evaluation of gravelless pipe systems for onsite wastewater

Soil
Classification
Results of Effluent Analyses
Table 1. Soil Classification by System
# of systems
with problems
# of systems with
no problems
Sand 3 1
Fine sand 5 2
Loam 1 >NA
Sandy clay
loam
1 NA
Loamy sand 1 NA
The results from the septic tanks and gravelless pipe for BOD, TSS and DO were all within normal
levels to be expected in a septic tank effluent. The BOD values were all below 220 mg/1 and the
TSS values were below 65 mg/1. Many of these were skewed because the first thing many
homeowners do when there is a problem is to pump the septic tank. This pumping affects these
results and the typical operation of these tanks may have been different. Visual inspection
indicates that there is reason for concern that some of these tanks may not be watertight. This was
not apparent during the site evaluations but these were not done during the spring when such high
water table conditions may exist, in the vicinity of the tanks.
Flow Results
Five of the eleven homeowners installed flow meters to monitor the flow. Flows were monitored for
periods of seven to fourteen days. Three of the homes had flows well below the design levels.
Two were close to or above their design flow rates. It is not possible to make a definitive
conclusion based on such limited time periods. However, consistent flows at or above design
values will shorten the life and reduce performance in any onsite system.
The other homes refused or could not install a flow meter. In these instances we do not know if the
system is being hydraulically overloaded. Based on the number of people living in these homes
and the number of water using devices, none of them appear to be exceeding the daily estimated
sewage flow rates.