Septic System Cost: An Installation and Replacement Guide for New Hampshire

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Septic system costs for NH.

How to Manage Your Septic System Cost

Managing septic system cost for home owners or business owners can be an overwhelming job for the average person unfamiliar with septic system design requirements.  Plumbers, septic system designers and contractor services are required for a septic system installation or replacement.  Area property water table, plumbing needs, home bedroom count and New Hampshire zoning laws are just a few of the problems and challenges your project will involve. You need a team with the right experience for the job, or you'll soon find yourself overwhelmed.

This project services guide is your area resource for managing your septic system design project. From pipes to drains, it details successful, affordable septic tank installation or replacement for your NH property.

Everything you need to get started is here. You’ll learn about area water tables, septic tank size, how a septic tank works, how a septic system leach field works, and the cost of a new septic system or cost to replace septic systems.

You’ll discover how to choose a service team of septic system designersinstallation contractors, and the best types of septic systems for your needs. You'll learn how maintenance of pipes and drains by a qualified professional septic system service provider, as well as regular inspection, can help avoid costly septic system repairs.

Plus, answers to frequently asked questions about engineered septic systems, alternative septic systems, septic companies and more!

How Much Does A New Septic System Cost In New Hampshire?

When building or improving an area home or business property, sooner or later you will begin to wonder, how much does a new septic system cost? The average job cost of a septic system and septic system design, is between $14,000 – $30,000.  Several factors determine the price of installing a common type of residential septic system in New Hampshire. Your home location, accessibility, lot size, and site specifics such as waterfront proximity and ledge conditions all affect job scope – and resulting investment.

Other plumbing service considerations include new septic installation cost versus replacement.  Depending on your property’s location, constraints, and site conditions, your septic system cost can vary by thousands of dollars.

Cost of New Septic System for Homes and Buildings in NH

RegionSeptic System TypeTime On Site*Price Range
Non-Lakes RegionAnaerobic Conventional System3-4 days$14,000 - $18,000
Non-Lakes RegionAerobic Advanced Treatment System3-4 days$19,000 - $28,000
Lakes Region or WetlandAnaerobic Conventional System4-6 days$18,000 - $24,000
Lakes Region or WetlandAerobic Advanced Treatment System4-6 days$20,000 - $30,000

*Factors that can slow the process of septic system replacement include:

  • Special conditions (Ledge, tight access, utilities discovery, etc.)
  • Permitting for wetland-area projects (can add several months to a year)
  • Weather conditions
New septic system installation cost.

Photo of a pipe and stone septic system installation in New Hampshire.

Cost to Install Septic Tank and Leach Field

Septic System Installation Cost Overview

The cost to install a septic system and leach field can range between $14,000 – $30,000 in NH.

It typically costs less to install than to replace a new septic system.

The main factors that affect new septic installation cost include:

Design – All new installations require design by a NH-licensed septic designer.  This investment can range from $1,800-2,400.

Equipment Access and Operation – Ledge lots, waterfront properties, and narrow properties with poor access often involve steep or uneven terrain and windy conditions that require or affect the use of heavy machinery and equipment.

For example, if a smaller excavator is required to navigate a site with limited access, it increases a septic installation cost because it increases a contractor’s time on site, which can average $1900+ per day, not including the intensive ground labor required (shoveling, raking, etc.)

Or if a truck cannot maneuver close enough to offload a concrete septic tank, and a plastic tank cannot be properly placed, a crane may be required, which adds to project scope and fees.

Materials Removal – Site conditions may necessitate removal and replacement of clay and rocks with clean fill material to support the wastewater disposal system.  Additional trucking also incurs fees.

Septic system costs with ledge removal.

Removing ledge can increase septic system costs.

Waterfront or Ledge Conditions – In the Lakes Region, the project budget is often double or more because of strict regulations such as the Shoreland Water Quality Protection Act, as well as access restrictions, property line issues, and high water table challenges.

Other Factors That Affect Project Scope and Cost of Septic Tank Systems

Season & Weather – Precipitation such as rain or snow can slow down the process. For winter septic installations, do not remove snow from the project area, since snow can insulate against deep frost.

Local Building Permits & Inspections – Many towns require and implement fees for building and installation permits, and/or inspections of wastewater disposal structures constructed in basal areas.

State & Federal Compliance – When permits such as Shoreland, Tidal, Wetlands, or Alteration of Terrain are required for Construction Approval, then the installation project scope may also require erosion control or other requirements.

Properties with Wetland issues require these additional permits:

  • Tidal Buffer Permit – for areas within 100-ft of tidal waters
  • Shoreland Permit – for areas within 250-ft of lakes & ponds larger than 10-acres; fourth-order or larger rivers or streams, tidal waters, etc.
  • Dredge & Fill Permit – for approval to travel through wetlands for site access
Properly vented leach field.

Properly vented septic system leach fields will extend the life of the system.

