Conference Agenda

Clean Water Services (District) provides sanitary and stormwater services to over 600,000 people in Washington County, Oregon. The District owns and operates four water resources recovery facilities (WRRFs) that discharge to the Tualatin River. In 1988, the Tualatin River basin was the subject of one of the Nation’s first basin-scale Total Maximum Daily Loads (TMDL). The TMDL established criteria for ammonia and phosphorus throughout the watershed that were incorporated into permit limits. However, population and industrial growth in the Tualatin River watershed, changes in the water flow management, and adaptive management principles have influenced water quality dynamics and motivated the update of the phosphorus TMDL. In addition, the District uses alum as part of the water treatment process to meet the stringent phosphorus limits, but EPA recently established an aluminum water quality standard for Oregon that makes alum use no longer viable at current levels. Therefore, to continue our mission to protect the Tualatin River and to comply with both aluminum and phosphorus water quality criteria, the TMDL needs to be reviewed. The Oregon DEQ is committed to priorities other than the Tualatin River phosphorus TMDL and ammonia criteria. To respond to this an uncertain compliance conditions the District in collaborations with DEQ in collaboration with DEQ, the District is developing the modeling and scenarios to understand and update the phosphorus TMDL using a highly detailed and well calibrated CE-QUAL-W2 water quality model for nearly 83 miles of the Tualatin River developed by Portland State University and the District. This model simulates a variety of scenarios to understand the assimilative capacity of the river for phosphorus as a function of flow rate, the impacts of various nutrient and temperature management strategies on the water quality of the river, the impacts of changes in dam operations and river flows over the last 30 years, and the potential effects of various changes to the TMDL on Lake Oswego and downstream waterbodies. This presentation will showcase the scenario development and findings as well as the lessons learned to date when working to update an existing TMDL with new data and modeling techniques

Excess nutrient discharge into receiving waters can pose a serious threat to human health and aquatic life. Nutrient enrichment of receiving streams can lead to depletion of dissolved oxygen resulting from eutrophication of the water body. DO deficits reported for portions of the Southern Puget Sound have raised concerns regarding nutrient loads discharged to the water body. While both point- and non-point sources could contribute towards these, domestic effluents, wastewater treated to secondary standards (limited N and P removal) have been identified as significant contributors.

Additionally, as population growth continues to place burdens on our existing water supplies, utilities are forced to cope with poor quality and limited quantity of potable water supplies. Contaminants of emerging concern (CEC) are recalcitrant chemicals that have tendency to bioaccumulate and are not fully removed by conventional treatment. On one hand, WRRFs are being challenged to meet increasingly stricter effluent limits and rely on advanced treatment; in parallel, water scarcity has driven utilities to embrace Integrated One Water Approach to be water-supply resilient. Although treatment technology selection in potable reuse is primarily governed by WRRF’s ability to meet strict nutrient limits (N, P), co-management of nutrients and CECs in water treated across robust multi-barrier treatment schemes can be an added benefit.

This presentation will focus on lessons learnt from two case studies that highlight two different co-management approaches. The first study (WRF 4790) was aimed identifying hotspots for pollutants (conventional and emerging) and implementing holistic co-management approaches to tackle non-point (agricultural run-off and urban stormwater) and point-sources (wastewater treatment) to improve the health of the Potomac River watershed.

The second case study is on HRSD’s Sustainable Water Infrastructure for Tomorrow (SWIFT) program. The drivers for advance treatment in Eastern Virginia include depletion of groundwater resources, water quality concerns in the Chesapeake Bay, sea level rise and wet weather concerns. The benefits of advanced (non-RO based) multi-barrier scheme (ozone-BAC-GAC-UVAOP) to meet strict nutrient limits (TN= 5 mg/L, TOC= 4 mg/L) and treat CECs will be discussed.