Evaluation of Greenhouse Gas Emissions from Septic ... - Geoflow

The main body of the flux chamber was constructed from a PVC pipe section (12"diameter, 12" length), inserted into a 12" diameter PVC cap. A 12-volt fan was installed inside ofthe cap to ensure that the gases were well mixed in the chamber. A 3/16" brass Swagelok fittingwas inserted into the PVC cap to hold 4' of Teflon tubing (3/16" external diameter). A secondbrass piece at the end of the tubing was fitted with a septum to comprise the sampling port usedto withdraw the gas samples. Two additional vinyl tubing vents were installed, one being a 1/4"internal vent that extended 8" inside of the cap and one a 1/2" diameter external vent of 6' inlength with a valve at the end as seen on Figure 3-1b.The purpose of the vents was to maintain atmospheric pressure inside the chamber. Thelarger vent was only used while initially submerging the flux chamber into the liquid to accountfor the large amount of air that needed to be displaced. The larger vent was closed after the fluxchamber was in position for sampling. The total gas volume inside of the flux chamber duringsampling was determined using a scale fixed to the side of the chamber; the scale was used tomeasure the depth of the chamber submergence. The chamber was suspended in the tank from anabove ground tripod using chains attached to the cap.3.1.2 Flux Chamber Inserts for Septic TanksA tank insert designed and used to prevent disturbance of the septic tank contents and tosupport the flux chamber when measurements were being taken is shown on Figures 3-2 and 3-3.This insert was necessary when there was a scum layer present on the liquid surface. The insertwas composed of a 10" diameter PVC pipe section with a length of 8" with a channel at the top.The insert was supported with PVC legs going to the bottom of the tank, such that the insert wassubmerged about 6" into the liquid in the tank. The channel was filled with water prior tosampling. The flux chamber was lowered into the water filled channel to seal the contents of thechamber. The tank inserts were left in place for the duration of the experiment. Some tanks hadlimited access and it was not possible to fit the 12" flux chambers inside the risers; therefore a 6"diameter flux chamber and inserts of the same diameter were built to address this situation. Asummary of the chamber size use per site and compartment is shown in Table 3-1.Table 3-1.Chamber Size Used in Each Site by Septic Tank Compartment.Septic tankDiameter of flux chamber used at each site (inch)compartment 1 2 3 4 5 6 7 8First 6 6 6 6 12 6 6 6Second 6 6 12 12 12 6 6 63-2