# Turbidity Analysis for Oregon Public Water Systems

Water Quality i n Coast Range Drinking Water Source Areas

June 20 1 0

Last Updated: 0 6 / 2 9/ 10 By: Joshua Seeds DEQ 09

- WQ

- 024 

## ReportThis report prepared by:

Oregon Department of Environmental Quality

811 SW 6 th Avenue Portland, OR 97204

1

- 800

- 452

- 4011

Contact:

Joshua Seeds (503) 229

- 5081 seeds.joshua@deq.state.or.us

### i 

## Turbidity Analysis for Oregon Public Water Systems



# Table of Contents

Table of Contents

................................ ................................ .......................... i

List of Figures

................................ ................................ .............................. iii

List of Tables

................................ ................................ ............................... i iv

List of Maps

................................ ................................ ................................ . i iv

Executive Summary

................................ ................................ ..................... 1

Introduction

................................ ................................ ................................ .. 2

Applicable Turbidity Standards for Water Quality

................................ ............... 2

Public Water System Evaluations

................................ ................................ ....... 3

Methods

................................ ................................ ................................ .......................... 5

Definitions of terms

................................ ................................ ................................ ......... 6

Summary of Results

................................ ................................ ................................ ....... 6



### Case Studies

................................ ................................ ................................ 8

Analysis of Public Water System Turbidity Data

................................ ................. 9

Arch Cape Water District (PWS #4100802)

................................ ................................ ... 9

City of Astoria (PWS #4100055)

................................ ................................ .................. 10

City of Carlton (PWS# 4100171)

................................ ................................ .................. 15

City of Falls Ci ty (PWS# 4100297)

................................ ................................ ............... 20

City of Forest Grove (PWS #4100305)

................................ ................................ ........ 23

Hillsboro

- Cherry Grove (PWS# 4100985)

................................ ................................ .... 27

City of Siletz (PWS# 4100821)

................................ ................................ ..................... 30

City of Yamhill (PWS# 4100968)

................................ ................................ .................. 33



### Ecological and Economic Implications

................................ ....................... 37

Natural Disturbances and Land Use Have Potential Effects on Sediment/Turbidity

... 37

Land Use May Alter Flow Regimes

................................ ................................ .............. 38

Climate Change Risks for Public Water Supplies

................................ ........................ 38

Potential Costs Related to Higher Turbidity

................................ ................................ . 38

Land Management Effectiveness for Source Water Protection

................................ ... 39



### Potential Followup

................................ ................................ ...................... 4 2

References

................................ ................................ ................................ . 4 4

Appendices

................................ ................................ ................................ 4 9

### ii 

## Turbidity Analysis for Oregon Public Water Systems

Appendix A: Public Water Systems with All or Part of DWSA in the Coast

Range

................................ ................................ ................................ ......... 4 9

Appendix B : Relationship of Stream Turbidity and Suspended Solids in the

Siletz River Basin: Analysis of Data Collected by Confederated Tribes of

Siletz Indians

................................ ................................ ............................... 5 2

### iii 

## Turbidity Analysis for Oregon Public Water Systems


# List of Figures

Figure 1: Number of Days with High Raw Water Turbidity

................................ .... 6
Figure 2: Total Duration of Treatment Shutdowns by Month (Ar ch Cape)

............. 9
Figure 3 a : Influent Turbidity for City of Astoria

................................ .................... 10
Figure 3 b: Turbidity in City of Astoria’s Source Water: Streams

.......................... 1 1
Figure 3 c: Turbidity in City of Astoria’s Source Water: Lakes

............................. 1 1
Figure 3 d: Precipitation for City of Astoria

................................ ........................... 1 2
Figure 3 e: R aw Water Turbidity Trend for City of Astoria

................................ .... 1 2
Figure 3 f: Number of Days with High Turbidity in Astoria’s Raw Water

............... 1 3
Figure 3 g: Trend for High Turbidity Days in Astoria’s Raw Water

....................... 1 4
Figure 4 a: Influent Turbidity for City of Carlton

................................ .................... 1 5
Figure 4 b: Preci pitation for City of Carlton

................................ .......................... 1 6
Figure 4 c: Raw Water Turbidity Trend for City of Carlton

(includes effects of 1999 landslide)

................................ ..................... 1 7
Figure 4 d: Raw Water Turbidity Trend for City of Carlton

( ex cludes effects of 1999 landsli de)

................................ ................... 1 7
Figure 4 e: Number of Days with High Turbidity in Carlton’s Raw Water

.............. 1 8
Figure 4 f: Trend for High Turbidity Days in Carlton’s Raw Water

........................ 1 8
Figure 4 g: Storage Capacity in City of Carlton’s Reservoir

................................ . 1 9
Figure 5 a: Influent Turbidity for City of Falls City

................................ ................. 20
Figure 5 b: Precipitation for City of Falls City

................................ ....................... 2 1
Figure 5 c: Raw Water Turbidity Trend for City of Falls City

................................ 2 1
Figure 5 d: Number of Days with High Turbidity in Falls City’s Raw Water

.......... 2 2
Figure 5 e: Trend for High Turbidity Days in Falls City’s Ra w Water

.................... 2 2
Figure 5 f: Turbidity Range & Mean for November 2006 Sedimentation Incident

. 2 3
Figure 6 a: Influent Turbidity for City of Forest Grove

................................ .......... 2 4
Figure 6 b: Precipitation for City of Forest Grove

................................ ................. 2 5
Figure 6 c: Raw Water Turbidity Trend for City of Forest Grove

.......................... 2 5
Figure 6 d: Number of Days with High Turbidity in Forest Grove’s Raw Water

.... 2 6
Figure 6 e: Trend for High Turbidity Days in Forest Grove’s Raw Water

.............. 2 6
Figure 7 a: Influent Turbidity for Hillsboro

- Cherry Grove

................................ ...... 2 7
Figure 7 b: Precipitation for Hillsboro

- Cherry Grove

................................ ............ 2 8
Figure 7 c: Raw Water Turbidity Trend for Hillsboro

- Cherry Grove

...................... 2 8
Figure 7 d: Number of Days with High Turbidity in Hillsboro

- Cherry Grove’s

Raw Water

................................ ................................ ........................ 2 9
Figure 7 e: Trend for High Turbidity Days in Hillsboro

- Cherry Grove ’s

Raw Water

................................ ................................ ........................ 2 9
Figure 8 a: Influent Turbidity for City of Siletz

................................ ...................... 30
Figure 8 b: Precipitation for City of Siletz

................................ ............................. 3 1

### iv 

## Turbidity Analysis for Oregon Public Water Systems

Figure 8 c: Raw Water Turbidity Trend for City of Siletz

................................ ...... 3 1
Figu re 8 d: Number of Days with High Turbidity in City of Siletz ’ Raw Water

....... 3 2
Figure 8 e: Trend for High Turbidity Days in City of Siletz’ Raw Water

................. 3 2
Figure 9 a: Influent Turbidity for City of Yamhill

................................ ................... 3 3
Figure 9 b: Precipitation for City of Yamhill

................................ .......................... 3 4
Figure 9 c: Raw Water Turbidity Trend for City of Yamhill

(includes effects of 1996 storms )

................................ ....................... 3 5
Fig ure 9 d: Raw Water Turbidity Trend for City of Yamhill

(ex cludes effects of 1996 storms )

................................ ...................... 3 5
Figure 9 e: Number of Days with High Turbidity in Yamhill ’s Raw Water

............. 3 6
Figure 9 f: Trend for High T urbidity Days in Yamhill ’s Raw Water

........................ 3 6
Figure 1 0 : Reductions in fine sediment generated from roads and

delivered to streams in Seattle’s Cedar River watershed

................... 40



# List of Tables

Table 1: Recommendations for future work based on turbidit y status and trend

.... 7

Table 2: Seasonally

- adjusted turbidity & high turbidity day trends

for Astoria’s water sources

................................ ................................ .... 1 3



# List of Maps

Map 1: Drinking water source areas originating in Oregon’s Coast Range

............ 5
Map 2: Turbidity case studies’ dr inking water source areas

................................ ... 8

### 1 

## Turbidity Analysis for Oregon Public Water Syste ms



# Executive Summary

After catastrophic storms and landslides hit the Oregon Coast in 2006 and 2007, the Oregon Department of Environmental Quality and Oregon Department of Human Services had concerns about the resiliency of publi c water systems that rely on surface waters in watersheds prone to heavy rains and landslides. Landslides in such areas can deposit large amounts of sediment that can increase turbidity and significantly lower the quality of drinking water obtained and tre ated by these water systems. Increasing levels of turbidity may interfere with public water system operations, can increase operational costs and can also cause shutdowns. In addition , DEQ and DHS were interested in the potential effects from climate chan ge in these watersheds.

DEQ sent e

- mail inquiries and interviewed staff at numerous public water systems in the Coast Range and Southwest Oregon. It also obtained and analyzed available daily turbidity data from seven water systems (Hillsboro

- Cherry Grove and the cities of Astoria, Carlton, Falls City, Forest Grove, Siletz and Yamhill) and

co lle cted data on water treatment facility shutdowns from Arch Cape Water District.

DEQ evaluated as case studies a total of eight public water systems in the North and Middle Oregon Coast Range area and used available turbidity data to analyze long

- term trends. DEQ‟s analysis concludes that there are long

term concerns about system viability or increased treatment costs at five systems (Arch Cape Water District and

the cities of Astoria, Carlton, Siletz, and Yamhill), based on large numbers of high

- turbidity days and/or increasing numbers of high

- turbidity days recorded in daily water samples for these systems. Also, DEQ found that turbidity is increasing in the long ter m in Drinking Water Source Areas for five systems, remains stable at one system, and is decreasing at two others.

Drinking Water Source Areas for these Coast Range systems are pr edominant ly forested. Only the City of Siletz has a significant amount of rur al residential and/or agricultural land in the lower part of its source area.

Precipitation has the greatest impact on turbidity patterns for these systems, with the largest spikes in turbidity occurring during the autumn months. In addition to this seaso nal variation, for the five systems with increasing turbidity trends, there are an increasing number of days reported with turbidity levels above 5 nephelometric turbidity units (a system of measuring water‟s clarity in terms of visible light), turbidity s pikes of increasing magnitude and/or increasing baseline turbidity. In addition to the problems high turbidity can cause on drinking water treatment and system operation, changes in turbidity may also adversely affect aquatic life or other

beneficial uses of the water, such as fishing and swimming.

High turbidity levels at some of these eight public water systems may be the result of inherent watershed characteristics, natural events (such as storms, slides and bank erosion), and land

- use activities ( for estry

, agriculture, rural residential, road building and maintenance ). Regardless of the source of turbidity, watershed protection and restoration activities can reduce unacceptable levels of sediment deposited into public water system

sources and can redu ce the cost of drinking water treatment.

This analysis was not designed or intended to answer cause

- and

- effect questions related to turbidity. Further statistical and Geographic Information System analysis is necessary to evaluate the effects of human

- cau sed changes, natural disturbances and inherent watershed features on public water systems. But collection of new data, further analysis of existing data, enhanced source water monitoring and evaluation and analysis of sediment

sources and movement will hel p DEQ and DHS further understand and manage risks to public water systems. In addition, changes in weather patterns and precipitation due to climate change should be considered as this topic is

studied further.

### 2 

## Turbidity Analysis for Oregon Public Water Syste ms



# Introduction

The storms of December 2007 re sulted in catastrophic flooding in the northern Coast Range of Oregon, destroying or harming homes, water supplies, fisheries, roads, farms, an d businesses. Many of Oregon‟s Public

W ater S ystems (PWSs) were directly impacted by the flooding, wind damage, and landslides in their municipal

watersheds. The Department of Human Services (DHS) and the Department of Environmental Quality (DEQ) had previously mapped all of these watersheds and prepared Source Water Assessment (SWA) reports for the community offic ials ( http://www.deq.state.or.us/wq/dwp/dwp.htm )

. The SWAs included maps of the source area boundaries, natural characteristics of the watersheds, and identified potential risks for the systems.

The damage from the storms raised questions about the sensitivity of these PWS s as the number of severe storms could increase due to climate change. The landslide near Clatskanie in northwest Oregon completely destroyed Westport‟s water system. DHS was concerned about the potential for complete loss of, or severe damage to, the systems due to storms. As part of the existing drinking water protection planning and implementation, DEQ

embarked on this analysis of potential turbidity problems for PWSs

. The purpose of this first phase of analysis is to use existing data to identify the PWS s that have ongoing turbidity problems and to conduct a trend analysis if

data is available

.

