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November 18, 1999 Job Number. S99307 Page 7 A four hour percolation test was conducted on November 10, 1999 in each of the percolation holes in accordance with the requirements of San Joaquin County Environmental Health Division. The last '/2 hour of the tests were observed by Mr. Johnny Yoakum of that office. The 2 foot deep "shallow"percolation test indicates a satisfactory peculation rate of 30.0 min/in and the 10 foot"deep"test had a rate of 15.0 min/inch (Plate 11). A shallow and deep test was performed because of our initial concern that the shallow test may not pass the County minimum requirement of 60 min/inch. The results indicate that either a standard leach field design or leach field with seepage pits could be used on the site. VII. NITRATE LOADING STUDY A build up of nitrates in the upper ground-water zones can cause a temporary blood disorder in infants called methemoglobinemia(blue baby). Serious and occasionally fatal poisonings of infants have occurred following the ingestion of water containing nitrate concentrations greater than 10 mg/1 nitrate as N or 45 mg/l nitrate as NO3. The nitrate loading analysis estimates the concentration of nitrate-N of the septic effluent combined with rain water after denitrification(prior to mixing and dilution with existing ground water). The method is based on a simple mass balance formula which takes into account soil denitrification, rain fall, and the proposed waste effluent quantity and nitrate level. Assumptions and calculations for the analysis are shown on Plates 9 and 10. The units of nitrate used in the mass balance equation is nitrate-N with a maximum drinking water contaminate level of 10 mg/l. Denitrification is the biological process in the soil whereby certain bacteria utilize the oxygen in the nitrate(NO3) and release nitrogen gas (NO to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10% to 25%_ Soils with higher clay content, moist soil conditions, and organic material denitrify about 25% or more but soils with higher sand content and fast peculation rates are estimated to denitrify about 10%. Due to the presence of silt and the slower percolation rates observed, the denitrification factor is estimated to be 25 %. Highly permeable soil conditions were not observed in the soil borings or in the percolation tests. To estimate the average concentration of the waste stream, the nitrate level of onsite water is added to the average waste level, normally considered to be 45 mg/1-N. The nitrate level of the water from the onsite well was found to be elevated to a level of 14.2 mgA-N. Therefore the total nitrate concentration of the waste stream is estimated to be 59.2 mg/1-N for the site. — � oERtOt 1 Z • O ` r