ADDENDUM TO THE FACT SHEET

FOR NATIONAL POLLUTANT DISCHARGE

ELIMINATION SYSTEM (NPDES)

PERMIT NO. WA0022772

March 1, 2013

I. GENERAL INFORMATION

Facility: Southwest Suburban Sewer District

Salmon Creek Wastewater Treatment Plant

12550 Shorewood Dr. SW

Burien, WA 98146 (King County)

II. APPLICATION REVIEW

Ecology received a permit application for the Salmon Creek WWTP from the Southwest Suburban 

Sewer District on October 29, 2012. Ecology issued a response letter on November 15, 2012, accepting 

the application and indicating that it was complete. Ecology has sufficiently reviewed the application, 

discharge monitoring reports, and other facility information in enough detail to ensure that: 

• The Southwest Suburban Sewer District has complied with the terms, conditions, requirements and 

schedules of compliance of the current permit (expiration date: June 30, 2013). 

• Ecology has up-to-date information on Salmon Creek WWTP waste treatment practices and the 

nature, content, volume, and frequency of its discharge.

• The discharge meets applicable effluent standards and limits, water quality standards, and other 

legally applicable requirements. Only one registered numeric effluent violation occurred during 

the current 5-year permit term. It consisted of a low pH reading of 4.4 standard units (rather than 

the minimum allowed 6 standard units).

III. PERMIT REAUTHORIZATION

When Ecology reauthorizes a discharge permit, it essentially reissues the permit with the existing limits, 

terms, and conditions. Alternatively, when Ecology renews a permit, it reevaluates the impact of the 

discharge on the receiving water which may lead to changes in the limits, terms, and conditions of the 

permit.

This fact sheet addendum accompanies the new permit, which Ecology proposes to reauthorize for the 

discharge of wastewater to Puget Sound. The previous fact sheet explains the basis for the discharge 

limitations and conditions of the reauthorized permit and remains as part of the administrative record.

Ecology determined it does not need to significantly change the existing permit requirements, including 

discharge limits and monitoring, to protect the receiving water quality. The previous fact sheet 

addressed conditions and issues at the facility at the time when Ecology issued the previous permit in 

2008. A permit modification then occurred in 2009, resulting in changes to effluent mass loading limits 

in Section S1.A of the permit. A fact sheet addendum was added at that time to explain those changes

to the 2008 permit. 

Since the issuance of the permit, Ecology has not received any additional information which indicates 

that environmental impacts from the discharge warrant a complete renewal of the permit. After an 

analysis of recent effluent monitoring data, it was furthermore determined that the limits of the new 

permit will be identical to the limits contained in the 2009 permit because there is no reasonable 

potential to violate the water quality standards based on the recent data.
Addendum to the Fact Sheet for NPDES No. WA0022772

Southwest Suburban Sewer District, Salmon Creek WWTP

Page 2 of 8

TABLE 1: REASONABLE POTENTIAL ANALYSIS

Water Body Type Marine Facility: 

Dilution Factors: Acute Chronic

160 770

1225

1025 Receiving Water Hardness = mg/L AMMONIA, Criteria as Total NH3 ANTIMONY (INORGANIC) 744036 1MARSENIC (inorganic) CADMIUM - 7440439 4M Hardness dependent CHLORINE (Total Residual) 7782505 COPPER - 744058 6M Hardness dependent LEAD - 7439921 7M Dependent on hardness MERCURY 7439976 8M NICKEL - 7440020 9M - Dependent on hardness SELENIUM 7782492 10M SILVER - 7740224 11M dependent on hardness. THALLIUM 7440280 12M ZINC- 7440666 13M hardness dependent

