Free PE Environmental Exam Flashcards

One gallon of water weighs 8.34 lb, and for dilute solutions 1 mg/L is approximately 1 ppm by mass, so Feed rate (lb/day) = Flow (MGD) x Dose (mg/L) x 8.34. This gives pounds of pure (100%) chemical; for a commercial product, divide by its purity fraction (e.g., divide by 0.65 for 65%-available HTH calcium hypochlorite) to get pounds of product needed.

Detention time t = Tank Volume (V) / Flow Rate (Q). Also called hydraulic retention time (HRT). Governs how long water stays in a basin for settling, mixing, or disinfection contact, and is central to sizing sedimentation basins and clearwells.

Measures the dissolved oxygen consumed by microorganisms decomposing organic matter in a water sample incubated at 20 degrees C for 5 days. A standard indicator of wastewater organic strength and treatment-plant loading; a higher BOD5 means more oxygen-demanding pollution.

A bench-scale procedure that simulates coagulation and flocculation at different coagulant doses (e.g., alum, ferric chloride) and pH values to identify the optimal full-scale dose before it is applied at the treatment plant.

The contact time in a CT calculation is T10, not the theoretical detention time V/Q, because short-circuiting means only part of the flow gets full contact. T10 = BF x V/Q, using minimum operating volume at peak hourly flow; a tracer study supersedes the table. EPA baffling factors: unbaffled 0.1, poor 0.3, average 0.5, superior 0.7, plug flow 1.0.

MCLG (Maximum Contaminant Level Goal) is the non-enforceable health-based goal, set at zero for known or probable carcinogens. MCL (Maximum Contaminant Level) is the enforceable legal limit, set as close to the MCLG as feasible given treatment technology and cost.

Currently 0.015 mg/L (15 ppb) at the 90th percentile of tap samples; an exceedance triggers corrosion-control and public-education requirements. EPA's Lead and Copper Rule Improvements lowers the action level to 0.010 mg/L (10 ppb), with a compliance date of November 1, 2027.

10 mg/L measured as nitrogen (NO3-N), under 40 CFR 141.62. Common sources are fertilizer runoff, septic systems, and animal waste; infants under 6 months are especially vulnerable to methemoglobinemia ('blue baby syndrome').

0.010 mg/L (10 ppb), with an MCLG of zero. EPA lowered the MCL from 0.050 mg/L to 0.010 mg/L, with full compliance required beginning in 2006, and 0.010 mg/L remains the current standard.

0.080 mg/L (80 ppb) under the Disinfectants and Disinfection Byproducts Rules (40 CFR Part 141). Stage 2 compliance (40 CFR 141.64(b)(2), Subpart V) is based on the Locational Running Annual Average (LRAA) calculated separately at each monitoring site; the earlier Stage 1 rule instead used a single system-wide Running Annual Average (RAA). TTHMs form when chlorine reacts with natural organic matter.

EPA's 2024 rule sets 4.0 ppt MCLs for PFOA and PFOS, due April 26, 2029. A May 18, 2026 proposal would let systems opt in for a 2-year extension, to April 26, 2031, and separately proposes rescinding four other PFAS limits. As of September 2026, both remain proposed, not final -- verify current status.

Hydraulic (filtration) loading rate = Flow (Q) / Filter surface area (A), in gpm/ft2. The Ten States Standards (Recommended Standards for Water Works) list typical rates of 2-4 gpm/ft2 and require the design engineer to justify the chosen rate to the reviewing authority; fixed caps come from state rules (e.g., Virginia: 2.0 rapid rate, 4.0 high rate). Excess rates risk poor particle removal and shorter filter runs.

Alkalinity measures water's capacity to neutralize acid (buffering capacity), reported as mg/L as CaCO3 and driven mainly by bicarbonate/carbonate ions. Hardness measures dissolved calcium and magnesium ions. Water can be hard with low alkalinity, or alkaline with low hardness -- they are not the same property.

SRT (sludge age) is the average time solids stay in an activated sludge process: SRT = (mass of solids in the aeration basin) / (mass of solids wasted plus solids lost in the effluent per day). Too-short SRT washes out nitrifiers, lowers BOD removal, raises sludge yield, and risks poor settling. Longer SRT allows nitrification and lowers observed yield, Yobs = Y/(1 + kd x SRT), but increases oxygen demand.

A liquid waste is characteristically ignitable if its flash point is below 60 degrees C (140 degrees F), per 40 CFR 261.21. Ignitable solids, oxidizers, and compressed ignitable gases are also covered under this characteristic.

An aqueous waste is characteristically corrosive if its pH is less than or equal to 2, or greater than or equal to 12.5, or if it corrodes steel at a specified rate, per 40 CFR 261.22. Corrosive wastes damage living tissue and containment materials on contact.

