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III. NITRATE LOADING STUDY FINDINGS WASTEWATER CHARACTERISTICS AND FLOW PROJECTIONS WASTEWATER CHARACTERISTICS The wastewater characteristics are anticipated to be those normally found in typical domestic or household systems. The scientific literature (Ref. 10) cites domestic wastewater nitrogen concentrations of 35 mg/L N. This concentration will be used in the calculations below. WASTEWATER FLOW VOLUME PROJECTIONS To determine nitrate-nitrogen loading from any project, wastewater flow volumes must be determined as accurately as possible. Domestic flow volume projections are typically approximated from the USEPA Onsite Wastewater Treatment Systems Manual, Pg. 3-4. However, for nitrate loading calculations, the EHD now requires wastewater flow volume projections from single family residential structures to be calculated as follows: 100 gallons per day (gpd) for the first bedroom and 50 gpd for all subsequent bedrooms within the structure. The flow volumes are calculated below using a maximum number of bedrooms for both the primary and accessory unit dwellings. Therefore, the flow volumes for this project are: 5 Bedroom Primary Structure: 100 + 50 + 50 + 50 + 50 = 300 gpd. 5 Bedroom Accessory Unit Dwelling Structure: 100 + 50 + 50 + 50 +50 = 300 gpd. Total Wastewater Flow Volume from the subject property: 300 + 300 = 600 gpd. CALCULATED NITRATE-NITROGEN LOADING NLS§ 3.3, 3.4, 3.5, 3.6. The calculated nitrate-nitrogen impact to the soil and potentially to the groundwater is difficult to determine due to the large number of variables involved and unknown at this time. These include: 1.) Variability in wastewater flows, nitrogen concentrations and dilution affects that may occur, 2.) Impact from upgradient nitrate sources, 3.) Changes in groundwater directional flow and elevation, 4.) Denitrification potential within the soil environment and within the confined and/or unconfined aquifers, and 5.) Landscape/native grass uptake of nitrogen. Various scientific methods exist to estimate nitrate-nitrogen loading. This Study uses the Hantzsche/Finnemore Equation to predict the average resultant concentration of nitrate-nitrogen in effluent recharge water from a conventional septic system. The effluent concentration must not exceed 10 ppm nitrate-nitrogen (45 ppm as nitrate). Wastewater researchers place the nitrogen reduction occurring in septic tanks at 10% to 20%. From the September 2004 Symposium "University Curriculum Development for Decentralized Wastewater Management - Onsite Nitrogen Removal," Dr. Stuart Oakley of California State University Chico states that "approximately 20% of the total nitrogen generated is removed in the septic tank" (Ref. 8). As noted below, this estimate of 20% is used for nitrogen reduction occurring in the septic tanks. 6 Chesney Consulting