Septic Tank Cost Additional Considerations

How much does a septic tank cost?  Septic system cost considerations differ based on water usage (measured in gallons of water per day). Septic tank prices differ and additional costs may apply for scenarios ranging from a single family home such as a 2-bedroom house, up to a 3-bedroom home or 4 or 5-bedroom house.

It usually costs more to replace an existing system than to install a new one, so it’s wise to select a seasoned professional designer, product manufacturer, and installer to ensure success for your project.

Pricing varies among installation contractors, so do your homework and contact septic tank companies to get more than one septic system cost estimate.

Compare the scope of work each contractor proposes to perform.  For example, causing only 3 inches of loam versus 5-6 inches represents a major difference in the look and health of your lawn.

Reputation matters.  Lower prices often stem from shortcuts that can represent more money, time and headaches for you in the long run.

Septic Tank Installation Cost

Septic tank installation cost is anywhere from $3,000 - $5,000 for the installation alone.  Considering the size of the tank and other installation variables, the complete cost including the installation and tank cost could be $4,200 - $9,000.

How Much Does it Cost to Replace a Septic System?

It’s typically more expensive to replace a septic system than install a new one.  The national average price depends largely on what caused the existing system or its components to fail.  In New England the approximate cost can range from $10,000 - $26,000 depending on the property size, location, labor costs (cost of labor) and type of septic system you need.

Average Septic System Replacement Cost Estimates

RegionSeptic System TypeTime On Site*Price Range
Non-Lakes RegionAnaerobic Conventional System3-5 days$14,000 - $18,000
Non-Lakes RegionAerobic Advanced Treatment System3-5 days$19,000 - $28,000
Lakes Region or WetlandAnaerobic Conventional System4-7 days$20,000 - $25,000
Lakes Region or WetlandAerobic Advanced Treatment System4-7 days$24,000 - $30,000

*Factors that can slow the process include:

  • Special conditions (Ledge, tight access, etc.)
  • Permitting for wetland-area projects (can add several months to a year)
  • Weather conditions

*Other considerations for Replacements:

Anaerobic systems are typically used as replacement systems throughout the Lakes Region because:

  • They are often the only option that meets current regulatory requirements
  • The new system must follow current guidelines not previously followed or required, such as being specified distances from wells, property lines, water bodies, and structures
  • A Site Assessment Study is required before any property located near water can be sold.  This Study identifies to potential buyers the condition of the current septic system, and whether it meets current NHDES regulations.
Septic system replacement.

Septic system replacement in Moultonborough, NH.

Septic Tank Cost and Leach Field Replacement Factors

  • Septic Tank Failure – If only the tank has failed, a new design is not required to install a new tank in the same place as the previous one.  This can represent significant savings since the process doesn’t affect the existing septic system leach field.
  • Leach Field Failure – Typically, however, system failures occur in the leach field.  This failure requires installation of a new subsurface disposal system, specified by a licensed NH septic designer, and approved by the NH Department of Environmental Services (NHDES).
  • Septic System Design – If required, septic system design cost typically ranges from $1,500-2,000.
  • Leach Field Removal – The installer must remove the old soil absorption area to make room for the new system by hauling away old material and components, and trucking in new clean replacement material.
  • Re-use of Existing Septic Tank – Although not often the case, sometimes the existing septic tank can be re-used if it is in good condition and the appropriate size, per current state regulations.  Re-use of the existing tank can potentially save $1,500 - $2,500, avoiding investment in a new one plus the contractor’s fees to dig out, crush, and re-plumb a new tank.
  • Equipment Operation and Labor – The average wastewater disposal system replacement requires use of an excavator and dump truck, ground labor, and 3-5 days of work depending on accessibility, weather, etc.  This can average $1,900+ per day.

Other Project Scope Factors for Existing Properties

Buried utilities, established landscaping, fences, retaining walls, pools, sheds, tarred driveways, overhead power lines, tree removal, and more can all affect the project scope.

The law requires that Dig Safe be given three business days to identify utilities prior to construction, but a private utility-location firm can reinforce health and safety by identifying privately-installed utilities.

Waterfront or Ledge Conditions – Properties with ledge conditions such as granite or rock, or homes located near water require a larger project budget. These areas have more stringent regulations, as well as access restrictions, high water table challenges, and property line considerations.

How Much Does a Septic Tank Replacement Cost?

Septic tank replacement cost depends on the size of the tank you need to support the number of bedrooms in your home.  Cost for tanks range from $1,187 for a 750 gallon tank, to $3,910 for a 3,500 gallon.  Our septic tank product page will provide septic tank costs and details for each type of tank we offer.

The Septic System Installation or Replacement Process

Here you’ll find everything you need to understand and oversee the installation or replacement of a quality wastewater disposal solution for your New Hampshire property.

How Much Does a Septic System Design Service Cost?

Installation of soil absorption field requires a septic system design service such as leach field design by a NH licensed Septic Designer.  The septic design cost of a septic system typically ranges from $1,500 - $2,000.  The price is determined by the scope of work that your specific property requires.

