Performance of aerobic treatment units: monitoring results from the Florida Keys.

* The Florida Keys are an ecologically sensitive environment.

* They are also a destination for growing numbers of permanent and transient visitors.

* To address the increasing negative ecological effects, statutory onsite wastewater treatment requirements have increased over the last 15 years.

* Consequently, the use of aerobic treatment units (ATUs) has become widespread.

* From 1985 through April 2001, approximately 1,200 such systems were installed in the Florida Keys.

* Florida requires a biennial operating permit for ATUs.

* It also requires a maintenance agreement between a maintenance entity and the system owner.

* The county health department permits and inspects onsite systems, and until 2001 sampled ATUs yearly.

* The study reported here assessed the performance of ATUs under real-life conditions.

* A county health department sampled two-thirds of the ATU systems on record during 2000 and 2001.

* Grab samples were analyzed for

-- five-day carbonaceous biochemical oxygen demand (CBO[D.sub.5]),

-- total suspended solids (TSS),

-- total nitrogen (TN), and

-- total phosphorus (TP).

* Answers to the following questions were sought:

-- How meaningful are grab samples?

-- Are ATUs consistently meeting expectations for NSF-certified, secondary wastewater treatment units?

-- Does it matter where and when a sample is taken?

-- How variable are concentrations with respect to time?

* Samples taken from tee ports and cross ports had higher concentrations of CBO[D.sub.5], TSS, and TN than did samples taken from the treatment unit itself.

* This result suggests that samples taken from such ports are not representative of treatment unit effectiveness.

* Alternative sampling-port designs should be evaluated.

* The effect of additional treatment (tank, sand filter, chlorination) between the treatment unit and pump chambers and injection wells was significant for all parameters.

* Such effects should be considered in defining the performance of systems.

* Between 8 a.m. and 2 p.m., time of day had no significant effect on sampling results.

* Concentrations for all parameters and all samples were higher on Wednesdays.

* Concentrations appeared also to vary significantly by month.

* Future studies of individual systems should clarify the relationship between effluent concentrations and loading variations.

* Effluent from a substantial fraction of systems exceeded limits set by the NSF-40 standard, standards for secondary treatment, or new local standards.

* The assumption that all these systems work well appears to be an oversimplification.

* There was no evidence that newer systems perform better than older systems.

* Opportunities to improve performance through user education and better maintenance and enforcement should be explored.

* Monitoring is crucial for determining and enforcing performance in an onsite sewage program.

* Currently, three elements are missing if there is to be an effective monitoring program:

-- funding for collection and evaluation of samples;

-- definition of performance boundary and consistency in sampling (treatment unit, pump chamber, or injection well); and

-- definition of an enforceable performance standard, which has been traditionally based on far more frequent sampling than is practicable.

This department, Practical Stuff! originated from you, our readers. Many of you have expressed to us that one of the main reasons you read the Journal of Environmental Health is to glean practical and useful information for your everyday work-related activities. In response to your feedback, we dedicate this section to you with salient points to remember about two to three articles in each issue.