40 CFR 261.23(a) lists eight reactivity criteria -- not just 'unstable' or 'reacts violently with water.' They also include forming explosive mixtures with water, generating toxic gases/vapors when mixed with water, cyanide- or sulfide-bearing waste that generates toxic gas at a pH between 2 and 12.5, and capability of detonation or explosive reaction. No single numeric threshold applies; any one of the eight criteria is sufficient.

Under 40 CFR 261.24 (55 FR 11798), EPA set most TCLP regulatory levels at about 100x the contaminant's health-based drinking-water level (a dilution-attenuation factor): benzene's 0.005 mg/L health level x 100 = 0.5 mg/L (D018); lead's former 0.05 mg/L MCL x 100 = 5.0 mg/L (D008). Never substitute a TCLP hazardous-waste threshold for a drinking-water MCL -- they answer different questions.

40 CFR 258.21 requires six inches of earthen material over exposed waste at the end of each operating day (or more frequently if needed) to control disease vectors, fires, odor, and scavenging. An alternative daily cover material or thickness must first be approved by the State Director.

40 CFR 258.60(a) requires a final cover with an infiltration layer (minimum 18 inches of soil) at a permeability at or below that of the bottom liner system or natural subsoils present, or 1x10^-5 cm/s, whichever is less, topped by an erosion layer (minimum 6 inches, able to sustain vegetation). Consequence: a composite-lined cell needs an equally tight cover, or infiltrating water becomes trapped inside like a bathtub.

40 CFR 262.13 sets three monthly generator categories: Very Small Quantity Generator (VSQG), 100 kg or less of hazardous waste (and 1 kg or less of acute hazardous waste); Small Quantity Generator (SQG), more than 100 kg but less than 1,000 kg; Large Quantity Generator (LQG), 1,000 kg or more, or more than 1 kg of acute hazardous waste. A site's category can change month to month and sets its accumulation-time and management requirements.

EPA ranks waste management approaches, most preferred first: source reduction/reuse, recycling/composting, energy recovery (combustion with energy recovery), and treatment/disposal (landfilling) last. The hierarchy guides sustainable materials-management decisions on a project.

ISO 14040 defines four LCA phases: (1) goal and scope definition, (2) life cycle inventory (LCI) -- cataloging inputs and outputs, (3) life cycle impact assessment (LCIA) -- translating flows into environmental impacts, and (4) interpretation. LCA quantifies environmental impacts across a product's or process's full life cycle.

Embodied carbon covers the greenhouse gas emissions tied to a structure's materials across their life cycle: extraction, manufacturing, transport, and installation up front, plus maintenance, replacement, and end-of-life deconstruction/disposal later. Operational carbon is separate -- the emissions from a structure's ongoing energy use during occupancy. Whole-life carbon accounting adds both together.

For independent components in series, overall reliability R = R1 x R2 x ... x Rn (each added component lowers reliability). For redundant components performing the same function in parallel, R = 1 - [(1-R1) x (1-R2) x ... x (1-Rn)] (the system fails only if every parallel component fails). Adding redundancy is a common resilience strategy for critical infrastructure.

An economic model that designs out waste by keeping materials in use through reuse, repair, remanufacturing, and recycling loops, in contrast to a linear 'take-make-dispose' model. It reduces demand for virgin raw materials and landfill disposal capacity.

Sustainability focuses on meeting present needs without compromising future resource availability (long-term stewardship). Resilience focuses on a system's ability to anticipate, withstand, and recover from disruptive events, such as floods or storms. A project can be designed for one without fully achieving the other.

The Clean Air Act designates six criteria pollutants with National Ambient Air Quality Standards: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM2.5/PM10), and sulfur dioxide (SO2). Primary standards protect public health; secondary standards protect public welfare, such as crops and visibility.

The primary annual PM2.5 standard is 9.0 micrograms per cubic meter, lowered from 12.0 in a February 2024 EPA rule and upheld by the D.C. Circuit Court of Appeals in June 2026. The 24-hour primary PM2.5 standard remains 35 micrograms per cubic meter.

Removes particulate matter by charging particles in a high-voltage electric field, then collecting them on oppositely charged plates. Effective at high efficiency on fine particulates, but performance is sensitive to particle electrical resistivity and can be reduced by fouling.

Removes particulate matter by passing dust-laden gas through woven or felted fabric bags, which trap particles on the surface and in a filter cake. Requires periodic cleaning (pulse-jet, reverse-air, or shaker) and is limited by gas temperature and moisture that can damage the fabric.

A wet particulate/gas control device that accelerates gas through a constricted throat where liquid droplets are injected, promoting particle-droplet contact and capture. A higher pressure drop across the venturi generally improves removal efficiency for finer particles.

Selective Catalytic Reduction (SCR) injects ammonia or urea over a catalyst at lower flue-gas temperatures for high NOx removal efficiency. Selective Non-Catalytic Reduction (SNCR) injects the reagent directly into a much hotter zone without a catalyst, giving lower removal efficiency at lower capital cost.

