Research Salinity

I often look at things, try to see if i have a good idea and then test it...this is such research, which ended up with me rejecting the use of salinity as a quick way of figuring out what might go wrong at Stamfords beaches....
There was something that i did find out that is useful, there has been some ideas that there is a large influx of fresh water going into the sound from "Ground water" as oposed to surface water. A quality control sample taked 1 mile off the Stamford shore line had no more salinity than the normal levels found at the beaches. Does not seem to be the case.
This also shows that no matter what test you might use, if you know your shoreline and what affects it, history and action because of that knowledg,e is far faster than any test.

Salinity– a tool without promise and not as quick as a preemptive closure

Abstract

Over the course of several years, the Stamford health Department Lab has been doing additional work on all Long Island Sound recreational waters. Besides the traditional bacteriological tests, various chemical parameters have been measured, pH salinity, chloride, nitrite and turbidity. While all have had some promising results and most had drawbacks, salinity showed the best correlation, in Stamford, with bacterial levels. The one very simple statement that can be made is that salinity gave us information we already knew. When fresh water intruded into the beach water, from rain that was significant enough to cause a significant decrease in the salinity, the beaches were already closed by a policy of preemptive closure due to a measured amount of rain. Small variances (± 0.5%) in salinity did not indicate more than normal tidal flow and were not useful in determining bacteriological quality, but could help in understanding currents along the shore.

Sampling Discussion

Since August of 2010, the Stamford Health Department has been analyzing all recreational beach water taken for enterococcus bacteriological quality for salinity also. This is only 195 samples for the Stamford recreational beaches, but does include samples taken at various tides and weather conditions. This is obviously not as large a sample set as our predictive model, based on rainfall amounts, which used over 8,000 samples to confirm its efficacy, however for Stamford, we can make conclusions even on this small sample set.

Previously, we attempted to use chloride measurement (using an US EPA titration method), however because dilutions needed to be great, large errors were introduced into the results and this data was not used.
Small variances (< 0.10%) between samples of each sample set were understood when comparing to known fresh water influences and the currents based on tides.

Instrumentation, Standards and Method

Oakton SALT 6 Acorn series battery operated Salinity meter

Salinity standards 3.5 % and 1.65%
Used in the laboratory only – though this is a portable model
Internal quality control check when turned on
Standardized with use at 0.165% and 3.5% initially
One standard reevaluated at 10 samples and at the end of the series
A sample was analyzed in duplicate for each set
A known amount of sample was added to perform a standard addition evaluation
Duplicate samples were taken and evaluated for each sample set
A sample set was taken from 1 mile off shore at Buoy 38 to ascertain if there is a “plume” of ground water influencing the salinity of bathing water
Temperatures were recorded before each sample set reading
Rain is recorded for each sample set

Quality Control

The low standard (0.165) average recovery was 102.33% with a minimum of 97.56% and maximum of 109.76%

The high standard (3.5) average recovery was 99.13% with a minimum of 93.71% and maximum of 100.29%
The standard addition average recovery was 99.32% with a minimum of 97.97% and maximum of 100.00%
Duplicate reading of the same sample had a comparison average of 100.26% with the minimum of 98.93% and a maximum of 101.65%
The end standard average recovery was 100.52% with a minimum of 98.57% and a maximum of 112.50%
Duplicate samples had an average difference of -0.01 with a standard deviation of 0.01
Samples from 1 mile off shore had % salinities of 2.84, 2.89, 2.88 and 2.89 which is a difference of less than 0.3 from the onshore average
Temperatures were in the range of 21 to 26 C during the readings

Results

8 samples had enterococcus levels greater than 104 CFUs/100 mL. Salinity measurements were below average in 3 of those samples. A rain event greater than one inch was recorded for 7 of the samples and the other sample had a rain event greater than 2”, two days previous and is near a storm drain. The salinity did not indicate a problem with fresh storm water intrusion at that sample, but previous testing had showed this particular sample location was prone to bacterial elevations 2 days after a rain event greater than one inch.

Conclusions

Not only was salinity not a good indicator of bacterial elevations more than 50% of the time, rain measurements had already closed the beach water for swimming before the samples were taken, making the identification of the problem using salinity pointless.