3 3 3 3 365 3 3 3 3 3 3 3 3

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

27,000 0.55 2.37 0.044 640 11.6 0.58 0.0074 2.3 1.4 0.24 0.017 44.2

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0

Acute 13,342 - - 42 13 4.8 210 1.8 74 290 1.9 - 90

Chronic 2,004 - - 9.3 7.5 3.1 8.1 0.025 8.2 71 - - 81

- 4300 0.14 - - - - 0.15 4600 4200 - 6.3 -

Acute - - - 0.994 - 0.83 0.951 0.85 0.99 - 0.85 - 0.946

Chronic - - - 0.994 - 0.83 0.951 - 0.99 - - - 0.946

N N Y N N N N N N N N N N

Aquatic Life Reasonable Potential

0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555

0.368 0.368 0.368 0.368 0.992 0.368 0.368 0.368 0.368 0.368 0.368 0.368 0.368

3.00 3.00 3.00 3.00 1.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00

Acute 506 0.010 0.044 0.001 4.000 0.181 0.010 0.000 0.043 0.026 0.004 0.000 0.784

Chronic 105 0.002 0.009 0.000 0.831 0.038 0.002 0.000 0.009 0.005 0.001 0.000 0.163

NO n/a n/a NO NO NO NO NO NO NO NO n/a NO

Human Health Reasonable Potential

0.555 0.555 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545

0.368 0.368 0.368 0.368 0.992 0.368 0.368 0.368 0.368 0.368 0.368 0.368 0.368

1.205 1.205 1.2049 1.2049 0.2641 1.2049 1.2049 1.2049 1.2049 1.2049 1.2049 1.2049 1.2049

1025 1025 1225 1025 1025 1025 1025 1025 1025 1025 1025 1025 1025

31.738 6E-04 0.0023 5E-05 0.1649 0.0136 6.8E-04 8.7E-06 2.7E-03 1.6E-03 0.0003 2E-05 0.052

n/a NO NO n/a n/a n/a n/a NO NO NO n/a NO n/a

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Reasonable Potential Calculation

Salmon Creek

Receiving Water Data 90th Percentile Conc., ug/L

Geo Mean, ug/L

Human Health Carcinogenic

Human Health Non-Carcinogenic

Aquatic Life

Coeff of Variation (Cv)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Effluent Data

# of Samples (n)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Aquatic Life Criteria, 

ug/L

Carcinogen?

s

WQ Criteria for Protection of 

Human Health, ug/L

Metal Criteria 

Translator, decimal

Water Quality Criteria

Pn

Multiplier

Dilution Factor

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential? Limit Required?

s

Pn

Multiplier

Max concentration (ug/L) at edge of...

Reasonable Potential? Limit Required?
Addendum to the Fact Sheet for NPDES No. WA0022772

Southwest Suburban Sewer District, Salmon Creek WWTP

Page 3 of 8

TABLE 2: AMMONIA CALCULATION

TABLE 3: HUMAN HEALTH PROTECTION ANALYSIS

1. Receiving Water Temperature, deg C (90th percentile): 11.9

2. Receiving Water pH, (90th percentile): 7.9

3. Receiving Water Salinity, g/kg (90th percentile): 30.1

4. Pressure, atm (EPA criteria assumes 1 atm): 1.0

5. Unionized ammonia criteria (mg un-ionized NH3 per liter)

 from EPA 440/5-88-004

 Acute: 0.233

 Chronic: 0.035

1. Molal Ionic Strength (not valid if >0.85): 0.619

2. pKa8 at 25 deg C (Whitfield model "B"): 9.317

3. Percent of Total Ammonia Present as Unionized: 1.4%

4. Total Ammonia Criteria (mg/L as NH3):

 Acute: 16.22

 Chronic: 2.44

Total Ammonia Criteria (mg/L as N)

 Acute: 13.34

 Chronic: 2.00

RESULTS

Marine Un-ionized Ammonia Criteria Calculation

INPUT

OUTPUT

Calculation of seawater fraction of un-ionized ammonia from Hampson 

(1977). Un-ionized ammonia criteria for salt water are from EPA 440/5-88-

004. Revised 19-Oct-93.

TOLUENE 108883 25VBIS(2-ETHYLHEXYL) PHTHALATE 

117817 13B

3 3

0.6 0.6

1.1 1.5

0 0

Acute - -

Chronic - -

2E+05 5.9

Acute - -

Chronic - -

N Y

Human Health Reasonable Potential

0.555 0.555

0.368 0.368

1.205 1.205

1025 1225

0.001 0.001

NO NO

Receiving Water Data 90th Percentile Conc., ug/L

Geo Mean, ug/L

Coeff of Variation (Cv)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Effluent Data

# of Samples (n)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Aquatic Life Criteria, 

ug/L

Carcinogen?