Ground-level centerline C = Q / (pi x u x sigma_y x sigma_z) x exp(-H^2 / 2*sigma_z^2), where H = physical stack height plus plume rise. C is inversely proportional to wind speed u, and a taller H lowers the peak. Unstable air mixes an elevated plume down quickly, so the highest ground concentration occurs close to the stack; stable air gives a lower peak much farther downwind. Ground-level releases behave oppositely: stable air gives the highest concentrations near the source.

An attainment area meets the NAAQS for a given criteria pollutant; a nonattainment area exceeds a NAAQS. States must submit State Implementation Plans (SIPs) describing how nonattainment areas will reach compliance, and new or modified sources there face stricter permitting and emissions-offset requirements.

Under the Clean Air Act Title V program (40 CFR Part 70), a stationary source is a major source if its potential to emit reaches 100 tons/year of any air pollutant subject to regulation under the Act, 10 tons/year of a single hazardous air pollutant (HAP), or 25 tons/year of combined HAPs; thresholds can be lower in nonattainment areas.

A non-intrusive records review, site reconnaissance, and interview process to identify recognized environmental conditions (RECs) without soil or groundwater sampling. Following ASTM E1527-21 satisfies EPA's All Appropriate Inquiries rule (40 CFR Part 312) for CERCLA innocent-landowner liability protections.

An intrusive investigation -- soil borings, groundwater monitoring wells, and laboratory analysis -- conducted when a Phase I ESA identifies a recognized environmental condition, to confirm and characterize the presence, concentration, and extent of contamination.

Hazard Quotient (HQ) = Exposure (or Intake) / Reference Dose (RfD). An HQ at or below 1 suggests exposure is unlikely to cause adverse non-cancer health effects; an HQ above 1 signals a potential health risk that needs further evaluation or action.

Excess lifetime cancer risk = Chronic Daily Intake x Cancer Slope Factor. EPA generally treats risks in the 10^-6 to 10^-4 range (1-in-1,000,000 to 1-in-10,000) as the acceptable range for site remediation decisions under CERCLA.

An in-situ remediation technology that applies vacuum through wells screened in the unsaturated (vadose) zone to volatilize and extract VOCs from soil pores; the extracted vapor is typically treated (e.g., activated carbon, thermal oxidation) before discharge.

Injects air below the water table to volatilize dissolved and sorbed VOCs from groundwater and the saturated zone, driving contaminants upward into the vadose zone. Often paired with soil vapor extraction to capture and treat the resulting vapors.

Extracts contaminated groundwater through wells, treats it above ground (e.g., air stripping, activated carbon), and discharges or reinjects it. Effective at containing plumes and removing dissolved-phase mass, but can plateau against slow-desorbing or sorbed contaminant mass, requiring long operating periods.

Injects strong oxidants -- such as potassium or sodium permanganate, sodium persulfate, or Fenton's reagent (hydrogen peroxide with an iron catalyst) -- directly into contaminated soil or groundwater to chemically destroy organic contaminants in place.

CERCLA (Superfund) authorizes EPA to identify and rank the nation's most seriously contaminated sites on the NPL for long-term remediation funding, and to hold Potentially Responsible Parties (PRPs) liable for cleanup costs under a joint-and-several, strict-liability standard.

OSHA's Permissible Exposure Limit (PEL) is a legally enforceable workplace exposure limit under 29 CFR 1910. ACGIH's Threshold Limit Value (TLV) is a voluntary, non-regulatory guideline that is often more protective (lower) and updated more frequently than OSHA's PELs, many of which date to the 1970s.

OSHA's permissible exposure limit (PEL) for occupational noise is 90 dBA as an 8-hour time-weighted average, using a 5-dB exchange rate (each 5-dB increase halves the allowable exposure time -- e.g., 95 dBA is allowed for only 4 hours). OSHA's own action level of 85 dBA (8-hour TWA) requires enrolling workers in a Hearing Conservation Program with audiometric testing (29 CFR 1910.95).

Level A: fully encapsulating chemical-resistant suit plus a positive-pressure, full-facepiece SCBA (or a positive-pressure supplied-air respirator with an escape SCBA) -- the highest skin and respiratory protection. Level B: the same high level of respiratory protection but with lesser skin protection (chemical-resistant clothing, not fully encapsulating). Level C: air-purifying respirator with chemical-resistant clothing, used when the contaminant and its concentration are known. Level D: work uniform only, used when no respiratory or skin hazard exists.

The 8-hour time-weighted average PEL is 1 ppm; the short-term exposure limit (STEL) is 5 ppm over any 15-minute period, per 29 CFR 1910.1028. The action level that triggers additional monitoring and medical surveillance is 0.5 ppm (8-hour TWA).

Under 29 CFR 1910.146, acceptable entry conditions require oxygen between 19.5% and 23.5% by volume, flammable gas or vapor below 10% of the lower flammable limit (LFL), and toxic contaminants below their permissible exposure limits. Test in this order: oxygen first, then flammability, then toxics.