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r s Currently, there is approximately(12 ppm (Avg.Analysis)NO3-N x 2 =24 lbs NO3-N/Ac) -�- (71 lbs NO3-N/Ac ENR) =95 lbs of NO3-N/Ac in the top five feet of the project site soils. However, during the walnut growing season, there may be 395 lbs of NO3-N/Ac - enough, and excess N to supply potential trees (300 lbs N) + (95 lbs residual N). This amounts to a theoretical excess of 145 lbs (395-250)NO3-N/Ac. Theoretically, 145 lbs excess NO3-N/Ae/yr may leach past the root zone during the growing season and that may ultimately percolate into the groundwater per year. If the project is 21 ac x 145 lbs NO3-N/Ac = 3,045 lbs NO3-N may enter the top groundwater. Converted to nitrate= 3,045 x 4.5 = 13,703 lbs of NO3. Calculated "worst-case" scenario impact: assume first aquifer mixing layer is one inch thick with a porosity of 37% and all of the excess nitrate travels to the mix layer. Wt. of groundwater under the 21 ac =914,760 ft2 x 0.0833 ft = 76,200 ft3 x:37% =28,194 ft3 x 62.4 lbs/ft3 = 1,759,306 lbs water. 13,703 lbs excess NO3 for every 6 inches of soil x (2 x 140 ft to mix layer water table) = 3.84 x 106 lbs NO3 - 1.76 x 106 lbs water= 2.2 ppm NO3 entering top mix layer every year. If the groundwater velocity is 2.3 ft/day, or 840 ft/yr, it can be estimated that the nitrate impact concentration from nitrogen fertilization could be comparable to the calculated septic system nitrate-nitrogen impact in the effluent recharge over a long period of time. III. CONCLUSIONS AND RECOMMENDATIONS FOR IMPACT MITIGATION ; Three separate scientific methods to assess and quantify nitrate loading were used for this Stud . The Hantzsc e _i_nnemore Equation predicts a resultant average concentration in the recharge water from the proposed Clements Oakridge Estates project to be 36.1 Dpm as-NQ,.,...The Maximum Contaminant Level (MCL) for nitrate in drinking water is 45 ppm as NO3. The Hantzsche/Finnemore Equation is the "industry standard" and predicts the resultant nitrate effluent recharge to be under the MCL, even when incorporating substantial safety factors into the equation. The "true" first water, or water table is unknown. As referenced in the 5JgAyJbgLc_is_a�aiguiFi=L: sand stratum from_2.1 lg , Q feet, which could act as a perched water table under certain conditions, and during specific times of the year. The Well Drillers Report does not specify when first water was encountered. The 1999 Lines of Equal Depth place the static water level at approximately 140 ft below ground surface, which is probably the true water table. There appears to be virtually no nitrate impact to the underlying aquifers that were analytically tested. It is assumed the well will be screened in these aquifers. Due to the density of surrounding on-site septic systems, and the surrounding areas upgradient to the property that are under intense agricultural production, nitrate impact may occur at some point in time in the future. However, the alkalinity of the underlying groundwater may impede nitrification. As a public well, the EHD will require periodic testing for nitrate. Additional l the EHD will require a 200-ft grout seal upon completion of the well. Given the strict EHD requirements for grout seals, this should prevent potential nitrate contamination from shallow aquifers, or perched water table conditions from entering the lower aquifers where the screened area of the well is anticipated. Page -15- Chesney Consulting