Norwich Fire District — Source Protection Cost/Benefit

Risk-weighted, 30-year present-value comparison of recommended alternatives. TODO: dropdown of assumptions

Results

Lowest expected total cost2. Impervious slab / barrier (excavator buys pit)$102,212 present value

Expected total cost (lower is better)

Alternative cost (capital + O&M) Expected cleanup cost of contamination events

Range of outcomes (Monte Carlo, 5,000 runs)

10th–90th percentile Median Mean

Table

Alternative	Alt. cost (PV)	Expected event cost (PV)	Expected total (PV)	Benefit vs. do nothing	Net benefit	B/C ratio	P(pfas) in 30 yr	P(transpo) in 30 yr	P(fuel) in 30 yr
1. Do nothing (excavator buys pit, no mitigation)	$0	$124,950	$124,950	$0	$0	—	45.5%	3.0%	45.5%
2. Impervious slab / barrier (excavator buys pit)	$11,960	$90,252	$102,212	$34,698	$22,738	2.90	26.0%	3.0%	45.5%
3. Install (3) monitoring wells on gravel pit	$83,683	$66,128	$149,812	$58,822	−$24,862	0.70	38.4%	3.0%	45.5%
4. NFD to buy & conserve 10 acres of gravel pit	$209,201	$14,566	$223,767	$110,384	−$98,817	0.53	3.0%	3.0%	3.0%

Benefit = expected contamination cleanup event cost avoided compared with Do-nothing scenario. B/C > 1 means the alternative pays for itself in avoided expected damages.

Global settings

Horizon (years)Real discount rate%Monte Carlo runs

Hazards

PFAS reaches the well

PFAS reaches well due to contaminated fill stored on gravel pit. Remediation would likely be at the treatment stage, using granular activated carbon (GAC).

Annual probability%One-time cost if it happens$Annual cost afterward$Can happen more than once

Emergency event: spill on transportation corridor contaminates groundwater

High consequence, low probability event. Remediation cost considers District's share of emergency response, temporary water connection, sampling, and cleanup.

Annual probability%One-time cost if it happens$Annual cost afterward$Can happen more than once

Fuel / hydraulic fluid spill from equipment stored on pit

A spill of diesel, gasoline, hydraulic fluid big enough to contaminate groundwater. Cleanup cost would fall on the repsonsible party under VT DEC rules.

Annual probability%One-time cost if it happens$Annual cost afterward$Can happen more than once

Alternatives

1. Do nothing (excavator buys pit, no mitigation)

Benchmark scenario. Every other alternative is compared to this.

Capital cost to District$Annual O&M$

Effect on: PFAS reaches the wellLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

Effect on: Emergency event: spill on transportation corridor contaminates groundwaterLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

Effect on: Fuel / hydraulic fluid spill from equipment stored on pitLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

2. Impervious slab / barrier (excavator buys pit)

Reduces infiltration from stored materials, depends on owner upkeep.

Capital cost to District$Annual O&M$

Effect on: PFAS reaches the wellLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

Effect on: Emergency event: spill on transportation corridor contaminates groundwaterLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

Effect on: Fuel / hydraulic fluid spill from equipment stored on pitLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

3. Install (3) monitoring wells on gravel pit

Early warning: time to install treatment and/or act on the source before customers are exposed.

Capital cost to District$Annual O&M$

Effect on: PFAS reaches the wellLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

Effect on: Emergency event: spill on transportation corridor contaminates groundwaterLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

Effect on: Fuel / hydraulic fluid spill from equipment stored on pitLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

4. NFD to buy & conserve 10 acres of gravel pit

Removes the gravel-pit sources. Does not affect transportation corridor.

Capital cost to District$Annual O&M$

Effect on: PFAS reaches the wellLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

Effect on: Emergency event: spill on transportation corridor contaminates groundwaterLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

Effect on: Fuel / hydraulic fluid spill from equipment stored on pitLikelihood ×1 = no change, 0.5 = half as likelyOne-time consequence ×e.g. early warning lowers emergency cost

Method: expected present value of each hazard = Σ over years of P(event in year t) × discounted one-time cost + discounted ongoing costs to end of horizon. Non-repeatable hazards (PFAS) occur at most once. Monte Carlo samples the same model to show the spread. See lib/model.js.