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Jim Tjosvold, P. E. Page 3 April 29, 1988 EPA Dioxin Study - The EPA is currently s=udying the bioaccumulation of dioxin in the vicinity of woodtreatir.g facilities. Fish samples have been collected from both Old and New Mormon Sloughs. Results of their study may be available to the Department in June . Task 6 - Background Soil Sampling Since samples were not collected outside of the McCormick and Baxter property, the report analyzes metal concentrations from past samples in "non-active" areas along with samples collected in the Lippincott Lead Company Area, another alleged "non-active" area. The reported maximum "background" concentrations are calculated from averaging a single maximum concentration for a discrete depth with the above described samples. The Department has several concerns with this statistical approach. The method used to determine the maximum background concentration does not consider the concentration directly above that depth. The assumption that no metals have migrated below two feet is shown incorrect for borings SA-11 and 12 . The mobility of chromium may not be limited to the two foot depth, based on the Department's interpretaion. These deeper soils being contaminated would result in a higher value for the arithmetic mean. The Department believes that the background level can be determined by a different method. Since a fair size population (N=145) has been established in less affected areas, the median value of the distribution for the background value can be determined. The median is less sensitive than the arithmetic mean to extreme values. The 50th percentile median value for the metals from 2 to 10 feet depth are: Arsenic 4 . 9 mg/kg, Chromium 31. 5 mg/kg, and Copper 33 . 5 mg/kg. McCormick and Baxter may pursue background soil sampling if it is believed that interpretation of on-site data is futile. Samples could be collected from additional offsite well drilling. JVS:ch JVS16. 048