Your designer must make three key decisions.  These include whether to use a conventional (anaerobic) or aerobic (advanced treatment system); the type of drain field to use; and the type of septic tank to use.

He or she must evaluate and review existing property lines, perform a lot and soil survey, create a septic design and submit it with fees to local & state authorities.

The designer determines the best solution for your site by comparing the cost effectiveness and anticipated life expectancy of each system option, as well as accessibility for heavy equipment, lot topography, and site restrictions.

Other Key Factors in the Scope of Wastewater Disposal System Design include:

Septic system test pit.

Septic system designer in test pit.

Location of Test Pit and Utilities – to mark areas to dig test pits in accordance with state and local setback regulations. Many towns require applications, fees, and scheduling with the town inspector. Test pits can be dug once they are staked and inspected, and Dig Safe has marked underground utilities if applicable.  (If the new system is installed immediately following the foundation-pour, underground utilities are not an issue.)

Coordination with Town Inspector – to schedule digging and inspection of test pits. A test pit must be large enough for the Designer to enter and observe the soil profile and characteristics.   Since test pits help identify the type and location of your subsurface wastewater disposal system, property owners are encouraged to be present for the testing, and any conversation with the inspector and project professionals.

Topographic Survey – is completed for an area of 75-ft to a 100-ft around the proposed Individual Subsurface Disposal System (ISDS), to determine relevant objects and elevations.

Septic Draft Plans – typically include test pit (soil survey) results, design objectives, system elements and specifications, a plan view, and other required lot information required by state and local authorities.

Preparation of Submittal Package – to include 3 sets of septic plans for the state (NH-DES), plus the number of sets your town requires, a stamped envelope addressed to NH-DES Subsurface Bureau (for your town to mail it directly to the state), and a state application form.  Some towns require a review of the plan, for a fee, before the plans are submitted to the state.  Most septic plans are processed by the state within 15 days; often much sooner, now that electronic permitting is commonly used.

As-built Plans – If any part of the plan changes, the designer is required to produce as-built plans before the state representative can perform an inspection prior to backfilling.

Project Scope Questions to Ask a Designer or Septic Professional

  • Does the quote include the price of mileage, drawings, delivery (mailed or in-person), etc.?
  • Will he or she be on-site, or available by phone for questions that arise in all stages of the process?
  • Is a Boundary Survey required? (Usually for tight lots; must be performed by a NH-Licensed Surveyor)
  • Are there any Wetland issues that require permits?
  • Is other site work required with individual subsurface disposal solution installation?

How to Choose a Septic System Designer

When considering a septic system designer for your subsurface septic systems design project, it’s vital to choose someone with experience with projects similar to yours.

For example, do they have residential experience, or mostly commercial?  If you live near a water body or wetlands, ask about their projects and experience with permit regulations such as the Shoreland Protection Act.

Can they demonstrate value engineering by showing you a variety of cost-effective solutions they have designed?  Ask for references, since it’s vital that a designer maintains a good reputation and rapport with other industry professionals.

The New Hampshire Department of Environmental Services provides an online search tool, the Subsurface Designer and Installer Query, for homeowners to determine if a designer is registered with the state.

Homeowners can enter any of the following project information into the tool’s search fields: Town, Last Name, County, License Type (Designer or Installer), Professional Engineer, Designer Number, or Installer Number.

NH Septic System Designers by County

CountyTownDesignersPhone NumberWeb Contact
BelknapAlton603 Septic
BelknapTiltonGranite State Septic Designs603-286-4644Granite State Septic Designs
CarrollOssipeeWhite Mountain
GraftonHebronBruce Barnard Enterprises603-744-2696Bruce Barnard Enterprises
GraftonLittletonConnecticut Valley Designs603-444-2072
RockinghamNottinghamThe Wright
RockinghamRaymondJohn Taylor & Sons603-490-2785John Taylor & Sons
StraffordBarringtonBerry Survey &

Types of Septic Systems and How to Choose the Right One

The role of a septic system is to safely transport wastewater from a property, back into the ground without polluting the ground water or introducing water pollution into nearby bodies of water.

Here we discuss how these treatment structures work, and how to choose the right one for your home’s size and site conditions.

How Do Septic Systems Work?

Septic systems function as below-ground wastewater treatment structures.  They are often used in rural areas that do not tie into municipal sewage treatment systems.

Combining natural processes with proven technology, these structures effectively treat waste water from residential plumbing such as kitchen sinks, bathrooms, washing machines and laundry drains.

Typical septic system components include a septic tank and a septic leach field design.

The function of a septic tank is to provide primary treatment and holding for waste solids, allowing them to be digested by organisms or to settle out in the tank bottom.

This wastewater treatment structure works by digesting organic components and separating solids and floatable components (such as grease and oils) from the waste water.

Traditional soil-based wastewater treatment structures release the liquid waste (or effluent) from the tank into a sequence of perforated pipes buried in a soil absorption area, chambers, or other types of technology that slowly release treated effluent back into the soil.

