Two New Techniques for Evaluating Connectivity of Septic Fields to Great Lake Watersheds and Embayments

Abstract

Pictometry Oblique Imagery was successfully used to map septic fields in Oak Orchard watershed. Analysis of the imagery proved to be efficient for finding leach fields, and between 66 to 81% of the septic fields previously mapped by the Genesee Orleans County Department of Health, were identified. The remainder were not identified because of canopy cover, or were either septic systems without leach fields, the septic field postdated the imagery, or were not visible. Consequently under ideal conditions (septic systems with leach fields and no canopy or shadows) the method should be able to identify over 80% of the systems. Imagery taken during the transition from dormant to growing season proved best for identifying leach fields. One example of a plume from a short circuited system was recorded. A total of 1277 septic fields were mapped in the watershed. Spatial distribution was heterogenous, with dense sites of septic fields concentrated along residential road corridors. Approximately 4.2% of the leach fields were located less than 100 feet of a tributary. This is below the minimum separation distance of a leach field to a waterbody that is required by the NYS Department of Health code. The average distance of a leach field to a tributary is 327 meters with 50% of the leach fields occurring within 240 meters of mapped tributaries. Maps of important septic field “hotspots” were developed for watershed stakeholders and include tributaries along Batavia-Elba Townline Rd., Marsh Creek, and tributaries near the intersections of Alleghany and Lockport Rds, Judge Rd and Knowlesville Rd., and Lockport and Albion Rd. Considerable numbers of septic fields occur along Lake Alice in the main stem of the river, however this stretch is probably diluted by water input from the Erie Canal at the Glendale Dam. In a second set of experiments, a new DNA-based groundwater tracer was introduced to two septic systems to see if it could be used to trace individual septic systems. The tracer was not discovered in one site, however, a breakthrough curve was obtained in the second site 31 days after being introduced into the toilet. This tracer passed through at least 200 meters of groundwater flowpath and 1 km of stream. The results of these experiments suggest that frequent, systematic sampling and careful lab protocols to identify the signal to noise threshold of the procedure are critical to the success of the technique. In summary we suggest that Pictometry Oblique Imagery can be used to map septic fields in a watershed and that the DNA Tracer technique may be successful in some septic systems. Further research needs to be conducted to improve the success of the latter.