have the local knowledge 

and community contacts that are essential to the success of these programs. 

The municipalities of Oroville, Tonasket, Omak and Okanogan are responsible for the 

compliance of their municipal wastewater treatment plants with their NPDES permits. The 

linkage between the NPDES and TMDL programs through the US Clean Water Act assures that 

the goals of the TMDL will be reflected in their NPDES permits. 

Ecology will be responsible for the periodic monitoring of DDT and PCBs in fish tissues. 

Maintaining this responsibility within the state agency should provide consistent data quality. 

Ecology is the responsible entity for determining compliance of interim and final targets, and 

conducting Effectiveness Monitoring in the future. 

Adaptive Management 

These implementation activities are centered on the maintenance and improvement of long term

activities that have reduced water contaminant levels since the banning of DDT and PCBs. The 

inclusion long-term data collection and monitoring of fish tissue in the implementation activities 

is necessary due to the persistent nature of these legacy contaminants. The monitoring activities 

will serve to better define the rate that the water quality in the basin is improving. Re-evaluation 

of the long-term trends with additional data will allow the restoration timeframe to be determined 

with greater precession. If the water quality monitoring activities show unexpected long-term

rises of contaminants in fish tissues, an examination of any potential new sources of DDT or 

sediments should also be undertaken. Additionally, intensive surveys and watershed 

investigation should be sought to identify significant events in the watershed that could resuspend sediments. 

Persistent elevated values of DDT or PCB contamination, or data that does not show the 

expected gradual declines over time, will trigger additional investigation under adaptive 

management. This should include, but not be limited to, further the investigations of tributary 

streams and potential groundwater transport of DDT. 

Potential Funding Sources 

Funding sources will be more fully explored in the development of the DIP. 

At this time funding for the periodic (repeating every five years) monitoring of the lower 

Okanogan basin fish tissue is expected be accomplished with project funding through the normal 

operations of Ecology. Opportunities for external funding sources and adjustment to the 

frequency of study events will be considered as the body of data and time related trends are 

accumulated. 

Funding for the Washington Department of Agriculture’s waste pesticide pickup program is 

currently sustained through the Department of Agriculture. The benefits of such a program to 

water quality are direct but difficult to quantify as it is a preventive program. At this time the 

program appears to be well supported and will continue to be available in the Okanogan Valley. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 47 
The communities of Tonasket and Okanogan are seeking grant funding for the experimental 

effort to collect and test sediment from storm drains in municipal areas. This independent work 

by the cities may be facilitated through the efforts of the Okanogan Conservation District. 

Detailed Implementation Plan 

A DIP will be prepared within a year following approval by EPA of this document. Further 

public input will be sought to help prepare the plan. The plan will identify in more detail how, 

when, and where monitoring activities will be implemented. Ecology and other entities will 

provide technical assistance and seek additional funding for these monitoring activities and any 

restoration activities that may be identified as the body of data grows. It is the goal of this 

TMDL to meet the water quality standards for DDT in surface waters and 4,4’-DDD, 4,4’-DDE 

and PCBs in fish tissues by 2054. 

Page 48 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Activities that Support this TMDL 

Implementation Strategy 

The implementation strategy for the Okanogan DDT and PCB TMDL is designed to address 

legacy loading of DDT and PCBs in the watershed from historic agricultural, industrial, 

commercial and domestic practices in the watershed. Implementation activities include 

continued implementation of activities that have reduced or controlled releases of contaminants 

to the surface waters and the continued investigation of potential contaminant sources in the 

Okanogan River Tributaries. 

Supporting Regulations and Land 

Management Plans 

Routine implementation of Washington’s State Environmental Policy Act, the Okanogan County 

Comprehensive Plan and the Okanogan County Shoreline Master Program will assure the review

of projects proposed in the vicinity of the Okanogan River and tributaries for potential 

environmental impacts due to erosion. This review process should ensure best management 

practices are used for new projects and that permitted activities will not impact the 

implementation of this TMDL. Continued implementation of Washington’s Model Toxics 

Control Act should provide continued support for the investigation of potential contaminated 

sites that are uncovered over time, such as dump sites that include DDT and PCB containing 

materials.

