SITE INFORMATION AND CORRESPONDENCE

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P Scop-23-02 04: 36P SIER' PACIFIC GROUP 916 33 3197 P.03 *ftool Ms. Wendy Wyels April 23, 1997 Page 2 former Cargill facility contains very low concentrations of molasses-based feed product. Groundwater was (lowing S 830 L with a gradient of 0.005 on 4 February 1997. Inflow of surface water from the nearby San Joaquin River apparently drives the flow of ground water beneath the Port Road No. 8 facility (Table 2). Two rounds of'ground water testing show that nitrate (N-NO) and TKN concentrations are remarkably low. On 4 February 1997, Total-N concentrations in samples from the three monitoring wells ranged from 4.3 to 9.8 mg/l. • Fate and Transport of Nitrogen Compounds - Field evidence and chemical data suggest that anaerobic microbial denitrification is taking place beneath the site, and that feed products present in the subsurface apparently enhance the desired microbial activity. The Central Valley - RWQCB currently establishes soil clean-up levels for contaminants by applying the Designated Level Melhvdology For Waste Clasciftcalion and Clean-Up Level Determination (Marshack, 1986) and the Regional Board's Assessment and Cleanup of'Nitrogen Residuals inSoils at Retail Pertilizer Facilities (October 1992). Sierra-Pacific field evidence indicates that some parts of the Port Road No.8 facility are underlain by soils containing concentrations of molasses-based feed product constituents which contain ammoniacal and organic nitrogen. For purposes of establishing clean-up levels, the RWQCB assumes that all ammoniacal and organic nitrogen compounds ultimately convert to nitrates in the soil. Review of current soil science and waste-water engineering literature would indicate that this assumption is not necessarily valid. Under anaerobic and oxygen-deficient soil conditions, such as exist in the subsurface at the fort of Stockton, nitrogen compounds tend to convert to gaseous nitrogen (N,), nitrous oxide (N2 0), and ammonia (Nil,), "With respect to agricultural utilization of nitrogen fertilizers, the subject of gaseous losses due to denitrification has been extensively studied. Rolston (1981) presents a good review of this topic and gives data suggesting that anything from 10 to 75 percent of fertilizer nitrogen may be lost by this process (typically in the range of 20 percent)." (Jaffee, 1992, p. 270) (Appendix Q. • Saline Ground Watcr Intrusion- Shallow ground water at the Port of Stockton contains dissolved minerals. Flevated salt concentrations and specific conductance values appear to be caused by the influx of'mineralized water into the uppermost aquifer(Appendix A). The literature characterizes "marine intrusion" and "connate" waters as being the sources of saline minerals which tend to reduce the quality of Sacramento-San Joaquin deltaic ground water. The fact that deltaic ground water tends to be mineralized is indisputable. The mechanism by which the ground water degradation takes place is not fully understood, or well doctunentcd in the literature. Based on field observations and interpretation of the literature, it appears that much of the deltaic sediment deposited during the Tertiary Period was deposited under marine or estuarial conditions. Some of these sedimentary formations still retain saline minerals derived from the sea water in which they were deposited. Near-surface aquifers in the Stockton arca, and deeper