CHAPTER 3 – Population and Demand Forecast

Accurate data about projected water demand is essential for long-term water system planning. This chapter presents the Utility’s forecasts of population, households, employment and water demand. Following a review of historical and projected demographic data is a summary of use characteristics including production, consumption and related factors. The chapter concludes with a demand forecast for the next 50 years based on the demographics, water supply characteristics and related uncertainties.

3.1 DEMOGRAPHIC DATA

Demographic data presented here includes total population, number of single-family and multi-family households and total employment. Table 3.1 shows the historical and projected demographics at specific planning horizons from 2015 to 2064.

Forecasts are based on the Thurston Regional Planning Council (TRPC) November 2012 data set. See Appendix 3-1 for more information on how these demographics were developed and a breakdown of the demographics by pressure zone.

Table 3.1 Projected Demographics

Year

Population

Single-Family Households

Multi-family Households

Employment

2015 (Plan Year 1)

62,097

17,144

11,601

58,840

2020 (Plan Year 6)

68,011

18,147

13,644

62,825

2034 (Plan Year 20)

83,388

22,122

17,595

73,981

2064 (Plan Year 50)

113,427

29,815

25,600

102,026

3.2 Water Use Characteristics

This section describes the water use characteristics used in making the demand forecast:

•    Production and peaking factor

•    Customer categories and consumption

•    Non-revenue water and leakage

•    Water use factors and ERUs

Production and Peaking Factor

Olympia produces water from the McAllister Wellfield and six wells, as described in Chapter 4. Before the McAllister Wellfield came online in October 2014, Olympia obtained the majority of its drinking water from McAllister Springs. Table 3.2 shows average production over the last three years, by source and by month. The total average annual production has been 2,581 million gallons (Mg). Of that, 77 percent was derived from McAllister Springs (2010-2012) average. As is typical with most water utilities, production peaks in the summer months of May through October.

Figure 3.1 and Figure 3.2 show this same information graphically, and Figure 3.3 shows the annual production for each year from 2003 to 2012.

Table 3.2 Water Production Summary (2010 – 2012 average in million gallons)

Month

McAllister Springs (S01)

Kaiser Well 1 (S03)

Hoffman Well 3 (S08)

Allison Well 13 (S09)

Shana Park Well 11 (S10)

Allison Well 19 (S11)

Indian Summer 20 (S12)

Total

Percent

Jan

148.5

0.0

0.0

9.2

12.0

9.0

0.2

178.8

7%

Feb

140.4

0.0

0.0

3.6

17.0

4.9

0.2

166.2

6%

Mar

152.6

3.1

0.0

3.9

20.5

5.4

0.2

185.7

7%

Apr

151.2

4.2

0.0

3.8

19.7

5.9

0.2

185.0

7%

May

154.3

7.1

0.0

11.3

23.4

11.1

0.3

207.4

8%

Jun

170.8

8.7

0.0

13.9

17.9

13.9

5.1

230.2

9%

Jul

205.1

9.2

0.0

17.6

25.4

22.1

19.1

298.5

11%

Aug

219.0

4.6

0.0

20.9

34.8

25.4

19.4

324.1

12%

Sep

170.4

0.8

0.0

16.4

32.1

23.1

7.8

250.5

10%

Oct

132.6

3.0

0.0

13.0

26.0

15.5

0.0

190.2

7%

Nov

168.6

0.0

0.0

5.1

5.1

8.5

0.1

187.5

7%

Dec

167.5

0.0

0.0

4.1

0.2

5.3

0.0

177.1

7%

Total

1,981

41

0.08

123

234

150

53

2,581

100%

Percent

77%

2%

0.003%

5%

9%

6%

2%

100%

 

Note: Ten years of production data was analyzed. However, this table uses the most recent three years in order to focus on current trends.

View Figure 3.1 Water Production by Source (2010 – 2012 Average).

View Figure 3.2 Water Production Monthly Distribution (2010 – 2012 Average).

View Figure 3.3 Annual Production (2003 – 2012).

Table 3.3 gives the peaking factors from 2003 to 2012. The peaking factor has ranged from 1.6 to 2.5, and has averaged 1.7 for the most recent three years. Note that the demand forecast presented later in this chapter uses a slightly higher peaking factor of 2.0 for the current year (2013). This is approximately halfway between the average of the most recent three years and 2.3, which Olympia used in its 2009 Water System Plan.

Table 3.3 shows that the peaking factor has trended downward. To incorporate this decreasing trend in the peaking factor, a 0.3 percent annual decrease is applied to the peaking factor each year until the end of the forecast period.