The function of a leach field is to efficiently disperse the liquid discharge (or effluent) from a septic tank to efficiently enable natural treatment of effluent within the soil before it enters the groundwater.

Typical Septic System Diagram

Septic system infographic diagram with NH specs.

Septic System Types and Cost

Septic System Types and Cost

These are the features and benefits of the three types of subsurface waste water disposal structures:

Conventional Septic Systems – Anaerobic Systems

Traditional anaerobic septic systems with anaerobic bacteria treat wastewater without using oxygen. Up to 40 percent of the treatment occurs within the tank, and up to 70 percent occurs in a leach field.

This system requires a greater drain field footprint than an aerobic system. No electricity is required, nor is service required for the mechanical components.

The chambers of an anerobic unit must be pumped out by a professional every 3 to 4 years.

The cost to purchase, install, and maintain an anerobic septic system is typically less than an advanced treatment system. Depending on site conditions, the price can range from $1,000 to $3,000 for a conventional anaerobic septic tank.

Advanced Treatment Systems – Aerobic Treatment Unit Septic Systems

Aerobic septic systems (or advanced treatment systems) use oxygen to treat wastewater. Bacteria in aerobic wastewater treatment structures digest more organic solids than bacteria in anaerobic structures.  An aerobic septic system costs or advanced septic system cost, between $15,000 – $26,000.

This means that up to 90 percent of treatment occurs in an advanced treatment septic tank, while about 10 percent happens in a soil absorption field.

This aerobic process facilitates use of a smaller leach field (approximately half the size of a conventional system), because the released effluent is much cleaner.

This smaller size unit is ideal for properties on small lots or located near water.  Electricity is required, as well as service for mechanical parts such as the aerator.

It costs more to purchase and maintain an advanced treatment unit (ATU) than a conventional system.  Depending on site conditions, the price can range from $6,300 - $12,000 for an ATU system.

Alternative Septic Systems – Sand Filter Septic, Pressure Distribution Septic, and more

Alternative systems use pumps or gravity to enable septic tank effluent to trickle through sand, organic matter (peat and sawdust), constructed wetlands, or other media to remove or neutralize contaminants such as pathogens, phosphorus, nitrogen and more.

Alternative solutions can be designed to evaporate or disinfect effluent before it is discharged into soil.

Percolation Tests, Soil Testing and Soil Surveys

New Hampshire Licensed Septic System Designers perform Percolation Tests and Soil Surveys.

These tests provide data to help the septic leach field designer specify the best type of leach field for the soil content and site conditions.  The tests are used along with the State’s leach field table chart to calculate the size of effluent dispersal area required to support the number of bedrooms in a new, renovated, or existing house.

For lot-loading calculations, each bedroom represents the use of 150 GPD (Gallons Per Day), which is how many gallons a drain field is designed to disperse each day.

For example, a four-bedroom system requires absorption of 600 GPD.  Most modern homes use less water than this due to high efficiency washing machines, dishwashers, and showerheads – but over-design is more prudent than under-design.

The lot survey is used to determine the best location of a leach field.  This involves the knowledge and application of restrictions or setbacks from property lines, foundation, well, house, water bodies, etc.

Sometimes a designer will ask the NH DES to waive a particular rule or requirement.  For example:  A septic tank is required to be sited at least 75 ft. from a well.  But if the tank is sealed with an external coating, the required distance could be reduced to 50 ft.

What is a Percolation Test?

Percolation testing (or a Perc Test) evaluates and measures how quickly water is absorbed by the soil that is actually going to be part of the leach field.

After solid waste settles in a septic tank, excess waste water is the discharged into the leach field through a configuration of perforated pipes.

Any contaminants from the waste water then collect in the soil, and are broken down through natural processes such as percolation, as well as evaporation and absorption by tree and plant roots. Ultimately, excess water enters the ground or surface water.

To conduct a Perc Test, a smaller hole is dug, usually by shovel, measuring 4-12 inches wide, 18-36 inches deep into the ground.

Water is added into the hole, and the length of time it takes for the soil to absorb it is recorded.  The longer it takes for the water to be dispelled, the bigger the leach field will need to be.

This is because when water is discharged from the house, the field must be able to handle the volume of water dumped into it. Shallow soil depth, sandy soil, or waterlogged soil cannot absorb as quickly as well-drained soils.

Property Soil Type Considerations

Soil composition is the first critical factor in determining a home’s drain field size.

House Size Considerations (3-Bedroom Houses, etc.)

The number of bedrooms is the second critical factor in determining whether a home needs a larger leach field.

For example, a property with a four bedroom home may only require 1,000 sq. ft. of a pipe & stone field, while a property with a four bedroom home that’s two streets away may require 1,300 sq.ft. for the field – all because of the difference in soil composition. The number of bedrooms + Percolation Rate = Dispersal Field Size.

