A common mistake on Denver projects is assuming that a standard sieve stack tells the whole story. You run the coarse fraction, see a well-graded curve, and move on. Then the first big storm hits your detention basin or the subgrade under a slab heaves, and nobody connects the dots back to the lab report that never measured the minus #200 fraction. The Denver metro sits on a mix of weathered Pierre Shale, old alluvial terrace deposits, and wind-blown silts that can carry 15 to 40 percent fines without looking obviously clayey in the field. A complete grain size analysis — sieves plus hydrometer — catches that fraction before it catches you. We see this pattern regularly when contractors bring in samples from sites near the South Platte River or out east toward the plains, where the sand lenses look clean but the silt content is quietly high. Pairing this with an Atterberg limits run on the same sample gives you the full picture of how the material will behave under moisture, and if you are dealing with a structural fill, a Proctor test tells you whether that gradation will actually compact to spec.
Twenty-two percent passing the #200 could be a drainable silt or a swelling clay — the hydrometer tells you which one you are really dealing with.
Methodology and scope
Local considerations
Denver's geology changes fast over short distances, and that directly affects what a grain size curve means for your project. Take two sites five miles apart: one on the claystone bedrock near the foothills in Golden, where the weathered material crumbles into a well-graded silty sand with angular particles, and another out in the sand hills near DIA, where the surface is predominantly aeolian sand with very few fines. On the foothills site, skipping the hydrometer could mean misclassifying a gap-graded residual soil as a clean structural fill — and then wondering why it holds water and softens after a wet spring. On the DIA site, the sieve curve might look perfect for a drainage blanket, but a small silt lens at the borrow source can shift the D10 enough to fail filter criteria against a perforated pipe. The Front Range's semi-arid climate adds another wrinkle: soils that sit dry for months can look granular in a hand-auger sample, yet the first lab wash reveals 18 percent fines that control the hydraulic conductivity. Getting the full grain size distribution is cheap insurance compared to a failed infiltration test or a retaining wall drain that clogs two years in.
Explanatory video
Applicable standards
ASTM D422 – Particle-Size Analysis of Soils (hydrometer method), ASTM D6913 – Particle-Size Distribution of Soils Using Sieve Analysis, ASTM D2487 – Unified Soil Classification System (USCS), AASHTO T 88 – Particle Size Analysis of Soils, ASTM E11 – Standard Specification for Woven Wire Test Sieve Cloth
Associated technical services
Full Gradation with USCS Classification
Complete ASTM D422 + D6913 package covering mechanical sieving from coarse gravel down to the silt-clay boundary, followed by hydrometer sedimentation on the minus #200 fraction. You receive a semi-log particle size distribution curve, D10/D30/D60 values, uniformity and curvature coefficients, and the official USCS group symbol per ASTM D2487. This is the minimum required for structural fill approval, drainage media specification, and filter design on Denver-area retaining structures.
Combined Physical Properties Package
Grain size analysis bundled with Atterberg limits and Proctor compaction on the same sample, giving you the gradation, plasticity, and moisture-density relationship from one submittal. This package saves time on earthwork projects where the spec requires all three — common on City and County of Denver public works jobs and CDOT roadway fill acceptance. The combined data set lets your geotechnical engineer nail the USCS classification and compaction target in one review cycle.
Typical parameters
Frequently asked questions
How much does a grain size analysis with hydrometer cost in Denver?
A combined sieve plus hydrometer analysis typically runs between US$110 and US$170 per sample in the Denver metro, depending on whether it is part of a larger testing package and how quickly you need results. Samples with high clay content that require extended sedimentation readings may fall toward the upper end. Rush turnaround usually adds a surcharge, but standard 3-to-5-day reporting is included in that range.
When do I actually need the hydrometer instead of just a washed sieve?
Any time the material has more than about 12 percent passing the #200 sieve, the hydrometer becomes worth its weight. Denver's residual soils from the Pierre and Denver Formations routinely hit 20 to 50 percent fines, and the hydrometer separates the silt-sized particles from the clay-sized ones. That distinction drives the USCS classification, the drainage design, and the swell potential assessment — all things a simple wash cannot resolve.
How long does the full test take from sample drop-off to report?
Standard turnaround is three to five business days. The sedimentation portion of the hydrometer test alone requires readings over a 24-hour period minimum, and oven-drying and sieving the coarse fraction adds another day. If the material has high clay content, the hydrometer run may extend to 48 hours to capture the fine end of the curve accurately. We can usually accommodate a two-day rush on the sieve portion with the hydrometer to follow, but a complete combined rush runs about four days.