WQ Criteria for Protection of 

Human Health, ug/L

Metal Criteria 

Translator, decimal

Water Quality Criteria

Pn

Multiplier

Dilution Factor

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential? Limit Required?

s
Addendum to the Fact Sheet for NPDES No. WA0022772

Southwest Suburban Sewer District, Salmon Creek WWTP

Page 4 of 8

TABLE 4: EFFLUENT MONITORING DATA

Outfall 001

Monitoring 

Point 001

Parameter

Biochemical 

Oxygen 

Demand 

(BOD5)

Biochemical 

Oxygen 

Demand 

(BOD5)

Biochemical 

Oxygen 

Demand 

(BOD5)

Biochemical 

Oxygen 

Demand 

(BOD5)

Chlorine 

(Total 

residual)

Chlorine 

(Total 

residual)

Fecal 

Coliform

Fecal 

Coliform

Temperature 

(Measured)

Total 

Suspended 

Solids (TSS)

Total 

Suspended 

Solids (TSS)

Total 

Suspended 

Solids (TSS)

Total 

Suspended 

Solids (TSS)

pH pH

Units Lbs/Day Lbs/Day Milligrams/L 

(mg/L)

Milligrams/L 

(mg/L)

Milligrams/L 

(mg/L)

Milligrams/L 

(mg/L) #/100ml #/100ml Degrees C Lbs/Day Lbs/Day Milligrams/L (mg/L)

Milligrams/L 

(mg/L)

Standard 

Units

Standard 

Units

Statistical 

Base

Average Weekly 

Average Average Weekly Average Average Maximum Geometric 

Mean

Weekly 

Geometric 

Mean

Maximum Average Weekly 

Average Average Weekly Average Maximum Minimum

Limits - / 2026 - / 3039 - / 30 - / 45 - / .5 - / .75 - / 200 - / 400 - / - - / 2026 - / 3039 - / 30 - / 45 - / 9 6 / -

Date Value Value Value Value Value Value Value Value Value Value Value Value Value Value Value

