Projected use of Innovative/Alternative On-site Sewage Treatment Systems in Eastham under Current Regulations and Policies

Susan Rask, M.S., R.S.
Barnstable County Department of Health and the Environment
Barntable, Massachusetts

 Funding by Barnstable County

May 2007                                                Download Full Report Here

Project Summary

Wastewater management is one of the largest planning and financial tasks that a town as a whole can undertake. Decisions about wastewater management become increasingly more complicated in areas where onsite septic systems occupy the same parcel as drinking water wells, as occurs in Eastham. As Eastham develops strategies to deal with drinking water and wastewater needs, it is crucial to have a good assessment of the existing situation, and a reasonable projection of how the situation will develop should they continue on a course of action dictated by present regulations and policies.

The report projects the number of advanced onsite treatment systems (also called innovative/alternative or I/A systems) that will be installed over the next 20 years, provided an alternate wastewater or drinking water strategy is not implemented. The report also provides integration of location and performance data from alternative septic systems into the town’s overall water quality database. Finally, the report projected the extent and costs of onsite alternative septic systems installed in the future. The report facilitates comparison with other feasible options for wastewater treatment or installation of a municipal public water supply that the town may investigate.

Key Findings

• A GIS data base for Eastham was created including location of all currently permitted I/A systems, all properties with public water, location of undersized lots (i.e.all properties where number of bedrooms exceeds 1 bedroom (BR) per 10,000 s.f. parcel size, and a geographically linked drinking water nitrate level database for private and public water supplies.

• The GIS database was linked to the Barnstable County Department of Health and Environment I/A tracking database to allow the Eastham Health Agent to access and download information on I/A system location and effluent water quality results.

•  Using parcel data and I/A installation threshold criteria projects were made of the number of I/A systems that could be installed town-wide in the future- over a 20 year timeline.  I/A installation thresholds included: BOH septic system setback thresholds for wetlands or private water supply, lots with small volume public water systems, densely developed lots (septic system flow greater than 440 gpd/acre)

• Using present value costs, total cost were then projected over the next 20 years for installation and operation of all I/A systems installed under the various threshold scenarios. Costs may be compared to other solutions, such as installation of a municipal water system or small cluster or satellite collection and treatment systems.

• Eastham has approximately 6152 parcels. Of these, 5049 are residential (single family, multi-family and condominiums). As of February 2007, Eastham has 116 innovative/alternative (I/A) systems permitted, and 93 were actually installed. Based on the initial threshold criteria, a total of 3970 I/A systems were projected to be installed at time of next septic upgrade. The report recommended that a more realistic future development scenario would only include densely developed lots that also are experiencing water quality problems, lowering the total Potential 1/A systems to 1027.

The analysis is summarized in the table below:

• Threshold Criteria for Installation	Initial Analysis	Modified Analysis
  Currently permitted I/As	93	93
  Projected I/A for small lots (parcels <10,000 s.f.)	276	276
  Projected I/A for small lots with water quality impairment: (parcels >10,000 s.f. but <20,000 s.f.)	282	90 PLUS: nitrates>3 mg/L
  Projected I/A systems to meet wetland setback criteria:	472	372
  Properties with public water supply wells.	49	49
  Densely developed lots Lots> 4 br/acre	2798	147 lots > 6 br/acre and nitrates > 5 mg/L
  Total Potential I/A systems	3970	1027

ECONOMIC ANALYSIS

The installation of an I/A on-septic treatment system is often viewed as an easy, readily available, and relatively inexpensive solution for remediating wastewater problems. It is important to recognize that I/A systems have significant ongoing operation and maintenance costs. When these costs are considered, it becomes clear that I/A systems are not inexpensive in the long term, and impose significant management burdens on both the homeowner and the town to ensure that they are operated reliably to meet nitrogen reduction requirements.

In order to allow Eastham to compare the costs of widespread installation of I/A systems with other possible solutions for protecting ground- and drinking water quality, an economic present value analysis of the cost of I/A systems was performed. Present value analysis considers the time value of money using a discount rate and adjusts expenditures in future years to current dollars so that costs incurred throughout the life of the system can be understood in present dollars.

These costs were then be compared the construction of small sewage collection and treatment systems for a limited number of homes. In that sense, they may be similar to scenarios that Eastham could consider for building small collection and treatment systems to serve neighborhood areas. The costs associated with these projects are rough estimates, and are presented for general comparison purposes only. The results are summarized below:

     *amortized cost of $55,000 over 20 years

   **annual sewer fees over 20 years

The installation of individual I/A systems is often assumed to be the easiest and least expensive option for remediating existing sewage problems. It is important to recognize that, over the long term, most I/A systems installed for nitrogen removal will have significant annual O&M costs. This in turn significantly increases life cycle costs to the point where these systems may not be significantly less costly than installing small collection and treatment systems.

All wastewater treatment systems, whether onsite I/A systems or larger treatment units, require operator oversight if they are to perform reliably to produce wastewater of desired quality. O&M costs are a significant amount of the total cost of wastewater treatment over time. When I/A systems are installed at individual homes, 17 each homeowner must bear the full cost of O&M for his system. Conversely, O&M costs for larger collection systems, while they may be somewhat higher than for an individual system, are spread over a larger number of owners, resulting in lower costs for individual owners.

Of the numerous I/A systems that might be installed under the various scenarios investigated in this report, it is important to note that the vast majority will not needed if Eastham chooses to install a municipal drinking water system throughout town. Installation of municipal water will save substantial amounts money for homeowners who otherwise would be required to install and pay for operation of I/A systems. It will also alleviate a significant management burden that would be imposed upon the town to ensure that I/A systems are operated, maintained and monitored as required.