W ork was initiated in January 2008 with an email/phone questionnaire to 148 s urface water systems in Oregon. DEQ asked them if there were any recent landslides in their watershed that impacted the intake(s). We indicated

our purpose was to evaluate whether we need to put more resources into this problem at the state level. Out o f this initial query, we received information from 17 different systems that had turbidity impacts, but not necessarily from landslides. Several system operators asked for assistance to determine what was causing the turbidity and to assist them in reduci ng the loading to the source stream. At that point, both DHS and DEQ determined that we should proceed with an analysis of the turbidity issues and follow this with recommendations for reducing the risks for those systems.



# Applicable Turbidity Standards for Water Quality

The turbidity water quality standard (OAR 340

- 41

- 0036) is:

Turbidity (Nephelometric Turbidity Units, NTU): No more than a ten percent cumulative increase in natural stream turbidities may be allowed, as measured relative to a control poi nt immediately upstream of the turbidity causing activity. However, limited duration activities necessary to address an emergency or to accommodate essential dredging, construction or other legitimate activities and which cause the standard to be exceeded may be authorized provided all practicable turbidity control techniques have been applied and one of the following has been granted:

(1) Emergency activities: Approval coordinated by the Department with the Oregon Department of Fish and Wildlife under

cond itions they may prescribe to accommodate response to emergencies or to protect public health and welfare;

(2) Dredging, Construction or other Legitimate Activities: Permit or certification authorized under terms of section 401 or 404 (Permits and Licenses, Federal Water Pollution Control Act) or OAR 14l

- 085

- 0100 et seq. (Removal and Fill Permits, Division of State Lands), with limitations and conditions governing the activity set forth in the permit or certificate.

In Oregon, there are many waters with low NTU levels and a 10 % increase is very difficult to measure in a clear

stream. In addition, the original 10% Turbidity water quality standard was based on Jackson turbidity units (JTUs) which are measureable to 25 JTU with an accuracy of ± of 1 JTU. The standard switched to NTU s which

are measureable to 1 NTU with an accuracy of ± 0.1 NTU. This has led to claims that DEQ‟s turbidity standards cannot by implemented. In reality, the 10% exceedence criteria was designed to take into account the fact that

### 3 

## Turbidity Analysis for Oregon Public Water Syste ms

natural conditions in streams do not produce consistent low turbidity at all times. DEQ recognizes that there is some natural variation and this creates difficulty in determining whether turbidity levels exceed the criteria of a

10% increase. There are s everal characteristics of turbidity by which a 10% increase could be documented: the baseline turbidity of a stream, the number of spikes in a stream‟s turbidity, the median or 75 th percentile of turbidity, and/or the statistical trend that the stream‟s tu rbidity is following. However, the standard relates to a control point immediately upstream and is not applicable at the watershed scale but at the reach scale. The turbidity WQS may be revisited in 2009 or 2010.

Turbidity is one of the primary pollutan ts regulated in finished drinking water under the Safe Drinking Water Act (SDWA). To protect human health, t he EPA has set the level of allowable turbidity in finished drinking water at : 0.3 Nephelometric Turbidity Units (NTU) in 95% of samples (1 NTU abs olute maximum) for conventional (sedimentation and rapid sand filtration) and direct (rapid sand only) filtration; and 1 NTU in 95% of samples (5 NTU absolute maximum) for membrane, cartridge, slow sand

, and diatomaceous earth filtration ( US EPA 1998

, US E PA 2001 , US EPA 2002b ). Turbidity limits prevent drinking water from having excessive level s of suspended fine sediment ( US EPA 1999 )

. Suspended sediment is of concern for drinking water safety as it can reduce the effectiveness of disinfection treatment s ( LeChevallier et al 1981 ), harbor pathogens (e.g. Chang et al 1960, Tracy et al 1966, Sen & Jacobs 1969, Meschke & Sobsey 1998 ), contribute to formation of disinfection by

products ( Nikolaou et al 1999, US EPA 2002 a ), and carry nutrients , heavy metals, p esticides , and other toxic

chemicals ( Lick 2008 ). Unpleasant tastes and odors frequently co

- occur with e xcessive turbidity ( US EPA 1998 )

. Prevention or removal of fine sediment pollution from water reduces these risks to acceptable levels ( US EPA

2001 )

.

Most drinking water treatment facilities run by Public Water Systems (PWSs) have the capacity to remove

turbidit y

- causing sediments during treatment of raw water; however, the amount of turbidity that can be effectively removed depends on the treatment te chnology in use (US EPA 1999

, personal communication with PWS managers )

. For example, water can be treated using a flocculent/coagulant agent to collect fine sediments into larger particles which are then removed by rapid pressurized filtration through a bed of sand. Another common drinking water treatment system, slow sand filtration, allows water to slowly percolate through a large bed of sand to be collected through an underdrain. When source water turbidity exceeds 5 NTU, a treatment plant using the s e treatment system s will usually need to shut down ( National Drinking Water Clearinghouse (NDWC)

1996

, pers comm with PWS managers )

. PWSs with additional pre

- filtration or pre

- sedimentation basins can treat

source water with turbidity high er than 5 or 10 NTU ( US EPA 2004, pers comm with PWS managers)

. Some
systems in Oregon with frequent high turbidity install advanced filtration systems that can treat water with turbidity higher than 50 or 100 NTU ( e.g. City of Coquille )

. These advanced filtration syste ms are expensive to install and maintain and may not be affordable for all small PWSs. Some studies have shown that p revention of turbidity and fine sediment pollution is a cost effective way to ensure that current PWS treatment can meet the

SDWA Maximum Contaminant Level (MCL) for turbidity ( Brown 2000 )

.



# Public Water System Evaluation s

Some Public Water Systems have historic and/or current problems with turbidity in the ir source water. There are 161 PWSs with all or part of their Drinking Water Source A reas (DWSAs) in the Coast Range and mountains of Southwestern Oregon (Appendix A). This report focuses on 8 PWS Case Studie s in the North Coast and Mid Coast regions that included interviews with PWS directors/supervisors and analysis of available raw wat er turbidity data . We also conducted field visits in the DWSAs for the Arch Cape, Siletz, and Yamhill PWSs

. The

PWS examined in th is report are: Arch Cape Water District, City of Astoria, City of Carlton, City of Falls City,

### 4 

## Turbidity Analysis for Oregon Public Water Syste ms

City of Forest Grove,

Hillsbo ro

- Cherry Grove, City of Siletz, City of Yamhill.

I n addition, the following PWS were also interviewed and status reports were written based on the interview. The status reports give some history of each PWS, the operators‟ opinions of the current situat ion, and their concerns about potential threats to the PWS. Those status reports a re not included in th is report becau s e we could not get turbidity data or conduct a site visit : City of Clatskanie, City of Coquille, Langlois Water District, City of Myrtle Point, City of Port Orford, City of Powers, Rainier Water Department, Seaside Water Department, City of Waldport, Westport Water Association. Some water systems did not have daily turbidity data available in an accessible format, and not all PWSs collect precipitation data. Several were affected by a large landslide in December 2007 above Highway 30 near the Columbia River. One (Westport Water Association) had their intake and associated infrastructure completely destroyed by the slide. Out of the 18 wa ter systems that were interviewed, 14 had problems or expressed concerns about high and/or increasing turbidity in their source water.

### 5 

## Turbidity Analysis for Oregon Public Water Syste ms

Methods We received beginning

- of

- the

- day turbidity data from 7 PWSs, giving a snapshot of turbidity conditions at about 8am each day. One PWS (Arch Cape) gave us data with the dates of treatment shutdowns due to turbidity. Data were organized and counts of high turbidity days per water year were done using Microsoft Excel 2007. Minitab v15.1 was used for graphing and data analysis, including time series trend a nalysis for high turbidity days using the method of Box and Jenkins (1994) and seasonally

- adjusted trend analysis of turbidity data over time (Makridakis et al 1998). The trend analysis of high turbidity day s show ed whether the number of days with turbidity ≥5 NTU (“high turbidity days”) is changing directionally over time. We fitted linear, quadratic, and exponential models and cho se the model with the best accuracy, as shown by lower Mean Absolute Percent Error 

### Map 1

### 6 

## Turbidity Analysis for Oregon Public Water Syste ms

(MAPE), Mean Absolute Deviation (MAD), and Mean Squared Deviation (MSD) scores. In no cases did the exponential model have the best fit. The seasonally

- adjusted trend analysis of turbidity separate d the data into seasonal and linear trend component s. The decomposition of seasonal and linear trends allow ed examination of long

- term change while accounting for the tendency of stream systems to have elevated turbidity at the beginning of the autumn rainy season. Trend equations take the form:

Linear: Y t =α+βt Quadratic: Y t =α+βt+γt 2

where Y

t is the turbidity at time t

, α is the y

- axis intercept, and β and γ are the coefficients of change for t and t 2

, respectively.

We used ArcGIS v9.3, operator interviews, and field visits to evaluate patterns in land o wnership and conditions on the ground.



### Definitions of terms

Low T urbidity S tatus― T urbidity baseline lower than 5 NTU greater than or equal to 5 0% of the time High T urbidity S tatus―T urbidity baseline low er than 5 NTU less than 5 0% of the time

Occasional S p ikes―S udden increases in turbidity that exceed 5 NTU occurring less than 3 0 times/year Frequent Spikes―S udden incr eases in turbidity that exceed 5 NTU occurring more than 3 0 times/year Increasing Trend― β > 0.000150 for seasonally

- adjusted turbidity trend

D ecreasing Trend― β <

- 0.000150 for seasonally

- adjusted turbidity trend

Stable Trend― 0.000150 ≥ β ≥

- 0.000150 for seasonally

- adjusted turbidity trend



### Summary of Results

Conditio n s range d from low turbidity with occasional spikes to frequent large spikes th at require interven tion by

operators to consistently high turbidity throughout the late autumn, winter, and early spring. T urbidity t rends range from historic problems that are improving to steady turbidity patterns (whether high or low) to increasing

tur bidity leading to more frequent problems. There is significant variation among Public Water Systems, with some having noticeably more high turbidity days than others (Figure 1.) Currently, the Cities of Astoria and Falls City have the most consistently

l ow turbidity while the Cities of Carlton, Siletz, and Yamhill have frequent high turbidity days. Arch Cape was analyzed differently because daily turbidity data were

unavailable.

Below are suggested approaches for PWSs or agencies to address a

situation , generally Figure 1: Count of days when influent water turbidity equal or exceeds 5 NTU by water year for 1994 through 2008. The water year is October 1 st through September 30 th

.

### 7 

## Turbidity Analysis for Oregon Public Water Syste ms

speaking. Specifics will vary from system to system based on their particular watershed (s) and the level of resource protection within it. It is also important to note that many PWSs do not have resources beyond those needed for day

- to

- day op erations and maintenance; additional protection measures require additional funding (Drinking Water Needs Survey 2009).

Table 1: Recommendations for Future Work Based on Turbidity Status and Trend Low Turbidity (Occasional Spikes) Low Turbidity (Frequen t Spikes) Consistent High Turbidity

Trend of Decreasing Turbidity N/A Evaluate situation/
Consider DWSA protection measures Find causes/Consider
additional DWSA protection measures

Trend of Stable Turbidity Evaluate situation/
Consider DWSA protection m easures Find causes/Consider
additional DWSA protection measures Find causes/C hange DWSA mgmt. & implement restoration

Trend of Increasing Turbidity Find causes/
Consider additional DWSA protection

measures Find causes/C hange

DWSA mgmt. & implement restor ation Find causes/C hange DWSA mgmt. & implement restoration

### 8 

## Turbidity Analysis for Oregon Public Water Syste ms



# Ca se Studies

Map 2

### 9 

## Turbidity Analysis for Oregon Public Water Syste ms



# Analysis of Public Water System Turbidity Data

Arch Cape Water District (PWS# 4100802)

Thomas Merrell

, Director

503

- 436

- 2790

Increasing Trend [Reported by PWS] : Low Turbidity (Occasional Spikes) transitioned to Low Turbidity (Frequent Spikes) Arch Cape is small coastal community in southern Clatsop County with a mixture of year

- round and part

- time residents. The treatment plant uses chemical coagulation and pressurized (rapid ) sand filtration to remove particulates from the source water. The district has two drinking water intakes in its 1,250 acre Drinking Water Source Area (DWSA): on Asbury Creek, a medium

- sized coastal stream, and on Shark Creek, a medium

- sized tributary o f Asbury Creek. The primary intake on Shark Creek is behind a small dam that forms an intake pool, and the secondary intake is on Asbury Creek below its confluence with Shark Creek. T he land of the forested

DWSA has been owned by a succession of p rivate industrial timber companies . Arch Cape Water District does not have a backup source of water.

Arch Cape Water District has difficulty with operations due to high turbidity and spends a significant proportion of

each month shutdown due to turbidity with the exception of the summer

months (Figure 2) . Arch Cape Water District does not have a backup source

of water. If the PWS

cannot use the Shark Creek intake, then they must use the Asbury Creek intake (downstream

of the confluence of Shark and Asbury Cr eeks ). If

neither intake is usable

, then the PWS must shut down water purification and use stored water (3 to 7 day supply).

