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CHEVRON EMC 9 58420213 03/29 '00 14:31 NO.689 03/06 ' • • 4003/U06 Wendy Wyels ' August 13, 1997 Page 2 R_U document are required, please reference this written memorandum as documenting the ' approval byDTSC of both the risk evaluation a stochastic analysis. work plan and the input distributions for the Since a stochastic assessment is an estimate based upon random sampling from,the input spreadshouts, individual "runs" n 5,000 to 10,000 trials, we commonly require the electronic spreadsheets developed for the analysis, so that we may independently verify the run results, the ' shape of the frequency distributions, and the sensitivity analyses. ?hese cleckonic spreadsheets run results constituted the bulk of our have been supplied by Geomatrix, and our analysis of the review. Finally, a supplemental risk evaluation was rrcommcnded by DTSC to evaluate public exposures to unconventional media,of exposure, i.e., neither soil, air or water, These include that oily material ' which exists underground at Alden park to which only occasional contact is expected. Standard risk assessment Parameters, such as daily ingestion rates, doroti exist for such materia] so this Cons with our experience with buried wastes, the impact of requires separate evaluation. Con ' short-term exposures to relatively high concentrations of this material was evaluated. GENERAL COMMENTS Potency Equival.encv Factors for Carcinogenic Polycyclic Aromatic Hydrocarbons (Section 4.0,page 11; also Table 4) Please be advised that the potency equivalency factnr(PEF) for dibenzo h an OA is applicable only to the oral route of exposure. 1t is based upon a comparisons o theof ' known oral potency of benzo(a)pyrenc (12 mg/kg-day-1)to that of dibenzo (4.1 mg/kg-da (a h)anthracen,ene is e inhalation Potency of. dibenzo(a h)antbracene is irectly eof rxtrapolated gtheaoral potency, ' Therefore, the inhalation PEF of dibenzo(a h)anthracenc should be J. While this represents a technical error in the document it does not contribute significantly to the overall risk . The detection frequency for this individual chemical was quite low, and it's proportional contribution via the inhalation pathway to the additive risk of all alone, polycyclic aromatic hydrocarbons do not warrant revision of the document for this reason ' 2, Stochastic Risk Analysis to Produce Refined Screening Levels The electronic spreadsheet used to generate the "Refined Screening Levels" was reviewed, rather than the main text of the document itself This fle is representative of the earlier ' agreements reached with technical staff, and all elements of the report'under review essentially reproduced. We recommewere that a wntp-protected and password-protected version of this spreadsheet be submitted to your Board and accornpany the document in the