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OT Corporation 4005 Port Chicago Highway Concord, CA 94520-1120 Tel. 925.288.9898 Fax.925.288.0888 the 'group- A Alemher of The IT Croup April 12, 2000 Mr. Joseph Mello California Regional Water Quality Control Board 3443 Routier Road, Suite A Sacramento, California 95827-3003 Subject: Offsite VOC Investigation Pioneer Americas, Inc., Tracy Facility (Formerly All-Pure Chemical Company) Dear Mr. Mello: This letter has been prepared to summarize the offsite groundwater investigation completed to date at the Pioneer Americas, Inc. (Pioneer) facility located at 26700 South Banta Road (site), Tracy, San Joaquin County, California. This letter also proposes additional work to attempt to finalize the investigation. The RWQCB requested in a December 16, 1998 letter to All-Pure that the offsite investigation of groundwater at the All-Pure facility be expanded to "determine the relationship between the All Pure Chemical site and the carbon tetrachloride/chloroform plume, and to define the extent of the plume." A Groundwater Investigation Work Plan was submitted to the RWQCB on March 3, 1999, and approved in a letter from the RWQCB dated March 24, 1999. The scope of work entailed the completion of 12 cone penetrometer test (CPT) points to a depth of approximately 100 feet below ground surface (bgs) to assess subsurface lithology. Upon completion of the CPT points, groundwater samples were collected at three discrete intervals between the surface and 100 feet BGS, at points directly adjacent to each of the twelve CPT locations. The field work was completed in November, 1999. The CPT/groundwater sample locations are shown on Figure 1. The 36 groundwater samples collected during the investigation were analyzed for volatile organic compounds (VOCs) by U.S. Environmental Protection Agency (EPA) Method 8010. Chloroform and carbon tetrachloride were the only volatile constituents detected in the samples. These detected constituents, along with the associated sample location, sample depth, and sample horizon are listed in Table 1.