Table 3.3 Peaking Factors

Year

Average Day (Mgd)

Peak Day

Peaking Factor

(Mgd)

Date

2003

8.0

15.6

7/29/2003

2.0

2004

7.7

19.5

7/20/2004

2.5

2005

7.8

15.0

8/6/2005

1.9

2006

8.6

16.1

7/6/2006

1.9

2007

8.6

15.1

7/11/2007

1.8

2008

8.3

13.8

8/15/2008

1.7

2009

8.1

15.9

7/29/2009

1.9

2010

7.1

12.5

8/14/2010

1.8

2011

7.2

11.7

8/4/2011

1.6

2012

7.0

11.6

8/15/2012

1.7

2010-2012 Avg

7.07

11.92

n/a

1.7

Note: Data is presented for ten years to show a lengthy history.

Customer Categories and Consumption

Olympia has six retail customer categories. Each category has standard connections and irrigation-only connections.

•    Single-family. Detached residential buildings serving a single family, duplex, triplex or four-plex.

•    Multi-family. Residential buildings such as apartment buildings or condominiums that serve multiple households.

•    Commercial. Business and governmental customers.

•    Municipal. City of Olympia facilities.

•    Political subdivision. Includes quasi-governmental customers such as Intercity Transit, Port of Olympia and schools.

•    State. State of Washington facilities.

The City also sells water wholesale to the City of Lacey and Thurston Public Utility District No. 1 (PUD). Prior to June 2005, Olympia provided retail service to customers in the PUD’s service area. From 2005-2015, Olympia sold water wholesale to the PUD, which in turn provided water service to its customers. Over the past several years the PUD has moved toward securing its own water supply and plans to stop purchasing wholesale water from Olympia completely in early 2015.

The amount of water expected to be wholesaled to the City of Lacey was developed based on the wholesale agreement with Lacey. The agreement states that Olympia will provide Lacey with up to 2 Mgd from November to June and up to 1 Mgd from July to October. The agreement is valid until December 31, 2016. After this date, the demand associated with Lacey is assumed to be zero.

Table 3.4 gives the number of connections for each customer category from 2003 to 2012. Most connections are either single-family (86%) or commercial (9%).

Average consumption, by customer category and by month, over the last three years, is shown in Table 3.5. The largest share of water consumption is accounted for by the single-family customer category (40%), followed by commercial (20%), and multi-family (15%). These collectively represent 75 percent of consumption.

Figure 3.4 and Figure 3.5 show the same information as Table 3.5, graphically.

Actual monthly consumption of water may differ slightly from the data presented in Table 3.5 and Figures 3.4 and Figure 3.5. Most water meters are read bi-monthly and consumption is assigned to the month in which the meter is read.

Table 3.4 Connections by Customer Category (Retail Only, No Wholesale)

