FIELD DOCUMENTS AND WORK PLANS 2004-2014

Home Browse Search

Appendix C:Initial Study checklist Former Marley Cooling Tourer Company,Stockton,CA concentration as high as 0,33 mg/L can be present in groundwater without endangering public health assuming an individual ingests 75 percent of their daily intake of 1.4 liters of water at home every day of the year for nine years, and weighs 70 kilograms. The cleanup goal established for chromium in groundwater in the 1990 RAP is 0.050 mg1L based on the California MCL for total chromium.The RAP Amendment proposes to maintain this goal for cleanup. A major toxicological study is underway to determine if ingested hexavalent chromium from water causes cancer. One result may be the establishment of a Public Health Goal which is a step towards an MCL value. An ecological assessment was completed in 1990 (Ecological Assessment by Clement Associates in May 1990 as part of the Remedial Investigation/Feasibility Study (RI/FS) Volume IV, dated May 1990). This report concluded that no adverse effects are expected in terrestrial wildlife consuming water or fish from the Stockton Diverting Canal assuming chemical concentrations in the canal do not exceed the NPDES permit limits. Aquatic life in the Stockton Diverting Canal is not expected to be adversely affected by the aquatic concentration limits of arsenic, copper, and chromium set by the NPDES permit because these levels are based on United States I Environmental Protection Agency(U.S. EPA) Ambient Water Quality Criteria, or more restrictive health-based criteria, In addition, aquatic toxicity studies with the treatment plant effluent have shown no significant adverse effects. No adverse effects are expected to the Giant garter snake, a state-listed threatened species that may inhabit the Stockton Diverting Canal. Snakes living in the Stockton Diverting Canal could potentially be exposed to the chemicals of concern through ingestion of water and fish in the Stockton Diverting Canal; however,snakes are not expected to experience adverse effects because the margins of safety for birds and mammals are so high. The site is completely paved and surrounded by a residential and light industrial area. There are no natural habitats that will be affected by the proposed action and, due to the highly disturbed nature of the project site; no sensitive species are expected to inhabit the area or surrounding lands. Pumping and treating extracted groundwater is currently on-going at the site. The treated groundwater is discharged to the Stockton Drainage Canal under an existing NPDES permit. As a result of no significant biological change in the immediate area of the site, information provided within the 1990 Ecological Assessment has been determined relevant today. Additional ecological assessment isnot suggested at this time based on the proposed remedial action for the site and surrounding areas. Risk of exposure to hazardous substances from soil has been mitigated since the 1990 Remedial Investigation (RI). Surface and shallow soil contamination identified in samples collected from drainage ditches on-site in 1989 have been remadiated by removing soil with concentrations exceeding the established levels and covering the entire site with asphalt. Shallow soil with elevated levels of chromium, arsenic, and copper at depths from near surface to approximately 15 feet below ground -surface are covered with an engineered RCRA cap in the Immediate area of the retort pits. An environmental restriction has been implemented prohibiting disturbance of the cap without authorization from DISC. The site is fenced and secure and all storm water is captured and pumped to the treatment system for processing before being discharged under an NPDES permit to the Stockton Diverting Canal. The calcium polysuifide solution used in the pilot studies was a 3% concentration in a water solution. The RAP Amendment proposes to use a calcium polysuifide solution as the injection fluid. An official NSF International Standard 60 Listing allows the use of safe use of CASCADE calcium polysulfide solution as a treatment solution in drinking water. The product is used for the destruction of residual chlorine in the water, Chromium is the contaminant of concern in groundwater in the shallow and intermediate zones (60-200')beneath and emanating from the site. Direct ingestion of groundwater containing chromium represents a potentially complete exposure pathway. There are five (5) domestic wells, one (1) irrigation, and four (4) municipal production water wells that have been identified downgradient from the site that continue to be monitored and sampled to ensure chromium concentrations are below the MCL. The existing extraction and treatment system has reduced the concentrations on and off site and maintains hydraulic control. References Used., 1, 3 Page 4of 25