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F t t' F. IV. CONCLUSIONS, AND RECOMMENDATIONS FOR NITRATE LOADING MITIGATION The Hantzsche/Finnemore Formula predicts a resultant average nitrate-nitrogen concentration in the ,, effluent recharge water from the proposed project to be 5.2 ppm as nitrate-nitrogen (NO3-N), or 23.2 ppm as nitrate (NO3). Based upon this Formula, the nitrate impact from the proposed development will be approximately one-half the Maximum Contaminant Level (MCL) for nitrate contamination of F drinking water. This calculated impact of 5.2 ppm has taken into account three, new single family residences and the existing residence at the east end of the property. If second unit dwellings were . allowed to be built on each of the three proposed parcels, this may theoretically increase the nitrate concentration in the effluent recharge water close to, but not above the MCL. The calculations shown below illustrate the nitrate impact from second unit dwellings containing four persons, as was Fcalculated in the Hantzsche/ Finnemore Formula above for the primary residences: 68 gals/person/day gals/person/dayx 4 people per household x 6 new houses+ 1 existin house/7.32 Ac x 365 d/)E 3.50 in/yr. I= 43,560 cu ft/Ac ft x 7.48 gal/cu ft x (I ft/12 in) i 3.50 in/yl(53„my NIL) (1 -0.251+(13.5 in/yr x 0.1 mg/L) Nr = (3,50 in/yr+ 13.5 in/yr) Nr = 8.3 ppm as NO,-N or 37.0 ppm as NO, Since concentration is reported in parts per million, which is a mass-to-mass ratio, the percolating effluent from the proposed project of three new residential parcels and one existing parcel may theoretically contribute to a dilution effect within the water table mixing layer. If it is assumed that the underlying top aquifer, or water table possesses a nitrate concentration of 52 ppm N031 then percolating effluent on a mass-to-mass ratio basis will theoretically dilute a 5.72 inch depth of the water table groundwater to the following extent: 2.00 in/yr recharge x 27,154 gals/ac-in. x 7.32 ac = 398,000 gallons/yr @ 23.2 ppm NO3 recharge water f 27,154 gals/ac-in x 5.72 inches x 7.32 ac x 35%porosity= 398,000 gallons @ 52 ppm NO3 = 37.6 ppm NO3s which reduces EF. approximately six inches of the water table nitrate concentration below the MCL. From the USDA Soil Map aerial photo, it can be noted that the housing development on the south side of Orford Road and agricultural production land to the south are upgradient to the subject property. In all probability, both of these land uses are contributing nitrate to the upper groundwater. Without highly.sophisticated testing and modeling, it would be impossible to predict the percentages Fill each source contributes to the nitrate concentration that was observed in the on-site well. No well log was available for this well. It is assumed to have been drilled in the 1950s, probably to a ` comparatively shallow depth which may explain the high nitrate concentration and the presence of F; DBCP. 10 ! y' Chesney. Consulting