Customer Category

Number of Connections

2003

2004

2005

2006

2008

2009

2010

2011

2012

2010-2012 Avg

#

%

1. Single-family

Standard

14,768

15,122

15,201

15,492

14,648

14,905

15,284

15,625

15,962

15,624

85%

Irrigation

161

161

166

170

60

65

63

63

69

65

0.4%

Total

14,929

15,283

15,367

15,662

14,708

14,970

15,347

15,688

16,031

15,689

86%

2. Multi-family

Standard

610

622

643

644

666

688

702

709

720

710

4%

Irrigation

18

20

22

22

21

24

23

29

30

27

0.1%

Total

628

642

665

666

687

712

725

738

750

738

4%

3. Commercial

Standard

1,495

1,510

1,528

1,549

1,402

1,415

1,427

1,424

1,427

1,426

8%

Irrigation

259

271

282

291

228

237

238

243

251

244

1.3%

Total

1,754

1,781

1,810

1,840

1,630

1,652

1,665

1,667

1,678

1,670

9%

4. Municipal

Standard

58

57

55

56

55

54

53

58

60

57

0.3%

Irrigation

50

50

48

53

10

10

12

13

16

14

0.1%

Total

108

107

103

109

65

64

65

71

76

71

0.4%

5. Political Subdivision

Standard

59

60

60

61

55

55

55

58

64

59

0.3%

Irrigation

30

30

32

32

13

13

13

14

13

13

0.1%

Total

89

90

92

93

68

68

68

72

77

72

0.4%

6. State

Standard

94

95

97

97

58

57

62

63

63

63

0.3%

Irrigation

50

53

56

56

30

31

32

35

36

34

0.2%

Total

144

148

153

153

88

88

94

98

99

97

0.5%

Total

Standard

17,084

17,466

17,584

17,899

16,884

17,174

17,583

17,937

18,296

17,939

98%

Irrigation

568

585

606

624

362

380

381

397

415

398

2%

Total

17,652

18,051

18,190

18,523

17,246

17,554

17,964

18,334

18,711

18,336

100%

Table 3.5 Average Metered Water Consumption 2010 – 2012 (Mg)1

Customer Category

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Total

Percent

1. Single-family

Standard

51

74

56

60

65

86

56

148

82

113

56

77

923

39%

Irrigation

0.03

0.02

0.03

0.04

0.02

1.25

0.41

9.85

2.65

7.80

0.39

0.14

23

1%

Total

51

74

56

60

65

87

56

158

85

121

57

77

946

40%

2. Multi-family

Standard

23

31

25

26

27

32

24

39

28

34

28

31

348

15%

Irrigation

0

0

0

0

0

1

1

3

3

3

1

0

12

0%

Total

23

31

25

26

27

33

26

42

31

36

29

31

360

15%

3. Commercial

Standard

33

29

34

25

39

30

35

37

41

31

39

28

402

17%

Irrigation

0

0

0

0

1

5

8

25

16

19

3

1

79

3%

Total

33

30

34

25

40

36

42

61

57

50

42

29

481

20%

4. Municipal

Standard

1

1

1

0

1

1

1

1

2

1

1

1

11

0%

Irrigation

0.1

0.0

0.1

0.2

0.5

1.3

1.8

4.4

3.5

2.5

1.0

0.1

16

1%

Total

1

1

1

1

2

2

3

6

5

3

2

1

27

1%

5. Political Subdivision

Standard

4

5

4

5

4

5

5

7

5

5

6

5

60

3%

Irrigation

0.1

-0.1

0.2

0.1

0.6

2.2

3.0

7.0

3.7

3.0

1.2

0.4

21

1%

Total

4

5

4

5

5

7

8

14

9

8

7

5

82

3%

6. State

Standard

3

6

5

3

6

7

5

9

4

6

8

5

66

3%

Irrigation

0.0

0.0

0.0

0.1

0.0

0.5

1.0

5.7

5.8

3.3

0.3

0.0

17

1%

Total

3

6

5

3

6

7

6

14

10

9

8

5

83

4%

7. Billed Construction Sites

0.3

0.3

0.3

0.3

0.3

0.3

0.3

0.3

0.3

0.3

0.3

0.3

3

0%

8. Lacey Wholesale

17.8

18.1

27.6

26.2

26.0

27.9

30.9

31.8

23.2

20.2

20.2

20.9

291

12%

9. PUD Wholesale

7.9

7.6

9.7

11.1

11.3

11.3

7.1

7.2

5.5

3.8

3.6

3.3

89

4%

Total

Standard

115

147

124

120

142

160

126

241

163

190

139

146

1,815

77%

Irrigation

0

0

1

1

2

11

15

55

35

39

6

2

167

7%

Wholesale

26

26

37

37

37

39

38

39

29

24

24

24

380

16%

Total

141

173

162

158

182

211

179

335

226

253

170

172

2,362

100%

Percent

6%

7%

7%

7%

8%

9%

8%

14%

10%

11%

7%

7%

100%

 

View Figure 3.4 Monthly Distribution of Water Consumption (2010 – 2012 Average).

View Figure 3.5 Water Consumption by Customer Category (2010 – 2012 Average).

Comparing the percent of connections to the percent of consumption can be useful, since water consumption does not always follow the same proportion as customer connections. This comparison is shown in Figure 3.6, which focuses on retail deliveries. Three customer categories stand out in this comparison. Single-family has a much larger percent of connections (86%) compared to the percent of retail consumption (48%). Multi-family has a much smaller percent of connections (4%) compared to the percent of retail consumption (18%). This is because one multi-family connection serves many multi-family households. Commercial has a much smaller percent of connections (9.1%) compared to retail consumption (24%).

View Figure 3.6 Retail Connections and Consumption Comparison (2010 – 2012 Average).

Customers with large water demand are of interest since their demand could have significant impact on overall demand. This is particularly true when the largest customers are commercial and industrial customers. Table 3.6 summarizes water use for the customers with the highest water use for 2011 and 2012.

Given the nature of these customers, any changes in their future demand would likely be reflected in the demographic projections; therefore no special treatment of these customers was used for the demand forecast.