Properties that quickly pass percolation tests are typically in areas with low water tables, or with higher concentrations of sand, since sand can absorb water faster than silt or clay.

What is a Soil Survey?

A Soil Survey for sensitive soil conditions is important for determining the appropriate location for septic systems relative to underlying water table depth and bodies of surface water.

Soil tests for soil permeability are a key factor of soil conditions. Soil permeability is measured as the flow-rate of water through a cross section of saturated soil.

The measure of soil permeability is different than soil percolation. (A Perc Test does not take into consideration the soil’s ability to filter pollutants.)

A soil survey takes into consideration that certain soil conditions require a long minimum distance to remove pollutants, and nitrates in particular.

To achieve proper placement of an individual subsurface disposal structure, the soil permeability must be mid-range between impermeable and too permeable.

Ultimately, enough permeable soil must be available below the absorption field to adequately filter and treat the effluent before it reaches the water table.

To conduct a Soil Survey (Test Pit), an excavator or backhoe is used to dig a hole large enough for a person to climb down into.

The hole must be at least 4-ft. below the bottom of the proposed bed location and 20-ft. to the edge of the proposed leach field.

The location must be the same soil and slope conditions of the actual proposed septic leach field design. The designer must able to visually inspect the vertical differences of the soil to see soil color changes, and indications of water & roots.

This will determine the seasonal high water table (SWHT).  The SWHT determines the bottom of the leach field, which must be between 4 and 2 feet above the SHWT, depending on the chosen type of leach field.

For example:  A Pipe & stone field requires a 4-ft. separation, while Advanced Enviro septic requires a 2-ft. separation.

The Natural Resources Conservation Service of the U.S. Department of Agriculture (USDA) explains more in a brochure for homebuyers titled Soil Surveys Can Help You.

Questions a Designer May Consider Before Specifying a Drain Field:

  • Are the soil conditions and available space appropriate for a traditional pipe and stone system?
  • Can the leach field have 4+ feet of vertical separation to the SHWT (Seasonal High Water Table), so as not to require a mound system or a pump septic system, or the need to bring in extra fill?
  • Does a land survey of the lot size require the use of alternatives to septic systems such as Innovative Technology or an Advanced Treatment Unit?
  • Does the state allow any reduction in size of effluent disposal area?

Types of Leach Fields and the Benefits of Each

The type of leach field that is specified depends on the individual subsurface wastewater structure (conventional or aerobic) it supports.

How a Leach Field Works

A leach field is a soil absorption area that receives the liquid discharge from a septic tank, and facilitates natural treatment of effluent within the soil before it enters the groundwater.

A leach field contains gravel or soil that absorbs the waste water as it flows into the field through pipes with tiny holes along the bottom and sides into soil where bacteria purifies the water.   Only wastewater is meant to flow into the leach field.

Do not plant trees or bushes within 10 feet of the field, since roots can damage the pipes. Do not park or drive over a drain field, since the weight can also damage the system.

The types and benefits of leach fields commonly specified throughout New England include:

Pipe and stone leach field installation.

Pipe and stone leach field installation in Sandwich, NH.

Pipe and Stone

A conventional pipe and stone septic system is the most common and the oldest type. It’s created by digging a series of trenches in the septic field to disperse waste.

The number and length of trenches depends on the home it is designed to support, and the site’s soil conditions.  Historically, pipe and stone leach fields last the longest, but their size requires substantial space, which isn’t always practical in New Hampshire.

Concrete Chamber Septic System

A concrete chamber system uses a series of connected chambers to carry wastewater to different areas where it is filtered out through holes in the sides of the chamber as well as the bottom before entering the surrounding soil.

Microbes in the soil then treat and purify the effluent. Concrete chambers offer several benefits, including space-efficiency due to the effluent seeping out of the sides as well as the bottom.

This is ideal for small properties or where a leach field must be located in a driveway or parking lot, because concrete chambers can be traffic-rated (H20).

A chamber solution also qualifies for a 40% reduction in leach field size, compared to a pipe and stone system.  The component cost for concrete chambers is now similar to an enviro septic field, and is faster to install.

Septic Leach Field Trench System

A trench system is the most standard type of drain field.  Effluent is pumped or gravity fed from the septic tank to several shallow underground trenches constructed of stone or gravel.

Fabric is used to cover the top of each trench to keep out contaminants.  This enables the effluent to filter through, and be treated by the bacteria in the soil below each trench.

This solution spans a large area, which may not be available for all homes.

Mound Septic Systems for Septic Drain Field

Mound septic systems work best for areas with high ground water, low soil depth, or shallow bedrock. A network of sand mounds is constructed, each containing a drain field trench.

Effluent from the tank flows into a chamber, and is then pumped into sand mounds in measured amounts for treatment by filtering through the sand, before entering the soil.

A sand mound system typically requires the installation of an alternative treatment unit (ATU) to pretreat the effluent before it reaches the sand mounds.

