Engineer Soil Environment cheat sheet

Cation exchange capacity (CEC) in cmol(+)/kg equals the sum of exchangeable bases plus exchangeable Al and H; base saturation (%) = (sum of exchangeable bases / CEC) x 100.

Soil texture classes follow the USDA particle-size boundaries: sand 0.05-2.0 mm, silt 0.002-0.05 mm, clay <0.002 mm; the textural triangle assigns the class from the three percentages.

Porosity n = 1 - (bulk density / particle density); with particle density 2.65 g/cm3, a bulk density of 1.33 g/cm3 gives n = 0.50.

Saturated hydraulic conductivity is described by Darcy's law: q = -K (dH/dl), where q is specific discharge, K is conductivity, and dH/dl is the hydraulic gradient.

Soil pH controls metal speciation and mobility: at low pH, Cd, Zn, Ni, and Cu become more soluble and bioavailable; Pb and As behavior differs and must be evaluated separately.

Redox potential (Eh) governs terminal electron acceptors in sequence: O2, then NO3-, then Mn(IV)/Fe(III), then SO4(2-), then CO2 (methanogenesis).

Organic matter raises CEC and water-holding capacity; organic carbon is converted to organic matter with the Van Bemmelen factor of about 1.724.

The soil water balance is dS/dt = P + I - ET - R - D, where P is precipitation, I irrigation, ET evapotranspiration, R runoff, and D deep drainage.

Soil food web trophic levels run from primary producers and detritus to microbes, bacterivorous and fungivorous fauna, predators, and higher predators; each level transfers energy with substantial respiratory loss.

Rhizosphere effects are strongest within about 1-2 mm of roots, where root exudates fuel microbial biomass and mycorrhizal colonization.

Mycorrhizal fungi extend the effective absorbing surface of roots; arbuscular mycorrhizae trade phosphorus for plant carbon, and the symbiosis is disrupted by tillage and high soil P.

Nitrification is performed by ammonia-oxidizing bacteria and archaea and nitrite-oxidizing bacteria; it acidifies soil and produces the mobile anion nitrate.

Denitrification converts nitrate to N2O and N2 under low oxygen; it is the main pathway for gaseous N loss and a source of the greenhouse gas N2O.

Earthworms and other macrofauna create biopores and casts, increasing macroporosity, infiltration, and aggregate stability; their abundance is an indicator of soil biological quality.

Soil respiration (CO2 efflux) is a common proxy for microbial activity; it rises with temperature and moisture up to a threshold, then declines under saturation because of oxygen limitation.

Biological indicators for monitoring include microbial biomass carbon, potentially mineralizable N, earthworm counts, and the ratio of fungal to bacterial biomass.

The conceptual site model links sources, release mechanisms, transport pathways, and receptors; a complete exposure pathway requires all four elements to coexist.

Contaminant partitioning between soil and water is described by Kd = Cs/Cw; the organic-carbon-normalized coefficient is Koc = Kd/foc, and Kd = Koc x foc.

The soil screening level for a volatilization or leaching pathway is derived from risk-based equations that include Kd and dilution factors; screening levels are not cleanup standards.

Light non-aqueous phase liquids (LNAPL) float on the water table; dense non-aqueous phase liquids (DNAPL) sink below it and form pools on low-permeability layers.

Site characterization proceeds in phases: preliminary assessment, then intrusive investigation, then delineation of the extent of contamination in three dimensions.

A soil boring log must record lithology, moisture, staining, odor, PID or FID readings, and sample depth intervals; these data support the conceptual site model.

Background concentrations are established from upgradient or off-site reference locations and are used to distinguish contamination from natural soil constituents.

Contaminant mass in a soil volume equals the sum over layers of concentration x bulk density x volume; this estimate drives remediation sizing.

Soil vapor extraction (SVE) removes volatile organic compounds from the unsaturated zone; design depends on air permeability, vapor pressure, and the number of pore volumes extracted.

In situ chemical oxidation (ISCO) uses persulfate, peroxide, permanganate, or ozone; oxidant demand from soil organic matter and reduced minerals consumes reagent before contaminant destruction.

Bioremediation design controls electron acceptor, nutrient, moisture, and temperature; monitored natural attenuation requires demonstration of decreasing concentration trends and geochemical evidence.

Thermal desorption heats soil to volatilize contaminants; low-temperature units operate around 90-320 degrees C and high-temperature units above 320 degrees C.

Soil washing transfers contaminants from soil to a liquid phase using particle-size separation and surfactants; it is most effective for coarse-grained soils with low fines content.