F urther increases in suspended sediment in Arch Cape‟s DWSA could be very problematic. As little as 0.5 inches

of rain raise s st

ream turbidity to the point that Arch Cape‟s rapid sand filtration c an not remove enough fine

sediment to meet finished water standards ( T. Merrell, pers comm )

. For the last 3 years, t he intake pool has

need ed to be dredged yearly by necessity where durin g the previous decade the PWS only dredged it once every 3 or 4 years as routine maintenance. To cope with the increased turbidity, Arch Cape recently applied for and received over $1 million in American Recovery and Reinvestment Act (“stimulus”) funds to replace their rapid sand filtration and chlorination treatment with membrane filtration and UV disinfection. Leaking distribution pipes will also be replaced with these funds. Figure 2: Number of days per month that Arch Cape Water District‟s treatment plant spent shutdown due to high turbidity from January 2007 through March 2010. Bar colors highlight the calendar year.

### 10 

## Turbidity Analysis for Oregon Public Water Syste ms

City of Astoria (PWS #4100 0 5 5)

Jim Hatcher , Public Works Operations

503

- 325

- 3 524

Increasing Trend: Low Turbidity (Occasional Spikes) The City of Astoria is located on the Columbia River estuary. Astoria has water supply intakes on two lakes (Middle and Main Lakes) and t wo creeks (Cedar and Bear Creeks). They can switch among int akes as needed, depending on weather and source conditions. Astoria typically draws more water from the creeks during the

summer and more from the lakes in winter due to turbidity fluctuations. Th is ability to change sources is an important asset. Asto ria uses a slow

- sand filter to remove particulates, and these filters can be easily clogged by turbidity higher than 5 NTU. Since 1956, t he City of Astoria has own ed nearly all of the 2,736 acre forested Drinking Water Source Area (DWSA), in addition to a small part of neighboring Wikiup‟s DWSA

. The City

does harvest timber from the DWSA

. The Forest Stewardship Council (FSC) certified Astoria‟s management and harvest operations as “Well Managed” forestland (the highest classification) in 2003. A private industrial timber (PI) company owns less than 5% of Astoria‟s DWSA , of the southern and northern edges

. Private industrial companies own the land surrounding Astoria‟s DWSA

.

Turbidit y for water entering Astoria‟s water treatment plant is shown below ( Figure 3 a ). When the source supplying the treatment plant begins to be too turbid, then operators survey all

sources to determine

which has the lowest turbidity and is most

suitable for use (Figures

3 b&c)

. The refore, the source in use is typically

the on e with the lowest turbidity. Rises in turbidity are frequently triggered by precipitation (Figure 3 d). The turbidity

patterns in Astoria‟s water

s ources are fairly stable and easily managed with the multitude of potential

intakes. However,

influent tur bidity is slightly increasing overall (Figure 3 e ), albeit at low rate and well below levels that would drive serious concerns. All of the individual sources except Cedar Creek show at least some recent increase in turbidity ( Table 2 ). Spur

14 Creek has v ery low turbidity, so its fluctuations in turbidity may appear meaningful when in fact they are very

small.

As the influent turbidity approaches 5 NTU, Astoria‟s drinking water system switches to another source with lower turbidity. High turbidity days i n the influent water are therefore rare, even when several of the sources have elevated turbidity (Figure 3 f). The flexibility among sources created a flat , and extremely low, trend in high turbidity days (for influent) over the last 6 years (Figure 3 g). Bear Creek‟s trend in high turbidity days remained Figure 3 a: Turbidity for City of Astoria‟s drinking water system. Since the City can switch between sources as needed, this represents a composite of whichever source has the lowest turbidity at any given time. Other sources within the DWSA probably h ad higher turbidity at the time.

### 11 

## Turbidity Analysis for Oregon Public Water Syste ms

level after a jump in 2005, and Middle and Main Lakes had noticeable increasing trends in the last two years (Table 2 ). The turbidity increase s in Bear Creek and the two lakes may be cause for concern an d are likely contributed to by ground

disturbed as trees toppled in large numbers during

the December 2007

windstorm that struck Oregon‟s North Coast.

Much of this blowdown was adjacent to clearcuts on neighboring private

land.

Figure 3 b: Turbidity for the stream sources of Astoria‟s drinking water (Bear Creek, Cedar Creek, and Spur 14 Creek).

Figure 3 c : Turbidity for the lake sources of Astoria‟s drinking water (Middle Lake and Main Lake).

### 12 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 3 d: Precipitation at the Astoria WSO Airport co

- op weather station, the nearest weather data to Astoria‟s DWSAs. The seasonal pattern of precipitation drives the seasonal pattern i n turbidity.

Figure 3 e: The turbidity trend for the influent (raw) water is gradually increasing (Y t =0.85+0.000183*t), but the trend is not strong. Generally, the turbidity remains low.

### 13 

## Turbidity Analysis for Oregon Public Water Syste ms

Seasonally

- Adjusted Turbidity & High Turbidity Day Trends for Astoria’s Water Sources



### Source Water Turbidity Trend

Equation Direction of Change Days >5 NTU Tre nd
Equation

Bear Creek Y t = 1.27+0.000455*t Increasing Y t =

- 4.27+8.44*t

- 0.82*t 2

Cedar Creek Y t = 1.93+0.000065*t Stable Y t = 6.27+1.69*t

Spur 14 Creek Y t = 0.455+0.000169*t Increasing Y t = 1.20

- 0.057*t

Main Lake Y t = 0.975+0.000728*t Increasing Y t = 31.9

- 31.2 *t+6.05*t 2

Middle Lake Y t = 0.8 90 +0.000 572*t Increasing Y t = 11.3

- 11.4*t+2.66*t 2

Figure 3 f: Number of high turbidity days (>5NTU) per water year in Astoria‟s DWSA

as measured at the d rinking water treatment plant from the intake(s) in use (Influent) and

as measured at each source . The water year runs from October 1 st through September

30 th

. Table 2: Trend for seasonally

- adjusted turbidity and trend in the number of days with high turbidity for each of Astoria‟s water source. Trends are calculated for time period between November 2002 and September 2008.

### 14 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 3 g: Trend in number of high turbidity days in Astoria‟s DWSA for 2003 through

2008.

### 15 

## Turbidity Analysis for Oregon Public Water Syste ms

City of Carlton (PWS# 4100171)
Bryan Burnham, Public Works Supervisor

503

- 852

- 7575 bburnham@ci.carl ton.or.us

Increas ing Trend: Low Turbidity (Occasional Spikes) transitioned to Low Turbidity (Frequent Spikes) The City of Carlton is in Yamhill County near the eastern foothills of the Coast Range. Carlton has a reservoir on

Panther Creek with their int ake on the downstream end. Panther Creek is a tributary of the North Yamhill River on the east side of the Coast Range. The City has a dam and intake structure ; a reservoir behind the dam store s water for use during low flows. Carlton installed a floati ng intake structure in 2001 to draw water from the top of the reservoir rather than the bottom, as a means of reducing sediment entering the intake. The treatment plant filters out particulates by coagulation and flocculation with chemicals, followed by p ressurized (rapid) sand

filtration. Carlton owns 17 acres of their nearly 2100 acre DWSA; the City ‟s triangular parcel includes the reservoir and intake and a small section of forestland directly south of the reservoir. The remainder is a

checkerboard of Bureau of Land Management (BLM) land and private industrial forest land (approximately 50% each)

. The BLM land is currently managed under NWFP

. T he private industrial landowners have clearcut most
of their forestland in the watershed since 2000 ; some sma ll harvests occurred in the 1970‟s, 80‟s, and early 90‟s.

The Panther Creek intake is the sole year

- round water source; Carlton does not have an emergency or backup

source.

T urbidity data collected by the Carlton PWS at their intake from February

1998 t hrough September

2008 was used (Figure

4 a). In February 1999, a

debris flow occurred on

BLM land several hundred meters upstream
of Carlton‟s reservoir. Turbidity levels in 1999 and 2000 were higher than

in 1998 and returned to 1998 levels by 2001

, altho ugh this decrease may be due to the change to a floating intake . In the last five years, baseline turbidity is rising and the frequency and magnitude of spikes is increasing.

The seasonal weather patterns appear to have

been consistent (Figure

4 b) and in dicate that other factors may be contributing to the turbidity trends. The debris flow created a short

- term impact to the water system that was resolved within two years. The event was of a great enough magnitude that the PWS‟s turbidity trend appears to be declining when the debris flow is included in the trend analysis (Figure 4 c). However , trend analysis of the post

- recovery data (2001

- 2008) demonstrates that either turbidity in the DWSA is becoming steadily worse since 2001 or the sediment deposited b y the debris flow is moving deeper into the reservoir and being pulled into the intake (Figure 4 d). F igure 4 a: Carlton DWSA intake turbidity levels from February 1998 through September 2008. In 1999, a debris flow occurred in a tributary 600ft upstream of the reservoir. Turbidity returned to 1998 levels by 2001. More recently, spikes in turbidity

incr eased.

### 16 

## Turbidity Analysis for Oregon Public Water Syste ms

As stated above, days with turbidity ≥5 NTU

were characterized as “high turbidity days”

because at this level the PWS risks clogging its

sand filter un less it has a

means to pre

- treat the raw

water . Carlton‟s DWSA

reached its maximum of 271 high turbidity days in 1999 before returning to a low of 13 days in 2001. Since then, the maximum

number of high turbidity days has increased gradually to 98 days i n Water Year 2008, the

maximum since

stabilization of th e

t ributary landslide (Figure

4 e). A nalysis of the

trend in high turbidity days shows a linear increase in high turbidity episodes over the last eight years (Figure 4 f ). Carlton has advanced filtra tion systems and is usually able to purify water adequately. The PWS supervisor report ed that during the winter of 2007

- 08 a silt bar formed where Panther

Creek flows into the reservoir. In addition, reservoir st o rage is being lost due to sediment settli ng out in the reservoir (F igure 4 g). Carlton plans to dredge the reservoir to restore lost capacity and prevent future problems

. Figure 4 b: Precipitation at Carlton‟s water treatment facility. The seasonal pattern of precipitation drives the seasonal pattern in turbidity. Many of the changes in turbidity appear seasonal and weather

- driven , but other factors are also suspected.

### 17 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 4 c: The trend decreases over time (Y t =7.88

- 0.00139*t). The linear shape of the trend fails to capture the true trend of the data, which has a curved (quadratic) shape. The accuracy measures are relatively high (MAD of 3.896 NTU), showing that the fit of the trend is somewhat poor.

Figure 4 d: Turbidity levels in 2001 are similar to those in 1998 and subsequently show an increasing trend of turbidity levels (Y t =2.62+0.00079 6*t). The lower values of the accuracy measures (MAD of 1.711 NTU) reflect a better fitting trend than in Figure 2c.

### 18 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 4 e: Number of high turbidity days (≥5NTU) per water year at Carlton‟s drinking water intake. The water year runs from October 1 st through September 30 th

.

Figure 4 f: Trend in number of high turbidity days in Carlton‟s DWSA for 2001 through

2008.

### 19 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 4 g: Storage capacity of Carlton‟s reservoir from soundings done in 1998, 2004, and 2008. The decrease in capacity is thought to be due to a landslide that occurred in

1999.

### 20 

## Turbidity Analysis for Oregon Public Water Syste ms

City of Falls City (PWS# 4100297)

PWS # 4100297

Don Poe Public Works Supervisor

503

- 787

- 1305

Stable Trend: Low Turbidity (Occasional Spikes) The City of Falls City is in Pol k County near the Coast Range ; Falls City ‟s treatment facility uses slow sand

filtration for removal of particulates. T hey cease water purification when turbidity goes above 5 NTU , as higher turbidity clog s the filters . Their 3,2 19 acre combined Drinking Water S ource Areas are located on the eastern slopes of the Coast Range. Falls City has two drinking water intakes: one on Glaze Creek and the other on Teal

Creek. The intake on Glaze Creek is only 1⁄2 mile from the springs, resulting in very low turbidit y the majority of

the time. The Glaze Creek intake is usually the sole intake in use during late autumn and winter, water from Glaze and Teal Creeks are mixed during spring and early summer, and only Teal Creek is used in the late summer and early autumn when flows are too low on Glaze Creek. The use pattern of the intakes probably keeps influent turbidity low by relying on Glaze Creek during the early rainy season when high turbidity events are most common ( personal communication w/ PWS staff). Ownershi p of t he Glaze Creek DWSA (648 acres) is split

between a private industrial (PI) c ompany and the Bureau of Land Management with each owning about half of the drainage. The Teal Creek DWSA (2571 acres) is ~90% owned by the PI company . The BLM owns

~ 10% o f

th e drainage with an un identified private non

- industrial landowner own ing ~50 acre s near the intake

. Falls City does not own any of the land in the ir DWSA s

. Private landowners logged half of the Teal Creek DWSA and

about 15% of the Glaze Creek DWSA in the last ten years. Water quality in the watershed is historically very good.

