NSN ORD-1995-003 Proposed Zoning Ordinance Text Amendment Article 6.23 - IX-A

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12a MEMORANDUM TO: Mary Willis , Planner III FROM: Paul Thames , County Engineer DATE: January 10, 1995 SUBJECT: Zoning Ordinance regulation of septic tank setbacks at reservoirs As you are aware from our telephone conversation of last week, the County Manager has asked me to evaluate strategies proposed to identify potential impact on water quality of those leaking or failing septic tank system( s ) located within 300 feet of a reservoir' s normal pool surface. My charge was specifically to review the section of the draft zoning regulations requiring that, prior to allowing the installation of a septic tank system within 300 feet of a reservoir, the Health Department determine that there are no existing water quality impacts that can be attributed to other failing septic systems installed within 300 feet of that reservoir. It is my opinion that this requirement would prove to be impractical in that it will be very difficult for the Health Department to make such a determination. It is possible for Health staff to compare the fecal coliform/strep ratios from two or more samples containing those indicators and determine if the indicators are being generated by the same source. However, the likelihood is that on site conditions including water and air temperature, ultraviolet light exposure , dilution, currents , winds , proximity -and habitation by livestock and wildlife , etc . , will combine to make it exceeding difficult to utilize fecal coliform analysis to pinpoint a source of pollution from all but the most prolific or obvious sources. The real impact of failing septic systems on water quality is not likely to be a disease bearing bacteria, most of which would find the open waters of a reservoir a very hostile environment and most of which are removed by the most rudimentary water treatment processes. The primary problem from leaking septic systems , as pointed out in the CDM studies for the Durham and OWASA reservoirs , would be from nutrient loadings of phosphate and nitrogen. Tracing the source of these compounds would probably at least as difficult as pinpointing a source by tracking bacteriological content. I have reviewed your draft resolution dealing with the problem of detecting failing septic system impacts by delaying implementation of requirements to identify those impacts until such time as staff can evaluate potential identification methods . I concur that this delay represents a prudent approach. If I may provide additional information or comment, please . advise.