Solidification/stabilization reduces mobility by physical encapsulation or chemical fixation; effectiveness is measured by leachate testing such as the TCLP or SPLP.

Permeable reactive barriers treat groundwater in situ; zero-valent iron is used for chlorinated solvents and hexavalent chromium reduction.

Remedy selection criteria include effectiveness, implementability, cost, time to achieve cleanup, and long-term monitoring requirements under the applicable regulatory framework.

Sampling plans must specify sample density, depth intervals, compositing rules, and quality assurance objectives before field work begins.

Soil sampling with a hand auger or direct-push rig must use dedicated or decontaminated equipment; cross-contamination between depths is avoided by cleaning between intervals.

Field duplicates, trip blanks, equipment blanks, and matrix spikes quantify precision and bias; typically 10 percent of samples are quality control samples.

Volatile organic compound samples should be collected with minimal headspace and preserved at 4 degrees C; holding times are shortest for VOCs, often 14 days to analysis.

Groundwater monitoring wells must be purged before sampling until field parameters (pH, conductivity, temperature, dissolved oxygen, ORP) stabilize.

Low-flow purging minimizes turbidity and disturbance; it is preferred for metals and other parameters sensitive to colloid mobilization.

Analytical methods for metals include ICP-AES and ICP-MS; for organics, GC-MS is standard, and results are reported with detection and quantitation limits.

A chain-of-custody record must accompany samples from collection through laboratory receipt and must document date, time, sampler, and analyses requested.

Risk assessment follows the four-step framework: hazard identification, dose-response assessment, exposure assessment, and risk characterization.

The reference dose (RfD) is the daily exposure likely to be without appreciable risk over a lifetime; the hazard quotient is HQ = exposure / RfD, and HQ > 1 signals concern.

For carcinogens, risk = exposure x slope factor (SF); acceptable risk ranges are typically 1 x 10^-6 to 1 x 10^-4 for a lifetime exposure.

Exposure is calculated as intake = (C x IR x EF x ED) / (BW x AT), where C is concentration, IR intake rate, EF exposure frequency, ED exposure duration, BW body weight, and AT averaging time.

Regulatory frameworks include CERCLA for site cleanup, RCRA for waste management, and state voluntary cleanup programs; each sets its own screening levels and cleanup standards.

The TCLP determines whether a waste is hazardous for toxicity characteristic metals and organics; the SPLP is used for leaching assessment.

Groundwater classification and beneficial-use designations determine applicable water quality standards and cleanup targets at a site.

Risk communication must present assumptions transparently; the exposure scenario (residential, industrial, or recreational) drives the land-use-based cleanup level.

The Universal Soil Loss Equation is A = R x K x LS x C x P, where A is soil loss, R rainfall erosivity, K soil erodibility, LS slope length and steepness, C cover management, and P support practice.

The Revised Universal Soil Loss Equation (RUSLE) retains the same factor structure but updates factor estimation for climate, cropping, and topography.

The Revised Wind Erosion Equation relates wind erosion to climatic factor, soil erodibility, surface roughness, and unsheltered field length.

Terracing, contour farming, strip cropping, and grassed waterways reduce the P and LS factors; conservation tillage reduces the C factor.

Sediment delivery ratio is the fraction of eroded soil that reaches a downstream point; it decreases as drainage area increases.

The sediment yield from a watershed equals gross erosion times the sediment delivery ratio; deposition and storage along the path reduce yield.

Vegetative filter strips and riparian buffers trap sediment and nutrients; effectiveness depends on width, slope, vegetation density, and flow uniformity.

Gully erosion is assessed by measuring cross-sections and length over time; it is distinct from sheet and rill erosion and requires structural or vegetative treatment.

A project work plan defines scope, schedule, budget, deliverables, and health and safety requirements; it is the baseline for change control.

Health and safety plans must include hazard assessment, PPE requirements, monitoring for explosive gas and oxygen, and emergency response procedures.

Field quality control includes calibration records, equipment logs, and daily field reports that document conditions and deviations from the plan.

Cost estimating for remediation uses unit rates for excavation, transportation, disposal, and treatment; contingency is added for uncertainty in contaminant extent.

Critical path scheduling identifies the sequence of activities that determines project duration; delays on the critical path delay the whole project.

Stakeholder engagement and regulatory coordination should begin early; public participation requirements vary by program and jurisdiction.

Data quality objectives (DQO) define the type, quantity, and quality of data needed for decisions; the DQO process drives sampling design.

Closeout documentation includes as-built records, verification sampling results, and a final report demonstrating that cleanup objectives were met.