Reasonable Assurance 

During the development of the DDT and PCB TMDL for the lower Okanogan River basin, 

available data for water quality throughout the watershed was collected and evaluated. The mass 

balance approach to the TMDL and the quantity of data has shown that the loading of these 

legacy contaminants are far reduced from the time that they were in active use. Without new 

sources of contaminant entering the watershed, the downward trend should continue though at a 

much declined rate from what has been seen in recent years as indicated by the sediment core 

samples and dating conducted as part of the TMDL technical assessment. The rate of natural 

attenuation due to degradation, dilution and sequestering of materials in the deep sediments can 

only be estimated with the current set in data. Documentation of the attenuation will take longterm monitoring of fish tissue in the river system. The conservative assumptions used in setting 

the regulatory criteria, and the work by the NPDES permitted facilities should provide sufficient 

assurance that, with time, water quality is improving. 

Each of these conservative measures will assure that the Okanogan Watershed will be monitored 

and protected from activities that would threaten the water quality while the legacy loading is 

mitigated through time and nature. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 49 
Public Participation 

Public involvement is a required part of the TMDL process. The public participation activities 

performed to date for this TMDL are included in appendix A “Summary of Public Involvement”. 

Additional public involvement activities will be included in preparation of the Detailed 

Implementation Plan. 

Page 50 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
References 

Davis, D. and A. Johnson, 1994. Washington State Pesticide Monitoring Program –

Reconnaissance Sampling of Fish Tissue and Sediments (1992). Washington State 

Department of Ecology, Olympia, WA. Ecology Pub. No. 94-194. 

Davis, D. and D. Serdar, 1996. Washington State Pesticide Monitoring Program - 1994 Fish 

Tissue and Sediment Sampling Report. Washington State Department of Ecology, 

Olympia, WA. Ecology Pub. No. 96-352. 

Davis, D., D. Serdar, and A. Johnson, 1998. Washington State Pesticide Monitoring Program -

1995 Fish Tissue Sampling Report. Washington State Department of Ecology, Olympia, 

WA. Ecology Pub. No. 98-312. 

Ecology, 1993 (Revised 1997 and 2002). Assessment of Water Quality for the Section 303(d) 

List. WQP Policy 1-11, Washington State Department of Ecology Water Quality 

Program, Olympia, WA. 

Ecology, 1995. Department of Ecology Investigation of PCBs in the Spokane River. Washington 

State Department of Ecology, Olympia, WA. Ecology Pub. No. 95-310. 

Ehinger, W., 1994. Ambient Monitoring Scoping Report for the Okanogan Planning Basin 

(WRIAs 48-51). Washington State Department of Ecology Environmental Investigations 

and Laboratory Services Program, Olympia, WA. 

EPA, 1980a. Ambient Water Quality Criteria for DDT. U.S. Environmental Protection Agency, 

Office of Water, Regulations and Standards, Criteria and Standards Division, Washington 

DC. EPA 440/5-80-038. 

EPA, 1980b. Ambient Water Quality Criteria for Polychlorinated Biphenyls. U.S. Environmental 

Protection Agency, Office of Water, Regulations and Standards, Criteria and Standards 

Division, Washington DC. EPA 440/5-80-068. 

Harris, M.J., L.K. Wilson, J.E. Elliott, C.A. Bishop, A.D. Tomlin, and K.V. Henning, 2000. 

Transfer of DDT and Metabolites from Fruit Orchard Soils to American Robins (Turdus 

migratorius) Twenty Years after Agricultural Use of DDT in Canada. Archives of 

Environmental Contamination and Toxicology 39: 205-220. 

Hopkins, B., D. Clark, and M. Stinson, 1985. Basic Water Monitoring Program Fish Tissue and 

Sediment Sampling for 1984. Ecology Pub. No. 85-7, Washington State Department of 

Ecology, Olympia, WA. 

Hurst, D., Fulcrum Environmental Consulting, Inc., written communication, October 15, 2001. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 51 
Hurst, D. and P. Stone, 2002. Signature or Static? Distribution of Arsenic, Lead, and t-DDT in 

Sediments of the Okanogan River from Lake Osoyoos to the Columbia River. 

Presentation at Columbia River Transboundary Conference, April 27 – May 1, 2002, 

Spokane, WA. 

Johnson, A., D. Norton, and B. Yake, 1988. Persistence of DDT in the Yakima River Drainage, 

Washington. Arch. Environ. Contam. Toxicol. 17:289-297. 