Mound septic systems are ideal for soil conditions that do not support a traditional subsurface wastewater disposal system.  However, mound solutions require a large dispersal area and regular maintenance.

Enviro-septic leach field installation in NH.

Enviro septic leach field installation in Concord, NH.

Enviro Septic

Enviro septic systems consist of a series of tubing lined with geotextile fabric and coarse fibers. They work by skimming the waste and mixing air with the filtered waste.

This facilitates purification of the waste into a cleaner, purer liquid. This option is typically smaller and more efficient than other options, and tends to cost less to install, since it can be placed within two feet of the Seasonal High Water Table.

Dry Well

A dry well system is also known as a seepage pit, which is a covered pit with a perforated lining.  Effluent seeps through the lining and into the soil.

It’s one of the oldest and simplest methods of managing a septic system, although not as long-lasting as other options. Dry wells are required to be located at least four feet from the Seasonal High Water Table.

Infiltrator leach field installed in NH.

Infiltrator chamber leach field installation in Campton, NH.

Infiltrator Chambers

Infiltrator chambers can be used in almost any leach field design.  They are highly adaptable, which is a key feature.

Whenever stone and pipe is an option, infiltrator systems are an option as well. The primary benefit of infiltrator chambers is that they provide superior treatment capabilities due to pressure dosing, level distribution, serial distribution, evapotranspiration, and sand filter applications.

Drip Septic Systems

Drip septic systems are also known as pressure systems. They can be used in several different types of drain fields.

They are ideal because the drip distribution system doesn’t require a large pile of soil to work. Instead, drip laterals are installed into the top 6-12 inches of the leach field, making this system much easier to install than most other options.

However, a pressure system requires a large pump tank from which to draw water so that it can control the flow of wastewater to the leach field.

Otherwise, the leach field can become overwhelmed by effluent. This system also requires electricity and regular maintenance.

Types of Septic Tanks and the Benefits of Each

How septic tanks work.

This diagram outlines key features of a septic tank

How Do Septic Tanks Work

The role of a septic tank is to condition sewage, as the first function of a subsurface disposal system. It ensures that untreated sewage does not clog the receiving soil, and promotes the purification process of leaching and soil percolation.

Septic tanks function to remove solids, promote bacterial action, and store sludge and scum in a single or or multi-compartment holding chamber that collects wastewater from household toilets and drains.

The natural process starts in the treatment chamber, and liquid sewage is discharged to a designated below-ground effluent dispersal area.

Types of Septic Tanks

Precast Concrete Septic Tanks

Precast concrete is practical for subsurface wastewater disposal systems in New England, since it is cost effective, long-lasting (50+ years), environmentally friendly, strong, weather resistant, fire resistant, environmentally friendly, UV insensitive, watertight, readily available, quickly and easily installed, and low maintenance.

Quality precast concrete products conform to ASTM C31 and C39 quality testing guidelines.

Benefits of precast concrete septic tanks
    • Large selection of sizes, in-stock and delivery-ready
    • Several types of traffic-rated tanks for various loading requirements
    • Enables design specification of H-10/Heavy Duty vehicle or H-20 loading
    • Multiple Compartment Options include 2 or 3-compartment tanks, which help to settle solids before effluent is dispersed, and extend leach field longevity
    • Water tightness - A quality precast concrete manufacturer will specify a pump and accessories, and offer built in plastic risers to maintain water tightness
    • Access to drawings – A quality concrete precast tank manufacturer will include AutoCad or PDF drawings for reference
    • Design flexibility enables efficient effluent distribution from the side or end of tank
    • Allows for access points to service or pump the tank
    • Can be installed in one piece, up to 1,750 Gallons
Types of Pump Systems
    • Grinder pump – is used in a single compartment tank, to grind up solids in effluent that is pumped into a municipal sewer system
    • Effluent pump – is used by a 2 or 3 compartment tank or a pump box, to distribute liquids to an effluent disposal area
    • Solids handling pump – is used by a single component tank that enables solids to settle in a septic manhole being pumped into a municipal sewer system
Plastic Septic Tanks

Plastic tanks are appropriate for sites with limited access, small lots where only small excavators can fit, and when only light excavation is possible.

Benefits of plastic septic tanks include
    • Light weight – for transport and manipulation during installation
    • Durability – Typically 20 to 30 years
    • Consistent Dimensions – since few manufacturers produce plastic tanks, dimensions do not fluctuate greatly – while precast concrete tank sizing can vary by manufacturer
    • Contain plastic risers – that can be brought to grade
    • Factory-sealed – for water tightness

New Hampshire Septic Systems Laws

In New Hampshire, the Subsurface Systems Bureau of the NH Dept. of Environmental Services oversees the rules and regulations regarding septic system design and installation in the state.

The mission of the Subsurface Systems Bureau is to prevent contamination of all below ground and surface sources of water, whether public or private.

