This document models dissolved inorganic nitrogen (DIN) loading from wastewater treatment plants (WWTPs) in Puget Sound under different effluent standards scenarios. It finds that reducing WWTP DIN effluent concentrations from 8 mg/L to below 3 mg/L could decrease nitrogen loading but at increased capital and operating costs of $248-513 million annually. The model has limitations as it does not capture time-varying or three-dimensional aspects but provides a starting point for further modeling of Puget Sound dissolved oxygen levels from human-caused nitrogen sources.

1. Dissolved Inorganic Nitrogen in
Puget Sound from Human Point
Sources
A modeling approach using the InVEST Marine Water Quality Model
Matthew Ringel
GEOG 562
December 3, 2013

2. 1. Nitrogen and Water Quality
Source: Washington Department of Ecology
• Nitrogen is not inherently harmful
• Not normally regulated by the EPA
• Depending on the physical environment (i.e.
water temperature, sunlight, current, and
phosphorus levels) nitrogen may lead to
eutrophication (low dissolved oxygen)
• Dissolved oxygen level standards have been
established by Washington Department of
Ecology under the Clean Water Act, which sets
the maximum amount of eutrophication allowed
by human activities

3. 2. Sources of Nitrogen
Source: Washington Department of Ecology

4. 3. Human Sources of Nitrogen
Source: Washington Department of Ecology

5. 4. Seasonality of Nitrogen Loading to
Puget Sound
(Mohamedali, Roberts and Sackmann 2011)

6. 5. Research Design
• Focus on nitrogen loading from Waste Water Treatment Plants (WWTPs) in
southern Puget Sound (from Kingston southward, excluding Hood Canal)
• Use the InVEST Marine Water Quality Model to model nitrogen yield from
these WWTPs based on the three scenarios below
 Scenarios were chosen based on a Washington Department of Ecology study
evaluating nitrogen and phosphorous removal at WWTPs
Scenario Baseline Objective A Objective B
WWTP Effluent
Nitrogen (TIN)
Derived from
1999-2008
measured output
< 8 mg/L < 3 mg/L

7. 6. Methods – Input Data
Input Source
Area of Interest Chosen based on area of greatest
human impact
Land Polygon Washington GIS Portal
Output Pixel Size in Meters Initially crashed due to memory error.
Used 500 without issue.
Grid Cell Depth 1.0 (Default)
Source Point Centroids Wash. DoE Water Quality Permitting
and Reporting Information System
Source Point Loading Table Based on permit information and
scenarios
Decay Coefficient 0.001 (Default)
Tidal Diffusion Constants 5.0 (Created)

8. 7. Results

9. 8. Results

10. 9. Results
“The LOTT facility in
Olympia has the
lowest effluent DIN
concentrations (2.6
mg/L) because of
more stringent
permit requirements
which include a
seasonal limit on
nitrogen loads
discharged into Budd
Inlet in South Puget
Sound.”
(Roberts et al. 2013)

11. 10. Economic Evaluation
Objective A (DIN < 8
mg/L)
Objective B (DIN < 3
mg/L)
Year Round
Annual Statewide Capital
and O&M Costs (Million,
2010)
$421 $513
Monthly Household Sewer
Rate Increase (Weighted
Average)
$16.00 $19.48
Dry Season Only
Annual Statewide Capital
and O&M Costs (Million,
2010)
$248 $300
Monthly Household Sewer
Rate Increase (Weighted
Average)
$9.43 $11.41
(Markus et al. 2011)

12. 11. Simplifying Assumptions
• Model uses 2-D steady state solution
 Time varying aspects such as seasonality of WWTP output, tides, and other physical
processes were not captured
 2-D nature means nitrogen loading is assumed to be near the surface, but WWTP
outflows are typically submerged near the bottom
• Physical transport (Tidal Diffusion Constant) and Decay Coefficient were
not well understood for the AOI
• WWTP outflow locations were not always known. The actual location of the
outfall was used when known. When not known, the location of the outfall
was abstracted from the location of the WWTP

13. 12. Discussion
• Results show the expected decrease in nitrogen loading from WWTPs due to
investments in nitrogen removal technologies
• Judging the impact of reduced nitrogen concentration is challenging
 There are currently no standards for dissolved oxygen in Puget Sound
 Amount of eutrophication depends on nitrogen as well as many other biophysical
factors
• This proof-of-concept would be one small piece of a much larger effort to
model dissolved oxygen levels in Puget Sound

14. 13. Future Implementation
Pacific Northwest National Laboratory, Washington State Department of
Ecology, and U.S. Environmental Protection Agency Model under development
(Khangaonkar et al. 2011)

15. 14. References
Albertson, S.L. 1993. Relative Dispersion of Water Masses Near Department of Ecology Long-Term
Monitoring Stations in Puget Sound Model. Study Result, Olympia: Washington Department of
Ecology Environmental Assessment Program.
Geyer, W. Rockwell, and Richard P. Signell. 1992. "A Reassessment of the Role of Tidal Dispersion
in Estuaries and Bays." Estuaries 97-108.
Khangaonkar, Tarang, Brandon Sackmann, Wen Long, Teizen Mohamedali, and Mindy Roberts.
2012. "Simulation of annual biogeochemical cycles of nutrient balance, phytoplankton bloom(s), and
DO in Puget Sound using an unstructured grid model." Ocean Dynamics 1353-1379.
Mohamedali, Teizeen, Mindy Roberts, and Brandon Sackmann. 2011. Puget Sound Dissolved Oxygen
Model: Nutrient Load Summary for 1999-2008. Study, Olympia: Washington State Department of
Ecology Environmental Assessment Program.
Roberts, Mindy, and Teizeen, Sackman, Brandon Mohamedali. 2013. Dissolved Oxygen Assessment
for Puget Sound and the Straights: Impacts of Current and Future Nitrogen Sources and Climate
Change through 2070. External Review Draft, Olympia: Washington State Department of Ecology
Environmental Assessment Program.
Tetra Tech Engineering & Architecture Services. 2011. Technical and Economic Evaluation of
Nitrogen and Phosphorous Removal at Municipal Wastewater Treatment Facilities. Technical Study,
Olympia: Washington State Department of Ecology Water Quality Program.