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,A& 0 1 0 <br /> SIERRA-PACIFIC GROUP <br /> GEOLOGISTS O ENGINEERS O SCIENTISTS O COM-PLIr)NCE SPECIALISTS <br /> February 5, 1999 <br /> Ms, Wendy Wyels - Site Cleanup Unit <br /> Central Valley -Regional Water Quality Control Board <br /> 3443 Routier Road, Suite A <br /> San Ramon, California 95827-3098 <br /> Subject. Proposed Preliminary Fate and Transport Modeling Summary for Health Risk <br /> Assessment, Former PureGro/Brea Facility, 1905 North Broadway Avenue, Stockton, <br /> California, Sierra-Pacific Project No. 94-055.08 <br /> Dear Ms. Wyels: <br /> On behalf of Unocal Corporation, Sierra-Pacific Groundwater Consultants, Inc. is pleased to submit the <br /> enclosed proposed preliminary fate and transport modeling summary for the health risk assessment at the <br /> former PureGro/Brea facility. This summary was prepared by our subcontractor,Newfields, Inc. with site <br /> specific data input from Sierra-Pacific. <br /> We note in reviewing some of the models that factors such as the extent of existing paving on the site,the <br /> construction of liner/cap systems above the two former evaporation ponds, and other site-specific <br /> considerations are not factored in,due to constraints inherent in the configuration of the models. Also,while <br /> all potential exposure pathways and all potential future land use scenarios are included herein,we would like <br /> the opportunity to discuss with you the appropriateness of assessing the risk of some of these. <br /> We would like to meet with you and with your reviewer(s) at OEHHA after your review is complete and <br /> before their finalization and incorporation into the health risk assessment. Please call either Nick Nickerson <br /> at Unocal or me if you have any questions, and to schedule the requested meeting. Thank you for your <br /> consideration of this request. <br /> Sincerely, <br /> SIERRA-PACIFIC GROUP <br /> V rt_ <br /> Eric D. Chase, CEG <br /> Senior Engineering Geologist <br /> EDC/dk <br /> C. Nick Nickerson, Unocal DBG/AMG <br /> Jan Wagoner, Unocal DBG/AMG <br /> Mike Infuma, San Joaquin County <br /> 4911 Windplay Drive,Suite 4 El Dorado Hills California 95762 <br /> Phone:(916)933-1468 Fax:(916)933-3197 E-Mail: sppi@sactonet.org <br />