Can We Quantify the Environmental Impact of Inappropriate Development in the Mountain Overlay District?
As currently drafted (January 2023), the Loudoun County zoning ordinance would permit all uses allowed in zoning districts AR-1 or AR-2 to be built in the Mountain Overlay District (MOD). Friends of the Blue Ridge Mountains and other conservation organizations contend that many of these uses are too intense and generate too much traffic to be permitted on the thin soils, steep slopes, and dense tree cover characteristic of the mountains. Friends has identified 14 specific uses that would be permitted by the current draft that are inappropriate. These uses include rural retreat, sit-down restaurants, general retail establishments and sawmills.
There are many reasons these and similar uses are inappropriate including the negative impact on the beauty, biodiversity and wildlife of the region, the negative environmental impacts are of primary concern.
While recognizing that the exact impact on the environment of a proposed project depends upon the specifics such as dimensions, building material and design of the building(s), as well as the characteristics of the lot including slope, tree cover, and soil conditions, it is possible to estimate the approximate impact based upon the general characteristics of the type of land use and the mountain environment.
Environmental Impact of one (1) Rural Retreat
The current draft of the zoning ordinance would permit by right construction of a rural retreat in the MOD (Table 3.02.03-2). The performance standards for the rural retreat (4.05.17) specify: 1) minimum size of 50 acres; 2) 75% of the land must be agriculture/open space or forest; and 3) an average of 100 daily users per 50 acres.
Given these performance standards we can estimate that the impact on the environment will be:
- ¨ Approximately 1,500 trees will be eliminated from the mountain tree canopy.
- ¨ Approximately 195 tons of oxygen per year will not be produced because of the loss of tree cover.
- ¨ Approximately 36 tons of CO2 per year will not be removed from the atmosphere because of the loss of tree cover.
- ¨ Approximately 304.5 tons of CO2 per year will be added to the environment because of the associated car trips for a net impact of 340.5 tons of additional CO2 per year.
- ¨ Approximately 4.5 million gallons of precipitation per year will not be slowed by the tree canopy or filtered by tree roots before flowing into Loudoun County’s rivers, streams, wells, and ultimately the Chesapeake. It is beyond the scope of this report to estimate the amount of pollutants associated with these 4.5 million gallons, but such an analysis would be beneficial.
The above listed environmental impacts per year of building one (1) rural retreat in the MOD are based upon the following:
- ¨ For a 50-acre site (the minimum permitted) we assume that 25% (12.5 acres) will be cleared for buildings, parking, driveways, etc. Of the 75% (37.5 acres) that can not be cleared, we assume that 50% (18.75 acres) will be used for agriculture, walking paths, trails etc. The remainder (18.75 acres) will remain forest. In other words, for a 50-acre site there will not be trees on approximately 31.25 acres.
- ¨ According to the US Forest Service, a healthy forest contains 40 to 60 trees per acre. Assuming a middle ground of 50 trees per acre, the 31.25 acres of trees lost to the rural retreat could contain approximately 1,562 trees. For simplicity we round down to 1,500 trees that will not be growing on this site.
- ¨ According to the Arbor Day Foundation a mature tree can sequester approximately 48 pounds of CO2 per year. The exact amount sequestered varies significantly depending upon the type of tree.
- ¨ A mature tree will produce approximately 260 pounds of oxygen per year.
- ¨ Our calculations for CO2 not sequestered and oxygen not generated are as follows:
- CO2 – 1,500 trees X 48 pounds per tree = 72,000 pounds/2,000 pounds per ton = 36 tons of CO2 per year not captured.
- Oxygen – 1,500 trees X 260 pounds per tree = 390,000 pounds/2,000 pounds per ton = 195 tons.
- ¨ Performance standards limit average daily users to 100 per fifty acres. Assuming 75 cars per day, 365 days per year we estimate 27,375 trips per year. Assuming trips average 25 miles roundtrip, we estimate 684,375 miles of travel per year associated with the rural retreat. According to the US Environmental Protection Agency (EPA), the typical passenger vehicle emits 404 grams of CO2 per mile (0.89 pounds per mile). At 0.89 pounds per mile the 684,375 miles of travel per year associated with the Rural Retreat will result in 609,093 pounds of CO2 per year or 304.5 tons.
- ¨ The net CO2 impact of the rural retreat:
36 tons of CO2 not captured because of the loss of tree cover
+ 304.5 tons of CO2 associated with trips to and from the rural retreat
340.5 tons of CO2 added to the environment per year.
- ¨ According to the Nature Conservancy a tree cover helps prevent water pollution in two ways: 1) The tree canopy intercepts precipitation, slowing the water flow thus reducing erosion and reducing the flow of pollutants downstream; 2) The tree roots and leaf litter promote slow absorption of the water and filter out pollutants recharging the ground water. The amount of rainfall intercepted by a tree canopy varies tremendously depending upon the type of tree. A single deciduous tree can intercept from 500 to 760 gallons per year. A mature evergreen can intercept more than 4,000 gallons per year.
- ¨ Assuming the 31.25-acre Rural Retreat site could have contained 1,500 trees and assuming each tree could intercept 3,000 gallons per year the site could intercept approximately 4.5 million gallons of precipitation per year.
It is possible to calculate rough estimates of the financial burden associated with these levels of pollutants associated with a Rural Retreat.
- ¨ The Federal Inflation Reduction Act updated the tax credit to corporations for direct air capture of CO2 to $180 per ton. Assuming that the tax credit reflects the actual cost – Calculation — 5 tons per year X $180 per ton = $54,810 per year.
- ¨ The cost of generating oxygen is approximately $0.07 /kilogram ($0.03175 per pound) – Calculation — $03175 X 390,000 pounds = $12,383 per year
- ¨ On the basis of the information available to us through this report it is not possible to calculate a cost associated with the 4.5 million gallons of precipitation per year that is not slowed and filtered by the tree cover. However, there are some indications of the costs:
- Fairfax County, VA estimated that forested landscapes provided almost $57 million (in 1999), which equates to about $95 million in 2022, in stormwater reduction benefits annually to local taxpayers.
- According to a 2017 article by published by the World Resources Institute – Three Surprising Ways Water Depends Upon Health Forests — New York City has invested $1.5 billion to protect a 1 million acres of mostly forested lands in the Catskills. Saving the tree cover saved on water filtration costs ultimately avoiding $6-8 billion on the cost of building a water filtration plant.