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Ralph's Square 2122 S Airport, Stockton Page 2 by petroleum hydrocarbons and additives such as MTBE. The vertical and lateral extent of the contamination plume has not been defined. You are directed to submit to EHD a work plan that will define the extent of the contamination by August 11, 2006. Failure to comply with these directives may result in referral to the Central Valley Regional Water Quality Control Board (CVRWQCB) for enforcement actions. The CVRWQCB has informed EHD that in order to justify leaving contaminated soil in place, the potential health hazards of direct exposure, vapor emissions to indoor air, and gross contamination (odor, nuisance, gross pollution) from the soil must be evaluated. Currently, the CVRWQCB and EHD use the San Francisco Bay Regional Water Quality Control Board (SFBRWQCB) Environmental Screening Levels electronic version lookup tables (ESL Surfer - October 2005) to evaluate if the contaminated soil can remain in place. The ESL Surfer - October 2005 lookup tables can be found on the SFBRWQCB web site at httn:www.waterboards ca gov/sanfranciscobay/esl htm Sites that have contaminant concentrations in soil that exceed the SFBCVRWQCB ESL Surfer concentrations must provide additional justification such as soil vapor sampling data or use of a model like the Johnson & Ettinger Model. The Department of Toxic Substances Control (DTSC) has a guidance document that may assist you in preparing a work plan to collect soil vapor samples. The DTSC guidance document can be found on their web site at http:www.dtsc.ca.gov under human risk assessment. Please feel free to contact Jeffrey Wong at (209) 468-0335 if you have any questions. Donna Heran, REHS, Director Environmental Health Department Jeffrey Wong, REHS Margaret Lagorio, REHS LOP/Site Mitigation Unit IV Supervisor Cc: SJCADA — David Irey Cc: CRWQCB, Central Valley Region — James Barton, PG Cc: Advanced GeoEnvironmental Inc. (AGE) — William Little