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INFORMATION SHEET UNITED STATES ARMY CORPS OF ENGINEERS AND THE PORT OF STOCKTON STOCKTON DEEP WATER SHIP CHANNEL AND TURNING BASIN MAINTENANCE DREDGING PROJECT MILE 36.5 TO MILE 41 .0 SAN JOAQUIN COUNTY The United States Army Corps of Engineers (Corps) in conjunction with the Port of Stockton (Port) have proposed to dredge approximately 267,000 cubic yards of sediment from the San Joaquin River from the turning basin at the Port of Stockton to Buckley Cove, a distance of nearly 4.5 miles. The area to be dredged is located entirely within San Joaquin County, within, and to the west of the City of Stockton. The sediments will be dredged from the upper three feet of material along the river bottom by hydraulic cutter head. The sediment and water will then be pumped to sedimentation basins on Roberts Island. The sedimentation basins are designed based on the settleability of the sediments, and are designed to minimize carryover of suspended material . Decant water from the basins will be discharged back to the San Joaquin River. The dredged material will remain at the disposal site on Roberts Island. The disposal location is owned by the Port and has received dredge materials in the past from previous dredging operations along the same stretch of the San Joaquin River. The Corps has pretested the sediments to be dredged for chemical and physical characteristics. Compliance with the requirements contained in the Order should result in a minimal threat to water quality from the dredging and disposal of the dredged material . The requirements call for analysis of the San Joaquin River during dredging operations at the dredge site and at the site of the return flow from the sedimentation basins. The return flow is also monitored to help assess the impacts, and potential impacts, on the San Joaquin River. Effluent and Receiving Water Limitations. Discharge limits are primarily based on the Second Edition of the Water Quality Control Plan for the San Joaquin Delta Basin (5B) (Basin Plan) (adopted by the Regional Water Quality Control Board on 31 March 1989) , the California Inland Surface Waters Plan, and the California Enclosed Bays and Estuaries Plan (adopted by the State Water Resources Control Board on 11 April 1991) . Receiving water limitations are established for metals of concern based on assumed hardness of 50 mg/l as CaCO, (a conservative value) and using the formulas found in the California Inland Surface Waters Plan. Limitations for arsenic and mercury are not hardness related and are based on protection of human health. The criteria for these metals are also found in the California Inland Surface Waters Plan. Other chemical constituents do not have numerical limitations established in the permit as they are believed will be absent from the discharge. The Corps and the Port are required to perform quarterly biotoxicity monitoring on 100% effluent according to USEPA protocol . If chronic toxicity is found, the testing calls for performing biotoxicity testing using a dilution series during the next sampling period. Consistent indications of chronic in-stream toxicity will require the submittal of a work plan to determine the cause of, and eliminate/reduce the toxicity. AMM