7/1/2008 260 416 18 25.1 0.3 0.56 52 155 113 145 7.8 9.9 7.5 7.1

8/1/2008 240 265 15.2 17.8 0.22 0.39 20 121 174 7.7 11.6 7.6 7

9/1/2008 132 167 9.1 11.3 0.2 0.32 38 21 93 109 6.4 7.7 7.6 6.8

10/1/2008 116 143 7.7 9.7 0.18 0.24 10 16 20 106 176 7.1 12 7 6.5

11/1/2008 136 171 7.4 10.6 0.22 0.37 7 15 18 137 148 7.4 8.2 7.1 6.5

12/1/2008 118 142 6.2 8.3 0.21 0.32 5 10 17 89 113 4.7 6.6 8.2 6.2

1/1/2009 231 545 6.5 8.1 0.16 0.28 12 82 14 251 649 6.5 9.2 6.9 4.4

2/1/2009 125 151 7.4 9.2 0.12 0.17 19 70 15 104 114 6.2 7.1 7 6.5

3/1/2009 186 220 9.8 12.3 0.14 0.26 8 12 14 166 187 8.7 10.5 6.9 6.4

4/1/2009 242 258 13.2 14.5 0.2 0.27 12 29 16 185 206 10.2 11.6 7.1 6.5

5/1/2009 229 293 10.9 12.4 0.23 0.37 6 10 17 187 286 8.7 10.7 7.3 6.6

6/1/2009 188 242 12.6 16 0.14 0.23 17 46 19 123 137 8.3 9.1 7.1 6.6

7/1/2009 161 177 11.1 12.5 0.26 0.6 8 12 22 121 137 8.3 9.7 7.1 6.6

8/1/2009 141 172 9.6 12.1 0.26 0.44 11 19 22 114 150 7.7 10.5 7.1 6.7

9/1/2009 175 202 11.5 13 0.18 0.33 21 45 21 189 219 12.6 14.7 7.2 6.5

10/1/2009 162 211 9.7 12 0.23 0.53 16 46 19 170 247 10.1 10.9 7.2 6.6

11/1/2009 261 367 9.8 11.7 0.17 0.31 32 46 18 200 223 8.2 12.8 7 6.5

12/1/2009 241 334 11.3 18.2 0.22 0.3 10 15 16 167 225 7.8 12.4 7 6.6

1/1/2010 337 500 9.5 11.1 0.19 0.46 8 10 15 286 402 8.4 12.5 6.9 6.4

2/1/2010 316 374 14 15.1 0.12 0.3 32 78 14 288 332 12.7 14.5 6.9 6.5

3/1/2010 293 353 14.6 18.8 0.14 0.34 44 110 15 233 274 11.4 12.5 7.5 6.6

4/1/2010 268 314 12.6 14.3 0.15 0.22 15 36 16 249 270 11.8 13.1 7 6.4

5/1/2010 262 324 15.8 19.7 0.24 0.45 62 130 17 174 205 10.5 12.8 7.5 6.7

6/1/2010 271 370 17.2 25 0.19 0.34 44 95 19 150 197 9.6 13.3 7.6 6.9

7/1/2010 216 316 15 20 0.25 0.42 32 34 20 117 157 8.2 11.2 7.7 7.3

8/1/2010 224 282 15.6 18.7 0.22 0.31 33 46 21 122 169 8.5 11.3 7.6 7.3

9/1/2010 188 210 13 14 0.28 0.29 17 43 21 113 142 7.8 9.8 7.7 7.1

10/1/2010 177 238 10.3 11.1 0.12 0.27 23 42 20 119 171 6.9 7.6 7.3 6

11/1/2010 265 404 11.2 14.8 0.16 0.61 26 152 18 168 307 6.8 7.9 7.7 6.8

12/1/2010 467 1186 12.2 23 0.26 0.64 47 317 16 333 926 8.5 18.1 7.3 6.8

1/1/2011 204 303 7.2 8 0.15 0.3 38 83 14 159 227 5.6 6.7 7.1 6.7

2/1/2011 178 227 8.4 11.4 0.14 0.25 17 39 15 191 214 8.9 11.2 6.8 7.1

3/1/2011 291 428 9.5 10.6 0.15 0.29 11 19 14 251 421 8.1 10.4 7 6.7

4/1/2011 244 289 10.9 12 0.11 0.17 20 47 16 224 315 9.8 11.2 7.1 6.5

5/1/2011 274 352 14.3 19.1 0.14 0.28 62 258 17 191 231 10 12.6 7.5 6.9

6/1/2011 178 231 10.3 13.1 0.19 0.25 34 58 18 150 170 8.7 9.6 7.6 6.9

7/1/2011 197 296 12.1 17.8 0.15 0.15 42 77 20 147 172 9.1 10.4 7.6 7

8/1/2011 266 358 17 22.2 0.19 0.24 47 132 21 140 208 8.9 12.9 7.6 7

9/1/2011 243 313 15.5 21.5 0.28 0.4 18 26 21 79 107 4.9 6.2 7.5 6.8

10/1/2011 129 149 7.9 9.1 0.18 0.29 8 11 20 61 81 3.7 4.9 7.2 6.5

11/1/2011 171 241 8.6 12.3 0.17 0.26 14 27 18 87 118 4.3 4.8 7.3 6.5

12/1/2011 232 265 12.9 15.1 0.11 0.25 38 75 16 142 186 7.8 8.7 7.5 6.7

