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April 7, 2006 FOR: Mr. Mike Huggins, REHS, RDI, Land Use Program Supervisor San Joaquin County Environmental Health Department 304 East Weber Ave. Stockton, CA 95202 PROJECT: Proposed Preston Pipelines Commercial Development and Office Expansion 12833 South Manthey Road, Lathrop Land Use Application #PA-04-646 SUBJECT: Preliminary Soil Suitability Study/Nitrate Loading Study Information Dear Mr. Huggins: Preston Pipelines Company is proposing to construct a new commercial facility for their offices at the above-referenced location. Since the subject property does not have access to public water and sewer, an on-site well and two septic systems for two separate office locations must be installed. Future utility connections will occur based upon the development that is taking place directly south of the property. With regard to the Studies required by EHD, I have completed the preliminary document research, and the soil and groundwater sampling and testing. The soil test results (See Attached) show an incredibly high denitrification potential within the soil column. This is evidenced by the two soil borings to 20 foot depths completed in the proposed leachfield areas. As illustrated, the nitrate- nitrogen concentrations are very high at the five foot depths for both the proposed West Leachfield (WLF)location,and the proposed East Leachfield(ELF),but dramatically decrease in concentration at the deeper depths. Groundwater chemical analysis on the water table from the proposed East Leachfield and West Leachfield locations have also been completed (See Attached). The nitrate concentration is high at 159 ppm for the ELF, but Below Detectable Limits (BDL) for the WLF. Although it appears that the on-site soils posses high denitrification capability, this may not be the case in soils upgradient to the site. Consequently,we see this high nitrate concentration in the water table that may have occurred upgradient due to agricultural sources that `overwhelmed" the denitrification potential of the soil. The water table under the WLF shows extremely abnormal chemistry. However, the denitrification potential must be very high for nitrate not to be present in the water table. All of these test results referenced above will be discussed in detail in the Soil Suitability/Nitrate Loading Studies. The rains we have experienced through March and now through the second week of April have prevented the completion of the percolation testing. It appears that it may be another two to three weeks, at least, before perc testing may commence. Although testing would be appropriate under moist soil conditions normally found at this time of the year, I have monitored the soils and have found them to be super-saturated for the past three weeks. The test borings were actually full of water after each significant storm. Consequently, a representative perc rate would be unattainable. IP.. O. BoX3794 4 Turlock, CA 95381 4 Office(209)668-1403 ♦ Ewc(209)668-2598