SITE INFORMATION AND CORRESPONDENCE

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Mr.Stephen A.Johnson -2- 29 March 1994 approximately 4 and 12 carbons, while TPH-diesel by USEPA Method 8015 Modified (35 10) covers hydrocarbons containing between approximately 10 and 23 hydrocarbons. Therefore, a positive TRPH measurement in the absence of measurable TPH-gasoline and TPH-diesel indicates the presence of petroleum hydrocarbons in the range of approximately 24 to 35 carbons. 3) On page 3 of your letter, you indicate that petroleum hydrocarbon measurements in ground water samples are the result of general soil contamination in the area, unrelated to the operation of the waste pile unit at the Ogden facility. However,TPH-gasoline and TPH- diesel were never detected in monitoring wells at the site, before the recent two monitoring events. The former waste pile contained soils contaminated with a variety of petroleum hydrocarbons. We know from soil staining and soil samples taken from beneath the liner that the former waste pile leaked petroleum hydrocarbons. For this reason, it is impossible to rule out leakage from the waste pile as a probable source of the TPH measurements in recent ground water samples. Due to its proximity to the waste pile and the relatively flat gradient of the water table, data from samples of monitoring well No. 3 cannot be considered to represent background ground water conditions. For this reason, I support Ogden's decision to install a new background monitoring well at the Stockton site. 4) Pages 3 and 4 of your letter present limited information on the construction and development of the proposed background monitoring well. Since the ground water table has been measured as close as 10.05 feet from ground surface, screening of the well for ten feet above the water table would not permit installation of a sufficient sanitary seal to prevent surface water infiltration. Ponded storm water has been observed on several occasions at the Ogden site. Also important is the nature of the filter media used to pack the annulus adjacent to the well screen. The particle size of this packing material should be selected so as to be able to adequately filter out sediment after sufficient well development has occurred. Sediment in monitoring wells has been problematic in past ground water sampling efforts at the site. Installation of the new well would be subject to the San Joaquin County well ordinance. Information on the ordinance's requirements and permit applications may be obtained by contacting: Diane Hinson San Joaquin County Public Health Services Environmental Health Division P.O. Box 388 Stockton, CA 95201-0388 (209) 468-3452 Ms. Hinson is familiar with the Tillie Lewis/ Ogden case. 5) Page 4 of your letter contains proposed sampling and analytical protocols. Prior to sampling of the wells, bailing should continue until pH, temperature, and conductivity are reasonably stable, rather than bailing a fixed volume of water. In-line field filtration should be used for