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NITRATE LOADING STUDY FINDINGS WASTEWATER FLOW VOLUME PROJECTIONS AND CHARACTERISTICS Wastewater Flow Volume Projections To determine nitrate-nitrogen loading from any project, wastewater flow volumes must be determined as accurately as possible. Domestic flow volumes have been approximated from the USEPA Onsite Wastewater Treatment Systems Manual, Pg. 3-4. However,the EHD has promulgated residential flow volumes pertaining specifically to Nitrate Loading Studies. Under EHD guidelines,the first bedroom of a structure is assigned 100 gpd and all remaining bedrooms of the subject structure are assigned 50 gpd, 365 dpy. As referenced, the primary dwelling has two bedrooms and the proposed modular home will have three bedrooms. Therefore,total flow volume projection= (100 +50 = 150; primary residence) +(100 + 50 + 50 =200; modular)=350 gallons wastewater/day. Wastewater Characteristics The USEPA OWTS Design Manual states residential nitrogen concentrations in domestic septic effluent typically ranging from 35 to 100 mg N/L. An initial nitrogen concentration of 45 mg N/L in the septic tank effluent will be used. An accounting for the loss of nitrogen within the septic tank of between 10% - 30%has been described in Dr. Stewart Oakley's paper(See Ref. 10, Pg. 10). A removal percentage of 20% is used to calculate nitrate-nitrogen loading for this project: 45 mg N/L- 20%=36 mg N/L. 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 variables unknown at this time. These include: 1.) Impact from upgradient agricultural and septic system sources, 2.) Variability in wastewater flows, nitrogen concentrations and dilution effects from irrigation and stormwater recharge, 3.) Changes in groundwater directional flow and elevation,4.) Denitrification potential within the clay soil fractions, and within confined and/or unconfined aquifers. The Hantzsche/Finnemore Formula is used below to predict the average resultant concentration of nitrate-nitrogen in effluent recharge water. As calculated,the property has been assessed on a total areal loading basis correlated with the total projected yearly wastewater flow volumes calculated above. These two factors primarily estimate the average resultant concentration of nitrate-nitrogen in the recharge water. This concentration should not exceed the Maximum Contaminant Level (MCL) of 10 ppm nitrate-nitrogen(45 ppm as nitrate). Page-6- Chesney Consulting