Turbidity data collected daily at approximately

8am by the Falls City

PWS from November

1999 through September 2008 was used (Figure

5 a). [ Falls City must

shutdown their int ake for 1 to 3 days during storm

triggered turbidity spike s greater than 5 NTU

. Data were censored (>5 NTU

but of indeterminate value) on days of treatment plant shutdowns due to high turbidity. These data are

counted as 5 NTU in the analyses, but the va lues are likely to be higher.]

Th e collected data

represent the source wa ter being used at the time, so they cannot characterize Teal Creek during the winter or Glaze Creek during the late summer, for example. Teal Creek could have high or low turbidity during the winter, but it cannot be evaluate d with this data. The composite influent for Falls City has very low baseline turbidity with few spikes, relative to other PWSs in this report. The seasonal weather

pattern had few large storms earlier in the d ecade ( 2001

- 2004; Figure 5 b). This appears to have been a calm Figure 5 a: Falls City‟s influent turbidity levels from November 1999 through September 2008. Water from Falls City‟s DWSAs generally has low baseline turbidity with infrequent spikes.

### 21 

## Turbidity Analysis for Oregon Public Water Syste ms

period relative to 2000 and 2005 onward. Seasonally

- adjusted t rend analysis of the data (1999

- 2008)

demonstrates that influent turbidity is remaining

stead y in the time period analyzed (Figur e 5 c ).

As stated above, days with turbidity ≥5 NTU

were characterized as “high turbidity days”

because at this level the PWS risks clogging its

sand filter without the

means to pre

- treat the raw

water. Falls City ‟s

influent water reached its

maximum of 8 high turbidity days in 2007 (Figure 5 d)

. Three years did not have any high turbidity days at all

. Analysis of the trend in high turbidity days shows

a slight quadratic increase in high turbidity episodes over the last eight years (Figure 5 e ). Fal ls City reports that they currently get spikes in turbidity during moderate

- to

- heavy rain that requires

shutdowns. Nevertheless, Falls City experiences high turbidity days very rarely compared to other Coast Range PWSs examined in this report

, so the phys ical significance of this trend may be minimal

. If this trend continues, it would

be cause for concern. Figure 5 b: Precipitation at the Rockhouse1 R AWS weather station, the nearest weather data to Falls City‟s DWSAs. The seasonal pattern of precipitation drives the seasonal pattern in turbidity.

Figure 5 c: The trend remains relatively steady over time (Y t =0.62

- 0.000076*t).

Censored data from treat ment plant shutdowns due to high turbidity (in 2003, 2006, and 2007) are entered as 5 NTU when the values were possibly higher. However, the trend does not change much and remains “stable” even if censored data are assigned higher values (15 NTU, Y t =0.61

- 0.000037*t; 50 NTU, Y t =0.62+0.000093*t).

### 22 

## Turbidity Analysis for Oregon Public Water Syste ms

In November of 2006, Falls City had several days of high turbidity triggered by logging and hauling operations near the springs of Glaze

Creek in th e midst of heavy rains

. O regon D epartment of F orestry
later determined that there

were violations of forest practice rules including wet weather hauling

limitations

. Shortly after the incident, DEQ acquired minimum, maximum, and mean daily turbidity da ta for 11/01/2006 through 11/10/2006. We graphed

this data with the 8am data used in this analysis of Falls City (Figure 5 f

). The 8am data is fairly close to the mean, but does not accurately show the extremes, especially

the maximum. More systematic d ata collection that shows the range of daily turbidity is probably

needed to characterize DWSAs accurately.

Figure 5 e: Trend in number of high turbidity days in Falls City‟s influent water for 2000 through 2008

. Figure 5 d: Number of high turbidity days (≥5NTU) per water year in Falls City‟s influent drinking water. The water year runs from October 1 st t hrough September 30 th

.

### 23 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 5 f: Comparison of daily means, minima, and maxima with 8am „snapshot‟ data during sedimentation incident in Novem ber, 2006. 8am data are close to the mean, but inexact. 8am data do not reflect maximum turbidity well.

### 24 

## Turbidity Analysis for Oregon Public Water Syste ms

City of Forest Grove (PWS #4100305)
Randy Smith, Water System Supervisor

503

- 992

- 3259

Decreasi ng Trend: Low Turbidity (Frequent Spikes ) trending towards Low Turbidity (Occasional Spikes) The City of Forest Grove is located to the west of Portland in Washington County

. The PWS removes particulates with a sedimentation basin, followed by chemical coagulation and flocculation with rapid sa nd

filtration. They own 4300 acres, most of which is in the ir small DWSA on the east side of Oregon‟s north Coast Range. Forest Grove‟s ownership is ~75% of the DWSA; the balance is ~ 7 % state forest, ~ 7 % private industrial (various owners ) , and ~10% priv ate non

- industrial. The streams in the DWSA are Clear Creek, Deep Creek, Roaring Creek, Smith Creek, and Thomas Creek, all upper tributaries of the Tualatin River. These watersheds are used most of the year; however, Forest Grove gets water from the Join t Water Commission (JWC, Hillsboro

, Beaverton, and other municipalitie s) in summer if stream levels get too low to keep the intake at an adequate depth or in November and December if flushing of sediment from the stream system force s a shutdown of drinking water treatment

. I n 2000

, the City Council approved a Forest Stewardship Council (FSC)

- certified management plan. Trout Mountain Forestry manages the watershed sustainably on the City‟s behalf.

T urbidity data collected by the Forest Grove PWS

at th eir intake from November 1994 through September 2008 was evaluated . The re is a decreasing trend in turbidity (Figure 6 a). The turbidity patterns are unlikely to be explained by weather, as the seasonal weather patterns appear to be consistent (Figure 6 b)

. Trend analysis of the turbidity data shows the declining turbidity in the system

since the mid

- 1990‟s (Figure 6 c). In particular,

1996 and 1997 showed a great many large spikes in turbidity before and after the February 1996 storms. With time, the Cre eks

flushed out the additional fine sediment.

D ays with turbidity ≥5 NTU can adversely affect the treatment of water for the Forest Grove PWSs. The number of high turbidity days for Forest Grove‟s DWSA reached a maximum of 103 days in 1997. The number of high turbidity days has stayed low during the last eight years (F igure 6 d)

. Trend analysis shows the initial rapid decrease in high turbidity days is leveling off (Figure 6 e ). Their FSC

- certified plan has allow ed Forest Grove to generate revenue and solve the legacy problems from previous activity , including remov al o f risky/unnecessary

roads and culverts

, revegetation

, and geoengineering. H ighly erosive or steep areas are not harvested . Riparian protectio n zones are 75 to 200 feet wide with the following requirements: Figure 6 a: Turbidity for the Forest Grove DWSA intake from November 1994 through September 2008. Note that while the seasonal patterns remained, the baseline turbidity declined, and the frequency and intensity of spikes decreased.

### 25 

## Turbidity Analysis for Oregon Public Water Syste ms

Timber removal is prohibited within riparian pr otection zones, except for restoration activities (no commercial harvest is allowed). Practices promote older

forest structure and diversity.

Skid trails or roads in riparian areas are

retired or relocated wherever possible. Equipment operation in ripari an areas is prohibited, except for

restoration activities.

Restoration activities within riparian

areas use methods with the lightest possible impacts. (Forest Grove Watershed
Plan, Chapter 4 )

.

T he current turbidity and

fine sediment situation is easily managed by PWS

staff because of the generally low turbidity,

the identification of problem sources by their forester, and their ability

to switch to JWC water when necessary

. In 2001,

Forest Grove received a League of Oregon Cities

award for their effort s. Figure 6 b: Precipitation in Forest Grove‟s DWSA. The seasonal patt ern of precipitation drives the seasonal pattern in turbidity.

Figure 6 c: Turbidity trend for Forest Grove (Y t =3.97

- 0.000401*t). The decreases in both baseline turbidity and the frequency of spikes results in a downward linear trend. The trend without the effects of the 1996 flood is similar (Y t =3.90

- 0.000482*t; graph of

1997

- 2008 not shown).

### 26 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 6 e: Trend in number of high turbidity days in Forest Grove‟s DWSA. Figure 6 d: Number of high turbidity days (>5NTU) per water year in Forest Grove‟s DWSA as measured at the drinking water intake . The water year runs from October 1 st
through September 30 th

.

### 27 

## Turbidity Analysis for Oregon Public Water Syste ms

Hillsboro

- Cherry Grove (PWS# 4100985)

Niki Iverson Water Resources Manager

503

- 615

- 6770 nikii@ci.hillsboro.or.us

Sta ble Trend: Low Turbidity (Occasional Spikes) [Formerly a Decreas ing Trend: Transitioned from Low Turbidity (Frequent Spikes) to Low Turbidity (Occasional Spikes)]

The Hillsboro

- Cherry Grove Public Water System (PWS) is the sole provider of drinking water to the community of Cherry Grove and the primary provider for the City of Gaston, the community of Dilley, and the LA Water Co

op

. (The other provider is the Joint Water Commission, PWS# 4100379.) The se communities are west of

Portland near the Coast Ra nge. The PWS has two water sources: the upper Tualatin River and Barney Reservoir, on the upper Trask River. Water from Barney Reservoir is piped into the upper reaches of the Tualatin River during drier months (June through October ) to supplement the Tu alatin‟s flow. The PWSs Slow Sand Filtration

Plant (SSFP) , which removes particulates by means of a settling pond (sedimentation) and slow sand filtration, is currently benefitting from low turbidity in the upper Tualatin River , but, a s a precaution, the water district shuts

the slow

- sand plant when turbidity is 5 NTU or greater

. The forested Drinking Water Source Area (DWSA) in the upper Tualatin River is over 15,500 acres of mixed public and private ownership

. The terrain is landslide prone in the area near the slow

- sand water filtration plant. The southeas tern corner of the DWSA (near the intake)

is a checkerboard of land

owned by the PW S (~3% of DWSA) and the B ureau of L and M anagement (~5%)

. A small parcel (

~ 1% of DWSA ) of private non

- industrial

tim berland straddles the southern edge. A private industrial (PI) c ompany

owns the Lee Creek drainage and the headwaters of Sunday Creek, amounting to the eastern edge and the

north east ern third of the

DWSA (~45% of the DWSA)

. The remaining (~45 %) area of t he

DWSA is in the

Tillamook State Forest

, including most of Sunday Creek and nearly all of Maple Creek

, in addition

to the headwaters of the

Tualatin River

. Some parti al cuts (thinning) occurred on s tate and federal lands. Since 2000, the major private

i ndustrial (PI) landowner has harvested approximately half of their land by clearcutting. The forested DWSA for

the intake on Barney Reservoir is 5275 acres of mixed ownership. The PWS owns land surrounding the Reservoir (~ 8 % of the DWSA). The lower (no rthern) part of the DWSA contains most of the Reservoir; it is in the

T illamook State Forest (~40%). T he upper (southern) part is PI forestland (~45%). BLM owns scattered parcels (~7%) around the edges of the Barney DWSA

. The Barney Reservoir (North For k Trask) DWSA experienced Figure 7 a: Turbidity for the Hillsboro

- Cherry Grove DWSA intake from May 1993 through December 2008

. The frequ ency and intensity of turbidity spikes decreased during the early part of this decade. Recently, the number and int ensity of spikes has increased

. Most of the 2003 data is missing.

### 28 

## Turbidity Analysis for Oregon Public Water Syste ms

some scattered clearcuts in the last 10 years on PI land and some partial cuts

on State Forest land. Conditions in the upper

Tualatin River DWSA probably have the greatest impact on source water turbidity.

Figure 7 a show s th e improvement in turbidity in the upper Tualatin

River watershed. While spikes in turbidity above

5 NTU were common 12 years ago, the watershed

recovered from

disturbances in the mid

1990‟s and now has

cons iste ntly low turbidity

. Baseline turbidity has

d ecreased also. Large spikes do occur from time to time, as do periods of high turbidity. These spikes do appear to be triggered by extreme precipi tation events at times (Figure 7 b), but other factors may contribute to surges in stream turbidity.

Seasona lly

- adjusted trend analysis shows a

downward trend in the watershed‟s turbidity (Figure 7 c), although

some recent winters had multiple large turbidity spikes that reduce the fit

of the trend and may indicate potential problems

.

The number of high

turbidit y days (≥ 5NTU) decreased from a high of 47 days during the 1996 water year to a low of 2 days in the 2001 water year (Figure 7 d). This shows a healthy recovery from the effects of disturbances before and during the February 1996 floods. A nalysis of the trend in high turbidity days shows that the number of days greater than 5 NTU decreased until 2001 when there were only Figure 7 b: Precipitation at Hillsboro

- Cherry Grove‟s slow

- sand filtration plant. The seasonal pattern of precipitation drives the seasonal pattern in turbidity.