Table 3.6 Customers with Highest Water Use (2010 – 2012 Average Consumption)

Rank

Customer Name

Service Address

Total Consumption (Mg)

1

Crown Beverage & Packaging Company

1202 Fones Road SE

41.5

2

St Peters Hospital

413 Lilly Road NE

33.2

3

Evergreen State College

2700 Evergreen Parkway NW

33.1

4

Olympia School District #111

Multiple Locations

28.7

5

LOTT Clean Water Alliance

500 Adams Street NE

26.1

6

Cambridge Court Apartments

2323 9th Avenue SW

17.0

7

Black Lake LLC

1900 Black Lake Boulevard SW

16.5

8

Capital Medical Center

3900 Capital Mall Drive SW

16.5

9

City Of Olympia Parks

Multiple Locations

14.6

10

Colonial Estates

3601 18th Avenue SE

13.5

11

Capitol Building & Grounds

Multiple Locations

13.4

12

Courtside Apartments

515 Courtside Street SW

13.1

13

Bellwether Apartments 2

1400 Fones Road SE

12.6

14

Apple Park Apartments

3200 Capital Mall Drive SW

12.4

15

Thurston County Facilities 1

2000 Lakeridge Drive SW

11.7

16

Extendicare Health/Assisted

430 Lilly Rd Ne/4001 Capital Mall Drive SW

11.2

17

Olympic Heights Apartments 2

300 Kenyon Street NW

10.3

18

Western Heritage / Coopers Glen 2

3138 Overhulse Road NW

9.6

Total

335.0

Percent

100%

Non-Revenue Water and Leakage

The forecast of future demand includes a calculation of “non-revenue water,” which includes leakage and all other unmetered and metered uses that are not sold for revenue. Authorized uses of unmetered (and therefore, unbilled) water include firefighting and hydrant flushing, sampling, water and sewer line flushing and testing, street cleaning and other maintenance. For this purpose, a simple calculation of production minus sales was used to determine non-revenue water, as shown in Table 3.7. Distribution System Losses (DSL) aredetermined by subtracting unbilled authorized use from non-revenue water. Figure 3.7 graphically shows distribution system losses for the last four years compared to the four-year average.

Table 3.7 Distribution System Losses and Non-Revenue Water (million gallons)

Year

Production1

Sales2

Unbilled Authorized Use

Distribution System Losses

Non-Revenue Water

Qty3

Percent of Production

Qty4

Percent of Production

Qty5

Percent of Production

Percent of Sales

2004

2,809

2,581

41

1.5%

187

6.7%

228

8.1%

8.85%

2005

2,832

2,616

41

1.5%

175

6.2%

217

7.6%

8.28%

2006

3,129

2,757

46

1.5%

327

10.4%

372

11.9%

13.51%

2007

3,074

2,713

45

1.5%

316

10.3%

361

11.7%

13.31%

2008

3,030

2,662

--

--

--

--

368

12.2%

13.84%

2009

2,973

2,651

15

0.5%

307

10.3%

322

10.8%

12.13%

2010

2,573

2,355

14

0.5%

204

7.9%

218

8.5%

9.25%

2011

2,611

2,433

27

1.0%

151

5.8%

178

6.8%

7.31%

2012

2,559

2,297

18

0.7%

244

9.5%

262

10.2%

11.41%

2010-2012 Average6

2,581

2,362

20

0.8%

200

7.7%

219

8.5%

9.3%

View Figure 3.7 Distribution System Losses (2009 – 2012).

Water Use Factors and ERUs

Water use factors were calculated for three customer categories: single-family; multi-family; and industrial, commercial and institutional (ICI). Table 3.8 shows the data used for the calculations, including the number of Equivalent Residential Units (ERUs) in each customer category.

ERUs are a method of representing water use by non-residential customers as an equivalent number of residential customers. An ERU is the amount of water used by a single-family household, which in Olympia averages 166 gallons per day (gpd). The number of ERUs for each customer category is obtained by dividing the consumption (in gpd) for a customer category by 166. Therefore, the single-family customer category equates to 15,624 ERUs; the multi-family category to 5,940 ERUs; and the industrial, commercial, institutional category to 11,099 ERUs.

Below are the key water use factors and how they were calculated:

•    166 gpd per single-family household. Single-family consumption (2,591,885 gpd) divided by the number of households (15,624).

•    92 gpd per multi-family household. Multi-family consumption (986,023 gpd) divided by the number of households (10,748).

•    33 gpd per employee. Industrial, commercial, institutional consumption (1,842,518 gpd) divided by the number of employees (55,834).

Water use factors have trended downward in the last decade. To incorporate the downward trend in water use factors, the forecast assumes a 0.3% annual decrease in the water use factors for single-family residential and multi-family residential throughout the forecast period. Due to the variability in ICI demand, the water use factor for ICI remains the same throughout the forecast period.

