Enman Newsletter
PERC TESTS & LAND BASED WASTEWATER DISPOSAL SYSTEMS (last updated January 25, 2004)
Welcome to our web page on land based wastewater disposal systems. This document is not intended to be specific to any individual property or project. For a more detailed evaluation of your property and how this process applies to you, please contact Enman Engineering, P.C.
The process of designing, permitting and constructing a land based wastewater disposal system may be tedious and time consuming. The narrative below is provided to present a client with a general overview of the process, the terminology used, and general permitting requirements.
The process consists of four steps; "site evaluation", "design", "permitting" and "construction."
Site Evaluation (Test Pits, Perc Tests & Topographic Survey)
Soils evaluation generally consists of the following three activities:
Test Pits: Test pits consist of evaluating soil conditions in a backhoe excavated hole, generally assessed to a depth of four to six feet. The purpose of the test pits is to assess soil type (gravels, clay, silt), depth to bedrock/ledge, and depth to seasonal high groundwater. These are the criteria which determine what type of disposal system, if any, may be designed and constructed.
When a state permit is required, observation of the test pits by state personnel is recommended.
Perc Tests: A perc test consists of pouring water into a small diameter hole and measuring the rate of water level drop. In general, the slower the rate, the larger the wastewater disposal system. Soils with too slow a perc are considered to be impervious and unacceptable under the regulations.
Please note, the term "perc test" is often mis-applied in the design and permitting process. A perc test is one of the required components for site evaluation, but the perc test is not the most important. Knowing the type of soil, depth to bedrock, and depth to seasonal high water table is paramount to site evaluation. The soils evaluation (test pits) should be performed prior to a perc test.
Topographic survey: A topographic survey is required to show land features, and to eventually design a wastewater disposal system. Land features such as existing development, wells, other wastewater disposal systems, wet areas, steep slopes, etc. must be mapped both horizontally and vertically to accurately depict the area proposed for the wastewater disposal system. Please note, a topographic survey is not the same as a boundary survey. A boundary survey is generally recommended and must be performed by a VT registered Land Surveyor.
There are two other site evaluation tools that are available to landowners in assessing wastewater disposal options, a Site Walkover and Springtime Monitoring. These items are used for properties with special considerations.
Site Walkover: This is recommended for larger (approaching and greater than 5 acres) properties. The walkover consists of walking the property and identifying areas that may be more suitable for a soil based disposal system (away from wet areas, streams, steep slopes) and better define where test pits may be successful. Typically, conducting a walkover streamlines the test pit process.
Springtime Monitoring: Springtime monitoring requires weekly (or bi-weekly) water level measurements for the period of March 1 through May 31 (13 weeks). Monitoring tubes are installed in augered holes to a depth of 3 to 4 feet below the proposed depth of the wastewater disposal system. On sites where soil indicators show a seasonal high water table close to ground surface, springtime monitoring may be used to assess the actual depth to groundwater.
Design (preliminary & final)
For sites successfully negotiating the evaluation phase, a preliminary design is recommended. For sites proposed for springtime monitoring, a preliminary design is required.
The preliminary design consists of an initial siting of the wastewater disposal system, the well, the proposed structure(s) and other improvements such as driveways, parking areas, retaining walls, storage areas and areas of general use. A preliminary design often helps to clarify for the owner or developer issues of conflict between uses. Final adjustment for competing site uses should be accomplished in the preliminary design phase, as alterations later are often at additional expense.
Following owner or developer approval of the preliminary design, final design usually commences. Final design requires detailed planning for construction of the entire wastewater system such as the septic tank, advanced wastewater treatment, a pumping station, piping and force main, and pumps.
There are generally three types of regulatory approved disposal systems; mound, at-grade and in-ground. For regulatory approved systems, both a primary (constructed) system and a replacement (un-constructed, held in reserve) system are necessary.
Mounds are generally proposed for sites with depths to seasonal high water table greater than 24" but less than 36". Mounds vary in size depending on wastewater flows. The greater the flow, the larger the mound. Mounds often rise above native ground elevation by 4 to 5 feet and often require a 40 foot to 60 foot base area for a single family home. Commercial and multi-family systems may be larger.
At-grade systems are generally proposed for sites with seasonal high water table greater than 36" but less than 48". At-grade systems are shallower in profile than mounds, rising generally 20" to 30" above native ground. They may often be "blended" into the existing topography to reduce visibility. At-grades are generally a single trench extending along a contour. For a three bedroom single family home, an at-grade is typically 90 feet long.
In-ground systems are generally proposed for sites with greater than 48" to seasonal high water table . In-ground systems are most often completely buried. In some instances, shallow in-ground systems may rise above native ground by 6"-12".
"Advanced treatment" may be proposed for certain state and town permit approvals. Where treatment is proposed, at-grade systems may be considered for sites with seasonal high water table greater than 18" but less than 36", and in-ground systems may be considered for sites with greater than 36" to seasonal high water table. Except for extenuating circumstances, treatment is not used with mounds.
