COMPLIANCE INFO_1990-1998 - Laserfiche WebLink

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CITY OF TRACY 2 30 August 1990 SLUDGE MANAGEMENT PLAN JULY 1990 depths, are consistent with soils under careful water management practices which have minimal available irrigation water supplies for leaching. 2. The textural analyses indicate considerable variation in the amount of clay in the surface soils. This may have resulted from the major earthmoving activities during the 1950s when these fields were graded for flood irrigation. In general , Capay soils have clay and clay loam surfaces; however, samples taken from two of the test pits, TP-1 and TP-4, indicate considerably less clay in the surface soils. 3. The cation exchange capacity (CEC) values range from 12 to 23 milliequivalents/100 grams with a weighted average (30-inch profile) ranging from 15.5 to 22.7. These CEC levels fall within the EPA >15 meq/ 100 grams criteria for sludge metal loading determinations. 4. The soluble and extractable cations (calcium, magnesium, sodium, and potassium) are within normal ranges for irrigated soils within the area and show no significant buildup of sodium salts within the tested profiles. The presence of high concentrations of calcium salts, i .e. AH-5 from 45 to 65 inches, indicates an abundance of precipitated calcium salts in the lower profile. 5. The extractable metal concentrations (cadmium, copper, nickel , zinc, and lead) are all relatively low. 6. Hot water soluble boron levels show significant buildup in some samples in the lower profile, i .e. AH-5 from 18 to 45 inches and 45 to 65 inches. These levels are attributed to the boron levels of the site's irrigation waters (shown in Table 3 of the Report) and the limited availability of water for off-season leaching. The indicated boron levels may constrain crop selection, especially for boron-sensitive crops such as orchards and some vegetables. Additionally, the Report states the field investigation was focused on the airport property; however, if sludge is applied beyond airport property then additional soil sampling will be required to document the existing soil conditions. Based on the soil survey data and the on-site soils investigation of the 300 acres on the airport property, the site soils are suitable for long-term sludge land application at agronomic rates. The sludge application schedule must be based on crop utilization of nutrients, principally nitrogen. GROUND WATER CHARACTERISTICS The Report states that geologic logs for wells in the vicinity of the site have alternating sand and clay layer down to the Corcoran Clay. The average depth to the Corcoran Clay is 200 feet with an average thickness of 90 feet. The Corcoran Clay separates the upper and lower aquifers. Typically, the upper aquifer contains fresh ground water which may be used for drinking water or agricultural supply while the