1/1/2012 198 255 7.7 9 0.14 0.31 17 20 15 135 188 5.2 6.6 6.6 7.5

2/1/2012 230 248 9.6 11.2 0.17 0.35 24 103 14 123 130 5.1 5.6 7.1 6.4

3/1/2012 251 304 9.3 10.3 0.1 0.15 44 62 14 127 169 4.7 5.1 7.8 6.4

4/1/2012 257 334 11.9 15.7 0.09 0.11 42 108 15 189 221 8.8 10.4 7.3 6.4

5/1/2012 323 413 17.1 20.9 0.12 0.2 49 95 18 225 288 11.9 16.5 7.5 7

6/1/2012 275 324 15.3 17 0.24 0.49 26 95 19 129 184 7.2 9.6 7.6 6.7

7/1/2012 247 282 14.8 17.1 0.31 0.5 15 44 20 116 169 7 10.2 7.4 6.9

8/1/2012 228 268 14 16.5 0.3 0.55 26 60 21 111 141 6.8 8.6 7.7 7.2

9/1/2012 187 205 11.9 13.4 0.3 0.63 13 31 21 69 86 4.4 5.2 7.7 7.2

10/1/2012 204 296 11.5 17.8 0.2 0.43 38 76 21 133 235 7.3 14.1 7.5 6.7

11/1/2012 468 1351 10.6 16 0.19 0.41 34 211 18 458 1373 9.6 16 7.1 6.5

Min 116 142 6.2 8 0.09 0.11 5 10 14 61 81 3.7 4.8 6.6 4.4

Max 468.00 1351.00 18.00 25.10 0.31 0.64 62.00 317.00 22.00 458.00 1373.00 12.70 18.10 8.2 7.5

Avg 228.36 322.25 11.63 14.67 0.19 0.34 25.61 67.62 17.83 162.74 242.09 7.99 10.33 7.3 6.7

Median 230.00 289.00 11.30 14.00 0.19 0.31 21.00 46.00 18.00 142.00 187.00 8.10 10.40 7.3 6.7

95th % 328.60 518.00 17.04 22.52 0.30 0.60 50.50 180.20 21.00 286.80 512.20 11.84 15.22 7.7 7.2

PUGET SOUND (S-CENTRAL) AND EAST PASSAGE

EFFLUENT
Addendum to the Fact Sheet for NPDES No. WA0022772

Southwest Suburban Sewer District, Salmon Creek WWTP

Page 5 of 8

TABLE 5: EFFLUENT MONITORING DATA (% REMOVAL)

Monitoring Point 

001C

Parameter

Biochemical 

Oxygen Demand 

(BOD5)

Total Suspended 

Solids (TSS)

Units Percent Percent

Statistical Base Average Average

Limits 85 / - 85 / -

Date Value Value

11/1/2008 97 97

12/1/2008 97 97

1/1/2009 95 96

2/1/2009 98 97

3/1/2009 96 96

4/1/2009 95 95

5/1/2009 95 96

6/1/2009 96 97

7/1/2009 97 97

8/1/2009 97 97

9/1/2009 96 95

10/1/2009 97 95

11/1/2009 95 95

12/1/2009 95 96

1/1/2010 337 93

2/1/2010 94 92

3/1/2010 94 94

4/1/2010 95 93

5/1/2010 94 95

6/1/2010 94 96

7/1/2010 95 97

8/1/2010 95 97

9/1/2010 95 97

10/1/2010 96 97

11/1/2010 94 96

12/1/2010 91 91

1/1/2011 96 96

2/1/2011 97 95

3/1/2011 95 94

4/1/2011 95 94

5/1/2011 94 95

6/1/2011 96 96

7/1/2011 96 96

8/1/2011 95 96

9/1/2011 97 98

10/1/2011 98 98

11/1/2011 97 98

12/1/2011 96 96

1/1/2012 96 97

2/1/2012 96 97

3/1/2012 96 97

4/1/2012 95 95

5/1/2012 94 95

6/1/2012 96 97

7/1/2012 96 97

8/1/2012 96 97

9/1/2012 96 98

10/1/2012 96 97

11/1/2012 93 92

Min 91 91

Max 337 98

Avg 100.45 95.82

Median 96 96

95th % 97.6 98

PERCENT REMOVAL
Addendum to the Fact Sheet for NPDES No. WA0022772

Southwest Suburban Sewer District, Salmon Creek WWTP

Page 6 of 8

TABLE 6: INFLUENT MONITORING DATA

Monitoring Point 

IN1

Parameter

Biochemical 

Oxygen 

Demand 

(BOD5)

Biochemical 

Oxygen 

Demand 

(BOD5)

Biochemical 

Oxygen 

Demand 

(BOD5)

Biochemical 

Oxygen 

Demand 

(BOD5)

Total 

Suspended 

Solids (TSS)