Figu re 7 c: Turbidity trend for the Hillsboro

- Cherry Grove Slow Sand Filtration Plant (Y t =2.79

- 0.000297*t). After frequent large spikes in the 1990‟s, the frequency and intensity of high turbidity events declined. The trend without the effects of the 1996 flood is similar (Y t =2.33

- 0.000269*t; graph of 1997

- 2008 not shown).

### 29 

## Turbidity Analysis for Oregon Public Water Syste ms

2 high turbidity days (Figure 7 e). Turbidity stayed low before climbing somewhat recently (14, 12, and 10 days in 2006, 2007, and 2008, respectively). It is

unknown if th e 2006

- 2008 level represents the typical equilibrium for this watershed, or if the lower turbidity of 2001

- 2004 is the norm. The

result is a curved trend with sharp declines in high turbidity events followed by leveling off. If the trend continues, then the slight upward

inflection at the end could become a steady upward climb in stream turbidity.

Lee Creek drains into the

Tualatin River approximately 1500 meters upstream of the SSFP, so any individual

or cumulative ti mber

harvest effects could be felt quickly. The next several years will

demonstrate whether land

use activities are likely to increase turbidity and negatively impact water quality in the upper

Tualatin River watershed. Figure 7 d: Number of high turbidity days (≥5NTU) per water year in Hillsboro

- Cherry Grove‟s DWSA as measured at the drinking water intake. The water year runs from

October 1 st through September 30 th

.

Figure 7 e: Trend in number of high turbidity days in Hillsboro

- Cherry Grove‟s DWSA by water year.

### 30 

## Turbidity Analysis for Oregon Public Water Syste ms

City of Siletz (PWS# 4100821)
Allen Middaugh

, Superintendent of Public Works

541

- 444

- 2521

Increasing Trend: Low Turbidity (Occasional Spikes) transitioned to Low Turbidity (Frequent Spikes) Baseline Turbidity Increasing In the western foothills of the middle Coast Range, t he City of Siletz is located on the banks of the Siletz River in Lincoln County. The City uses the Siletz River as their year round water source. The PWS accomplishes particulate removal with chemical coagulation and flocculation and rapid sand filtration

. The City ha s a small storage tank for raw water

. I t does not hold more than a roughly two day supply , so Siletz is planning construction of a water storage pond to provide a backup supply of water when the River‟s turbidity is too high. Approximately 1/ 3 of the PWS‟s finished water is purchased by the Confederated Tribes of Siletz Indians . At 131,540 acres, the Drinking Water Source Area is larger than any other PWS cited in this study. Most of the DWSA is made up of steep terrain with large amounts of rainfall. The majority (~75%) of the DWSA is privately owned by industrial timber companies. Landowners logged some of the Boulder Creek drainage in the 1980‟s, and, i n 1988, Boise Cascade removed the Valsetz Lake dam

. Mr. Middaugh (PWS supervisor) rep orts that the

River is flashier now

- more prone to sudden rises and falls in turbidity and flow. In the 1990‟s and 2000‟s, landowners logged extensively in the Gravel Creek and South Fork Siletz River drainages and along the mainstem Siletz River (“the Gor ge”)

. The Siletz tribe owns scattered portions of the watershed (~2.5% of the DWSA) . The low gradient properties along the river (just upstream of the City ) are occupied by agricultural and rural residential lands, making up a very small (~7%) but import ant portion of the DWSA‟s area. S mall landowners along the river in lower part of the DWSA occasionally conduct land disturbing activities, such as the illegal clearing of vegetation and fill operations by a riverfront landowner in September 2008, just a couple of miles upstream of Siletz‟ intake. Public ownership includes some state land in the south

- east corner (~5% of the DWSA) and BLM land in the northern headwaters portion (~10% of the DWSA)

. BLM did some small scale clearcut logging on their land a round the North Fork Siletz River an d Boulder Creek in the 1980‟s. The City of Siletz does not own or manage any of the DWSA.

The City of Siletz PWS started monitoring Siletz

River tur bidity year round in April of 2000 , after they built a new water

tre atment plant and begin using the Siletz River as a water source all year long

. From 1967 to 2000

, they used Tangerman Creek except in the summer/early autumn. (Prior to that, Logan

Creek was the water source. Source changes have been driven by

water qua lity problems. ) The years 2000 and 2001 had low turbidity with few large spikes, but in subsequent years

, large spikes in turbidity occur frequently before Figure 8 a: Influent turbidity for the City of Siletz‟ drinking water intake on the Siletz from April 2000 through December 2008.

### 31 

## Turbidity Analysis for Oregon Public Water Syste ms

dropping back to the baseline (Figure 8 a ). The baseline turbidity itself is higher, especially du ring

the winter rains. Turbidity follows the

seasonal precipitation pattern (Figure 8 b ), but the biggest storms frequently do not coincide with the high turbidity

events. The seasonally

adjusted trend analysis demonstrates a gradually increasing trend (F igure

8 c); the relatively les s turbid 2007/2008 rainy season slightly reduces the slope of the trend.

The Siletz River experienced few high

turbi dity (≥5NTU) days in

the latter half of the 2000 water year (4 days, April

September) and in the whole 2001 water year (15 days; Figure 8 d ). In contrast, the following water year (WY2002) had 85 high turbidity days, the highest number since

year

- round use of the Siletz River began. The number of high turbidity days has not returned to

the levels seen in 2001

, being 52 days in the 2008

water year

. After excluding the incomplete data for WY2000, analysis of the count data show a generally

increasi ng trend in turbidity (Figure 8 e ). The turbidity varies around a central tendency since

2002

. I t is possible that

WY2000 and WY2001 were anomal ou s ly low. Alternately, events since WY2001 may also have c re a ted sediment sources, accounting for the elevated turbidi ty since 2002

. Analysis of turbidity and Total Suspended Solids (TSS) data collected by the Siletz Tribe indicates that turbidity is spatially and temporally complex and Figure 8 b: Precipit ation at Siletz‟ water treatment facility. The seasonal pattern of precipitation drives the seasonal pattern in turbidity.

Figure 8 c: Turbidity trend for the City of Siletz (Y t =2.87+0.000197*t). The frequency and intensity of high turbidity events increased starting in the autumn of 2001.

### 32 

## Turbidity Analysis for Oregon Public Water Syste ms

generally higher f

a rther do wn in the watershed (Appendix B ). Source identification i nformation and turbidity

d ata prior to April 2000 would be useful to better evaluate the trend in the DWSA.

Figure 8 d: Number of high turbidity days (≥5NTU) per water year in the Siletz River as measured at the drinking water intake. The water year runs from October 1 st through September 30 th

.

Figure 8 e: Trend in number of high turbidity days at Siletz‟ intake. The linear trend model shows the increase in high turbidity days since 2001.

### 33 

## Turbidity Analysis for Oregon Public Water Syste ms

City of Yamhill (PWS# 4100968)

Richard Howard Public Water System Superv isor

503

- 662

- 4344 pwsuper@cityofyamhill.com

Stable / Increas ing Trend: Low Turbidity (Frequent Spikes) The City of Yamhill is in Yamhill County near the foothills of the Coast Range, north of Carlton. Yamhill‟ s PWS removes particulates by settling in their upper reservoir, chemical coagulatio n and flocculation, and rapid sand

filtration. Yamhill‟s Drinking Water Source Area is 2900 acres of the Turner Creek watershed, a tributary of the

North Yamhill River on the eastern slopes of the Coa st Range. A small dam forming a pool keep s the intake submerged during lower flow periods . Another structure upstream forms an impoundment to store water to supplement low flows in the late summer and early autumn. The DWSA is mostly rolling hills with steeper slopes in the valleys and occasional steep slopes in the uplands. The watershed ownership is a patchwork pattern of public and private ownership with nearly all the private land harvested within the last ten or fifteen years. Yamhill owns 60 acres of mature forest just upstream of the intake (given to the City by President Calvin Coolidge) and another 10 acres on the south side of their water storage impoundment in the upper reaches of the

watershed. BLM owns approxim ately 27% of the watershed. The remainder is private industrial forestland (70% of the DWSA total). T here is a 75 acre parcel near the intake owned by a small woodland owner ; the portion of it in the DWSA is roughly 20 acres (<1% of the DWSA)

.

We grap hed and analyzed the turbidity data collected by the Yamhill

PWS at their intake from January 1996 through September 2008 (Figure

9 a ). Following the impacts of the 1996 storm, the turbidity

decreased with fewer large spikes and falling

baseline turbidity

. Turbidity then increases starting in 2003 with frequent large spikes and

a baseline that varies

around 5 NTU. The large

storm that hit the northern Coast Range in December

of 2007 washed sediment

into Turner Creek and

initiated a landslide above

the int ake, filling the pool

behind the dam with fine sediment and gravel. Poor road placement and a blocked culvert contribut ed to the slide. The intake turbidity data represents stream turbidity after fine sediment settle s out in the impoundment and , to a les ser degree, the intake pool. The seasonal weather patterns appear to have been consistent, so storms alone cannot explain the changes in turbidity (Figure 9 b ). Seasonally

- adjusted trend analysis shows a flat, stable trend when 1996 data is included (Figu re 9 c). Analysis without 1996 data (to account for the extreme and historically rare nature o f the

1996 storm and high

- flow events ) shows an upward linear trend in turbidity (Figure 9 d)

. Figure 9 a: Turbidity for the Yamhill DWSA intak e from January 1996 through September 2008. Note the effect of the 1996 storm followed by relatively low turbidity until 2003. More recently, large turbidity spikes occur with greater frequently.

### 34 

## Turbidity Analysis for Oregon Public Water Syste ms

High turbidity days (≥5 NTU) are most problematic for PWSs. Yamhil l‟s DWSA reached a maximum of 149 high turbidity days in 2004; the low of 42 days was in 2001. The count of high turbidity days has stayed near 100 days since 2004 and was 113 days in the 2008 water year (Figure 9 e). This is much greater than the 2008 co unt of high turbidity days for Forest Grove and comparable to the curr ent situation in Carlton. S tatistical analysis of the trend shows a decline in high turbidity episodes until six years ago, followed by increased episodes in recent years (Figure 9 f). Data prior to 1996 would help

to evaluate whether the high turbidity events in

the late 1990‟s are due to

1996 flood effects or some other process es in the

DWSA. The intake will eventually need to be

moved to a more stable location and designed in a

way t hat allows adequate fish passage

. Yamhill

needs to dredg e the intake pool and t he impoundment in the upper

watershed to restore lost

storage capacity.

Figure 9 b: Precipitation at Yamhill‟s water treatment facility. The seasonal pattern of precipitation drives the seasonal pattern in turbidity. Analysis shows that many of the changes in turbidity are seasonal and weather

- driven, but other fa ctors are also at work.

### 35 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 9 c: Turbidity trend for the City of Yamhill for 1996

- 2008 (Y t =6.88

- 0.000122*t). The frequency and intensity of high turbidity events decreased through 2001 and

increased thereafter.

Figure 9 d: Turbidity trend for the Cit y of Yamhill for 1997

- 2008 (Y t =4.58+0.000688*t). Removal of 1996 alters the trend noticeably.

### 36 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 9 e: Count of high turbidity days (≥5NTU) per water year in Yamhill‟s DWSA as measured at the drinking water intake. The water year runs from October 1 st through September 30 th

.

Figure 9 f: Trend in count of high turbidity days in Yamhill‟s DWSA. The quadratic trend model reflects the dip in high turbidity days in 2000 and 2001. The trend is largely

flat with substantial variation around the mean.

### 37 

## Turbidity Analysis for Oregon Public Water Syste ms 

# Ecological and Economic Implications

In 2002, Oregon Departments of Forestry (ODF) and Environmental Quality (DEQ) released a review of the then

current rules under the Fo rest Practices Act (FPA): “Sufficiency Analysis: A Statewide Evaluation of FPA Effectiveness in Protecting Water Quality” (ODF/ODEQ 2002). The report examined the ability of forest practice rules to meet some of DEQ‟s water quality standards, including turbidity and sedime ntation (accumulation of bedded sediment). The Sufficiency Analysis (SA) discussion of turbidity and sedimentation focused primarily on the effects of roads and landslides, the largest sources of sediment. The SA states that roads built to post

- 1984

road construction standards are less likely to fail, cause landslides, or otherwise contribute sediment. However, roads can generate substantial amounts of fine sediment the first few years after road construction and during wet

weather log hauling. The SA a lso discussed the effects of yarding (moving logs across the ground) on erosion, the increased incidence of landslides on clearcut forestland, and the effects of landslides on stream channels.

