SITE HISTORY - Laserfiche WebLink

Home Browse Search

PRE-TANK REPLACEMENT Site Assessment Results 880 VICTOR ROAD LODI, CA. Aegis Project No. 89-014 Page 10 2 . 9 . 1 Mehrten Formation The Miocene/Pliocene Mehrten Formation is composed of andesitic sand and sandstone units derived from Sierran andesitic flows and agglomerates interbedded with conglomerate tufaceous siltstone and claystone horizons. Beneath the center of the San Joaquin Valley the upper surface of the Mehrten Formation is 800 to 1000 feet below the surface. The formation outcrops along the eastern margins of the valley, dips toward the west and is nearly flat lying near the center of the valley. The unit thickens to approximately 600 feet at its western margin (DWR 1967) . 2 . 9 . 2 Laguna Formation The Pleistocene Laguna Formation unconformably overlays the Mehrten Formation. The Laguna Formation consists of heterogeneous fluvial continental sediments of non-volcanic sands and gravels. Included within the Formation is the Arroyo Seco gravel, a thin unit south of the Mokelumne River consisting of weathered sand and cemented gravels. The Laguna Formation outcrops along the eastern margins of the valley, dips toward the west and is nearly flat lying beneath the center of the valley. The unit thickens in a westerly direction to a approximately 1000 feet beneath the Lodi area (DWR 1967) . 2 . 9. 3 Victor Formation/Recent Alluvium The Victor Formation/Recent Alluvium occurs near the center of the valley and is generally coarser grained than the underlying Laguna Formation. The formation consists of heterogeneous deposits of sand and gravels with discontinuous lenses of silt and clay. The Formation dips gently and thickens to the west. At it 's western margin the Formation is approximately 100 feet thick (DWR 1967) . 2 . 9 . 4 Structure San Joaquin County lies near the northwest trending axis of a regional syncline with a gently dipping east flank and a fairly steeply dipping west flank. Evidence has been found of extensive folding and faulting of the basement rocks and pre-Pleistocene marine sediments. There is no evidence of faulting or folding in the continental sediments of the valley except along the western flank. (DWR 1967) 2 . 10 Regional Hvdrogeology Three water-bearing formations have been identified beneath the area including the Mehrten Formation, the Laguna Formation and the Victor Formation. Ground water occurs in the Mehrten Formation under semi- confined conditions. Permeability in the Mehrten Formation ranges from