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a ' II <br /> feature of such magnitude would have fairly widespread <br /> lateral extent . <br /> An additional complexity to the problem of intrusion <br /> of inferior quality ground water from the Delta is that <br /> eastward movement varies with depth. Most of the data <br /> used to compute rate of intrusion were from wells producing <br /> a <br /> mostly from below about 150 feet . <br /> There is very little data within the City of <br /> Stockton on the zone from the surface down to 150-200 feet . <br /> However, based on historic records , and sampling south of � . <br /> the City, it is believed that this shallow zone has invaded Gli <br /> farther eastward and at a greater rate than the lower <br /> strata. This accounts for many of the past difficulties j <br /> in trying to interpret the water quality changes . A more <br /> II <br /> detailed description of this phenomenon is included in I , <br /> discussion of the Lathrop-French Camp area. { <br /> The old abandoned gas wells in the Stockton area <br /> have long been considered a possible source of degradation . <br /> Report No. 7 by a predecessor of this Department (11) , <br /> published in 1955 , investigated this subject . The findings <br /> I <br /> were that 34 abandoned gas wells were located; of these, <br /> 16 were properly sealed, two were probably adequately sealed <br /> and the 15 remaining were either filled with debris , open, <br /> or their condition unknown. <br /> The only one of these wells that indicated that I' <br /> it was causing pollution problems , was a well that was <br /> located in an inaccessible site on the Stockton State <br /> -115- <br />