C hanges to wet weather hauling, management of ground

- based yar ding on steep or erosive slopes

, and management of landslide

- prone locations were recommended. The SA does not discuss the effects of windthrow on sediment regimes or the adequacy of riparian buffers to prevent production of fine sediment or intercept

sed iment before it reaches water bodies. The SA identifies that the effects of practices along small non

- fish

bearing streams on downstream sediment regimes is an issue that needs research and that data are lacking on turbidity and fine sediment effects of f orest practices

. The data and scientific literature in this report may be able

to meet some of these identified data gaps and research needs.



### Natural Disturbances and Land Use Have Potential Effects on Sediment/Turbidity Turbidity fluctuations are a norma l part of stream systems and an inherent risk in the use of surface water for drinking water supplies

. Disturbances affect even unmanaged watersheds in the form of bank erosion, landslides, fires, floods, and windthrow. The 1999 debris flow in Carlton‟s Drinking Water Source Area is an example of a natural disturbance resulting in impacts to a Public Water System. General ly , natural disturbances are infrequent and stream systems can flush the additional fine sediment from the stream (Reeves et al 1995, G omi et al 2004,

Gomi et al 2005)

. Episodic l andslides move a much greater volume of fine sediment into stream networks than small, frequent disturbance s ; h owever, landslides are discrete events to which biological systems are adapted

while chronic sedimen tation creates chronic stress that has detrimental effects (Kirchner et al 2001). The woody

debris and coarse sediment in land slides can enhance fish habitat, even though there are short term impacts to aquatic life and drinking water uses (Reeves et al 1 995

, Reeves et al 2006 ). The data for the Hillsboro

- Cherry Grove and the Cities of Forest Grove and Yamhill show impacts from the February 1996 storms, but within two or three years, turbidity is equal to or lower than pre

- storm levels. This may confirm the short

- term impacts of

natural disturbance s discussed by Reeves and Kirchner. The Institute for Natural Resources completed ODF‟s Dynamic Ecosystem Policy Project in 2009, and the synthesis documents and seminar white papers give more

information about the dynamic nature of forest ecosystems and the importance of planning for natural events ( http://egov.oregon.gov/ODF/STATE_FORESTS/FRP/RP_Home.shtml#Dy namic_Forest_Ecosystems ).

Forests are the major land use in the Drinking Water Source Areas described in this report, but DWSAs throughout the state contain a variety of land uses. There are three major categories of forest ownership in Oregon: privatel y owned (industrial and non

- industrial), state owned, and federally owned. There are also smaller amounts of forestlands owned by Native American nations, counties, cities, and public water systems. Impacts from land management (such as agriculture, silv iculture, roads, and (sub) urban development) can create chronic

sediment sources that take time and resources to resolve , such as production of fine sediment by forest roads ( see Sufficiency Analysis and Reid & Dunne 19 84 )

. A temporary 2

- 4 hour increase i n turbidity due to legitimate land

us e activities is allowable under DEQ‟s water quality standards , but chronic introduction of fine sediment is not

allowed

. It is also possible for management to increase the rate of other disturbances, as in the case of clearcut

### 38 

## Turbidity Analysis for Oregon Public Water Syste ms

timber harvests increasing rates of landslides and windthrown trees ( Sidle et al 1985, Grizzel & Wolff 1998

, Robison et al 1999 ). Klein and others (2008) found a significant association of large scale clearcutting and increased turbidity in North ern California redwood forests. Agriculture and suburban development introduces

sediment and toxics into source water, resulting in increased turbidity, toxic chemical s
, and disinfection by

products in finished drinking water ( Ritter et al 2002, Carpenter et al 2008). PWSs may not have resources to mitigate disasters or to upgrade equipment

. Future studies should examine how land management practices affect operations and costs of PWSs.



### Land Use May Alter Flow Regimes

Fluctuations in stream flow and mod ifications due to land use are another potential risk for PWSs with human use

in Drinking Water Source Areas. Urban or suburban development modifies stormwater flows, creating flash i er system s with larger high flow s, smaller low flows

, and more concentrat ed pollutants, including fine sediment and toxics ( Schueler 2000 ). Agricultural uses can consume large amounts of water during s ummer low flows,

contribut e to flashier stream systems , and pollute waterways ( Hunter 1992, Perkins et al 2009 ). Silviculture, particularly clearcutting and road building, increases soil moisture during the rainy season and the likelihood of damaging flood events and landslides ( Keppeler & Brown 1998 ). Peak flows can increase during the first fall storms because of clearcutting (Grant et al 2008) ; flows can increase due to roads (Jones & Grant 1996), potentially moving more sediment through channels and carrying sediment from roads. Several years following

harvest and re planting, rapidly growing young trees consume large amount s of water and may result in lower base

fl ows (Jones & Post 2004). Summer flow deficits are especially great in 35

- 50 year

- old plantations (Perry 2007)

. F ast

- growing trees in previously harvested riparian areas consume large amounts of water and reduce l ow flows (Hicks et al 1991)

, while o lder riparian forests consume significantly less water (Moore et al 2004). It should be

noted that any flow alterations due to timber harvest are small in comparison to effects of agriculture or urbanization

. Regardles s of the cause, c hanges in flow regimes can make planning for adequate wa ter supplies difficult for PWSs and potentially contribute to water shortages during summer when water use is highest.



### Climate Change Risks for Public Water Supplies

Global climate c hange compounds the risks of detrimental effects on stream flow and sediment regimes

. Generally, w etter winter s and higher storm intensity could create more risk of flooding and erosion

, and drier,

hotter summers could contribute to smaller low flows and g reater risk of water shortages ( Bates et al 2008 ). In the Coast Range and Western Cascades geologies, low flows are likely to stay similar but begin earlier in the year ( Tague et al 2008 , G. Grant personal communication ). Scientists do not know whether t he streamflow effects of changes in vegetation (such as re

- growing trees) and climate will compound each other and create greater problems or whether th os e effects will negate each other to some extent

. More storms of high intensity are likely

to interact with land use effects to amplify sediment generation ( Grizzel & Beschta 1993 ). For example, soil exposed by agriculture or log skidding is more vulnerable to erosion in intense storms, especially exposed soil near streams (Gomi et al 2005, Gomi et al 200 6). The compounding effects of land use and climate change could severely impact publ ic water supplies, especially for small PWSs. It is not yet known what the biggest effects of climate change are likely to be, what the risks are , or how these risks in teract with vegetation changes such as

harvest and succession. Scientists are studying this topic intensively

.



### Potential Costs Related to Higher Turbidity

F inancial resources are a crucial concern for the operation of small communities‟ Public Water Syst ems. A typical small PWS has sufficient income to maintain facilities, pay staff, and fund other operating costs , but water

rates are not usually high enough to absorb substantial cost increases or the need for upgraded equipment

. S everal examples of add itional costs attri butable to higher turbidity are : Increased use of coagulation/flocculation chemicals to remove sediment from raw water; Dredging of sediment

- filled reservoirs, impoundments, and intake pools;

### 39 

## Turbidity Analysis for Oregon Public Water Syste ms

Increased staff time to monitor turbidity, fl ush filters, inspect waterways and facilities, and apply for funding and permits to do additional maintenance work such as dredging ; Equipment upgrades such as new filter systems and pre

- filters to remove high levels of fine sediment if high turbidity c ond itions are or become chronic; Installation of new intake structures and/or switching to another water source, such as groundwater or a neighboring PWS; In the case of extended shutdowns during high turbidity events, there is a risk of catastrophic loss of structures if a fire occurs when there is insufficient water in the PWS‟s reservoirs with which to fight the fire. (Falls City and Arch Cape officials expressed this concern to the Salem Statesman

- Journal

newspaper and to DEQ staff, respectively);

Costs to procure water from a vendor or neighboring PWS if extended shutdowns are too prevalent;

Short

- term public health risks due to loss of a water supply, the inability to sufficien tly purify water, and/or toxics; and Long

- term health risks and costs as a result of toxic chemicals (such as pesticides, solvents, and heavy metals) adsorbed onto the surface of fine sediment ( Ambachtsheer et al 2007 ).

M onitoring effectiveness of land use BMPs is necessar y to e nsure that land management is not increasing public health risks and PWS operating costs.



### Land Management Effectiveness f o r Source Water Protection It is cheaper and more effective to protect source water quality than it is to clean up degraded water prior to use (Freeman et al 2008). The recent award o f $1 million in ARRA funds to Arch Cape for membrane filtration is

driven in large part by rising turbidity. In addition, modern treatment methods are not able to remove all contaminants (Stackelburg et al 2004). Of particular concern are w a s t e w a t e r contam inants like pharmaceuticals and personal care products (Benotti et al 2009) and the synergistic effects of multiple contaminants (Hayes et al 2006) . These contaminants can sorb to or move with turbidity

- causing particles

. Postel and Thompson (2005)

summa rize the hydrological services provided by healthy watersheds and the economic costs of losing or reducing

those services. Some municipalities embarked on source water protection and restoration approaches to both reduce present and future costs and to en sure that their delivered water is free of contaminants that treatment cannot effectively remove. Seattle, Washington, and New York City, New York, are two notable examples, but there are others such as Boston, Massachusetts. Their examples showcase pote ntial management directions that

may be of use to Public Water Systems in Oregon.

New York City needed to correct water quality problems. Faced with US Environmental Protection Agency (EPA) requirements to upgrade treatment facilities, New York applied f or a waiver (Limited Alternative to Filtration) and took the more cost

- effective approach of engaging land owners in their municipal watershed, changing land management practices, and monitoring watershed conditions and water quality. In 1995, negotiation s took place around watershed protection and included representatives of EPA , New York City, New York State, environmental groups, local governments, and residents of the watershed. New York City protected

their resource and created benefits for the water shed communities through a comp rehensive program that includes

l and acquisition

, conservation easements

, regulatory revisions, s tream restoration , and i ncentives for farm

- and

forest

- owners to keep land safe from development and encourage Best Management P ractices that protect water quality (Watershed Agricultural Program and Watershed Forestry Program, respectively). The watershed communities benefit from economic development money, infrastructure improvements, and a healthier environment. New York City benefits by saving money and protecting its source water for the long

- term. Through forward

- thinking efforts and working closely with partners, New York City‟s approach saves millions of dollars, improves the quality of life for watershed residents, and p rotects and restores the environment in their municipal watershed ( http://www.nyc.gov/watershed , NRC 2000).

Seattle , in Washington State, gets 2/3 of its water supply from the Cedar River. After buying up the C edar River watershed over the last 100+ years, Seattle owns nearly the entire 90,000 acre watershed. ( The remaining 1/3 of

### 40 

## Turbidity Analysis for Oregon Public Water Syste ms

the water supply comes from the Tolt River ‟s 11,000 acre watershed of which Seattle owns 70% .) A ctive logging

in the Cedar River wa tershed until the middle of the 1990‟s left numerous roads and legacy effects from clearcutting. Seattle buil t an $80 million disinfection system early in this decade, but they also needed to build a new $100 million filtration plant because of turbidity from roads and landslides. (The cost to build the plant would now be $150 million with an additional $3

- 5 million per year in operating costs.) Instead , Seattle Public Utilities (SPU) received permission to use a Limited Alternative to Filtration under S DWA, requiring watershed protection with an annual survey of conditions. Their comprehensive protection strategy includes roads, culverts, bridges, bank stabilization, security, dealing with problematic downed trees, road removal and maintenance, and

cult ural resources protection. SPU crafted the Cedar Transportation Plan to manage their 650 miles of roads and reduce sediment pollution. They have a road inventory for their watersheds and use WARSEM (Washington Road Surface Erosion Model) to find the wors t road segments and estimate the cumulative effects on the watershed. They have decommissioned 105 miles of roads as of September, 2008, and will decommission almost

300 miles of roads over a 10 year period . Reductions in fine sediment pollution are alre ady apparent (Figure 1 0

, graph provided by Seattle Public Utilities). Combined with the other measures, such as prohibiting public access to the watershed to prevent microbial contamination and vandalism, the restoration and protection measures taken by S eattle create significant savings in money, materials, and energy (Source: Todd Bohle, Seattle Public Utilities).

The City of Portland has special management and legislative protections on the US Forest Service land (the Bull Run watershed) that p rovides drinking water to the largest city in Oregon. These protections give Portland clean,

easy

- to

- treat source water that is free of contamination. The Cities of Astoria and Forest Grove own their watershed forestlands; both are Forest Stewardship Cou ncil (FSC) certified and use FSC guidelines to manage the Figure 1 0 : Reductions in the amount of fine sediment generated from roads and delivered to streams in Seattle‟s Cedar River watershed. These reductions are due to the decommissioning of the worst actors for sediment delivery.