Table 3.8 Water Use Factors and ERUs (2010 – 2012 Average)

Customer Category

Sales (gpd)1

Households or Employees

Sales Per Household or Employee (gpd)

Number of ERUs5

Residential

Single-family (SF)

2,591,885

15,624

2

166

4

15,624

Multi-family (MF)

986,023

10,748

3

92

 

5,940

Non-Residential

Commercial

1,317,595

39,927

6

33

7

7,937

Municipal

73,963

2,241

6

33

7

446

Political Subdivision

223,799

6,782

6

33

7

1,348

State

227,161

6,884

6

33

7

1,368

Lacey Wholesale

796,596

N/A

 

N/A

 

4,799

PUD Wholesale

245,136

N/A

 

N/A

 

1,477

Unbilled Authorized Use

53,777

N/A

 

N/A

 

324

Distribution System Leakage

547,082

N/A

 

N/A

 

3,296

Total ERUs

42,560

 

 

3.3 Demand Forecast

Olympia’s Comprehensive Plan requires the Utility to reserve water supply rights for at least 50 years in advance of need, so that supplies can be protected from contamination or commitment to lower priority uses (Policy PU 5.1). This section describes the methodology used in developing the demand forecast and provides the results with and without additional conservation.

Demand Forecast Methodology

The methodology used to develop the demand forecast for retail consumption is illustrated in Figure 3.8. The basic process is to combine demographic data with water use factors to calculate customer demands. Demand components for non-revenue water, the PUD wholesale water and Lacey wholesale water are then added to create the total average day demand (ADD). To generate the total maximum day demand, a peaking factor is applied to all demands except the Lacey and PUD demands. See Appendix 3-1, Planning Data and Demand Forecast Technical Memorandum from HDR Engineering, Inc., for more information on the methodology.

View Figure 3.8 Demand Forecast Methodology.

Demand Forecast with and without Conservation

Projected demand for average day and maximum day are shown in Table 3.9 and Figure 3.9, with and without additional conservation. Additional conservation as shown reflects what demand would look like if conservation goals are met (Chapter 5). Figure 3.10 shows the six components of the average day demand in order to illustrate the relative impact of each component. The decrease in demand in 2017 reflects the end of the City’s wholesale water agreement with the PUD in early 2015 and the end of the agreement with Lacey in December 2016. Beyond 2017, demand is projected to increase every year.

Table 3.9 Projected Demand with and without Additional Conservation

Year

Demand without Additional Conservation

Demand with Additional Conservation

Average Day Demand (mgd)

Max Day Demand (Mgd)

Total ERU

Average Day Demand (Mgd)

Max Day Demand (Mgd)

Total ERU

Retail

PUD

Lacey1

Total

Retail

PUD

Lacey1

Total

2015

(Plan Yr 1)

6.4

0.5

1.7

8.6

14.9

51,560

6.3

0.5

1.7

8.5

14.8

51,183

2020

(Plan Yr 6)

6.8

0

0

6.8

13.4

41,166

6.7

0

0

6.7

13.3

40,339

2034

(Plan Yr 20)

8.1

0

0

8.1

15.2

48,782

8.0

0

0

8.0

15.1

48,171

2064

(Plan Yr 50)

10.5

0

0

10.5

18.1

63,431

10.4

0

0

10.4

18.0

62,628

View Figure 3.9 Average Day and Maximum Day Demand Forecast with and without Conservation.

View Figure 3.10 Average Day Demand Forecast Details.

3.4 UNCERTAINTY ANALYSIS OF DEMAND FORECAST

The baseline demand forecast is an estimate of what future demand might be. To understand the uncertainty in the future values, an uncertainty analysis was conducted to define a range of possible future demands relative to the base demand forecast. The analysis takes into consideration uncertainty of demographics, peaking factor and water use factors by using Monte Carlo computational algorithms to determine an overall uncertainty range for demand. Appendix 3.2 is a technical memorandum from HDR Engineering, Inc. presenting the methodology and additional information on the analysis.

The results of the analysis are shown in Figure 3.11 and are compared with the baseline demand forecast presented in Section 3.3. The figure shows the range of Average Day Demands (ADD) and Maximum Day Demands (MDD) for the planning period through 2064. The 50th percentile curve generated by the uncertainty analysis closely matches the baseline demand forecast presented in Section 3.3. The 90 percent confidence interval increases (widens) over time because the uncertainty increases over time. In 2034, the 90 percent confidence interval for ADD ranges from 7.2 to 8.9 Mgd and for MDD ranges from 12.0 to 17.7 Mgd. In 2064, the 90 percent confidence interval for ADD ranges from 8.7 to 14.3 Mgd and for MDD ranges from 13.6 to 24.4 Mgd.

View Figure 3.11 Results of Demand Forecast Uncertainty Analysis.