Question 7 of 7: Water Resource Management, Greenhouse Effect and Noise Pollution

Question 7: Water Resource Management, Greenhouse Effect and Noise Pollution (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(i) Protecting a Drinking-Water Reservoir from Agricultural Runoff

Because the reservoir supplies drinking water, the most effective and lowest-cost long-term protection strategy is source-water protection rather than relying solely on more intensive downstream treatment: designating a watershed protection/buffer zone around the reservoir and its tributaries where farming practices are regulated — vegetated riparian buffer strips along watercourses to filter runoff before it reaches surface water, restrictions on the timing/rate of manure and fertilizer application near watercourses, and fencing livestock out of streams — directly reduces the nutrient (phosphorus, nitrogen), pathogen and sediment loading entering the reservoir at the source, which is far cheaper than continuously upgrading treatment to remove a growing pollutant load.

A second, complementary strategy is a watershed-scale nutrient/agricultural best-management-practice (BMP) program developed jointly with the local farming community: cost-shared implementation of controlled-drainage systems, precision (variable-rate) fertilizer application to reduce excess nutrient loss, and constructed wetlands or sediment ponds intercepting field drainage before it reaches the reservoir. Combined with ongoing water-quality and land-use monitoring against the CCME/provincial source-water-protection framework, this second strategy targets the diffuse (non-point) nature of agricultural runoff pollution that end-of-pipe treatment alone cannot economically address, protecting the reservoir's long-term viability as a supply source rather than only its year-to-year treatability.

(ii) Causes of the Greenhouse Effect and Technical Mitigation

The greenhouse effect intensifies (beyond its natural, life-sustaining baseline) primarily from two anthropogenic causes. First, combustion of fossil fuels for electricity generation, transportation and industrial heat releases $\text{CO}_2$ that had been sequestered underground for millions of years, adding it to the active atmosphere-ocean-biosphere carbon cycle faster than natural sinks (ocean uptake, photosynthesis) can remove it, so atmospheric $\text{CO}_2$ concentration rises. Second, land-use change — deforestation and conversion of natural land to agriculture or urban development — both releases the carbon stored in cleared vegetation/soil and permanently reduces the biosphere's capacity to re-absorb $\text{CO}_2$, compounding the first cause; agriculture additionally contributes methane ($\text{CH}_4$, from livestock and rice paddies) and nitrous oxide ($\text{N}_2\text{O}$, from fertilized soils), both far more potent per molecule than $\text{CO}_2$ over a 100-year horizon.

Two technical solutions follow directly from the two causes: (1) decarbonizing energy supply — shifting electricity and, increasingly, transportation and heating from fossil combustion to low-carbon sources (wind, solar, hydro, nuclear) directly cuts the $\text{CO}_2$ added at the source, reinforced by energy-efficiency measures that reduce the total energy demanded in the first place; and (2) carbon-sink protection and restoration — afforestation/reforestation and wetland protection restore biosphere carbon-sequestration capacity, while engineered carbon capture and storage (CCS) on remaining large point sources (cement, steel, gas-fired power) directly intercepts $\text{CO}_2$ before atmospheric release, addressing sources that cannot yet be fully decarbonized.

(iii) Highway Noise Mitigation for an Adjacent Residential Community

Two established engineering methods reduce highway traffic noise reaching a residential community. The first is a noise barrier (wall or earth berm) constructed along the highway right-of-way between the traffic lanes and the community, which works by interrupting the direct line-of-sight sound path and forcing sound energy to diffract over the barrier top, attenuating the received level (a well-designed barrier that breaks line of sight typically achieves 5–10 dB of reduction, and Canadian provincial noise-policy practice generally targets keeping traffic-noise increases within a roughly 3 dB exchange-rate framework of the applicable guideline level). The second is source-side mitigation via pavement and traffic management — specifying quieter (e.g., open-graded or rubberized-asphalt) pavement surfaces that reduce tire-pavement interaction noise, combined with speed management (since traffic noise rises roughly with the log of vehicle speed) and truck-route/time-of-day restrictions that reduce the loudest vehicle events near the community.

Of the two, the noise barrier is generally the preferred method where a right-of-way exists to build one, because it directly and reliably attenuates noise regardless of the vehicle fleet or driver behaviour, and its performance is independent of future traffic growth in a way source-side measures are not. Its limitations are visual/aesthetic impact on the corridor, cost (especially for a berm requiring significant land and fill), and reduced effectiveness for residences on upper floors that see over the barrier's line-of-sight shadow. Pavement/traffic-management mitigation is comparatively lower-cost and improves the whole corridor (not just one community), but its noise reduction is smaller and degrades over the pavement's service life as it wears, and speed/route restrictions require ongoing enforcement to remain effective — so the two are often specified together, with the barrier providing the durable, primary reduction and pavement/traffic measures providing an incremental, corridor-wide improvement.