### 41 

## Turbidity Analysis for Oregon Public Water Syste ms

forests in their watersheds ( Forest Stewardship Council 2005 ). According an analysis by EPA ( US EPA 2005 ), FSC guidelines are at least as effective in protecting source water quality and salmon id f isheries as EPA and

NOAA

- Fisheries guidelines. FSC certification also allows the harvested wood to be sold with a price premium that adds an economic benefit to FSC management (Bensel et al

, in press ) . Other private land management

methods (such as SFI, the Sustainable Forestry Initiative) c an potentially protect source water quality, but they need to be monitored and evaluated to insure that they are in fact adequate. Currently, Oregon State Forest Management Plans, the federal Northwest Forest Plan, FS C

- certified private operations, and other forest management schemes meeting or exceeding EPA and NOAA

- Fisheries guidelines are the demonstrated means most likely to protect and restore source water quality and limit turbidity impacts while producing timber

.

The examples of New York City and Seattle suggest that restoration and protection of source water is an effective means of reducing treatment costs and ensuring safe, high qual ity water. Source water protection is a critical part

of the Multi

- Barrier A pproach to providing safe drinking water (NRC 2000, Barnes et al 2009). Roads are the greatest source of fine sediment and landslide initiation sites ( Montgomery 1994 ) and can be significant sources of toxic pollutants (Christensen et al 1997) . Therefore , road removal can be an extremely effective means of protecting source water quality ( Switalski et al 2004 ). When roads are needed, p roper ro ad placement and

maintenance contribute to water quality protection ( Jones et al 2000 ). A 30

- year turbidity stud y of managed forestland in Western Washington by Reiter et al (2009) found that turbidity decreased over the life of the study with the implication that road improvement and sediment controls were responsible. Thinning and multi

- age management in plantati ons avoid s large changes in peak flows ( Grant et al 2008 ) and increases resiliency ( Bisson

et al 2003, Brown et al 2004 ), leaving forests and streams less vulnerable to climate change and disturbances such

as fires . For example, t he management strategies for the Tillamook and Clatsop State Forests incorporate thinning and multi

- age management in addition to a robust riparian protection strategy ( ODF 2001 ). As a result, water quality in state forests are on a generally improving trend ( Rockwell et al 2006 )

. The Northwest Forest Plan Aquatic Conservation Strategy, coupled with restoration in key watersheds, is also effective in improving water quality (Gallo et al 2005 ). Boston, Massachusetts, uses active management of its Quabbin watershed to

increase res iliency and protect water quality and reduce treatment costs (Barten et al 1998). Watershed protection can be a very important part of providing safe drinking water in a manner that is cost effective overall (Brown 2000) , although costs associated with pr otection can be a significant economic challenge for timber producers (Ice

et al 2006)

. Incentives or ecosystem services payments could help producers meet economic challenges associated with source water protection and prevent conversion to non

- forest us e. The economic benefits of riparian protection are potentially massive (Palone & Todd 1997). New York City‟s example particularly suggests that voluntary measures by the owners and managers of working forests and farms can protect source

water quality.

### 42 

## Turbidity Analysis for Oregon Public Water Syste ms 

# Potential Followup

There are several additional tasks that should be done to better understand turbidity dynamics and potential cause

and

- effect relationships between stream conditions and natural conditions, land use activities, and climate change

. The first is to continue acquiring information about the issues that Public Water Systems face, especially in small

communities. This should include turbidity

, precipitation

, roads, and land use data for DWSAs. Continuous turbidity monitoring will show patt erns more fully than once

- per

- day measurements, as shown by the comparison of Falls City‟s daily data with the more detailed data from November 1 st

- 10 th , 2007. Light Ranging and Detection (L i DAR) data would be an extremely effective tool for evaluating la ndscape conditions and characteristics

. The results of the Drinking Water State Revolving Fund Needs Survey can be used to help assess the financial challenges faced by PWSs. Understanding the risks posed by climate change is essential. Further collecti on, examination, and analysis of data and expanding the geographic area of analysis will enable an improved understanding of source water protection

.

Improved turbidity monitor ing and assess ment of source waters is needed when consistent turbidity proble ms or identified risks are present

. As needed , waterbodies with newly identified problems can be put on the 303(d) list, and TMDLs or other protection and restoration plans can be developed to meet the requirements of the Clean

Water Act. DEQ plans to re visit the turbidity water quality standard in 2010. A revised turbidity standard would provide more effective implementation through its existing programs in NPDES permits, CWA 303(d) water quality assessment and impaired waters listings, 401 certificatio ns, TMDL development, drinking water protection, and nonpoint source programs. Another critical part of addressing turbidity issues where risks have been identified is ensuring that nonpoint source programs at other agencies (e.g. Oregon Departments of Ag riculture and Forestry) are adequately funded and staffed to ensure best management practices are being applied and water quality standards are being met.

In order to accurately assess sources of fine sediment that lead to elevated turbidity in Coast Rang e DWSAs, an analysis of land use patterns and disturbances and how they relate to source water turbidity is needed . A thorough analysis would also include landslides and significant windthrow events (if known) , precipitation effects, and

sediment contribu tion s from roads , new and old . Washington‟s WARSEM model is one potential tool for modeling the effects of roads on DWSA sediment movement. Eugene Water and Electric Board have a source water monitoring and assessment program that provides methods which could be applied to small PWSs. Ice et al (2006) explore methods for evaluating the areal extent of riparian protection. Other evaluation methods and examples exist as well

.

DEQ should provide technical assistance to PWSs whenever such assistance is wan ted . In the short term, DEQ can assist PWSs in applying for SDWA grants for testing and data collection to enhance our knowledge of what is actually happening on the landscape. Since small communities typically do not have the expertise or resources to

t horoughly examine the collected data, the Drinking Water Protection program (DWP) can assist with analysis and inform them of Best Management Practices that may be of use. In the long term, the D WP program can help communities to develop land use plans fo r their DWSAs that are consistent with protecting their drinking water for generations to come. Such plans may include land acquisition through fee title and/or conservation easements

or incentives /ecosystem services payments to land owners if more protec tive management practices are found to be necessary

. The DWP program can assist PWSs in identification of funding needs and sources, such as loans and grants to implement plans for source water protection or collection of fees from water system users for ecosystem services payments

.

DEQ works closely with the Oregon Department of Human Services on drinking water issues. In a ddition, close

c oordinat ion with other state agencies such as Department of Forestry, Department of Land Conservation and Developm ent, Department of Agriculture, and Department of Geology and Mineral Industries (DOGAMI) could enable the DWP to better target assistance to PWSs. DOGAMI, for example, has done excellent work recently to

### 43 

## Turbidity Analysis for Oregon Public Water Syste ms

identify active landslides and landslide risk area s. EPA , NRCS, and NOAA

- Fisheries are federal agencies with

whom DEQ can increase cooperat ion to resolve concerns common to source water protection and implementation

of the CWA and ESA.

### 44 

## Turbidity Analysis for Oregon Public Water Syste ms



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02

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- Federal

### 48 

## Turbidity Analysis for Oregon Public Water Syste ms

Lands and Pacific Salmon Conservation; and the EPA Guidance Specifying Management Measures for Sources of Nonpoint Source Pollution in Coastal Waters (EPA 840

- B

- 92

- 002, C hapt. 3 Forestry Measures, January 1993).

### 49 

## Turbidity Analysis for Oregon Public Water Syste ms 

# Appendices

Appendix A: Pu blic Water Systems with All or P art of DWSA in the Coast Range

ID # PWS Name Water Source C ounty Area (acres)

4100003 ADAIR VILLAGE WATER SYSTEM WILLAMETTE R. BENTON 234501.88

4100012 A LBANY, CITY OF S. SANTIAM CANAL LINN 7665.94

4100041 AMITY, CITY OF S. YAMHILL R. YAMHILL 17504.87

4100047 ASHLAND WATER DEPARTMENT ASHLAND CR. JACKSON 12736.58

4100055 ASTORIA, CITY OF BEAR & CEDAR CR., MIDDLE LAKE CLATSOP 2735.95

4100062 YOUNG'S RIVE R

- LEWIS & CLARK

WD N. & S. FORKS BARNEY CR. CLATSOP 1899.51

4100063 WICKIUP WATER DISTRICT LITTLE CR. & BIG/LITTLE FAT BUCK

CR. CLATSOP 1359.47

4100074 BANDON, CITY OF GEIGER & FERRY CR. COOS 2555.48

4100124 FISHHAWK LAKE RECREATION

CLUB FISHAWK CR. COL UMBIA 10004.88

4100164 CANNON BEACH, CITY OF W. FORK ELK CR. CLATSOP 5277.47

4100169 CANYONVILLE, CITY OF CANYON CR. DOUGLAS 22656.81

4100171 CARLTON, CITY OF PANTHER CR. YAMHILL 2075.02

4100194 CLATSKANIE, CITY OF ROARING & WEST CR. COLUMBIA 1799.90

4100199 BEAVER WATER DISTRICT BEAVER CR. TILLAMOOK 18647.16

4100205 COOS BAY

- NORTH BEND WATER

BD. PONY CR. COOS 2557.01

4100213 COQUILLE, CITY OF RINK CR. COOS 429.18

4100214 GARDEN VALLEY WTR

ASSOCIATION CHINA CR. COOS 419.24

4100225 CORVALLIS, CITY O F WILLAMETTE R, S.&N. FORKS ROCK CR, GRIFFITH CR. BENTON 47005.87

4100239 LONDON WATER CO

- OP BEAVER CR. LANE 867.67

4100246 CRESWELL, CITY OF COAST FORK WILLAMETTE R. LANE 123064.39

4100248 DALLAS, CITY OF RICKREAL CR. POLK 17953.92

4100250 MILO ACADEM Y S. UMPQUA R, LICKEY CR. DOUGLAS 21934.54

4100254 DEPOE BAY, CITY OF ROCKY &DEPOE BAY CR. LINCOLN 6695.81

4100260 DRAIN, CITY OF BEAR & ALAN CR. DOUGLAS 4017.17

4100276 ELKTON, CITY OF UMPQUA RIVER DOUGLAS 316072.91

4100297 FALLS CITY, CITY OF TEAL &G LAZE CR. POLK 3218.60

4100301 HECETA WATER DISTRICT CLEAR LAKE LANE 614.69

4100302 SILTCOOS HEIGHTS SILTCOOS LAKE LANE 39670.56

4100304 ALDERWOOD WATER

DEVELOPMENT CO WOAHINK LAKE LANE 4334.51

4100305 FOREST GROVE, CITY OF ROARING, CLEAR, THOMAS, DEEP, &

SMITH CR. WASHINGTON 4856.58

4100323 GLENDALE, CITY OF COW, SECTION, & MILL CR. DOUGLAS 119381.66

4100324 KERNVILLE

- GLENEDEN

- LINCOLN

BCH W D DRIFT CREEK LINCOLN 22229.85

4100326 GLIDE WATER ASSOCIATION NORTH UMPQUA RIVER DOUGLAS 428437.01

4100333 GO LD HILL, CITY OF ROGUE RIVER JACKSON 284024.61

4100337 ROCK CREEK HIDEOUT WATER CO UNNAMED CREEK POLK 26.74

4100342 GRANTS PASS, CITY OF ROGUE RIVER JOSEPHINE 170961.64

4100379 HILLSBORO

- FOREST GROVE

BEAVERTON TUALATIN R. & N. FORK TRASK R. (BARNEY RES. ) WASHINGTON 120691.98

4100463 LAKESIDE WATER DISTRICT EEL LAKE COOS 3872.15

4100466 LANGLOIS WATER DISTRICT FLORAS CREEK CURRY 39049.91

4100483 LINCOLN CITY WATER DISTRICT SCHOONER CREEK LINCOLN 9591.86

4100497 MCMINNVILLE WATER AND LIGHT HASKINS & MC GUIRE RES. YAMHILL 6213.11

4100505 MANZANITA WATER

DEPARTMENT N.&W. FORKS ANDERSON CR. TILLAMOOK 569.36

### 50 

## Turbidity Analysis for Oregon Public Water Syste ms

4100507 MAPLETON WATER DISTRICT BERKSHIRE CREEK LANE 501.69

4100513 MEDFORD WATER COMMISSION ROGUE RIVER JACKSON 290653.71

4100548 CLARKS BRANCH WTR

.

