Abstract:
Tillamook Bay is used for recreational activities such as swimming and
diving, as well as recreational clam harvesting. The bay is also used for one
of Tillamook's most prominent industries, oyster harvesting. Bacterial
contamination of Tillamook Bay has been a recognized problem since 1962.
There are a number of known sources of bacterial contamination in
Tillamook Bay including municipal wastewater treatment facilities, cattle and
other livestock, and on-site systems. In order to comply with federal
regulations and because of the serious consequences that contamination
poses to the Tillamook economy, the Tillamook County Environmental
Health Department conducted a shoreline survey of on-site systems in the
Tillamook Bay Watershed. The purpose of this study was to determine the
failure rate of on-site systems in a selected area of Tillamook County,
Oregon. This shoreline survey was conducted in accordance with the
minimum requirements for performing shoreline surveys in shellfish growing areas, as set forth in Appendix B of the National Shellfish Sanitation
Program Manual of Operations, 1995 edition. A total of 385 on-site systems
were surveyed. This study used three sets of data to develop the on-site
system profile of the area: (1) information gathered from the Tillamook
County Community Development department files; (2) date acquired during
a survey with on-site system homeowners; and (3) on-site inspection of the
system. None of the on-site systems appeared to be failing, but the rates of
marginal systems ranged from 1.7/100 to 6.4/100. The failure rate was
lower than the expected rate of 6% to 7%; this is most likely due to the fact
that the survey was conducted during the dry season when indicators of
failing on-site systems are not apparent. Another possible explanation for
the lack of failing on-site systems is that forty-nine systems were not
surveyed because the owners chose to not participate in the survey.
Recommendations for future surveys include using dye tracing to identify
failing systems, surveying during the winter when failing systems are
evident, knowing soil types before surveying, using questionnaires to elicit
information from homeowners, and public education about on-site systems
and their maintenance requirements.
