Henderson Inlet Effectiveness Monitroing Study, Washington State Department of Ecology

Henderson Inlet and several streams in the Henderson Basin were placed on the 1996 and 1998 303(d) list of impaired water bodies, due to violations of one or more Washington State water quality criteria. The basin has tributaries that do not meet water quality standards for pH, dissolved oxygen, and temperature. To address the listings, the Washington State Department of Ecology (Ecology), with assistance from Thurston County Environmental Health and the Thurston County Conservation District, conducted a study in the basin from 2002 to 2005. The evaluation characterized pH and dissolved oxygen and established Total Maximum Daily Loads (TMDLs) for fecal coliform bacteria (FC).
In 2008 Ecology published the Henderson Inlet Watershed Fecal Coliform Total Maximum Daily Load: Water Quality Implementation Plan (Ecology, 2008) which outlined recommendations for reducing FC in the watershed. The plan also set target reductions for FC and recommended additional monitoring to measure progress toward improving water quality.
Since the development of the implementation plan, the Henderson Inlet Watershed Technical Advisory Group determined that most action items identified in the implementation plan have been completed. Subsequently, the group recommended a study to monitor the effectiveness of cleanup action.
This effectiveness monitoring Quality Assurance Project Plan describes a technical study in which Ecology will monitor and compare FC with target reductions outlined in the TMDL. In addition, Ecology will conduct bioassessment monitoring at several locations within the watershed to determine the effectiveness of pollution control measures implemented to mitigate impacts from stormwater discharges into surface waters of the basin. Results of this study will be used to evaluate the effectiveness of implementation actions in the basin.