Stockton’s position at the head of the Sacramento-San Joaquin Delta means the subsurface is rarely predictable. The city’s soils range from tight, overconsolidated clays near the port to loose silty loams deposited by historic flooding across the 37.95°N corridor. When a grain size analysis skips the full sieve-plus-hydrometer workflow, contractors risk misclassifying a low-plasticity silt as a clean sand—an error that cascades into drainage failures and differential settlement. Our laboratory runs the complete ASTM D2487 suite, combining mechanical shaking through a stack of sieves down to No. 200 with a hydrometer sedimentation test calibrated for the 0.075 mm to 0.001 mm range. The result captures everything from coarse sand to the colloidal fraction that often defines the behavior of Stockton basin soils. For deeper Delta deposits where organics appear, we pair particle sizing with an Atterberg limits evaluation to confirm whether the fine fraction behaves as silt or clay under the Unified Soil Classification System.
Missing the clay fraction in a Stockton Delta silt can inflate bearing capacity estimates by 40 percent—full hydrometer analysis prevents that blind spot.