"Failed systems" are generally described as having surfacing of effluent or backup in the disposal system. For failed systems, strict compliance with state and/or municipal regulations is often waived. However, isolation to groundwater and drinking water sources is generally held to the regulatory standard except under the most extreme conditions.
At this time, there are several different permit programs in Vermont that determine the design standards that can be applied to a property. The standard that applies to any particular property is determined by the property location (town), property size, and when the property was created. There is a plan to enact a universal permitting program in 2007.
For a "prescriptive" (cook book) based design, a minimum of 24", naturally occurring, unsaturated soil must exist. If less than 24" exists to water table or bedrock (ledge), depending on regulatory jurisdiction, no soil based system may be permitted.
For certain sites with less than 24" of naturally occurring, unsaturated soils, "springtime monitoring" of the seasonal high water table may be appropriate. The state and many local regulations allow site specific springtime monitoring for the seasonal high water table . If a statistical analysis demonstrates greater than 24" naturally occurring, unsaturated soils exists, the site may be suitable for design and further evaluation.
For a "performance" (site specific) based design, a site with less than 24" may be considered. These are only allowed in communities with approved zoning, an approved town plan and generally no local sewage ordinance or a community that has adopted the 2002 state code. Performance based design sites require significantly greater evaluation and are beyond the scope of this guidance.
Properties having greater than 24" naturally occurring, unsaturated soils, must next have perc tests and topographic survey conducted prior to moving forward with design.
PERMITTING
At this time, there are several different permit programs that determine what design standards may be applied to a property. The standard that applies to any particular property is determined by the property location (town), property size, and when the property was last subdivided. There is a plan to enact a universal permitting program in 2007 that would apply to all properties.
The state adopted the Environmental Protection Rules on August 16, 2002. These regulations contain over 14 pages of exemptions. The outline below is to provide a general overview of the permit process, but each lot proposed for development must be evaluated individually for compliance with the rules.
As of November 1, 2004 all wastewater disposal system construction must be in strict compliance with the State of Vermont , Agency of Natural Resources, Department of Environmental Conservation, Wastewater Management Division regulations. Non-conforming municipal regulations sunset (expire) on that date as do all permits issued by local municipalities.
Lots greater than 10 acres, last subdivided prior to January 1, 1999 or any lot last subdivided prior to September 18, 1969 remain exempt from state regulations until November 1, 2004. Development on these parcels of land must be "substantially complete" prior to November 1, 2004 to not require compliance with the state rules.
Many villages, towns and cities have their own sewage regulations. Where dual jurisdiction (state and municipal) occurs, the more stringent of the two regulations must be applied. In cases where two sets of regulations apply, design, permitting, and construction costs are generally higher.
On June 1, 2007 wastewater disposal system design and construction requires the issuance of a State of Vermont permit. Until June 1, 2007 municipalities without zoning and approved planning process are not eligible for use of "performance" based design.
Permit application fees and review durations vary at both the municipal and state jurisdictions.
CONSTRUCTION
Following issuance of all permits (other permit requirements may apply so be sure to have all permits in place), construction generally commences. The contractor is selected by the owner / developer based on experience, qualifications, availability and cost.
Engineers are often asked to supervise or inspect the quality and quantity of the contractor's work. Most engineer's insurance excludes this coverage and Enman Engineering, P.C. does not offer supervision or inspection. Where an owner wishes a higher assurance of construction oversight, independent construction managers are recommended.
Enman Engineering, P.C. will continue to work directly with the owner / developer during the construction phase. Enman Engineering, P.C. is available (if requested) for periodic observation of construction, for witnessing of contractor conducted performance tests, and preparation of a report documenting observations. Observation frequency is dependent on the owner / developer desires and should be discussed with a representative from Enman Engineering, P.C. for each individual project.
Enman Engineering, P.C. does not recommend land acquisition or purchase until all permits have been issued.
Enman Engineering, P.C. recommends the owner's recording of a document at the municipal offices testifying to the installation of any wastewater disposal system or water supply at the completion of construction.
RELEASE
Enman Engineering, P.C. is a professional engineering consulting firm engaged in the design and permitting of civil and sanitary engineering works. Publishing and distribution rights are held by Enman Engineering, P.C., 230 N. Main St , Rutland , VT 05701 . No part of this document may be reproduced by any means, nor transmitted, nor translated into a machine language without the prior written permission of Enman Engineering, P.C.
The information contained in this reference material is provided as a guide only, it has been compiled from sources believed to be reliable and to represent the current opinion on the subject. No warranty, guarantee or representation is made to the absolute correctness or sufficiency of any representation contained in this material, and Enman Engineering P.C. assumes no responsibility in connection therewith except where a contract for services is engaged.
While Enman Engineering, P.C. does not undertake to provide a service or guarantee of accuracy, Enman Engineering, P.C. is pleased to respond to your individual requests for site evaluation, design, permitting or construction phase services requirements.
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