Call Brian today at (509) 885-5989 for a FREE site consultation or email us at   We look forward to hearing from you!

           Septic System Designs


Residential and Commercial

A septic system is the most expensive appliance you may ever own on your home or business.  Yet most folks never give it a second thought of where their sewage goes…as long as it goes away.  At Blackstone Septic Design we know that long term satisfaction with your septic system begins with proper planning.

Our goal is to provide a septic system design that accurately depicts the soil/site conditions to provide wastewater disposal and treatment.  We also emphasize long term operation and maintenance details which will help your system provide years of dependable service to your home or business.

What we do for each design project:

  • Contact your county health department for any background information such as asbuilts or previous soil logs.  
  • Call for utility locates.  
  • Research parcel for property line survey or plat drawings.
  • Field visit(s) to log test pits, system layout staking with wood lath and surveyors tape, elevations of critical system components with a laser level, field locate established property corners with a metal detector and tape measures, and to establish horizontal and vertical controls over the project.
  • Contact owner/developer with site sketch proposal and further project approval.
  • Complete the design package on CAD, mailed and/or emailed to owner/builder.  We can also deliver the design package to your local health department.
  • If desired, conduct a cover inspection with the installer and compete an asbuilt drawing which is given to the installer who then submits the drawing to the county health department.



The Design Package

You will receive a set of paper designs which include the scaled site plan, calculations, construction details, and owner’s manual for your system.  We can also scan and email your package to you or your installer.


Click HERE for an example of a complete design package.


  New Construction and Repairs


With nearly 20 years of experience as a county health regulator and private site septic system designer, we can help at any stage of your project.  A septic system design starts with a soil evaluation by examining test pits dug with a backhoe as the soil is the primary driver of what kind of septic system will be required (wastewater treatment) and how big the drainfield will need to be (wastewater disposal).  For commercial systems a wastewater sample will need to be analyzed for Biological Oxygen Demand, Total Suspended Solids, and Fats, Oil, and Grease to determine if secondary wastewater treatment will be required to reduce waste strength before effluent is sent to the drainfield.  Our turn around time is about two weeks for residential projects.


  • Residential Site Eval and Basic Design Package: $750 (gravity drainfield), $850 (pressure drainfield), to $950 (Aerobic Treatment Unit or Sandfilter to drip field)  – new construction or repairs.  This price includes any number of test pit evaluations for the project, field visits to the site, phone calls, etc. 
  • Commercial design projects: $1.75/gallon of wastewater ($750 minimum) plus at least one wastewater sampling event ($350) in most cases.  The sampling event would discover the “waste strength” of the effluent which determines what kind of pre-treatment the effluent needs prior to discharging into the soil.  Samples are ran through Cascade Analytical here in Wenatchee.
  • $350 – Soil test pits evaluation (no design services requested, just the soil/site evaluation).  For subdivisions: $350 plus $75 per lot.
  • $200 – Final inspection and asbuilt drawing.
  • $150 – Change orders by the owner/developer after the design project is completed (a construction permit was issued by the Health Department).
  •  Please note there is also an 8.2% Washington sales tax added to the above design fees.

Costs for a septic system design usually depend upon the complexity of the system.  For example, a gravity drainfield design will cost less to design than a sandfilter to drip disposal field system.


Typically the owner supply’s the backhoe for digging the soil test pits but Blackstone Septic Design can make the backhoe service arrangements for you and pass the direct cost along to you.  Typical backhoe fees are about $250 to $350 which includes any number of test pits.


 If the county health department requires changes to the design or if errors are identified, there is no  additional fees from Blackstone Septic Design for a revision as we stand by our designs 100%.