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Soil Suitability and Nitrate Loading Evaluation Page 8 U of P-Golf Practice Facility Expansion 6301 West Eight Mile Road Stockton, California May 13, 2019 CTE Job#25-0711 G R = Average recharge rate due to rainfall (taken as 80%of annual 13.5 in/yr with 20% assumed lost to offsite drainage & evapotranspiration) = 10.8 in/year(average taken from USDA SCS Soil Survey of San Joaquin County, Fig 3,page 8, dated October 1992). Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table typically falls between 0.5 and 1.0 mg/1 (per Hantzsche and Finnemore; 1992) and is assumed to be 1.0 mg/1. Our nitrate calculation is as follows: Ne _ [I (N,,,)(1-D)+R(Nb)] /(I+R) Nc _ [0.907(40) (1.0-0.25)+ 10.8 (1.0)] /(0.907+ 10.8) = 3.25 mg/I as N As indicated in Table 1 above, the existing nitrate nitrogen concentration in groundwater based on the average of the three nearest wells is 0.623 mg/l. Based on this background level, the total nitrate (N) at groundwater level is estimated to be 3.873 mg/l. The calculated nitrate (3.873 mg/L as N) for groundwater Nitrate-Nitrogen Impacts is below the State drinking water standard of 10 mg/L for nitrogen (N). 10.0 CONCLUSIONS A suitable soil condition for septic percolation tests in San Joaquin County is defined as a stratum capable of percolating water between 1 and 60 minutes per inch (min/inch) at a depth of up to 3.5 feet below existing site grade or 30 min/inch for deeper tests. CTE's percolation test results at the proposed leach field were 60.0 min/inch at a depth of 36 inches Based on these results, it is our professional opinion that soil conditions are adequate for use of a conventional septic tank/leach trench sewage disposal system with leach field sized based a percolation rate of 60 min/inch Based on EHD Document 42- 01-002, revised 4/14/2018, the bottom of the disposal field should be at least 5 feet from groundwater. Based on the groundwater level (10.2 fbgs) obtained from this study, such clearance can be maintained. As stated in Section 9.0 above, CTE estimates that the potential nitrate-nitrogen (N) concentration in groundwater resulting from the new leach field is calculated to be below the state standard of 10 mg/L. A L.IN:-