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ARCO 10NePst Seventh Street 055 J_Tfi Post Office Box 2570 " Los Angeles, California 900510570 � Telephone 213 486 3511 n 2'a ( � 31 P;'' 2: 38 Ms. Wendy Cohen December 22, 1993 California Regional Water Quality Control Board Central Valley Region 3443 Routier Road, Suite A Sacramento, CA. 95827-3098 Subject: Response to December 14, 1993 RWQCB letter to STTC Dear Ms. Cohen: This letter will serve as the formal response you requested in the subject letter. As my voice mail message indicated to Mr. Phil Isorena on December 16th, it was not possible to get a written response to this recent request within 24-hours. However, as Mr. Isorena stated in his November 29, 1993 memo to you the STTC has continued to work with the RWQCB on clarification of the issues at hand. Based on Mr. Steve Lofholm (Emcon) and my telephone discussion of November 24, 1993 with Mr. Isorena, there appeared to be a misunderstanding with Mr. Isorena as to the intended clean-up effort at the Stockton terminals. There are many unknowns that the STTC is working towards answering, including the determination as to whether there is a separation of A and B zones. What is known from the groundwater monitoring data over the last five years, as well as the 1993 Phase I Assessment, is that there is minimal lateral migration in the A- zone. The STTC is also trying to obtain copies of all data generated from the SFPPL and Unocal sites to integrate this data into our analysis. However, the STTC is moving forward with an interim remediation plan that will mitigate the downgradient off-site migration of petroleum contamination within the A-zone to the extent necessary to insure future plume control, while moving forward with the vertical assessment. Once all the assessment data has been gathered and reviewed by both the STTC and the RWQCB appropriate remediation plans will be implemented for this concern as well. The specific responses to the RWQCB's November 18, 1993 letter are as follows: Summary item #1) The STTC realizes that there is not an appreciable amount of free-product. The IRAP is entirely separate from the approved free-product recovery plan. In fact, the IRAP is primarily focusing on dissolved phase hydrocarbons within the A-zone through the usage of two viable long term remedial alternatives, air sparging and enhanced biodegradation. As agreed upon in the April 1992 EMCON free-product APPC-7011-1 110-86) ARCO Products company Is a Division of Aildr iCR¢ulle'd0nmpeny