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r <br /> luesandAssumptions for a maximum of sixteen houses68 gals/berson/day x 4 people per household x 16 total houses/17 4 Ac x 365 d/yr= 3.4 in.43,560 cu ft/Ac ft x 7.48 gal/cu ft x (1 ft/12 in) <br /> Nw=66 mg/L -20% reduction from typ. septic tank =53 mg/L N <br /> d = 10%from biomat and 15% from saturated soil conditions under leachlines. <br /> Nb= Assumed to be 0.1 ppm NO3-N <br /> 3.4 in/yr(53 mg N/L) (1 -.0.25)+01 in/yr x 0.1 m / ) <br /> Nr = (3.4 in/yr+ I I in/yr) <br /> Nr = 9.5 ppm as N0;N or 42.1 ppm as NO3 <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> From the calculations, it theoretically appears that the areal subject acreage of 17.4 acres could <br /> support 16 houses without the nitrate concentration of the sewage effluent exceeding the Drinking <br /> Water Standard of 45 ppm as NO3. However, the current nitrate concentration in the underlying <br /> groundwater must be considered. From the nitrate concentration test data of the wells tested for <br /> the original Study, it is evident there has been, and probably will continue to be, nitrate impact to <br /> the underlying groundwater. Attempting to assess the quantified impact calculated above with the <br /> existing nitrate concentration in the groundwater is extremely difficult. <br /> Because of the current nitrate impact to the groundwater under the project, it is recommended the <br /> San Joaquin County Environmental Health Department consider the following: Rather than <br /> attempt to determine when an additional house within this project (with a conventional septic <br /> system) will raise the nitrate in the underlying groundwater closer to unacceptable concentrations, <br /> all additional septic systems above the initial eight should be engineered sewage disposal systems <br /> to alleviate to the greatest extent possible, the overall accumulation of nitrate in the first water <br /> aquifer. Adding a second dwelling raises several significant issues such as available land area for <br /> sewage disposal, etc. In addition, greater nitrate impact from the nitrogen fertilization of lawns, <br /> gardens and landscaping can occur,which cannot be regulated. Therefore, it is my opinion that <br /> engineered, or alternative-type septic systems should be considered for all second dwellings in this <br /> project. <br /> If there should be any questions from the San Joaquin County Environmental Health Department <br /> regarding this addendum, please contact the undersigned. <br /> ®rp AAA" r <br /> Respectfully submitted, gw ' CNF +c <br /> VALLEY Ag RESEARCH ~� No. 04675 <br /> LCZsney, <br /> 7 <br /> Expires: .3J /2 <br /> R.E.A. <br /> CA.ifo <br /> Page 2 of 2 <br /> Vaffey Ag Research <br />