Natural Resource Inventory and Assessment - Town of Guilford

Freshwater
C6
C.5 Threats and Concerns
Pollutants, nutrient loading/toxins/contaminants: Nearly all contaminants that alter the water
chemistry of Guilford’s freshwater systems derive from nonpoint sources (e.g., surface runoff), rather than
point sources (e.g., pipe discharge). Rainfall or snowmelt that cannot filter directly into the ground picks
up an array of contaminants as it washes over the ground and before it enters ground- or surfacewaterbodies.
Stratified drift deposits are quite vulnerable to pollution, given their extreme permeability.
Map C-3 illustrates the locations of public water supply wells, groundwater protection districts, aquifer
protection areas and various threats to water quality. Among the latter are DEP leachate wastewater sites,
EPA identified waste sites, the Town’s Transfer Station and Stump Dump and Areas of Concern as identified
by the Guilford Water Pollution Control Authority - WPCA. In spite of its title, Guilford’s WPCA only has
jurisdiction over implementation of Guilford’s sewer avoidance program. The WPCA works closely with
other Town Commissions and departments to carry out its mandates but it does not have responsibility for
dealing with pollution from any source other than septic systems. The IWWC only has jurisdiction over
inland wetlands and watercourses. The Conservation Commission has no regulatory power. Preservation of
water resources requires on-going monitoring, sensitive land use regulations, and planning to guarantee the
quality of our surface water resources and the quantity and quality of groundwater supplies as drinking
water for future generations of Guilford residents. (See Appendix C-3 for water-related agencies with
jurisdiction in Guilford.)
An impervious surface is any material that resists infiltration. Roads, parking lots, and rooftops all
contribute to the total impervious surface cover of a land area. National studies show that residential
development can generate 15 to 65 percent impervious surface, varying with lot size. Commercial and
industrial development can generate 70 to 95 percent impervious surface coverage.
Scientific studies have shown that as impervious surface coverage within a watershed approaches 10
percent, the health of rivers that drain that area has declined. A recent USGS study on New England
coastal basins shows that aquatic ecosystems begin to decline when 4 to 5 percent of the watershed is
urbanized. Studies in other states confirm a direct inverse relationship between impervious surface and
biological health, starting with impervious surface areas as low as 4 to 6 percent. Where impervious surface
area exceeds 25 percent, significant damage to water quality occurs and few kinds of fish can survive.
Of the 103 local watersheds in Guilford, 47 have impervious surface coverage of less than 4 percent,
39 have between 4 and 10 percent, and 17 between 10 and 25 percent. (See Map C-4.) Local basins with
impervious cover in the 10 to 25 percent range are located on the coast (including the four local basins that
comprise the Sluice Creek sub-watershed), in the lower West River sub-watershed, and north of West Lake.
Together these local watersheds with high impervious cover comprise roughly 20 percent of the Town’s total
land area.
Most of the watersheds in central and southern Guilford contain 4 to 10 percent impervious surface
cover, and therefore are approaching the critical threshold above which water quality and freshwater
wildlife habitats decline rapidly. Areas of Guilford comprised of watersheds with under 4 percent
impervious cover are dominated by forested land: north of Route 80, the lower East River drainage basin,
and the Westwoods/Cockaponset State Forest area.
Although nutrients like nitrogen and phosphorous are necessary for plant and animal life, elevated
concentrations of these nutrients degrade freshwater ecosystems. Contamination of ground water by septic
effluent or salt water intrusion (on the coast) is also a concern in Guilford. Since 1981, the Town’s
Department of Health routinely evaluates fifteen designated areas for water quality deterioration and
frequency of septic system failure. (See Map C-3.) Failure frequency has decreased markedly over the past
23 years due to numerous repairs and careful construction of new septic systems. Non-performing septic
systems are either self-reported or reported by neighbors. Connecticut DEP has recommended a re-
Natural Resource Inventory and Assessment Town of Guilford, CT