Biomat effects on wastewater infiltration from onsite system dispersal trenches
Finch, Shelby Dee
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The objective of this study was to evaluate the reduction in water movement rates associated with biomat formation in common soils in Georgia. Saturated hydraulic conductivity (Ks) was measured on undisturbed cylindrical (7.6/9 cm diameter by 7.6/9 cm length) soil cores collected from the bottom and sidewall of mature dispersal fields and from adjacent un-impacted soil of seven sites in the Georgia Piedmont and Coastal Plain. Four sites had 34 to 93% Ks reduction in samples from dispersal field trenches as compared to natural soil. Lack of Ks reduction was attributed to Ks variability, low Ks, and variability in biomat development because of system design and installation. Model simulations, using Hydrus-2D, indicated that 99.8 % flow through the trench bottom was 99.8% for the Coastal Plain system and 67.8 % for the Georgia Piedmont. Low sidewall biomat hydraulic resistance increased flow through the biomat-affected sidewall soil and decreased ponding.