Johnson, A. and D. Norton, 1990. 1989 Lakes and Reservoir Water Quality Assessment 

Program: Survey of Chemical Contaminants in Ten Washington Lakes. Washington State 

Department of Ecology, Olympia, WA. 

Johnson, A., D. Serdar, and D. Davis, 1997. DDT Sources to the Okanogan River and Lake 

Osoyoos. Memorandum to Jim Milton, Washington State Department of Ecology, 

Olympia, WA. 

Johnson, A. and R. Polotnikoff, 2000. Review of Sediment Quality Data for the Similkameen 

River. Washington State Department of Ecology, Olympia, WA. Ecology Pub. No. 00-

03-027. 

Johnson, A., Washington State Department of Ecology, personal communication, 2001. 

Joy, J. and B. Patterson, 1997. A Suspended Sediment and DDT Total Maximum Daily Load 

Evaluation Report for the Yakima River. Washington State Department of Ecology, 

Olympia, WA. Ecology Pub. No. 00-03-027. 

Neslen, T., Okanogan County Conservation District, personal communication, 2001. 

Reif, D., 1990. Okanogan Wastewater Treatment Plant Class II Inspection: October 18-19, 1988. 

Washington State Department of Ecology, Olympia, WA. 

Serdar, D., D. Davis, and A. Johnson, 1998. DDT in Osoyoos Lake Fish. Washington State 

Department of Ecology, Olympia, WA. Ecology Pub. No. 98-337. 

Serdar, D., 2002. TMDL Technical Assessment of DDT and PCBs in the Okanogan River 

Quality Assurance Project Plan. Washington State Department of Ecology, Olympia, 

WA. 

Sinclair, P.H. and J.E. Elliott, 1993. A Survey of Birds and Pesticide Use in Orchards in the 

South Okanogan/Similkameen Region of British Columbia, 1991. Canadian Wildlife 

Service, Pacific and Yukon Region. Tech. Rep. Series No. 185. 

WEST Consultants, Inc. and Hammond, Collier, & Wade-Livingstone, Inc., 1999 (Draft). Water

Quality Modeling Assessment of the Okanogan River. Prepared for Okanogan County 

Water Resources Department, Okanogan, WA. 

Page 52 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Definitions and Acronyms 

303(d) Section 303(d) of the federal Clean Water Act 

B.C. British Columbia 

BAF bioaccumulation factor

BCF bioconcentration factor 

BSAF biota-sediment accumulation factor

BW body weight 

Cs concentration in sediment 

Ct concentration in tissue 

Cw concentration in water 

CCT Colville Confederated Tribes 

CFR Code of Federal Regulations, usually preceded by chapter number and followed 

by a section number (i.e. 40CFR131.36) 

cfs cubic feet per second 

CWA Clean Water Act 

DDD 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (a.k.a. 4,4’-DDD) 

DDE 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (a.k.a. 4,4’-DDE)

DDT 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (a.k.a. 4,4’-DDT and also used to refer 

to the DDD and DDE analogs) 

DIP Detailed Implementation Plan 

Ecology Washington State Department of Ecology 

ECD electron capture detector 

EPA U.S. Environmental Protection Agency 

FC fish consumption 

g/day grams per day 

GC gas chromatography 

HHC human health criteria 

LA load allocation 

MEL Manchester Environmental Laboratory 

mg/l milligrams per liter (parts per billion)

MOS margin of safety 

m.s.l. mean sea level 

NDIR nondispersive infrared 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page 53 
ng/g nanograms per gram (parts per billion) 

ng/l nanograms per liter (parts per trillion) 

NIST National Institute of Standards and Technology

NPDES National Pollutant Discharge Elimination System

NTR National Toxics Rule (40CFR131.36) 

Q discharge 

q1* cancer slope factor 

Pb lead 

PCB polychlorinated biphenyl 

Ra radium

RCW Revised Code of Washington 

RF risk factor

RM river mile 

Rn radon 

SIS Summary Implementation Plan 

SRM standard reference material

STP sewage treatment plant 

t-DDT total DDT (sum of 4,4’-DDD, 4,4’-DDE, and 4,4’-DDT in this report) 

TMDL Total Maximum Daily Load 

TOC total organic carbon 

TSS total suspended solids 

μg/l microgram per liter (parts per billion)

USDA U.S. Department of Agriculture 

USGS U.S. Geological Survey 

WAC Washington Administrative Code 

WC water consumption 

WDFW Washington Department of Fish and Wildlife 

WLA waste load allocation

WWTP Wastewater Treatment Plant 

μg/L micrograms per liter 

Page 54 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Appendix A 

Summary of Public Involvement 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page A- 1 
Summary of Public Involvement 

September 12, 2000 Met with the Okanogan Health District Board to present 

introductory information on the Okanogan DDT/PCB and 

Similkameen arsenic TMDLs. 