Specifically, the Bureau’s role is to:

  • Review all applications for land subdivision and individual subsurface disposal system design
  • Perform on-site inspection of all installed systems, to verify compliance with approved plans
  • Implement and administer licensure of subsurface disposal system designers and installers. Licensure is required before application submission and project installation.
  • Investigate documented complaints registered with the NH Dept. of Environmental Services relative to situations that could potentially degrade water bodies in the state
  • Coordinate other required permits for specific projects

NH septic system permit.Permits / State Approvals

NH-DES grants permits to septic system designers and installers to ensure that subsurface waste disposal systems are suitably designed and installed for all NH property sizes and site conditions.

Title L – Water Management and Protection – was developed to protect the state’s water supplies, and prevent contamination of groundwater and surface waters, as well as potential health hazards

The NH Code of Administrative Rules - details state regulations regarding subdivisions and individual sewage disposal systems.

Tidal Buffer Permit – for areas within 100-ft of tidal waters

Shoreland Impact Permit – for areas within 250-ft of lakes & ponds larger than 10-acres; fourth-order or larger rivers or streams, tidal waters, etc.

Dredge & Fill Permit – for approval to travel through wetlands for site access

Why a Site Assessment is Important

A site assessment is an examination of a site and its existing development, to determine if the site and septic system meet the current standards of the NH-DES Subsurface Systems Bureau.

This assessment is required before a Purchase and Sale (P&S) agreement can be completed for any developed waterfront property with a wastewater disposal system.  The property owner must hire a licensed NH designer to conduct a site assessment to establish whether the site meets the state’s current criteria for subsurface disposal systems.

This study is required if any part of the property is sited within 200 feet of the reference line or high water mark.  A completed Site Assessment Study Form is included as part of the P&S agreement.

The NH DES provides this Fact Sheet regarding site assessment prior to the sale of developed waterfront property.

How to Choose A Septic System Installer

Choosing a professional installation contractor for your subsurface septic design project involves determining the contractor’s experience with projects like yours.

For example, is their experience mostly residential or commercial?  If your project has ledge conditions or is near water, ask the installer about their expertise and familiarity with permitting for areas with ledge issues or a high water table.

Do they have the right kind of heavy equipment to handle site-specific conditions (such as excavators, jackhammers, and cranes)?

Ask more than one contractor for a quote and references, since reputations can vary.  Expertise, experience and equipment make a difference in the cost and success of your project.

In order to provide you with a project estimate and proposed schedule, a NH-licensed installer must review the official stamped plans, letter of conditions, project site and areas around your property.

The NH Dept of Environmental Services offers an online search tool, the Subsurface Designer and Installer Query, that helps property owners to determine if an installer is registered with the state.

The the tool’s search fields include: Town, Last Name, County, License Type, Professional Engineer, Designer Number, or Installer Number.

NH Septic System Installers by County

CountyTownCompanyPhone NumberWeb Contact
BelknapAltonDavid Avery Excavation603-569-9162David Avery Excavation
BelknapCenter HarborLemien Excavation603-476-2244Lemien Excavation
BelknapSanborntonAuger Siteworks603-455-5808Auger Siteworks
CarrollCenter ConwayGE Brown603-356-0870GE Brown
CarrollCenter ConwayLBI
CarrollCenter SandwichRandy Brown603-651-9054
Randy Brown
CarrollChocoruaJohn Roberts Excavation603-323-8764
John Roberts Excavation
CarrollConwayGeorge Fadden Septic603-356-2747George Fadden Septic
CarrollFreedomMcConkey Construction603-539-7736McConkey Construction
CarrollMoultonboroughRA Dunlap &
CarrollNorth SandwichFullerton
CarrollOssipeeGeoff Downing603-455-3262
CarrollSanbornvilleLakes Region
CarrollTuftonboroGillum Excavating 603-393-7105Gillum Excavating
CarrollUnionLances Landscaping603-834-2208Lances Landscaping
CoosWhitefieldWendell Rexford &
GraftonAshlandDon Latulippe Excavating603-536-5200
Don Latulippe Excavating
GraftonAshlandME Latulippe Construction603-968-7332ME Latulippe Construction
GraftonCamptonJim Sanborn & Sons Construction603-726-4899Jim Sanborn & Sons Construction
MerrimackCanterburyCochrane & Sons603-783-4494Cochrane & Sons
MerrimackCanterburyJames Lilly Construction603-783-4295
James Lilly Construction
RockinghamHampsteadDependable Construction603-329-5016
RockinghamNorthwoodM.D. Tasker Construction603-942-8601
RockinghamPortsmouthChris-Co Construction603-436-0315Chris-Co Construction Facebook
RockinghamRaymondJohn Taylor & Sons603-490-2785John Taylor & Sons
RockinghamStrathamK.G. Blood & Son603-235-5622K.G. Blood & Son Facebook
StraffordBarringtonD&D Hatch Excavation603-332-5670D&D Hatch Excavation Facebook
StraffordFarmingtonS. Cardinal & Sons603-755-3623S. Cardinal & Sons
StraffordMiltonBurrows Excavation603-783-6196Burrows Excavation Facebook
StraffordStraffordJNL Excavation603-817-6158JNL Excavation
StraffordStraffordRadford Messenger603-332-0349Radford Messenger
StraffordStraffordRoscoe Tasker603-435-6608Roscoe Tasker

Frequently Asked Questions

A precast concrete septic tank costs anywhere from $1,200 - $8,400 depending on a number of variables.  For a complete list of septic tank sizes and options visit the, 'septic tank costs' link in this FAQ.