Total 

Suspended 

Solids (TSS)

Total 

Suspended 

Solids (TSS)

Total 

Suspended 

Solids (TSS)

Units Lbs/Day Lbs/Day Milligrams/L (mg/L)

Milligrams/L 

(mg/L) Lbs/Day Lbs/Day Milligrams/L (mg/L)

Milligrams/L 

(mg/L)

Statistical Base Average Maximum Average Maximum Average Maximum Average Maximum

Design Limit 9200 9200

Date Value Value Value Value Value Value Value Value

7/1/2008 5171 6363 358 441 3414 4281 237 290

8/1/2008 4375 5295 313 350 3094 3693 222 252

9/1/2008 4098 4759 281 317 3506 3764 240 256

10/1/2008 3725 4203 256 294 3616 4212 241 264

11/1/2008 4028 4646 221 264 4202 6075 244 278

12/1/2008 4373 5869 235 359 3341 4111 183 244

1/1/2009 4302 5000 176 277 4478 9454 163 210

2/1/2009 5109 5863 305 348 3789 4012 226 238

3/1/2009 4792 5466 252 302 3935 4886 207 270

4/1/2009 5123 6753 279 316 3867 4801 212 272

5/1/2009 5007 6330 241 285 4262 5321 206 258

6/1/2009 4703 5149 318 348 3540 4083 239 272

7/1/2009 4933 5740 339 372 3964 4732 273 328

8/1/2009 4972 5269 336 358 3695 4222 250 286

9/1/2009 4672 5452 309 360 3888 4640 258 304

10/1/2009 4961 5982 304 370 3788 4575 230 288

11/1/2009 5488 6968 221 325 3920 5981 155 210

12/1/2009 5237 5987 244 309 4129 5964 191 272

1/1/2010 3508 6607 177 256 2634 6404 131 182

2/1/2010 5164 5770 231 269 3670 4243 164 200

3/1/2010 5236 6358 262 315 3640 4117 182 222

4/1/2010 5198 5547 248 287 3759 4596 179 202

5/1/2010 4709 5235 283 325 3393 3981 204 234

6/1/2010 4861 5519 305 376 3504 4189 220 276

7/1/2010 4495 5049 315 352 3475 3898 243 260

8/1/2010 4901 8122 343 518 3680 4484 259 286

9/1/2010 4037 5138 279 333 3485 4289 240 296

10/1/2010 4846 5209 293 361 3578 3843 216 254

11/1/2010 4677 5874 217 301 3863 5172 174 202

12/1/2010 5100 5926 167 296 3755 4469 123 216

1/1/2011 5147 6186 200 265 3808 4747 148 186

2/1/2011 5181 7724 238 277 4340 8070 196 256

3/1/2011 5660 6828 204 256 4058 7467 142 186

4/1/2011 5212 6229 237 329 3983 4998 182 264

5/1/2011 4737 5260 249 284 3755 4477 199 244

6/1/2011 4686 6215 272 354 4034 5448 233 284

7/1/2011 4753 5818 296 355 4057 4849 254 340

8/1/2011 5809 6841 374 440 3800 4445 243 274

9/1/2011 6983 7594 442 499 3757 4385 237 262

10/1/2011 5208 6037 321 339 3934 5069 242 270

11/1/2011 5548 6999 289 328 3969 5055 208 278

12/1/2011 5574 5981 316 355 3809 4596 214 246

1/1/2012 5551 6073 223 316 4012 4702 161 228

2/1/2012 6144 7573 263 333 4480 6602 192 308

3/1/2012 6322 8763 237 318 4516 5692 171 236

4/1/2012 5613 6979 261 332 4181 5599 194 274

5/1/2012 5712 6635 302 349 4158 4787 220 254

6/1/2012 6152 7211 344 386 4799 6165 268 330

7/1/2012 6331 8186 380 468 4753 8439 286 544

8/1/2012 5420 6013 332 366 4145 6013 254 366

9/1/2012 5159 5683 327 352 3819 4256 242 270

10/1/2012 5323 6723 305 382 3940 5167 230 352

11/1/2012 5453 7944 216 304 3979 8239 147 188

Min 3508 4203 167 256 2634 3693 123 182

Max 6983 8763 442 518 4799 9454 286 544

Avg 5084.51 6168.74 278.04 339.08 3866.98 5127.53 210.85 265.32

Median 5123 5987 279 333 3863 4732 216 264

95th % 6220 8015.2 364.4 451.8 4494.4 8137.6 262.6 344.8

INFLUENT
Addendum to the Fact Sheet for NPDES No. WA0022772

Southwest Suburban Sewer District, Salmon Creek WWTP

Page 7 of 8

Ecology also reviewed inspection reports and other compliance documents to assess the compliance 