November 7, 2000 Presentation on the Okanogan and Similkameen TMDLs made to 

the environmental science class at Wenatchee Community 

College class at the Omak branch campus. 

September 7, 2000 Presentation to the Okanogan Conservation District Supervisor’s 

meeting to introduce the Similkameen arsenic and Okanogan 

DDT/PCB TMDLs. 

February 22, 2001 Public meeting at Okanogan PUD to kick -off Okanogan 

DDT/PCB and Similkameen Arsenic TMDLs. 

July 26, 2001 Presentation on the Okanogan DDT/PCB and Similkameen 

arsenic TMDLs to the Okanogan Watershed Implementation 

committee. 

August 9, 2001 Presentation to the Oroville-Tonasket irrigation District on the 

Okanogan DDT/PCB and Similkameen arsenic TMDLs. 

October 25, 2002 Meeting with the Okanogan Watershed Implementation 

Committee to discuss the Similkameen River arsenic TMDL and 

the Okanogan River DDT/PCB TMDL. 

February 24, 2003 Meeting with the Okanogan Watershed Implementation 

Committee to discuss the Similkameen River arsenic TMDL and 

the Okanogan River DDT/PCB TMDL. 

June 24 2003 Meeting with Tonasket City Council to discuss the Okanogan 

DDT TMDL and the implications for the newly permitted 

municipal waste water discharge. 

July 24, 2003 Meeting with the Okanogan Watershed Implementation 

Committee to discuss the Similkameen River arsenic TMDL and 

the Okanogan River DDT/PCB TMDL. 

September 2003 Okanogan DDT/PCB Technical Assessment Report was posted 

to the Washington Department of Ecology Web Page. 

Notifications of report availability were sent to implementation 

committee inviting them to contact Ecology for a report copy(s) 

suited to their needs, downloaded from the internet/e-mail, 

mailed digital copy on disk or printed hard copy. 

June 8, 2004 Notification of public comment period and public meetings 

placed on the Washington Department of Ecology’s internet 

public involvement calendar. 

Page A- 2 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
June 11 through 

July 12, 2004 Public Comment Period for the Lower Okanogan Rive 

DDT/PCB TMDL Submittal report. Advertisements for the 

public comment period and public meetings were placed in the 

larges local newspapers Okanogan Chomical and the Okanogan 

Valley Gazette Tribune June 7 to 11 and again on the week of 

June 14 to 18. 

June 16, 2004 Public meeting held in the evening at the Okanogan Public 

Utility District #1 Office in Okanogan. Meeting provided a 

forum to discuss the TMDL Submittal Report. 

June 29, 2004 Public meeting held in the evening at the Oroville City Hall. 

Meeting provided a forum to discuss the TMDL Submittal 

Report. 

Responses to Public Comments on the Lower Okanogan 

River Basin DDT and PCB Submittal Report Draft 

No public comments were received on the Lower Okanogan River Basin DDT and PCB 

Submittal Report Draft. Changes to the document were made as a result of comments 

received from the United States Environmental Protection Agency in regards to required 

contents and clarification. Adjustments to the load allocation were made due to the 

inclusion of a Waste Load Allocation for the recently permitted discharge for the 

Tonasket Waste Water Treatment Plant. 

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page A- 3 
PageA-4 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load 
Appendix B 

Technical Report 

TMDL Technical Assessment of 

DDT and PCBs in the Lower Okanogan River Basin 

July 2003 

Ecology Publication Number 03-03-013 

This publication may be viewed at the following website: 

 http://www.ecy.wa.gov/pubs/0303013.pdf 

Paper copy may be obtained upon request.

Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load Page B-1 
Page B-2 Lower Okanogan River Basin DDT and PCBs Total Maximum Daily Load