DES is required by law to publish guidelines and provide a copy with each approval for construction it issues. For existing systems, the recommendation is that the tank should be pumped at regular intervals (approximately once every 3 years) by a professional experienced with pumping septic systems. A neglected septic tank can become clogged with sludge and cause excess solids to enter the absorption leach field, causing failure.

Lot size, percolation rate, soil composition, distance to setbacks, topography, building location, accessibility to site, trees, ledge, & seasonal high water table all play a part in what your septic designer specifies.

Every septic system requires a system of vents because they enable gases to safely exit the system, and help to avoid formation of dangerous gas buildup or airlocks.  Three types of pipe ventilation should be incorporated into your system, including:  inlet & outlet vents, roof vent, and yard-based pipe vents.

You can use it after you receive Approval for Construction & Approval of Operation.

You need a NH-approved design if your septic system fails and you cannot replace it in the exact same location; or when you are expanding an existing structure (adding bedrooms, converting from seasonal to year round use, or changing use from residential to commercial); or when you are building a new house in an area that does not offer municipal sewer services.

The system size depends on your bedroom count and the percolation rate of soil on your property.  Page 37 of the NH DES doc, New Hampshire Code of Administrative Rules, includes a chart for determining leach field size required depending on these factors.  Using an aerobic treatment unit such as a Norweco Singulair Treatment Unit can decrease the size by 50-75% versus a conventional arrangement.

The size depends on the number of bedrooms it supports. The most common size used in NH is 1,250 gallons, which is appropriate for up to 4-bedrooms.

Yes, but the tank must be traffic-rated for the weight of the vehicles it will carry.  Various vehicles such as pickup trucks, propane trucks, oil trucks, etc. require different traffic ratings.

Yes. In New Hampshire you can install your own septic system, but only for your own domicile that you live in; not for a property that you plan to flip or remodel to sell.  You must follow all the same steps as a licensed contractor follows. You also need a state-approved septic plan, and the system must pass all required inspections.  You may not install your own septic system for a new building, according to how the rules are interpreted.

Several considerations include:  Does your situation require a new septic design? State inspection? Accessibility for heavy equipment? The on-site time is typically 3-5 days, although weather or unexpected things can increase this timeline.

A biomat is a layer of bacteria that forms in the soil surrounding and underneath effluent dispersal field trenches where wastewater is released.  This biomat layer is vital for processing the fine biological solids and contaminants found in effluent.  Without it, a disposal area cannot adequately treat effluent. Inadequately-treated effluent discharged into the ground poses the risk of polluting nearby bodies of water.

The 3 primary ways to prolong the life of a septic system are:

  • Proper Use – Avoid flushing or rinsing things down the drain that can clog the unit or disposal field
  • Maintain and Inspect the System – Schedule professional septic system pumping as needed (usually 3-5 years) and plan for annual inspection,
  • Obtain Quality Septic Systems Parts – Ask your precast concrete manufacturer for quality replacement parts, such as distribution boxes, tank covers, pumps for septic systems, holding tanks, dosing tanks, etc.

A septic field will fail when the volume of water discharged to the septic disposal field is greater than the volume of water that is can be absorbed into the soil or evaporated into the air.

The primary causes of leach field failure include:

  • Improper discharge of solids from the tank causes the field to clog so it cannot absorb water
  • Supply lines are clogged or damaged by tree roots, so water cannot be dispersed through the field
  • Evaporation is prevented by compacting or covering the surface of the leach field
  • More water is injected into the field than it was designed to handle

According to the NH DHHS, Division of Public Health Services, the legal definition of septic failure is: “The condition produced when a subsurface sewage or waste disposal system does not properly contain or treat sewage, or causes or threatens to cause the discharge of sewage on the ground surface or into adjacent surface or groundwaters.” (RSA 485-A-2:IV)

It is vital to the protection of ground and surface waters that wastewater effluent is appropriately treated and discharged by subsurface disposal systems.  Inadequately designed, improperly operated, and poorly-maintained systems can cause partially treated wastewater to contaminate ground or surface waters.

Obvious signs of septic system failure include sewage backups in your home, or on the surface of your yard. Difficult to detect yet equally unhealthy signs of failure include pollutants entering ground or surface waters.

The average cost in NH to replace a septic system is between $10,000 - $26,000 depending on where the property is located in the state and the type of septic system you are installing.

The average cost of a septic system in NH is between $9,000 – $26,000.

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