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• <br /> -4- <br /> Figure 2 shows the collection vaults that we designed to remove <br /> the oil seeps. The soil below each seep was excavated. The hole <br /> was filled with gravel, and a collection vault was installed. <br /> Oil flows into the collection vault instead of toward the <br /> surface. <br /> Six vaults and several smaller excavations were installed. They <br /> worked well--no oil has reappeared at the surface. Some of the <br /> vaults have accumulated a small amount of oil, and this oil will <br /> be removed if necessary. If oil seeps appear in new locations, <br /> seep vaults can be installed with minimal disruption to the <br /> neighborhood. <br /> Liquids Pumping Test <br /> Chevron hired Dames & Moore to conduct a test of liquids pumping. <br /> Their results are summarized here, and the details have been <br /> described in a separate report . 2 <br /> They used a submersible pump to remove a mixture of oil and water <br /> from Monitoring Well 16 in the north-east area of the park. The <br /> oil and water were separated by gravity in a baffled tank . The <br /> water was pumped to a large tank and then removed by Chevron for <br /> further treatment and disposal . <br /> Figure 3 shows the results of the 15-day test . The water rate <br /> was initially 700 gal ./day (gpd) and it decreased to about <br /> 250 gpd after 15 days. The average oil pumping rate was 2. 8 gpd. <br /> On the average, 150 gal. of ground water had to be pumped to <br /> recover 1 gal. of oil . This water-to-oil ratio is about the same <br /> as our experience at other sites. Dames & Moore measured the <br /> area of influence or "reach" of the liquids pumping well, but the <br /> measurement was inconclusive. We estimate that the reach would <br /> be about 100 ft. <br /> We measured the oil and grease content of the groundwater after <br /> the oil separation step. The baffled tank separator reduced the <br /> oil and grease to less than 100 ppm. <br /> The liquids pumping test was intentionally located at a well <br /> where the viscosity of the oil was low. Figure 4 shows that the <br /> oil in the rest of the park is about ten times more viscous . In <br /> those wells, liquids pumping would recover much less oil (about <br /> 0 . 3 gpd) . <br />