Tennessee Valley Marina and Campground Wastewater Characterization Screening Study Follow-Up Report
Abstract:This completed study, funded by Tennessee Valley Authority (TVA), is a follow-up to the 2003 TVA Project Report, "Tennessee Valley Marina and Campground Wastewater Characterization Screening Study" (Matassa 2003) which was presented at WEFTEC 2005. The 2003 report concluded that marina and campground pump-out wastewaters were highly concentrated in comparison to traditional residential wastewater. Concerns over whether marina and campground onsite/decentralized wastewater systems (DWS) adequately treat wastewaters led to this follow-up study which examined treated effluent below three drainfields. Several water quality parameters were collected and analyzed including toxicity, pH, nutrients, and biochemical and chemical oxygen demand.
Three sites (one marina and two campgrounds) from the original fourteen studied and characterized in 2003 were investigated. Site selection considerations included strength of wastewater, mix of campgrounds and marinas, and including DWS designs based both on current and older DWS state regulations. Site characteristics are shown in Table 1.
In order to determine the level of treatment accomplished by campground and marina onsite/decentralized wastewater treatment systems (DWS), pressure-vacuum soil water samplers were used to collect samples below drainfield trenches. Nine samplers were placed in each DWS drainfield. Samplers were placed in groups of three at the head (closest to septic tank inflow), middle, and end of the drainfield (farthest distance from septic tank inflow) approximately two feet down slope from the centerline of each trench. Samplers were spaced about three feet apart as shown in Figure 1. The bottom of the ceramic cup was installed to collect treated wastewater from approximately two feet below the bottom of the drain field trenches.
Four sampling events were conducted at each marina or campground from September 2005 through July 2006. There was an emphasis on sampling during the non-peak (resting) season (1 sample), during peak season, around the Independence Day holiday (1 sample), and near the end of summer (2 samples).
Samples were collected, analyzed, and compared to 2003 septic tank effluent samples. Also, facility treatment effectiveness, seasonal trends, and sample concentrations along the length of the trench were investigated. Table 2 presents minimum and maximum sample values below the drainfield trenches and percent difference from septic tank effluent sample.
Nutrients (except for nitrate-nitrite as N), COD, and BOD5 had removal rates from 83 to 98% when compared to 2003 septic tank effluent. Nitrate-nitrite increased below the drainfield trenches compared to the septic tank effluent samples because of the expected conversion of oxidation of ammonia to nitrate. Toxicity of the treated effluent, as indicated by Microtox values, was greatly reduced as well.
Facilities designed to current state standards provided the highest level of treatment. Older facilities receiving pumpout wastes which are located near sensitive areas should be evaluated for impacts and potential upgrades.
To show the differing levels of treatment between Facility A (newer) and Facility C (50+ years old) the ammonia and BOD5 values are compared in Figure 2. This figure shows significantly lower concentrations of both BOD and ammonia at Facility A compared to those at Facility C at all locations in the drainfields. The data from Facility B (designed to current state standards) implies an even higher level of treatment.
Other trends including seasonal variations and sample concentrations along the length of the trench were examined. Most marinas and campgrounds are closed during winter months. As a result, seasonal variations in wastewater concentrations were expected. Surprisingly, no strong association was apparent.
Along the trench length, trends were observed in sample volume and wastewater concentrations. Both were generally greater toward the head of each system. For example, At Facility A, a serial distribution system, wastewater effluent was apparently dispersed throughout the field, as evidenced by the proliferation of samples (compared to Facility C). Nutrient concentrations, except for Nitrate-Nitrite N, and COD and BOD5 concentrations generally decrease from the head to the end of the field. This could be explained by more saturated conditions at the head of each system accompanied by biomat build-up.
Overall, findings indicated that all three DWS studied seem to provide a significant and high level of treatment despite heavy loadings associated with marina and campground pump-out wastes, when compared to the 2003 septic tank effluent samples.
Document Type: Research Article
Publication date: October 1, 2007
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