ASSOCIATION SOUTH UMPQUA RIVER DOUGLAS 84099.45

4100549 TRI

- CITY WATER DISTRICT SOUTH UMPQUA RIVER DOUGLAS 106502.61

4100550 MYRTLE CREEK, CITY OF S. UMPQUA R. & SPRINGBROOK

SPRINGS DOUGLAS 4809.62

4100551 MYRTLE POINT, CITY OF NORTH FORK COQUILLE RIV ER COOS 180885.59

4100554 NEHALEM, CITY OF BOB'S CREEK TILLAMOOK 425.21

4100556 NETARTS WATER DISTRICT EAST FALL CREEK TILLAMOOK 367.50

4100564 BAY HILLS WATER ASSOCIATION UNNAMED CREEK LINCOLN 26.21

4100566 NEWPORT, CITY OF BIG CR.&SILETZ R. LINCOLN 2 150.12

4100568 BEVERLY BEACH WATER

DISTRICT WADE CREEK LINCOLN 1460.17

4100581 OAKLAND, CITY OF CALAPOOYA CREEK DOUGLAS 64894.66

4100585 OCEANSIDE WATER DISTRICT SHORT CREEK TILLAMOOK 1304.36

4100603 PANTHER CREEK WATER

DISTRICT PANTHER CREEK LINCOLN 1 106.43

4100610 TIERRA DEL MAR WATER

COMPANY BELTZ CREEK TILLAMOOK 160.06

4100624 PHILOMATH PUBLIC WORKS MARY'S RIVER BENTON 85972.99

4100670 PORT ORFORD, CITY OF HUBBARD CR. & GARRISON LAKE CURRY 2845.60

4100672 POWERS, CITY OF S. FORK COQUILLE R. & BI NGHAM CR. COOS 94207.20

4100689 RAINIER WATER DEPARTMENT COLUMBIA R. & FOX CR. COLUMBIA 44917.84

4100699 REEDSPORT, CITY OF CLEAR LAKE DOUGLAS 1382.96

4100706 RIDDLE, CITY OF COW CREEK DOUGLAS 192495.04

4100707 LAWSON ACRES WATER

ASSOCIATION COW CREEK DOUGLAS 7025.14

4100708 ROCKAWAY BEACH WATER DEPT JETTY CREEK TILLAMOOK 1310.52

4100712 ROGUE RIVER, CITY OF ROGUE RIVER JACKSON 69007.97

4100717 ROBERTS CREEK WATER DISTRICT S. UMPQUA RIVER DOUGLAS 3094.75

4100719 UMPQUA BASIN WATER

ASSOCIATION N. UM PQUA RIVER DOUGLAS 33475.75

4100720 ROSEBURG, CITY OF

-

WINCHESTER N. UMPQUA RIVER DOUGLAS 131134.54

4100731 SALEM PUBLIC WORKS N. SANTIAM RIVER & IG MARION 17149.09

4100792 SCAPPOOSE, CITY OF GOURLEY, LAZY, & S.FK SCAPPOOSE

CR COLUMBIA 6059.81

4100799 SEASIDE WATER DEPARTMENT NECANICUM R. CLATSOP 30069.02

4100802 ARCH CAPE WATER SERVICE

DISTRICT ASBURY & SHARK CR. CLATSOP 1249.34

4100808 COUNTRY VIEW MH ESTATES ROGUE RIVER JACKSON 734031.45

4100811 SHERIDAN, CITY OF SOUTH YAMHILL RIVER YAMHILL 13537 5.06

4100821 SILETZ, CITY OF SILETZ R. & TANGERMAN CR. LINCOLN 131836.17

4100843 STAYTON WATER SUPPLY NORTH SANTIAM RIVER MARION 4535.87

4100847 SUTHERLIN, CITY OF CALAPOOYA & COOPER CR. DOUGLAS 57605.19

4100893 TILLAMOOK WATER COMMISSION KILLAM & FAWC ETT CR. TILLAMOOK 6176.20

4100898 TIMBER WATER ASSOCIATION NEHALEM RIVER WASHINGTON 7787.26

4100899 TOLEDO WATER UTILITIES MILL CR. & SILETZ R. LINCOLN 2680.81

4100922 VERNONIA, CITY OF ROCK CREEK COLUMBIA 3561.18

4100925 S.W. LINCOLN COUNTY WTR. DIST. BIG, VINGIE, STARR, DICK‟S FORK CR. LINCOLN 3451.89

4100926 WALDPORT, CITY OF ECKMAN & WEIST CR. LINCOLN 3186.26

4100932 WARRENTON WATER SYSTEM LEWIS&CLARK R. CAMP C CR. CLATSOP 18375.81

4100950 WESTPORT WATER ASSOCIATION WEST CREEK CLATSOP 1326.04

41 00952 WHEELER WATER DISTRICT VOSBURG & JARVIS CR. TILLAMOOK 365.23

4100953 CITY OF WILLAMINA WATER

DEPARTMENT WILLAMINA CREEK YAMHILL 52478.62

4100954 WILSONVILLE, CITY OF WILLAMETTE RIVER CLACKAMAS 1050979.75

4100957 WINSTON

- DILLARD WATER

DISTRICT SOUT H UMPQUA RIVER DOUGLAS 111553.38

4100958 YONCALLA, CITY OF ADAMS & WILSON CR. DOUGLAS 1676.22

4100966 YACHATS, CITY OF SALMON & REEDY CR. LINCOLN 773.12

4100968 YAMHILL, CITY OF TURNER CREEK YAMHILL 2916.76

4100970 NESKOWIN REGIONAL WD HAWK CREEK TILLA MOOK 1542.70

4100971 CITY OF CAVE JUNCTION EAST FORK ILLINOIS RIVER JOSEPHINE 148775.61

### 51 

## Turbidity Analysis for Oregon Public Water Syste ms

4100985 HILLSBORO

- CHERRY GROVE TUALATIN RIVER WASHINGTON 15565.00

4101012 PP&L

- TOKETEE VILLAGE TOKETEE LAKE (N. UMPQUA) DOUGLAS 224207.72

4101062 RAINBOW ROCK VILLA GE MHP TAYLOR CREEK WELLS CURRY 1039.25

4101072 JOHNSON CREEK WATER SERVICE

CO JOHNSON CREEK LINCOLN 660.07

4101092 USFS TILLER RANGER STATION SOUTH UMPQUA RIVER DOUGLAS 288525.43

4101095 USFS WOLF CREEK JOB CORPS LITTLE RIVER DOUGLAS 57801.95

4101139 MIDLAND WATER ASSOCIATION GRAHAM CREEK COLUMBIA 988.93

4101174 BUELL

- RED PRAIRIE WATER ASSN GOOSENECK CREEK POLK 1057.58

4101361 RAINBOW ROCK CONDOMINIUMS UNNAMED CREEK CURRY 155.21

4101483 ANGLERS COVE/SCHWC ROGUE RIVER JACKSON 10705.24

4105246 PGE BE AVER GENERATING

STATION COLUMBIA RIVER COLUMBIA 57081.64

4105581 WEISS ESTATES WATER SYSTEM FAHY'S LAKE COOS 1028.96

4105737 BERNDT CREEK WATER CORP ROCK CREEK COLUMBIA 35304.09

4190416 FORT JAMES OPERATING

COMPANY COLUMBIA RIVER COLUMBIA 87190.52

4192 139 TILLER ELEMENTARY, SD #15 SOUTH UMPQUA RIVER DOUGLAS 54986.13

4192152 POPE & TALBOT, INC., WILLAMETTE RIVER LANE 528459.96

4192674 USFS STAR RANGER STATION APPLEGATE RIVER JACKSON 178577.82

4194300 ROSEBURG FOREST PROD

DILLARD SOUTH UMPQUA RIVER DOU GLAS 28863.00

### 52 

## Turbidity Analysis for Oregon Public Water Syste ms



# Appendix B : Relationship of Stream Turbidity and Suspended Solids in the Siletz River Basin:
Analysis of Data Collected by the Confederated Tribes of Siletz

Indians

Joshua Seeds, Nonpoint Source Analyst, Oregon DEQ

The Confederated Tribe s of Siletz Indians collected winter turbidity data from numerous sites on the Siletz River and its tributaries in 2002 through 2006. For some of the sampling events, tribal staff also collected samples for measuring total suspended solids (TSS), a measur e of sediment in the water column. The sites with TSS data include 11 tributaries and 8 sites along the mainstem of the Siletz River. As Public Water Systems collect turbidity data, and since DEQ wrote a report detailing turbidity in Coast Range PWSs in 2009, it is important to understand what is contributing to elevated turbidity levels when they are present. High turbidity is typically caused by fine sediment, but algae and other factors may also be responsible. We needed to establish to what degree f ine sediment pollution is driving turbidity in Coast Range streams, so we used the available data for the Siletz River to test this relationship.



## Analysis of Relationships between Turbidity and Total Suspended Solids
We graphed the relationships with turb idity as the independent variable (X axis) and TSS as the dependent variable (Y axis) for the tributaries (Figure 1) and the mainstem of the Siletz River (Figure 2).

Figure 1

### 53 

## Turbidity Analysis for Oregon Public Water Syste ms

DEQ then graphed and analyzed the data using least

- squares regressions to evaluate the relationship between turbidity and TSS in the Siletz River basin. We evaluated the combined data in three different groups: the pooled tributaries, the pooled mainstem sites, and both tributaries and mainstem sites (the whole system). To insure the validity of the least

- squares regression analysis, we needed to make sure that the assumption that data are normally distributed was met. Least

- squares regressions can be especially sensit ive to outliers that skew the line and give a false impression of its accuracy. Histograms of turbidity and TSS for the three groups all show lognormal distributions for the data sets (Figures 3

- 8). Analysis using a Ryan

- Joiner test for normality confirm s that transforming the data with a

base10 logarithm results in normal distributions for all the variables except TSS for the tributaries (Figure 4). Because the data appear lognormally distributed, the likelihood that failure of the normality test is due to a couple outliers, and other data transformations did not result in a normal distribution, we proceeded with the regression on the tributary data in addition to the other two groups. Figure 2

Figure 3 Figure 4

Figure 6

Figure 8

### 54 

## Turbidity Analysis for Oregon Public Water Syste ms

The least

- squares regressions on the log transform ed data for the tributaries, the mainstem, and the whole stream system show high correlations between turbidity and TSS (R 2 =81.4%, 89.9%, 82.5%, respectively; Figures 9

- 11). The accuracy of the regression is excellent for the lower and middle reaches of t he river (Figure 10). Confidence and prediction intervals are narrow at the lower end of the turbidity and TSS ranges, but widen greatly near the upper end of the range, showing less certainty about values at the upper end of the ranges. Therefore, turbi dity is a good predictor of the combined organic and mineral suspended solids in the Siletz River system, but caution must be used in translating turbidity values into TSS at turbidities greater than 100 or 150 NTU. Figure 7 Figure 5 Figure 6

Figure 8

### 55 

## Turbidity Analysis for Oregon Public Water Syste ms

Figure 9

Figure 10

### 56 

## Turbidity Analysis for Oregon Public Water Syste ms

Two tributaries of the Siletz River (Dewey and Bentilla Creeks) have much steeper slopes to their TSS vs. Turbidity lines, seen in Figure 1. Cedar Creek also has an

outlier near the D ewey and Bentilla data. An analysis of variance on the logarithm

- transformed ratio of TSS

- to

Turbidity showed a statistically significant difference among sites (F=3.13, p<0.001). Bentilla and Dewey Creeks do indeed have the highest mean ratios, but Litt le Rock Creek, Mill Creek (near the City of Siletz), and Sam‟s Creek also have higher than average TSS:Turbidity

ratios. 

### ANOVA: TSS:Turbidity by Site

Source DF SS MS F P

Sites 18 13.80 0.767 3.13 0.000

Error 138 33.85 0.245

Total 156 47.66

S = 0.4953 R

- Sq = 29.0% R

- Sq(adj) = 19.7% Figure 11

Figure 12

### 57 

## Turbidity Analysis for Oregon Public Water Syste ms

Possible explanations for these

differences in sediment characteristics among sites include soil type, differences in road surfacing or density, land use differences, or a lower proportion of organic sediments

in the total sediment in the stream. A USGS report (Madej et al 2002) indicates that organic sediments stay suspended in the water column and thereby contribute more to turbidity

than mineral sediments of the same size. Some of the TSS samples collected by the tribe were analyzed

for mineral and organic content. We plotted the percent of organic matter in TSS samples with that samples TSS:Turbidity ratio to see if there was

a cl ear pattern, but no relationship exists (Figure 13). Soil type or other factors are therefore more likely to drive patterns in relationship between TSS and turbidity in the Siletz River watershed.



## Conclusions
Turbidity is a useful predictor of sediment m ass loads in the Siletz River and tributaries. I recommend using the regression equation for the whole system when estimating sediment loads(Figure 11), as the results are based on greater amounts of data and are thereby more robust. The equation from ma instem sites could be used on the middle and lower reaches of the mainstem where most of the mainstem sample sites were located (Figure 10). Caution should be used when applying the regression equations in the uppermost portions of the basin (above

Gravel Creek or in the North and South Forks) because there are no TSS data for this part of the basin. Caution should also be used when turbidities exceed 100 NTU. Some tributaries (such as Bentilla and Dewey Creeks)

have anomalous TSS

- to

- Turbidity relationsh ips, so it may be necessary to derive individual regression equations

for those streams.

References: Madej, MA, M Wilzbach, K Cummins, C Ellis, and S Hadden. 2002. The contribution of suspended organic sediments to turbidity and sediment flux. Turbidit y and Other Sediment Surrogates Workshop , Reno, NV. Figure 13