of Salmon Creek’s discharge with the terms and conditions in the previous permit. The records 

indicate that the Southwest Suburban Sewer District notified Ecology of a temporary disinfection 

failure that took place on May 28, 2012. An Administrative Order was issued to the District, who 

responded by installing an automatic alarm call-out for the disinfection system and by installing a 

redundant disinfection pump. The District also ordered an Uninterruptable Power Supply with battery 

back-up for the disinfection pump, and prepared a disinfection failure response protocol. Ecology was 

satisfied with the prompt and thorough response.

Ecology assigns a high priority for permit renewals in situations where water quality would benefit from 

a more stringent permit during the next five-year cycle. Given the overall good compliance history and 

the fact that no new or more stringent limits are needed for this permit, Ecology did not feel that it 

should rank the facility as a high priority for permit renewal. The permit reauthorization process, along 

with the renewal of high priority permits, allows Ecology to reissue permits in a timely manner and 

minimize the number of active permits that have passed their expiration dates. For permit reissuance 

planning purposes, Ecology follows a system of ranking that considers the benefit gained by renewing a 

permit rather than reauthorizing a permit during its annual permit planning process. Ecology assesses 

each permit that is expiring and due for reissuance and compares it with other permits due for 

reissuance. Ecology notifies the public and seeks input after it has tentatively established the initial 

draft ranking of the permits it plans to renew and those it plans to reauthorize. Ecology considers all 

relevant comments and suggestions before it makes a final decision.

Ecology carried over the discharge limits and conditions in effect at the time of expiration of the 

previous permit to this reauthorized permit. Ecology then updated the reauthorized permit 

requirements and fact sheet descriptions as discussed below:

• Sediment monitoring was required by the previous permit. Ecology’s Aquatic Lands Cleanup Unit 

approved the resulting May 2011 data report and recommended that sediment monitoring not 

be required in the new permit cycle. The sediment monitoring requirement was therefore 

removed from the new permit. 

• An outfall inspection was required by the previous permit. The resulting May 15, 2012, report 

(and associated video) indicated that the outfall had no impaired function or structural 

deficiency. As a marine outfall with a recently passed inspection, it was deemed reasonable to 

not require another outfall evaluation during the new permit cycle.

• An effluent study of temperature was required by the previous permit. Sufficient data was 

subsequently collected, and there was no reasonable potential for a violation of the water 

quality standard. This requirement was therefore removed. 

• The new permit increases nutrients monitoring to a monthly frequency (see permit condition 

S2.A. Monitoring Schedule). Expanded nutrients monitoring is being required of discharges 

across the Puget Sound following the preliminary results of studies that implicated nutrients in 

the creation of areas of insufficient dissolved oxygen in Puget Sound. The nutrients data will be 

used to further assess Puget Sound water quality, and to inform a Total Maximum Daily Load 

study should one become necessary.

• Additional updates to the permit documents include Updated General Conditions, an updated 

Department of Health Shellfish telephone number, and new King County health department 

emergency contact info.
Addendum to the Fact Sheet for NPDES No. WA0022772

Southwest Suburban Sewer District, Salmon Creek WWTP

Page 8 of 8

Ecology public noticed the availability of the draft reauthorized permit thirty (30) days before it reissued 

the permit per Washington Administrative Code 173-220-050. The public comment period began as 

advertised in The Seattle Times on January 23, 2013, and closed February 22, 2013. No comments were 

received.

IV. RECOMMENDATION FOR PERMIT ISSUANCE

Ecology proposes to reissue this permit for five (5) years.