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Step 5: Data Interpretation

Optical Brightener results, especially when combined with other information can be an invaluable tool in identifying and locating sources of waste water pollution. The table in Appendix C, which is based on over 1,000 O.B. samples collected in Gloucester demonstrates the many ways this data can be utilized. Appendix B is a breakdown of all the results from those samples in Gloucester and is probably representative of what one might expect in a watershed based approach to a sampling program. The following are examples of case studies which demonstrate some of the different ways that Optical Brightener sampling has been used.

A. Storm Drain Cross-Connection

In Ipswich during routine storm drain monitoring, a sampling site repeatedly tested positive for Optical Brightener and yet parallel bacterial sampling indicated the site was relatively free from dry weather fecal coliform bacteria. When the upstream portion of this drainage system was subsequently sampled through use of Optical Brightener, a direct discharge from a washing machine was found connected into the storm drain. The homeowner had separated the laundry waste from his septic waste in an attempt to reduce flow to a very stressed septic system.

B. Sewage Exfiltration

In a nearby City, a local monitoring group found extremely high fecal coliform levels in a storm drain that discharged into the harbor. Since the City was totally sewered, it was first thought that the source of bacteria must be non-human in origin. Optical Brightener sampling was then conducted at this site and results were consistently positive. After tracing the Optical Brightener through the street drain system, the group located the source of the problem, a leaky sewer pipe. Similar work done within this City identified several similar cases of sewer system exfiltration and even entire City streets in the older sections of town which were never tied into the central sewer system.

C. Human/Animal Waste Differentiation

In 1996 voluntary sampling was conducted in Gloucester prior to the seasonal opening of a conditionally approved shellfishing area.

  • During dry weather, sampling was conducted at the discharge point of a perennial feeder stream. Volume measurements were taken and while Optical Brightener results were negative, fecal coliform results were unacceptably high.

  • This site was again sampled in dry weather as was an additional site located further upstream.

  • Fecal coliform results for the discharge point were once again unacceptably high and Optical Brightener results once again were negative.

  • While volume measurements and Optical Brightener results for the upstream site mirrored those taken at the discharge point, fecal coliform results were significantly lower.

  • Bacterial loading was then calculated for the discharge point and converted into human equivalents. Bacterial loading sometimes is expressed as human equivalents (H.E.). One H.E. is the amount of fecal coliform produced by an adult human in one day, or two billion fecal coliforms per day. The H.E. calculated at the discharge point was 11.75 people per day.

  • It was known from previous experience (as well as volume measurements) that there was no other inflow to this stream between the two sampling sites. From past experience it was also known that this section of the stream is fairly urbanized and was bordered by only four houses.

  • Negative Optical Brightener results and knowledge of the surrounding watershed suggested that it was unlikely this amount of bacterial loading was human in origin. Based on the negative Optical Brightener results, the dry weather bacterial loading, and previous watershed knowledge it was predicted that the likely source for the unacceptably high fecal coliform results was probably non-human in source. Because of the urbanized nature of the stream and the limited number of warm blooded species that could be expected to reside there, it was further predicted that the non-human source was very likely to be waterfowl. Whatever the source, it still needed to be pinpointed and remediated.

  • The stream was then walked and sampled by the two Local Shellfish Constables. Midway up the stream between the two sampling sites they found several waterfowl penned in the middle of the stream. Fecal coliform results taken above the pen were low and fecal coliform results taken below the pen were very high. The source had been “boxed in".

  • The Local Health Department was contacted and a Health Agent spoke to the residents of the property. The problem was explained to them in detail and they agreed to remove the pen from the stream.

  • Subsequent sampling confirmed that the penned waterfowl were the cause of the unacceptably high fecal coliform results and the shellfishing area was opened on schedule.

Next: Conclusions