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First Quarter 1993 Monitoring Report ssl+. Western Slone Products,Tracy, CA Project No.W0195.00 Page 3 Given the fact that the area of residual soil contamination cannot be excavated without demolishing the structure; the area of residual contaminants is capped with concrete which limits infiltration and leaching potential; and that the much greater magnitude of soil contamination previously existing in the former tank pit did not result in groundwater contamination in former monitoring well MW-4 we must conclude that no threat to groundwater exists. No further action is recommended. 2. The Baker tank which was installed during the excavation of the former tank pit and used to store the groundwater pumped from the excavation has been sampled on a regular basis. The tank was sampled on October 9 and December 21, 1992, January 26, 1993, and February 23, 1993 for BTEX, and TPHD. Additionally the Baker tank samples were analyzed for nitrate, potassium, phosphorus and standard bacterial plate count on December 21, 1992, January 26, 1993, and February 23, 1993. On December 21, 1992 50 lbs. of 20-20-20 fertilizer and 5 lbs. of "soli-nar" bacteria were added to the tank subsequent to sampling, and the tank was agitated for 30 minutes to distribute nutrients and bacteria. On February 23, 1993 following sampling, an %rr additional inoculation of 3 lbs. of bacteria and 5 lbs. of ammonium nitrate were added to the water. Table 2 contains analytical data for the Baker Tank. Analyses indicate that the biotreatment system has worked. Although an increase in TPHD levels was seen from the first sampling round (10109192) to the second sampling round (12129192) the cause of the increase is doubtless due to the fact that the samples were collected from different locations in the tank. The first sample was collected from the surface of the tank and the second sample was collected from the valve at the bottom of the tank. Two factors which could affect the concentration of TPHD at the bottom of the tank are: 1) the decrease of oxygen in the bottom of the tank due to algal growth could inhibit the growth of the bacteria which are biodegrading the TPHD; 2) TPHD levels could have increased due to the silt particles which have settled to the bottom of the tank releasing TPHD to the water. The sample collected on January 26 did not contain detectable concentrations of TPHD, benzene or toluene. Trace levels of ethylbenzene and xylenes were detected. The sample collected on February 23 did not contain detectable concentrations of TPHD or BTEX. These last two samples were collected from the valve at the bottom of the tank subsequent to circulating the tank water. This collection methodology should minimize any stratification within the tank and result in representative samples. Bioremediation appears to be complete. 3. The estimated quantity and extent of contamination left in place has been calculated from the data collected during excavation of the tank area. The contamination left in place is 1 QMR1993.FN L